chem 112a lab book w16 final

8/19/2019 Chem 112A Lab Book W16 Final

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Chem 112A Lab Manual Winter 2016

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Chem 112A

Organic ChemistryLaboratory Manual

UC Riverside Winter 2016


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CHEMISTRY 112A LABORATORY EXPERIMENTSWinter 2016TEXTBOOKSThe Organic Chem Lab Survival ManualZubrick, 9th edition John Wiley & Sons*NOTE: Hold onto th is boo k. It is used in112B, 112C.

Darling Model Kits (UCR Edition)Lab coatStudent Lab Notebook: 100 Spiral

LABORATORY INSTRUCTORProfessor Richard HooleyChemical Sciences 1, Room 444(951)-827-4924 email: [email protected]

ACADEMIC COORDINATORDr. Rena HayashiScience Laboratories 1, Room 103(951) 827-3143, email: [email protected]

LECTURE INSTRUCTORProfessor Ming Lee TangChemical Sciences 1, Room 138(951)-827-5964 email: [email protected]

SPECIAL LABORATORY INFORMATION(1) It is not possible to get a passing grade for the course without completing the laboratory with a

passing grade.

(2) Academic dishonesty in any form will not be tolerated in this lab. In addition to the sanctionsimposed on laboratory grades, all such incidents will be reported to the Office of Student Conductfor administrative review. Students found to be cheating will receive a zero grade for the experimentand may be subject to dismissal from the class with a failing grade. Cheating includes (but is notlimited to) turning in a report without doing the experiment, interfering with another student's work,removing chemicals or glassware from the laboratory, or providing test questions or answers to othersections. All students enrolled in this class are also responsible for familiarizing themselves with theStudent Code of Conduct. The general rules and student rights in that document apply to this lab.

(3) Attendance at your assigned laboratory meetings is mandatory. If you miss a laboratory you will notbe able to make-up that laboratory. For one absence only, with a verifiable medical excuse acceptedby Dr. Hayashi, your laboratory score will be pro-rated. You must contact Dr. Hayashi by telephone[(951) 827-3143] immediately upon learning you will miss a lab, leave a phone number where youcan be reached, and provide a medical excuse (signed by a licensed medical doctor (M.D.)) to Dr.Hayashi as soon as you return to campus. Your TA may not alter this policy.

(4) Lab Preparation Write-ups (Pre-Labs) are due at the beginning of the lab period in which theexperiment is to be done.

(5) Laboratory Reports are due at the beginning of the lab period following completion of theexperiment.

(6) Enrollment questions concerning laboratory or lecture must be directed to Dr. Hayashi.

(7) Note on laboratory fees : Your laboratory fee will be paying for chemicals, glassware, hotplates,and other allowable teaching items and apparatus.

(8) Cellular Phones : For safety reasons cellular phones may not be operated in the laboratory. Makecertain that your phone is in the off position before entering.

(9) Important : Be sure to record key information about this lab, including TA name, lab room, lockernumber, and combination, in a place that is secure and will be accessible to you during lab.


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Fire and Emergency

a) Make sure to know the locations of safety showers, eyewash fountains, fire extinguishers,emergency telephones, fire alarms and all exits. These are clearly marked in the laboratory.

b) FIRE: Immediately notify the supervising TA. A fire confined to a small flask or container canusually be extinguished by covering the flask with a large nonflammable container (e.g. beaker).Only attempt this is the fire can be easily contained: otherwise pull the fire alarm and exit thebuilding. Go to the designated assembly area and do not use the elevator.

If a person's clothing is on fire, use the safety shower to put out the flames. If this is not possible,douse the person with water, cover them with a fire resistant coat and roll the person on the floor.

c) INJURY: Immediately report ANY injury to a TA, no matter how minor. The TA will initiateemergency procedures and arrange transportation to a medical facility.

If you are a member of the Campus Student Health Plan, then during normal business hours goto the Campus Health Center (for current business hours go to www.campushealth.ucr.edu).

After hours until 9 pm: go to Riverside Medical Clinic Urgent Care.

All other times: Riverside Community Hospital.

If you are NOT a member of the Campus Student Health Plan, then during normal business hoursgo to the Campus Health Center and inform them that you are not on the health plan but wereinjured while on campus. At all other times, obtain medical treatment through your personal healthinsurance coverage (i.e. HMO, PPO).

d) CHEMICAL SPILL: Chemical contact with eyes and skin must be washed immediately withwater for at least 15 minutes (use the eye wash/safety shower). Remove contaminated clothingand immediately report the incident to a TA.

Other Laboratory Rules

Do not put lab chemicals in your drawer, unless specifically instructed to do so by your TA. NO ignition sources (matches, lighters, etc) are allowed in the laboratory. There is absolutely no smoking allowed anywhere at any time in the Sciences Laboratories

building. Do not pour chemicals into the sink or dispose into the trash: use the proper waste containers. Dispose of chemical waste in the specified containers - some chemicals are dangerous if mixed. Do not use unlabeled chemicals, and if you find any, report this to your TA Do not drink from lab faucets or use the ice from lab ice machines to chill food. The water may

not be safe to drink. NEVER mix chemical reagents unless instructed to do so by your TA as part of your lab

procedure. NEVER taste or smell chemicals.


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Schedule of Experiments - Chem 112A (Winter 2016)

Dates Experiment

01/05-01/08 Labo ratory Safety & Check-in . You MUST make sure that you have all of the necessarylab equipment and glassware in your assigned drawer before you leave. Read Zubrick, pp1-37, 77-79 (clean and dry). Read p3-4 of this handout on lab safety.

01/12-01/15 Experim ent 1: Molecular Model Exercises (30 pts). Lab Handout p9-11. Read Klein 2ndEd. pp 52-67, 158-172. Bring your molecular models to lab.

01/19-01/22 Experim ent 2: Techniq ues Lab 1 - Separat ion and Purif icat ion s (30 pts). Lab Handoutp12-15. Read Zubrick, pp 87-92 (melting point), 141-144 (liquid-liquid extraction).

01/26-01/29 Experim ent 3: Techniqu es Lab 2 - Separation and Chro matog raphy (30 pts). LabHandout p16-19. Read Zubrick, pp 234-241 (column chromatography) .

02/02-02/05 Experim ent 4: Techniq ues Lab 3 - Dist i l la t ion (30 pts). Simple Distillative Separation ofgasoline additives, Lab Handout p20-22. Read Zubrick pp 164-189 (distillation).

02/09-02/12 Experim ent 5: Isolat ion and Character izat ion of Limo nene from Citru s Peel (30 pts).Lab Handout p23-25. Read Zubrick, pp 164-189 (distillation), 242-247 (refractometer).You will need to get a distillation head from the front table (return it clean at the end of thelab period). Failure to return that piece of glassware as directed will affect your grade.Make sure to br ing a fresh c i t rus p eel to lab!

02/16-02/19 Exper iment 6 : Brom ina t ion of t rans -s t i lbene (30 pts). Lab Handout p31-32. ReadZubrick, pp 120-126 (recrystallization), Klein 2nd Ed. p435-437 (olefin halogenation).Exp. 6 Case Study Reports due.

02/23-02/26 Experiment 7: Dehydrobromina t ion of meso-St i lbene Dibromide (30 pts). LabHandout p28-30, read Klein 2nd Ed. Ch 8.

03/01-03/04 Exper iment 8 : Nucleophi l i c Subs t i tu t ion Reac t ions – React ivi ty of Alky l Hal ides (30pts). Lab Handout p33-35. Read Klein 2nd Ed. Ch. 7.

03/08-03/11 Check-Out ---Exp. 8 Reports due.

Laboratory is worth a total of 240 points.


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Sunday Monday Tuesday Wednesday Thursday Friday Saturday

01/04 01/05 01/06 01/07 01/08 01/09

No Lab Lab Safety &Check-in.

01/10 01/11 01/12 01/13 01/14 01/15 01/16No Lab Exp. 1:

MolecularModeling

01/17 1/18 01/19 01/20 01/21 01/22 01/23AcademicHoliday

Exp. 2: Techniques 1:

01/24 01/25 01/26 01/27 01/28 01/29 01/30No Lab Exp. 3:

Techniques 2

01/31 02/01 02/02 02/03 02/04 02/05 02/06No Lab Exp.4:

Techniques 3

02/07 02/08No Lab

02/09Exp. 5: LimoneneDistillation

02/10

02/11

02/12

02/13

02/14 02/15

AcademicHoliday

02/16Exp.6:Bromination ofStilbene

02/17

02/18

02/19

02/20

02/21 02/22No Lab

02/23Exp.7: Dehydro-bromination

02/24

02/25

02/26

02/27

02/28 02/29No Lab

03/01Exp. 8:

NucleophilicSubstitutions

03/02

03/03

03/04

03/05

03/06 03/07No Lab

03/08Check-outReports due

03/09

03/10

03/11

03/12


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FORMAT FOR LABORATORY NOTEBOOK REPORTS (Read Zubrick p11-26)

Keeping an accurate laboratory notebook is essential to your success in this class. Some guidelines aregiven below:a) The laboratory notebook must not be loose leaf or spiral bound. Lab notebooks are available from the

campus bookstore and are designed so that they permanantly contain the original pages of your Prelab

and Postlab reports.b) Use permanent blue or black ink only (ballpoint pen, NO red ink!).c) Other textbooks, lab manuals, loose sheets of paper, iPads or cellphones are not allowed in the

laboratory. The complete outline of procedures must be written in your laboratory notebook prior toperforming the experiment.

d) Copies of your lab notebook pages are required for grading. The assigned notebooks are designedso that the carbon copies can be removed and handed in to your TA.

e) Your TA may periodically inspect your notebook. YOUR LAB REPORT CONSISTS OF THREE (3) PARTS

Part I - Prelab Report. A copy of your lab notebook pages containing the lab writeup and answers to anyprelab questions. This is due at the star t of each experiment.

Part II - Results. A copy of your notebook pages containing observations noted during the labexperiment.

Part III - Postlab Report. A summary of results and answers to postlab questions. This can be writtenon separate loose-leaf paper.

I. PRELAB REPORT (40% of the report grade)

There wi l l be two types o f p re lab repor t in th i s quarter’s laboratory. Experiments 2 -4 wil l emplo ya “flipped” lab, whereby the bulk of the prelab requirements will be to watch a video on techniquesin org anic chem istry and answ er pre-lab quest ion s. Experim ents 5, 6 , 7 and 8 follow the “classic”prelab form at that wil l cont inue in Chem 112B and 112C. Note that Expt 1 is a dry lab, with n oprelab requirement .

PRELAB REPORT (Expts 2-4)

The pre-lab activities for Expts 2-4 consist of viewing the Technique Video (posted on iLearn), and writinga pre-lab report that consists of answering questions from the video and writing a procedure for theupcoming experiment.

We will record whether you viewed the video before the lab – completing the viewing is worth 2 pts inyour lab report.

The initial part of your lab report must be written in your laboratory notebook. A copy of the original pagesof this report will be collected prior to the experiment and will be returned to you after the whole lab isgraded. It will consist of:

a) Your name, lab section and the name of your TA (on each page).b) The title and number of the experiment.c) Outline of procedure. This must be sufficiently detailed to allow you to perform the experiment. Makesure you note any necessary safety precautions.d) Prelab question answers. These will always require an analysis of the hazards and risks associatedwith the experiment.The copy pages of this report must be handed in BEFORE you begin the experiment.


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PRELAB REPORT (Expts 5-8)

The initial part of your lab report must be written in your laboratory notebook. A copy of the original pagesof this report will be collected prior to the experiment and will be returned to you after the whole lab isgraded. It will consist of:a) Your name, lab section and the name of your TA (on each page).

b) The title and number of the experiment.c) Objectives. This should include hypotheses about the outcome of the lab, which you will test byexperiment. I t i s your respons ib i l i ty to p ropose what you expec t to de te rmine f rom eachexper iment . d) List of chemicals: masses or volumes. Look up molecular masses and calculate the material amountin moles (if appropriate), boiling/melting points (bp/mp) and density (if appropriate).e) List of equipment (sketch complex apparatus).f) Outline of procedure. This must be sufficiently detailed to allow you to perform the experiment. Makesure you note any necessary safety precautions.g) Prelab question answers. These will always require an analysis of the hazards and risks associatedwith the experiment.The copy pages of this report must be handed in BEFORE you begin the experiment.

II. RESULTS (10% of the report grade)

This section should be started on a fresh page of your notebook, after the prelab report. A combined copyof the Results/Postlab report will be stapled and turned in to your TA after the experiment is complete.This section should be completed d u r i n g the lab session and consists of:a) Your name, lab section and the name of your TA (on each page).b) The title and number of the experiment.c) Results: Date, times, measured masses and volumes used in the experiment (if you use differentamounts from the procedure, note this), measured mp/bp of your products and any other observations(color changes, etc) recorded during the lab session.d) Characterization materials: include copies of spectra, etc., recorded during the lab session.

Turn in your product(s) from the experiment in a suitably labeled vial to your TA at the end of thelab session.

III. POSTLAB REPORT (50% of the report grade)

This section does not need to be written in your lab notebook - it can be written on separate loose leafsheets and stapled to your results copy pages. It is to be completed after the lab period at home, andconsists of:a) Your name, lab section and the name of your TA (on each page).b) The title and number of the experiment.

c) Analysis of results: In 5-10 sentences, comment on the outcome of your experiment, notably the qualityof your results. Describe problems that may have occurred and possible solutions. How and why did theoutcome differ from that predicted in your prelab report? What was learned from the experiment?d) Answers to postlab questions.Staple Parts II and III together and turn into your TA at the beginning of the next week's labsession. You should keep a copy of Part III for yourself.


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Experiment 1 - Molecular Modeling Exercises

Reading: Klein 2 nd Ed pp 52-67, 158-172.

You will perform each exercise using your Darling molecular model kit. Learning how to effectivelymanipulate molecular models will help you considerably in the visualization of the shapes of organicmolecules in three dimensions.

There will be no prelab report to turn in for this experiment. For a postlab report, write answers to eachquestion in your notebook and turn in at the end of the exercise.

Exercise No. 1:

1.1 Assemble two molecular models of methane, CH 4. Draw a representation of the methane moleculeyou just built using solid ( ), wedged ( ), and dashed ( ) lines. The solid lines represent bondsin the plane of the paper, wedged lines represents a bond coming out of the plane, and the dashed linerepresents a bond going back behind the plane of the paper.

1.2 What configuration does the carbon center have?

1.3 Replace any one hydrogen atom in each of the two methane models with a halogen atom (green) toform two molecules of CH 3X.

a) Are the two structures identical?b) Does it make a difference which of the four hydrogen atoms on a methane molecule you replace?

1.4 Replace two hydrogen atoms in each of the two methane models with two identical halogens to formtwo molecules of CH 2X2.

a) Are the two structures identical?

b) Does it make a difference which two of the four hydrogen atoms on a methane molecule youreplace?

1.5 Repeat 1.4 with two different halogens to form two molecules of CH 2XY. Use two different coloredatoms for this.

a) Are the two structures identical?

b) Does it make a difference which two of the four hydrogen atoms on a methane molecule youreplace?

1.6 Construct two identical models of a trisubstituted methane molecule, CHXYZ, using four differentcolored atoms attached to a central tetrahedral carbon atom. Compare these models.

a) Are the two structures superimposable?b) Interchange any two substituents on one of the carbon atoms on one of the models. Are the two

CHXYZ molecules superimposable now?c) Compare the two models that were not superimposable. What is the relationship between them?

Exercise No. 2:

2.1 Make a model of ethane, CH 3CH 3.

a) Does each of the carbon atoms retain a tetrahedral configuration?


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b) Can the carbon atoms be rotated with respect to each other without breaking the carbon-carbonbond?

c) Hold the model such that you are looking at one carbon and the other carbon is directly behind it.This is the perspective of a Newman projection. Rotate about the carbon-carbon bond until thecarbon-hydrogen bonds of one carbon atom are aligned with those of the other carbon atom. Thisis called the eclipsed conformation. Draw the Newman projection of the eclipsed conformation.

d) Rotate the carbon-carbon-bond until the C-H bond of one carbon atom bisects the H-C-H angleof the other carbon atom. This conformation is called staggered . Draw the Newman projection ofthe staggered conformation.

e) In which of these two conformations of ethane are the hydrogen atoms of one carbon closest tothose of the other carbon?

2.2 Replace any one hydrogen on the ethane model with a substituent such as a halogen to form amodel of CH 3CH 2X.

a) How many staggered conformations are possible?b) How many eclipsed conformations are possible?

2.3 Prepare a second model of CH 3CH 2X.

a) Are the structures identical?b) If not, can they be made identical by rotation about the C-C bond?

2.4 Assemble a model of a 1,2-disubstituted ethane molecule, CH 2XCH 2X. Note how the orientation andthe distance between the X groups changes with rotation of the carbon-carbon bond.

a) How many eclipsed conformations are possible?b) Draw the Newman projection of the eclipsed conformation where the two halogen atoms are

closest to each other.c) The arrangement in which the X substituents are at maximum separation is called the anti

conformation. How many anti conformations are possible?d) The other staggered conformations are called gauche conformations. How many gauche

conformations are possible?e) Are all gauche conformations identical?

Exercise No. 3:

Build a model of 2-butene, CH 3CHCHCH 3.

a) How many different structures are there? Draw the structures.b) Are those structures identical?c) Compare the two structures that are not identical, is it possible to rotate the bond between C2-C3

to make them identical?

Exercise No. 4:

4.1 Build a model of cyclopentane, C 5H10 . Cyclopentane is a more flexible ring system than cyclobutaneor cyclopropane. A model of cyclopentane in a conformation with all the ring carbon atoms coplanarexhibits minimal deviation of the C-C-C bond angles from the normal tetrahedral bond angle.


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a) How many eclipsing interactions are there in this planar conformation?b) If one of the ring carbon atoms is pushed slightly above (or below) the plane of the other carbon

atoms a model of the envelope conformation is obtained. Does the envelope conformationrelieve some of the eclipsing interactions?

Exercise No. 5:5.1 Assemble the six-membered ring compound cyclohexane, C 6H12 . Rotate about the carbon-carbonbonds of the ring to show a chair conformation. In the chair conformation carbon atoms 2, 3, 5, and 6 arein the same plane and carbon atoms 1 and 4 are above and below the plane, respectively.

a) Draw a chair conformation in Newman projection.

b) Are the hydrogen atoms in the chair conformation staggered or eclipsed?c) How many eclipsing interactions are there?d) Do carbon atoms 1 and 4 have an anti or a gauche relationship? (Hint: Look down the C-2, C-

3 bond).

5.2 From the chair conformation, rotate about the carbon-carbon bonds of the ring to form a boatconformation. In the boat conformation carbon atoms 1 and 4 are both above (they could also both bebelow) the plane described by carbon atoms 2, 3, 5 and 6.

a) Are the hydrogen atoms in the boat conformation staggered or eclipsed?b) How many eclipsing interactions are there?c) Do carbon atoms 1 and 4 have an anti or a gauche relationship?

5.3 A twist-boat conformation of cyclohexane may be obtained by slightly twisting carbon atoms 2 and 5of the boat conformation. Note that the C-2, C-3 and the C-5, C-6 bonds no longer retain their parallelorientation in the twist conformation. If the ring system is twisted too far, another boat conformationresults.

a) Compare the number of eclipsing interactions present in the boat, twist and chair conformationsof cyclohexane. Predict the relative order of thermodynamic stabilities between chair, twist, andboat conformation.


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Experiment 2 - Techniques Lab 1: Extraction of Solids

Reading: The Organic Chem Lab Surv ival Manual : pp. 104-119, 128-140, 196-199, 223-234.

IntroductionIn this experiment, you will be separating a mixture of three different chemicals: acetaminophen, aspirin,

and caffeine. You will also be purifying each individual chemical. These chemicals can be found togetherin many over-the-counter headache medicines. To perform this experiment, you will also learn thetechniques of solution-phase extraction and how to use a rotary evaporator.

The three components of the mixture have different properties - caffeine is an organic base, aspirin is anacid, and acetaminophen is a neutral compound. You will use these properties to separate thecomponents from each other.

Prelab

In this experiment, we will use a “flipped lab” concept. Your prelab exercises will mainly consist of viewinga video (posted on iLearn) that shows you a generic procedure for separations, gravity filtration and theuse of the rotary evaporator.

1) Watch the Week 2 video posted on iLearn (entitled “Separations and Rotovap”). We will trackthe views of the video - you get 2 pts towards your lab score for watching the video.

2) Read the relevant passages of The Organic Chem Lab Survival Manual and the summary passagesbelow.

3) Answer the prelab questions and hand the answers into your TA, along with an outline of theexperimental procedure. Remember to include your name, lab section and the name of your TA (on eachpage), and the title and number of the experiment. See p7 for more detailed prelab instructions.

Techniqu e Summ ar ies

A. Extract ion

“ Ext rac t ion and Washing ” - The Organic Chem Lab Survival Manual, pp. 128-140. Pay particular to thesection entitled “How to Extract and Wash What”, pp . 134-135.

Solution-phase extractions are one of the more complicated parts of organic lab, and it is very importantto understand which compounds are extracted into which phases. It is also important to keep track ofwhich phase is the organic phase and which is the aqueous phase.

Some relevant points to remember:• The two layers must be immiscible with each other (e.g. acetone is a poor extraction solvent, as it ismiscible with water - you will use dichloromethane most often). Depending on its density, the organicphase may be the top or the bottom layer. NOTE - dichloromethane is HEAVIER THAN WATER!• Extracting a layer more than once will yield better results.• Strong organic acids may be extracted with saturated NaHCO 3 solution.

Figure 1. Structures of acetaminophen, aspirin, and caffeine.


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• Weak organic acids may be extracted with 10% NaOH solution. • Organic bases may be extracted with 10% HCl solution. • Adding 2 -3 drops of the top layer to a small test tube half-full of water can help you determine if the toplayer is the aqueous layer. If drops dissolve into the water, the layer is the aqueous layer. If not, then it isthe organic layer.

• Save both layers until you know i t i s sa fe to th row away the unwanted layer.B . The Rotary Evaporator (“Rotovap”) “ The Rotary Evaporator ” - The Organic Chem Lab Survival Manual, pp. 196-199.The rotovap is used to evaporate solvent from a sample under reduced pressure – it is typically a moreefficient method than a steam bath or a still. In order to maintain the equipment, the following steps shouldbe taken:• Make sure the condenser has dry ice/acetone in it to allow for collection of the solvent.• Only half-fill your flask with the organic solution to avoid “bumping". Also, e nsure that only one phaseis present in the flask and do not set the water bath temperature too high, as this may also lead tobumping.

Prelab Questions (Read Klein, p98-105)

Safety and Preparedness :

1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Readthese and answer the following questions:

a) Which chemical is the most dangerous in this lab?

b) Explain w h y you chose your answer for part a), and the safety precautions you will take when handlingthis material.

Video Questions:

2) Why is an extraction a useful method of “pre -purification” of organic compounds? What physicalproperties does the process rely on?

3) The video showed the washing of a dichloromethane solution by water, and the dichloromethaneformed the lower layer in the separatory funnel. Look up the densities of dichloromethane, diethyl etherand water: if you used diethyl ether as the organic solvent, would it form the upper, or lower layer? Why?

4) How long should the combined organic layers dry over Na 2SO 4 before filtering?

5) How can you tell if you have added sufficient Na 2SO 4 to dry your compound?

6) Why do you always vent the separatory funnel towards the back of the fumehood?

7) What is the purpose of the “Bump trap” attached to the rotary evaporator?

8) Why do you only fill the round bottomed flask 50% full when using the rotary evaporator?

Experiment1. Prel iminary Separat ion

Obtain a sample (approximately 1.0 g) of the mixture in a vial from the instructor. Weigh the sample, andrecord the weight. This sample should consist of a 2:1:1 mixture (by mass) of aspirin, acetaminophenand caffeine, respectively.

Assemble the apparatus for a vacuum filtration (Zubrick p110), making sure the receiving flask is clean;you will be keeping b o t h the filtrate and the insoluble material.


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Transfer the sample to your smallest Erlenmeyer flask, add 10 mL of dichloromethane, and warm themixture for ten minutes on a hot plate at 35-40 °C. Note that a portion of the sample will not dissolve. Wetthe filter paper in the Hirsch funnel with dichloromethane, and filter the mixture.

The filtration must be performed while the mixture is still warm – the success of your separationdepends on this. Ensure that you have good suction in your filtration apparatus, and pour the

solution quickly and smoothly to avoid crystallization in the filter.Rinse the Erlenmeyer flask out with an additional 2 mL of warm dichloromethane to transfer as muchsolid material to the Hirsch funnel. Add an additional 5 mL of dichloromethane to the filtrate to redissolveany crystals that might have formed during the filtration. Label the filtrate Solution A. Allow the insolublematerial to dry until you have completed steps 2 and 3.

2. Separat ion of Asp ir in

Solution A should contain the aspirin (an organic acid) and caffeine (an organic base). Aspirin may beseparated from caffeine by extraction with 10% NaOH solution. Transfer Solution A to a 125 mLseparatory funnel and add 10 mL of 10% NaOH solution. Shake the mixture 3 or 4 times and rememberto vent the separatory funnel intermittently to relieve pressure (make sure you point the funnel away fromboth yourself and your labmates!). Remove the bottom layer into a clean 25 mL Erlenmeyer flask, and

transfer the top layer to a separate clean 50 mL Erlenmeyer flask. Label the flask containing the top layerSolution B . Pour the bottom layer back into the separatory funnel (remember to close the stopcock), add5 mL of distilled water, and shake again.

Remove the bottom (organic) layer into a clean, dry 25 mL Erlenmeyer flask, and add anhydrous sodiumsulfate until the drying agent no longer clumps together. Label this mixture Solution C . The remainingaqueous layer (the top layer still in the separatory funnel) should be added to Solution B.

3. Recrystal l izat ion of Asp ir in

Solution B contains the aspirin in the form of a water-soluble sodium salt. Slowly add 4M hydrochloricacid solution to Solution B until it becomes strongly acidic and an obvious persistent precipitate forms.Test the acidity using pH paper. The aspirin should rapidly precipitate (“crash”) from solution. On a hotplate, heat the solution until all the aspirin has re-dissolved, then allow the solution to slowly cool to roomtemperature and place it in an ice bath. Isolate the formed crystals by vacuum filtration.

4. Isolat ion of Caffeine

Solution C contains neutral caffeine. Decant the solution from the drying agent using a transfer pipette,and transfer the material to a clean, pre-weighed, 50 mL round-bottomed flask. Remove thedichloromethane using the rotovap to yield the caffeine.

Weigh each of the isolated materials (aspirin, acetaminophen and caffeine), and record their masses inyour laboratory notebook. Determine the melting point range of your caffeine sample, using a Mel-Tempapparatus.

Post Lab Questions

(1) Compare your melting point data to the literature values. How can this tell you the purity of thematerials you isolated?

(2) This experiment centers around exploiting the acidic and/or basic nature of organic molecules in orderto separate them from each other. The important skill here is to determine whether the molecules areacidic or basic, and whether they react with HCl (an acid) or NaOH (a base).

a) For the molecules below, identify whether they are acids, bases or neutral.


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b) For each of the molecules above, draw the product of reaction with either HCl or NaOH - if you defined

the molecule as a base, draw the conjugate acid formed upon reaction with HCl. If you defined themolecule as an acid, draw the conjugate base formed upon reaction with NaOH. If you defined themolecule as neutral, state "no reaction".

(3) Aspirin was extracted upon treatment with NaOH ( base) . Write the structure of the conjugate base ofaspirin (after treatment with NaOH) and explain why it dissolved in the aqueous layer.

(4) You could extract caffeine from neutral organics by treatment with aqueous HCl ( acid) . Write thestructure of the conjugate acid of caffeine (after treatment with HCl) and explain why it would dissolve inthe aqueous layer.

(5) Draw the structure of acetaminophen and explain why no reaction occurs upon treatment with either mild base or acid solution. Why is acetaminophen different from caffeine or aspirin?

(6) Using the arrow formalism, draw the mechanism of the reaction of aspirin with aqueous sodiumhydroxide to form the corresponding salt (the structure of which you drew in q3.)

(7) Explain why one never obtains a 100% recovery from an extraction.

(8) In the event that one does apparently obtain a 100% or better recovery from an extraction, what mightbe responsible for such an observation?

(9) Look up the density of dichloromethane and compare it to that of water. When using dichloromethaneas the extraction solvent, why is it the LOWER layer?

(10) Look up the density of diethyl ether and compare it to that of water and dichloromethane. If you hadused diethyl ether as the extraction solvent, would it be the UPPER or LOWER layer? Explain youranswer.


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Experiment 3: Techniques Lab 2 - Purification by Chromatography and Recrystallization

Reading: The Organic Chem Lab Surv ival Manual : pp. 88-103, 104-119, 223-234, 235-241

Introduction

In this experiment, you will attempt to purify a neutral organic compound that is not amenable to

purification by a simple extraction procedure. The target compound, biphenyl, will be purified by columnchromatography and recrystallization, and you will determine its solubility in various organic solvents priorto purification.

Prelab

In this experiment, we will use a “flipped lab” concept. Your prelab exercises will mainly consist of viewinga video (posted on iLearn) that shows you a generic procedure for performing recrystallization and thinlayer chromatography.

1) Watch the Week 3 video posted on iLearn (entitled “Recrystallization and TLC”). We will trackthe views of the video - you get 2 pts towards your lab score for watching the video.


3) Answer the prelab questions and hand the answers into your TA, along with an outline of theexperimental procedure. Remember to include your name, lab section and the name of your TA (on eachpage), and the title and number of the experiment. See p7 for more detailed prelab instructions.Techniqu e Summ ar ies

A. Recrystallization" General Recrystal l izat ion Proc edure ” - The Organic Chem Lab Survival Manual, pp. 104-119.

Begin by placing your crude solid in a round-bottomed flask, Erlenmeyer flask or beaker. Secure thisflask in a heating apparatus (sand bath, water bath, etc) slightly below the boiling temperature of yoursolvent. In a separate beaker, warm your recrystallization solvent to just below boiling. Using a Pasteurpipette, add the solvent dropwise while agitating the test tube until there is just enough solvent tocompletely dissolve the sample. Having a minimal amount of solvent is crucial. Remove the test tubefrom the water bath and allow to cool to room temperature. If no crystals form, place the test tube on ice.If crystals still do not form, scratch the inside of the test tube with a metal spatula to seed crystal growth.

B. Thin-Layer Chro matog raphy (TLC)“ Thin-Layer Chrom atography ” - The Organic Chem Lab Survival Manual, pp. 223-234.

Thin Layer Chromatography is a method for the identification of organic compounds, and thedetermination the purity of that compound. To get the best results:

• Make sure to mark both the origin line and the solvent front on the TLC plate in pencil.• Avoid getting fingerprints on the TLC plate - hold the plate by the sides when handling.

Figure 1. Structures of biphenyl and Methyl Orange.


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• When spotting TLC plates, try to make the smallest spot possible. This will ensure that different spotsdon’t run together. • When placing TLC Plate in the development chamber ensure that the solvent level lies below the originline.Prelab Questions


1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Readthese and answer the following questions:

a) Which chemical is the most dangerous in this lab?


Video Ques t ions :

2) Why do you need to use a minimal amount of hot solvent when recrystallizing? What happens if youuse too much?

3) Why should the hot solution be cooled slowly, rather than immediately adding the beaker to an icebath once all the solid has dissolved?

4) When choosing a solvent in which to perform a recrystallization, what are the most important propertiesto consider?

5) Why should you rinse with ice cold solvent when collecting your crystals?

6) When choosing a solvent to use in Thin Layer Chromatography, what are the most important propertiesto consider?

7) Why should you make your product spot on the TLC plate as small as possible?

8) Why should you let the solvent evaporate after spotting, before you add your plate to the developingchamber?

Experimental

1. Determinat ion of a Sui table Recrystal l izat ion So lvent

You will require five medium sized test tubes (1.3 x 10 cm). Measure out 1 mL of each of the followingsolvents and add the solvent to each of the five test tubes: methanol, acetone, dichloromethane, toluene,and hexanes. [Note: each test tube will contain a different solvent].

Determine the solubility of pure biphenyl in the solvents specified in your lab report book and record yourobservations for solubilities in both cold and hot solvent. The aim is to find a solvent that will not dissolvebiphenyl at room temperature, but will dissolve when hot.

2. Purif icat ion by Recrys tal l izat ion

Next, weigh and transfer approximately 0.5 g of your crude sample to an Erlenmeyer flask. Record theamount of crude material used. Over a sand bath, slowly add hot hexanes to your sample until no moresolid dissolves. Remove the dye by vacuum filtration (using a vacuum trap) into a pre-weighed 50 mLside arm flask. The solvent in the sidearm flask should evaporate under the vacuum. Record the weightof crude biphenyl in the filter flask.

To recrystallize the biphenyl, prepare a hot saturated solution by adding a minimum amount of hotmethanol dropwise until all the solid has dissolved. When all the solid has dissolved, remove the solutionfrom the heat source, allowing the hot saturated solution to cool to room temperature. Then place the


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flask into an ice bath and let the crystals form. Collect the crystals by vacuum filtration then using ice-cold methanol rinse the flask and wash the crystals. Record the weight of the dried crystals. You will berequired to use your product, as well as the remaining crude, for the next experiment.

3. An alysis by TLC

Set up two clean, dry test tubes a nd label them as ‘Crude’ and ‘Recrystallized ' Biphenyl. Transfer a small amount (e.g. the tip of a spatula) of your recrystallized sample to the appropriately labeled test tube. Add1 mL of acetone and shake to dissolve. (Caution: take care not to let the contents of the test tube comeinto contact with the test tube stopper). Place a small amount of crude compound into the second labeledtest tube and add 1 mL of acetone to dissolve. On a silica TLC plate, draw a baseline and mark 2 positionsfor the ‘Crude’ and ‘Recrystallized ' Biphenyl. Using a micropipette, spot each of the solutions above ontothe corresponding position on the TLC plate. Use hexane:ethyl acetate (4:1) as the eluent to develop theTLC plate and then visualize under a UV lamp.

4. Purif icat ion by Si l ica Gel Chrom atograph y and TLC Analysis

Take a long Pasteur pipette and lightly push a small ball of cotton into the base of the pipette. This willserve as your pipette column. Take your pipette to the fume hood and add silica to about half way up thepipette column. Carefully, clamp the pipette at your bench. In a 10 mL graduated cylinder, make up a 4:1

solution of hexane:ethyl acetate and then transfer the solution (eluent) to an Erlenmeyer flask. Using afresh pipette, transfer some of this eluent to your micropipette and allow the eluent to slowly pass throughthe column using the pipette bulb. Place a clean test tube under the tip of the column to collect the eluentthat passes through. Once the eluent has eluted through the column, add 50 mg of your crude sample(dissolved in a minimum amount of acetone) to the surface of the silica. (Due to acetone’s polarity, addingtoo much can damage the column). Pass eluent through the column and collect approximately 1 mL ofthe eluent in small numbered test tubes. (This is also known as ‘collecting fractions’). Collect fractionsuntil a colored band can be observed in the middle of the pipette column (collect at least 3 fractions).

On a TLC plate, spot all of these fractions to determine if you have collected biphenyl and in whichfractions it is contained. Develop the TLC plate and visualize with a UV lamp. Combine the fractions thatcontain pure biphenyl into a dry, weighed, 50 mL round-bottomed flask. Make sure to record the mass ofyour flask! Remove the solvent on the rotary evaporator, then determine the mass of biphenyl byobtaining the weight of the flask plus the biphenyl sample.

5. Melt ing Po int Determinat ion : Read Zubrick , pp. 88-103

Follow the procedure for acquiring melting points and determine the melting points for:

a) The original sample (crude)

b) The recrystallized biphenyl

Postlab Questions

(1) In which solvent was biphenyl most soluble ?

(2) In which solvent was biphenyl least soluble ?

(3) Explain those observations in terms of the molecular structure of biphenyl and the solvents used.(4) Compare your TLC analysis with the results of the column chromatography. More polar moleculesmove more slowly through silica than less polar molecules. Describe why silica gel chromatography isa good method of separating methyl orange from biphenyl. Based on the structure of Biphenyl and MethylOrange, predict which compound will have a higher R f value on TLC and explain your choice.

(5) Why did you push a small ball of cotton to the base of your pipette column?


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(6) More polar solvents (eluents) move molecules more rapidly than less polar solvents. If you used a 1:1hexanes:methanol mixture as solvent, would you expect the products to elute faster or slower? Based onyour experiment, would a 1:1 hexanes:methanol mixture be a good choice as eluent? Explain why/whynot.

(7) Impure compounds tend to have lower melting points than pure samples. Explain why this occurs,

using biphenyl as an example. Make sure you consider what happens upon melting in molecular terms.(8) Naphthalene (below) has melting point of 80.3 ºC. Is this higher or lower than that of biphenyl? Makea molecular model of both biphenyl and naphthalene and explain the relative melting points in molecularterms (i.e. why is one higher than the other?).


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Experiment 4: Purification of Liquids – Distillation

Reading : The Organic Chem Lab Surviv al Manual , pp.164-170, 271-284.

Introduction

Organic liquids are often purified by distillation. In this experiment, you will investigate the factors that

affect the efficiency of a distillation, by attempting to separate a mixture of two miscible liquids usingsimple distillation techniques.

Safety Notes

• The use of bunsen burners in this experiment is s t r i c t ly p roh ib i ted . Heating mantles or sand baths areto be used. Carefully inspect your glassware for star cracks.

• You require either a stirrer or boiling chips in your flask to allow controlled boiling of the liquid. If yourdistillation “bumps”, you will have to start again.

Prelab

In this experimen t, we will use a “flipped lab” concept. Your prelab exercises will mainly consist of viewinga video (posted on iLearn) that shows you a generic procedure for distillation.

1) Watch the Week 4 video posted on iLearn (entitled “ Distillation ”). We will track the views of thevideo - you get 2 pts towards your lab score for watching the video.


3) Answer the prelab questions and hand the answers into your TA, along with an outline of theexperimental procedure. Remember toinclude your name, lab section and the nameof your TA (on each page), and the title andnumber of the experiment. See p7 for moredetailed prelab instructions.

Techniqu e Summ ar iesDistillation

1. “Simple Dist i l la t ion ” - The Organic ChemLab Survival Manual, pp. 166- 170.

Simple Distillation is a useful technique forseparating miscible liquids with boiling pointsbelow 150 °C, and differ by at least 25 °C.Below are things to remember when doingany simple distillation.

• Make sure that there is some solid surface

present in the liquid that allows bubbles tonucleate on its surface, and ensures smoothboiling. Rough or intermittent boiling due tosuperheated solvent spontaneouslyvaporizing (bumping) leads to poorseparation, and can be dangerous. A boilingchip is added to the distilling flask, but neverto a hot liquid. Figure 1. Schematic of a simple distillation apparatus


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• Make sure that water is running through the condenser to ensure collection of the distillate.• Make sure that you clamp down all pieces of glassware securely and all joints are properly securedusing Keck clips or rubber bands.• DO NOT heat too quickly, as this will lead to a poor separation.

2. “Infra-red Spectro sco py ” - The Organic Chem Lab Survival Manual, pp. 271-284.

We will be covering much of the theory and application of infra-red spectroscopy later in the coursesequence (112B). At this juncture, it suffices to know that IR spectroscopy provides a way of identifyingorganic compounds on the basis of the functional groups present in that compound – many functionalgroups have characteristic regions in the infra-red spectrum where they absorb. It is possible to identifythese functional groups (and in some cases, as in this one) to determine structural information from infra-red spectra. You will take IR spectra of your two products from this distillation and analyze the differences.

Prelab Questions


1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Readthese and answer the following questions:a) Which chemical is the most dangerous in this lab?


Video Ques t ions :

2) How deep into the sand should you position your flask, and why?

3) Why should you discard the first few drops of material collected?

4) Why should the “water in” hose be at the bottom of the condense r, rather than the top?

5) Why is insulating the stillhead important?

6) Explain why you must clamp the f lask , not the distillation head.

7) Fill in the table below. Make sure you correctly calculate the molar amounts of your two materials.name formula M W bp/ºC moles density amount

Methyl tert -butylether (MTBE) 10 mL

Butan-1-ol 10 mL

Experiment

Collect 10 mL of methyl tert-butyl ether and 10 mL of n-butanol, and combine them in a 50 mL roundbottom flask.

Add a single boiling chip to the flask, and set up the distillation still (see Figure 1). The stills must beclamped as shown in Figure 1 for structural stability. Note that certain clamps should only supply supportand should not be clamped too tightly. Tight clamping may place strain on the glass, causing it to break.Condensers and take-off adapters should be held in place with rubber bands or Keck clips.

Heat the flask to 80 ºC and collect the distillate. DO NOT HEAT TOO VIGOROUSLY AT THE START.Once the solution stops boiling, heat to 140 ºC until boiling occurs, then collect fraction #2. Do not al lowthe f lask to bo i l d ry .


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Determine the boiling point range for the two fractions by reading the thermometer attached to thestillhead as the fractions are distilling. For each fraction, note the boiling point in your lab notebook.

NOTE - Ensure your flask is properly heated so that distillation proceeds smoothly. Make surethe level of the sand in the sand bath is at the level of the solvent in the flask. If the product is notdistilling, wrap the condenser and stillhead in aluminum foil.

CharacterizationObtain the infra-red spectrum of a thin film of the material – your instructor will show you how to do this.Make sure that you have identified the frequencies of the major absorbance peaks on your infra-redspectrum.

• The infra -red spectrum is usually collected in transmission mode – therefore absorbance is indicatedby troughs in the spectrum (% transmission < 100%), rather than peaks.

• The frequency of light in the infra-red spectrum is typically expressed in terms of wavenumbers (cm-1),rather than the usual hertz (s -1). Wavenumbers are in fact reciprocal wavelength (1/λ) where λ isexpressed in cm, rather than m. It can be shown from the wave equation for light that reciprocalwavelength is in fact proportional to frequency.

Take IR spectra of your two fractions (which should have different boiling points). Print out the spectraand hand them in with your report.

Postlab Questions

(1) Draw the structure of methyl tert -butyl ether and n-butanol and identify the functional groups in each.(2) Boiling point is directly related to the strength of the intermolecular forces between each molecule.Describe three different intermolecular forces that are present in a liquid sample of n-butanol. Which ofthese intermolecular forces is s t ronges t?(3) Only two of those intermolecular forces are present in a liquid sample of MTBE. What are they?(4) Which molecule has a higher boiling point, methyl tert -butyl ether or n-butanol? Using your analysisof intermolecular forces, explain your answer.

(5) Van der Waals forces are determined by the size of the molecule. Which of the two molecules islarger ? Are Van der Waals forces an important contributor to the relative boiling points of these twosamples? Why/why not?(6) There is one glaring difference (i.e. an obvious extra peak in one of the spectra) in the IR spectra ofmethyl tert -butyl ether and n-butanol. What is it? What functional group does this peak denote?


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Experiment 5: Natural Products - Isolation and Characterization of Limonene from CitrusPeel

Reading : The Organic Chem Lab Surviv al Manual , pp. 183-185, 271-284.

Bring a fresh ci t rus peel to the lab with y ou for this experiment . The type of citrus

does not matter (orange, mandarin, lime, lemon, etc.), but the larger the fruit, the easier it will be to obtainlimonene. You are at UC Riverside, so take advantage of this and bring in an interesting varietal of citrus! IntroductionIn this experiment, we will extract a natural product from plant material (in this case citrus peel), thenpurify and characterize it. This type of experiment forms the historical foundation to organic chemistry,and is still used today to obtain interesting chemicals ( e.g . pharmaceuticals) from biological materials.

1. Steam Distillation“Steam Dist i l la t ion ” - The Organic Chem Lab Survival Manual, pp. 183-187.Steam Distillation is used to isolate tars, oils, and natural products that are either slightly soluble orinsoluble in water. Below are a few pointers to remember when doing a steam distillation.• Be careful when handling any piece of glassware as it will be extremely hot. • In this lab, you will not be doing a steam distillation as described in Zubrick, but a variation which involvesa simple distillation of a water/citrus peel mixture.

2. Specific Optical RotationThe natural product obtained from distillation of citrus peel is limonene, which is a chiral molecule. Todetermine the optical purity of your product, you will analyze it by determining its specific optical rotation,a method used to identify and gauge the purity of chiral compounds. There is no section in Zubrickregarding the measurement of specific optical rotation, so we will describe it briefly here. You may recallfrom lecture (and Klein, p209-212) that two enantiomers of a chiral compound share identical physicalproperties – the only way they differ is in their reaction with plane-polarized light. An enantiomer allowedto interact with plane polarized light is capable of rotating the plane of that polarization – an optical rotationthat may be to the left or right. The opposite enantiomer will exhibit the same magnitude of rotation, butin the opposite direction . The angle of rotation may be measured using a polarimeter, for which asimplified schematic is shown in Figure 1.

Figure 1 . Simplified schematic of a polarimeter

The magnitude of the optical rotation depends on a number of factors: the temperature, the wavelengthof the incoming light, the length of the cell l (in dm), and the concentration c (in g/mL or mol/L; and opticalor enantiomeric purity) of the sample, among others. Thus, we need a standard formalism for opticalrotation, which is the specific o ptical rotation, [α 25 D], measured at 25 °C, using the wavelength of thesodium “D -line” at 589 nm. The specific optical rotation is determined from the observed optical rotationα25 D by:


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• The infra -red spectrum is usually collected in transmission mode – therefore absorbance is indicatedby troughs in the spectrum (% transmission < 100%), rather than peaks.

• The frequency of light in the infra -red spectrum is typically expressed in terms of wavenumbers (cm -1),rather than the usual hertz (s -1). Wavenumbers are in fact reciprocal wavelength (1/λ) where λ isexpressed in cm, rather than m. It can be shown from the wave equation for light that reciprocal

wavelength is in fact proportional to frequency.3. Characterization - Optical RotationTransfer the remainder of your material to a measuring cylinder, and make a solution of limonene inhexane. Calculate and record the concentration in your worksheet. Make sure that you wash all of theorange oil into the flask (i.e. rinse your receiving flask with hexane, and transfer your rinses into thevolumetric flask before filling to the line).

Fill the polarimeter cell with this solution. The polarimeter cell is a long glass tube, with two screwtop endcaps (each end cap has a quartz plate to allow light to pass through the sample). Make sure that one endis sealed before you transfer your material, and that both ends have a good seal before you place thecell in the polarimeter. Our current cell has a path length of 0.5 dm (50 mm).

Measure the experimental optical rotation, taking note of the sign (+/- ie. the direction) of the rotation.

Post Lab Questions

(1) Citrus oil is made up of a number of organic compounds, but only one (limonene) is predominant, andis a liquid with specific optical rotation of +125.6°. On the basis of your value, is the citrus oil pure?

(2) On the IR spectrum, what functional groups are indicated by the following absorbance frequencies(Zubrick p280, Klein p701), and are they present in your sample?

3010-3050 cm -1 2950-2980 cm -1 1750-1730 cm -1 1630-1675 cm -1

(3) The structure of limonene (without identified stereochemistry) is shown below. Identify thestereocenter in the molecule, and using the Cahn-Ingold-Prelog rules, draw the structure of (R)-limonene.Note - an alkene has higher priority than an aliphatic CH 2.

(4) The natural enantiomer of limonene found in citrus is of the R configuration. ( S )-Limonene is found inpine oil - what would be the specific optical rotation of ( S )-limonene? Why?

(5) The boiling point of limonene is 176 ºC. You purified it by steam distillation, which allowed isolation atlower temperature. Why was this successful ( hin t - look up the term "azeotrope")?

(6) Another possible method of purification would be column chromatography. Compare the structure oflimonene to that of biphenyl (experiment 3). What solvent mixture would you use to purify limonene bycolumn chromatography?


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Experiment 6: Bromination of t rans- Stilbene

Reading: Klein 2 nd Ed p435-437 (olef in h alogenat ion ) .

Introduction

In this experiment, you will perform the first of a number of reactions involving alkenes that we will coverin the 112 series. You have covered the bromination of alkenes in lecture and discussed thestereoselectivity of the process. Here you will do the reaction yourself.

Bromine is a highly corrosive liquid that fumes and is generally unpleasant to handle, so instead of usingbromine itself, you will use a surrogate reagent pyridinium bromide perbromide. This is a combination ofbromine, pyridine and hydrobromic acid that is a stable solid. In acetic acid solution, bromine (Br 2) isreversibly released from this mixture and can react with a suitable alkene, in this case trans-stilbene (1,2-diphenylethene).

Prelab Questions

1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Readthese and answer the following questions:a) Which chemical is the most dangerous in this lab?b) Explain w h y you chose your answer for part a), and the safety precautions you will take when handlingthis material.

2) Fill in the reaction table below. Make sure you correctly calculate the molar amounts of your reactivematerials.

name formula mol.-eq. M W mmol amount

Stilbene 1.00 600 mg

Pyridinium BromidePerbromide 1.10 1.2 g

Glacial Acetic Acid -- -- -- 12 mL

product

3) Based on your answers to Q2, which is the limiting reagent in this reaction?

4) Calculate the Theoretical Yield of your product, i.e. the mass you would expect to recover, assuming100% conversion to product.

Experiment

Figure 1. Reaction Scheme.


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1. React ion Setup Into a 50 mL round-bottomed flask containing a magnetic spinbar and equipped withan air condenser, weigh and place 600 mg of trans-(E)- stilbene. Transfer the flask to a sand bath on amagnetic stirrer. ( NOTE - clamp the flask joint, not the condenser!). Glacial Acetic Acid is corrosive and toxic - all manipulations should be performed in thefumehood.

Using a measuring cylinder, add 12 mL glacial acetic acid to the flask and subsequently heat the flask(with stirring) to 130 ºC until the solid dissolves (~5 mins). Raise the flaskfrom the sand bath ( Caution - HOT! ), remove the air condenser and leaveto cool for 5 mins.

Pyridinium Bromide Perbromide is a lachrymator (stings the eyes,causes tears) - perform all manipulations in the fumehood.

Weigh 1.20 g of Pyridinium Bromide Perbromide and add the solid to thereaction flask in one portion. Some perbromide may stick to the sides of theflask - wash it down with some additional (no more than 5 mL) acetic acid.Reattach the air condenser and lower the flask apparatus back into the sandbath. Heat at 130 ºC for 10 min. The product should begin to precipitate outduring the reaction.

2. Isolat ion of Produ ct

Remove the reaction flask from the sand bath and allow it to cool to ambienttemperature. Add 12 mL of water, with swirling, and then place the flask inan ice bath for 10 mins. Collect the crystalline solid by vacuum filtrationusing a Hirsch funnel and side-arm flask. Wash the material with three 2 mLportions of cold water, then with two 2 mL portions of cold acetone. Dry theproduct by leaving it on the filter and applying a vacuum.

3. Purif icat ion b y Recrystal l izat ion

Dissolve the solid product in a minimum amount of hot xylenes and thenallow to cool to room temperature slowly. Once recrystallization is complete, isolate the pure product byvacuum filtration.

4. Charac terization .

Weigh your purified product to determine the yield, and determine the melting point of your purifiedproduct and compare it to the literature value. NOTE - SAVE your p rodu ct . You may n eed i t for nextweek's lab experim ent .

Post Lab Questions(1) Draw the mechanism of the reaction, using bromine (Br 2) as your brominating agent rather thanpyridinium bromide perbromide.

(2) There are two possible diastereoisomers of stilbene dibromide - draw both of them, and label eachstereocenter ( R ) or ( S ).

(3) Why is only one diastereomer formed in this reaction? Relate your answer to the mechanism youdrew in Q1.

(4) Draw the mechanism of the bromination of cis -(Z)-stilbene. Is the product of this reaction the same ordifferent from the product you made in the experiment?

(5) ( E )-Stilbene is a useful starting material for alkene-based reactions. Draw the product(s) obtainedupon reaction of ( E )-stilbene with a) H 2, Pd/C; b) B 2H6, followed by NaOH/H 2O 2; c) OsO 4, followed byNaHSO 3; d) HBr. Make sure you identify the stereochemistry of the products.

Figure 1. Schematic ofthe reaction apparatus


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(6) Draw the product(s) obtained upon reaction of ( E )-stilbene with ozone (O 3), followed by a) Zn metal;b) KMnO 4 (see Klein p444). If you performed these reactions on ( Z )-stilbene, what would the productsbe?

Experiment 7: Dehydrobromination of meso- Stilbene Dibromide

Reading: Klein 2nd Ed Ch 8.

Introduction

In this experiment, you will react the product you made in last week's experiment ( meso -stilbenedibromide) with strong base in an elimination experiment. This reaction with yield an alkyne,diphenylacetylene. The strong base you will use is potassium hydroxide. The second step of the reactionis quite unfavorable, so you will strongly heat the reaction to allow conversion. This requires a high boilingsolvent, and you will use triethylene glycol.

Prelab Questions

1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Readthese and answer the following questions:a) Which chemical is the most dangerous in this lab?b) Explain w h y you chose your answer for part a), and the safety precautions you will take when handlingthis material.

2) Fill in the reaction table below. Make sure you correctly calculate the molar amounts of your reactive

materials.name formula mol.-eq. M W mmol amount

Meso- Stilbene Dibromide 1.00 400 mg

Potassium Hydroxide 5.75 387 mg

Triethylene glycol -- -- -- 2 mL

product

3) Based on your answers to Q2, which is the limiting reagent in this reaction?

4) Calculate the Theoretical Yield of your product, i.e. the mass you would expect to recover, assuming100% conversion to product.

5) Potassium hydroxide is hygroscopic. Will it be easy to weigh exactly 387 mg? Will the exact amountof potassium hydroxide be critical to this reaction and why?

Experiment

1. React ion Setup

Figure 1. Reaction Scheme.


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Into a 25 mL round-bottomed flask containing a magnetic spinbar and equipped with an air condenser,weigh and place 400 mg of meso -stilbene dibromide and 387 mg of potassium hydroxide (Caution -hygroscopic and corrosive). Transfer the flask to a sand bath on a magnetic stirrer. ( NOTE - clamp theflask joint, not the condenser!).

Using a measuring cylinder, add 2 mL triethyleneglycol to the flask and

subsequently heat the flask (with stirring) to 190 ºC for 10 mins). Raisethe flask from the sand bath ( Caution - HOT! ), remove the air condenserand leave to cool for 10 mins.

2. Isolat ion of Produ ct

Remove the reaction flask from the sand bath and allow it to cool toambient temperature. Add 5 mL of water, with swirling, and then placethe flask in an ice bath for 15 mins. Collect the crystalline solid byvacuum filtration using a Hirsch funnel and side-arm flask. Wash thematerial with two 2 mL portions of cold 70% ethanol. Dry the product byleaving it on the filter and applying a vacuum.

3. Purif icat ion b y Recrystal l izat ion

Dissolve the solid product in a minimum amount of hot 95% ethanol andthen allow cool to room temperature slowly. Once recrystallization iscomplete, isolate the pure product by vacuum filtration.

4. Charac terization .

Weigh your purified product to determine the yield, and determine themelting point of your purified product and compare it to the literaturevalue.

Post Lab Questions(1) Draw the mechanism of the reaction - remember, there are tw o steps in the process.

(2) Draw the structure of the intermediate in the first step of the reaction. What type of elimination isoccurring here?

(3) Which step of the process is rate-determining? Explain your choice.

Double elimination reactions to form alkynes are relatively limited in scope, but eliminations to form alkeneare far more flexible. Read Klein Ch 8 and answer the following questions.

(4) Draw the products of the following reactions. The relevant mechanism is given in each case – justdraw the products. Remember to include stereochemistry if necessary!

Figure 1. Schematic of thereaction apparatus


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(5) Draw the products of the following reactions. In each case, state which mechanism governs thereaction (E1, E2) and explain your choice.

(6) Draw the structure of the INTERMEDIATE in the following reaction.

(7) Is the product drawn for the above reaction (in Q6) the only product obtained? Draw another possibleproduct and determine which would be the major product or if there would be no selectivity. Explain youranswer.


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Experiment 8: Nucleophilic Substitution Reactions – Reactivity of Alkyl Halides

Reading: Klein 2 nd Ed. Ch . 7.

IntroductionThe reaction rate of nucleophilic substitution reactions depends on two primary factors: substratestructure and reaction conditions. In this experiment, we will investigate six representative alkyl halidesubstrates and will compare their respective reaction rates under two sets of conditions.

Sodium iodide dissolved in acetone is a useful reagent for determining the S N2 order of reactivity of thealkyl halides above. Iodide anion is an excellent nucleophile, and acetone is a polar, aprotic solvent – conditions that favor S N2 reactions. Sodium iodide is readily soluble in acetone, but sodium bromide andsodium chloride are not, and will precipitate from the reaction mixture.

On the other hand, silver nitrate dissolved in ethanol is a useful reagent for determining the S N1 order ofreactivity of the alkyl halides above. The silver cation coordinates to a lone pair of electrons on thehalogen atom. As a result, the carbon-halogen bond is weakened, resulting in heterolysis of the C-Xbond, and formation of a carbocation intermediate.

Ethanol promotes S N1 reactions because it is a highly polar, protic solvent, and stabilizes the formedcarbocation by solvation. As you may recall from General Chemistry, silver halide salts are highlyinsoluble, and will precipitate from solution.

In each case, the amount of time required to see a change in a solution of alkyl halide upon addition ofeither (a) sodium iodide, or (b) alcoholic silver nitrate, gives us a measure of how reactive each substrate(alkyl halide) is under these different conditions.

Prelab Questions

1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Readthese and answer the following questions:a) Which chemical is the most dangerous in this lab?

b) Explain w h y you chose your answer for part a), and the safety precautions you will take when handlingthis material. NOTE - one of the chemica l s used in th i s l ab i s a kn own carc inogen . Make sure youde te rmine which o ne , and no te what p recau t ions to t ake.

2) The reaction of 2-chloropropane with sodium hydroxide can occur via both S N1 and S N2 mechanisms.Draw arrow pushing schematics for each S N1 and S N2 mechanism for this reaction.

3) Identify the rate determining step for each of the mechanisms you drew in Q2.

4) Draw the structure of the intermediate of the S N1 process, and the t r ans i t ion s ta te of the S N2 process.


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In your Laboratory Notebook, you should create two experimental sections. Each section of theexperiment should have a short description of the experiments you will conduct (a synopsis) so that youcan record your observations during the experiment. Create a table for each experiment so that you cannote the appearance of each reaction (12 in total) at 1 minute intervals, both at room temperature andelevated temperature.

ExperimentSet up and stabilize a hot water bath at 45 °C.

1. Sodium Iodide in Aceton e (S N 2 cond i t ions)

Label six clean, dry, small test tubes. Add 0.1 mL of one of the alkyl halides to each tube. Make sure tonote and keep track of which alkyl halide is contained in each tube. Keep your tubes in the hood tominimize vapors in the lab. To each tube, rapidly add 1 mL of a 12% sodium iodide in acetone solutionin one portion, mix thoroughly, and record the beginning time. Watch the reactions and record the timeyou first notice precipitate in each of the tubes. After 10 minutes at room temperature, place any tubesthat do not yet have a precipitate into the water bath. Make sure the temperature is not above 45 °C toavoid evaporating acetone. After 10 minutes in the bath, remove the tubes and note any additionalsamples with precipitate.

Beware of false positives ! If any acetone evaporated during heating, some sodium iodide may haveprecipitated on the walls of the test tube. Agitate the test tube for a few minutes to ensure that theprecipitate persists before recording a positive test. In the absence of precipitate notice any color changesin the tubes.

Ultimately, you should be able to rank the alkyl halides from 1-6 in terms of S N2 reactivity.

2. Si lver Nitrate in Eth anol (S N 1 cond i t ions)

Label six clean, dry, small test tubes. Add 0.1 mL of one of the alkyl halides to each tube. Make sure tonote and keep track of which alkyl halide is contained in each tube. Keep your tubes in the hood tominimize vapors in the lab. To each tube, rapidly add 1 mL of a 1% silver nitrate in ethanol solution inone portion, mix thoroughly, and record the beginning time. Watch the reactions and record the time you

first notice precipitate in each of the tubes. After 10 minutes at room temperature, place any tubes thatdo not yet have a precipitate into the 45 °C water bath. After 10 minutes in the bath, remove the tubesand note any additional samples with precipitate. Rank the alkyl halides from 1-6.

Investigative Lab Report

Using your data from this experiment, you will determine the factors that control rate of S N1 and S N2reactions of various alkyl halides. Your final report should contain:

• Introduction – This section should introduce the background and purpose of the experiment.

• Experimental Procedure – This section should be complete and specific enough so that another organicchemistry student could use your report to complete the experiment with similar results. Figures anddiagrams are useful in this section.

• Data/Results – This section should report your results as succinctly and clearly as possible. Nodiscussion is required and tables and graphs are useful ways to report data.

• Analysis/Discussion/Conclusions – This section is the most important part of the report and is whereyou convey that you understand the experiment and can interpret the data to make meaningfulconclusions. This section should be written in complete sentences and your analysis and conclusionsshould be written clearly to convey your point.

In this section, consider the following questions:


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a) Which alkyl halides were the most reactive under S N2 conditions? Which were the least reactive?Explain the order of reactivity under S N2 conditions by considering alkyl halide structure, nature of theleaving group, temperature, solvent, etc. Does the experimentally determined order fit what youpredicted? Account for any anomalous observations.

b) Which alkyl halides were the most reactive under S N1 conditions? Which were the least reactive?

Explain the order of reactivity under S N1 conditions by considering alkyl halide structure, nature of theleaving group, temperature, solvent, etc. Does the experimentally determined order fit what youpredicted? Account for any anomalous observations.

Post Lab Questions

(1) Two of your six alkyl halides cannot react via an S N1 mechanism. Which are they? Why are theyunreactive under S N1 conditions?

(2) One of your six alkyl halides reacts rapidly via b o t h S N1 and S N2 mechanisms. Which is it, and why isit reactive under both mechanisms?

(3) One of your six alkyl halides is essentially unreactive via ei ther S N1 or S N2 mechanisms. Which is it,and why is it unreactive?

(4) Explain why we used acetone as solvent for the S N2 reactions, and ethanol as solvent for the S N1reactions.

(5) Allyl chloride is carcinogenic, as you determined in the prelab. Carcinogenic alkylating agents reactwith DNA bases such as cytosine (below), causing a change in the base structure, DNA mismatches andmutations which can lead to cancer. Draw a plausible reaction of allyl chloride with cytosine, and basedon your results from this experiment, explain why allyl chloride is carcinogenic but 2-chlorobutane is not.

chem 112a lab book w16 final

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