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The University of Western OntarioFaculty of Engineering Science

DEPARTMENT OF CHEMICAL AND BIOCHEMICAL ENGINEERING

INDUSTRIAL ORGANIC CHEMISTRY II

CBE2207

LABORATORY MANUAL

Prepared by P. Charpentier, E. R. Gillies and J. Herrera

8th Edition

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CBE2207 Edited by J. Herrera, 2014

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TABLE OF CONTENTS

1 INTRODUCTION .................................................................................... 31.1 CONVERSIONFACTORS .................................................................... 31.2 COMMONITEMSOFGLASSWAREAND APPARATUS ...................... 5

1.3 ANOTETOTHESTUDENT ................................................................... 91.4 SAFETYGUIDELINES ........................................................................... 91.5 GENERALHOUSEKEEPINGANDLABORATORYWORK ................. 141.6 GUIDELINESFORPREPARATIONOFLABORATORYREPORTS .... 16

LABORATORY1-ANATTEMPTATTHESYNTHESISOFASECONDARYALCOHOL:THEUNCERTAINREDUCTIONOFAKETONE.......................22

LABORATORY 2- REACTIONS OF ALCOHOLS: SYNTHESIS, PURIFICATIONAND STRUCTURE ELUCIDATION OF AN ORGANOLEPTIC MOLECULE......27

LABORATORY 3 -THE ALDOL CONDENSATION - SYNTHESIS OFBENZYL AND DIBENZYLACETONES...............................................................32

LABORATORY 4- ALDOL CONDENSATION, BENZYNE FORMATION AND THEDIELS-ALDER REACTION : A MULTI-STEP REACTION SEQUENCE39

APPENDIX ..47

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INTRODUCTION

1.1 CONVERSION FACTORS FOR SOMECOMMONLY USED UNITS OF MEASUREMENT

Acceleration m/s2 ft/s2 3.281X100 3.048X10-1

g (accel. of gravity) 1.020X10-1 9.807X100

Area m2 ft2 1.076X101 9.290X10-2

inch2 1.550X103 6.452X10-4

yard2 1.197X10

08.361X10

-1

Density kg/m2

g/cm 1.000X10-3

1.000X103

lb/gallon 8.345X10-3

1.198X102

lb/ft3 6.242X10-2 1.602X101

Energy J btu 9.484X10-1 1.054X103

(includes work) calorie 2.387X10-1

4.184X100

(thermochemical)erg 1.000X107 1.000X10-7

ft-lb 7.375X10-1

1.356X100

kW-hr 2.778X107 3.600X10

-6

Force N dyne 1.000X105 1.000X10

-5

pound force 2.248X10-1 4.448X100

Heat capacity J/kg*K btu/lb*oF 2.390X10-4 4.184X103

(includes entropy) cal/g*oC 2.390X10

-4 4.184X10

3

Length m 1.000X1010 1.000X10-10

in 3.937X101 2.540X10

-2

ft 3.281X100 3.048X10

-1

micron 1.000X106 1.000X10-6mile 6.213X10

-4 1.609X10

3

yard 1.094X100 9.144X10

-1

Mass kg ounce 3.527X102 2.835X10

-1

lb 2.205X100 4.536X10-1

Power W btu/hr 3.414X100 2.929X10-1

btu/sec 9.484X10-4 1.054X101

cal/sec 2.390X10-1

4.184X100

ft-lb/sec 7.376X10-1

1.356X100

horsepower 1.341X10-1 7.457X102

(550 ft*lb/sec)

Pressure Pa atm 9.869X10-6

1.013X105

(76cm Hg)bar 1.000X10-5 1.000X105

cm of Hg 7.506X10-3

1.333X103

dyne/cm2 1.000X10

1 1.000X10

-1

in of Hg 2.961X10-4 3.337X103

kg force/cm2 1.020X10-5 9.807X104

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CONVERSION FACTORS FOR SOME

COMMONLY USED UNITS OF MEASUREMENT CONTD

lb/in2(psi) 1.450X10

-4 6.895X10

3

torr 7.501X10

-3

1.332X10

2

(mm of Hg)

Volume m3 ft

3 3.531X10

1 2.832X10

2

(includes capacity) in3 6.102X10

-1 1.639X10

-5

gallon (U.S.) 2.642X102 3.785X10-3

L 1.000X103 1.000X10-3

ounce (U.S.) 3.381X104 2.957X10

-5

psig =pounds per square inch gaugepsia =ponds per square inch absolute

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1.2 COMMON ITEMS OF GLASSWARE AND APPARATUS

Most of the apparatus used will be familiar to you, but the following notes may help

you in identifying and using specific pieces.

The ERLENMEYER or CONICAL FLASK is used for handling

solutions, and for titrations. It is designed with a narrow neck to

minimize loss of solution through splashing or evaporation.

The FILTER or BUCHNER FLASK is used in conjunction with the

Buchner funnel for vacuum-assisted filtration. It is heavy-walled to give pressure

resistance; for this reason, a Buchner funnel should never be

used to heat a solution. Attach it to the vacuum line or water

aspirator with heavy-wall rubber tubing. For any operation

involving vacuum, always use heavy walled rubber tubing -

never use soft tubes like Tygon. If a water aspirator is used,

an empty flask should come between the filter and the pump to

avoid suck-back if the water pressure falls. The Buchner

assembly is top-heavy and should be supported when in

operation.

The BUCHNER FUNNEL is used for filtration. It fits through a rubber

bung or cone into the Buchner flask. To use, assemble the flask and

funnel, place a filter-paper flat across the perforated porcelain plate,

and wet the paper with the solvent being used (usually distilled

water). Turn on the vacuum and make sure the paper is correctly seated in thefunnel; the filter paper should be cut slightly smaller than the funnel, but make sure it

covers all the holes. Stir the suspension to be filtered and quickly pour it onto the

center of the paper, using a glass rod to guide it. Filtration will go more quickly if you

keep liquid in the funnel. If all of the liquid is filtered off, the residual solid will pack

down into a solid cake, slowing filtration. To empty the funnel after the solid cake has

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been washed and sucked as dry as possible, loosen the cake around the edge with

a spatula, carefully invert the funnel onto a watch-glass and tap it gently.

The EVAPORATING DISH is used to provide a large surface area to

speed up evaporation. It can be heated on the steam-bath but should

never be heated with a direct flame.

The BURETTE accurately measures volumes to 0.1ml accuracy. When titrating,

always fill the burette to the zero milliliter marking. Your eye should be level with the

bottom of the meniscus in order to take a proper reading of the liquid level.

The TRANSFER PIPETTE accurately deliversone volume (e.g. 5 or10 or25ml).

The PASTEUR or DROPPING PIPETTE is for transferring a few drops.

The SEPARATORY FUNNEL is used for the separation of

liquids with differing densities and for washing. The funnel

should have a properly working stopcock and a stopper of the

correct size. The solution to be separated is poured into the

funnel with the stopcock closedand the funnel stoppered. It is

then shaken vigorously with two hands; one holding the bottom

of the flask between first and second fingers and the other on

the stopper so it does not fall out. This maneuver is performed

with the flask upside down and the stem directed away from

people standing by in case of any splashing. The pressure

which may build up inside the flask is released by holding the funnel upside down

and opening the stopcock. Next, the funnel is placed in a proper size support ring.

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Enough time is given for the solutions to separate into two distinct layers after which

the bottom layer can be removed and the procedure repeated until necessary. (It is

assumed that one knows which layer is to be kept!)

GAS CYLINDERS with the safety cap off need to be securely strapped to the wall or

a desk in order to prevent them from falling. There is considerable pressure in these

cylinders and care must be taken to control the flow of gases from them. The main

cylinder or tank valve should be closed when not in operation. This valve measures

the pressure present in the tank (i.e. how much gas is left in the tank). The control

valve, usually the second one, gives the pressure reading present in the line

connected to the tank. This is usually a backwards valve, meaning that to

reduce pressure it needs to be turned in the counterclockwise direction. A

BUBBLER is usually inserted in the gas line between the cylinder and the

connection to the apparatus to be filled with the gas. This is advantageous for

two reasons: 1) the flow of gas is actually seen as it bubbles through the oil in

the bubbler and 2) this is an outlet for the gas if the pressure becomes too high so

that it exits via the bubbler rather than blowing the glassware or connecting tubes.

When working with gas cylinders it is very important that you know and understand

how everything is connected and what function each piece of equipment has.

There are many different shapes of

CONDENSERS available for use. All of them

serve the same purpose in conjunction with

distillation apparatus. Their purpose is to cool

the vapors inside the condenser usually with

water as coolant. The condenser is placed

before and is tilted toward the receiving

flasks. The glass is blown so that the cooling

liquid is separated from the vapors which are

to be condensed. To have good cooling cold

water should flow through the condenser at

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all times. This is achieved by connecting the water inlet to the bottom end of the

condenser and the outlet to the top so the water flows from the bottom up the

condenser and out the top.

ERROR DATA

Volumetric flasks Volumetric pipettes

Volume (ml) Error Volume (ml) Error

10 0.04 1 0.006

25 0.06 2 0.006

50 0.10 5 0.01

100 0.16 10 0.01

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1.3 A NOTE TO THE STUDENT

The objective of this laboratory is to introduce the student to basic organic reactions

and analytical instrumentation, as used in industrial operations and processes. By

performing the prescribed experiments the student will become familiar with a typical

organic chemical laboratory and the operation of typical analytical instruments.

She/he will also obtain a feeling and routine for generation of analytical results and

the technical capabilities of various instruments. The generated knowledge will

enable the student to better understand the basic chemical principles and control of

industrial processes, which is essential for proper operation of individual units in the

plant and the management of processes for optimum performance and product

quality, and environmental effects. Whether in management, processing, design or

laboratory, an engineer should have good knowledge and understanding of the

chemistry, measurements and instrumentation being used in the plant. The

important decisions and modifications that an engineer must make in industry will be

based on the results obtained from the laboratory. A good understanding of possible

errors in procedures and instruments is also required and particularly a good

understanding of variables that could affect a result. A lack of this understanding

very often results in erroneous judgments that can affect considerably bothproduction and quality of the final product.

1.4 SAFETY GUIDELINES

Although this laboratory does not involve extensive manipulation of hazardous

chemicals, some of the materials that will be used are often flammable and volatile

as well as toxic. Each student must therefore follow strictly all safety procedures and

not perform any unauthorized manipulations with these chemicals prior to

consultation with the instructor or the demonstrator. Although most of laboratory

safety is common sense, this is a general guideline, and therefore may be

incomplete. If you are ever unsure about safety, please ask.

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Remember: ACCIDENTS ARE CAUSED AND CAN BE PREVENTED!

VIOLATION OF ANY OF THE REGULATIONS DESCRIBED BELOW WILL MEAN

THAT YOU WILL NOT BE PERMITTED TO WORK IN THE LABORATORY AND

THEREFORE RECEIVE A MARK OF ZERO FOR THE LABORATORY REPORT.

1.4.1 Laboratory Apparel Rules

-Safety goggles are required in the laboratory AT ALL TIMES! Eyes are extremely

sensitive and delicate to minimum amount of most chemicals. You are responsible to

provide your own goggles.

-Contact lenses should not be worn in the laboratory. Goggles protect the eyes from

spill hazards, but do nothing to protect them from fumes, which can easily dry or

dissolve contact lenses and may result in the necessity of eye surgery for their

removal. Moreover contact lenses can also absorb chemicals from the air (especially

those breathable lenses), concentrate and hold them against the eye, and/or

prevent proper flushing of the eye should a chemical be splashed into the eyes.

-Laboratory coats must be worn at all times inside the laboratory. If you need to step

outside the laboratory for a while, your coat must be removed and left behind in the

laboratory.

-Sandals, open-toed shoes and high heels are not permitted in the lab. Shorts or

skirts cut above the knee are not permitted either. If a spill occurs, your clothing will

protect you from direct exposure. Open toe and shorts or skirts are prohibited to

protect your feet from splashes and spills. The restriction on high heels is for

balance. If you must wear some of this gear for a later appointment or situation you

should consider carrying with you a pair of sneakers and sweat pants to wear during

the lab.

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- Careful consideration should be given before wearing any jewelry into the lab.

Some chemicals can get beneath a ring, watch or some other form of jewelry, this

prevent them from evaporating and hold them against the skin increase the risk of

injury. If you decide to wear jewelry to the laboratory be particularly mindful of

itching, burning or any other irritation under or around your jewelry. Some gems and

precious metals might be easily damaged by the laboratory environment (for

instance silver and opal jewelry). If you decide to ear jewelry you do it at your own

risk.

- Never wear clothes that hang, such as loose sleeves. Ties and scarves must be

tucked inside your laboratory coat

- A good suggestion is to wear only very old clothes to the laboratory. Some

students might consider bringing lab-suitable clothing with them in a gym bag and

change right before and after lab. If you have a very tight schedule (must be

documented) and decide to change into suitable clothes before the lab we can

arrange for 10 minutes for you to change clothes.

- Long hair is to be constrained at all times.

1.4.2 Safety rules

- Eating and drinking in the laboratory is strictly forbidden.

- No radios, tape players, CD players, iPods or any other devices of this type will be

permitted in the laboratory at any time.

-Use of cell phones is not permitted in the laboratory.

-Identify all of the laboratory safety equipment, and keep their location in

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your mind at all times. We might ask you to close your eyes any time during a lab

and point to such safety equipment as the fire extinguisher, the emergency eyewash

stations, the safety shower, the nearest exit etc. This exercise might save you from

a big injury. For instance if you were to splash a chemical in your eyes, you'd better

be able to find that eyewash station without your eyes well before permanent

damage can occur (which can be seconds depending on the nature of the chemical).

- Develop good working habits. Keep your area clean and tidy. Your working area

reflects your working habits and also the quality of your work and results. A clean

and tidy environment decreases the probability of a laboratory accident.

- ALL FLASKS, BEAKERS AND CONTAINERS WITH ANY CHEMICALS OR

SYNTHESIS PRODUCTS THAT YOU LEAVE BEIND AFTER A LABORATORY

SESSION MUST BE CLEARLY LABELED WITH THE NAME OF THE CHEMICAL,

THE OWNER AND DATE! UNLABELED VIALS CONTAINING CHEMICALS WILLL

BE DISCARDED.

1.4.3 Handling Chemicals and Equipment

Students will work in groups of two or three and enough time will be provided to

finish all the prescribed experiments. If any piece of equipment fails or does not

function properly, students are required to report the problem immediately to the

demonstrator or the instructor and are not allowed to attempt to fix the instrument on

their own.

1. Do not taste chemicals.

2. Do not pipet any chemicals by mouth. Use rubber bulb (propipette).

3. Do not pour liquids that are flammable or that do not mix with water into sinks.

Pour them into the provided and labeled containers.

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4. Do not mix incompatible chemicals. If you do not know their compatibility ask.

5. Do not heat flammable liquids with an open flame.

6. Operations involving volatile or toxic materials are to be conducted in the fume

hood.

7. Dispose of solid wastes in garbage pails. Do not use the sinks.

8. Clean up spills (solid or liquid) at once.

9. Return chipped or broken glassware to the laboratory TAs or technician.

10. Be sure the apparatus is placed properly. Do not move instruments without

proper consultation with the laboratory TAs or technician.

11. When heating a test tube make sure that it is not pointing towards yourself or

other people in the vicinity, so no damage will result if the contents suddenlydump out.

12. Never apply force to any glass apparatus. Many serious cuts are caused by the

sudden fracture of glass under strain from misuse. In particular, never use force

in an attempt to push a thermometer or glass tube through a hole in a cork or

rubber.

13. Never heat a tightly sealed flask even if it is empty-----it will explode.

14. Do not attempt to buttress a laboratory assembly with makeshift supports such

as books, pencils and the like. Use several ring stands if necessary. Round

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bottom flasks cannot stand freely on the bench----use a special cork support or

place the flask into a beaker.

15. Do not attempt to break up a solid in the bottom of a flask by punching the solid

with a glass stirring rod. The rod may either fracture in your hand or puncture the

bottom of the flask.

16. Avoid shortcuts! If you have an idea for an improvement talk it over with your

demonstrator; if no objections, try it; if it is successful, tell us about it, you will

get extra marks.

17. There are certain necessary precautions associated with particular chemicals or

experiments. Your demonstrator will point these out when required.

18. If you are not familiar with a piece of apparatus or an experimental procedure

ask for help. Dont just try to muddle through without knowing what you are

doing.

19. Chemical waste should be disposed of in the labeled waste containersprovided.Halogenated chemicals must be disposed of separately from non-

halogenated chemicals. Nothing should go down the drain! Dispose of all

chemicals in the bottles marked for the specific lab.

1.5 GENERAL HOUSEKEEPING AND LABORATORY WORK

ALL STUDENTS MUST HAVE A LABORATORY BOOK IN WHICH TO RECORD

ALL LAB DATA DURING THE LABORATORY PERIOD. The lab book used in

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industry is a legal document. Loose papers for recording of data or comments are

not allowed and will be removed from the lab.

Each student must read the instructions for the particular experiment PRIOR to

coming to the laboratory. He/she should understand the whole procedure and what

must be done in the experiment. This knowledge will be checked periodically by the

instructor or the demonstrator and it will be evaluated.

Equations for all reactions should be written out in your lab notebook before coming

to the laboratory. Also, any calculations required (e.g. theoretical yield, preparation

of solutions) should be written in full in your laboratory notebook before coming to

the laboratory. Record all observations in the lab book including any color changes,

unexpected events, smells, etc. The notebook will be marked from time to time

during the term. Plan your working time in the laboratory! By doing this your

laboratory will be a useful and pleasant experience rather than a frustrating one.

ALL LABORATORY EXPERIMENTS MUST BE DONE DURING THE ALLOCATED

TIME PERIOD. THERE WILL BE NO EXTENSION OF THE LAB AND NO

ADDITIONAL TIME PERIOD AVAILABLE FOR THE EXPERIMENTS, except underspecial circumstances such as illness verified by a doctors note.

1. Keep benches clean and orderly and sinks clean. You must leave your portion of

the bench and all glassware and equipment clean at the end of the lab period.

2. Aisles and floors are to be kept free of obstructions. Keep cupboard doors and

drawers closed when not in use.

3. Hang coats on the rack. No coats are permitted on tables or benches.

4. Laboratory doors MUST be unlocked during lab period.

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1.6 GUIDELINES FOR PREPARATION OF LABORATORY REPORTS

Laboratory reports should be written as though they were short technical reports.

Thus Tables and Figures should always be referred to in the prose text of the report,

i.e. they should not appear on their own.

The report should be written in the past tense, since it is a description and a

correlation of past observations. The present tense may be used in referring to laws

of nature, properties of materials etc. which are independent of time. Thus, for

instance, in a particular experiment The ambient temperature equaled 22C; on

the other hand, The ambient temperature equals about 20 C .

TITLE PAGE

Title of experiment

Name of person writing the report

Name of experimenters

Date when the experiment was performed

All Formal reports must be TYPED

ABSTRACT

The Abstract should summarize the entire report. It should state clearly and briefly

the objectives, methods, results and conclusions of the lab.

Objective: State the objective or purpose of the lab

Method: In one or two sentences, summarize the methods, including scientific

and common names of chemicals and techniques used.

Results: Summarize what was found in the study

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Conclusions: State the significance of the results in relation to the objective.

INTRODUCTION

The Introduction should describe the scope and the purpose of the lab and include

any background information necessary to understand the experiment.

State the general problem. Give a brief statement of why the general topic is

relevant and important. Define any specialized terms or concepts (e.g. the concept

of distillation) likely to be encountered later in the lab report. Supply sufficient

background (historical and theoretical) information to allow the reader to evaluate

and understand the results of the study without needing to refer to other

publications. The introduction to each experiment in this manual can be used as a

guide but must not be copied and cannot be used as the backbone of the

introduction in the report.

State the specific objective or purpose of the lab and the approach to be used. The

purpose states what you are investigating and why; how you perform theinvestigation should be described later in the Methods and Materials.

MATERIALS AND METHODS

The Methods section should describe what was done and how it was done. It should

be written in the past tense with active voice, and in paragraph form.

The Materials and Methods section should provide only enough detail to permit a

competent worker to evaluate the validity of the experiment and to repeat it, if

necessary. It should not be simply a recipe of all the steps involved. State the names

(IUPAC if possible) of the chemicals used, the instruments, equipment and pattern of

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replication. Describe any unusual numerical calculations and state the statistical

technique used to analyze the data.

RESULTS

The Results section should present the data collected in a summarized form and

describe only the key features of these data, emphasizing trends or patterns that are

relevant to the hypotheses being tested. Interpretation of the data is reserved for the

discussion section.

Do not present the same data in both a table and figure i.e. place table of raw data in

an appendix and place figure in the results section. Titles of tables and figures

should contain enough information to understand the contents without reference to

the text. The number and title are placed at the top of a table, and at the bottom of

figure.

Guide the reader through your figure (s) and table (s) in a logical and systematic

manner, pointing out trends and differences that pertain to the objective (s) of the

report. Simply state what you found in your study, without inference or reference to"expected" results.

DISCUSSION

The Discussion section should provide an explanation and interpretation of your

results and indicate the significance of the results to the hypothesis being tested.

Results of previous studies on the same topic should be compared with yours, with

an explanation of why your results are different from previous studies, if necessary.

State how and why your results either support or do not support the objectives and

hypotheses. REMEMBER: results are results, they are never wrong simply by being

different from either your expectations or from other investigations.

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CONCLUSIONS

Draw conclusions about the hypotheses (objectives) of your study, based on all

data available in the current studies.

APPENDIX

Includes all raw experimental data, e.g. time vs. temperature data points, sample

calculations, and any other information or data used for the experiment and

calculations.

REFERENCES

The Reference section should be a list of all books, journals, and other materials

cited in the body of the paper. Please notice that all reference sources must be peer

reviewed and scientifically validated. Wikipedia or other non-refereed materials

available on the World Wide Web are not acceptable as reference sources in a

technical report.

The surname of the author(s) and the year of publication should be inserted in the

text at an appropriate place:

"Smith (1991) compared..." or "... have been recently compared (Smith, 1991)."

If the reference has more than 2 authors, include only the surname of the first

author, followed by "et al."

"Smith et al. (1991) compared..." or "... have been recently compared (Smith et al.,

1991)."

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When listing more than one citation at a given point in the text, list them in

chronologically by first author, but for 2 (or more) papers, published in the same

year, list these alphabetically:

"(Jones, 1978; Black et al., 1989; Smith, 1989; Jones and Smith, 1991)"

If an author or group of authors has published more than one article in a given year,

you can distinguish between these articles by placing a letter postscript after the

publication year:

"(Black and Smith, 1990a; Black and Smith, 1990b)"

List all references in alphabetical order, sorted by the author(s)' last name(s). In

cases where the same author or group of authors has/have published multiple

papers that you have cited, then arrange these references in chronological order.. All

authors must be given in the reference list - the abbreviation "et al." Is used only in

the text. The following are examples of the punctuation, style and abbreviations that

may be used for references (note: the headings given here are not to be included in

your reference list).

Journal article:

Jones, R.S., E.J. Gutherz, W.R. Nelson and G.C. Matlock. 1989. Burrow utilization

by yellowedge grouper, Epinephelusflavolimbatus, in the northwestern Gulf of

Mexico. Env. Biol. Fish. 26: 277-284.

Chapter in a Book:

Gross, M.T. 1984. Sunfish, Salmon and evolution of alternative reproductive

strategies and tactics in fishes. Pp. 55-57. In: G.W. Potts and R.J. Wooten (eds.)

Fish reproduction: strategies and tactics. Academic Press, London.

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Book:

Siegel, S. 1956. Nonparametric statistics for the behavioral sciences. McGraw-Hill,

New York. pp. 312.

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LABORATORY 1

AN ATTEMPT AT THE SYNTHESIS OF A SECONDARY

ALCOHOL: THE UNCERTAIN REDUCTION OF A KETONE(2 lab periods)

ABSTRACT

During this laboratory session you will attempt to reduce a ketone. Somegroups will be using sodium borohydride and some sodium chloride. Sodiumchloride is not a reducing agent so the ketone will not transform into the alcohol.However, even if sodium borohydride is used the reaction should be carefully carriedout to obtain the alcohol. You will find out whether your synthesis was successful

using IR spectroscopy.

INTRODUCTION

As you have learned in class, aldehydes and ketones can be converted to

alcohols by a process known as reduction. In this case the reduction process

involves the creation of a new set of C-H and O-H bonds.

CH3 CH2

O

C H CH3 CH2 CH2 OH

CH3

O

C CH3 CH3 CH3CH

OH

(1)

(2)

There are several reagents available for this reaction. For example, lithium

aluminum hydride (LiAlH4) is a commonly used reducing agent; however, it is

extremely reactive with water and rapidly decomposes in air, making it difficult tohandle. Sodium borohydride (NaBH4) is also a commonly used reducing agent and

is easier to handle safely. The reaction of sodium borohydride with water is

sufficiently slow at room temperature to allow its use as a reducing agent in an

aqueous medium. However, many organic compounds are insoluble in water, so it is

frequently necessary to use ethanol as a solvent.

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Sodium borohydride serves as a source of H- (hydride, a very powerful

nucleophile), which attacks the electrophilic carbon of the carbonyl group in the

ketone. However, sodium borohydride does react to some extent with the solvent

ethanol and it is therefore necessary to use excess sodium borohydride to overcome

this effect so that the reducing agent does not become the limiting factor in this

experiment.

The product benzhydrol is soluble in the ethanol-water mixture which was

used for the reaction but is insoluble in water. Thus, if the reaction mixture is diluted

with cold water the product precipitates. However, if the reaction was unsuccessful

unreacted benzophenone will precipitate as well. Sodium borate remains in solution

since it is a salt and is very soluble in water. Following the precipitation of your

reaction product, you will purify it further by recrystallization (Appendix 1A).

In order to evaluate the success of your experiment, you will use infrared

spectroscopy. The most important aspect to understand is that the bonds in the

molecules stretch and bend and that this stretching and bending is linked to the

absorption of infrared light. The wavelength of the infrared light absorbed in these

processes depends on the specific atoms and bonds (ie. single, double, or triple)involved. The absorbed wavelengths for a given sample can be determined using an

instrument called an infrared spectrometer and plotted to provide a spectrum. As

different functional groups absorb light of characteristic wavelengths, leading to

characteristic peaks in the spectrum, this technique can be very useful in

determining which functional groups are present in a molecule. This aids in verifying

the identity of the compound. More details on infrared spectroscopy can be found in

the text (Wade Ch. 12-1 12-12) and your lecture notes.

MATERIALS

125mL Erlenmeyer flask

Ceramic Boiling chips

50mL, 500mL beakers

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Buchner funnel and filtering flask

Whatman #4 Filter paper

Disposable Pasteur pipette

6.0 g Benzophenone

50mL 96% EtOH (ethanol)

0.60 g of Reactant A or B (these will be either sodium borohydride or

sodium chloride but you will not know the exact identity of the reactant you

are using).

5mL 6N NaOH

Hot Plate/ Magnetic stirrer

FT-IR Spectrophotometer

METHODS

Lab One

1. In a 125 ml Erlenmeyer flask dissolve 6.0 g of benzophenone in 50 ml of ethanol.

You will need to use a magnetic bar and stir plate.

2. In a 50 ml beaker dissolve 0.6 g of Reactant A or B in 25 drops of distilled water,

and using a Pasteur pipette add this solution drop-wise, with stirring, to the solution

of benzophenone. Continue stirring the reaction for 15 minutes.

3. Using a 10ml graduated pipette add 4 ml of a 6N NaOH solution and a boiling chip

to your flask, and boil the reaction mixture on a hot plate for 10 minutes.

4. Being cautious, pour the reaction mixture into 400 ml of cold water and ice and stir

with a glass rod until the ice is all melted. Collect the resulting precipitate on filter

paper using a Buchner funnel.

6. Wash the crude product with 100ml cold H2O, and let the product sit on the filter

for 5 minutes to remove as much water from the crude product as possible. Using a

metal spatula carefully transfer your product to a tared plastic weighing boat and

place it in the dessicator until next lab period.

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Lab Two

1. Weigh your dried crude product and assuming a successful synthesis determine

the percentage yield.

2. Weigh out 1.0g of your crude product and recrystallize it using an appropriate

solvent (ask your TA which one to use) Do this recrystallization in a 250 ml

Erlenmyer flask. Suspend your product in approximately 50 mL of solvent, heat it

gently using a hot plate (do not boil) and swirl until complete dissolution. You will

need to add more solvent (use 10 mL aliquots) until the solid is dissolved. Be

patient. After cooling, first at room temperature and then on ice, filter your

recrystallized product on a Buchner funnel, air dry the crystals for 10 minutes on

the filter paper, weigh the product to calculate yield and do a melting point

determination.

3. Obtain an infrared spectrum of your purified final product (benzhydrol if the

synthesis was successful), compare it with the one of bezophenone provided.

PRE LAB QUESTIONS Week 1

1. Draw Lewis structures for benzophenone, benzhydrol, and sodium borohydride.

2. Draw the reaction mechanism (arrow diagram) for the reduction benzophenone to

benzohydrol.

3. Calculate the theoretical yield of benzohydrol assuming 100% reduction of

benzophenone. You should include your calculations.

PRE LAB QUESTIONS Week 2

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1. What do you expect to be the main change in the infrared spectrum as you go

from the benzophenone starting material to the benzhydrol product?

2. What was the purpose of using 6N NaOH during the benzophenone reduction

experiment last week?

SUMMARY OF SPECIFIC REQUIREMENTS FOR THE REPORT

1. Assuming a successful synthesis, show calculations of the % yield for the crude

and recrystallized product.

2. Compare the infrared spectra of the starting material benzophenone and that one

of your product. Which peaks are common and which are different? Using the data

in the text book (Wade sec 12-1 12-12) assign the major peaks that correspond to

the functional groups in benzophenone and benzhydrol. Does the spectrum indicate

that your reaction was successful or unsuccessful?

3. Establish the identity of Reactants A and B.

4. Propose and discuss (using a minimum of 200 words) another way, besides anyform of spectroscopy, to evaluate whether your reaction was successful.

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LABORATORY 2

REACTIONS OF ALCOHOLS: SYNTHESIS, PURIFICATIONAND STRUCTURE ELUCIDATION OF AN ORGANOLEPTICMOLECULE.

( 2 lab periods )

ABSTRACTDuring this laboratory session you will run a common reaction of alcohols tosynthesize a molecule that is used in the food and flavours industry. You willelucidate the structure of the molecule using IR and NMR.

INTRODUCTION

Organoleptic substances are commonly used in the industry to fabricate consumer

products. In general an organoleptic material is defined as a substance that has

sensory properties, such as odour, colour, taste or feel. Specifically in the food

industry organoleptic refers to substances used to improve or impart odours and

flavours to materials, making the product more appealing to consumers. While a

wide range of organoleptic substances are used in the flavours and fragrances

industry (for instance, orange extract or lavender oil); it is more desirable to use

single molecules with strong organoleptic properties rather than the very expensive

and complex mixture obtained as oil extract from a natural product.

During this laboratory you will synthesize a molecule with high organoleptic

properties. The procedure in based on an equilibrium reaction involving a carboxylic

acid and an alcohol. Since this is an equilibrium reaction, an excess of reactants isrequired to drive the reaction to completion. In our case the carboxylic acid will be

used in excess since it is less expensive than the alcohols we are using and more

easily removed from the reaction mixture. In the isolation procedure, the excess

acetic acid and the unreacted alcohol is removed by extraction with water since the

product has a low water solubility. Any remaining acid is removed by extraction with

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aqueous sodium bicarbonate (NaHCO3). The resulting product is dried over

Na2SO4.


An alcohol (you will not know the structure of the alcohol you are using).

Either one of these acids:

Glacial Acetic Acid

Formic Acid

H2SO4 (conc.) (CAUTION : highly corrosive )

Sodium Sulfate (anhydrous)

5% aqueous Sodium Bicarbonate

Saturated NaCL solution

100 ml Round bottom boiling flask

Reflux condenserShort path Distillation head with thermometer and condenser

Boiling stones

Heating mantle

250 ml separatory funnel

Glass funnel and filter paper

Sample vial

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Synthesis and purification steps

1. Place 15 ml of the alcohol in a 100 ml RB flask and add 20 ml of the

carboxylic acid

2. Swirl to mix and carefully add 4 ml of conc. H2SO4.

3. Add a few boiling stones, attach a reflux condenser, start the cooling water,

and reflux the mixture for 1 hour. Cool to room temperature.

4. Transfer the mixture to a separatory funnel and add 55 ml of cold water.

Rinse the 100 ml RB flask with 10 ml of cold water and add it to the contents

of the separatory funnel. Mix the two phases by inversion 20 30 times. If

you shake the mixture too vigorously it will form an unbreakable emulsion.

5. Allow the phases to separate and drain off the lower aqueous layer.

6. Add 25 ml of 5% NaHCO3to the separatory funnel. Do this carefully as there

will be gas evolved. Mix by inversion, drain, and check the pH of the aqueous

phase with litmus paper. If it is not basic you will have to repeat the 5%

NaHCO3 washing step.

7. A final extraction with 20 ml of saturated NaCl will remove residual water from

the product.

8. Fold a piece of filter paper, put it in a glass funnel, and add 1 g ofanhydrous Sodium Sulfate ( Na2SO4) to the filter. Clean, dry, and weigh a

100 ml RB flask and filter your product into it. The Na2SO4 will complete the

drying process. Weigh your product and then seal the flask with a stopper and

some parafilm and label it clearly.

Week 2 - Spectroscopic analysis of the product.

1. Obtain the infrared spectrum of your product.

2. Obtain the 1H-NMR of your product. (These will be provided).

3. Obtain the MS of your product. (These will be provided)

4. Using the spectroscopic information and the synthesis protocol used,

elucidate the structure of your product. You must solve this structure before

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leaving the lab. Feel free to bring any reference materials you think will help

you in this task.

PRE-LAB QUESTIONS Week 1

1. Provide an example of an organoleptic molecule used in the food insdutry

2. Which gas in evolving during step 6 of the synthesis and purification protocol?

PRE-LAB Questions Week 2

1. What will be the position of the infrared O-H stretching band for carboxylic acid

and the alcohol. Would you expect to see a difference between the two bands?

2. What are the typical MS fragmentation patterns of alcohols and acetic acid? How

would those differentiate form the MS fragmentation pattern of your product?

SUMMARY OF REQUIREMENTS FOR YOUR LAB REPORT

1. Show step by step how you elucidated the structure of the molecule you

synthesized. These should include assignment of each 1H-NMR peak and main

infrared bands. Indicate how the MS spectrum contributes to structure elucidation.

2. Clearly identify the reaction and mechanism involved in the synthesis procedure.

2. Calculate your yield. Suggest possible reasons why your yield might be less than

100%.

3. Sulphuric acid is also a strong oxidizing and dehydrating agent, what do you

predict as by products of the reaction between the alcohol and sulphuric acid? Will

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all these by-products remain in liquid phase? Propose an analytical technique to

identify these.

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LABORATORY 3

THE ALDOL CONDENSATION - SYNTHESIS OF

BENZYL AND DIBENZYLACETONES

INTRODUCTION

The Aldol condensation is perhaps one of the most important and versatile

organic reactions that leads to the formation of a new carbon-carbon bond. In it

simplest form the aldol condensation combines two carbonyl compounds (ketones

and/or aldehydes) to yield a new -hydroxy- aldehyde or ketone (know also as

aldol)

Under the basic conditions required to run the condensation reaction the aldol

product normally undergoes water elimination, to yield the final ,unsaturated

aldehyde or ketone:

The mechanism for the aldol condensation requires the formation of the enolate ion

of the ketone or aldehyde under strong basic conditions. This step involves the

abstraction of a proton (H+) from the alpha position in the carbonyl compound. The

resulting ion is resonance stabilized in the form of an enolate:

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Enolate ions are strong nucleophiles and will add to a molecule containing a

carbonyl group:

The resulting aldol undergoes base-catalyzed dehydration

In this experiment we will perform a cross-aldol condensation. A cross condensation

is a reaction in which one aldehyde or ketone adds to the carbonyl group of a

different compound. It is very important that for a cross aldol condensation the

electrophile (the carbonyl compound being attacked by the enolate) cannot form

enolate ions itself. Otherwise a mixture of products can be obtained.

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To avoid a mixture of products usually one of the reactants chosen should not have

the ability of forming an enolate ion. In other words, the reactant should not have

protons available in the alpha position.

Another complication arises when the resulting product has also protons available in

the alpha position, in this case a double condensation can occur:

In this experiment you will use acetone as the enolate forming nucleophile and

benzaldehyde as the electrophile. As in the previous example, acetone has alpha

hydrogen on both sides of the carbonyl group, so acetone can add either one or two

molecules of benzaldehyde to yield benzalacetone (4 phenyl -3 penten-2-one) or

dibenzalacetone (1,5-diphenyl-1,4 petadien-3-one) respectively.

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You will synthesize both products and characterize them using UV spectroscopy and

melting point measurements.


95 % Ethanol

Acetone

Benzaldehyde

600 ml beaker to use as an ice bath

125 ml Erlenmyer flask

16 x 100 test tube

Pasteur pipette

Thermometer

Buchner funnel, filter paper, and vacuum flask

Melting point apparatus

UV spectrophotometer

Week 1 Synthesis of dibenzal acetone.

1. Half fill a 600 ml beaker with crushed ice

2. In a 150 mL Erlenmeyer mix 30mL of Ethanol (95%) and 40mL of a 10%

NaOH. Put a thermometer into the reaction mixture and place the flask into

the ice bath. Stir the mixture occasionally by swirling.

3. In a 16 x 100 test tube mix 4mL of benzaldehyde and 1.5mL of acetone, mix.

4. Using the Pasteur pipette add the benzaldehyde acetone mixture to the

ethanolic NaOH solution drop by drop stirring frequently. The addition should

be done over a period of 20 min. Keep track of the temperature of the

reaction mixture. By moving back and forth between the ice bath and the

bench you can keep the mixture greater than 20 C but less than 28 C.

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Cloudiness of the solution indicates formation of the product. If cloudiness is

not observed let the mixture reach room temperature.

5. After finishing the addition stir manually for 10 minutes and then let the

reaction mixture stand for 10 minutes at room temperature. Slowly add 2 ml

of ice water to the mixture to force precipitation of product. Put the reaction

mixture in the ice bath for 10 more minutes.

6. Filter the reaction mixture using a Bchner funnel and vacuum, wash the

mixture with cold water until the pH of the filtrate is neutral (basic pH will

interfere with recrystallization), and continue to draw air through your product

to partially dry it.

7. Weight your crude product

8. Recrystallize your product from ethanol. You should obtain yellow , needle-

like crystals.

9. Weight your recrystallized product and determine its melting point.

10. Use a single crystal dissolved in 20mL of ethanol to obtain the UV spectra

(400 to 200nm). This solution might be too concentrated for the UV so it might

be necessary to dilute in ethanol even more.

Week 2 Synthesis of benzal acetone.

1. Half fill a 600 ml beaker with crushed ice

2. In a 150 mL Erlenmeyer mix 30mL of Ethanol (95%) and 40mL of a 10%

NaOH. Put a thermometer into the reaction mixture and place the flask into

the ice bath. Stir the mixture occasionally by swirling.

3. In a 16 x 100 test tube mix 4mL of benzaldehyde and 6mL of acetone, mix.

4. Using the Pasteur pipette add the benzaldehyde acetone mixture to the

ethanolic NaOH solution drop by drop stirring frequently. The addition

should be done over a period of 20 min. Keep track of the temperature of

the reaction mixture. By moving back and forth between the ice bath and

the bench you can keep the mixture greater than 20 C but less than 28 C.

White cloudiness of the solution indicates formation of the product. If the

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mixture begins to turn brown this indicates product decomposition and that

the reaction temperature is too high. If cloudiness is not observed let the

mixture reach room temperature.

5. After finishing the addition stir manually for 10 minutes and then let the

reaction mixture stand for 10 minutes at room temperature. Slowly add 2

ml of ice water to he mixture to force precipitation of product. Put the

reaction mixture in the ice bath for 10 more minutes.

6. Filter the reaction mixture using a Buchner and vacuum. Discard the liquid

filtrate and rinse the vacuum flask.

7. Using 100mL of 50 % Ethanol wash the precipitate. In this step we are

extracting benzalacetone (that becomes an oily suspension) and goes to

the filtrate from the dibenzalacetone (that remains as solid in the Buchner).

Benzalacetone has low melting point (close to 40, 42oC) therefore it is very difficult

to recrystallize. We will extract it to get the UV spectra

8. Take 5mL of the aqueous oily suspension and put it in a 16 x 100 test tube .

9. Add 3mL of chloroform and vortex the mixture to extract the oily

suspension into the organic phase.10. Take one drop of the chloroform phase (bottom phase), mix it with 5mL of

EtOH, and obtain the UV spectra of this mixture (400 - 200 nm ). Dilution

or concentration might be required to get good quality spectra.

PRE-LAB QUESTIONS

Week 1

1. Do you think is possible to run the Aldol condensation in acidic instead of basic

conditions?

2. Write four possible products that can result from an attempt to run a crossed

aldol condensation between acetone and 2-propanal.

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Week 2

1. In the last step, chloroform is used to extract benzalacetone from water. Do you

anticipate that the organic phase (chloroform) will sit above or below the aqueous

phase? Justify your answer.

2. Recrystallization of benzalacetone is very difficult due to its low melting point,

suggest another method of purification for the product. Justify your answer

SUMMARY OF REQUIREMENTS FOR YOUR LAB REPORT

1. Calculate your yield of dibenzalacetone. Suggest possible reasons why your yield

might be less than 100%.

2. Based on the scientific literature(available in the library and the web) propose

a method for the isolation from the reaction mixture and purification of

benzalacetone .

3. The UV/Vis spectrum of Benzaldehyde is shown below. Compare this spectrum

with the spectra you obtained for your products, discuss the differences and

similarities in terms on conjugation of pi systems.

benzaldehyde

0

1

2

3

4

5

6

200 220 240 260 280 300 320 340 360 380 400

w avelength (nm)

Absorbance

benzaldehyde

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LABORATORY 4

ALDOL CONDENSATION, BENZYNE FORMATION AND

THE DIELS-ALDER REACTION : A MULTI-STEP

REACTION SEQUENCE

( 2 lab periods )

ABSTRACT

In this laboratory experiment you will run an Aldol condensation reaction tosynthesize Tetraphenylcyclopentadienone. Then, you will usetetraphenylcyclopentadienone in a Diels-Alder reaction to obtain 1,2,3,4-tetraphenylnaphthalene. Since this is your last laboratory, you are expected toclearly understand the chemistry involved on each of the synthetic steps and befamiliar with all techniques. These will be evaluated during the laboratory session.There will not be written report required for this laboratory; instead you will beevaluated on your knowledge of reactions and procedures involved and the finalyield of your product.

INTRODUCTION

In this laboratory experiment you will again utilize the Aldol condensation to

synthesize a highly coloured organic molecule; Tetraphenylcyclopentadienone.

Then, you will use this compound in a Diels-Alder reaction to obtain 1,2,3,4-

tetraphenylnaphthalene. During this last step you will be constructing a new aromatic

ring structure utilizing benzyne, an unusual and unstable reactant that must be

generated in situ.

In the first part of this experiment you will use diphenylacetone as the enolate

forming nucleophile and benzil as the electrophile. Diphenyl acetone has alpha

hydrogens on both sides of the carbonyl group, while benzyl has two carbonyl

groups. If the stoichiometry and reaction conditions are carefully controlled, a cross

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double Aldol condensation takes place, and the product obtained is a highly

substituted cyclopentadienone:

Notice that in his case a very strong base is needed (potassium ethoxide). The

resulting product is an aldol, however under the very strong basic conditions the

aldol undergoes dehydration to yield the unsaturated, highly conjugated ketone.

In the second part of the experiment you will react the tetraphenylcyclopentadienone

obtained with benzyne in a Diels Alder reaction to form 1,2,3,4-

tetraphenylnaphthalene.

Since benzyne is very unstable it is necessary to generate it in situ. Our strategy will

be then to form benzyne from the unstable diazonium salt of anthranilic acid:

To obtain the diazonium salt of anthranilic acid it is necessary first to run a

diazotization reaction on anthranilic acid. Diazotation reactions often involve the use

of sodium nitrite and HCl to generate nitrous acid (HONO). HONO protonates and

loses water to give the nitrosonium ion (NO+) used as electrophile that attacks the

Diazonium salt of anthranilic acid

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amino group to yield the diazonium salt. In this case, however we will use isopentyl

nitrite to form the nitrosonium ion:

Then, the sequence for the formation of the diazonium salt is:

Once the diazonium salt is formed, it rapidly undergoes decomposition, losing CO2

and N2 to yield benzyne:

Benzyne is a very reactive molecule and extremely difficult to isolate. In our case

benzyne will react with the tetraphenylcyclopentadienone obtained in the first part of

the laboratory session. The process is a DielsAlder reaction that in turns gives

another unstable intermediate:

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The intermediate readily loses carbon monoxide (CO) to yield the fully aromatized

1,2,3,4-tetraphenylnaphthalene:

Please refer to the next page for a full synthetic pathway for this experiment.

In the first part of the experiment you will synthesize tetraphenylcyclopentadienone,

characterize it by FTIR, UV and melting point measurement. In the second part you

will synthesize 1,2,3,4-tetraphenylnaphthalene through a Diels Alder reaction

between tetraphenylcyclopentadienone and benzyne. You will characterize the

product by by FTIR, UV and melting point measurements.

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Figure 9.1Synthetic diagram for the synthesis of 1,2,3,4-tetraphenylnap

tetraphenylcyclopentadienonetetraphenylcyclopentadienone

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Benzil

1,3-Diphenyl Acetone

Ethanol (anhydrous)

Anthranilic acid

1,2-Dimethoxyethane ( DME )

Isoamyl Nitrite

Methanol

Dichloromethane

1.25 % KOH in Ethanol

50 and 100 ml RB flasks

Reflux condenser

Claisen adapter

Heating mantle and controller

Hirsh funnel and vacuum flask

Screw cap vialsMelting point apparatus

FT IR and UV/VIS spectrophotometers

Part 1 Synthesis of tetraphenylcyclopentadienone.

1. In a 50 ml round bottom flask dissolve 1 g of Benzil and 1 gram of 1,3-

diphenyl acetone in 30 ml of Ethanol (abs). A little heat may be necessary to

help dissolution.

2. Slowly add 20 ml of 1.25 % KOH/Ethanol to the reaction mixture. Add a few

boiling chips, attach a reflux condenser to the flask, start the cooling water,

and heat the mixture at reflux for 15 min. The mixture should change color to

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a dark purple (might be dark brown). After 15 minutes stop the reflux, and

allow the reaction flask to cool to room temperature, and then cool down in

an ice bath.

3. Set aside 50 mL of ethanol and put it in an ice batch, this will be used for

washing the product.

4. After reaction mixture is cold, filtrate it using vacuum and a Hirsh funnel.

Wash the crystals using ice cold ethanol. Keep washing until the filtrate is

transparent or light pink. Keep sucking air over the crystals in the filter to dry

them. Crystals are very dark purple with a slightly metallic sheen. There is not

need to recrystallize as the product is quite pure.

5. Weight the tetraphenylcyclopentadienone obtained and calculate your yield.

6. Obtain a UV spectrum for your product. For the UV dissolve a few crystals in

hexane (a very light pink solution) and scan from 650 nm down to 200 nm.

The FTIR of the product will be provided.

Part 2 Synthesis of 1,2,3,4-tetraphenylnaphthalene.

1. In a 50ml RB flask dissolve 0.5g of the tetraphenylcyclopentadienoneobtained in the first part and 0.23g of anthranilic acid in 10mL of 1,2

dimethoxy ethane (DME). Warning DME is toxic, it should be measured in

the fumehood, transported in a stoppered flask and uncapped only under the

elephant trunks located over your lab bench. Attach the flask containing the

reaction mixture to a reflux condenser and heat up to reflux.

2. Add 4 ml of DME to a screw cap vial and place the vial in an ice bath. After

the DME is cold and right before the next step add 0.5ml of isopentyl nitrite to

the vial and reseal it. IMPORTANT - if mixture is not ice cold and/or is

exposed to air for long time the nitrite will decompose and no reaction will

occur.

3. Once reflux is established carefully add the DME solution containing the

isopentyl nitrite through the top of the condenser. The solution should be

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added slowly (over a period of 2 minutes) If the addition is too fast foaming

might occur and the reaction mixture can boil over.

4. Keep the reaction mixture at reflux for 15 more minutes; the reaction mixture

should change to an orange-yellow color. If color change is not observed

prepare a new mixture of isopentyl nitrite in DME with a higher concentration

and add it slowly to the reaction mixture following the same procedure.

5. Set aside 50 ml of ethanol, mixed with 10 ml of water , in a ice bath.

6. Cool the reaction mixture to room temperature. In a 250 ml beaker mix of 25

ml of water and 10 ml of ethanol. Add the reaction mixture to the beaker

slowly using a dropper. A precipitate should form.

7. Use a Hirsh vacuum filter to separate the solid 1,2,3,4

tetraphenylnaphthalene. Wash the solid with the cold ethanol/water mixture.

8. Recrystallize your crude product from 2-propanol. If not all the solid is

dissolved at the boiling point of the solvent the mixture might need to be

filtrated hot to remove insoluble impurities.

9. Needle like crystals should be obtained

10. Measure the melting point and obtain the IR spectra. Compare it to the

spectrum obtained for tetraphenylcyclopentadienone.

11. Obtain the UV spectra using 2-propanol as solvent. Compare it with thespectrum obtained for tetraphenylcyclopentadienone.

PRE-LAB QUESTIONS

There are not prelab questions, on this session all questions will be asked orally and

will heavily influence the mark assigned to the lab.

.

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APPENDIX: RECRYSTALLIZATION, MELTING POINT DETERMINATION, AND

EXTRACTION

A. RECRYSTALLIZATION

1. Theory

(a) General Methods of Recrystallization

Chemical transformations lead invariably to mixtures of products, and therefore

various techniques of separation or purification must be employed to isolate

individual components in pure form, from the crude reaction mixtures. In the case of

solid substances the most commonly employed technique, at least until the advent

of chromatographic methods, was that of recrystallization (or more simply

"crystallization").

As commonly practiced, purification by recrystallization depends upon the fact that

most solids are more soluble in hot than in cold solvents. The solid to be purified is

dissolved in the solvent at its boiling point, the hot mixture is filtered to remove all

insoluble impurities, and then crystallization is allowed to proceed as the solutioncools. In the ideal case, all of the desired substance separates nicely in crystalline

form and all the soluble impurities remain dissolved in the mother liquor. Finally, the

crystals are collected on a filter, washed and dried. If a single recrystallization

operation does not yield a pure substance, the process may be repeated with the

same or another solvent.

(b) Nature of Suitable Solvents

The single most important factor contributing to a successful recrystallization is the

proper choice of solvent. In general, the most "suitable" solvent for recrystallization

purposes is one in which the compound to be purified is only very slightly soluble at

low temperatures but very soluble at higher temperatures (e.g. at the boiling point of

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the solvent). Most compounds exhibit positive temperature coefficients of solubility.

Ideally of course, the impurities to be removed should be readily soluble in the cold

solvent in which they will remain after the crystallization process or almost

completely insoluble even at elevated temperatures.

It should be realized that the solvent selected must be inert and not enter into

chemical reaction with the sample. In addition, it is desirable that the solvent be

reasonably volatile (low boiling point) so that it can be fairly easily removed from the

crystals by evaporation. Where two or more solvents are comparable with respect to

the properties already cited, factors such as inflammability, toxicity and cost are to

be considered.

The lower the solubility of the compound to be purified in the cold solvent, the

greater will be the recovery of purified material from the crude mixture. The fact that

the solubility of the impurities may be comparable to that of the desired compound

does not preclude the use of a particular solvent, since most impurities are present

in relatively small amounts. As an example, consider the recrystallization of a

mixture of solids consisting of 10 g of A and 1 g of B from a solvent in which the

solubility of each is 1.5 g per 100 ml at room temperature and 10 g per 100 ml at the

boiling point. One hundred milliliters of hot solvent would be required to dissolve themixture, and upon cooling the solution would precipitate 8.5 g of A (i.e. 85%

recovery) and no B because the solubility of B had not been exceeded. Only if there

were more than 1.5 g of B and 10 g of A would any B crystallize, and even then a

second recrystallization would complete the separation of up to 2.5 g of B.

(c) Choosing a Suitable Solvent

If no information concerning the solubility characteristics of the substance to be

recrystallized is available, the choice of solvent becomes an experimental problem. It

is necessary to test various solvents for their suitability according to the criteria

outlined above. As a rule, solvents of decreasing polarity are tried in succession and

the solubility behavior in each case observed. To do this, small-scale trial

recrystallizations are carried out rapidly in micro (10 X 75 mm) test tubes. A few

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drops of various common solvents (see table below) are added to small portions of

the crude, finely divided solid mixture and the crystals are stirred and crushed under

the cold solvent with a stirring rod. If solution occurs at room temperature the solvent

is obviously unsuitable. If solution does not occur, the test tube is heated gently on a

steam bath or over a small flame with stirring or shaking. A few more drops of

solvent are added if only partial solution has occurred. (Transfer of solvent is most

conveniently done with small clean dropping tubes drawn out at the end like

pipettes). If a homogenous solution is obtained it is cooled, and the inside walls of

the test tubes are scratched if crystallization does not occur readily. If no crystals

can be obtained or if solution does not occur on warming, the solvent is unsuitable

and another should be tried. To avoid misleading observations, some care and

judgment must be exercised in choosing the relative amounts of solid and solvent to

be used in these solubility tests.

Choosing a Suitable Solvent

The ultimate proof of the suitability of a particular solvent is in achieving a separation

of the desired component from the unwanted impurities. This can be established by

collecting the crystals which precipitate from the solvent being tested and

determining their melting point.

In many cases it is difficult to predict a suitable solvent. In general, it is said that "like

dissolves like" -that is, a substance will dissolve in a solvent containing similar

groups -or better, that polar solvents will dissolve polar molecules and nonpolar

solvents will dissolve nonpolar molecules; but a good recrystallization solvent cannot

be too like the compound being purified. The accompanying table lists, in order of

decreasing polarity, some of the common solvents used for recrystallization.

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2. DETAILED DESCRIPTION OF EXPERIMENTAL STEPS AND APPARATUS

(a) Preparation of Hot Solution

At this stage the key words are saturated and minimum. Since the compound to be

purified will invariably be soluble in cold solvent to some extent, however small, the

recovery of pure material will be a maximum only by employing no more solvent than

is absolutely essential to obtain a complete solution at the elevated temperature. By

working at or near the boiling point of the solvent, full advantage is taken of the

temperature coefficient of solubility for that particular solute/solvent combination.

Quantitative solubility data are not essential, and the following general approach

may be applied to any solute/solvent combination. The solid is placed in a flask of

suitable size and just covered with a small quantity of solvent (use a volume

comparable to that of the solid phase, but certainly less than will be required

ultimately). The flask and contents are heated gently on a steam bath, shaking or

swirling, to a temperature just below the solvent's boiling point. Heating may then be

interrupted, an additional small quantity of solvent added, and heating resumed. This

procedure is repeated until the last bit of solid just dissolves or until no further

decrease in the amount of undissolved material is apparent. In many instances it willnot be possible to obtain complete solution because of the presence of insoluable

impurities in the mixture.

For this and all subsequent operations in the recrystallization sequence, it is

convenient to use the conically shaped Erlenmeyer flask, but never beakers. This

particular design offers many practical advantages. It minimizes both solvent loss

(the upper walls acting as a condenser) and the distribution of crystals on the vessel

walls out of reach of the solvent phase. It is also particularly convenient for handling

in the transfer operations or for corking or fitting with a condenser. In this way, hot,

ascending solvent vapor does not escape but is condensed and continuously

returned to the solution flask. This is particularly important with solvents such as

ethyl ether, benzene, and petroleum ether, but in practice it is advantageous with

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any solvent because loss of solvent over the period of time taken by the subsequent

filtration step will cause the solution to become supersaturated prematurely. In fact, it

is often desirable to have the solution slightly below saturation at this point to

minimize difficulties in the hot filtration (see below). This is especially true for highly

volatile solvents (e.g., b.p.

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the results of the single trial. In practice, one seldom uses more than 20 mg of

charcoal per gram of dry compound.

(c) Hot Filtration

The hot solution must be filtered to achieve separation from any insoluble impurities

or other undissolved materials. If charcoal is used for decolorization the necessity for

filtration is obvious. If no undissolved material is evident (which is very seldom) this

step may be omitted. The chief difficulty encountered in this operation is that of

keeping the solution hot enough to avoid premature crystallization in the filter. This

means that the filtration must be done as rapidly as possible with minimal cooling of

the solution.

Rapid filtration of small quantities of solution is best done by gravity through a fluted

filter paper supported in a stemless glass funnel. Fluting of the filter paper (the

technique of folding will be demonstrated in the laboratory) increases the rate of

filtration by presenting a much larger surface area to the solution. If a regular funnel

with a stem is used, there is a good possibility of filtrate cooling in the stem, with

crystallization resulting. The relatively narrow stem thus becomes clogged and

filtration is impeded. It is often advantageous to preheat the glass funnel simply by

briefly heating it in a flame or by pouring a quantity of hot solvent through itimmediately prior to filtration. If water is used as the solvent, the filter funnel may be

warmed conveniently on a steam bath.

When working with particularly volatile solvents or with solids having very large

temperature coefficients of solubility, it is particularly difficult to avoid premature

crystallization. In these cases it is usually better to prepare the hot solution with

excess solvent (i.e. the solution is not saturated at the boiling point). After the hot

solution has been filtered the excess solvent must, of course, be removed by

evaporation before inducing crystallization.

It should be emphasized that the hot filtration is done by gravity (at least in an

elementary laboratory) and not by suction filtration as described below for the

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collection of the crystallized product. The use of suction for filtering a hot, nearly

saturated solution is nearly always highly unsatisfactory, because the reduced

pressure in the filter flask causes rapid evaporation of the hot solvent; consequently,

the solution is not only more concentrated but it is cooled by the heat of vaporization

and becomes supersaturated.

Crystallization in the funnel is then almost inevitable and the funnel may become

completely plugged by the deposited crystals.

In carrying out the actual filtration, the fluted paper is inserted into the stemless

funnel so that the lower tip of the paper projects into the opening at the bottom of the

funnel. The hot solution is decanted quickly but carefully into the paper, keeping the

level of solvent well below the top of the paper. When all of the solution cannot be

put into the funnel at once, the remainder is kept warm on the steam bath or hotplate

until it can be transferred to the funnel.

After the solution has run through the paper, a crust of crystals often remains around

the tip of the funnel and ill-formed crystals often form in the body of the cooling

filtrate. It is common practice to rinse the original flask with a little hot solvent and tofilter this through the filter paper to redissolve the crystals adhering thereto. The

filtrate which has been collected in an Erlenmeyer flask should be reheated to

redissolve any material that has crystallized and, if significantly diluted below the

saturation point, should be concentrated to its original optimal volume prior to

cooling and crystallization.

If the various precautions outlined above fail to prevent excessive crystallization of

the solute in the filter paper, the simplest expedient is to return the complete filter

paper and its contents to the original flask, add additional solvent, boil briefly to

ensure complete solution, and begin a new filtration.

(d) Cooling/Crystallization

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Crystallization is accomplished by allowing the hot filtrate to cool slowly, undisturbed,

to room temperature (or at least until crystallization has begun) and then chilling the

mixture in ice or cold water to complete the precipitation. The objective is, of course,

that the desired substance be deposited as pure crystals while any "insoluble"

impurities remain dissolved in the "mother liquor". The lower the temperature to

which the solution is cooled, the more the desired substance will crystallize;

however, at some point the impurities may also begin to separate from solution. The

size of the crystals which separate will vary with the rate of cooling and the degree of

agitation of the solution. Rapid cooling with stirring tends to produce small crystals,

while slow cooling of an undisturbed solution tends to give larger crystals. In general,

either very large or very small crystals are undesirable. There are problems

associated with the collection of very fine crystals because of clogging of the pores

in the filter paper and of adhesion of the small particles to the walls of the

crystallization flask. Moreover, if the solubility of the impurities is comparable to that

of the desired compound, sudden chilling may result in the co-deposition of the

impurities; whereas, with slow, undisturbed cooling these tend to remain in

supersaturated solution and more complete separation is effected. On the other

hand, with very large crystals there is a tendency for the mother liquors to be

occluded within the crystals. In the subsequent drying operations, evaporation of thesolvent will leave a deposit of impurities on the crystals.

Yet another problem associated with too rapid chilling of the solution, especially in

the case of low melting solids, is the tendency for the solute to separate first from the

solution as an "oil" which subsequently solidifies to a crystalline cake. If this

happens, it is possible for impurities to be distributed between the solvent layer and

the "oily" layer (see discussion of principles of extraction). The impurities will then be

entrapped when the oil solidifies. For this reason it is often desirable to choose a

solvent for recrystallization whose boiling point is lower than the melting point of the

solid being purified.

(e) Collection of Crystals -Cold Filtration

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The important objective in the collection of a purified product is complete separation

of the crystals from the "mother liquor" containing the dissolved impurities. This is

achieved most effectively by employing suction filtration. The necessary apparatus

consists of a Buchner funnel attached to a heavy-walled filter flask which is

connected through a "trap" bottle to the source of suction (water aspirator or vacuum

pump) -see accompanying illustration.

The Buchner funnel is prepared for filtration by attaching it to the filter-flask by

means of a cork or rubber adapter, inserting a piece of filter paper whose diameter is

just sufficient to cover the holes in the filter plate (the paper must not fold up against

the sides of the funnel), wetting the paper with a-small quantity of the solvent being

used, then smoothing the paper snugly against the filter plate by the application of

gentle suction.

The cold contents of the crystallization flask are stirred to break up any lumps and

swirled to obtain suspension of crystals. The suspension is decanted quickly into the

funnel in such a way that a layer of uniform thickness is obtained across the whole

surface of the filter bed. This is essential for obtaining complete separation of the

mother liquor. It is important, particularly in the early stages, to use only sufficientsuction to obtain a steady flow of filtrate. Very strong suction at this stage will draw

the finer particles into the pores of the paper, clogging them, and slowing the rate of

filtration unnecessarily. The bulk of the crystals remaining in the flask may be

transferred to the funnel with the aid of a metal spatula. Any crystals still remaining

are most efficiently transferred to the funnel by rinsing the flask with a portion of the

filtrate (which is already saturated with solute) rather than using fresh solvent.

When the bulk of the mother liquor has drained through, the cake of crystals is

pressed down quickly with a spatula or glass stopper and the suction is interrupted

by removing the rubber tubing from the filter flask. It is particularly important at this

stage not to draw air through the crystal cake, because this will cause evaporation of

the mother liquor and the impurities that were dissolved therein will be deposited on

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the surface of the crystals. If it is intended to use the mother liquor to obtain a

second "crop" of crystals after concentration to a suitable volume, it should be

transferred at this point to a separate vessel (or the Buchner funnel attached to a

clean filter flask).

(f) Washing the Crystals

To complete the separation of the mother liquor, the crystalline cake must be

washed with small quantities of fresh, clean solvent. This is done conveniently by

covering the filter cake completely with a thin layer of solvent, with the suction

disconnected. If possible the crystalline cake should be loosened with a spatula to

ensure complete wetting by the wash solvent, but care must be exercised not to

disturb the filter paper. The suction is reapplied and the wash solvent drawn down

through the crystals, which are then pressed down firmly as before to remove the

wash liquid as completely as possible. For complete removal of the mother liquor

from the crystals two or three such washes are recommended; however, to minimize

loss of product, the wash portions should be small in volume and the solvent should

be cold. After the last wash, full suction is applied to draw air through the filter cake

to suck it as dry as possible.

(g) Drying the Crystals

The final operation in the recrystallization of a product, is the drying of the solid. If

the solvent employed in the recrystallization is rather volatile, it is possible that it will

have evaporated completely during the last stages of the suction filtration.

Otherwise, further drying is necessary. As used here the term "drying" refers to the

complete removal of solvent, be it organic or aqueous.

The cake of crystals is transferred, with the aid of a spatula, to a sheet of glazed

paper, a watch glass, or any suitable container having a relatively large surface

area. The solid sample should be spread out and permitted to stand in air with

periodic stirring with a spatula. In many instances, however, simple "air-drying" as

just described will be inadequate or much too slow. The last traces of solvent (and/or

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atmospheric moisture) are removed most conveniently by using a drying oven, a

dessicator, or by evaporation under vacuum. A dessicator is simply a closed vessel

with a lower compartment containing an anhydrous salt such as phosphorus

pentoxide which can remove water vapor by forming a hydrated salt. When using

either an oven or a dessicator the rate of drying can be enhanced even further by

reducing the pressure in the system. The temperature at which the crystalline solid is

dried in an oven should, of course, be significantly lower than the melting point.

B. MELTING POINT DETERMINATION

1. Use of Melting Points for Analysis

Most crystalline organic compounds have characteristic melting points that are

sufficiently low (50 300 C) to be conveniently determined with simple equipment.

Organic chemists routinely use melting points to a) get an indication of the purity of

crystalline compounds and b) help identify such compounds.

Pure crystalline compounds usually have a sharp melting point. That is, the melting-point range or the difference between the temperature at which the sample begins to

melt and the temperature at which the sample is completely melted, is relatively

small (narrow). Impurities, even when present in small amounts, usually depress the

melting point and broaden the melting point range. A wide melting-point range (more

than 5 C) usually indicates that the substance is impure, while a narrow melting

point range of about 0.5 2 C usually indicates that the substance is fairly pure.

However, there are some exceptions to both of these generalizations. Small

differences in melting point (on the order of 2 3 C

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