Organic Chemistry Laboratory CHE 327 

Cornell College Term 7, 2004/2005

Addison Ault, Andrea Pionek, Mary Anne Teague, Charley Liberko

 

Laboratory Information

 

Text:  Addison Ault, Techniques and Experiments for Organic Chemistry, Sixth Edition.

Goggles may be purchased from the stockroom for $5.00. A Bound notebook is required.

 

Daily Schedule

            Each day we will meet at 9:00 AM in West Science 100 to review the previous day’s results and to discuss the experiments for the day.   It is expected that all equipment be set up and ready to go by 12:30.  All experimental work must be carried out between 12:30 and 3:00 PM.  Any other time between 8:00 and 5:00, the lab may be used for setting up equipment, cleaning glassware, weighing products, and taking melting points.   On Fridays, we will meet at 9:00 AM for review, discussion, and a quiz.  Friday afternoons are available for makeup; make arrangements with your instructor beforehand if you need to complete or make up a lab. 

 

Preparation

            Before coming into the lab each day, each student must be adequately prepared in order that the lab time is spent safely and efficiently.  Proper preparation includes reading the lab procedure and relevant background material (you may need to do this several times in order to understand it), and preparation of the notebook with all necessary physical data (relevant melting points, boiling points, densities, and solubilities). 

 

Grading

All data and observations will be recorded directly in the notebook.   Notebooks will be turned in for grading at 9:00 AM, and returned after lecture to complete the previous day’s lab.  Notebooks will be due again at 11:00 AM.  If grading is not completed by 12:30 the notebooks will be resubmitted at 3:00 and available by 5:00PM.  Unless otherwise noted, notebooks, products, and questions are due at 11:00 AM the day after the lab was performed.    Write ups will be due the day after the lab was completed at 9:00 AM.

 

 

Point Breakdown                                Points                          Approx. %     

Notebook                                  130                                           22

Write-ups                                  130                                           22

Products                                     40                                              7

Quizzes                                     120                                           20

Final Exam                                100                                           17

Technique                                   60                                           10

Other                                         20                                              3      

            Total                                         600                                           100

 

As a general guide for grading, the following cut -offs will be used:

 

90%                 A-                                            80%                 B-

70%                 C-                                            60%                 D-


 

 

Day

Experiment

Reference

(pages)

Techniques / Reactions

M   2 / 28

1. Isolation of Acetylsalicylic Acid from Aspirin Tablets

43-54, 150-159, 332-333

heating, filtration, crystallization, melting points

Tu   3 / 1

2.  Preparation of 2,4-Dinitrodiphenylamine

475-476

116-119

Nucleophilic aromatic substitution, recrystallization, TLC

W   3 / 2

3. Distillation of  a

methanol / water mixture

62-72; 75-80, 305

Distillation

 

Th  3 / 3

4. Separation of malachite green and phenolphthalein

92-109

Acid base extraction

F    3 / 4

NMR Unknown, Quiz 1

207-330

 

M   3 / 7

5.  Prep. of Cyclohexene from Cyclohexanol

376-380

122-128

acid catalyzed dehydration

GC analysis

Tu  3 / 8

6. Prep. of Cyclohexanone from cyclohexanol

387-389

87-90

182-199

oxidation, steam distillation, IR

W   3 / 9

7.  Preparation of

 “banana oil”

417-426

Fischer esterification,

SN2 substitution

Th  3 / 10

8. Unknowns

169-181

239-272

Solubility, chemical tests for functional groups

F    3 / 11

Quiz 2

 

 

M  3 / 14

 

9.  Preparation of tetraphenylcyclopentadieneone

595-597

Aldol reaction

Tu 3 / 15

 

10. Preparation of a photochromic compound

564-566

electrophilic aromatic substitution, nitration

W 3 / 16

 

11. Preparation of Malachite Green, Crystal Violet

439-440

 

Grignard reaction, preparation of dyes

Th  3 / 17

12. Student's Choice

 

 

F    3 / 18

Quiz 3

 

 

M  3 / 21

13.  Preparation of norbornene-2,3-dicarboxylic anhydride

507,

510-514

Diels-Alder reaction

Tu 3 / 22

Review, Check out

Pizza Frenzy

 

 

W   3 / 23

Final Exam  9:00 - Noon

 

 


Safety

 

            Keeping the lab safe is the number one priority and it is everyone’s responsibility.  Before you begin, read Section 1 in your lab book.  Several rules are worth repeating:

 

Eye protection must be worn at all times in the lab. 

(Wearing contact lenses is discouraged.)

 

Appropriate attire must be worn in the lab. Long hair should be tied back.

 

Memorize the location of all exits, showers, eye-washes, fire extinguishers, and fire blankets.

 

No food or beverages are allowed in the lab. Leave backpacks and coats in the hallway.

 

Be certain that there are no flammables in the area when lighting a flame.

 

Be alert for hazards in the lab.  Do not proceed with any experiment until you understand the hazards involved.

 

Report all injuries to your instructor, even if they appear to be minor.

 

Do not come into contact with any of the solvents or reagents used in this lab other than soap and water.  Remove gloves and wash hands before leaving lab.

 

Clean up all chemical spills immediately, this includes drips on bottles.

 

Do not leave any bottle uncapped.  

 

Dispose of all wastes as directed.  (Ask before you dump.)

 

Come to the lab prepared. 

 

Material Safety Data Sheets (MSDS)

            You have a right to be informed as to all the known hazards and potential hazards of the materials you will work with.  MSDS’s are provided by chemical suppliers which describe risks and proper handling of the reagents you will use.  Copies of these forms are available from the stockroom.

             As an example, consider the MSDS for acetone.  Pay particular attention to the “Precautionary Labeling” section.  Each compound is rated for its health, flammability, reactivity, and contact hazards. The rating is on a scale of 0 (very low or nonexistent hazard) to 4 (extreme hazard).  Acetone poses a low health and contact hazard (rating of 1), it has a very low reactivity (rating of 0), but severe flammability (rating of 3).  Keep in mind that you may already be familiar with acetone as it is commonly used as a “nail polish remover”. 

            A few danger words that you should get to know include:

Toxic - poisonous

Mutagen / carcinogen – causing mutations or cancer respectively

Teratogen – (literally “monster-forming”) causing birth defects

Lacrymator – causing watering of eyes irritation to mucus membranes

Caustic – causing chemical burns


Grading Guidelines

 

Notebooks

            Each student must keep a bound notebook with all data recorded immediately in ink. Consult your text and this syllabus for guidelines on keeping a notebook.  Your notebook will be a significant portion of your grade for this course. 

            For each experiment, your notebook will be graded on a 10-point scale.  The work should include the following and be in the order listed.

 

            1          Descriptive title and date*

            2          Structures / balanced equations* (equations in this manual are not balanced)

            2          Data table of reagents*

            1          Photo-copied procedure or reference*

            1          Procedure summary as performed (note all changes to procedure)

1          Qualitative observations during procedure

2          Results (quantitative observations / properties of product, physical appearance, m.p., b.p., IR, amount obtained, % yield, etc.)

            10         Total

 

*these items are expected to be completed by 9:00 AM for that day’s lab.

 

            Refer to pages 26-31 in your lab text for instructions on keeping a notebook.  A few points are worth noting.  Use only the right-hand page for recording data.  Keep the left hand page for calculations and comments by the grader.  Before coming to the lab, have you notebook prepared with the following information: descriptive title and date, structures / balanced equations, data table of reagents, and a photocopied procedure or reference.  You should have the structures written out for all of the organic compounds used in the lab (including solvents).  Be sure to write balanced equations for each reaction (including acid / base) that you perform in lab.  All data must be recorded immediately in ink.  When reporting measured physical data, include the literature value with reference for comparison.  The results section should include a theoretical yield with calculation.  Indicate which of the reagents is limiting.  Be sure to list actual yield in grams and moles.

A copy of all spectra should be placed permanently (with glue or tape) into the notebook.  Spectra may not cover up data or stick out from edges of the notebook.  Spectra may be photocopied and reduced or trimmed down to size if necessary.  Be sure to include a caption.   

 

Write up

After the lab has been completed you will prepare a short but formal write up on a separate piece of paper.  These write ups should be word processed (hand drawing of structures is allowable if they are done neatly) and are limited to one page of text.  The write-ups are due at 9:00 AM the day after the lab work was completed and will be graded on a 10 point scale.  The write-ups will include a short summary of lab procedure, observations, and results.  It will also include a discussion of the pertinent lab concepts for that day.  The discussion should describe the molecular basis for what was going on.  Describe each step and interpret observations.  Include a mechanism for any reactions carried out in the lab.  Refer to the sample write-up below.


_______________________________________________________________________

[Sample Write-up]

 

Experiment 15

Isolation of caffeine from tea

Ben der Dunthat

 

[This is a big-picture overview to bring the reader up to speed on what you did.]

Summary:  Caffeine was isolated from Lipton brand black tea (12.5 g) by extraction into hot water. Calcium carbonate was included to precipitate out the tannins, which were removed by filtration.  After cooling the filtrate, the caffeine was extracted into chloroform.  Evaporation of the chloroform gave a white semisolid (0.47g) that was recrystallized from 95% ethanol giving small colorless needles. 0.23g, 1.2 mmol, 1.8% isolated yield, Mp 229-232, (235-236 lit.*)

 

 

 

[This is a more detailed account of why things happened the way that they did.]

Discussion:  Caffeine is an organic compound with a high degree of polarity and it is quite soluble in both hot water and chloroform.   The high solubility in hot water (0.67g/ml) allows caffeine to be extracted from the tea leaves.  The tannic acid in tea, however, is also water soluble and is extracted along with the caffeine.  Since calcium salts of carboxylic acids are insoluble, the calcium carbonate acts to de-protonate the tannic acid and to precipitate it as the calcium salt making it possible to remove it by filtration.  As the aqueous solution cools, the solubility of caffeine is greatly decreased allowing most of it to be extracted into the chloroform layer.  Since caffeine is soluble in the cold water (0.02g/ml), the extraction will not remove all of the caffeine and some will remain in the aqueous layer.  Caffeine has a reasonable solubility in cold ethanol (0.02 g/ml) and a fair amount would have remained in the ethanol solution after the recyrstallization.  The recovered yield is 1.8%, which compares to the reported range of caffeine in tea of 2-5%.  The isolated compound melts over a three-degree range close to the reported value for caffeine showing it to be reasonably pure.

 

*Literature value from Aldrich Catalog, 1996-1997.

            _______________________________________________________________


Answers to questions

            Questions are presented for each experiment to stimulate thinking about important concepts and should be considered before writing your discussion.  The questions may serve as fodder for quizzes and exams.  Answers to questions may be written on a separate piece of paper and turned in for extra credit. Be sure to include your name and the experiment number.  Bonus points will be given for answers to the questions as follows:

 

            2          thoughtful, correct answers

            1          reasonable answers

            0          poor or no answers

 

Extra bonus points for exceptional work may be awarded at the discretion of the instructor. 

 

Product Labels

            Each product should be properly labeled and placed on your bench with an accompanying information card.  The product vial should contain a meaningful identification number containing the student’s initials and notebook page number (i.e. CAL-43).  The accompanying card should contain the student’s name, product ID number (matching the vial), product name, product amount (in grams), percent yield (or percent recovery if appropriate) and measured physical data such as melting or boiling point range.  If a spectrum was obtained, a labeled copy should be stapled to the card.  Product cards will graded on a five-point scale and weighted to ten points overall.

 

Product Quality

            The quality of your products will be graded on a three-point scale as given below:

 

            3          High yield, good quality

            2          average yield, average quality

            1          poor yield, poor quality

            0          no product

 

Technique

            Your technique will be evaluated at the end of the term and will be worth 10% of your overall grade.  Technique points will be awarded at the discretion of the instructors.    The maximum number of points will be awarded to students who:

 

- Show up on time

- Are fully prepared for lab

- Follow all safety rules

- Perform laboratory functions safely and efficiently

- Work carefully in the lab to avoid breakage, spills, contamination, and fire

- Properly dispose of waste

- Clean up their bench and common work areas

 

Time Management

            It is expected that students will come to lab fully prepared with major glassware setup in advance and will work at a reasonable pace when in lab.  All of our experiments have been designed and tested so that they may be completed in less than two and one-half hours if the student is adequately prepared.  If for some un-foreseen circumstance a fully prepared student who works efficiently is unable to complete an experiment by 3:00 PM, the student may make arrangements to complete the experiment on Friday afternoon at no penalty.  This option is available at the discretion of the instructor. 

 

Describing your products

            Science begins with observation.   Communicating science must always include descriptions of your observations.  In the organic lab, we must not only say that we obtained a product, but we must be able to describe it.  The most fundamental distinction will be the phase of matter of your product; is it a solid, liquid, or a gas?  But that is only the beginning; you should also describe its physical appearance and properties.  For example, if it is a liquid, you should describe whether it is clear or cloudy (opaque).  You should describe whether it is colored or colorless.  Note that clear and colorless are two different properties.  If you obtain a solid you should describe its crystalline form; are the crystals needline, platy, or prismatic?  If the crystals are too small to be observed they could be described as powdery.  Smell is also an important distinguishing characteristic; is the smell pleasant or pungent?  Words to describe smells might include sweet, fruity (esters), sour (carboxylic acids), fishy (amines), balsamic (cinnamon, cocoa, vanilla etc.), camphoric, citrus (lemon or lime), floral or earthy to name just a few. 

 

 

Commonly misspelled words

Science is worthless without good communication.  When communicating, it is important to spell and use words correctly.  The following is a list of words commonly misspelled or misused in this course.  Learn to use these words properly.

 

Data (a noun, plural)

Distillate (the object; a noun)

Dye / dyed

Filter (the action; a verb)

Filter (the object; a noun)

Filtrate (the material, a noun), (“Filtrated” is not a recognized word)

Ketone

Precipitate (the action, a verb)

Precipitate (the material, a noun)

Separated

Separatory funnel

Summary

Theoretical

Vial

Yield


Experiment 1

Isolation of Acetylsalicylic Acid from Aspirin Tablets

 

Read pp. 43-54, 150-159, 332-333

 

 

 

            Aspirin is an analgesic, an antipyretic, and an anti-inflammatory agent.  It was first produced synthetically by Felix Hoffmann in 1893 and marketed by Bayer as a wonder-drug.  Recently, aspirin has been marketed for its ability to thin the blood and prevent or lessen the severity of heart attacks.   In this experiment, we will isolate the acetylsalicylic acid from aspirin tablets. 

 

            Aspirin tablets contain acetylsalicylic acid (the active ingredient) as well as “inert” binders to hold the tablet together.  We will take advantage of the fact that acetylsalicylic acid is quite soluble in hot ethanol while the binders are insoluble and can be removed by filtration. The solubility of acetylsalicylic acid will be reduced by the addition of water to the solution, allowing the acetylsalicylic acid to crystallize out.  

           

            Follow the procedure in the text for isolating acetyl salicylic acid.  After allowing your product to dry overnight, determine its mass and melting point range. 

 

Report

Discuss the chemical principles used in this lab.  Be sure to record the amount of product you obtained (recovered yield) as well as calculate the percent recovery.  The amount of acetylsalicylic acid in each tablet is reported on the product label.  In your discussion, include the theory of purification by crystallization.

The following information may be helpful for this experiment: Acetyl salicylic acid, M.W. 180.15 g / mol, pKa 3.49, m.p 135 oC.  Solubility: 1 g acetylsalicylic acid dissolves in 300 ml water at 25 oC or 100 ml water at 37oC, 5 ml ethanol, or 17 ml CHCl3. 

 

 

Questions:  no extra questions from this lab.


Experiment 2

Preparation of 2,4-Dinitrodiphenylamine

 

Read pp. 92-109, 116-119, 475-476

 

 

Caution:  dinitrobromobenzene is an irritant, contact with skin should be avoided.

 

            In this experiment, we will prepare dinitrodiphenylamine via nucleophilic aromatic substitution.  Two equivalents of the amine are needed to get the reaction to go; one does the substitution and the other acts as a base.  As the reaction proceeds, the mixture will be set aside for one hour to crystallize.  During this crystallization time, we will use thin layer chromatography to determine if the reaction has gone to completion.  After isolating our product, we will purify it further by recrystallization. 

 

Thin Layer Chromatography (TLC)

We will use thin layer chromatography to follow the progress of this reaction.   We will compare the TLC behavior of our product mixture with that of our two starting materials.  The visible disappearance of one of the starting materials (limiting reagent) from the reaction mixture will be taken as evidence that the reaction has gone to completion.  In addition, we will explore the effect of solvent polarity on Rf values.  

 

The procedure for thin layer chromatography is detailed in your text (pp-116-119) and is summarized for this experiment below. 

1) Prepare at least 3 micropipets by heating capillary pipets in a flame and drawing them out. 

2) Prepare at least three TLC plates by marking them with a soft pencil as shown in the figure below. 

3) Spot each plate with each starting materials and the product mixture.

4) Elute one plate in hexane (non-polar), one in acetone (most polar of the three), and one in toluene (intermediate polarity).

5) Use UV light to visualize each plate and mark the location of the spots with a pencil.  After they have been marked, expose the plates to iodine vapors and note any changes. 

            6) Using the eluting solvent that gives the best separation of spots, run another TLC plate with the product mixture after it has sat for an hour and note if there any differences from the plate spotted with the fresh reaction mixture. 

 

 

Report

            Discuss the chemical principles used in this lab.  Be sure to include a mechanism for the reaction.  In your discussion, explain how the eluting solvent polarity affects the Rf values for the substances.  Also, make a correlation between the relative Rf values of each compound and their relative affinities to the mobile and stationary phases.  A second part of your discussion should include the theory behind recrystallization. 

 

 

 

Marking plates for Thin Layer Chromatography

 

 

 

Rf = distance traveled by substance / distance traveled by solvent front.

 

Note: avoid spotting compounds too close to the edge of the plate.  Be sure that the spots are above the level of the eluting solvent in the chamber. 

 

 

Questions

            1)  In previous years, the waste bottle from this lab developed a large mass of long orange needles.  What does this tell us about our procedure? (be specific)  How could we fix this problem?

 

2)  A student ran out of bromodinitrobenzene and substituted chlorodinitrobenzene in the reaction and found that the reaction with the chlorodinitrobenzene went faster.  Explain. 

 

3)  After developing a TLC plate, a student observed that the plate had dark spots running from the origin to the solvent front.  What did the student do wrong?

 


Experiment 3

 

Simple vs. Fractional Distillation of a Methanol / Water Mixture. 

 

Read pp. 62-72; 75-80, 305

 

In this experiment you will perform both a simple and a fractional distillation on a mixture of methanol and water and compare the two techniques. While the goal of most distillations is to separate a mixture of volatile substances by collecting them in separate containers, the goal of these particular distillations is to compare the mole fractions of the distillate as a function of volume collected for the two techniques.  We will do this by monitoring the temperature of the distillate and using the vapor diagram to relate temperature to composition. 

 

You will work with a partner, one will perform the distillation and the other will record the data.  You will trade duties for the second distillation. 

 

Prepare a 0.5 mole fraction methanol/water mixture by combining 40 ml methanol with 18 ml water.  You will use this mixture for both distillations.  After the first distillation, make the necessary modifications in the glassware setup and pour the distillate back into the boiling flask.

 

Simple Distillation

Set up a simple distillation apparatus as shown on page 66 with a flame used as the source of heat as shown on page 375.  Collect the distillate in a graduated cylinder.  When carrying out your distillation, record the volume collected and temperature every 3-4 ml. The entire bulb of the thermometer must be in contact with the vapors when taking a reading of the thermometer or the value will not be accurate; only take a reading when liquid is being collected.  Note whether or not any mixing lines are observed as the distillate is being collected.

Plot the temperature of the distillate (y-axis) vs. the volume collected (x-axis). Be sure to label the axis and give your graph a meaningful title.  For each recorded temperature, use the boiling point diagram p.73 to estimate the mole fraction of methanol in the mixture being collected at each point.  Plot the mole fraction of methanol vs. the amount collected.  How do the two graphs compare?  Is it reasonable to simply use the boiling temperature of the distillate to monitor how well the components have been separated?

 

Fractional distillation

For this experiment, we will modify a fractional distillation apparatus in order to help us understand the role of the fractionating column. (All future distillations will use the standard glassware set-up.) We will use two thermometers, one below the fractionating column and the other in the standard place above the column in the still head (connecting adapter).  This will allow us to monitor the difference in vapor composition in the two regions of the apparatus.  The lower thermometer will be placed in the straight neck of a Claisen adaptor and adjusted so that the bulb is just above the boiling liquid.  The fractionating column will be placed on the other neck of the Claisen adaptor.  When carrying out your distillation, record the volume collected and temperature of both thermometers every 3-4 ml. Note whether or not any mixing lines are observed as the distillate is being collected. Continue the distillation until at least 45 ml distillate has been collected being sure to stop before the pot runs dry.  Plot the temperature of the distillate (upper thermometer) vs. the volume collected.  Do the same for the temperature of the vapor in the distillation pot (lower thermometer). 

 

Helpful hints:  1) Do not use plastic clips or rubber coated clamps on any parts of the distillation which will be heated with a flame.  2) Be sure that all ground glass joints are clean and properly fitted or the vapors may escape and may catch fire.  3) Don’t forget boiling stones. 4) Never distill to dryness. 

 

Report

            Discuss the theory of distillation using your results as an example.  Plot your graphs side by side for easy comparison.  Explain the significance of your graphs, the temperature differences between the two thermometers, and any other observations you made.        

 

Questions:  see questions in the text on p.79

Experiment 4

Separation of malachite green and phenolphthalein by acid base extraction

 

Read pp. 92-109

 

 

 

 

 

In this experiment you will be given a mixture of the indicator dyes malachite green and phenolphthalein.  We will take advantage of their acid/base properties to separate the mixture.  Phenolphthalein is commonly used in acid/base titrations and has the pink color in basic solution familiar to many chemistry students.  The compound is also a cathartic and was once the active ingredient in “Ex-Lax” brand laxative.  Malachite green in its solid form has a color similar to the mineral known as malachite, CuCO3.Cu(OH)2.  In strongly basic solutions a hydroxide ion adds to malachite green giving a colorless (neutral) carbinol form.  Malachite green is used to dye silk, wool, leather, jute, and can also be used on cotton if a mordant is used.  It has been used as a biological stain and as a fungicide and parasiticide in fish. 

 

Caution: Malachite green will stain your skin and clothing.

 

 


Separation of Malachite Green and Phenolphthalein by Acid-Base Extraction

 

 

Procedure

            Be sure to note the observed colors during the procedure and estimate the intensity of each color.  Add 0.5 g of the dye mixture (0.3 g of phenolphthalein and 0.2 g of Malachite Green) to 30 ml 3M NaOH in a separatory funnel with mixing.  Add 20 mL of diethyl ether to the separatory funnel and mix the solvents slowly and thoroughly.  Be sure to vent the separatory funnel frequently.  Drain off the aqueous layer through the stopcock and decant the ether layer into a flask.  Return the aqueous layer to the separatory funnel and wash with 2 more 20 ml portions of ether combining all three ether layers.

 

Isolation Malachite Green Oxalate

            Dissolve 0.16g oxalic acid in 10 mL of ether and add to the combined ether layers from above with.  Note any color changes.  Allow the mixture to sit at room temperature for 10 minutes and place on ice for an additional 10 minutes. (The solid forms slowly and longer times will allow more solid to form.)  Collect the product via suction filtration and wash with ether.

 

Phenolphthalein

            The aqueous layer from above should be filtered by gravity if any solid is present. Any remaining ether should be removed with a pipet.   Acidify the aqueous layer by slowly adding 6M HCl (about 15 ml total will be needed).  How will you know when the mixture is acidic?  Set the mixture aside to allow the solid to form for at least 10 minutes. Cool in an ice bath an additional 10 minutes and collect the solid by suction filtration, washing with water.   (Again the solid forms slowly and longer cooling times will result in a higher yield.) 

The solid can be purified by dissolving in 3 ml hot ethanol and slowly adding 10 ml water with heating.  Allow the mixture to slowly crystallize.  Collect the solid by suction filtration.  Obtain a melting point for your purified product.

             

Helpful hints: 1) Label all flasks containing solutions.   2) Do not throw anything away until you have the final products in hand.  3) Emulsions may sometimes be broken by gently stirring with a glass stir rod or by sitting for a few minutes.  If the emulsion is not easily broken in a few minutes just leave it in the separatory funnel and go on.   4) Save the ether that you distilled off for reuse.

 

Report

Discuss the principles of acid base extraction.  Be sure to explain your observations for each step.  Relate colors to species present and intensities to amounts of species present.

 

Questions

1) Calculate the pH of each aqueous solution in this experiment.

a.  30 ml 3M NaOH

b.  Aqueous layer after 16 ml 6M HCl was added.

 

2)  a.  A student proposed to separate this mixture by using 20 ml 3M HCl and ether in the first step instead of the NaOH.  How would this change the separation?  What would be in each layer? 

b.  Assuming that the student was successful above, what would the second step need to be to complete the separation? (hint : what pH would the student need to obtain?)


 Experiment 5

Dehydration of Cyclohexanol to Cyclohexene

 

Read pp. 376-380, 122-128

 

Use caution when handling the phosphoric acid.

 

            We will use a strong acid to dehydrate an alcohol to obtain an alkene.  Le Chatelier’s principle will be used to explain why we were able to drive the unfavorable reaction to completion.

Helpful hints: 1) Remember that it takes time to reach equilibrium so do not rush the first distillation.  2) The collection flask should be kept on ice.  3) Be sure to save at least one drop of your crude material for GC analysis.  4) Before your final distillation, be sure that your entire apparatus is clean and dry (and free from acetone residue).  5) If your final product becomes cloudy by picking up water, a small amount of drying agent can be used to dry it (be sure to remove it before turning in your product).

 

GC Analysis

            We will analyze both the crude and the distilled products by gas chromatography.  In order to save time we will do our analyses as a group (by lab benches) on mixed batches prepared by combining one drop from each student at your bench.  This will provide us with a picture of the average purity for each bench.  If time permits, individual samples may be run after that.   Prepare a 1% sample of your crude cyclohexene in diethyl ether by combining one drop from each student (6 drops total) and diluting that mixture down with 10 mL ether.  Do the same for the purified cyclohexene.  Your instructor will make the injections into the GC.  Compare the amount of cyclohexene in the sample to the amount of cyclohexanol.   The amount of ether in the sample is not a controlled amount and we will ignore the height of this peak. Note that the peak areas reported from GC run represent the amount of signal from the detector not the number of molecules detected.  (The peak ratio between the ether signal and the cyclohexene signal does not accurately reflect the mole ratio of the two.)  We are assuming that molecules like cyclohexene and the cyclohexanol are similar enough to have similar response factors. 

 

Report

Discuss the chemical principles used in this lab.  Be sure to include a mechanism for the reaction in your report.  Your discussion should comment on the purity of your product as determined by GC, the equilibrium of the reaction, and how it was brought to completion. 

 

Questions

1)  Two “distillations” were done during this lab.  What was the purpose of each?

2) Why was it critical to have the cyclohexene dry and acid free before performing the second distillation?

3) If 2-methyl cyclohexanol were dehydrated, what products would be expected?  Which one would be the major product?  What technique could be used to identify the products? Be specific.


Experiment 6

Cyclohexanone from Cyclohexanol

 

Read pp. 387-389, 87-90, 182-199. 

 

 

Caution:  Before you begin, check the actual concentration of bleach on the bottle's label and adjust your amounts accordingly.

 

Oxidations are very important reactions in organic chemistry.  While oxidations may look relatively simple to perform on paper, in the lab they may become more complicated due to the need to ensure the reaction has gone to completion and that the product is adequately isolated.  There are several interesting features to this lab.  Pay attention to the purpose of each step as you read the lab.  First, you will need to add the oxidizing agent over a period of time in order to avoid having too large of a concentration of poisonous chlorine gas at any one time.  Our goal will be to maintain a steady state concentration of our oxidant in order to avoid losing it as chlorine gas.  Also, you will need to control the reaction temperature to minimize the loss of Cl2 gas.  As the reaction proceeds, the concentration of cyclohexanol will decrease slowing the rate of the reaction while the concentration of chloride will increase, increasing the rate of formation of chlorine gas.  You will need to check the reaction mixture to ensure that excess oxidizing agent is present to ensure that reaction has gone to completion.  After the reaction has been completed, the remaining oxidizing agent will have to be destroyed to avoid over-oxidizing the product. Finally, the product is insoluble in water and will be isolated by steam distillation before being purified by regular distillation. 

 

Helpful hints: 1) It may be difficult to keep the reaction temperature under 35 oC as stated in the lab text; keeping the temp under 40 oC should be sufficient.  2) The reaction flask can be cooled with a Ziploc bag filled with ice if necessary but cooling will slow the reaction.  3) After your final addition, be sure to give the reaction a few minutes to come to completion before testing for excess chlorine.  4) It is much easier to purify your product if the reaction has gone to completion.

 

Obtain an IR spectrum of your product.  Comment on the purity of your product based on its IR spectrum and its boiling range.  Be sure to include a mechanism for the reaction.  Discuss the chemical principles used in this lab including the importance of each step in the procedure in obtaining the maximum amount of product. 

 

Questions

See question 1 and 2 p.389. 

 

3) After you isolate the product, why is it necessary to neutralize the remaining acetic acid with base?  Be specific. 


Experiment 7

Preparation of Isoamyl Acetate

 

Read pp. 417-426

            Esters are an important functional group, particularly for their flavor and fragrance properties.  In this lab isoamyl acetate, a component of banana oil (as well as an alarm pheromone of the honey bee) will be prepared by two methods.  One, is an acid catalyzed Fischer esterification, and the other, is an SN2 substitution in a polar aprotic solvent. 

 

            You will work in pairs for this lab.  One person will carry out the esterification by the Fischer method (procedure 58.1) while the other person will carry out the nucleophilic substitution (procedure 58.2).  Pay attention to any color changes or precipitate formation in these reactions.  Be sure to obtain an IR spectrum of your purified product in order to determine its purity. 

 

Report

Discuss the chemical principles used in this lab.   Propose what the most likely impurities are in the sample based on your IR spectrum. In your discussion compare the two methods used to prepare the ester.

 

 

 

Questions

1) Consider equilibrium (which depends on the likelihood that the reverse reactions will occur).  Is one esterification method more likely to bring the reaction to completion than the other?  Explain.

 

2) Given that NaBr is much more soluble (>5X) in DMF than KBr explain why potassium was a good choice for a counter ion in this reaction.  How ill it affect the yield?

 

3) A company wished to produce isopentenyl acetate, (3-methyl-2-pentenyl acetate), the flavor known as “juicy fruit”. What would be the starting materials in each reaction and what would be the likely products?  Which esterification method would be better suited to produce the desired product? (Hint: consider possible side reactions) Explain.

 


Experiment 8

Identification of two unknown functional groups 

Identification of an unknown substance

Read pp. 169-181, 239-272, appendix

 

In this lab, you will use solubility and chemical reactivity to determine the identity of two unknown functional groups and report your results orally to your instructor.   After you have identified the unknown functional groups, you will determine the functional group and chemical identity of a third substance based on its reactivity and physical properties.  You will be given three vials containing unknown substances.  These are the only amounts that you will receive so guard them carefully.  Be sure to protect them from spills and losses due to evaporation. You will also want to make sure that you do not squander your unknowns by using too much for any test or by running unnecessary tests.

 

Solubility

            The solubility of a compound is an excellent way to rapidly narrow down the number of possible functional groups that it might contain.  Using Section 23 of your book as a guide, test the solubility of several known compounds as well as each of your unknowns.  Combine a few mg of the compound (one drop of liquid) with a 3-5 mL solvent and note whether or not the compound dissolved.   Remember not to use too much compound as you may saturate the solution or waste your unknown; but you do need enough to be able to see it in the test tube.  Check the solubility of the compound in water.  If the compound is soluble in water check the pH of the aqueous solution.  If the compound is insoluble in water, check the solubility of your compound in 5% HCl, and 5% NaOH.   Remember that the term soluble means that the solute and solvent form a single phase; a single phase solution may be colored but must not be cloudy or contain any precipitate or oily droplets.  Sometimes a compound is soluble but may go into solution slowly.  Be sure that you allow enough time for each to go into solution.   The flow chart below will help you make sense of your results.  Keep in mind that this chart is limited to the functional groups that we will be testing in this lab. 

 

Classification tests

            Chemical classification tests take advantage of the fact that different compounds that contain the same functional group have similar reactivity.  You will compare the reactivity of your unknown functional groups with compounds that have known functional groups.  The key to success here is to always run a blank and a control and to carefully record your observations.  Also, as with any test, the results should not be trusted if they are not reproducible.  Be sure to repeat your tests if there is any ambiguity. 

            Run a blank – run each test side by side with a compound that will give a negative result.

            Run a control – run each test side by side with a compound that will give a positive test.  By always having a positive and a negative test alongside an unknown, the interpretation of the results will be more straightforward. 

            Carefully record your observations .  When conflicting data is obtained, you must decide what evidence should carry more weight.  This is easier to do when you have observations rather than just your interpretation.  For example, it is more helpful, and more correct to report that the Tollens test produced a gray precipitate on heating for 15 minutes than to write down that the Tollens test was positive.  Simply writing a ‘+’ sign in your notebook may be misleading.

            Before attempting any classification tests on your unknowns, practice each test on known compounds to get a sense of what positive and negative tests look like.  Results will inevitably vary each time the tests are run.  Your observations may be different from those reported in the book.  Pay attention.

 

 

The recommended functional group tests are summarized below not necessarily in the order that they should be run.

 

Helpful hints: 1) Run a control and a blank side by side for each of the tests.  These will help you interpret your results.  2) If a result from a classification test is ambiguous, it is usually quicker to repeat the test than to try to interpret poor data. 

 

Acetyl chloride test for alcohols and amines (do this in the hood)

Cautiously add 3-5 drops of acetyl chloride to a dry test tube containing a few mg unknown.  Evolution of heat and/or HCl gas indicates a positive test.  It may difficult to determine the production of a small amount of heat with a small amount of reactant. If your unknown is less reactive it may a slightly larger amount of unknown to determine if a reaction has occurred.  Amines and alcohols give positive tests but with noticeable differences.  When the reaction mixture is carefully diluted with water, a precipitate may form.  Alcohols often give a solid acyl ester and 1o and 2o amines often give a solid acetaminde derivative; 3o amines do not. 

 

Test

 

Reference

Controls

Hinsberg (Be sure to consult your instructor before attempting this test)

 

29.2

Amines; 1o, 2o, 3o, (be sure to test an aromatic amine as well)

2,4-dinitrophenyhydrazine

 

29.5

Aldehydes and ketones

Chromic anhydride  (run on alcohols and aldehydes/ ketones)

 

29.4

Alcohols; (1o, 2o, 3o),

aldehydes

Acetyl chloride

 

Procedure above

Alcohols and amines

 

 

Amines

If solubility indicates that the unknown is an amine:

            Confirm the presence of an amine by running the acetyl chloride test.

            If an amine is present, run the Hinsberg test to distinguish 1o, 2o, and 3o.  

                        1o amines will be soluble after step 1 and insoluble after step 2 of Hinsberg.

                        2o amines will be insoluble after both steps 1 and 2 of Hinsberg.

                        3o amine will not react and observations will reflect the solubility behavior of the amine. 

 

Aldehydes, Ketones and Alcohols

If solubility indicates that the unknown is an alcohol, aldehyde or ketone:

Test for the presence of an alcohol using acetyl chloride.

If and alcohol is indicated, run chromic anhydride test to distinguish 1o and 2o, from 3o

            1o and 2o alcohols will react quickly

3o alcohols give no visible reaction.

            If alcohol is not present run the 2,4-dinitrophenyl hydrazine test (+ for aldehydes and ketones).

            If and aldehyde or ketone is present, run chromic anhydride test (+ for aldehydes)

 

Carboxylic Acids

We will not use a positive test to confirm the presence of a carboxylic acid.

 

Functional Group Oral Reports. 

            After you have completed your solubility and chemical classification tests on your two functional group unknowns, you will report your results orally to your instructor.  These reports will graded on a 10 point scale (3 points for being correct, 3 points for organization, and 4 points for logic).  For your report, you may only use your notebook as a reference.  Start by giving the unknown number and describing its physical characteristics.  Give the results of the solubility tests and your conclusions based on solubility.  State the results of any functional group tests you performed and conclude with the identity of your unknown functional group. 

 

 

Identification of an unknown structure

            For your unknown compound you will follow the same procedure that you used to identify the unknown functional groups.  After that you will use additional information to determine the identity of the compound based on a comparison of its properties with those of compounds reported in the literature.  

 

Determine the physical characteristics.

            There are clues to the compound’s identity in its physical characteristics.  Is it a solid or a liquid?  Does it have a distinct color?  Does it have a characteristic odor? 

 

Determine a melting or boiling point range

            If your unknown is a liquid determine its boiling point by placing a small amount it in a Pyrex test tube with a thermometer suspended a few centimeters above the liquid level.    Using a flame and a wire screen gently heat the tube until the reflux ring completely covers the bulb of the thermometer.  Be sure not to heat the sides of the test tube above the liquid or you will superheat your vapor. 

 

Choose a derivative

            With the information obtained above, you should be able to go to the appropriate table and make a short list of possible compounds.  For example, if you have an ester with a boiling range of 190-194 oC you could go to the table of esters and choose esters that have a boiling point within a 5 -10 o range of the observed value.  Remember that your value is a measured quantity and will have some error associated with it.  In the table, there are three esters which fall into that range: heptyl acetate, phenyl acetate and methyl benzoate.  Since you cannot distinguish between these based on your boiling point, you will need to consider a derivative.  Note that of the three possible derivatives, the DNB derivative is the best choice because the three possible compounds have drastically different melting points with this derivative.  The NBz derivative for two of the compounds has the same melting point and it will not be helpful in distinguishing between the two.   The Acid derivative is not even listed for two of the possible compounds so it is also not helpful in this case.  

            Due to time constraints, you will not actually prepare these derivatives but you will obtain the information from the instructor.  After you have decided what derivative would be most useful in helping you identify your unknown substance, fill out the preliminary report form and turn it in to your instructor.  It will be returned to you with experimental data consistent with your compound.  Based on all of the available information, you will determine the identity of your compound. 

 

Write up:

            Your report should include the unknown number and the identity of the unknown. Attach your preliminary report form and explain more fully what can be concluded from your observations.  Be sure to include the list of candidate compounds and explain how you made your final determination. 

 

 

 Leave the remainder of your unknown out on the bench-top so that we can double-check it. 


Experiment 9

Preparation of Tetraphenylcyclopentadienone

 Read pp. 595-597

 

This lab utilizes a pair of aldol condensations between dibenzylketone and benzil to produce tetraphenylcyclopentadienone.  The product is unique for two reasons.  First, the product is a deep purple color.  It is quite unusual for a compound with such a short conjugation length to be so highly colored.  Due to sterics, the phenyl groups are not in the same plane as the cyclopentadienone ring and are not fully conjugated with it.   While cyclopentadienone is quite reactive with itself toward Diels Alder reactions and it cannot be isolated on its own, the bulky phenyl groups in the tetraphenylcyclopentadienone protect the molecule from reacting with itself. 

This reaction is catalyzed by base.  The base used in this reaction will be trimethylbenzylammonium hydroxide because it has a higher solubility in our solvent than sodium hydroxide. 

Prepare the compound on ½ scale as described in the text noting all color changes observed during the procedure.   Explain these observations in your discussion.   Also, be sure to include a complete mechanism for the reaction.  (Since two identical aldol reactions occur, you only need to show one complete reaction.)

 

TLC

We will use thin layer chromatography as an indicator of the purity of our product.  Dissolve a small amount of your product in dichloromethane and spot it on a TCL plate along with each of the two starting materials.  Elute the plate with toluene.  Determine if either of the starting materials is present in the product.

 

Solid phase IR

Obtain an IR spectrum of your dried product by grinding ~5 mg compound with 50 mg KBr with a mortar and pestle into a fine powder.  Fill the sample compartment of the specular reflectance attachment, level it smooth, and insert the sample holder into the chamber. 

 

Questions

1)  What did you observe that would support the idea that the trimethylbenzylammonium hydroxide is a catalyst in this reaction?  Explain

2)  How does your mechanism suggest that the hydroxide is a catalyst? (Start with the definition of a catalyst)

3)  What is the driving force for the removal of the water in this reaction?

 


Experiment 10

Preparation of a Photochromic Compound

 

 

Read pp. 564-566

 

 

Caution: nitric and sulfuric acid can cause severe burns.  Handle with care.

 

            Follow the procedure in the book but increase the amount of nitric acid to at least 2.0 mL as two equivalents of the nitronium ion are needed for the complete conversion. 

 

Helpful hints:  1) Calculate out the number of moles of all reactants and be sure that there is a slight excess of nitric acid.  2) It may be easier to do the extraction in several smaller batches rather than one large batch.  3) When distilling off the ether, reduce its volume to 25 ml not 50 ml as it says in the book. 

 

The source of the photochromism in this compound has been the topic of debate.  An alternate structure for the purple isomer has also been proposed and is shown below. 

 

 

 

Write up:  Discuss the chemical principles used in this lab.

 

Questions

1) Explain the regioselectivity of the nitration.  Why was only the one ring nitrated and why were those two positions nitrated?

 

2) After the nitration, why was it necessary to add the base? What would have happened in the end if we didn’t add the base?


Experiment 11

Preparation of Malachite Green and Crystal Violet

 

Reference: Tabor, D.F., Meagley, R.P, Supplee, D.; J. Chem. Ed. 1996, 73, 259.

 

 

 

Caution:    Malachite Green and Crystal Violet are biological stains and will readily stain skin and clothing.   Be sure dyed clothing is washed (separate from other clothing) before wearing. 

 

 

Helpful hints:  1) If the Grignard reaction does not appear to be proceeding, consult your instructor. 2) Before heating, be sure that the ground glass joint in your reflux apparatus is clean or it may lock up. 

 

Procedure

  A dry, 125 mL erlenmeyer flask with ground glass joint is rinsed with 5 mL dry THF.  A magnetic stir bar, magnesium turnings (0.40 g), dry THF (20 mL), 4-bromo-N,N-dimethyl aniline (2.5 g) are added to the flask.  A glass stirring rod is used to gently crush several of the magnesium turnings to expose a fresh surface.  The flask is equipped with a reflux condenser and heated to gentle reflux for 30 minutes on a stirring hot plate (low setting).  During heating, the magnesium should be partially consumed and the color should change to a  cloudy “dishwater” gray.  After cooling to room temperature, methyl benzoate (0.42g) or dimethyl carbonate (0.24g) is added in one portion.  The mixture is returned to reflux for an additional 5 minutes.  After cooling to room temperature, HCl (8 mL, 10%) is slowly added. 

 

Dying

 A sample of cotton fabric is placed in the solution and soaked for several minutes.  After removing the sample, the cloth is thoroughly rinsed in cold running water.  Be sure that the cloth is thoroughly rinsed before touching it with your bare hands.  You are free to use the remaining dye to experiment with dying your own samples.  When you are finished, pour the extra dye mixtures into the waste container in the hood. 

 

Note:  you will not isolate your product from this experiment but you should still calculate a theoretical yield.  This will give you an idea about the amount of coverage you get from your dye.

 

 

Report:  Discuss the chemical principles used in this lab. 

 

 

Questions

1) When producing the dye, explain why the color of the dye does not appear until addition of the acid in the final step. 

 


Experiment 12

Choose your own experiment

 

You will plan and carry out a lab experiment of your own choosing.  You may choose an experiment from the list below or, with the instructor's approval, from another source.  You will be responsible for checking to make sure that the necessary reagents and glassware are available.  You will also be responsible for making sure that all safety precautions are followed. 

 

Proposal

You will write a short proposal for the experiment that you will carry out.  Be sure to include the following:  an informative title, an introduction telling why you are doing what you are proposing (why is this interesting?), a procedure with reference and any proposed modifications, a description of the chemistry, and balanced equations.  Some of the procedures can take a long time.  Be sure to make arrangements to start any long procedures in advance.  On a separate sheet of paper provide a list of materials you will need, and any special equipment or needs. 

 

 

Lab

Reference page

Preparation of Adamantane

364

N,N-DiethylToluamide ("Off")

461

Reactions of Vanillin

485

Preparation of Diazonium Dyes

498

p-Acetamidophenol ("Tylenol")

529

Coconut Aldehyde

543

Thermochromic compounds

559

Chemiluminescence : Luminol

567

Solvatochromic Dyes:  MOED

627

Liquid Crystals:  MBBA

Handout

Isolation of Cholesterol from Gallstones

327-329

Biodeisel from vegetable oil

Handout

 

 


EXPERIMENT 13

Preparation of Norbornene-2,3-dicarboxylic Anhydride

 

 

Read pp. 507, 510-514

            Your instructor will “crack” the cyclopentadiene for you but you are still responsible for understanding the chemistry involved. 

 

 Perform the Diels Alder addition as described in the text.  The expected product of the reaction is the endo product shown, which melts at 165o C.  In the literature, the product is also known as “carbic anhydride” or “nadic anhydride”. 

 

 

 

Note that it is very important to keep this reaction dry.  Be sure that the joint in your glassware is tightly sealed to prevent water from the steam bath from getting into your reaction.  Be sure to dry the outside of the joint before removing the reflux condensor. 

           

Report

Discuss the chemical principles used in this lab.

 

 

Questions:  See Questions 1-3 pp. 513-514.

 

What will happen if water gets into the reaction mixture?  Be specific.