Spring 2015 Revision (01/16/2015) VERY IMPORTANT: STUDENTS REGISTERED FOR THIS LABORATORY COURSE MUST

ALSO BE REGISTERED FOR THE ACCOMPANYING RECITATION – CHEM 223RC! Recitation class attendance is mandatory for any student enrolled in the lab and a significant portion of

the CHEM 223 lab grade comes from exams & quizzes given in the recitation class!

Table of Contents

Welcome to CHEM 223 Lab – Introduction & Common Policies page 2

Experiment 1: Melting Point page 6

Experiment 2: Recrystallization page 7

Experiment 3: Simple & Fractional Distillation page 10

Experiment 4: Chromatography page 13

Experiment 5: Acid-Base Extraction page 21

Experiment 6: Molecular Modelling page 24

Experiment 7: Oxidation of Cyclohexanol page 31

Experiment 8: Nucleophilic Substitution and IR Spectroscopy page 33

Experiment 9: Synthesis and Reactions of Alkenes page 37

Appendix I – Properties of Selected Hazardous Chemicals page 42

Appendix II – Microscale Extraction page 43

Appendix III – Microscale Recrystallization page 45

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Welcome to CHEM 223 Lab – Introduction & Common Policies COURSE DESCRIPTION & GRADING OVERVIEW In this course, you will first learn how to separate and purify organic compounds. You will then synthesize a number of organic compounds yourself and employ the techniques that you have learned earlier (as well as learn some new ones) to separate, purify, and study your reaction products. Your grade will be assigned on a 1350-point schedule. Your point totals will be based on pre-lab quizzes, your lab performance, written lab reports and recitation class assessments. Keep in mind that good execution of laboratory techniques, adherence to safe laboratory practices (including cleanliness and proper disposal), the quality & quantity of the products you hand in, the organization of your work (including how well you have planned your work beforehand) and how well you understand the chemical processes that occur are all factored into your grade! REQUIRED TEXT: Pavia, Kriz, Lampman, and Engel: A Small Scale Approach to Organic Laboratory Techniques, Third Edition. (This lab manual will refer to this textbook as “Pavia”) PLANNING AND EXECUTION In the Organic Chemistry laboratory, you will plan and execute your work more independently than in previous laboratory courses that you have taken so far. You must do a lot of preparation work before you work on an experiment. In addition to reading the text, you must attend the lab recitation class. Take good notes in the lab recitation and review them carefully when planning each experiment. The pre-laboratory assignments for each experiment must be completed BEFORE you come to class! Many of the experiments that you will complete this semester are not taken directly from the Pavia textbook though you may find many similarities. Part Six of the Pavia textbook (starting at page 546) should be especially helpful to you as it contains descriptions of the techniques you will use throughout the term. The importance of studying the recitation material and applying what you have learned cannot be exaggerated. The key to success is planning your work carefully before you enter the laboratory! It is essential that you start working promptly as soon as possible, rather than socialize with other students. You will be so busy in some experiments that you probably won't have time to talk at length to anyone. Sometimes, you will need to work on different parts of an experiment at the same time in order to finish on time. It is very important that you finish all work within the scheduled class time and within the total time allotted for the experiment (if more than one class session is dedicated for an experiment). No work will be allowed outside the scheduled class time, including washing glassware and taking melting points. Everybody must physically leave the laboratory by the scheduled end of class time! No additional time will be given to any student who falls behind on work. You will work individually on some procedures, but there are also some procedures in an experiment that you will perform in pairs or as a small group. Your instructor will let you know about the working arrangement on the day of the experiment. One set of equipment will be issued to a pair of students – you and your assigned partner will be responsible for keeping them in good condition throughout the semester (even if the two of you don’t necessarily work together on any experiment). When you hold a flask in front of your instructor to ask a question about the contents, you must be able to describe exactly what you put in the flask, and the exact sequence of operations you have carried out in arriving at that point. Your lab instructor will not simply provide answers! You should always be prepared to intelligently discuss what you are doing and try to arrive at a solution to your own problem rather than rely on your instructor to solve all of your problems.

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LABORATORY SAFETY For safety reasons, ALL STUDENTS must wait outside the laboratory until their instructor has entered and has given everyone permission to enter the room. Every student is REQUIRED to attend the first meeting of their lab section for the semester. During that session, all students will be acquainted with safe laboratory practices, the safety features of the laboratory and the procedures to be followed in the case of an emergency. Students will also be provided with a copy of laboratory rules. Appendix I of this lab manual contains additional information on the hazardous properties of chemicals used in CHEM 223. You will not be allowed to proceed with the lab course until you are familiar with the rules and safety procedures. If you miss the first meeting due to registration delays, you should contact the Chemistry Lab Stockroom (Room 1414, Hunter North building) immediately to schedule a make-up time to perform the check-in procedure and go through the safety protocols. *** REMEMBER THAT SAFETY GOGGLES MUST BE WORN AT ALL TIMES IN THE LABORATORY! *** Failure to comply with this regulation will result in deduction of points and/or ejection from the laboratory.

WARNING: If you are pregnant or intend to become pregnant during the semester, you are not allowed to work in the Organic Chemistry Lab for reasons significant to the safety of the unborn child! LAB CLEANLINESS 1. Make sure that the area around your workspace is clean while you’re working on your experiment

AND before you leave the laboratory. Your instructor will not clean up after you! 2. If you spill something or otherwise make a mess during a procedure, you must clean it up. 3. There are designated disposal containers for broken glass, chemicals (solid and liquid), gloves, etc.

located throughout the room. If you are not sure where to dispose something, ask your lab instructor. MAKING UP A LAB (Fall & Spring Semesters ONLY) In the Fall & Spring semesters, you may make-up for a missed lab session ONLY ONCE FOR THE ENTIRE SEMESTER AND ONLY WITH THE PERMISSION OF THE PROFESSOR COORDINATING THE LABS (“lab coordinator”). The absence must be due to a proven emergency or a documented reason that the lab coordinator deems legitimate. First, contact your lab instructor and the lab coordinator as soon as possible after your absence (or before your absence, if it is anticipated in advance). Then, obtain a Make-Up Permission Form from the Chemistry Lab Stockroom (Room 1414, Hunter North). Arrange to meet with the lab coordinator. Be prepared to explain the reason for your absence, provide documentation and select times on when you would be able to make up for the missed lab based on the schedule of experiments. Obtain the signature of the lab coordinator on the make-up form for final approval and attend the authorized make-up section.

** STUDENTS MAY NOT ATTEND ANY SECTION THEY’RE NOT REGISTERED IN WITHOUT A MAKE-UP PERMISSION FORM SIGNED BY THE LAB COORDINATOR! **

Every effort MUST be made to schedule makeup sessions during a time when that same experiment is being done by another section. Please make every attempt to complete all experiments during your regular lab session and reserve make-ups for emergencies only. Permission for make-up will not be granted in cases of student misconduct (e.g.: thrown out of lab for violating rules), negligence (e.g.: slept in, forgot about class, etc.) or failure to complete an experiment on time.

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MAKING UP A LAB (Summer Semester ONLY) Due to the highly condensed nature of the Summer semester schedule, make-up lab sessions are NOT available. THE LABORATORY NOTEBOOK All your lab reports and the answers to assigned questions are to be written in a dedicated laboratory notebook. The notebook must have numbered, duplicate pages so that you can keep one copy of your lab report and turn in the second copy for grading. Suitable Organic Chemistry Laboratory Notebooks are sold at the Hunter College Bookstore. The notebook is to be sufficiently complete and well organized so that anyone who reads it can know what has been done in each experiment and can repeat the procedures from what’s written in it. This laboratory notebook has essentially the same requirements as a notebook used to record data in a research laboratory. All data are to be recorded at the time they are observed or obtained. This includes weights, boiling and melting points, observations of physical changes, results, and conclusions. Separate pieces of copy/looseleaf paper are NOT to be used for recording data to be transcribed later. Your laboratory instructor may check your notebooks at the end of each laboratory session to ensure that your data was properly recorded at the time when you conducted the experiment. The notebook should be neat but this is less important than having it be a complete, original record. Copying data is a waste of time and leads to copying errors. The record made at the time of the observation is the important record. If changes or corrections are to be made, the material considered wrong is to be cancelled by drawing a line through it. The revised material is then to be added. It may be necessary to refer to the record to determine how an experiment might best be revised or interpreted. You should have a Table of Contents on the first page of the notebook and all of the pages should be numbered. Start every experiment on a new page. Make all records in ink (DO NOT WRITE WITH A PENCIL!). Instead of copying details of a procedure verbatim, refer to the page in the lab manual (or other sources) where the procedure is started. The notebook is a log of your work and should be dated regularly. As you conduct the experiment, you must write a short description of the actual procedure that you followed including all observations. The preliminary write-up, as indicated in each experiment, must be in your notebook before you begin the experiment. All preliminary write-ups must include a list of hazards and toxicities of the compounds involved. Experiments designed to develop familiarity of techniques can be recorded in terms of an introduction which states the objective; a description of the procedure, which may be identified by a reference to the manual; the observations; the conclusions (identify the unknown and state the supporting data and reasoning); answers to the question, and a discussion of the theory behind the experiment and its relationship to the observed results. If your own procedure is at all different from that in these notes (or manual), tell exactly how it differs. Data tables will also be used for the later preparative experiments (from Experiment 6 onward) and you will need to know how to carefully and accurately tabulate data to include all your results. We must emphasize that your notebook should be up to date at all times during the laboratory period and your instructor will periodically examine it to ensure this. We repeat: you must only use indelible ink and you are NOT permitted to use corrective fluid (“white-out”) or tape.

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THE RECITATION Please remember that the recitation is the equivalent of a challenging one-credit course. Don't let yourself become one of the many students who receive a low grade for the entire course due to low scores on their recitation examinations! It is essential from a viewpoint of safety alone to attend all the recitations and attendance will be taken for that reason. However, the Recitation is also critical from the standpoint of your grade since your exam scores from that portion of the course will account for about 19% of the total possible points. We would like to stress again the importance of studying and planning your work before you start the experiment! Students who really understand what they are doing in the lab will enjoy the work and might even look back on their organic chemistry laboratory as a really pleasurable learning experience. Those who do not understand the experiments will experience frustration and likely failure in addition to exposing themselves and others to the risk of a serious accident. We will do our best to help you enjoy the course and achieve successful results, but if you don't do your homework and planning, no one will be able to help you. If an instructor determines that a student has not adequately prepared for an experiment, the student will be sent away from the laboratory and will not be allowed to do make-up work in another section.

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Experiment 1: Melting Point

Reference: Pavia – Technique 9 – pages 643-652

A. INTRODUCTION The melting point is the ultimate criterion of the purity of a solid since pure compounds melt within very precise temperature ranges. Your lab instructor will explain to you the use of the melting point apparatus as well as show you how to fill the melting point capillary. Please note that you need only a very small amount of compound (less than 0.1 g) for melting point determination. B. EXPERIMENTAL PROCEDURE Part A: Determine the melting point of the following compounds and observe the changes due to the presence of an "impurity."

a. trans-Cinnamic acid b. Urea c. a 1:1 mixture of both trans-Cinnamic acid and Urea.

Record your observations.

HINT: There are three slots for inserting melting point capillary tubes inside the melting point apparatus. You should use up all available slots in the apparatus at one time to determine melting points for each sample instead of melting one sample at a time. Part B: Determine the melting range of an unknown compound given by your instructor. The identity of your unknown compound will be one of the following:

Compound Melting Range (°C) Compound Melting Range (°C) Naphthalene 80-82 4-Methoxybenzoic acid 182-185 Anthracene 216-217 1-Naphthol 95-96

Benzoic acid 122-123 3-Nitroaniline 112-114 Benzophenone 49-51 4-Nitrophenol 112-114

p-Bromoacetanilide 165-169 3-Nitrobenzoic acid 140-143 Cholesterol 147-148 Salicylic acid 159-160

4-Chlorobenzoic acid 239-242 o-Toluic acid 103-105 Cinnamic acid 133-135 p-Toluic acid 180

Part C: Confirm the identity of the unknown compound from Part C by recording a mixed melting point measurement with a reference sample provided by your lab instructor. This is a routine part of any melting point procedure and should always be performed as long as a reference sample is available. You should try to remember this for later experiments! C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). There are NO ASSIGNED POST-LAB QUESTIONS for this Experiment. (You may omit Item 9.)

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Experiment 2: Recrystallization

Reference: Pavia - Techniques 8, 9, 10 and 11 - pages 630-680. Also read pages 546-579.

A. INTRODUCTION The technique of crystallization is one of the most valuable available for the purification of solids. The basic idea of purification is easily understood and the manipulations are straightforward. In spite of this, crystallization remains more of an art than a science. A part of the trouble arises because a good crystallization frequently requires much patience. A more serious problem is that the best solvent to use cannot be chosen by a convenient magic rule, but must be found by trial and error. Since you have little or no experience, you will have to rely on our judgment. The most fundamental property of a good solvent for crystallization of a solid is that the hot solvent must dissolve the substance readily while the cold solvent must dissolve it sparingly. This means that you would start your hunt for a good solvent by looking for one that gave borderline solubility. From here you would have to adjust the temperature range, the ratio of solid to solvent, or try combinations of solvents to find a mixture with just the right solvent properties. In crystallization of a mixture of solids one is always faced with the practical problem of knowing how much solvent to use. If one of the components is poorly soluble in the chosen solvent one could go on adding the hot solvent for a long time before the mixture is dissolved completely. If you use too much solvent the desired compound will not come out of solution when you cool it. In practice, you probably will make this mistake many times and the only way to recover your compound is to concentrate the solution and see if the desired solid precipitates. Therefore, for best results, you must be able to judge whether any un-dissolved solid is the compound that you are trying to recrystallize or some poorly soluble impurity. Recrystallization using a solvent mixture (solvent pair) is very useful for purification of certain compounds. In this technique one dissolves the compound in a warm solution of the solvent component in which the compound is more soluble, and then the second solvent (in which the compound is less soluble) is added until a slight turbidity appears (dropwise). The solution is reheated (or a drop of the first solvent is added) to obtain a clear solution. The solution is cooled to obtain the recrystallized compound.

For this experiment, you will recrystallize an unknown compound using water. Your unknown compound could be: Benzoic acid, Salicylic acid or Sorbic acid. Thermometers are delicate and must be handled gently! You should pick a digital scale that you will use to measure weights for all the experiments. Since each balance has been calibrated differently, it is important that you use the same balance for every weighing! It is your responsibility to make sure that your balance is kept clean. Please refrain from making any adjustments to the scale. Report to your instructor if there is a problem.

PLEASE NOTE:

** DUE TO THE IRRITATING NATURE OF FUMES GIVEN OFF WHEN THE SOLUTIONS FOR RECRYSTALLIZATION ARE HEATED,

THIS EXPERIMENT MUST BE CONDUCTED IN THE FUME HOOD! **

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B. EXPERIMENTAL PROCEDURE Recrystallization Of An Unknown From Water. First, obtain a sample of your unknown compound from the lab instructor. Then, take a melting point of your impure sample. Set up all the apparatus that you will need for recrystallization in the fume hood. Boil approximately 150 mL of water. Pour 5-10 mL of this hot solvent into a flask equipped with funnel and filter paper. Place on a hot plate to warm up while you go on with your other preparations. Weigh out 2 g. of your impure unknown and place it in a 125 mL Erlenmeyer flask. Carefully add (in small amounts) the hot solvent. Remember the importance of using the minimum amount of hot solvent. (You may have to decide whether the last traces of un-dissolved solid are samples or an insoluble impurity, so look carefully for changes in the amount of solid present). Swirl the flask between additions and when almost completely dissolved, add a boiling chip and bring back to boiling on the hot plate. Remove the boiling solution from the hotplate, add gradually a small amount of decolorizing carbon (Norite, caution-frothing), and swirl the solution gently. Heat the solution to boiling for approximately 5 minutes. Filter the hot solution using a heated funnel and fluted filter paper.

NOTE: It is important to keep the solution and the filtering apparatus hot during the filtration. Since the solubility of benzoic acid decreases rapidly as the temperature decreases, the crystals may begin to crash out while you are filtering and this could result in considerable loss of product. To avoid this, add slightly more water than is needed to completely dissolve the impure solid. The excess water can then be evaporated after the Norite has been filtered off. The purpose of Norite is to remove small amounts of colored impurities. It is usually not necessary to use Norite in situations where you do not seem to have any colored impurities. While we are using Norite in this experiment for practice, you should only use Norite if it seems necessary to do so in the future. Cover the mouth of the flask containing the hot filtrate with a watch glass and allow to cool first to room temperature, then let it stand undisturbed in an ice bath. The more slowly a solution is allowed to cool, the better the quality and purity of the crystals you will obtain. When the product has crystallized completely, collect the crystals in a Buchner funnel. Rinse the Erlenmeyer flask with part of the filtrate to ensure complete transfer. Discontinue the suction when the crystals are still slightly moist. Wash the crystals with cold water. Apply suction again and press the crystals firmly with a clean glass stopper. Allow the crystals to dry in the air for a moment and then gently “bake” them in the oven.

HINT: While air drying the wet crystals is often the safest way to remove the solvent, it can also be very time consuming. Depending on the solvent that you have used (for example: water is fine for this), you may gently “bake” your wet crystals on a watch glass in the oven to evaporate the solvent faster. You must be careful to check the oven temperature and avoid overheating the crystals inside the oven!

(Think! At what temperature should you remove your crystals from the oven?) Determine the weight, yield, and the melting point of the dried recrystallized material. Based on the melting point range and the table of melting points (p. 5), identify your unknown. To be certain of the identity of your compound, you must also take a mixed melting point with a reference sample of the known material. Submit your sample to your instructor (see next pg.). Remember, your sample will be graded both on the quality of the crystals and the yield obtained. The yield in this case will be based on the mass of purified unknown solid that you recover. The yield can also be expressed as a Percent Recovery, which is the mass of purified solid obtained is divided by the mass of impure solid that you started with times 100%.

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After the experiment is completed, you should hand in a sample of your recrystallized compound to your instructor. (A proper container for solid samples is a small test tube or vial. If using a test tube, make sure to cover the top with a small piece of Parafilm). The container should bear a label that states: (a) your name and unknown # (b) the name of the substance and its melting point (c) the page of your notebook describing the sample (d) the weight of the sample and the tare weight. All weights must be in your notebook and recorded to two places past the decimal (in grams). C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). In addition, your lab report should include the following at the appropriate section: Results & Observations – For results, you should include all recorded weights (including actual yield of crystals), melting point, calculated percent yields, etc. Be sure to write down your in-class observations! Discussion: You should comment on your yields, provide identification and the melting point of your recrystallized compounds. (Make sure that you clearly indicate the number of your unknown sample… No credit will be given for your work if you fail to include your unknown number!). Assigned Questions: Answer Questions 1, 2 and 6 on Pavia page 679-680, as well as the following question:

“The solubility of benzoic acid in water is 6.8 g/100 mL at 95°C and 0.3 g/100 mL at 25°C. You are given 10 g of benzoic acid. Calculate the amount of water that you would use to recrystallize the sample. If the crystals are collected at 25°C what is the maximum possible recovery?”

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Experiment 3: Simple & Fractional Distillation

Reference: Pavia - Techniques 14 and 15 - pages 719-748.

A. INTRODUCTION Distillation can be used as a method for purifying a single liquid and also as a means of separating a liquid from a dissolved solid or from a mixture of miscible liquids. The liquid (or mixture) is heated and when it boils, the vapors are condensed into a separate receiver. The resultant liquid (distillate) is collected in one or more fractions. i) Purification of a Single Liquid: A single liquid will begin to boil when its vapor pressure is equal to the vapor pressure of the atmosphere. For a pure liquid the boiling temperature should remain constant (within 2°C) for the duration of the distillation. ii) Separation of a mixture: When a solution of 2 miscible liquids is distilled, boiling will begin when the total pressure of the solution is equal to the atmospheric pressure. If the solution is 'ideal' (follows Raoult's Law), the total pressure will be the sum of the partial pressures of each liquid. These partial pressures are dependent upon the vapor pressure of the pure liquid and its mole fraction in the solution.

If the boiling points of liquids differ by more than 100°C, good separation can be obtained by simple distillation, as the partial pressures of the two liquids will be very different. However, if the boiling points are fairly close to each other (say within a 40°C difference), one cannot obtain sharp separation by simple distillation. A different method must be employed to increase the efficiency of the distillation. This is accomplished by the use of a fractionating column. Our column will consist of a condenser filled with a packing material. iii) Fractional Distillation: In order to understand the behavior of two liquids as they are distilled using a fractionating column, you must understand the liquid/vapor composition curves in Pavia on pages 723, 730, 732, 742 and 743. You will have to spend a great deal of time studying Techniques 14 and 15 to understand distillation. Sections 14.2, 14.3, and 15.1-15.6 should be particularly helpful. The column packing provides a surface for these multiple condensation and vaporizations to occur. In order for the column to function successfully, a temperature gradient must be maintained along its length (i.e.: the bottom of the column must be hotter than the top). This can be accomplished by heating the boiling flask very slowly and also by insulating the column with glass wool or cotton secured with aluminum foil. The mixture must move up the column slowly, thus ensuring an equilibrium of vapor and liquid all along the column. The temperature gradient is also dependent upon the heats of vaporization (HV) of the two liquids. As the difference between of the two components increase, a larger temperature differential is possible and the efficiency of the separation increases.

** If the flask is heated too quickly or too vigorously, poor separation will occur. ** Theoretically, if one performs a fractional distillation at maximum efficiency, a plot of temperature vs. volume of the distillate would resemble Figure 1 (see next page).

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Figu

re 1

: Dist

illat

ion

of a

Mix

ture

B. EXPERIMENTAL PROCEDURE You will work with a partner to distill a mixture of methanol-water, once with a simple distillation set-up and also by using a fractionating column. It is possible to run both set-ups at the same time. You should assemble both sets of apparatus at the beginning of the lab period, but you should focus on the fractional distillation first. After collecting about 15 mL of distillate, one of the partners in a pair should begin the simple distillation procedure. The results of both distillations will be compared. i) Apparatus Simple Distillation: Follow figure 14.1 on Pavia page 720 with the following modifications: Use a heating mantle/regulator apparatus. Start with the regulator set at 50 and lower to approximately 30 immediately when you observe the liquid boiling. Using a 100 mL round bottom flask, secure both the flask and the heating mantle. Use a 10 mL graduated cylinder to collect your distillate. Have a beaker handy to empty the graduated cylinder as it fills up. You will be collecting more than 10 mL of distillate. Describe your apparatus in your notebook. Fractional Distillation: The same basic set-up is required except that your fractionating column (filled with steel wool or glass beads) should be placed between the boiling flask and the still (see Pavia p. 731). Do not run water through your fractionating column. Use glass or cotton wool to insulate the column and secure the insulation with aluminum foil. Again, describe your apparatus in your notebook. ii) Procedure Simple Distillation: Obtain approximately 60 mL of the methanol-water mixture assigned to you and pour it into the boiling flask. Add one or two Carborundum boiling stones. Make sure that all of the ground glass joints are securely fitted and that the water is flowing through your condenser properly (in the bottom, out the top). Have your instructor check your apparatus before you begin the distillation. The mantle regulator should be set to maintain boiling in the flask. The distillate should come out at a rate of 1 drop every two seconds. Record the boiling point for each mL of distillate in your notebook (use tabular form). Fractional Distillation: Carry out the distillation of a separate 60 mL sample of your unknown using the fractional distillation set-up. As soon as boiling starts turn down the regulator to keep the liquid boiling SLOWLY. As you heat slowly, a ring of condensate will rise slowly in the column. This rise should be gradual to allow for equilibration within the column. The ring of condensate should take at least several minutes to reach the top of the column. Once again, distill at a rate of 1 drop of distillate every 1-2 seconds. Once distillation actually begins maintain a constant rate by slowly increasing the heat as required. Record the boiling temperature for each mL of distillate in your notebook. If possible, make more frequent readings when the temperature starts to rise quickly. You may stop distilling after a second steady temperature is reached for 4-5 consecutive mL.

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C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). In addition, your lab report should include the following at the appropriate section: Results & Observations: For results, you should include the table of data collected (mL/temperature), graphic display of your result on graph paper. Be sure to write down your in-class observations! For your graph, plot mL of distillate (x-axis) vs. Temperature (y-axis) for your two distillations. Make sure to plot both curves on the same paper using different symbols (or colors) for the 2 sets of data. Draw the best curves for each of your data sets. Discussion: In addition to your normal write-up, your discussion should cover all of these aspects: 1. Discuss the results you obtained for the 2 distillations. Include a discussion of your own observations during the distillations and also a discussion of the theoretical aspects of simple vs. fractional distillation. 2. What can you conclude from your own distillations? 3. If your fractional distillation showed no better separation than your simple distillation, give possible reasons for this result. 4. What are possible sources of error in this experiment? 5. Use your graph to estimate the volumes of methanol and water in the mixture. Calculate the percent composition of your mixture? Comment on the accuracy of this determination. Assigned Questions: Answer Questions 1, 2, 6 and 9 on Pavia page 747-748, as well as the following three questions: 1. Why is the ability to separate 2 liquids by fractional distillation drastically reduced if heat is applied too rapidly to the distillation flask? 2. The bulb of the thermometer placed at the head of a distillation apparatus should be adjacent to the condenser. Explain the effects on the temperature recorded if the thermometer were placed (a) below the exit to the condenser and (b) above the exit. 3. Answer the following question using the table below as a reference. The components of a methanol-water and carbon tetrachloride-toluene mixture differ from each other in boiling point by about the same amount. However, the methanol-water mixture can be separated more efficiently by fractional distillation. Explain.

SOLVENT B.P. Heat of Vaporization* Acetone 56.5 125.3 Methanol 64.7 261.7 Hexane 68.7 79.2

Carbon Tetrachloride 76.7 46.4 Benzene 80.1 93.5

Cyclohexane 80.7 93.2 Water 100.0 536.6

Toluene 110.6 86.8 * In Calories per gram at the boiling point (b.p.)

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Experiment 4: Chromatography

Reference: Pavia - Techniques 19 and 20 - pages 777 - 811.

A. INTRODUCTION Separation of a mixture into its pure components is an essential part of organic chemistry. For example, a chemist may want to purify the crude extract of a medicinal plant, isolate the pure product(s) of a chemical reaction from the reaction mixture, or identify foreign compounds in a urine sample. Experiments 2-5 in this course cover basic separation and purification techniques: filtration, recrystallization, distillation, chromatography, and extraction. These techniques can be distinguished by the important physical properties involved: solubility, boiling point or polarity. Essentially, the purification of a mixture takes advantage of the way any physical property varies between the components of a mixture. i) Background Information Chromatography is one of the most ubiquitous methods of analyzing and purifying organic compounds. Flash column chromatography separates large quantities of compounds under air pressure while TLC (thin layer chromatography) is more useful for qualitative and small-scale separations or the identification of compounds in a mixture. The fundamental principle of chromatography is the distribution equilibrium that forms when a compound is either dissolved in a mobile phase or adsorbed on a stationary phase.

When a compound is dissolved in the mobile phase, it is carried along the direction of flow. But when it is adsorbed on the stationary phase, it does not move. If compound B spends more time in the mobile phase than compound A, B will move further along the direction of flow than A, and will eventually be separated in space from A. The longer the mobile phase travels, the better the separation between A and B. Stationary phases are usually very polar, while mobile phases vary widely in polarity, but are less polar than the stationary phase. The exception is reverse phase (RP) chromatography, in which a polar mobile phase, and a less polar stationary phase are used.

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ii) Thin layer chromatography This technique is performed on a glass or plastic plate that is coated with a thin layer (thus the name) of dry adsorbent. Usually these plates are pre-coated with a layer of silica gel or alumina. The sample mixture is spotted on the plate near the bottom, and the plate is put in a closed beaker or jar with a small amount of the appropriate solvent or solvent mixture. Capillary action draws the solvent up the plate. When the solvent front is near the top, the plate is removed from the beaker and a separation of the sample's components may be observed (See figure below).

iii) Visualizing the TLC Plate If the compounds are colored, the plate can be read easily. If the compounds are not colored then they can be visualized using an ultraviolet lamp or a chemical stain. There are a wide variety of chemical stains based on the functional groups present. The following methods of detection will be used in this laboratory: iv) Ultraviolet Light Detection This is a nondestructive visualization technique, which will show any compounds that absorb UV light when looking at the slide under the UV lamp. Compounds containing benzene rings, or conjugated systems usually absorb light in the Ultraviolet region of the electromagnetic spectrum. Commercial TLC plates have phosphor in the adsorbent, which fluoresces when exposed to long-wave UV light. If a compound is present on the plate that absorbs this light, it blocks the glow and appears as a dark spot. (This is technically true only for compounds that quench the fluorescence). Some organic compounds fluoresce themselves, and will show up as bright spots under short-wave UV light. v) Staining With Iodine This is also a nondestructive visualization technique. A few crystals of iodine are placed in a closed chamber, such as a capped jar containing silica gel, and the slide is placed into the chamber to collect iodine on the spots by a weak electronic attraction. Iodine forms a yellow or brown complex with most organic compounds, except for saturated hydrocarbons and alkyl halides. The reaction is reversible, so that I2 staining can be followed by another chemical stain if the plate is allowed to sit in air for several minutes so that the iodine can sublime off the plate.

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vi) Rf values For each spot on the TLC plate, a characteristic value called the ratio to the front (or Rf) can be calculated. Rf is defined as the ratio of the distance traveled by a spot (measured from the center of the spot) to the distance traveled by the solvent. (See illustration of TLC plate below).

Although the Rf is characteristic for a given compound, it depends greatly on the solvent and the type of adsorbent used. Consequently, the CRC Handbook of Chemistry and Physics, or Merck Index does not contain tables of Rf values. The difference in Rf values between two spots on a plate, ∆Rf, which also varies with the solvent, is used as a measure of the performance of the separation. The choice of solvent system is crucial for good separation. With a high polarity of a developing solvent, all of the spots will run to the top of the plate, and ∆Rf will be zero. With a very non-polar solvent, the spots will not move from their initial positions, and again ∆Rf = 0. The best separation is often achieved by using a mixture of a non-polar solvent with a polar solvent. The polarity of the developing solvent is adjusted by changing the ratio of polar to non- polar solvents in the mixture. The appropriate developing solvent should give an Rf of 0.3 to 0.7 for the desired compound and a ∆Rf of at least 0.1 between the desired compound and any impurities. Once an appropriate mixture is chosen for TLC, the same mixture can be used to develop a column. vii) Column Chromatography This technique is performed by packing a glass tube with an adsorbent as shown on the next page. There are many different types of adsorbents (solid phase) that are used in column chromatography, and the choice of adsorbent depends on the types of compounds to be separated. The most common adsorbents used are: silica gel and alumina. Silica gel is used to separate a wide variety of functional groups such as hydrocarbons, alcohols, ketones, esters, acids, azo compounds and amines. Alumina is also used extensively, and comes in three forms: acidic, basic, and neutral. Acidic alumina is used for separating acidic materials such as carboxylic acids and amino acids. Basic alumina is used to separate amines, while neutral alumina can be used to separate non-acidic and non-basic compounds. Likewise, cellulose, starch, and sugars are used to separate natural products, and magnesium silicate is used in the separation of acetylated sugars, steroids, and essential oils. A column may be packed 'wet' by mixing together a slurry of the solvent and adsorbent and pouring it into the tube. Alternatively, it can be filled with the dry adsorbent. The mixture to be purified is then

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dissolved in a small amount of the appropriate solvent and added carefully to the top of the solid adsorbent. It is added carefully to ensure that the packing is not disturbed. You develop the column by adding more of the solvent to the top, and then collecting the fractions of eluent that come out at the bottom. For 'flash' column chromatography, moderate air pressure is used to push the solvent through the column. The success of the separation and the contents of the fractions can be determined by spotting the fractions along with the initial mixture on TLC.

A column can be developed with a single solvent, or a solvent gradient (a solvent system which gradually increases in polarity). For example, a column may be developed first with a low-polarity solvent, such as hexane, and as fractions are collected the developing solvent is changed to 10:1, 5:1, and 1:1 hexane-methylene chloride. The solvent is changed by adding it as soon as the previous solvent is level with the silica gel and before the top of the column to runs dry. A polarity gradient is used for mixtures of compounds with very different polarities. Non-polar compounds adsorb less readily to the polar stationary phase, and consequently will travel more along with the mobile phase. Since polar compounds are better adsorbed onto the polar stationary phase, they tend to travel more slowly. A polar solvent can best compete with the stationary phase to attract more polar analytic, thus carrying it along with the mobile phase. So, the best mobile-phase/solvent system will be sufficiently polar to compete with the stationary phase so that the analyze is carried far enough down the column, (or away from the baseline) but is still sufficiently attracted to the stationary phase so that the compound will not travel all the way down the column (or along the solvent front). Solvents: A common non-polar solvent for chromatography is hexane. It can be used with a variety of polar solvents. The following solvents are listed in approximate order of increasing polarity: cyclohexane, petroleum ether, pentane, carbon tetrachloride, benzene, toluene, chloroform, ethyl ether, ethyl acetate, ethanol, acetone, acetic acid, methanol, and water. Elution sequence: The order of elution for common compounds from fastest (moves with a non-polar solvent) to the slowest (where a more polar solvent is necessary) is as follows: hydrocarbons, olefins, ethers, halocarbons, aromatics, ketones, aldehydes, esters, alcohols, amines, and acids, strong bases.

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B. EXPERIMENTAL PROCEDURE i) Experimental Outline TLC will be used to determine Rf values and an appropriate solvent system for the separation of four organic compounds (anthracene, cholesterol, 1,4-naphthoquinone, and para-nitroaniline).

Small-scale column chromatography will be used to separate three organometallic compounds: ferrocene, acetylferrocene, and diacetylferrocene. The separation will be on the microscale level, using a Pasteur pipette as your column. Prior to the column separation, TLC will be used to demonstrate the efficiency of separation in different solvent mixtures. Thus, you will be using TLC to determine the appropriate solvent system for running your column. As a general guideline, an Rf value of about 0.4 in a TLC is best for eluting a particular compound from a column.

ii) Procedure Part I. Thin Layer Chromatography Preparing the TLC Plate The goal of this experiment is to determine a solvent system in which all four spots will move up the plate, and to calculate the Rf -values for the four compounds. First, with a pencil, lightly mark a baseline on a TLC plate, about 1 cm from the bottom. Do not touch the silica face of the TLC plate with your fingers, and never use a pen to mark your TLC plate because the ink will also migrate with the solvent! On the very top of the TLC plate, label the spots in pencil according to what is being spotted (e.g. A = anthracene). Obtain a small amount of the four compounds and dissolve each separately (in a small test tube, or on a watch glass) in a small amount of methylene chloride (dichloromethane). A small amount of compound is considered a trace amount on the small ends of your spatula tips. In preparing sample solutions, the concentration must be adjusted so that isolable, discrete spots can be

HO

O

O

NH2

NO2

Anthracene Cholesterol 1,4-Naphthoquinone para-Nitroaniline

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developed. A solution that is too low in concentration results in very faint spots, which can be difficult to visualize, while streaking and poor separation is observed when the concentration is too high.

HINT: Methylene chloride (dichloromethane) evaporates VERY QUICKLY! You must work very quickly as soon as you pour the methylene chloride from its glass container to the watch glass. Spot the plate, by dipping either end of the capillary tube into the solution. The solution will be drawn up by capillary action. You then empty the capillary tube by touching it lightly on the surface of the TLC plate. This will transfer the solution to the plate as a small spot. You should only hold the micropipette in contact with the plate very briefly, otherwise, the entire contents may be delivered to the plate and your spot will be too large. It may be a good idea to gently blow on the plate as the sample is applied. This will help the solvent to evaporate quickly, keeping the spot small. Developing the TLC Plate Choose a solvent or solvent mixture (preferably a mixture of ethyl acetate, CH3CO2C2H5, and hexane. Petroleum ether can be used as a substitute for hexane) and prepare the developing chamber as shown in the illustration on page 13. Start by developing one plate with pure petroleum ether and another with pure ethyl acetate. Then use a one to one mixture of ethyl acetate and hexane. By examining these TLC plates, you can decide whether to increase or decrease the polarity as needed by adding more of either solvent. Be sure that you know what proportions of the solvents are used as you adjust the polarity of the mixture. The level of the solvent in the jar must be below the level of the spots, and the atmosphere in the jar should be saturated with solvent vapors. (If the jar is not saturated with solvent vapors, the solvent will not run all the way up the plate!). When the solvent front is near the top of the plate, immediately remove the plate from the beaker with forceps, and mark the solvent front with a pencil, before the solvent completely evaporates. Visualizing the Spots on the TLC Plate Allow the TLC plates to dry. First, check your plate with the UV lamp (short-wave). Lightly outline the spots which you observe with a pencil, and make a sketch of the TLC plate in your notebook. Note any differences in the appearance of the spots. CAUTION: Do not look directly at the UV lamp, or shine it at anyone else! If the spots are not visible under UV light, place the slide inside an iodine chamber and allow it to sit until the subliming iodine coats the TLC plate. Mark any new spots that become visible.

Calculating the Rf Values Next, measure the position of the original spotting to the spot (baseline), and of the solvent front. Calculate the Rf values. For each compound record in tabular form, the solvent (or solvent mixture) and the Rf value. Part II. Column Chromatography Packing the Micro-column Silica gel should always be transferred inside the hood, since the small particle size makes it very hazardous to the respiratory system if it is breathed in. Prepare a column from a Pasteur pipette by carefully pushing a small piece of cotton down to the narrow part. Clamp the pipette with a thermometer clamp and add about 1/4 inch of sand (use weighing paper as a funnel). Then add about 2-1/2 inches of silica gel. Get a small quantity (just a spatula tip full) of the mixture of ferrocenes and add it directly to the top of the silica gel in your column. Then add another quarter of an inch of sand.

HINT: Save some chemicals and time! If you add too much of the ferrocene mixture in your column, you will have to use more solvent and spend more time to separate your mixture…

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Separation of Ferrocene, Acetylferrocene, and 1,1-Diacetylferrocene Begin eluting the column by first adding 100 % hexane (b.p. 68-70°C) with another Pasteur pipette, in order to move the non-polar compound down the column. After completely eluting with 100% hexane, you should gradually increase the solvent polarity in order to force the more polar compounds down the column. Increase the polarity of the solution by utilizing a 20:80 mixture of ethyl acetate and hexane, and finally work your way up to a 50:50 mixture of ethyl acetate to hexane. (Notice the different colored bands and determine which band belongs to which compound and why.)

HINT: Solvents you pour down the column will take a LONG time to travel the column by gravity alone. Attach a pipette bulb at the top of your column and gently squeeze between solvent pours to help push the liquid down faster. Ask your instructor to demonstrate this technique before attempting it! To ensure a clean separation of the three metallocenes, you should completely elute each band before adding the increasingly polar solvent mixture. You should also collect the solvent between each band in a separate test tube. (Diluting the components with excess solvent will cause ill-defined spots during the final TLC separation.) NOTE: For best results, DO NOT let the top of the column run dry until you are finished! Collect (1 milliliter fractions per test tube) in labeled test tubes and run a TLC plate to check the effectiveness of column separation using a 60:40 mixture of hexane to ethyl acetate. Part III. TLC to Identify Unknown Mixture To Be Used In Experiment 5

Very Important: THIS PART MUST BE COMPLETED ON THE SAME DAY YOU ARE WORKING ON EXPERIMENT 4! Make sure to save the developed TLC plate for this part, as you will need the data for Experiment 5 pre-lab and post-lab write-up! Your instructor will assign you an “unknown” mixture that you will use in Experiment 5. Make sure that you record the sample number! You must develop a TLC plate with your unknown in order to determine the identity of compounds that are in your mixture. Your mixture contains TWO of the following compounds: acetylsalicylic acid (aspirin), phenacetin and caffeine. Prepare a TLC plate by marking its baseline and labeling the top with “A,” “P,” “C,” and “Mx” (for the three compounds mentioned earlier and the unknown mixture respectively). After you have marked your TLC plate, obtain and dissolve a small amount of your unknown mixture with dichloromethane in a clean small test tube / watch glass. Spot it with a clean capillary tube at the appropriate position on your TLC plate. Repeat the dissolving/spotting process with the three reference compounds. Be careful not to mix up your four spots (A, P, C, and Mx)! Develop your TLC plate with the following solvent mixture: 95% ethyl acetate, 5% acetic acid (you may use a communal solvent chamber with your classmates). Be careful to quickly mark the solvent front. Mark the developed spots first with the aid of the UV light. If necessary, you may place your developed TLC plate in the iodine chamber (allow 5-10 min for the I2 to absorb). At this point, you should know what compounds your unknown mixture is made up of. You will need this information for Experiment 5. Your pre-lab write-up for that experiment should be tailored to the specific combination of compounds that you have in your unknown.

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C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). In addition, your lab report should include the following at the appropriate section: Results & Observations: Table of Rf data for both parts. Be sure to write down your in-class observations and attach a photocopy of your TLC plates produced from both parts! Discussion: In addition to your normal write-up, your discussion should cover all of these aspects:

(1) Relative polarity of all the compounds and how this correlates with their structures (2) Nature of silica gel.

Assigned Questions: Answer Questions 3 on Pavia page 800 and Question 4 on Pavia page 812

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Experiment 5: Identification Of An Unknown Mixture By TLC and

Separation Of That Mixture Using Acid-Base Extraction

Reference: Pavia - Technique 12 - pages 681-702. Read the Essays on Aspirin (p. 53), Analgesics (p. 60), Identification of Drugs (p. 67), Caffeine (p. 73), and any others of interest such as Local Anesthetics (p. 343).In the above reading assignments you must pay special attention to the principles behind the separation techniques employed (pages 681-702). Pay attention to sections on extraction (sections 12.1-12.8) and drying agents (section 12.9). It is also essential to understand the fundamental principles of acidity and basicity, and the application of these principles in organic chemistry. You must spend a substantial amount of time studying your lecture textbook to develop this understanding. A. INTRODUCTION The separation of acids and bases from neutral compounds by extraction is routinely employed in research laboratories. Aspirin (acetylsalicylic acid) readily donates a proton to hydroxide, carbonate, or bicarbonate ion. Its resulting conjugate base (an anion) is more soluble in water solutions of these bases than in common organic solvents. Caffeine is basic and readily accepts a proton in aqueous acid. Its conjugate acid (a cation) is more soluble in water than in the relatively non-polar common organic solvents. Phenacetin is neutral and does not easily accept or donate a proton. All three compounds are pressed together with a starch binder to form APC tablets. Please note that phenacetin has been found to cause kidney damage and is no longer in common medicinal use. Your unknown mixture contains TWO of the three compounds: acetylsalicylic acid (aspirin), phenacetin or caffeine. You will determine which two compounds are present in your mixture, and then separate the components from each other to obtain pure samples of each. The compounds in your mixture are industrial chemicals and are not intended for human consumption! After separating the two compounds, you will use thin layer chromatography to test the completeness of your separation.

Success in this experiment requires a particularly large amount of planning and careful preparation!!

B. EXPERIMENTAL PROCEDURE Based on the chemical composition of your assigned unknown mixture, you must plan a suitable separation process for your unknown. Some general hints on separation technique: Weigh out exactly 3.00 g of the unknown mixture. (You will experience solubility problems later if you use more than this!). Dissolve the unknown mixture in approx. 30 mL of dichloromethane in a small Erlenmeyer flask. Transfer the resulting solution to a small separatory funnel (Make sure that the stopcock of the funnel is closed!). Rinse the flask with an additional 5 mL of dichloromethane and add this to the separatory funnel to insure complete transfer of the unknown mixture. If you observe some crystals in the solution, do not be concerned. This could be phenacetin, which will go into solution when you begin the extraction steps. At this point, you must decide which reagent to use for your separation of components by extraction of the dichloromethane layer. Since you know (from TLC results) what the components of your mixture are, you should be able to decide upon a separation scheme. Remember that your goal is to use an

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extraction method that will cause one of the components of your mixture to become soluble in the aqueous phase. The aqueous phase is separable from the dichloromethane phase, so the material that has become soluble in the aqueous phase can be separated from the material that remains in the dichloromethane. When you add your extracting reagent, two phases will appear. Remember to save all your phases, properly labeled in flasks, until you have recovered all the components of your mixture. SAFETY NOTE: Although dichloromethane is much less toxic than the other common chlorinated hydrocarbon solvents, keep containers stoppered as far as possible, to minimize your exposure. When draining your separatory funnel, you should consider inserting a narrow strip of paper between the stopper and funnel rather than removing the stopper altogether. Air must enter the funnel as it drains off. (Otherwise, a vacuum is created within the funnel and your liquid will stop draining out). Dichloromethane is denser than water. Swirl the 2-phase mixture well before you stopper the funnel. Relieve the pressure frequently by inverting the funnel and opening the stopcock. Point it away from people! Additional Notes

1. CAUTION: A great deal of gas is evolved when bicarbonate is used. (What is it?)

2. Acetylsalicylic acid (aspirin) slowly hydrolyses in water. It should be isolated in the same lab period and not left standing in water for a long time.

3. Caffeine has enough water solubility that it does not precipitate from water easily. It must therefore be removed from aqueous layers by extraction with dichloromethane.

4. The best way to acidify bicarbonate washes is to add 10% HCl slowly to them until the acid is in excess, rather than the inverse procedure. Check to make sure the final pH is acidic.

5. The best way to neutralize HCl extracts is to add 10% NaOH to the extract slowly. Make sure the final pH is basic.

6. Dichloromethane layers must be dried with anhydrous Na2SO4 before evaporating them to recover components of your unknown.

7. The dichloromethane layers, once over Na2SO4 may stand over the week in your lab kit.

8. Remember to tare your flasks before evaporation of dichloromethane so you can get a weight of your unknown.

9. Determine the weight, the mp and the TLC of each component.

10. Recrystallize each component, re-measure each mp and perform TLC.

11. Caffeine may be recrystallized from acetone.

12. Phenacetin may be recrystallized from 95% ethanol-water.

13. Aspirin may be recrystallized by dissolving it in a minimal amount of 95% ethanol and then adding more water to the resulting solution.

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C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). Your lab report MUST have a proper flowchart that provides ALL necessary steps to properly separate your mixture. (You will NOT get full credit for a generic or incomplete flowchart that omits steps). In addition, your lab report should include the following at the appropriate section: Results & Observations: Be sure to write down your in-class observations and attach a photocopy of your TLC plates produced from both parts! Use the tables below as a model for tabulating your data and include them (only the portions relevant to your work in the laboratory) in your lab report. Part I. Calculate the Rf values for each spot on your TLC plate(s). Tabulate your data as shown below.

TLC of Mixture - Stationary Phase: Silica Gel; Mobile Phase: 95% ethyl acetate / 5% acetic acid TLC Results - Rf of Spots

MIXTURE UNKNOWN # ________ Mixture

Spot 1: X/Y = _______ Aspirin

X/Y = _______ Phenacetin

X/Y = _______ Caffeine

X/Y = _______ Part II. Tabulate your data as shown below. When calculating % yield, assume that you begin with equal weights of each component (e.g.: 6 g of mixture = 3 g of compound A + 3 g of compound B)

Separation of Unknown Mixture (Assume that you begin with equal weights of each component) Extraction / Recrystallization Results MIXTURE UNKNOWN # ________

Name of Component 1 Crude Weight: ______ g % Yield: _______ % M.P.: _________ °C Rf of Spot: X / Y = _________

Name of Component 2 Crude Weight: ______ g % Yield: _______ % M.P.: _________ °C Rf of Spot: X / Y = _________

Name of Component 1 (Recrystallized) Recrystallized Weight: ______ g Recrystallized % Yield: _______ % M.P.: _________ °C Rf of Spot: X / Y = _________

Name of Component 2 (Recrystallized) Recrystallized Weight: ______ g Recrystallized % Yield: _______ % M.P.: _________ °C Rf of Spot: X / Y = _________

Discussion: In addition to your normal write-up, your discussion should cover all of these aspects: (i) a conclusion about the composition of your unknown mixture; (ii) a statement on the purity of your isolated compounds; (iii) an analysis of relative polarities of your compounds and how their structure contributes to its relative polarity; (iv) sources of error in the experiment (e.g: Why are the Rf’s of identical materials not identical); (v) If you had any particular problems in the separation experiment, discuss them along with relevant observations (e.g.: low yields or yields over 100% , poor separation, inconsistent Rf, mp’s). You may do this by referring to your flow chart. Assigned Questions: Answer Question 1 on Pavia page 707, as well as the following question: Explain the results of the TLC errors: a) using too much sample; b) using too little sample; c) using a too-polar solvent; d) trying to elute a spot of crystalline material which is insoluble in the eluent.

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Experiment 6: Molecular Modelling

Reference: Please consult the relevant section in your lecture textbook. Pay close attention to the definitions of Torsional Strain, Steric Strain, Angle Strain, and 1,3-Diaxial Interactions.

A. INTRODUCTION The approximate shapes of molecules can be visualized with the aid of molecular models. These might be physical model kits with solid pieces that represent different types of atoms or molecules, or virtual model kits in which computer software is used to calculate and represent the three dimensional shapes of molecules. In this exercise, molecular model kits will be used to build the three-dimensional structures of molecules and illustrate the conformations of acyclic compounds as well as various derivatives of cyclohexane.

Proteus® Molecular Modeling Kit

Proteus® molecular modeling kits will be used for this exercise. These model kits have pre-formed pieces that represent sp3, sp2 and sp hybridized atoms. They are designed to approximate the bond angles within molecules and to give some indication of spatial relationships between different groups on a molecular structure. Black colored pieces are meant to represent carbon atoms, red pieces are used for oxygen and the blue pieces are designed to represent nitrogen. In addition, there are other colored extensions that are used as framework pieces representing atoms such as hydrogen, fluorine, chlorine and iodine. A unique feature of these Proteus® model kits is that each of the bonding arms has a locking mechanism that allows you to manipulate and change the conformations of the models that you build without them coming apart. This is especially important when working with the chair conformations of cyclohexane derivatives, allowing you to see the impact that a simple conformational change (ring flip) can have on the relationship between substituents on the cyclohexane ring.

Examples of Assembled Molecular Models with the Proteus® Kit

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DEFINITIONS: It will be helpful here to define a few terms related to symmetry since you will have to examine the symmetry properties of the molecular models that you construct.

A Plane of Symmetry divides a geometric figure or molecule into two equal halves so that one half of the shape is the mirror image of the other. A plane of symmetry is also referred to as a mirror plane and examples of planes of symmetry of a variety of geometric shapes and molecules are illustrated below:

A Center of Symmetry is a point about which a molecule or three- dimensional structure can be rotated so that all parts of the molecule or structure equidistant from that point becomes identical. For example, each point on the surface of a sphere is equidistant from its center, which is also a center of symmetry. In another example, there are a variety of ways in which the bipyramidal figure illustrated here might rotated about the point at its center to give an image that cannot be distinguished from the original structure. An Axis of Symmetry is a line or lines along which a two-dimensional structure or a molecule can be folded so that each of the folded segments is identical to the other. For example, an equilateral triangle and a trigonal planar molecule such as boron trifluoride both have threefold axes of symmetry. Alternatively, what this means is that rotation of a molecule with an x-fold axis of symmetry through an angle equal to 360/x degrees, will result in what appears to be an identical structure. For example, BF3, with a three-fold axis of symmetry will appear to be exactly the same whenever it is rotated through 360/3 = 120°. A hexagonal molecule like benzene has a six-fold axis of symmetry and appears to be identical when rotated through 60°.

However, geometric shapes and molecules can have several different types of symmetry axes. For example, both a triangle and a hexagon can also have two-fold axes of symmetry. For a two-dimensional structure, a two-fold axis of symmetry is the equivalent to a mirror plane. ‘

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B. PROCEDURE PART I – CONFORMATIONS OF ACYCLIC COMPOUNDS

A. Conformations of Ethane. The molecular formula, condensed formula and dash formula of ethane are illustrated below:

Construct a molecule of ethane by connecting two of the black pieces representing carbon atoms together using one of the bonding arms and then attaching white or gray framework tubes to the remaining six valence positions (three on each carbon) to represent the six hydrogen atoms. Hold the molecule in such a way that you are looking down the axis from one carbon to the other. Grasp the ends of the molecule near the hydrogen atoms and slowly rotate one end or the other until the three hydrogen atoms attached to one carbon are directly behind the three hydrogen atoms on the other carbon. This is referred to as the eclipsed conformation of ethane.

This eclipsed conformation of ethane is illustrated below in three different types of structural representations. The Sawhorse Formula, depicted in the middle, shows how the hydrogen atoms on each carbon are positioned relative to each other. The three-dimensional dash-wedge formula on the far left uses regular lines to show bonds that are in the plane of the paper, dashed lines to show bonds that are projecting backward into the paper and solid wedges to show bonds that are projecting out toward the viewer.

The Newman Projection, shown on the far right, emphasizes the dihedral angle between atoms or substituents as viewed along a particular molecular axis. The illustration shows the Newman Projection of the eclipsed conformation of ethane viewed along the C1-C2 axis. The front carbon is represented by the point of intersection of the lines connected to three hydrogen atoms while the circle represents the carbon at the back, which is also connected to three hydrogen atoms. In the eclipsed conformation of ethane, each of the hydrogens on the front carbon is directly in front of another hydrogen on the back carbon. Corresponding hydrogen atoms on front and back carbons are spatially closest together with a 0° dihedral angle between them.

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Now rotate one end of your model of ethane while holding the other end constant. Observe the changes in the dihedral angle between front and back hydrogens as you perform this rotation. Set the front and back hydrogen atoms so that there is a 60° dihedral angle between them. Draw the Three-Dimensional Dash-Wedge Formula, Sawhorse Formula and Newman Projection of this version of the structure, which is known as the Staggered Conformation of ethane. Based on your models, compare and contrast the eclipsed and staggered conformations of ethane in terms of symmetry – the presence or absence of a mirror plane, center of symmetry, number and types of axes of symmetry. Also compare the relative torsional strain and steric strain of each and use this to evaluate the overall energy of the two conformations. Combinations of torsional strain and steric strain produce measurable differences in overall energy. The energy associated with a variety of strain-producing interactions is summarized in Table 1.

Table 1. Energy Associated With Different Types of Strain Interactions

Type of Strain Interaction Associated Energy Eclipsing of a pair of H's 4 kJ/mol Eclipsing of a H and a CH3 group 6 kJ/mol Eclipsing of a pair of CH3 groups 11 kJ/mol Gauche (60) Interaction between CH3 Groups 3.8 kJ/mol 1,3 CH3 to H Interaction on Cyclohexane Chair 3.8 kJ/mol 1,3 CH3 to CH3 Interaction on Cyclohexane Chair 15.5 kJ/mol

Use the data in Table 1 to help you plot a graph of energy versus the angle of rotation for ethane. You may use the template below as a model for your graph. Your graph should show data for a full 360° rotation of the carbon-to-carbon bond. Label the y-axis with appropriate values for relative energy based on the values in Table 1. Draw the structures of the eclipsed and staggered conformations of ethane in the spaces above their associated positions on your graph.

Ener

gy (k

J/m

ol)

0° 60° 120° 180° 240° 270° 360° Angle of Rotation

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B. Conformations of Propane Build a molecular model of propane, CH3CH2CH3. Holding one end of the molecule, take a look down the C1 - C2 axis as you rotate the remaining CH3 group. Draw Newman Projections of all of the significantly different conformations of propane. Comment on the symmetry elements associated with these different conformations of propane. Again, using the data from Table 1, plot a graph of Energy versus Dihedral Angle for propane. Include your Newman Projection drawings in the appropriate positions on your graph. Draw a Three-Dimensional Dash-Wedge Formula and Sawhorse Formula of the lowest energy conformation of propane. C. Conformations of Butane Build a molecular model of butane, CH3CH2CH2CH3. Holding one CH3 group at the end of the molecule, look down the C2 - C3 axis as you rotate the CH3 group at the opposite end. Draw Newman Projections of all of the significantly different conformations of butane. For butane and other higher alkanes, the conformation in which the two largest substituents (in this case the two methyl groups at either end) are furthest away from each other with a 180° dihedral angle separating them is referred to as Anti while the conformation in which substituents are separated by a 60° dihedral angle is referred to as Gauche. Comment on the different symmetry elements of these different conformations. Again, using the data from Table 1, plot a graph of Energy versus Dihedral Angle for butane. Include your Newman Projection drawings in the appropriate positions above your graph. As you did for your model of propane, draw a Three-Dimensional Dash-Wedge Formula and Sawhorse Formula for the lowest energy conformation of butane. PART II – CONFORMATIONS OF CYCLIC COMPOUNDS A. Conformations of Cyclohexane

Construct a model of the chair conformation of Cyclohexane. Examine your model carefully. Check to ensure that all of the bond angles are approximately equal and that each carbon is at the center of a regular tetrahedron. Turn the model to face you in such a way that you are looking down the axis of any two parallel carbon-to-carbon bonds. Evaluate whether the conformation along each carbon-to-carbon bond is eclipsed or staggered. Evaluate the different symmetry elements of the molecule. An illustration showing the conventions for drawing the chair conformation of cyclohexane is shown below, including the positions of axial (ax) and equatorial (eq) substituents relative to the carbons in the ring. Substituents are considered to be cis on the ring if the bonds connecting them to the ring both point in the same general up or down direction relative to the ring itself. It does not matter if the groups are on axial or equatorial positions. It is their relative relationship with respect to the ring that matters. In the illustration below on the right, for example, A, B, and C are all cis. B and E are trans, but so are B and D. Pay close attention to the direction in which axial and equatorial bonds are directed as you go from one carbon to the next around the ring.

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Draw a Newman Projection of your model of the chair conformation, sighting along the two parallel axes on either side. Grasp your model firmly by two of the parallel carbon-to-carbon bonds and push either end up or down to make the boat conformation. Compare and contrast the boat and chair conformations in terms of symmetry, torsional strain, steric strain, angle strain and overall energy. Draw the Newman Projection of the boat conformation, sighting down the two parallel carbon-to-carbon bonds. Now push the opposite end of the molecule up or down to convert it to the completely interconverted chair conformation as illustrated below.

Repeat this chair-to-chair interconversion (ring flip) several times. Make note of the relationship between axial and equatorial hydrogens as you do so. An actual sample of cyclohexane is a mixture of these rapidly interconverting chair conformations. Since both forms of the chair are equal in energy they contribute equally to the composition of their equilibrium mixture. B. Constitutional Isomers and Conformations of Dimethylcyclohexane Replace one of the axial hydrogen atoms on your model of cyclohexane with a methyl group. Then replace another axial hydrogen atom in position #3 on the same side of the ring to make cis-1,3-dimethylcyclohexane. Analyze the different symmetry elements of this molecule. When a non-hydrogen substituent is in an axial position on a chair conformation, it comes close enough to other substituents or axial hydrogens to interfere with them sterically. This produces a type of strain known as a 1,3-Diaxial Interaction. As shown in Table 1, the 1,3-Diaxial interaction between a methyl group and one axial hydrogen increases the molecule’s energy by 3.8 kJ/mol. Perform a ring flip to convert cis-1,3-dimethylcyclohexane to the opposite chair conformation. Observe the orientation of the two methyl groups in each conformation. Describe their relative energies in terms of torsional strain, steric strain and 1,3-diaxial interactions. Keeping one methyl group in a fixed position, move the second methyl group to the other bond on position #3 to make trans-1,3-dimethylcyclohexane. Execute a ring flip and draw the chair and Newman Projection of both conformations. Perform the same analysis of this isomer in terms of its symmetry and energy that you did with cis-1,3-dimethylcyclohexane. Now move the second methyl group to different points around the ring until you have made all of the cis and trans isomers of dimethylcyclohexane. How many different constitutional isomers are there? Do a ring flip with each isomer that you make. Set up a table to include your illustrations of each isomer and its ring flipped conformation as both a chair and Newman Projection. Describe the relative energy of each pair of conformers.

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C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). Your lab report should include all drawings, graphs, and tables as well as any discussions of symmetry and energy that you have been asked to consider for this experiment. The summary table below lists what you should include in your report for each covered compound.

Ethane, Propane, Butane

Drawings: Sawhorse, Wedge, and Newman projections Graph: Energy Levels Discussion: Symmetry Elements, Energy/Angle Strain and Stability

Cyclohexane, Dimethylcyclohexane

Drawings: Newman projection Discussion: Symmetry Elements, Energy/Angle Strain and Stability

Be sure to number the carbons in all drawings of cyclohexane and dimethylcyclohexane!

In addition, you should also provide answers to the following questions under “Assigned Questions”: (1) Using data from Table 1, calculate the difference in energy between:

a) the lowest energy conformations of cis- and trans-1,2-dimethylcyclohexane b) the highest and lowest energy conformations of methyl cyclohexane,

trans-1,2-di-methylcyclohexane and cis-1,3-dimethylcyclohexane (2) The table below shows the relationship between the difference in energy (∆G°) of two conformers of

the same compound and the percentages of the more stable (A) and the less stable (B) conformers in their equilibrium mixture.

∆G° (kJ/mol)

% A more stable

% B more stable

0 50 50 1.7 67 33 2.7 75 25 3.4 80 20 4.0 83 17 5.9 91 9 7.5 95 5 11 99 1 17 99.9 0.1 23 99.99 0.01

a) Plot a double-y graph showing ∆G° versus the percentages of A and B using these data, with ∆G°

values on your x-axis and two separate curves showing %A and %B on the same y-axis.

b) Using your graph from part A and the values you calculated for Question 1 part B, estimate the percentages of methylcyclohexane, trans-1,2-di- methylcyclohexane and cis-1,3-dimethylcyclohexane in their respective equilibrium mixtures.

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Experiment 7: Oxidation of Cyclohexanol

Reference: Pavia - Techniques 6, 7, 8, 9, 12, 20, 22, 25, 26 and 27. Also read relevant sections in your lecture textbook concerning oxidation of alcohols and IR spectroscopy.

A. INTRODUCTION Oxidation reactions are very important in organic chemistry both on an academic laboratory as well as industrial scale. There are several reagents that are useful for conducting oxidations – many of the more common ones are based on chromium (e.g.: Jones reagent and PCC). Chromium compounds are often toxic and corrosive. A more environmentally friendly oxidizing agent is sodium hypochlorite (NaOCl, the active ingredient in commercial household bleach). The hypochlorite oxidation reaction is more rapid in an acidic environment and thus acetic acid is used to facilitate the reaction. Acetic acid converts sodium hypochlorite to hypochlorous acid (HOCl), which serves as the actual oxidizing agent. Potassium iodide-starch paper is used to check whether the oxidizing agent was completely used up in the reaction. If the solution changes the iodide-starch paper to a blue-black color this indicates that the solution contains an oxidizing agent. However, if the color of the iodide-starch paper remains colorless this means that no oxidizing agent is present. In this experiment you will oxidize a secondary alcohol (cyclohexanol) to a ketone (cyclohexanone) with a sodium hypochlorite solution. You will work in pairs for this experiment. Cyclohexanol is significantly more soluble than cyclohexanone in water. Because of the low miscibility of cyclohexanone and water, the cyclohexanone product will form a layer during the reaction. Sodium chloride is added in order to decrease the solubility of cyclohexanone in water. Infrared spectroscopy will be used to analyze the product of the reaction. B. EXPERIMENTAL PROCEDURE

Caution: There is the potential to evolve chlorine gas in this experiment! Make sure to conduct all procedures in a well-ventilated fume hood.

Be sure to record all observations during this experiment! Addition of Sodium Hypochlorite Pour about 2 mL of cyclohexanol in a 250 mL Erlenmeyer flask and then add 1 mL of glacial acetic acid to the cyclohexanol. Add a magnetic stir-bar to the flask and place the flask on top of a magnetic stirrer (Caution: Do NOT Turn On The Heat On The Stirrer!) in the fume-hood. Pour 60 mL of sodium hypochlorite solution (approximately 0.74 M) into the flask in small portions over a period of about 2 minutes while stirring the solution. The reaction is exothermic so you will notice that the flask will become warmer as the reaction progresses. Continue stirring the reaction for 20 minutes in the fume hood. Place a small piece of potassium iodide-starch indicator paper on a watch glass. By using a glass rod, place a drop of the reaction mixture onto the indicator paper. (Make sure that you dip the rod into the aqueous layer and not the organic layer). If the paper changes to a blue-black color, proceed to the quench step. If the paper remains colorless (oxidizing agent not present), add an additional 5 mL of sodium hypochlorite solution and stir the reaction for an additional 5 minutes. Test the solution for oxidizing agent repeating the procedure described above. If oxidizing agent is still not present add an additional 5 mL of sodium hypochlorite and stir the reaction for a further 5 minutes.

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Quench step Add 1 g of solid sodium thiosulphate (Na2S2O3) to the reaction mixture and stir for 2 minutes. Check for the presence of oxidizing agent by using the iodide-starch indicator paper as described previously. (No oxidizing agent should be present at this stage). Check the pH of the reaction mixture by placing a transferring a drop of the reaction mixture from the reaction to a strip of blue litmus paper on a watch glass. If the solution is acidic add 2g of solid sodium bicarbonate and repeat the pH test. If the reaction mixture is still acidic add another 1g of sodium bicarbonate to neutralize the solution. Workup and extraction of product Add 5g of solid sodium chloride solution to the mixture. (An appropriate amount of sodium chloride solution may be used if it is available). This is done to decrease the solubility of the product (cyclohexanone) in the aqueous phase. Stir the solution to dissolve most of the sodium chloride. If it all dissolves, add more sodium chloride and stir to dissolve as before. Decant the liquid from the solid sodium chloride that remains undissolved into a separatory funnel. A thin organic colorless organic layer should be present (on top of a cloudy aqueous layer) in the separatory funnel. Allow the solution to remain undisturbed in the separatory funnel for about five minutes. Open the tap on the separatory funnel and drain the bottom (aqueous layer) into an Erlenmeyer flask. Then drain the organic layer into a shell vial. You may notice a bubble of aqueous layer in the organic layer at this stage - This is ok, since the water can be easily removed. To do this, place a pipette into the solution and carefully remove the bubble of aqueous layer at the bottom of the vial. You may remove some of the organic layer in the pipette when this is done but the layers will separate in the pipette. Using the pipette as a mini separatory funnel, drain the bottom layer back into the Erlenmeyer flask being careful not to transfer any of the top layer in the process. Place the organic (top) layer back into the shell vial. Add sodium sulfate or magnesium sulfate drying agent. (Be careful not to use too much drying agent as this will cause loss of product). Allow the liquid to remain on the drying agent for about 5 minutes. The treated liquid should be clear and not cloudy. Transfer the product from the drying agent with a clean Pasteur pipette into a clean pre-weighed vial. Reweigh the vial to determine the yield. Spectroscopic analysis of the product Obtain an infrared spectrum of your product. Examine the peaks in the IR spectrum and determine if cyclohexanol and/or cyclohexanone are present. If cyclohexanol is present there will be an alcohol (-OH) stretch in the infrared spectrum. If cyclohexanone is present there will be a peak corresponding to the C=O stretch, for the ketone group in cyclohexanone.

C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). In addition, your lab report should include the following at the appropriate section: Results & Observations: Experimental data; Calculation of theoretical and actual yield of cyclohexanol Discussion: Provide a mechanistic proposal of the formation of cyclohexanol from cyclohexanone. Be sure to talk about your yield of product obtained and your interpretation of major absorption bands in the IR spectrum analysis. (Attach copy of IR spectra at the back of your report.) There are NO ASSIGNED POST-LAB QUESTIONS for this Experiment. (You may omit Item 9.)

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Experiment 8: Nucleophilic Substitution and IR Spectroscopy

Reference: Pavia - Techniques 7 (pages 608-629), 12 (pages 681-708) and 25 (pages 851-886). You should also read relevant sections in your textbook on nucleophilic substitution reactions.

A. INTRODUCTION For this experiment, we will carry out Experiment 19 in Pavia (pages 158-161) and Procedures 8A and 8B as described below. 8A and 8B are micro scale modifications of the macro scale experiments 20A and 20B, which are described in Pavia on pages 163 through 169. You will follow the procedure described in this handout, which only uses a single nucleophile instead of a mixture of competitive nucleophiles. The basic theory remains the same. In addition, your starting materials and products for 8A and 8B will be analyzed using infrared spectroscopy instead of gas chromatography. This technique is described in Pavia on pages 851-886. It will also be discussed in the Recitation class. You will obtain IR spectra under the guidance of your lab instructor for both the starting materials used and the products formed in procedures 8A and 8B. The presence or absence of characteristic peaks in the IR spectrum will help you to determine whether or not the reaction works and has gone to completion. Procedures for 8A take a long period of time, as it requires a 75-minute reflux period. The actual reaction time for 8B takes only about ten minutes, not including the workup and the isolation of the product. Procedures 8A and 8B also require IR analysis of both the starting materials and the products. Experiment 19 consists of a series of short test-tube reactions. Two class sessions are provided for the completion of this entire procedure but you should plan your work efficiently so that you will be assured of finishing all parts on time. You should definitely have enough time to complete 8A and perform IR analysis of the product during the first lab session. On the second lab session, you should complete both 8B and the test tube reactions of Pavia Experiment 19 as well. Again, ALWAYS PLAN YOUR WORK IN DETAIL so that you can complete your experiments properly and in an efficient manner.

Note: Procedures 8A and 8B uses hot, concentrated H2SO4. EXERCISE CAUTION AND ALWAYS WORK IN THE FUME HOODS! B. EXPERIMENTAL PROCEDURE You will perform procedures 8A and 8B in pairs. Preparing the Solvent-Nucleophile Medium (Necessary for BOTH PROCEDURES 8A and 8B) Each laboratory bench should make up a stock solution of the nucleophile medium to be used for this experiment. This solution should not be stored for a long time before use, so prepare only enough of the solution for Procedure 8A if you intend to perform Procedure 8B during the second week. First, place 10 g of ice in a 100-mL beaker and then carefully add 7.6 mL of concentrated sulfuric acid. (Safety Note: The ice must be in the beaker BEFORE you add the acid!). Carefully weigh 3.50 g of ammonium bromide into a beaker. Crush any lumps of the reagent and using a powder funnel, transfer the crushed solid to a 125-mL Erlenmeyer flask. Exercising caution, add the sulfuric acid mixture to the ammonium bromide. Swirl the mixture vigorously to dissolve the solid. It might be necessary to heat the mixture on a steam bath or a hot plate to achieve total dissolution. If necessary, you may add as much as 1 mL of water at this stage. Do not worry if a few granules of the solid do not dissolve.

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Procedure 8A: Reaction of 1-Butanol with Ammonium Bromide in the Presence of Sulfuric Acid Apparatus Set-Up: Assemble an apparatus for reflux using a 10 mL round bottom flask, a reflux condenser, and drying tube as shown in the figure below. Loosely insert dry glass wool into a drying tube and then add water until it is partially moistened. The moistened glass wool will trap the HCl and HBr gases produced during the reaction. Do not place the round bottom flask in the sand bath until the reaction mixture has been added to the flask. The sand bath should be adjusted to about 140°C.

REFLUX PERIOD Using a warm 10 mL graduated cylinder, obtain 6.5 mL of the solvent-nucleophile medium. The graduated cylinder must be warm in order to prevent precipitation of the ammonium bromide salt. It can be heated by running hot water over the outside of the cylinder. All of the salt must be dissolved when you transfer the solution to the reaction vessel. After you have transferred the solution, a small portion of the salts in the flask may precipitate as the solution cools. Do not worry about this; the salts will re-dissolve during the reaction. Add 0.5 mL of 1-butanol to the solvent-nucleophile medium contained in the reflux apparatus. Do this by removing the drying tube and with a graduated pipette, dispense the alcohol directly into the opening of the condenser. Add a boiling chip. Replace the drying tube and start circulating the cooling water. Adjust the heat from the heating mantle so that this mixture continues to boil gently. The sand bath temperature should be about 140°C. Observe the reflux ring. It should always remain in the lower fourth of the condenser. Violent boiling will cause loss of the somewhat volatile reaction products. The reaction mixture should be refluxed for about 75 minutes.

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END OF REFLUX PERIOD When the period of reflux has been completed, discontinue heating, remove the sand bath, and allow the reaction mixture to cool. Do not remove the condenser until the flask is cool. Be careful not to shake the hot solution as you remove the sand bath (or a violent boiling and bubbling action will result; this could allow material to be lost out the top of the condenser!). After the mixture has cooled for about five minutes, immerse the round bottom flask in a beaker of cold (not ice) water and wait for this mixture to cool down to room temperature. There should be an organic layer present at the top of the reaction mixture. Use the following micro scale extraction procedure to obtain your product (review Appendix II for details).

1. Add 1 mL dichloromethane to the cool reaction mixture, and shake the stoppered flask. Using a Pasteur pipette, transfer the organic layer to a clean screw cap vial. Caution: Do you know which is the organic layer?

2. Shake the organic phase with water (1 mL), separate again, and then shake the organic phase with sodium bicarbonate (1 mL) solution. Remove the aqueous layer. Caution: Do you know which is the organic layer?

3. Transfer the remaining organic layer into a small test tube and dry by adding anhydrous sodium

sulfate.

4. Using a clean dry Pasteur pipette, transfer the solution into a small dry screw cap vial, taking care not to transfer any solid. (When transferring the solution, filter through another Pasteur plugged with cotton if necessary). Be sure the cap is screwed on tightly.

5. Test solution with moist pH paper before submitting your sample for analysis.

IR SPECTROSCOPY Under the guidance of your lab instructor, obtain an IR spectrum of both your starting alcohol and your purified alkyl bromide product. Use sodium chloride plates as your sampling device as described in Technique 25, Section 25.3 on page 854 of your Pavia textbook. Please handle the sodium chloride plates very carefully as they are quite fragile. It’s best to rinse them with fairly anhydrous solvents such as dichloromethane, and they should always be stored in the desiccators when not in use. You should only use one drop of your samples in order to get sharp peaks in your IR spectrum but you will need to work quickly to obtain a spectrum before your product evaporates. Compare the IR spectrum of your starting material with that of your product.

Procedure 8B: Reaction of Ammonium Bromide with 2-Methyl-2-butanol (t-amyl alcohol) Place 3.0 mL of the solvent-nucleophile medium into a 5 mL screw cap vial. Allow the solution to cool to room temperature. Using a graduated pipette, transfer 0.5 mL of 2-methyl-2-butanol to the 5 mL vial. Replace the cap and shake the vial vigorously for 5 minutes. To allow gas to vent, be sure to open the cap periodically while shaking the vial! Any solids that were originally present in the vial should dissolve during this period. If all the solids do not dissolve, heat the vial (with the cap on) gently in the sand bath. After shaking allow the layer of alkyl halides to separate (one or two minutes at most). A fairly distinct top layer containing the products should have formed by this time. Slowly remove most of the aqueous layer with a Pasteur pipette and transfer it to a beaker. Again make sure you know which is the organic layer and which is the aqueous layer. Dilute the organic layer by adding 1 mL of dichloromethane to it, and repeat steps (2), (3) (4) and (5) from procedure 8A.

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IR SPECTROSCOPY Under the guidance of your lab instructor, obtain IR spectra of both your starting material, 2-methyl-2-butanol, and your purified alkyl bromide product. Use the same sampling technique that you used for Procedure 8A. Experiment 19 (Pavia): REACTIVITIES OF SOME ALKYL HALIDES **Each student should perform this part of the experiment independently** This experiment (Pavia, p 158-161) is relatively short and is to be run exactly as written. As noted on page 159, benzyl chloride is a severe eye irritant. (After you have finished the experiment, you should think about the reason why these compound cause the eyes' lachrymatory glands to produce a flow of tears.) Be sure not to spill a single drop of such "lachrymators" outside a fume hood - you may find your classmates and instructor very annoyed if you do.

NOTE: **DUE TO THE IRRITATING NATURE OF SOME OF THE REAGENTS USED, THIS EXPERIMENT MUST BE PERFORMED IN THE FUME HOOD!** Note that the 0.2 mL portion of each halide called for is no more than 10 to 20 drops from a pipette. Do not contaminate the reagents! Use only the labeled pipettes for transferring the different alkyl halides. C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). You should write ONE combined report that covers all three procedures completed for Experiment 8. However, you must take care to label the appropriate procedures for the Results and Discussion / Conclusion sections in your report at the minimum. (e.g.: You should create sub-sections for 8A, 8B and Pavia Experiment 19 under Results and Discussion/Conclusion) In addition, be sure to cover the points raised by the following guidelines at the appropriate section(s): GUIDELINES for Procedures 8A and 8B Neatly tabulate all recorded data. Your write up should include your observations and a clear comparison of the possible mechanisms (SN1 vs SN2) involved in the formation of each product formed in Procedures 8A and 8B. Also, compare and contrast the IR spectra of the starting alcohols with each other and with each of products obtained from them. Clearly describe how the IR results help to illustrate the synthetic chemistry performed in this set of reactions. Attach a copy of your IR spectra for all compounds used/created for this experiment. Be sure to label the relevant peaks directly on your spectra. GUIDELINES for Pavia Experiment 19 Neatly tabulate all recorded data. Your write up should include your observations and a clear comparison of the relative rates of product formation under the different reaction conditions. Be sure to explain your results in terms of the reaction mechanisms involved (SN1 or SN2) for all combinations. There are NO ASSIGNED POST-LAB QUESTIONS for this Experiment. (You may omit Item 9.)

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Experiment 9: Synthesis and Reactions of Alkenes

Reference: Pavia - pages 179-183; 464-467; 871-872; Technique 25

A. INTRODUCTION Alkenes can be prepared by a variety of methods, of which the dehydrohalogenation of alkyl halides and the dehydration of alcohols are perhaps most common. These general reaction types are illustrated below.

Both of these equations represent ELIMINATION reactions, in which small molecules such as HX and H2O are eliminated from the larger starting material. However, the actual mechanism by which this occurs can vary depending on the structure of the starting material, the conditions under which the reaction is carried out and the nature of the other reagents used. The two major classes of Elimination reactions involve E1 and E2 mechanisms, whose rates follow unimolecular and bimolecular kinetics respectively. E1 reactions occur in two steps with a positive carbocation intermediate being formed in the rate- determining step after the departure of a suitable “leaving group”. This is followed by the removal of a proton from the β-carbon adjacent to the positive charge and the formation of a double bond using the pair of electrons that it leaves behind. Since only the starting material is involved in the slow, rate-determining step, the overall rate of the reaction is only dependent on this species, hence the name E1 for unimolecular. Because a carbocation intermediate is formed, species undergoing E1 reactions are also prone to rearrangement if this will result in the formation of a more stable carbocation. An example of an E1 mechanism:

In contrast, E2 reactions occur in a single, concerted step when there is a strong enough base present to remove a β–hydrogen, forcing the leaving group to depart before the relatively slow carbocation formation has the chance to occur. The reaction is, therefore, bimolecular since the rate is dependent on both the starting material and the strong base involved.

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An example of an E2 mechanism:

Further details about the mechanisms of elimination reactions and the factors that affect them are beyond the scope of this manual. However, they are covered in detail in Organic Chemistry Lecture, as well as in the references listed on the previous page. You will also need to be familiar with the type of arrow-pushing mechanistic drawing used in these and other examples. GENERAL GUIDELINES FOR THE EXPERIMENT This experiment generally follows the procedures as outlined in Pavia Experiment 22, pages 179 – 183. 4-Methylcyclohexene will be made by dehydration of 4-methylcyclohexanol in the presence of an acid catalyst. The mechanism involves the initial protonation of the alcohol by a strong acid. This converts the -OH group into water, which is a much better leaving group. Loss of water naturally follows to give, in this case, a secondary carbocation. Subsequent removal of a proton from the β–position by H2O or HSO4

- (the conjugate base of sulfuric acid) results in the formation of 4-methylcyclohexene, which is the only product possible in this particular case. The entire process is reversible, as illustrated in the following scheme:

Once the synthesis is complete, the identity of the product will be verified using a combination of Infrared (IR) Spectroscopy and chemical tests for unsaturation, which indicate the presence of the double bond in the alkene product. These tests are illustrated in the following scheme:

You are required to work in pairs during this experiment and the apparatus is to be set up in the fume hood. 4-Methylcyclohexanol will be heated with a mixture of sulfuric and phosphoric acids in a flask equipped with a distilling head. Heating up the mixture in this way serves two functions: (1) it speeds up the reaction by shifting the equilibrium to the right and (2) it separates the product as it forms. 4-Methylyclohexene and water are immiscible with each other and steam-distill together (Pavia pg. 770-777). As described in the Pavia text, care has to be taken during the procedure to avoid the co-distillation of unreacted 4-methylcyclohexanol, which boils between 171 and 173 °C. Phosphoric acid is used in this reaction, mainly to minimize the volume of concentrated sulfuric acid that is needed. Concentrated sulfuric acid can often cause charring of the organic materials used and produced in this reaction, but it is essential in small quantities to ensure that the reaction occurs quickly. Small amounts of phosphoric acid may also distill over with the product, and this is removed by washing the crude product mixture with a saturated solution of sodium chloride. The product is then dried using anhydrous sodium sulfate. You will actually perform two distillations in the course of this exercise – one to facilitate the reaction and collection of the crude product, and the second to purify it.

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B. EXPERIMENTAL PROCEDURE Product Synthesis Place 7.5 mL of 4-methylcyclohexanol in a tared 50-mL round-bottomed flask. Reweigh the flask to get an accurate mass of the 4-methylcyclohexanol that you used. Add 2.0 mL of 85% phosphoric acid and 30 drops (approximately 0.40 mL) of concentrated sulfuric acid to. Mix the liquids together using a glass stirring rod and then add a boiling stone. Assemble the distillation apparatus as shown below:

Use a 25 mL flask as your receiving vessel and keep it immersed in an ice-water bath to minimize evaporation of 4-methylcyclohexene as it distills over. Turn on the water going to the condenser. Make sure that the water is flowing steadily but avoid using high pressure since this might cause the hoses to detach from the apparatus. Turn on the heating mantle and continue to increase the temperature slowly until the mixture boils and the product starts to distill and collect in the receiving flask. The distillation should take about 30 minutes. Don’t allow the mixture to distill too rapidly, since this will cause some of the starting alcohol to distill over before it has the chance to react. To avoid this, you should also closely monitor the temperature at the distilling head and ensure that it DOES NOT get close to the boiling point of your starting material. Continue the distillation until no more liquid is collected in the receiving flask. Add 1 or 2 mL of saturated sodium chloride solution directly into the test tube that you used as a receiving flask. Gently wash the distillate with the saturated sodium chloride solution by using a Pasteur pipette to mix the two layers. Allow the layers to separate and remove the lower aqueous layer using the same Pasteur pipette. Transfer the organic layer to a clean, dry Erlenmeyer flask using another dry Pasteur pipette. Add a small amount of anhydrous sodium sulfate and swirl the contents of the flask. If all of the drying agent clumps together, add a little more of it until you see that there is a small amount of loose solid in the flask. Stopper the Erlenmeyer flask and set it aside for 10-15 minutes to ensure that all traces of water are removed. While you are waiting, wash the 50 mL round-bottomed flask, distilling head, condenser and receiving flask that you used for the reaction. Rinse them all with a little bit of acetone and water. Allow the glassware to dry in the oven.

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Product Purification Transfer the dried liquid back into the cleaned and dried 50 mL round bottomed flask. Be careful NOT to transfer any of the drying agent along with it! This can be ensured by filtering the liquid through a Pasteur pipet fitted with a small cotton plug. Add a boiling chip, and then reassemble the distillation apparatus. Collect the distillate directly into a 10 mL graduated cylinder as your receiving flask. Again, minimize evaporation of your purified product by cooling the receiving vessel in an ice-water bath. Begin the circulation of water in the condenser and start heating the mixture using the heating mantle. Distill the 4-methylcyclohexene, collecting the material that boils over between 100 and 105 °C. Record your observed boiling point range in your notebook. Once the distillation is complete, you can read the volume of liquid collected directly from the graduated cylinder and then convert the volume measurement to mass in order to accurately determine the yield of your product. Calculate your percent yield based on the mass of 4-methyl-cyclohexanol that you started with. Verification of Product Formation 1. IR Spectroscopy: Under the guidance of your lab instructor, obtain an IR spectrum of your purified product, using sodium chloride plates as your sampling device (see Technique 25). You should only use one drop of your product in order to get sharp peaks in your IR spectrum but you will need to work quickly to obtain a spectrum before your product evaporates. Compare your IR spectrum with those of 4-methylcyclohexene and 4-methylcyclohexanol shown on Pavia pages 181 and 183 respectively. 2. Tests for Unsaturation: Place 4-5 drops of 4-methylcyclohexanol in each of two small test tubes. In another pair of small test tubes, place 4-5 drops of your purified alkene product. Label the tubes immediately so that you can be sure what is in each one. Be sure to record the initial color of your chemicals. You will perform two different tests, comparing the results of those tests on 4-methylcyclohexanol (which serves as the control) and your purified product. In one set of test tubes (control & purified product), add five drops of the bromine solution to both. Shake the test tubes well. Record the final color of the solution for both test tubes. In the second set of test tubes containing, add about 20 drops of 1,2-dimethoxyethane. This is simply a solvent that will help dissolve the permanganate solution. Shake the test tubes well. Now, add potassium permanganate solution dropwise to each tube. Be sure to shake the test tubes between each drop. This time, record the number of drops necessary for the color of the permanganate to persist in each test tube.

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C. WRITING YOUR LAB REPORT Write your Lab Report following the format written on the “ORGANIC CHEMISTRY LAB 223 & 225 GENERAL NOTEBOOK FORMAT” sheet (Items 1 to 4 for Pre-Lab and 5 to 9 for Post-Lab). Be sure to attach a copy of your IR results at the back of your report – label the relevant peaks on your spectra! In addition, your lab report should address the following at the appropriate sections: Results & Observations: Yield of 4-methylcyclohexene product and all Tests for Unsaturation results (including control experiment). Discussion: In addition to your normal write-up, your discussion should cover all of these aspects:

(1) How does dehydration reaction reaction result in alkene synthesis? (2) How the distillation of the product helps to increase yields by shifting equilibrium (3) Why is it important to cool the collection flask during the distillation? (4) How does the bromine and permanganate tests for unsaturation work? Provide an explanation of

the observed color changes. Assigned Questions: Answer the following questions:

(1) In this experiment, 1-2 mL of saturated aqueous sodium chloride is used to transfer the crude product after the initial distillation. Why is saturated sodium chloride, rather than pure water, used in this procedure?

(2) Write a reasonable and detailed mechanism for the dehydration of 4-methylcyclohexanol in the

presence of sulfuric acid to form 4-methylcyclohexene. Use curved arrows to show the flow of electrons and draw the structures of all intermediates and byproducts formed in the course of the reaction.

(3) What is the major alkene product that you would expect to be formed as a result of the dehydration of each of the following alcohols? a) Cyclohexanol b) 1-Methylcyclohexanol c) 2-Methylcyclohexanol d) 2,2-dimethylcyclohexanol

(4) When 1,2-cyclohexanediol is dehydrated in the presence of concentrated sulfuric acid, the major product is not an alkene. Instead, you get cyclohexanone as the major product as shown in the following scheme:

Write a reasonable and detailed mechanism for the dehydration of 1,2-cyclohexanediol to form cyclohexanone. Use curved arrows to show the flow of electrons and draw the structures of all intermediates and byproducts formed in the course of this reaction as well as any alternative resonance structures that will help you to account for the formation of the major product observed in this reaction.

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Appendix I Hazardous Properties of Some of the Chemicals

used in the CHEM 223 Laboratory Reference: N. l. Sax, Dangerous Properties of Industrial Materials (Also see CRC Handbook, under "Toxicity")

U = Unknown 3 = May cause death or permanent injury 2 = May cause temporary damage 1 = Fairly safe

• Benzoic acid-l

• p-Nitroaniline- Acute Local- U; Ingested -3; Skin absorption -3; Headache, nausea, vomiting,

stupor • Ethanol - moderate fire hazard

• Methanol - Acute local -1; Ingested -3; Inhalation -2; skin absorption A cumulative poison.

Fire hazard - moderate. • CH2Cl2 - Highly irritating to the eyes! Acute: local irritant - 2; Systemic: Ingestion -2; Skin

absorption -2; Inhalation -3; Chronic: Local -U; Systemic -1. Fire Hazard -none. For comparison, note the maximum allowed air concentrations in ppm: Benzene -10; CCl4-10; CHCl3-50; CH2Cl2-500 (CRC Handbook)

• Benzene - a recognized carcinogen. Acute -2; Chronic -3; a cumulative poison: People who

work with benzene routinely over a period of years must take particular care to minimize exposure. Fire hazard - high.

• Cyclohexane - Chronic -U; Acute -2. Fire hazard – high

• Chloroform - Chronic -U; Acute systemic -3 Considered more toxic than CH2Cl1 but less toxic

than CCl4 and benzene. Fire hazard -none. • Ethyl Acetate - Acute -2; Chronic -1; Fire hazard - high

• Dimethyl ether - Acute -2; Chronic -2; Fire hazard - extremely high!

• Iodine - Acute -3; Chronic -3; Extremely irritating to the lungs.

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Appendix II : MICROSCALE EXTRACTION See also Pavia: Technique 12.5 & 12.6

The extraction process consists of two parts: (I) mixing of the two immiscible solutions, and (II) separation of the two layers after the mixing process. Case 1: Organic layer more dense than aqueous layer (refer to Figure 1) Mixing (a) The aqueous solution is added to the vial containing the unknown mixture and dichloromethane. (b) The vial is capped and shaken to thoroughly mix the two phases. The vial is carefully vented by loosening the cap to release any pressure that may develop. (c) The vial is allowed to stand on a level surface to allow the phases to separate. A sharp boundary should be evident. Separation (a) The pipette bulb is squeezed to force air from the pipette. (b) The pipette is then inserted into the vial until close to the bottom. Be sure to hold the pipette in a vertical position.

Fig. 1: Pasteur pipette separation of two immiscible phases, with denser layer containing the product.

(c) Carefully allow the bulb to expand, drawing only the lower dichloromethane layer into the pipette. This is done in a smooth, steady manner so as not to disturb the boundary between the layers. With practice, one can judge the amount that the bulb must be squeezed so as to just separate the layers (Fig. 1) (d) Holding the pipette in a vertical position, place it over an empty vial and gently squeeze the bulb to transfer the dichloromethane solution into the vial. A second extraction can now be performed after addition of another portion of dichloromethane to the original vial. The identical procedure is repeated. In this manner multiple extractions can be performed with each dichloromethane extract being transferred to the same vial; that is the extracts are combined. The organic soluble material has now been transferred from the aqueous to the dichloromethane layer and the phases separated.

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Case 2: Organic layer less dense than aqueous layer (refer to Figure 2) In the case when the organic solvent (e.g. diethyl ether) is less dense than the aqueous layer, the procedure is identical to that outlined above with the exception that it is the top layer that is transferred to the new container. These steps are shown in Fig. 2.

Fig. 2: Pasteur pipette separation of two immiscible phases, with less dense layer containing the product

(a) Both phases are drawn into the pipette as outlined above (steps a and b). Try not to allow air to be sucked into the pipette since this will tend to mix the phases in the pipette. If mixing does occur, allow time for the boundary to reform. (b) The bottom aqueous layer is returned to the original container by gently squeezing the pipette bulb. (c) The separated ether layer is then transferred to a new vial. Comparison of macroscale and microscale techniques (refer to Figure 3): Both techniques consist of two parts: (i) mixing of the two immiscible solutions, and (ii) separation of the two layers after the mixing process. The separatory funnel is an effective device for extractions at the macro and semi-microscale. Mixing and separation are done in a single step. The microscale procedure uses a Pasteur pipette, which acts as a miniature separatory funnel. Mixing and separation are done in two steps.

Fig 3: Comparison of Microscale and Macroscale Extraction Devices

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Appendix III MICROSCALE RECRYSTALLIZATION

Dissolving the solute: Before you dissolve the solute, prepare a Pasteur pipette for filtering. Shorten the stem of the pipette to about 1/2", by etching the glass with a file, and snapping it while holding with a piece of cloth. Insert a tiny cotton plug into the pipette, and add a small amount of celite (~1/4" high). To a sample of the solute in a small test tube, carefully add dropwise via a pipette a small volume of hot solvent. Add a boiling chip, and maintain boiling of the solution while adding small portions of solvent. Swirl the test tube between additions to prevent bumping of the solution. Use a sand or water bath for heating. Remember the aim is to use the minimum volume of solvent to dissolve the solute. Decolorizing the Solution and Removing Suspended Solids: Remove the boiling solution from the heating bath, and after boiling has subsided, add gradually a small amount of decolorizing carbon, (Norite) (caution-frothing), and swirl the solution gently. Heat the solution to boiling, gently, for approximately 5 minutes. Record the weight of a second clean, dry, small test tube to the nearest 0.0001g. Flush the Pasteur pipette prepared above, with hot solvent, and quickly filter the hot solution into the test tube, (Fig 1). Use a small amount of hot water, to ensure complete transfer of the solution. It is important that the filtration equipment is as hot as possible, and filtration carried out quickly, otherwise, cooling of the solution may lead to crystallization and blockage of the plug in the pipette. Crystallizing the solute: Cover the mouth of the test tube containing the hot filtrate, by loosely replacing the cap, and allow to cool first to room temperature, then undisturbed, in an ice water bath. When the product has crystallized completely, collect, wash and dry the crystals according to Method I or II. Method I - Filtration Using the Pasteur Pipette: The ice-cold crystalline mixture is stirred with a Pasteur pipette, and while air is being expelled from the pipette, it is forced to the bottom of the test tube. The bulb is released and the solvent is drawn into the pipette through the very small space between the square tip of the pipette and the curved bottom of the tube (Fig. 2). When all the solvent has been withdrawn it is expelled into another test tube held next to the tube containing the crystals. It is sometimes useful to rap the tube containing the wet crystals against a hard surface to pack them so that more solvent can be removed. The tube is returned to the ice bath, and a few drops of cold solvent are added to the crystals. The mixture is stirred to wash the crystals, and the solvent is again removed. This process can be repeated as many times as necessary. Dry the product by connecting the test tube to the water aspirator (Fig. 3). If the tube is clamped in a beaker of hot water, the solvent will evaporate more rapidly under vacuum, but take care not to melt the product. Water, which has a high heat of vaporization, is difficult to remove this way. This may require taking the m.p. in the next lab period so that the crystals can air-dry over the week. Drying of the product may be hastened by scraping onto a filter paper and remove the last bit of solvent by squeezing the crystals between sheets of filter paper before drying them in air. Be careful with losses in transferring the crystals since you have to determine your percent recovery. Determine the weight, % recovery and m.p.'s of the recrystallized material.

REFER TO FIGURES 1-3 ON THE NEXT PAGE

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Method II- Filtration Using the Hirsch Funnel: When the quantity of material to be collected is larger than can be conveniently collected using the Pasteur pipette method, or when the crystals are so small that the method is ineffective, then the material is collected on the Hirsch funnel. Set up the micro Hirsch filtration assembly shown in Fig 4 (next page). The Hirsch funnel is made of polypropylene and has a molded tip, which fits into the thermometer adapter, so that it can be attached to the connecting adapter. The connecting adapter is secured to the reaction tube by means of the connector with support rod. The vacuum hose can be connected directly to the side arm on the apparatus or the side arm can be closed with a septum and the vacuum connected through a syringe needle. The Hirsch funnel comes fitted with a 20-micron polyethylene fritted disc, which is not meant to be disposable. While products can be collected directly on this disc it is good practice to place a 11- or 12- mm diameter piece of #1 filter paper on the disc. In this way, the frit will not become clogged with insoluble impurities. Set up the filtration apparatus, so that the reaction tube is in an ice bath. Wet the filter paper with the solvent used in the crystallization, turn on the aspirator and ascertain that the filter paper is pulled down onto the frit. Pour and scrape the crystals and the mother liquor onto the Hirsch funnel, and as soon as the liquid is gone from the crystals, break the vacuum at the filter flask by removing the rubber hose. The filtrate can be used to rinse out the original tube, which contained the crystals. Again break the vacuum as soon as the liquid has disappeared from the crystals; this prevents impurities from drying on the crystals. The reason for cooling the collecting tube is to keep the mother liquor cold so that it will not dissolve the crystals on the Hirsch funnel. With a few drops of ice-cold solvent, rinse the crystallization tube. That container should still be ice- cold. Place the ice-cold solvent on the crystals and then reapply the vacuum. As soon as the liquid is pulled from the crystals break the vacuum. Repeat this washing process as many times as necessary to remove colored material or other impurities from the crystals. In some cases only one very small wash will be needed. After the crystals have been washed with ice-cold solvent, the vacuum can be left on to dry the crystals.

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Fig. 4: Micro Hirsch Filtration Assembly

Record the weight of the dry sample. Remember to include the weight of any sample left in the original test tube. Determine the weight, % recovery and m.p.'s of the recrystallized material.