CHE 311 Sylabus - Gravity Waves · Web viewDRYING: an organic liquid that has been in contact with...

CHE 311 Syllabus

Instructor: Dr. J. L. LyleOffice: NSM D-323Phone: (310)243-3388;243-3376Office Hours: Will be announced in class; open door policyemail: [email protected]: http://chemistry.csudh.edu

Texts, etc.

Introduction to Organic Laboratory Techniques Pavia, Kriz, Lampman & Engel (required)CRC Handbook of Chemistry and Physics (highly recommended)Lab notebook (required)Safety goggles (required)

1. Grading: Traditional letter grades will be assigned on the same basis as in CHE-310. Lab reports 50% Notebook 10% Final Exam 25% Evaluation 15%

2. Lab reports. A typed lab report will be required for each experiment. The report is due one week after the scheduled completion of the lab. These reports are due at the scheduled start time for the lab. Late reports will be penalized one letter grade for the first 24 hours. Lab reports that are submitted more than 24 hours late will not be accepted!Please note that lab reports are not written in the lab notebook, but are separate requirements. You will be given explicit instructions about what each lab report is to contain. Lab reports are to be your own work and not plagiarised from some other student or lab report. Academic dishonesty will not be tolerated!

3. Notebook. A written record of what you are doing in the lab will be kept in your notebook. You are expected to have your notebook with you in the lab. Failure to do so can affect your grade. The notebook entries will be written in ink. The carbon copies that you make will be submitted with your lab reports.

4. Final Exam. A written final exam will be given at the end of the semester. Date and location will be announced later.

5. Evaluation. Part of your grade will be an evaluation of your lab technique, preparedness, punctuality, etc. by the instructor.

6. Safety. You must wear approved eye protection at all times in the lab. Failure to do so will result in expulsion from the lab.

mailto:[email protected]

7. Prerequisite. You must have completed both semesters of general chemistry. Corequisite is enrolment in CHE-310.

8. Attendance. You are expected to attend all laboratory sessions. Make ups will only be allowed if arrangements are made prior to the missed lab and for good reason. You must be punctual in coming to the laboratory. Students who arrive late and miss the pre-lab lecture will not be allowed to begin the experiment.

9. Course goals, objectives, and requirements are covered elsewhere in this syllabus.

CHE 311 Organic Chemistry Laboratory I

Week:1. Check in/ Orientation to lab

2. Simple distillation P. 706-713

3. Fractional distillation p. 733-744

4. Extraction p. 685-693, p.696-699

5. Steam distillation p.753-761

6. Recrystallization p. 648-663

7. " & melting point p. 666-674

8. Chromatography p. 792-806, p.761-770

9. " p. 808-823

10. Alkyl Halide Syntheses p. 204-211

11. "

12. Dehydration of 4-methylcylcohexanolp. 248-252

13. Nitration of a halobenzene see sylabus

14. "

15. Check out

16. TBA Final Exam

CHEM 311 ORGANIC CHEMISTRY NOTEBOOK

Your notebook is to be with you at all times in the laboratory. This is where you record what you have done and all of the data and obsevations that you take. Note that the lab notebook is not the lab report. Lab reports are written separately and the carbons from your notebook are attached to the end of the report.

Please use the following format for your lab notebook entries:

Title of experiment (be specific) NameDateUnk # (if any)

A step by step description of what you did (it must contain sufficient detail so that the experiment could be repeated by anyone reading your notes). One technique is to write in the steps you propose to do before you get to the lab and then add additional comments and observations as you actually do the lab.

All significant observations and measurements must be recorded directly into the notebook. Do not record data on other sheets of paper for later transcription into the notebook!

The original (white) sheets remain attached in the notebook, the carbon copies (blue or yellow) will be attached to your lab report.

EXPERIMENT: Simple Distillation and Determination of the Boiling Range of an unknown organic liquid

Read p. 706-713 in your lab text!

The principal purposes of this exercise are to familiarize you with the mechanics of the distillation technique and to permit you to observe the behavior of a single substance when it is distilled. You may regard this to be the situation in which a new compound whose actual boiling point is not known has just been made. You are in effect carrying out the last step of the preparative procedure - distilling the compound to purify it and at the same time measuring its boiling range.

You have an “unknown” organic liquid at your desk; record its number in your notebook.

Procedure

All glassware must be dry! (water is a volatile compound!)

Do not wash the glassware that is to be used for the distillation, unless it is obviously dirty. If you do wash them, all glass parts must be thoroughly dried before the apparatus is assembled.

Three ring stands are necessary to construct the distillation assembly described below. Be sure that the ring stand bases face forward (toward you) and are parallel with one another. Three clamps and one iron ring are needed. If they are available, 3-prong clamps should be used to support the condenser and the receiver; a burette clamp is best for the still pot.

1. Select a distilling flask of appropriate size (the still pot should be about half-full initially). The receiver for this distillation is a graduated cylinder large enough to contain the volume of sample you are given. Ordinarily, an Erlenmeyer or round-bottom flask, or even the bottle in which the product is to be packaged, is used as the receiver. You use a graduated cylinder here because you are to obtain a record of distillate volume vs. vapor temperature.

2. Set up the apparatus as shown on page 711 of your lab text and in the sample assembly in the laboratory. Pay particular attention to the following points:

a. Build the apparatus from the "bottom up." Begin by clamping the receiver (a graduated cylinder) to a ring stand.

b. If you are using standard-taper ground-glass-joint glassware, be sure to put a thin film of lubricant on the joint surfaces.

c. Arrange the assembly so that the receiver is as close to the end of the condenser as possible. To ensure that the flow of distillate from the condenser to the receiver is true, a bent adapter may be attached to the end of the condenser. The lower end of the adapter should protrude into the cylinder, but should not be "jammed" into the opening. The junction is not meant to be airtight.

d. Should you find that the receiver is too far from the end of the condenser (with or without an adapter), raise the receiver by clamping it to the ring stand. Do not use books, sponges, inverted beakers, etc., to support any part of the apparatus.

e. Make sure that the space between the flask bottom and the ring stand base below it is sufficient to allow easy placement and removal of the heating device.

f. The thermometer must be perfectly vertical. If it is not, make whatever adjustments are necessary in the angle of the condenser. If you experience any difficulty ask your instructor for help.

g. The top of the thermometer bulb must be level with the bottom of the sidearm opening of the still head.

h. Make certain that there are no kinks or restrictions in the rubber tubing through which the cooling water flows to and from the condenser. The tubing must be long enough to reach from the water source to the inlet tube of the condenser, and from the condenser to the drain. If only short pieces are available, they may be joined with short lengths of fire polished glass tubing or special plastic connecting tubes.

i. Turn on the cooling water cautiously! If the valve if opened too quickly, the pressure may force the rubber tubing from the condenser connection, and you and your neighbors may get an early shower.

3. If a heating mantle is to be used, observe the following precautions:a. The mantle must be of the proper size to fit exactly around the flask (unless the

heating unit is of the type that may be used for several flask sizes). The size is usually specified on a tag attached to the mantle or the cord.

b. The heat input is controlled by means of a variable transformer, to which the mantle cord should be connected. Do not plug the cord directly into the line outlet unless the mantle has a built-in variable control.

c. The mantle should be supported by an iron ring or other suitable device (not books!) so that it is at least several inches above the bench top and can be lowered away from the flask when necessary. Do not rest the mantle directly on the bench surface.

5. Pour the liquid sample into the still pot. Use a funnel with a stem long enough to reach past the sidearm opening.

6. Add three or four boiling chips to the still pot.

7. Make certain that water is flowing in the proper direction through the condenser jacket.

8. Heat the liquid until boiling commences. Adjust the flame or transformer setting so that gentle boiling is maintained. Apply aluminum foil insulation unless you are directed not to do so by your instructor.

9. Distill the liquid and follow the procedure as below.

Note the temperature when the first drop of distillate is collected. Record the temperature when the first volume measurement in the graduated cylinder is feasible, and at intervals of 1 or 2 mL of distillate collected thereafter. Do not distill the liquid to dryness. Stop the distillation when a few drops remain in the

still pot.

10. Stop the distillation by turning off the flame or the transformer. If a heating mantle was used, lower it away from the still pot. Allow the flask to cool for a few minutes before disassembling the apparatus.

11. Pour the distillate and any residue in the still pot back into the bottle in which the sample was received. Return the bottle to the place designated by your instructor.

Interpretation of Results and the Report

In addition to learning the technique of performing a distillation, you have had the opportunity to observe at first hand the behavior of a reasonably pure compound in the distillation process. You also measured quantities (temperatures) whose magnitudes you did not know before-hand.

Your report (see next page) should include the following:

1. A brief introductory discussion, in your own words, of the physical principles involved in the distillation of a liquid.

2. The Experimental section, in which you describe in your own words the procedure you have carried out. A tabulation of the volume and temperature measurements must be presented. The atmospheric pressure at the time of the distillation, if known, should be noted as well.

3. A brief Discussion of Results, excluding details of experimental procedures. This part provides the interpretation of the accumulated data and other pertinent observations. A graph of vapor temperature vs. distillate volume would be most helpful in presenting the conclusions to be drawn from the experimental results. An indication of the relative amount of forerun, if any, and the corresponding temperature range over which it was collected should be cited.

The boiling range of the distillate collected in a single container must be reported. As an example, consider the following distillation in which no forerun was collected separately. The temperature at which the first drop was collected was 110oC. The distillation was stopped when the still-head temperature registered 122oC. The boiling range of the distillate in that case was therefore 110-122oC. (Note that the boiling range has a beginning value and an end value. Thus, the range in the example is not 122o, but is 110-122oC.) If 5 mL

of forerun were collected first, and the main body of distillate (32mL) then collected from 120-122oC, the 120-122oC range is the boiling range of the major portion of the liquid.

Some comment on the appearance of the liquid before and after distillation is in order, as is any other significant observation.

Note: It is not considered good form to use the first person pronouns I or we in chemistry reports. Instead of “I added 30 mL” , write instead “Thirty mL was added.” (Use passive voice)

CHE 311 Lab Report for Simple Distillation

Your lab report for the first experiment should follow the format and consist of the following:

Title(be specific) namedatesection numberUnknown #

Introduction

(give a brief statement about what a simple distillation is, what it is used for and an explanation of how it works to separate compounds. Then state concisely what is to be done in this experiment. Do not draw the apparatus! Do not state a "purpose".)

Data(a table of the data collected, suitably labeled)

(a graph of the data. Use mm graph paper and make the graph professional. Do not use pages from the lab notebook!)

Results(a paragraph describing any observations or conclusions.)(See previous page)

Exercises

1. In a short paragraph, describe how simple distillation separates two compounds with different boiling points.

2. If the thermometer is placed above the outlet to the condenser, will the temperature measured be correct? If not, will it be higher or lower than the actual vapor temperature?

3. What are boiling stones and why are they added?

4. Describe the observations that one would make during the simple distillation of an "impure" substance.

5. What happens to the still head temperature during the simple distillation of a pure substance.

6. At 30oC, the vapor pressures (in torr) for methanol and ethanol are 350 and 180, respectively. Given a mixture at 30 degrees that contains 0.3 mole of methanol and 0.1 mole of ethanol, compute the partial pressures of each liquid and the total pressure.

7. In a simple distillation, you measure a boiling range that is 110-121 degrees; How pure do you think the liquid sample is? Explain

8. You have just completed a simple distillation and have made observations of the temperature as the distillate is collected. How would you know whether your distillation was successful and that the distillate is reasonably pure?

Answer the questions on Page 716 of your lab text.

Attach the carbon copies from your notebook.

EXPERIMENT: Fractional Distillation of a Two-Component Mixture

Read 733-745 in your lab text!

This exercise is intended to demonstrate the behavior of a pair of miscible liquids in a simple distillation, and to familiarize you with the technique of fractional distillation with a column. You will first carry out and observe the characteristics of a simple distillation of a mixture. Then the same mixture will be distilled through a fractionating column. Please note that the fractional distillation may not be completely effective - the column may not be efficient enough because of the kind and amount of packing used, or because of insufficient length, and heat losses due to inadequate insulation may contribute to less than perfect results. Since the distillation is to be conducted using continuous takeoff (near-zero reflux ratio), the best possible conditions for fractionation cannot be realized.

Bear in mind that the purposes of the experiment are to demonstrate the distillation behavior of a mixture of miscible liquids and to acquaint you with the basic technique of fractional distillation. Your goal is not to determine the boiling point of either component, nor is it to achieve a perfect separation.

Procedure

A. Simple Distillation of the Mixture

All glassware must be dry!

1. Set up a simple distillation apparatus. Use a 250-mL flask as the still pot. A 50-mL graduated cylinder serves as the receiver. Be sure to add boiling chips to the flask.

2. Distill the unknown mixture as in the previous experiment1. Note the still-head temperature when the first drops of distillate appear, and

record the vapor temperature at intervals of 1 or 2 mL of distillate thereafter. 2. Continue the distillation and collection until the still pot is almost dry.

B. Fractional Distillation of the Mixture

1. Set up a fractional distillation apparatus by inserting a fractionating column packed with steel wool between the still pot and the still head adapter.

2. Add a couple of fresh boiling chips to the still pot and using the liquid funnel, add the mixture that you distilled in the simple distillation.

3. Distill the unknown mixture as in the previous experiment, noting the still-head temperature at the first drop and every 1 or 2 mL of distillate thereafter. Continue the distillation until the still pot is almost dry.

4. Allow the still pot to cool. Pour the distillate and the distillation residue back into the sample bottle. Return the bottle to the designated place in the laboratory.

5. Disassemble the apparatus. If your fractionating column is packed with stainless steel sponge, do not wash it with water.


Follow the same format that was used in writing the report for the exercise on simple distillation of a single liquid.

Of particular importance in the interpretation of your observations is a comparison of the simple distillation of the mixture with the distillation of the same mixture through a fractionating column. A tabulation of temperature-volume data for each distillation serves as the basis for the construction of two graphs, one for the simple and one for the fractional distillation.

Some comment on the efficacy of the distillation using the column should be offered. For example, the data you obtained may have indicated that the fractions collected were mixtures, although of different composition than the original. Thus an ideal separation may not have been achieved because of deficiencies in the apparatus (or your technique?). Some recommendations about improvement of the fractionation assembly and conduct of the distillation are then in order. The primary purpose of the experiment was not a determination of the boiling points of the components, so do not dwell on the aspect of it.

Remember, too, that it is not necessary to go into great detail in either the preliminary discussion or the Experimental section about the simple distillation procedure used in this experiment. It is sufficient to state that the mixture was subjected to a simple distillation and to give the results of that operation. A full account of the fractional distillation, including details of the apparatus used, should be given since it is being reported by you for the first time.

CHE 311 Report for fractional distillation

1. As before: title (specific) name date CHE 311-0x unknown #

2. In your own words, explain how fractional distillation works to separate volatile liquids.

3. In one or two sentences, summarize what you did in this experiment.

4. Make a table of the data you collected.

5. Attach a graph (neat and professional on mm graph paper) of the still head temp. vs. volume collected for the simple distillation. On the same graph, plot the data for the fractional distillation in a different color.

6. Describe the results you obtained from the simple and fractional distillation. See if you can put into words the data that you collected and the resultant graph.

7. What conclusions can you make from the results of your experiment? Compare the two methods for efficacy. If you have an opinion, back it up with data. See previous page.

8. Answer the following questions:

a. What is Raoult’s Law?

b. What is Dalton’s Law?

c. Describe how Raoult’s and Dalton’s Laws relate to fractional distillation as a separation technique.

d. What’s the difference between a packed column and an unpacked column a fractional distillation?

e. What is a theoretical plate?

f. On page 735 of your lab text is a temperature composition diagram for mixtures of two compounds, A & B.

(1) From the graph, what are the boiling points of pure A & pure B?

(2) For a mixture that contains 50 mole% A and 50 mole% B, what is the boiling point? what is the composition of the first distillate and if this distillate were to be condensed, what at temperature would it boil? what is the composition of the vapor at this temperature?

(3) For a boiling mixture at 60oC, what is the composition of the vapor and the composition of the liquid?

g. At what point do you change receivers during a fractional distillation if you are trying to separate the components?

h. What observations during a simple distillation would cause you to redo the distillation using a fractionating column?

Answer questions 1, 4 on Page 752 of your lab text.

9. Attach notebook carbon copies.

EXTRACTION

Read p. 685-693, 696-699 in your lab text.

Extraction is a separation technique based on differences in solubilaiies of substances in two immiscible solvents (usually water and a water insoluble organic solvent).

solubility in solvent 1Kc = partition coefficient = -------------------------

solubility in solvent 2

example: Given compound A, Kc (ether:water) = 4.0, how much of A can be extracted from a solution of 10.0 g of A in 100 mL of water with a single portion of 100 mL of ether?

X / 100 mL etherKc = 4.0 = --------------------

(10.0 - X) / 100 mL water

X = 8.0 grams of A extracted into the ether

-same as above, but extract two times with 50 mL of ether each time. X / 50 mL ether

first extraction: Kc = 4.0 = ------------------- (10.0 - X) / 100 mL water

X = 6.67 grams of A extracted

Y / 50 mL ethersecond extraction: Kc = 4.0 = ------------------

(3.33 - Y) / 100 mL water

Y = 2.22 grams of A extracted

total extracted = X + Y = 6.67 + 2.22 = 8.89 grams

==> multiple extractions with smaller amounts of solvent are more efficient than a single extraction with the same total amount of solvent.

DRYING: an organic liquid that has been in contact with water is "wet" (contains some water). To "dry" it, use an inorganic drying agent. See Table 2.1 in your lab text.

"WASHING": extraction to remove an unwanted compound.

Today's experiment: HCl

CH3CH2CO2-Na+ ------> CH3CH2CO2H

sodium propionate propionic acid (solid) (liquid)

Your unknown contains an unknown % of sodium propionate. It is not necessary to weigh the unknown before you begin the experiment, assume that it weighs 30.0 grams. You will convert the solid sodium propionate into propionic acid by reacting it with hydrochloric acid. Propionic acid is both water and ether soluble, has a bp of 141 oC, and forms an azeotrope with water. To remove the propionic acid from the aqueous solution, you will extract with three 40 mL portions of diethyl ether. Do not throw anything away until you are absolutely certain you have kept the right layers. After combining the three ether extracts, dry them over anhydrous magnesium sulfate. Fractionally distill off the diethyl ether (<100oC). Then set up for simple distillation and simple distill the propionic acid, collecting as your final product all material boiling above 135oC. Package your product and label the bottle according to instructions below. You will turn it in with your report next week.

Note: Propionic acid is a “common” name. The IUPAC name for this compound is propanoic acid. It will be found in the CRC handbook under its IUPAC name.

“Salting Out” The addition of NaCl to an aqueous solution containing an organic compound will decrease the solubility of that compound in the aqueous solution. This is called “salting out.” Apparently, the salt increases the ionic strength of the solution, making it more polar and the weakly polar or non-polar organic compound is less soluble.

EXPERIMENT: Formation of a Water-Soluble Liquid Organic Acid and Its Extraction from an Aqueous Solution

In this experiment, a simple reaction followed by an extraction to separate the desired product from solution will illustrate a typical application of extraction.

Some liquid organic acids are very soluble in water. The sodium salts of these acids are ionic solids that are also very soluble in water. If an aqueous solution of one such salt is acidified with a strong mineral acid (e.g., hydrochloric or sulfuric acid) the weaker organic acid is produced, as is shown in the following representative equation:

Na+ + CH3CH2CO2- + H3O+ + Cl- ---> CH3CH2CO2H + Na+ + Cl- + H2O sodium propionate hydrochloric acid propionic acid (AKA propanoic acid)

The organic acid is largely unionized in the water solution.

No apparent change will be observed when the reaction is carried out because the solutions of the starting materials are colorless and the resulting solution containing the indicated products is also colorless. The acid is completely soluble in water and, thus, does not separate. Although propionic acid has a boiling point of 141oC, it cannot be separated from the water by fractional distillation because the two liquids form an azeotrope (bp 99.9oC; 17.7% propionic acid, 82.3% water). Therefore, it is necessary to resort to extraction with an organic solvent in which the organic acid is quite soluble. After drying the organic solution, the organic solvent may be removed by fractional distillation and the residual propionic acid purified by a simple distillation.

You will receive about 30 g of an unknown mixture of solid salts which contains 50-90% sodium propionate, the remainder being an inert inorganic salt.

Procedure

1. Place all of the unknown containing sodium propionate in a 250 mL beacker. 2. Add 100 mL of distilled water to the beaker and stir the mixture with a glass rod. 3. Pour 60 mL of 6 M hydrochloric acid into the sodium salt solution, while stirring with a

glass rod. 4. Transfer the aqueous solution to a 250-mL separatory funnel. (Be sure that the stopcock

is closed and that a beaker is placed beneath the funnel.)5. The aqueous solution is to be extracted with three 40 mL portions of diethyl ether as

follows:a. Add 40 mL of the solvent to the solution in the funnel. Perform the extraction.b. Drain the lower aqueous layer into the beaker, and pour the ether solution through

the top of the funnel into a 250-mL Erlenmeyer flask. c. Repeat the extraction twice more with 40 mL of diethyl ether each time.

DO NOT DISCARD ANY OF THE SOLUTIONS UNTIL YOU HAVE REACHED STEP 9.

6. Add just enough anhydrous magnesium sulfate to the combined ether extracts to just cover the bottom of the flask. Seal the flask with a cork stopper that does not extend more than

half its length into the flask neck. (Note: If the magnesium sulfate dissolves, you goofed! Go back through your procedure to see where you made the error.) Swirl the contents of the flask gently and allow the mixture to stand for at least 30 minutes. If necessary, you may let the flask stand until the next laboratory period.

7. Set up a fractional distillation apparatus, using a 250-mL round-bottom flask as the still pot. The receiver is a 250-mL Erlenmeyer or round-bottom flask. Surround the receiver with a small plastic bowl containing a mixture of ice and water.

8. Remove the still pot from the assembly and support it on a cork ring. Place a narrow-stem funnel in the flask neck, and insert a small plug of absorbent cotton at the top of the funnel stem.

9. Carefully decant the ether solution from the drying agent through the funnel into the flask. Rinse the Erlenmeyer flask containing residual drying agent with about 10 mL of ether and add the rinsings to the still pot. (Note: None of the drying agent should have entered the still pot. If some did, empty the still pot into the Erlenmeyer flask, and refilter the mixture into the round-bottom flask.)

10. Add three or four boiling chips to the still pot and reattach the flask to the fractionating column.

11. Slowly distill the ether from the solution. When distillate collection slows markedly or stops, or if the still-head temperature reaches 100C, discontinue the distillation. Do not attempt to distill the propionic acid through the fractionating column.

12. Allow the still pot to cool for several minutes. Then remove the fractionating column and receiver from the assembly. Pour the ether from the receiver into the special container labeled Recovered Ether from Extraction or Waste Organic Solvent.

13. Transfer the residual liquid in the still pot to a 50-mL round-bottom flask and incorporate the smaller flask in a simple distillation assembly.

14. Place two or three fresh boiling chips in the still pot and start the simple distillation. 15. Collect as forerun any distillate obtained up to a still-head temperature of 135oC. Then

carefully change receivers, placing a preweighed narrow-mouth bottle in position to collect the propionic acid.

16. Continue distilling the product, measuring the boiling range simultaneously. Do not distill the liquid to dryness, but leave a very small amount in the still pot.

17. Reweigh the receiver plus contents to obtain the weight of the distilled propionic acid. 18. Label the bottle in the manner shown below.

PROPIONIC ACID wt.: g br oC

Your name Date

The Report

In addition to a discussion of the principles of simple extraction and the function of drying agents, the Introductory section should include a statement of the problem - what you were to do.

In the Experimental section, be sure to specify the quantities of materials, as well as the weight and boiling range of the final product. The following is an example of how this information may be presented: "Unknown No. 12 (30.4 g) was dissolved in 100 mL of distilled water. To the salt solution was added 30 mL of 6 M HCL, and no apparent change was observed... . A total of 13.2 g of propionic acid, br 136 - 142oC (lit., 141oC) was obtained."

In the Discussion of Results, offer a comment on the purity of the distilled acid, based on your experimental observations. You may also calculate an approximation of the composition of the unknown mixture. The calculation is based on the balanced equation, which indicates that 1 mole of propionic acid is obtained from 1 mole of sodium propionate.

Calculation of Approximate Composition of Unknown

The balanced equation shows that one mole of sodium propionate yields one mole of propionic acid. From the weight of the propionic acid that you have collected, you must first calculate how many moles of propionic acid you have. That number of moles is the number of moles of sodium propionate that you must have started with. Convert the number of moles of sodium proionate to grams of sodium propionate. That number, divided by the weight of the unkown, times 100% is the approximate percent of the unknown that was sodium propionate. This number is, of course, approximate as (a) not all of the propionic acid was necessarily extracted; (b) mechanical losses of propionic acid were suffered during the distillation; and (c) the propionic acid obtained is not 100% pure, and the weight of the product includes the impurity.

CHE 311 Report for Extraction; Drying Methods

1. As before: name date CHE 311-0x unknown #2. State in a few sentences what you did in this experiment.

3. Include a table containing the following:

Weight of unknown 30.0 g Weight of propionic acid

obtained g Moles of propionic acid moles obtained

Moles of unknown moles as sodium propionateBoiling range of propionic acid oC

Literature value for the boiling point of propionic acid oC % sodium propionate in the original sample as calculated based on the amount of acid recovered % (note the calculation is based on the balanced equation that indicates that 1 mole of propionic acid is produced from 1 mole of sodium propionate.)


A. Explain the purpose of reacting the unknown with hydrochloric acid before the extractions?

B. A student made a mistake and did a single extraction with 120 ml of ether instead of three separate extractions with 40 mL of ether each time. How will his results be affected?

C. A student added anhydrous magnesium sulfate to his combined extracts and the magnesium sulfate dissolved. What error did the student make in the experiment? What should he do now?

D. During the second extraction, a student added ether to the layer in the separatory funnel and it did not separate. What mistake did the student make? What should he do now?

E. How pure do you think the propionic acid is that you recovered and how do you know?

F. If, in an extraction, you were uncertain about which layer was the aqueous layer and which layer was the organic layer, how could you quickly settle the issue?

G. Given 200 mL of an aqueous solution containing 10 g of compound A, from which it is desired to separate A, how many grams of A could be removed in a single extraction with 200 mL of diethyl ether? (The distribution coefficient, diethyl ether: water is 6.0).H. How many total grams of A could be removed if two successive extractions with 100 mL each were used in G?

Attach carbons

EXPERIMENT: Steam Distillation

Separation of a Volatile Component from a Mixture


In certain reactions, it is not feasible to remove the desired compound (or unreacted starting material) from the mixture by simple or fractional distillation, or by other physical methods. Steam distillation very often successfully effects the separation, and does so at a temperature considerably below the boiling point of the compound being removed. Steam distillation is also quite useful in the isolation of natural products.

An artificial mixture is to be steam distilled to recover one of the components. To add an element of mystery, the sample you receive is an "unknown" in that the quantity of the recovered compound is to be determined and reported.

The mixture to be separated is typical of that obtained in one of the methods of preparation of compounds called haloarenes. One byproduct of the reactions is a group of compounds called phenols. (Some other highly colored substances are present as nonvolatile contaminants.) Separation of the product haloarene from the phenol contaminant by fractional distillation is somewhat difficult because of the high boiling points of these compounds. Steam distillation is a more convenient way of isolating the desired product, but a pretreatment of the reaction mixture is necessary because the phenol is somewhat volatile and would also codistill with steam. Fortunately, the phenol is a weak acid and the haloarene is not. Treatment of the mixture with a solution of sodium hydroxide converts the phenol into a water-soluble, nonvolatile ionic salt, as is shown in the following illustrative equation.

C6H5OH + Na+ + OH- ---> C6H5O- + Na+ + HOH phenol base sodium phenoxide (acid) (salt)

The steam distillation is to be carried out using internal steam generation. The experimental procedure involves both the separation of haloarene and an attempted verification of the principles of steam distillation. The latter objective is effected by keeping a record of the vapor temperature during the codistillation process.

The mixture you will receive is

Phenol (C6H5OH), bp=182oC + Chlorobenzene (C6H5Cl), bp=132oCProcedure

1. Set up a simple distillation apparatus with a 500-mL flask as the still pot and a 50-mL graduated cylinder as the receiver.

2. Weigh the unknown. Place the sample in the flask using your liquid funnel, then add about 100 mL of tap water, 40 mL of 6 M NaOH, and two or three boiling chips.

3. Heat the contents of the flask to a vigorous boil. when distillation begins, make a record of the vapor temperature vs. distillate volume.

4. Continue the distillation as long as oily material is collected. If droplets of the oil remain in the condenser and cling to the walls they may be flushed out by the following procedure:

a. Turn off the flow of cooling water through the condenser jacket. b. Remove the rubber tube from the water tap and allow the water to drain from the

condenser jacket. c. Reconnect the tube to the water outlet, but do not turn on the water yet. when steam

begins to issue from the lower end of the condenser, turn on the cooling water again. 5. If it is not apparent from the vapor-temperature readings that no more organic material is

distilling, the following test may be performed. Remove the receiver and collect a few milliliters of the distillate in a small test tube, then replace the receiver. Examine the liquid in the test tube for the presence of oily drops. If none appear (distillate is water only), the distillation may be stopped.

6. Read the volume of organic material in the graduated cylinder as best you can and enter the value in your notebook.

7. Transfer the distillate to a separatory funnel and add about 50 mL of water. Do not shake! Allow the layers to separate, and then draw off the organic liquid and weigh it. Return the wet organic compound to your instructor in the same container in which the unknown was received.

The Report

A brief discussion of the basic principles of steam distillation should be followed by an account of your observations and measurements. The Experimental section should, of course, contain full details of the method by which you carried out the steam distillation as well as all relevant data. The Discussion of Results should include some comment on the observed vapor temperatures and their significance.

CHE-311 Report for Steam Distillation

1. Include the normal heading.

2. Discuss the basic principles of steam distillation.

3. State what you did in this experiment in one or two sentences; be explicit.

4. Tabulate all relevant data. Include the weight percent chlorobenzene in the unknown.

5. Discuss your data and observations. See previous page.

6. Questions:

a) What properties must a compound have in order to be steam distillable?

b) What properties do non-steam distillable compounds have?

c) What was the purpose of adding sodium hydroxide to the still pot?

d) When would you use a steam distillation as a method of separation and purification?

f) define Dalton’s Law and discuss how Dalton's Law is relevant to steam distillation.

Answer questions 1, 2, 3 on pages 760-761 of your lab text.

EXPERIMENT: Recrystallization


This experiment offers a taste of organic preparative work which includes a recrystallization as the final step. While you have no prior experience and certainly would not, at this stage, be expected to understand the chemistry involved in the reaction, you can carry out the preparation if you follow directions.

The type of compound to be made is called an amide, which is formed by the reaction of an amine with an acid anhydride (one of several ways by which an amide may be prepared). The reaction is represented by the following general equation:

RNH2 + (CH3CO)2O ----> CH3CONHR + CH3CO2H amine acetic amide acetic anhydride (substituted acid

acetamide)

In the formula for the amide, the R represents any organic group and NH2 is the amine group. The specific amide you are to prepare is a derivative of the compound acetamide (CH3CONH2), which is but one of the many compounds in the general class of amides. Different amides can be obtained by using different anhydrides or related reagents.

You will receive a sample of an "unknown" amine which is to be converted to the corresponding amide following the general procedure outlined below. The product of the reaction is then to be purified by recrystallization. Identification of the purified amide will be made by means of the melting point and mixture-melting-point determinations.

Procedure

Note: The type of amine to be used in this experiment has a tendency to undergo oxidative changes in storage, resulting in the formation of colored impurities. Most of the latter will be removed during the reaction, and the final purification of the product by recrystallization should eliminate any residual impurity.

The reaction is a relatively simple one; it requires no special apparatus and takes a relatively short time. The acetic anhydride is added to the amine salt solution. However, the anhydride will react only with the amine, and not with the salt that was formed by dissolving the amine in the hydrochloric acid solution. The acidic salt must therefore be neutralized to free the amine, and this is accomplished by adding the sodium acetate solution:

RNH2 + H3O+ + Cl- ---> RNH3+ + Cl- + H2O

base acid acid base

RNH3+ + Cl- + Na+ + C2H3O2- ------> RNH2 + HC2H3O2 + Na + Cl-acid base base acid

A. Reaction

Before carrying out the reaction, it is necessary to make up a solution that will be needed in a later step. Dissolve 8 g of sodium acetate trihydrate (NaC2H3O2 3 H2O) in 25 mL of water in a small beaker and set aside.

1. Prepare a solution of 5 mL concentrated hydrochloric acid in 125 mL water in a 250-mL beaker.

2. Weigh about 6 g of the liquid or solid amine into a 50-mL beaker. It is not necessary to measure out exactly 6.00 g, but the actual weight used should be recorded in your notebook. If the amine is liquid, a clean medicine dropper pipet may be used to transfer the compound from the vial to the beaker.

3. Transfer the amine to a 500-mL Erlenmeyer flask. Rinse the 50-mL beaker with small portions of the dilute hydrochloric acid you prepared, and add the rinsings to the flask. Pour any remaining hydrochloric acid solution into the flask. Swirl the flask carefully to dissolve the amine. Gentle warming may be necessary, and some insoluble matter may remain.

4. Carefully warm the solution of the amine in hydrochloric acid on a hot plate or steam bath. Place a thermometer in the solution, and when the temperature reaches 50-55oC, remove the flask from the heat source.

5. Caution: In this step you are to add the reagent acetic anhydride, which is both a lachrymator (induces the flow of tears) and corrosive. The reagent must be handled carefully. Should any of the liquid come into contact with your skin or clothing, wash the affected area immediately with large quantities of water.Measure out 6 mL of acetic anhydride in a dry graduated cylinder and carefully add the reagent to the warm acid solution of the amine. Swirl the mixture gently until the anhydride is completely dissolved.

6. Immediately add the sodium acetate solution you previously made and set aside, and thoroughly mix the reactants by swirling the flask. Allow the flask to stand for about 5 minutes, while occasionally stirring the contents.

7. Place the flask in an ice-water bath and stir the mixture vigorously with a glass rod. Within a few minutes a solid should separate from the solution. In some cases the product initially appears as an oil, but this should be no cause for concern at this stage. Allow the flask to remain in the cooling bath for 15 minutes.

B. Isolation and Preliminary Purification of Crude Product

1. While the reaction mixture is cooling, arrange a suction filtration apparatus. Be sure to clamp the flask to a ring stand or other support. Place a disk of filter paper in the funnel and moisten the paper with water.

2. Filter the crude product through the Buchner funnel. Rinse the Erlenmeyer flask with small quantities of ice-cold water to remove any solid that sticks to the walls.

Note: If the product separated as an oil and did not solidify after standing in the ice-water bath, carefully decant as much of the supernatant liquid as possible. Add a few grams of crushed ice to the oil in the flask and stir the mixture vigorously while cooling the flask in the ice-water bath. If the oil does not solidify, add about 20 mL of water, shake the mixture,

and let it stand for a minute or two. Carefully decant the upper aqueous layer and repeat the treatment with ice, with somewhat longer cooling periods in the ice-water bath, until solidification occurs.

3. Leave the crude solid in the Buchner funnel and wash the filter cake with 50 mL of ice-cold water. Resume the suction for about 5 minutes.

C. Purification

The amides may be recrystallizable from a number of different solvents, including water. Unless you are instructed otherwise, the solvent selection in this situation is restricted to water, methanol, and ethanol. Some of the amides that were prepared can be crystallized from one of these solvents, while others may require a mixed system (water plus either methanol or ethanol).

If it is known that a crude product is to be recrystallized from water or a water-miscible organic solvent, then it is not necessary that the solid be absolutely dry before carrying out the purification. Such is the case in this preparation. (On the other hand, if there is a possibility that a solvent which is not itself soluble in water will be needed, then steps must be taken to remove the residual water from the crude product.)

1. Selection of the solvent: try water first, followed by methanol and then ethanol, using fresh samples of crude in each case. If it is found that the solid is not sufficiently soluble in water, but too soluble in both of the alcohols, then it is necessary to try the mixed solvent approach.

2. Recrystallize the crude product following the general directions given below:

Recrystallization.

1. Select the appropriate solvent for recrystallization. Sometimes you can find data on solubility for your compound or related compounds in the CRC Handbook or in the chemical literature. Test one or more possible solvents using small amounts in test tubes. The compound you are trying to recrystallize should be insoluble in the cold solvent, dissolve in the solvent when heated, and recrystallize when the solvent is cooled. A mixed solvent may be required.

2. On a hot plate, heat some of the solvent you have selected in an erlenmeyer flask. Put the impure, solid compound in a beaker. Placing the beaker on the hot plate, quickly add a small amount of the hot solvent. If the compound does not completely dissolve, add additional small amounts of the solvent until complete dissolution is achieved. You want to use a minimum of the hot solvent to dissolve the compound. Do not needlessly boil off the solvent; if the compound is going to dissolve it will do so in a few seconds.

3. Once the impure compound is totally dissolved you must decide whether to decolorize or not. If necessary, add a small amount of decolorizing carbon to the hot solution. Place your stemless glass funnel in the top of a beaker. Fold a fluted filter paper (page 46 of your lab text) and place it in the stemless funnel. Add a few mL of the pure solvent to the beaker. Put the hot filtration assembly on the hot plate and add the hot, decolorized solution of your compound to the filter. The purpose of the stemless funnel, beaker, and hot plate is to keep the compound to be purified in solution while you filter out the carbon.

4. Let the hot solution cool to room temperature on the bench top. Then use an ice-water bath to cool the solution even more. If crystallization does not begin, try scratching the wall of the beaker with your glass rod.

5. Vacuum filter the cooled solution to recover the recrystallized solid. You may want to wash the compound with a small amount of cold solvent if the compound is not too soluble in the cold solvent.

6. After air drying for a couple of days you can weigh and take the melting point of the purified compound before packaging it.

D. Identification

When the product is completely dry, you are to determine the melting range. Positive identification can be made by means of the mixture-melting-range determination. Until this can be done, put your dry purified product in a clean, dry, wide mouth bottle or vial of appropriate size (the bottle should be at least half full), which has been weighed while empty. Reweigh the bottle plus contents to obtain the net weight of product, and record this information in your notebook.

After you have determined what the compound is, label the package as indicated below, or as directed by your instructor.

Your name DateName of compoundObserved melting rangeNet weight

You will turn in the product with your lab report.

Interpretation of Results and the ReportThe experiment involved both the preparation and purification of an organic compound.

The primary objective was the purification of the product by recrystallization, and so very little need by said about the chemistry of the preparative reaction. Greater emphasis should be placed on the determination of the best solvent system and the results of the purification process in terms of percentage recovery. Because identification of the compound by the mixture-melting-point technique is required, the actual writing of the report must be deferred until that operation is completed. A qualitative statement about the degree of purity as estimated from the observed melting range and comparison with the literature value is also in order. The Experimental section should, of course, provide complete details on the method that you actually followed.

Purified Substituted AmideIn the experiment, you prepared a substituted amide from an "unknown" amine. The melting range determination will indicate how pure your product is, and the identity of the compound may be verified by the mixed-melting-point method. 1. Determine the melting range of your product.

2. Refer to table on the next page, which lists the melting points of a number of amides, including the compound you have made. Select those which have melting points close to the range you determined for your product. Use a mixture-melting-point determination, employing authentic samples of the amides that may be identical to your compound, to find out which amide you prepared (Notes 1 and 2).

Notes

1. Even if you find that the first mixture tested shows no depression of the melting point, you still must carry out the mixture-melting-point determinations with the other possibilities in order to eliminate them with certainty.

2. The actual melting points of the authentic samples may not coincide with the literature values because the samples may not be 100% pure. The samples may nevertheless be utilized for the purpose intended. Do not measure the melting range of any of the standards, but accept the literature values given in the tables or listed on the container labels.

Melting Pointsof Some N-Substituted Acetamides

Amide (CH3CONHR) mp (oC)

m-chloroacetanilide 78o-ethoxyacetanilide 78o-methoxyacetanilide 58o-chloroacetanilide 87o-methylacetanilide 110o-ethylacetanilide 111acetanilide 1142,4-dimethylacetanilide 130p-methoxyacetanilide 1302,3-dimethylacetanilide 135p-ethoxyacetanilide 1372,5-dimethylacetanilide 139p-methylacetanilide 153m-nitroacetanilide 155


The results of the mixture-melting-point determinations should be presented in tabular form. List all of the possibilities tested and the corresponding measurements in such a way that your conclusions are obvious from your experimental results.

CHE 311 Report for recrytallization/mp determination

1. As before: name date CHE 311-0x unknown #

2. In your own words, explain what recrystallization is and how it works to separate solid compounds. Describe how the appropriate solvent is selected for recrystallization.

3. In a few sentences, summarize what you did in this experiment, be specific.

4. Write balanced equations for the reactions.

5. Make a table:

weight of the unknown g weight of product g observed melting range of unknown amide list of possible compounds and their literature mp's, and the observed mixed mp's with your product.

6. Conclusion as to the identity of the product amide and unknown amine? Justify your answer.

7. How pure do you think the product is? Explain?


a) For the following reported melting points, comment on the purity of the sample:

i) 78-79 oCii) 299-301 oCiii) 178 oC decomposesiv) 137-149 oC

b) If, in any recrystallization, an "oil" (liquid phase) comes out of solution rather than a solid, why did this happen? What can you do about it?

c) What happens in this experiment if more than the minimum of hot solvent is used in the recrystallization?

d) Based on the structure of the now known amine and amide, calculate the % yield of your product. If you can’t figure it out, ask the instructor for the formulas of the reactant and product.

Note: % yield = (actual yield / theoretical yield) * 100%

You will have to convert to moles and use the balanced equation to calculate theoretical yield!

e) What was the purpose of the hot filtration? Why didn’t you use gravity or suction filtration at this point?

f) Questions on page 664 of your lab text: 1, 2, 3, 4.

g) In the CRC Handbook, look up 1-bromo-2-nitrobenzene (look under benzene) and list the mp, crystal form, and the solvent used in the recrystallization of this compound.

9. Attach the blue carbons from your notebook.

10. Package, label and turn in your product. name, date, contents, weight, mp or bp, %yield.

CHE-311 Chromatography

chromatography ("colored writing")

separations based on differences in absorption on a stationary phase and differences in solubility in a moving phase.

I. Thin Layer Chromatography (tlc)

stationary phase = thin layer of solid silica gel, alumina, etc.

moving phase = liquid solvent (capillary action)

------------------------ +---------+ ¦ +---------+ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ +---------¦ ¦ ¦ ¦ ¦ ¦ o ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ o ¦ ¦ ¦ ¦ ¦ ¦ o ¦ ¦ mark--> + o ¦ initial ¦ + ¦ ¦ ¦ ¦ spot +----+---------+---¦ solvent +---------+ +------------------+ +---------+ mark--> +---------¦ - ¦ o ¦ - ¦ ¦ ¦ ¦ ¦ ¦ o ¦ - ¦ ¦ ¦ o ¦ - ¦ ¦ ¦ ¦ ¦ x1¦ x2¦ x3¦ y¦ ¦ ¦ ¦ ¦ ¦ ¦ + ¦ ------------------ ¦ ¦ +---------+ distance component traveled Rf = retention factor = ----------------------------- distance traveled by solvent front

Rf1 = x1/y; Rf2 = x2/y; etc.

application:

a) analysis of mixture : number of components(solids & non volatile liquids)

b) separation of mg amounts

c) identification (Rf's or direct comparison)

II. Column Chromatography

stationary phase = column of solid silica gel, alumina,etc.

moving phase = liquid solvent ¦ ¦

column preparation ¦ ¦ loading the mixture solvent->¦ ¦ development ¦ ¦ collection of fractions +---¦ analysis of fractions ¦ ¦ (tlc) absorbent->¦ ¦ ¦ ¦ ¦ ¦ +---¦ +---+ +---+ ¦ fractions +----¦ +----¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ +----¦ ¦ ¦ +----+ +----+ +----+ +----+

applications:

a) analysis of mixture(solids and liquids)

b) separations of 0.1 gram quantities

III. Gas Liquid Chromatography (glc)

stationary phase = column of non volatile liquid (carbowax,DNP, SE-30, etc.) on solid support.

moving phase = gas

Oven Recorder +------------------------+ +----------+ ¦ ¦ +-------¦ ¦ +---¦ +-+ +-+ +-+ +-+ +---+ ¦ ¦ injection¦ +--+ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ +---¦ + ¦ +------+ ¦ +---¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ +---+ +-¦ +-+ ¦ ¦ +-+ +-+ +-+ +-+ +-+ ¦ detector ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ +------+ ¦ +------------------------+ ¦ Gas

Gas Chromatograph:

+----------------------------------------------+ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ +----------------------------------------------+

distance after injectionretention time = ---------------------------

chart speed

area A%A = ------------------------------ X 100%

area A + area B + area C + etc.

area A = height X width (at half height)

applications:

a) analysis of mixture, # of components(volatile liquids or gases)

b) separation of mg samples

c) identification (retention time)

d) per cent composition

IV. Today's experiments:

1. tlc

do tlc on your unknown on both silica gel and alumina.

use each of the two solvent systems.

2. glc

glc on known 50/50 mixture of alcohol and ketone

glc on pure alcohol

glc on your unknown mixture of alcohol and ketone

EXPERIMENT: Thin-Layer and Column Chromatography

Read 792-807 in your lab text!

The following experiments include both thin-layer and column chromatographies that are based solely on the adsorption process. The main intent is to familiarize you with the techniques. Once you have learned the basic idea and procedure, you will be in a position to utilize one or both of these methods if you occasion arises during your later experiences with the preparative experiments.

You will obtain an "unknown" mixture consisting of a minimum of two solid compounds; one or more of the components may be colorless. a sample is to be subjected to thin-layer chromatography to determine the number of components and their Rf. (The same mixture could then be chromatographed in a column in an effort to separate and recover the individual compounds. Progress of the column chromatography could to be determined by thin-layer chromatography of each eluate fraction. You might also evaporate each eluate that is known to contain dissolved solid and determine the melting range of the residue; a comparison with the melting range of the original mixture would then be done.) It is quite possible that you will not achieve a complete separation by column chromatography because (a) the solvent system that is specified is not the best, (b) an insufficient number of eluate fractions are collected, (c) the adsorbent is not the optimum choice, or (d) the column is not long enough. Nevertheless, exposure to the method will provide experience in carrying out the chromatography and may well point up some of the difficulties that can be faced. If there were enough time, it is very probable that you could work out the optimum conditions for separation of your sample.

A. Thin-Layer Chromatography of the Original Mixture

The effectiveness of two different adsorbents, silica gel and alumina, will be compared using two solvent systems.

Procedure

1. Obtain a 5- or 10-mL beaker or a vial of similar capacity, two TLC strips coated with aluminum oxide, and two TLC strips coated with silica gel. Use a sharp pencil to carefully mark the top of each strip (e.g., A and S, respectively) so that they can be distinguished.

2. Place about 10 mg (estimated; do not weigh!) of the solid mixture in the small container and add about 1 mL of acetone to dissolve the sample.

3. Spot the solution on each of the strips. Mark the top of one alumina strip 1:1 and the other 1:3; do the same to the silica gel strips.

4. Develop the silica gel chromatograms using ethyl acetate-cyclohexane (1:1) for one and 25% ethyl acetate-75% cyclohexane (1:3) for the other. Develop the alumina strips in the same way. Note: Ethyl acetate alone is too polar and cyclohexane too nonpolar. One or both of the specified solvent mixtures may prove to be satisfactory, or neither may be the most desirable solvent system. A different single solvent or combination of solvents may be superior, but for expediency you are restricted to the two solutions indicated above.

Follow the instructions given. (Note that the solvent moves more slowly through the alumina then it does through silica gel.)

5. Calculate Rf values for all observed spots.

The Report

The introductory section should include the usual background discussion of the theoretical principles underlying the procedures, as well as a statement of the problem. Be sure to include all observations and measurements (Rf values) in the Experimental section. All thin-layer strips should be taped or stapled to a sheet of paper and attached to the report.

The discussion of results should provide a comparison of the thin-layer chromatographies on alumina and on silica gel and the two solvent systems. In the event that you did not obtain a complete separation of components, offer some possible reasons therefore and some suggestions as to how separation could be done more effectively if you were to repeat the attempt.

Che 311 Chromatography reports

You will submit two reports for the chromatography experiments, one for tlc/column and one for glc. Both of these reports will be due two weeks from today.

Thin Layer and Column Chromatography.

1. Include the regular heading.

2. Explain in your own words what chromatography is and how it works; with emphasis on tlc and column.

3. In a few sentences state what you did in this experiment; be specific.

4. Make a table showing the Rf values for each component for each adsorbent and each solvent system you used in the tlc.

5. Which adsorbent would you select for a column chromatography separation of your unknown and why? Which component would elude from the column last?

6. Discuss the results of your experiment.

7. Staple or tape all of the tlc strips to a piece of paper and label each one. This will be included as part of your report.

8. Answer questions:a) Two components, A and B, were separated by tlc. When the solvent front had moved 10.0 cm above the level of the original spot, the spot corresponding to A was 3.5 cm and that of B was 4.1 cm above the original spot. What are the retention factors for A and B? Which component would elude first from a column chromatography using the same absorbant and solvent?b) Describe how thin layer chromatography could be used to analyze a urine sample for the presence of cocaine if you had a known sample in the lab.c) Why is it important that the sample to be analzed by tlc be dry?d) Why must the solvent level be below the original spot on the tlc plate?e) Why must the cap be in place on the bottle during the tlc separation?

Answer questions 1, 2, 3, 4 on page 807 of your lab text.

9. Attach the carbons from your notebook.

Gas-Liquid Chromatography

EXPERIMENT: Analysis of Alcohol-Ketone Mixtures


A ketone is a type of organic compound that is represented by the general formula I; it is related to another kind of compound, a secondary alcohol (II).

I. R-C=O II. R-C-OH | |

R’ R’

A ketone can be made from the corresponding alcohol by oxidation; conversely, reduction of a ketone results in the formation of the secondary alcohol. (You need not be overly concerned with the chemistry of these substances now. The relationships just described will be amplified at the appropriate point later in the course.)

When a ketone is prepared from the alcohol, or vice versa, it is possible that not all of the starting material is converted to the end product. The final product may therefore be contaminated with some of the starting material. The difference between the boiling points of the alcohol and the ketone becomes smaller as their molecular weights increase, making it more difficult to separate them by conventional distillation procedures. Analysis by GLC, however, readily indicates the presence of the contaminant.

You will receive a mixture of a ketone and the corresponding secondary alcohol. Carry out a GLC analysis following the general instructions given and whatever special instructions are provided for the instrument available in your laboratory. You will also need to measure the chart speed (inches/minute or cm/min).

If your sample was given to you as an "unknown," compute the approximate percentage composition by measuring the areas of the peaks. If authentic samples of the various possibilities are available, attempt an identification of the components of your mixture. In this case, you need use either an authentic ketone or alcohol, but not both.

Gas Chromatography Report

1. Include the regular heading.

2. Explain in your own words the physical basis for gas chromatography and how it works to separate and purify compounds.

3. State in a few sentences what you did. Be sure to give information about the column(s) used and the temperature(s).

4. Make a table:

stationary phase: carbowax

column temperature:

carrier gas: air

detector: TDC

4-methyl-2-pentanol retention time =

Known: retention height width-1/2h area calculated time (sec) (units) (units) (units) weight %

4-methyl-2-pentanol

4-methyl-2-pentanone

Unknown: retention height width-1/2h area calculated time (sec) (units) (units) (units) weight %

4-methyl-2-pentanol

4-methyl-2-pentanone

5. Discuss the results of your experiment.

6. Attach the chromatograms that you ran, suitably labeled.(show your calculations!)

7. Attach the notebook carbons.


In a glc three peaks are observed and their areas are calculated as follows: A, 13.5 mm2; B, 20.2 mm2; C, 4.6 mm2. What is the % composition of each component in this mixture?Describe how the identity of each of the components could be determined if known samples of two of the compounds were available.

In the known 50%/50% mixture of alcohol and ketone, why are the areas of the two peaks not equal?

Page 823 of your lab text: problems 1, 2, 4.

CHE 311 Preparative reaction pre-labs

For all preparative reaction lab experiments you will have to submit a pre-lab writeup as well as the usual post-lab report. The pre-lab is due at least 24 hours before the lab. Failure to submit the pre-lab will result in your not being allowed to begin the synthesis in lab.

For the first preparative experiment, prepare the pre-lab in your notebook (the carbons should be submitted prior to the lab; turn them into my mailbox in the Chem. Office, NSM B-202).

The pre-lab should include the following:

1. A balanced equation for the reaction as you are going to carry it out.

2. A table of the physical properties (see lab handout) of the reactants/solvents and products. (a copy of the CRC is in the reserve book room and there is one in the lab)

3. A step by step procedure for the reaction as you are going to carry it out.

CHE-311 Syntheses of Alyl Halides

In this experiment you will synthesize two alkyl halides, a primary bromide (1-bromobutane) and a tertiary chloride (2-chloro-2-methyl-butane). You will have two weeks to complete both syntheses. The first lab period you will begin the synthesis of 1-bromobutane; once the reaction mixture is refluxing, you will start the synthesis of 2-chloro-2-methylbutane. Both syntheses will be finished during the second lab period.

Note: you must submit prelabs for both syntheses prior to the start of the lab!

See pages 204-211 in your text.

TABLE OF PHYSICAL PROPERTIES (This table must be completed before coming to lab!)

Reactants and fw Moles weight volume density bp mp solubilitysolvents (g) (mL) (g/mL)

sodium bromide 103 0.17 17.0 -- -- 1390 755 sw, sls al

water 18 0.94 17 17 1.00 100 0 --

1-butanol 74 0.109 8.1 10 0.81 117 -89 sw,sal

sulfuric acid 98 0.26 25.8 14 1.84 338 10 sw,d al

(HBr) 81 (0.17) (13.8) -- -- -67 -88.5 sw,sal

calcium chloride 183 -- -- -- -- -- 568 I ace; s eth(anhyd.)

Product(s)

1-bromobutane 137 (0.109)(14.9) (11.7) 1.28 102 -112 iw,sal

NaHSO4 120 (0.109)(13.1) -- -- d >315 sw,sls al

water 18 (0.109)(2.0) (2.0) 1.00 100 0 --

(theoretical)

CH3CH2CH2CH2-OH + NaBr + H2SO4 ---> CH3CH2CH2CH2-Br + NaHSO4 + H2O



Product(s)

Report for syntheses of 1-bromobutane name

1. Balanced equation for reaction as you carried it out:

2. Step-wise mechanism for the reaction. Use curved arrow formalism and label the RDS. Show how each product is formed if more than one product is possible. Use additional paper if necessary. Give the name of the mechanism.

3. weight of the starting alcohol

moles of alcohol

weight of the product halide

moles of product

% yield

boiling point (range) of the product

literature values for the bp of the expected product(s)

4. Discussion of results.

5. a) Why did you wash the crude product with NaHCO3?

b) Why did you then wash it with water?

c) Why was the 1-bromobutane treated with anydydrous calcium chloride?

d) State two purposes of the simple distillation of the product?

e) Was the product produced by an Sn1 or an Sn2 mechanism? How could you verify this?

f) What role did the sulfuric acid play in this experment? Explain! equations!

Answer questions 1, 2, 3, 5, 6 on p. 210-211 of your lab text.

6. Attach the carbons from your notebook, the pre-lab carbons, and table of physical properties. Label and turn in your product.

Report for syntheses of 2-chloro-2-methylbutane name

1. Balanced equation for reaction as you carried it out:

2. Step-wise mechanism for the reaction. Use curved arrow formalism and label the RDS. Name the mechanism! Show how each product is formed if more than one product is possible. Use additional paper if necessary.

3. weight of the starting alcohol

moles of alcohol

weight of the product halide

moles of product

% yield

boiling point (range) of the product

literature values for the bp of the expected product 4. Discussion of results. Be sure to compare the synthesis of 1-bromobutane with that of 2-chloro-2-methylbutane.

Include a table showing the following for the syntheses of n-butyl bromide and for tert-butyl choloride:

time of reactiontemperature of reactioncatalyst%yieldclass of alcoholmechanism

5. a) Draw all of the isomeric butanols. Number them in order of decreasing reactivity with conc. HCl.

b) Why did you wash the crude product in this experiment with aqueous sodium bicarbonate?

c) Why didn't you wash it with aqueous NaOH?

d) Why were you able to wash the crude 1-bromobutane with saturated NaHCO3 while 5% NaHCO3 was used in the washing of 2-chloro-2-methylbutane?

e) What is one major disadvantage of washing with sodium bicarbonate?

f) Neopentyl alcohol reacts with conc. HCl to produce tert-pentyl chloride. Outline all steps in the mechanism to show how this product is formed.

g) Why does 1-pentanol produce only 1-bromopentane and not 2-bromopentane when reacted with HBr?

h) Solid sodium hydroxide is a drying agent. Why did we not use it in place of calcium chloride when drying the crude product?

i) What were the two purposes for the simple distillation at the end of this synthesis?

Answer questions 2, 3, 4, 5 on page 211 of your lab text.

6. Attach the carbons from your notebook, the pre-lab carbons,and table of physical properties. Label and turn in your product.



Product(s)

name

Report for dehydration of 4-methylcyclohexanol

1. Balanced equations for the reactions as you carried them out:

2. Step-wise mechanism for the reaction. Use curved arrow formalism and label the RDS. Name of the mechanism?

3. weight of the limiting reagent

moles of limiting reagent

weight of the product

moles of product

% yield

boiling range of the product

literature value for the bp of the expected product(s)

4. How pure is your product? How do you know?

5. Discuss your results.

6. a) Predict the product(s) for the dehydration of 3-methyl-2-butanol.

b) Predict the product(s) of the dehydration of each of the following alcohols: 1-butanol, cyclohexanol, 1-methylcyclohexanol, 2-methylcylcohexanol, neopentyl alcohol, 4-methyl-1-pentanol.

7. Attach the carbons from your notebook, the pre-lab carbons. Don't forget to label and turn in your product.



Product(s)

CHE 311 Nitration of a halobenzeneThis will be your third preparative experiment. Remember that the pre-lab writeup is due 24 hours before the lab.

Notes:

1. Use your largest Erlenmeyer flask as the reaction vessel.

2. Include a magnetic stirrer in the apparatus. Leave roon between the bottom of the flask and the top of the stirrer base for insertion of a plastic bowl (water bath).

3. Wear rubber gloves to protect your hands, not only against the concentrated acids, but also the product which is a skin irritant.

4. If two or more products are expected (e.g. as from chlorobenzene), calculate the theoretical yield of the mixture as if it were a single substance. Calculate the percent yield of the actual product as if it were exclusively formed.

You will use 0.1 mole of the following halobenzene as the starting material:

desk number

1,10,20,4 bromobenzene 6,16,11 chlorobenzene

2,12,22,9 1,4-dichlorobenzene 7,17,21 1,4-dibromobenzene

3,13,23,19 1,3-dichlorobenzene 8,18,14 1,2-dichlorobenzene

5,15,24 1-bromo-4-chlorobenzene

Nitration of a Haloarene: Experimental Procedure

The starting haloarenes for this synthesis are either liquid or solid, but the desired product in each case is a solid. For some, only one possible product may be formed; some may react to form a mixture of two products, one of which predominates. The remaining compounds may theoretically be converted to a mixture of two or more products. Included in your assignment is the isolation and determination of the identity of the major product.

A.Apparatus

The standard-taper assembly described below could be used for this preparation. However, it is also possible to carry out the procedure in an Erlenmeyer flask (which you will do) but it is necessary to carry out the reaction in a fume hood.

1. A 500-mL Erlenmeyer flask will serve as the reaction vessel. The thermometer is placed in the flask, with its bulb resting on the bottom. When you must stir or shake the reaction mixture, hold the thermometer in place by grasping the neck of the flask and the thermometer simultaneously with one hand.

[alternatively: a. Fit a 250-mL two-neck flask with a Claisen adapter or use a 500-mL three-neck

flask. If you are provided with a magnetic stirrer, place a magnetic stirring bar in the flask.

b. Place a thermometer in the angled side neck of the flask and position the bulb so that it will be immersed in the reaction mixture. Attach a reflux condenser to the other side neck and connect the top opening of the condenser to a gas trop (oxides of nitrogen may be evolved).

c. Attach a dropping funnel to the center neck if the compound to be nitrated is a liquid. If your starting material is a solid, the center neck is to be plugged with a glass stopper.]

2. Surround the flask with a plastic bowl containing some tap water. Obtain some crushed ice in a separate container and keep it handy for cooling the reaction mixture as needed.

B. Reaction

3. Begin the preparation of the nitrating agent by pouring 20 mL (28.5 g; 0.32 mole) of concentrated nitric acid through a narrow-stem funnel into the flask. Do not use the addition funnel, if one is included in your assembly. Carefully add in small portions of 20 mL (37 g; 0.36 mole) of concentrated sulfuric acid. Stir the mixture mechanically or swirl the flask by hand while you are adding the sulfuric acid. When all of the sulfuric acid has been added, cool the mixture to 25-30oC by adding some ice to the water bath, if necessary. Do not cool the solution below 25oC.

If the temperature of the nitrating agent is allowed to fall much below 25oC it is possible that insufficient energy will be available to initiate the reaction. Continued addition of the substance to be nitrated will permit the concentration of unreacted starting material to build up. when the reaction does begin, and heat is evolved, all of the aromatic compound present may interact with the nitrating agent and the reaction may get out of control because of the excessive evolution of heat.

4. Measure out a quantity equivalent to 0.1 mole of the starting material you were assigned. Add the aryl halide to the nitrating agent as directed below. Stir or swirl the reaction mixture to mix the reactants thoroughly. Use the cooling bath to control the temperature so that it does not rise above 60oC, but do not allow the temperature to fall below 30oC. If the temperature does get too low, remove the cooling bath temporarily and allow the reaction mixture to warm up before continuing the addition.

5. Continue to add the starting material in the manner described above until all of it is consumed.

6. When the temperature of the reaction mixture no longer rises spontaneously, heat the mixture on a steam bath or hot water bath for 30 minutes. A heating mantle may also be used, but be certain to wipe the outside of the flask first to remove any adhering water. Heat the mixture to a temperature between 60 and 100oC.

7. Remove the flask from the heat source and allow the mixture to cool to room temperature. You may help it along by using a cooling bath.

C. Isolation and Preliminary Purification

8. Put a mixture of 150 mL of water and enough crushed ice to bring the volume to 200 mL into a 400- or 600-mL beaker. Carefully pour the contents of the flask into the cold water while stirring the mixture with a glass rod. Rinse the reaction flask with a small amount of ice water and add the rinsings to the beaker.

9. The crude product should separate as a solid. If it does so, it can be isolated by suction filtration. If the crude product separates from the aqueous phase as an oil, the following measures may be taken. a. Carefully decent as much of the aqueous phase as possible, leaving the

oily material behind. Add some crushed ice and vigorously stir the mixture with a glass rod. If this treatment does not effect solidification of the material, see step b (below).

b. Dissolve the crude oily product in about 50 mL of diethyl ether or dichloromethane by adding the solvent directly to the beaker that contains the product-water mixture. Transfer the contents of the beaker to a separatory funnel and separate and discard the aqueous phase. After completing step 11, continue with step 12b.

10. The reaction mixture contained a strongly acidic solution, some of which will remain admixed with the crude product. The product must therefore be washed

thoroughly with water. A solid may be washed while it is in the Buchner funnel; a product in solution should be washed in a separatory funnel.

D. Purification

11.a. The product is a solid, so a recrystallization is in order. Select a recrystallizing solvent from among those available to you in the laboratory.

b. If the crude product was dissolved in an organic solvent, that solvent must be removed at this point. A rotary evaporator would be best for this purpose, but any other suitable means may be employed. If the residue is still liquid, it may still be subjected to a crystallization procedure, just as if it were solid.

E. Verification of Identity and Purity

12. Determine the melting range of your product. 13. The product will be analyzed by thin-layer chromatography on silica gel, with the

eluting solvent 9:1 (v:v) hexane:chloroform. Pure samples of most of the possible reaction products are available, you should attempt an identification by comparison of Rf values for the authentic material(s) run alongside the reaction product on the same TLC strip.

14. Package the product and turn it in.

The Report

The Introductory section of the report should include a discussion of the reaction mechanism. A description of the intent of the experimental work, naming the specific compound to be nitrated, and a description of the anticipated outcome should precede the Experimental section and the Discussion of Results. In the latter, be sure to interpret the experimental results (including spectra) and to state conclusions about such steric and inductive effects as are applicable.

Report for nitration of a halobenzene name 1. Balanced equation for the reaction as you carried it out:

2. Step-wise mechanism for the reaction. Use curved arrow formalism and label the RDS. Name of the mechanism? Show how each product is formed if more than one product is possible. Use additional paper if necessary.

3. weight of the limiting reagent

moles of limiting reagent

weigt of the product

moles of product

% yield

melting point (range) of the product

literature values for the mps of the expected products

(name of each!)

tlc: substrate solvent

identity (if possible for each spot)

rf for each spot

4. What products did you expect this reaction to form? Explain the effect that the group(s) present in the starting material have on reactivity and orientation in this reaction and why. How many were actually formed? What evidence do you have for this? How did you identify them? If the number formed is different from the number expected, explain.

5. How pure is your product? How do you know?

6. Discuss your results further.

7. a)In the nitration of bromobenzene, the product after purification by recrystallization contains mostly the para-bromonitrobenzene and little of the ortho-isomer. Explain.

b) Bromo is a deactivating group in EAS but an ortho/para director. Use resonance structures to explain why no detectable amounts of the meta isomer are obtained.

8. Attach the carbons from your notebook, the pre-lab carbons, and the tlc. Don't forget to label and turn in your product.

CHE-311 Information for Final Exam

This exam is 20 questions long and consists of short essays and a few calculations (bring your calculator).

To study for this exam, go over each of the techniques that you have learned for separating and purifying organic compounds. You are expected to know the terminology and basic physical principles behind each method and technique. Know which methods you should use under which circumstances. You should also look at each of the preparatory experiments and know why you did each of the operations that you did.

Calculations that you should be capable of doing include:

partition coefficient in extractions

Rf

retention times

% in gas chromatography

% yield

CHE 311 Sylabus - Gravity Waves · Web viewDRYING: an organic liquid that has been in contact with...

Documents

Transcript of CHE 311 Sylabus - Gravity Waves · Web viewDRYING: an organic liquid that has been in contact with...