Don’t Panic! It’s More Organic
Chemistry Lab
ORGANIC CHEMISTRY 12B
LAB MANUAL
Lawrence Yee
2016, Version 6.2
Copyright © 2016 by Lawrence Yee
All rights reserved.
CCChemTeach.com (http://ccchemteach.com) for community college chemistry
ii
Contents
Organic Chemistry References ............................................................................................................................................... 1
Group and Collaborative Work ................................................................................................................................................ 2
General Laboratory Procedures and Conduct ........................................................................................................................ 3
Laboratory Safety Agreement ................................................................................................................................................. 4
Microwave Assisted Organic Reactions .................................................................................................................................. 5
Lab 1. Moonshine - Ethanol by Fermentation ......................................................................................................................... 6
Lab 2. What a Pain! Phenacetin Synthesis from Acetaminophen ........................................................................................ 11
Lab 3. What Did I Make? Structure Characterization: IR, NMR, and MS ............................................................................. 14
Lab 4a. Eat Your Vegetables: Tomato Rainbow ................................................................................................................... 17
Lab 4b. Eat Your Vegetables: Solar Cell from Plant Pigments ............................................................................................. 20
Lab 5. Ring Around: Electrophilic Aromatic Substitution Reactions ..................................................................................... 25
Lab 6. Making Big from Small: Grignard(-like) Reaction ....................................................................................................... 30
Lab 7. The Most Practiced Reaction in the World! Maillard Reaction................................................................................... 33
Lab 8. Lifesavers: Wintergreen from Salicylic Acid ............................................................................................................... 38
Lab 9. Biodiesel from Vegetable Oil ...................................................................................................................................... 41
Lab 10. Multistep Synthesis of a Sunscreen ......................................................................................................................... 44
iii
Organic Chemistry References
These references are some sources of organic chemistry information that we will use in Chem 12A lecture and lab. The
lab textbooks shown below were used to prepare this lab manual. The lab textbook references listed in the Table of
Contents are posted in the Chem 12 website. Please add your own references to this list (and tell me about them too).
Organic Chemistry Textbooks and Online Resources:
nd
1. D. Klein, “Organic Chemistry”, 2 ed., 2014
2. Klein, Organic Chemistry Companion Site: (http://bcs.wiley.com/hebcs/Books?action=index&itemId=0471756148&bcsId=6581)
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Virtual Textbook of Organic Chemistry: http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/intro1.htm
UC Davis Chem Wiki Organic Chemistry Textbook Maps:
http://chemwiki.ucdavis.edu/Textbook_Maps/Organic_Chemistry_Textbook_Maps
Daley and Daley Organic Chemistry online textbook: http://www.ochem4free.info/node/1
The OCHeM.com website “seeks to provide learning resources for students enrolled in Organic Chemistry”:
http://ochem.jsd.claremont.edu
ChemSpider: the free chemical database: http://www.chemspider.com/
WEB-sters’ Organic Chemistry is “A Living Document of Internet Resources, Information, and Applications”:
http://www.chemconnections.org/Websters/ This site has links to other sites for many topics in organic chemistry.
Check out the Synthesis and Reaction Mechanisms link.
The Organic Syntheses is a Publication of Reliable Methods for the Preparation of Organic Compounds:
http://www.orgsyn.org
Organic Compounds Database: http://www.colby.edu/chemistry/cmp/cmp.html Enter various properties, e.g., m.p.,
molecular weight, UV wavelengths, chemical types, into this 2500 compound database to identify organic
compounds.
Organic Chemistry Resources: http://www.chemtopics.com/orgo/orgo.htm
Organic Chemistry Directory: http://murov.info/orgchem.htm
th
Organic Chemistry On-Line Learning Center for Carey, Organic Chemistry, 4 ed.
http://www.chem.ucalgary.ca/courses/351/Carey5th/Carey.html#4
th
B.S. Furniss, A.J. Hannaford, P.W.G. Smith, and A.R. Mitchell, “Vogel’s Textbook of Practical Organic Chemistry", 5
ed., Longman, 1989.
Khan Academy: http://www.khanacademy.org/
Organic Chemistry Lab Resources:
1. Organic Chemistry at CU Boulder: Lab Procedures:
http://orgchem.colorado.edu/Technique/Procedures/Procedures.html
2. McMaster Univ. Microscale Laboratory Techniques:
http://www.chemistry.mcmaster.ca/~chem2o6/labmanual/microscale/complete.html
3. Wired Chemist Lab Tutorials: http://www.wiredchemist.com/chemistry/instructional/laboratory-tutorials
4. OCHeM.com In The Lab tutorials: http://ochem.jsd.claremont.edu/in-the-lab.html
5. Univ. of Nevada, Reno Chemistry YouTube videos: http://www.youtube.com/watch?v=5I1S6evKpe4
6. Not Voodoo: Demystifying Synthetic Organic Laboratory Technique: http://chem.chem.rochester.edu/~nvd/
7. NIST WebBook is a database of properties of substances: http://webbook.nist.gov/chemistry IR spectra for many
compounds are included in this site.
rd
8. Williamson, K., “Macroscale and Microscale Organic Experiments”, 3 ed., Houghton-Mifflin, 1999.
9. Pavia, G.M. Lampman, G.S. Kriz, and R.G. Engel, “Introduction to Organic Laboratory Techniques: Small-Scale
st
Approach”, 1 ed., Saunders, 1998.
10. Schoffstall, B.A. Gaddis, and M.L. Druelinger, Microscale and Miniscale Organic Chemistry Laboratory Experiments”,
McGraw-Hill, 2000.
11. Mohrig, C.N. Hammond, T.C. Morrill, and D.C. Neckers, “Experimental Organic Chemistry, A Balanced Approach:
Macroscale and Microscale”, W.H. Freeman, 1999.
Other Resources:
1. ChemAxon chemistry software (http://www.chemaxon.com/) – chemistry drawing and modeling software
(MarvinSketch is free).
2. Chemagic Virtual Molecular Modeling kit: http://chemagic.com/home/
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1
Group and Collaborative Work
The ability to work with people is an important skill that many employers value. A good group or team is
able to share their diverse experiences, knowledge, abilities, and opinions to work effectively and efficiently to accomplish
goals that one person may not be able to do as well or as quickly. Group or teamwork means members work together in a
non-competitive, collaborative atmosphere. Skills include listening to others, being assertive with your input but not
dominating the whole group, and taking responsibility for your role on the team and making sure other members are doing
their role. It helps to focus on the “big picture”, i.e., the overall goal of the group, rather than getting caught up in individual
issues.
You will work in a group of four in lab. Working in a larger group requires teamwork and communication. Each
group member will be assigned one of the following roles so that duties are shared equally:
Group Leader: responsible for supervising the group and makes sure each member contributes equally to the team.
Communicator: responsible for communicating with the instructor and for completing all materials to be submitted by the
team that reflects the thinking of all team members.
Record Keeper: responsible for keeping records of all materials discussed and is for informing absent team members of
work missed and progress made.
Counselor: responsible for making sure all members of the team agree on planning, execution, and presentation of work.
Roles should be rotated with each different lab so each member of the group has the opportunity to perform a different
function.
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2
General Laboratory Procedures and Conduct
A diagram of microscale equipment is posted on the Chem 12 website.
The following procedures for laboratory safety and practices must be followed by everyone (instructors, students, and
staff) using the chemistry laboratory. Disregard of these procedures will result in disciplinary action.
1. Protective goggles or safety glasses with side shields must be worn when performing or observing an experiment or
when in the vicinity of others performing experiments.
2. Learn the primary, secondary and handicapped escape routes from the laboratory.
3. Learn the locations of the fire extinguishers, shower, eyewash stations, fire blankets, and hoods.
4. Never perform unauthorized experiments.
5. Eating, drinking, and smoking in the laboratory are forbidden. Do not bring food or drink into the laboratory.
6. Become familiar with the use and operation of laboratory equipment and instruments. A diagram of laboratory
equipment is shown below.
7. Never taste a chemical.
8. If instructed to smell a chemical, do so by gently fanning the vapors toward your nose.
9. Never point a test tube that is being heated toward yourself or others.
10. Never pipet by mouth. Pipet filler bulbs are available and their use will be demonstrated when appropriate.
11. Read chemical labels carefully. Be sure that you are using the chemical required.
12. Never return unused chemicals to the stock bottles to avoid contamination.
13. Never discard solid residues or paper into the sinks.
14. Footwear should cover the feet completely. No open-toe shoes. Clothing should cover the body to the knees. Long
pants are preferred. Long hair and loose clothing should be secured.
15. When diluting acid, ALWAYS add the acid to the water.
16. When the experiment is completed, wipe the laboratory table; clean and dry equipment; compare the equipment and
chemicals in the tray with the check list; when complete, return the tray to the stockroom. Return all ring stands, hot
plates, Bunsen burners, etc. to their proper places.
Accidents
1. Clean up all spills immediately.
2. If a thermometer breaks, do not touch the mercury. Notify lab staff immediately.
3. In case of contact with a chemical, wash the affected area immediately and thoroughly with water. Notify lab staff.
4. In case of an injury, no matter how minor, notify lab staff.
Lab Policies
1. Safety glasses or goggles are required in lab. Prescription glasses are an adequate substitute for safety
glasses/goggles. For students who wear contact lenses, you will need to wear safety glasses/goggles over your contact
lenses. Try to be aware of your safety as well as the safety of others in lab.
2. FAILURE TO CHECK-IN YOUR LOCKER, whether you drop the course or complete it, results in a $25 LAB FEE plus
a charge for any broken or missing equipment.
3. All labs must be performed to pass this course.
4. Late lab assignments will be penalized 5% per calendar day.
5. The chemistry lab has 12 computers.
a. You cannot store your lab data and results on the hard drive of a computer you are using. Please bring a flash/thumb
drive to store lab files.
b. Each computer is connected to a network printer. You will need to supply your own printer paper. You and your lab
partner are asked to donate one ream of paper to lab (you and your lab partner can share the cost of paper) for your use
and other student’s to use.
c. These computers are connected to the internet so you can look up scientific information. Please do not download
images, files, or software onto these computers.
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Laboratory Safety Agreement
I have carefully read the instructions on good laboratory safety practices and procedures. I understand the importance of
good safety practices for my own welfare and of all people in the laboratory and I, therefore, pledge to follow the safety
regulations of the college.
Date: ____________________
Signature: ____________________
Drawer Number: ____________
Print Name: ___________________
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4
Microwave Assisted Organic Reactions
st
“The microwave oven is the Bunsen burner of the 21 century.”
- Ajay Bose, microwave chemistry researcher (http://cen.acs.org/articles/90/i39/Chemists-Crank-Heat-Microwaves.html)
General Use of a Microwave Oven:
1. Don’t operate an empty microwave oven.
2. Keep the microwave oven clean. Clean up any spills in the oven.
3. Do not use metals in the microwave oven.
4. No sealed containers in the microwave oven. Sealed containers may explode.
Microwave ovens provide intense heating and can replace a long reflux.
Microwaves work by dielectric polarization. This means substances with a non-zero dielectric constant absorb microwave
radiation.
Questions:
1. What is dielectric constant?
2. Name two solvents with a non-zero dielectric constant. Give the dielectric constant of each solvent.
3. Does glass heat up in a microwave oven?
Use polar solvents only, e.g., water, acids, alcohols, and amides.
Polar solvents usually have –OH bonds, which absorb microwave radiation.
Good solvents: methanol, ethanol, isopropanol, 1-butanol, ethylene glycol
Medium solvents: water, acetonitrile, acetone, ethyl acetate, tetrahydrofuran (THF), dimethyl formamide (DMF)
Poor solvents: chloroform, dichloromethane, CCl4, hexane, toluene, xylene
Questions:
1. How is dielectric constant related to polarity?
2. What makes a solvent a “good” solvent for a microwave reaction? Identify at least two properties of a good solvent.
3. “Be careful using volatile solvents.” Why?
A commercial microwave oven has a frequency of 2.45 GHz.
This gives a microwave penetration depth of approximately 2 cm.
Question:
1. Based on the microwave penetration depth, what lab container size should you use for a microwave reaction?
To perform organic reactions in a microwave oven, remember glass does not heat up in microwave and will condense
vapor (like a reflux condenser). For your reaction vessel,
a. use a test tube.
b. Attach a condenser to your test tube.
c. If you can’t use a test tube, use a beaker.
d. Important: Place a beaker or flask with water in the microwave with your reaction container.
Questions:
1. Should you seal your reaction vessel? Give reasons.
2. What Power Level or Setting on the microwave oven should you use for a “good” microwave solvent? Give reasons.
3. What Power Level or Setting on the microwave oven should you use for a volatile solvent? Give reasons.
4. How long should you run your reaction in a microwave oven?
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Lab 1. Moonshine - Ethanol by Fermentation
How do I make alcohol? Which sugar source produces a higher yield of ethanol?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
Bring apple juice or grape juice or potato starch or corn starch to lab.
1. Using the macroscale equipment in your locker, set up a fermenter. Fermentation is an anaerobic process. How will you
prevent air and oxygen from coming in contact with the reaction mixture?
2. Your group will be assigned to make ethanol from table sugar, grape juice, apple juice, potato starch, or corn starch.
z. Identify the sugar type (glucose, fructose, sucrose, etc.) in each sugar source.
a. Using Lewis structures, write a chemical equation that represents the fermentation of your assigned sugar to produce
ethanol.
b. Identify the functional group(s) in each reactant and product.
c. Which reactant is chiral? Identify the chirality center(s).
d. Which reactant is an acid? Identify the acidic H. State the pKa of this acid.
e. Which reactant is a base? Identify the basic atom. Draw the conjugate acid of this base. State the pKa of this acid.
f. Identify the nucleophile(s) and electrophile(s). If there is more than one nucleophile or electrophile, identify the best
nucleophile/electrophile. Use curved arrows to show how the nucleophile reacts with the electrophile.
g. This reaction is a ____ reaction.
o
o
o
i. Identify the alpha carbon. Is this carbon 1 , 2 , or 3 ?
h. Identify the leaving group. Is this leaving group a good or poor leaving group?
i. Identify the beta carbon. Is there a H bonded to this C?
j. Calculate the moles of each reactant in each reaction. Identify the limiting reactant. Calculate the theoretical yield of
product.
k. What property of the product distinguishes it from the reactant? How will you characterize the product?
Table 1. Chemical Properties of Lab 1 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
b.p./m.p.,
o
C
Polar
or nonpolar?
Objectives
1. Name and classify alcohols; identify their physical and chemical properties, especially reactivity trends.
2. make ethanol from sugar fermentation
3. determine the sugar source that gives the highest yield of ethanol
References: 1. Ethanol from sugar: http://faculty.tcc.fl.edu/scma/phelpsj/experiments/ethanol.pdf
2. J.L. Epstein, M. Vieira, B. Aryal, N. Vera, and M. Solis, “Developing Biofuel in the Teaching Laboratory: Ethanol from
Various Sources,” J. Chem. Educ., 2010, 87, 708-710.
Introduction
The fermentation of sugar is one route to make ethanol. The sugar can come from a variety of sources, e.g., corn,
grapes, plums, potatoes. Corn is the largest U.S. crop. In 2010, farmers produced 331 million metric tons (12.1 billion
bushels) in the U.S., of which more than half were grown in Iowa, Illinois, Nebraska and Minnesota. 40% of the corn is
used for animal feed, 40% is used to make ethanol, and 20% is used for food. (References:
http://blogs.scientificamerican.com/plugged-in/2011/10/07/the-u-s-now-uses-more-corn-for-fuel-than-for-feed/,
http://www.grains.org/corn)
Glucose is the sugar that undergoes fermentation. One glucose is metabolized to two pyruvates in glycolysis. See
Figure 1.
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6
Figure 1. The 10 Steps of Glycolysis
Fermentation occurs in anaerobic organisms. These organisms lack a respiratory chain and must re-oxidize NADH (a
+
+
biological reducing agent) to NAD so Step 6 of glycolysis can occur. Usually, NADH reacts with pyruvate to form NAD
and lactate. Some anaerobic organisms metabolize pyruvate to ethanol, which is excreted as a waste product. Pyruvate is
converted to acetaldehyde which is reduced to ethanol. The ethanol in your wine or beer or other adult beverage is
actually yeast ____. (www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/glycolysis.htm) See Figure 2. We will learn
the organic chemistry of each step of glycolysis and fermentation in CHM 12B.
Figure 2. Fermentation Produces Lactate or Ethanol
In this lab, you will make ethanol from sucrose and grape juice. You will determine the concentration of ethanol by
measuring the density of this solution. To a portion of this solution, you will perform a distillation. To a second portion of
this solution, you will treat it with an oxidizing agent to make an aldehyde and then an acid.
Materials
Sucrose
Students: Bring Grape juice, apple juice, corn starch, potato starch
Yeast
Solid sodium hydrogen phosphate (Na2HPO4)
6 M HCl
6 M NaOH
pH 6.2 phosphate buffer (To prepare 0.1 L: 13.6 g KH2PO4, 1.42 g Na2HPO4)
10X salt solution (To prepare 0.5L: 5 g KH2PO4,
0.5 g C aC l2, 2.5 g MgSO4, 50 g Ammonium tartrate, 0.5 g NaCl)
mineral oil or saturated Ca(OH)2 solution
pH paper
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7
glucose test strips
Procedure
Caution: The acids and bases in this experiment are corrosive. Be careful handling these substances.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
Work in a group of 4. Each group will be assigned to start with sucrose or grape juice or apple juice. The class will
combine data.
1. Fermentation. A typical fermentation takes one week.
a. Measure the mass of starting material (sucrose or grape juice or apple juice or corn starch or potato starch).
(i) For sucrose,
a)
b)
c)
d)
e)
f)
Add half an envelope of dry yeast (3.5 g) to 50 mL of water in a beaker. (What does yeast do?)
Add 0.35 g of sodium hydrogen phosphate. (What does Na2HPO4 do?)
Transfer the slurry to a 500-mL round bottom flask.
Dissolve 51.5 g sucrose in 150 mL of water. Add this sucrose solution to the slurry in the RB flask.
Shake to complete mixing.
Go to Step b.
(ii) For grape juice or apple juice, place 200 ml of fruit juice in a 500 ml round bottom flask. Add 3.0 g of dry yeast. Swirl
the mixture to dissolve the yeast. Then, go to Step b.
(iii) For potato starch,
a) Weigh approximately 50 g of potato starch and combine with 100 mL of water. The starch will not dissolve, but
swirl to get an even distribution.
b) Add 25-mL of 6M HCl to the mixture and heat to just below boiling for 45 minutes. (What does the acid do?)
c) Remove the mixture from the heat and cool to room temperature. The mixture will be a caramel/brown color.
d) Neutralize the acid by adding 25 mL of 6 M NaOH. (Which acid is neutralized?)
e) Then adjust the pH with 20 mL of 1 M pH 6 phosphate buffer (Why is it important to adjust the pH?). Use a pH
test strip to confirm that the pH is about 6.2 (a little lower is OK, but the pH should not exceed 6.5).
f) Test the glucose content with a glucose test strip. The glucose content should be at least 100 mM. If you do not
have sufficient glucose, repeat the acid treatment, because you will not obtain sufficient ______ next week. If your
glucose concentration exceeds 100 mM, you can obtain a more accurate reading by preparing a dilution of 1 mL
th
of your potato mash in 9 mL of water and measuring the glucose concentration of this 1/10 dilution.
g) Place the mixture in a 500 mL round bottom flask and add 20 mL of the 10X salt solution and 3.0 g of yeast. Swirl
the mixture to dissolve the yeast. The potato starch has been stripped of all cellular debris, and the 10X salts
provide essential salts and a nitrogen source for yeast metabolism.
h) Go to Step b.
(iv) For corn starch, do the same procedure as potato starch.
b. Fermentation set up:
Fit the RB flask with a one-hole rubber stopper containing a bent glass tube that dips below the surface of a saturated
aqueous solution of mineral oil in a test tube.
The seal will prevent air and unwanted enzymes from entering flask, but gases w illbe able to esc ape.
Place the set-up in a warm place for 1 week, at which time the evolution of CO2 gas w illhave ceased.
c. After a week, the fermentation reaction should be complete. Now you want to measure the volume of ethanol you
produced and the % ethanol
Separate the liquid (ethanol) from the solid sediment. Try one or a combination of these methods:
(i) carefully remove the glass tubing in the mineral oil without disturbing the sediment.
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8
Use a pipet to transfer the clear supernatant liquid from the flask to another container.
Avoid drawing any sediment into the pipet.
If you are not able to separate all of the liquid from the sediment, remove the sediment by centrifugation.
(ii) filter the mixture.
Add about 5 g of Celite filter aid for every 100 ml of fermented broth.
Swirl this mixture to wet the Celite.
Yeast cell debris can clog the pores of filter paper; Celite catches yeast cell debris before it reaches the filter paper.
(iii) if you see large pieces of solid, filter the fermented broth through a cheesecloth.
Then, filter the filtrate as in (ii).
d. (i) Measure the volume of the liquid you collected from Step 1c.
(ii) Measure the density of this liquid.
(iii) Determine the ethanol composition from density (see CHM 1A Lab 2). Use Table 2 to determine % ethanol.
(iv) Calculate the volume of ethanol produced per gram of sugar source you started with.
Hint: use the volume from Step 1d(i), the % ethanol from Step 1d(iv), and the mass of sugar source you used in Step ___.
(v) Share these data from (i) through (iv) with the rest of the class.
(vi) Summarize your data and results in Table 3.
Table 2. Density of Ethanol and Water Mixtures (Reference: D. D. Holmquist and D. Volz, “Chemistry With Computers”,
2000, Vernier Software and Technology, p. 8-3)
% Ethanol
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
Density, g/ml
0.998
0.995
0.991
0.988
0.985
0.982
0.979
0.977
0.974
0.971
0.969
0.966
0.964
0.960
0.957
0.954
0.950
% Ethanol
34
36
38
40
42
44
46
48
50
52
54
56
58
60
62
64
66
Density, g/ml
0.947
0.943
0.939
0.935
0.931
0.927
0.923
0.918
0.913
0.909
0.905
0.900
0.896
0.891
0.887
0.882
0.877
% Ethanol
68
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
Density, g/ml
0.872
0.868
0.863
0.858
0.853
0.848
0.843
0.839
0.834
0.828
0.823
0.818
0.813
0.807
0.801
0.795
0.789
2. Determine which sugar source produces the most ethanol. Rank the sugar sources from highest to lowest.
Table 3. Sugar fermentation data and results.
Sugar source
sucrose
Grape juice
Mass of sugar source, g
Volume of ethanol
solution, ml
Density, g/ml
% ethanol
Volume of ethanol, ml
Volume of ethanol/g
sugar source, ml/g
Apple juice
3. Optional. Do you want wine or moonshine?
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9
Corn starch
Potato starch
a. Distill your alcohol mixture. (Simple or fractional distillation? At what temperature should you collect distillate?) When
o
the distillation mixture starts boiling, collect 1 ml fractions until the temperature rises above 78 C. At this point, the
distillation will slow.
b. Determine the ethanol content in each fraction. (One way is by density.)
c. Did you get pure ethanol?
4. Optional. What happens to ethanol when a person drinks it?
a. To oxidize ethanol, I would use ____. The product of this oxidation reaction is ____.
b.
see alcohol oxidation with bleach http://ochemonline.pbworks.com/f/03_bleach_oxidation_handout.pdf
http://organic.chem.tamu.edu/Prelab.PowerPoints/Printed%20Slides%20%20237/Oxidation%20of%20a%20Secondary%20Alcohol-12c.pdf
http://faculty.ycp.edu/~khalliga/Courses/CHM%20236/Spring%202011/Lab/Experiments/Expt%202_Bleach%20Oxidation
%20of%20Secondary%20Alcohols%20to%20Ketones.pdf
Waste Disposal: solids – in trash.
Ethanol – in sink.
Questions
1. a. Show your Table 3.
b. Rank the sugar sources from best to worst to make ethanol. Include numbers.
c. Relate your ranking to the sugar type. In other words, does the best sugar source contain the most sucrose, glucose,
fructose, or other sugar?
d. You want to make 1000 liters of ethanol. Which sugar source would you use to make this volume? Give reasons.
2. a. What is the function of the yeast in the fermentation reaction?
b. For what reason is sodium hydrogen phosphate used in the sucrose fermentation? (Hint: under what conditions does
yeast work?)
c. Explain why the grape/apple juice preparation does not require the reagents needed to prepare sugar, potato starch,
and corn starch for fermentation. (Hint: what specific sugar undergoes fermentation? How is this sugar made from the
sugar source?)
d. Cheap wine turns to vinegar. What type of reaction occurs? What reagent makes this reaction occur?
3. See the 10 steps of glycolysis in Figure 1 in the Introduction.
a. Starting from the aldehyde carbon, label each carbon in glucose from 1 to 6. For each reaction step, map the location of
each carbon in glucose. In other words, label each carbon in each compound with the number that came from each
numbered carbon in glucose.
b. The first step of glycolysis is a substitution reaction. At which atom in glucose does substitution occur? (Note: this
reaction is a nucleophilic acyl substitution reaction, which is slightly different than the nucleophilic substitution reactions
we covered in CHM 12A.)
c. The second to last step of glycolysis is an ______ reaction. Which C is the alpha carbon? Which H is bonded to the
beta carbon? What is the leaving group?
d. See Figure 2 in the Introduction. Map the carbons in pyruvate to the carbons in ethanol.
e. Which carbons from glucose form the carbons in ethanol?
f. In glycolysis and fermentation, a C-C bond breaks so a big molecule produces small molecules. Name a CHM 12A
reaction that breaks a carbon-carbon bond.
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10
Lab 2. What a Pain! Phenacetin Synthesis from Acetaminophen
What reaction conditions converts acetaminophen to phenacetin? Which functional group reacts? What conditions makes
this reaction occur in the reverse direction?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. Take a look at an Acetaminophen tablet. Is it pure Acetaminophen? If not, what other substances are in the tablet?
2. a. Using Lewis structures, write a chemical equation that represents the synthesis of phenacetin from acetaminophen.
b. Identify the functional group(s) in each reactant and product.
c. Which reactant is chiral? Identify the chirality center(s).
d. Which reactant is an acid? Identify the acidic H. State the pKa of this acid.
e. Which reactant is a base? Identify the basic atom. Draw the conjugate acid of this base. State the pKa of this acid.
f. Identify the nucleophile(s) and electrophile(s). If there is more than one nucleophile or electrophile, identify the best
nucleophile/electrophile. Use curved arrows to show how the nucleophile reacts with the electrophile.
g. This reaction is a ____ reaction.
o
o
o
i. Identify the alpha carbon. Is this carbon 1 , 2 , or 3 ?
h. Identify the leaving group. Is this leaving group a good or poor leaving group?
i. Identify the beta carbon. Is there a H bonded to this C?
j. Calculate the moles of each reactant in each reaction. Identify the limiting reactant. Calculate the theoretical yield of
product.
k. What property of the product distinguishes it from the reactant? How will you characterize the product?
Table 1. Chemical Properties of Lab 2 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
m.p.,
o
C
Polar
or nonpolar?
Objectives
1. convert an alcohol to an ether by substitution reaction
2. synthesize phenacetin from Acetaminophen
3. analyze your sample by HPLC
4. propose a reaction mechanism
Reference: 1. B.D. Williams, B. Williams, and L. Rodino, “Synthesis of the Sweetener Dulcin from the Analgesic
Acetaminophen”, J. Chem. Educ., 2000, 77, 357-359.
Introduction
If you have a headache, you take a pain reliever, such as acetaminophen (Tylenol). In this lab, you will take
acetaminophen and convert it into phenacetin, another pain reliever. Phenacetin was banned by the Food and Drug
Admininstration (FDA) in 1983 due to adverse side effects including increased risk of certain cancers and kidney damage.
Phenacetin is metabolized to acetaminophen. Interestingly, acetaminophen replaced phenacetin in some over-the-counter
medications following the ban.
Once you make phenacetin, you will identify the reaction conditions to convert the phenacetin back to acetaminophen and
do your experiment. In other words, reverse the reaction.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
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11
•
Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
Materials
Tylenol tablets
1 M NaOH in ethanol
HPLC
ethyl iodide
1 M HCl (aq)
IR
NMR
Procedure
Caution: The acids and bases in this experiment are corrosive. Be careful handling these substances.
Part 1. Synthesize phenacetin from acetaminophen.
1. Synthesis
a. Grind 2 tablets of Tylenol (350 mg of acetaminophen per tablet or an equivalent amount) using a mortar and pestle.
Place the powder in a 50-mL round bottom flask with a magnetic stir bar.
b. Add 5.25-mL of 1M ethanolic NaOH solution to the Tylenol.
What does the ethanol or NaOH do?
c. Attach a condenser to the RB flask and bring to a vigorous reflux. Maintain reflux for 15 minutes. Then, remove the
flask from its heat source.
While you are refluxing, go to Step 4.
d. To the hot solution, add 0.7 mL of ethyl iodide.
Is the ethyl iodide the limiting reactant?
Reflux for an additional 15 minutes.
2. Workup
a. Filter the hot solution under vacuum through a Buchner funnel and into a filter flask containing a mixture of ice and
water. The insoluble starches should be collected on the filter paper.
b. The phenacetin precipitates from the filtrate as a white solid upon contact with the cold water.
c. While still cold, collect the solid phenacetin by vacuum filtration.
Wash with ______ water.
d. Dry the solid in the oven at 100 °C for 5 to 10 minutes or by place the sample on a watch glass over a heat source not
exceeding 100 °C.
e. The phenacetin prepared by this method is generally pure.
If necessary, you can further purify the phenacetin by recrystallization from hot water. Use decolorizing charcoal if the
impure phenacetin is ____.
Waste Disposal: solids – in solid waste.
Ethanolic NaOH – neutralize with acid and dispose in sink.
Any solution containing iodide – in halogenated waste.
3. a. Determine the % yield.
b. Characterize the product by:
(i) melting point.
(ii) IR.
(iii) HPLC.
(iv) NMR
c. Summarize your data and results in Table 3.
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12
Table 3. Phenacetin synthesis data and results.
Run 1
Method
reflux
Mass of acetaminophen
Moles of acetaminophen
Volume of 1 M NaOH
Moles of NaOH
Limiting reactant
Moles of Phenacetin
Theoretical yield of Phenacetin, g
Actual yield of Phenacetin, g
% yield of Phenacetin
o
Experimental melting point range, C
o
True melting point, C
Run 2
microwave
4. Repeat the experiment except this time use the microwave oven to heat your reaction mixture instead of doing a reflux.
Part 2. Synthesize acetaminophen from phenacetin. (Phenacetin is metabolized to acetaminophen.)
1. Identify the reaction conditions to convert phenacetin to acetaminophen. Explain the purpose of each step.
Use the mass of phenacetin you made in Part 1.
2. a. Do your experiment.
b. Characterize your product.
c. Summarize your data and results in a table.
Waste Disposal:
Questions
1. For each reaction, report the following:
a. % yield,
b. characterization data and results. Did you make your desired product?
2. In the synthesis of phenacetin from acetaminophen, an alcohol is converted to an ether.
a. Is the –OH in acetaminophen a nucleophile or electrophile?
b. What is the function of the ethanol/NaOH?
c. What is the function of the CH3CH2I?
d. Describe the mechanism of this reaction. Identify the nucleophile in each step. Use curved arrows to show bonds
breaking and forming. What is the leaving group?
e. Would you get phenacetin by treating acetaminophen with sulfuric acid followed by ethanol? Give reasons.
3. In the synthesis of acetaminophen from phenacetin, an ether is converted to an alcohol.
a. Explain the purpose of each reaction step in your procedure.
b. Describe the mechanism of the synthesis of phenacetin from acetaminophen. Identify the nucleophile in each step. Use
curved arrows to show bonds breaking and forming. What is the leaving group?
c. Is there another nucleophile or electrophile that can react with the reagent(s) you chose that could interfere with your
desired reaction? In other words, is there another atom in phenacetin that could react with your chosen reagent so
acetaminophen was not produced? If so, which atom in phenacetin reacted with your reagent and what compound was
produced?
d. How is the phenacetin to acetaminophen related to the sucrose hydrolysis to glucose and fructose reaction? (Hint: think
functional group conversion.)
e. In theory, can sucrose be hydrolyzed (see Lab 1) under the same reaction conditions as the conditions you used for the
phenacetin to acetaminophen reaction? Give reasons.
4. Is there a common intermediate in each mechanism? In so, what makes the reaction go in one direction or the other
once this intermediate forms? (Remember, many organic reactions are reversible.
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13
Lab 3. What Did I Make? Structure Characterization: IR, NMR, and MS
How do I determine the structure of a compound? Can one technique be used to determine structure or a combination of
techniques?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. a. What does “characterize a compound” mean?
b. Name two characterization methods that you used in Chem 12A lab.
2. a. Spectroscopy involves the interaction of _____ with _____.
b. Describe how light is produced.
c. Use your answer to 2b to explain how an IR spectrum of an organic compound is measured.
1
3. NMR spectroscopy gives information about the environment around a nucleus with non-zero nuclear spin, such as H.
a. In NMR, a magnetic field excites an electron in a lower energy nuclear spin state to a ____ nuclear spin state.
b. The number of peaks in a NMR spectrum is based on the number of non-equivalent nuclei in a molecule.
(i) Consider the carbon atoms in ethane. Is the environment (other atoms) around each C the same (equivalent) or
different (non-equivalent)?
Hint: make two molecular models of ethane. On one model, replace one C (black ball) with a blue ball.
On the second model, replace a different C (different black ball) with another blue ball.
Compare the two models. Are they the same? If so, the two C’s that you replaced with a blue ball are equivalent.
13
(ii) How many peaks would you expect to see in a C NMR spectrum?
c. (i) Consider the carbon atoms in propane. Is the environment (other atoms) around each C the same (equivalent) or
different (non-equivalent)?
Hint: make two molecular models of propane. On one model, replace one C (black ball) with a blue ball.
On the second model, replace a different C (different black ball) with another blue ball.
Compare the two models. Are they the same? If so, the two C’s that you replaced with a blue ball are equivalent.
13
(ii) How many peaks would you expect to see in a C NMR spectrum?
Objectves
1. Identify and distinguish between different characterization methods, e.g., IR, NMR, and MS, for organic compounds.
2. use and operate an IR spectrometer; interpret an IR spectrum. (You did this in CHM 12A Lab.)
1
13
1
3. Use and operate a NMR spectrometer; interpret a H and C NMR spectrum. (You did H NMR in CHM 12A Lab.)
4. interpret a mass spectrum.
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014, Ch. 15 and 16
rd
2. Williamson, “Macroscale and Microscale Organic Experiments”, 3 ed., Houghton-Mifflin, 1999, Chapters 12 and 13
3. NIST WebBook, http://webbook.nist.gov/chemistry/
4. UCLA WebSpectra, http://www.chem.ucla.edu/~webspectra/
5. Wired Chemist, http://www.wiredchemist.com/nmr/instructional/nmr_inst.html
Introduction
You’ve just synthesized, separated, isolated, and purified a compound. How do you determine, or characterize,
the structure of your compound? Organic chemists use infrared spectroscopy (IR), ultraviolet-visible (UV-VIS)
spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS) to help them identify
compounds. Each of these techniques requires a small amount of sample and a spectrum is quickly and easily obtained.
However, IR and UV-VIS spectrometers are relatively inexpensive whereas an NMR spectrometer is usually beyond the
budget of most community colleges. IR, UV-VIS, and NMR are non-destructive whereas MS is destructive to compounds.
MS provides information on the molecular weight of a compound, IR gives information regarding the functional groups
present, UV-VIS is used to identify conjugated π electron systems, and NMR is used to identify the carbon-hydrogen
framework. Each of these techniques by itself may not give enough information to determine the structure of a substance.
Used in conjunction with each other, these characterization techniques are a very powerful way to characterize a
compound.
Nuclear Magnetic Resonance Spectroscopy
NMR is another type of spectroscopic technique which involves absorption and emission. We know that electrons
1
13
have spin. Spin refers to its orientation in space. Certain nuclei, such as H and C, have spin. In NMR, nuclear spin is
studied. When an external magnetic field is applied to a molecule, the nuclear spins either aligns with the magnetic field or
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14
against the magnetic field. These nuclear spin states (levels) split into a high energy state and low energy state. When the
compound is irradiated with radio waves, these nuclear spins undergo a transition (called a spin flip in NMR) from a lower
1
energy state to a higher energy state. This is the NMR effect. Based on this description, we would think that a H nucleus
13
splits a certain amount and a C splits a different amount. If this were so, then we would not be able to determine the
structure of organic compounds using NMR. The NMR effect depends on the environment around each nucleus. The
environment is the electrons that surround each nucleus. Since electrons have charge and are in motion, they set up their
own local magnetic field around each nucleus (recall electricity and magnetism in your physics class). This local magnetic
field works against the applied magnetic field and changes the actual or effective magnetic field felt by each nucleus. For
1
example, if we were looking at H NMR, a H bonded to an O will have a different effective magnetic field than a H bonded
to C. We can see these differences in effective magnetic field in NMR and can determine the carbon-hydrogen framework
based on an NMR spectrum.
In NMR, intensity or absorbance is plotted on the y axis and chemical shift is plotted on the x axis. Chemical shift
1
13
refers to the effective magnetic field strength felt by the nucleus (usually H or C). Since magnetic field strength is very
1
small, the difference in magnetic field strength between the sample and a reference standard (TMS) is plotted. In a H
NMR spectrum, look at the following features:
1. number of peaks - gives information on the number of different types of H in compound.
2. size of peaks - gives information on number of each type of H in compound.
3. position of peaks - gives information on the environment around H, i.e., atoms or groups of atoms bonded to H.
4. splitting of the main peak into groups of peaks - gives information on the number of protons bonded to a neighboring
carbon.
The same features are also seen in NMR spectra for other nuclei.
Mass Spectrometry
In MS, a sample is bombarded with high energy electrons and dislodges a valence electron from the compound to
form a cation radical:
Sample + high energy electron ---> [sample] • + other fragments
+
(1)
where [sample] • is the molecular ion. The ions that are produced go through a magnetic or electric field and are
deflected. What determines the amount of deflection? (The amount of deflection depends on the fragment size of the ion.)
A mass spectrum is usually represented as a bar graph with the mass to charge (m/z) ratio of the ion plotted on the x axis
and the intensity plotted on the y axis. The base peak (tallest peak) is usually the molecular ion peak. The m/z ratio for the
base peak is used to determine the molecular weight of the compound. The sample is broken into smaller fragments.
These fragments can be used to determine identity of molecule. For Chem 12A, just know that the molecular ion peak
tells us the molecular weight of the compound.
+
Materials
molecular model kits
Bruker FT-IR
ChemDoodle NMR spectrum simulator (or Chemagic.com NMR simulator)
Various organic solvents
picoSpin NMR
Procedure
Caution: The organic solvents in this experiment are flammable and hazardous.
1. IR and MS. Klein, Ch. 15 Problems.
2. NMR and MS.
a. Consider the compounds: hexane, ethanol, acetic acid, ethyl acetate, methyl ethyl ketone, toluene, xylene isomers,
Ibuprofen.
For each compound, do the following:
(i) Draw the structure using ChemDoodle.
1
(ii) Select the structure. Then, go to the Spectrum menu, go to Generate, and choose H NMR to see the spectrum.
How many peaks (signals) are shown in the spectrum? Do the number of peaks match the different types of H’s?
Look at the integration of each peak. Does the integration match the equivalent H’s?
Check the splitting of each signal. Does the splitting match the structure?
Based on this information, match each peak to each H in your structure.
13
(iii) Select the structure. Then, go to the Spectrum menu, go to Generate, and choose C NMR to see the spectrum.
How many peaks (signals) are shown in the spectrum? Do the number of peaks match the different types of H’s?
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15
Match each peak to each C in your structure.
(iv) Select the structure. Then, go to the Spectrum menu, go to Generate, and choose Mass Parent Peak to see the
spectrum.
Does the Mass Parent Peak match the molecular weight of the compound?
b. Your group will learn to use the NMR spectrometer. Your instructor will demonstrate the use and operation of this
instrument.
c. You will work in groups to identify a compound from an NMR spectrum. You will present your results to the class.
Sketch spectrum on board, draw your proposed structure and interpret each H NMR spectrum. Look at the:
• number of peaks - number of different types of H in compound
• size of peaks - number of each type of H in compound
• chemical shift (position of peaks) - environment around H, i.e., atoms or groups of atoms bonded to H
• splittings into groups of peaks
Problems from UCLA WebSpectra, http://www.chem.ucla.edu/~webspectra/ Beginning Compounds 1-4.
The chemical formula is given for each compound. Use the degree of unsaturation formula to determine the number of pi
bonds or rings or both.
One way to determine structure: draw a possible structure based on formula, see if NMR spectrum (number of peaks =
number of non-equivalent H’s, peak height, chemical shift, and splitting) fits.
Another way to determine structure: number of peaks = number of non-equivalent H’s, match chemical shift to
environment, look at splitting patterns to determine number of H’s on adjacent carbon, compare peak height,
3. Klein, Chapter 16, Problems 62-64 combine IR, MS, and NMR to identify a compound.
4. More practice: http://www.chem.ucalgary.ca/courses/351/Carey5th/Carey.html#4 Chapter 13.
Waste Disposal: a mind is a terrible thing to waste.
Questions
1. IR spectroscopy gives information about bond types. Compare a C-H bond to a C-O bond. Identify the factors that
make these two bonds different. How are these differences shown in an IR spectrum?
1
2. NMR spectroscopy gives information about the environment around a nucleus with non-zero nuclear spin, such as H
13
and C. The number of peaks in a NMR spectrum is based on the number of non-equivalent nuclei in a molecule.
a. Consider the hydrogen atoms in ethane.
(i) Is the environment (other atoms) around each H the same (equivalent) or different (non-equivalent)? How many peaks
1
would you expect to see in a H NMR spectrum?
(ii) Is the environment (other atoms) around each C the same (equivalent) or different (non-equivalent)? How many peaks
13
would you expect to see in a C NMR spectrum?
b. Consider the hydrogen atoms in propane.
(i) Is the environment (other atoms) around each H the same (equivalent) or different (non-equivalent)? How many peaks
1
would you expect to see in a H NMR spectrum?
(ii) Is the environment (other atoms) around each C the same (equivalent) or different (non-equivalent)? How many peaks
13
would you expect to see in a C NMR spectrum?
3. In mass spectrometry (MS), an electron collides with a molecule and forms an ion and breaks the molecule into
fragments. What type of ion is formed? What information about a molecule does this ion in a MS tell you?
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16
Lab 4a. Eat Your Vegetables: Tomato Rainbow
What chemical causes the color of plant pigments? What structural feature causes the color of the pigment? How can I
change the pigment color?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. Lycopene is the red pigment in tomatoes.
a. Draw the structure of lycopene.
b. The Woodward-Feiser rules are used to predict λmax for a conjugated compound with four pi bonds or fewer. The
Fieser-Kuhn rules are used to predict λmax for a conjugated polyenes. See Reference 2 and apply these rules to predict
λmax for lycopene.
Table 1. Chemical Properties of Lab 4 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
b.p./m.p.,
o
C
Polar
or nonpolar?
Objectives
1. Name and classify conjugated dienes; identify their physical and chemical properties, especially reactivity trends.
2. Investigate addition and oxidation reactions of lycopene
3. Measure and interpret UV-VIS spectra of lycopene and addition/oxidation products
4. Develop a HPLC method to separate plant pigments
5. Use Woodward-Feiser rules to predict λmax.
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014, Ch. 17
2. Fieser-Kuhn rules: http://pharmaxchange.info/press/2013/05/ultraviolet-visible-uv-vis-spectroscopy-%E2%80%93fieser-kuhn-rules-to-calculate-wavelength-of-maximum-absorption-lambda-max-of-polyenes-with-sample-problems/
3. Tomato juice “rainbow”: http://spot.pcc.edu/~mdeming/102/Labs/CH102_Lab_7_Chromatography.pdf and
http://faculty.chemeketa.edu/jcammack/CH2413B%20Lab/CH241B%20Labs/7%20CH241%207%20%20Bromination%20of%20Tomato%20F13.pdf
Introduction
From drugs, such as caffeine, morphine, salicilin, and tamoxifen, to dyes, such as indigo, to fabrics, such as
cotton and wool, natural products have found many uses over the years. Chlorophyll, carotene, and lycopene are colored
pigments found in plants.
Chlorophyll, carotene, and lycopene have a conjugated system of alternating carbon-carbon single bonds and
carbon-carbon double bonds over which the pi electrons are delocalized. The color arises from π  π* transitions. UV-VIS
spectroscopy is a useful tool for studying conjugated systems.
The electronic transitions of an atom or molecule are studied using UV-VIS spectroscopy. A transition from one
electron energy state (energy level) to another involves much greater energies than a transition from one vibrational state
to another as in IR spectroscopy. In organic chemistry, UV-VIS spectroscopy is used to identify π electron systems, such
as conjugated dienes, aromatic compounds, and compounds containing the carbonyl (C=O) group. Molecular orbital (MO)
theory is used to describe these electronic transitions and its effect on bonding. In a typical conjugated organic molecule,
absorption of a visible or UV photon will excite an electron from the highest occupied molecular orbital (HOMO), which is
usually a π bonding molecular orbital, to the lowest unoccupied molecular orbital (LUMO), which is usually a π antibonding
molecular orbital. This π  π* transition often causes a bond to break. A chromophore is the structural unit associated
with the electronic transition. In general, a colored organic compound has a conjugated π system. A database of UV-VIS
spectra helps organic chemists identify the chromophores or structural units in organic compounds.
In this lab, you will investigate lycopene addition and oxidation reactions by observing color and measuring and
analyzing UV-VIS spectra. We will use HPLC to determine the number of products produced in each reaction.
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17
Woodward and Fieser developed rules to predict λmax for conjugate dienes up to 4 pi bonds. These rules don’t
work well for conjugated polyenes such as carotene and lycopene. Fieser and Kuhn came up with rules to predict λmax.
See Reference 2. You will apply these rules to the lycopene reactions to try to figure out the structure of products.
Materials
Tomato paste
Bromine water
1 M HCl
bleach
UV-VIS spectrometer
Procedure
Caution: Bromine and bleach are a strong oxidizers. HCl is corrosive.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
Lycopene and the tomato juice “rainbow”.
1. a. Weigh about 15 g of tomato paste in a beaker.
b. Add about 30 mL of water and stir.
c. Transfer the tomato juice into a 50 mL graduated cylinder.
d. Set aside about 2 ml of the tomato juice. Use 0.5 ml for a UV-VIS spectrum measurement, 0.5 ml for a HPLC sample,
and the remainder for tests with HCl and bleach.
2. a. In the fume hood, measure 10 mL of bromine water in a 10-mL graduated cylinder. Add about 5 mL of bromine water
to your tomato juice and stir gently with a glass rod. Then add the rest of the bromine water and stir gently with both a
circular motion and an up and down motion.
b. Observe the colors and their positions in the cylinder.
3. Carefully take a sample of each color. For each colored sample,
a. measure the UV-VIS spectrum.
b. Run a HPLC. Each group will contribute one sample for HPLC.
c. Based on the color and λmax from your UV-VIS spectrum, use Feiser-Kuhn rules to predict the number of pi bonds.
(Note: the textbook shows you how to determine λmax from the number of pi bonds. Here you are working backwards from
λmax to the number of pi bonds.)
4. Place 0.5 ml of the tomato paste sample you saved from Step 1d in a test tube. Add HCl dropwise until you see a color
change. Record the color(s).
5. Place 0.5 ml of the tomato paste sample you saved from Step 1d in a test tube. Add bleach dropwise until you see a
color change. Record the color(s).
6. Summarize your data and results in Table 2.
Table 2. Tomato rainbow data and results.
Method
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Run 1
reflux
Run 2
microwave
18
Waste Disposal: tomato juice – in sink. Bromine solution – in halogenated waste.
Questions
1. a. Summarize your data and results in a table (reaction, color, λmax)
b. Report the number of products in each reaction based on HPLC
2. a. For the lycopene + Br2 reaction, determine the structure of each colored substance based on color and number of pi
bonds based on color, λmax, and Fieser-Kuhn rules.
b. Based on the structures from part 2a, describe the mechanism of this reaction.
3. a. For the lycopene + HCl reaction, determine the structure of each colored substance based on color and number of pi
bonds based on color, λmax, and Fieser-Kuhn rules.
b. Based on the structures from part 3a, describe the mechanism of this reaction.
4. a. For the lycopene + bleach reaction, determine the structure of each colored substance based on color and number of
pi bonds based on color, λmax, and Fieser-Kuhn rules.
b. Based on the structures from part 4a, describe the mechanism of this reaction.
5. In CHM 12A, we looked at ozonolysis reactions. Does lycopene undergo ozonolysis? If so, draw the structure of the
products of this reaction.
6. a. UV-VIS spectroscopy gives information about conjugated π electron systems. What is a conjugated π electron
system? Name two functional groups that have a conjugated π electron system.
b. Carotene is treated with one molar equivalent of HCl. Draw the structure of the intermediate(s) and product(s) of this
reaction.
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19
Lab 4b. Eat Your Vegetables: Solar Cell from Plant Pigments
What chemical causes the color of plant pigments? What structural feature causes the color of the pigment? How can I
change the pigment color?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. a. What substance is responsible for the color in raspberries? Draw the structure of this substance. Is this substance
conjugated?
b. What substance is responsible for the color in blueberries? Draw the structure of this substance. Is this substance
conjugated?
c. What substance is responsible for the color in blackberries? Draw the structure of this substance. Is this substance
conjugated?
Objectives
1. Name and classify conjugated dienes; identify their physical and chemical properties, especially reactivity trends.
2. Make a dye sensitized solar cell (DSSC).
3. Measure and interpret UV-VIS spectra of lycopene, raspberry, and blueberry.
4. Use Woodward-Feiser rules to predict λmax.
Table 1. Chemical Properties of Lab 4 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
b.p./m.p.,
o
C
Polar
or nonpolar?
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014, Ch. 17
2. Fieser-Kuhn rules: http://pharmaxchange.info/press/2013/05/ultraviolet-visible-uv-vis-spectroscopy-%E2%80%93fieser-kuhn-rules-to-calculate-wavelength-of-maximum-absorption-lambda-max-of-polyenes-with-sample-problems/
3. Y.R. Smith, E. Cone, V. Subramanian, “A Simple Photocell to Demonstrate Solar Energy Using Benign Household
Ingredients”, J. Chem. Educ., 1013, 90, 1358-1361. DSSC using raspberries.
4. DSSC using blueberries: http://zenofstem.com/project/diy-solar-cells-with-blueberry-juice/
5. DSSC using blackberries: http://sciencegeekgirl.com/activities/Blackberry%20solar%20cell.pdf
Introduction
"MORE ENERGY—in the form of sunlight—strikes Earth in one hour than all of the energy consumed by humans in an
entire year.” -- Nathan Lewis, Cal Tech
Currently, on a global scale, energy usage is on the order of 14 terawatts (14 trillion W or 14 trillion joules per
second), of which roughly 85% is generated by burning fossil fuels. (CEN, 8/27/07, p. 16) The sun showers Earth with
an energy flow of some 120,000 TW. Energy from the sun is ____ but we haven’t figured out a way to cheaply convert
sunlight to electricity. So far, polysilicon solar cells are 14% efficient and thin film solar cells are 8% efficient. The latest
prototypes DSSC are 15% efficient with current DSSCs at 11%. DSSCs are lower cost and have higher power conversion
efficiencies than silicon-based solar cells.
In this lab, you will make a DSSC using different dyes. We will see which dye works best. Many plant pigments
have a conjugated system of alternating carbon-carbon single bonds and carbon-carbon double bonds over which the pi
electrons are delocalized. The color arises from π  π* transitions.
DSSC Operation: A solar cell is a type of electrochemical cell (see CHM 1B). Oxidation occurs at the anode; reduction
occurs at the cathode. Sunlight enters the cell through the transparent conductive glass slide (ITO – indium tin oxide) top
contact, striking the colored dye on the surface of the TiO2. Photons with enough energy are absorbed by the dye to
create an excited state of the dye, from which an electron can be "injected" directly into the conduction band of the TiO2
(see valence band and conduction band in band theory). From there it moves by diffusion (as a result of an electron
concentration gradient) to the clear anode on top.
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20
Meanwhile, the dye molecule has lost an electron and the molecule will decompose if another electron is not provided.
The dye strips one from iodide in electrolyte below the TiO2, oxidizing it into triiodide. This reaction occurs quite quickly
compared to the time that it takes for the injected electron to recombine with the oxidized dye molecule, preventing this
recombination reaction that would effectively short-circuit the solar cell.
The triiodide then recovers its missing electron by mechanically diffusing to the bottom of the cell, where the counter
electrode re-introduces the electrons after flowing through the external circuit.
Materials
Students: Bring one of the following fruits:
Tomato juice
Raspberry tea or raspberries
Conductive glass slides (ITO)
Pencil/graphite rod
Rubbing alcohol or 95% ethanol
Parafilm or wax paper or scotch tape
Bunsen burner or candle
Ceramic crucible
Multimeter (Voltmeter/ammeter/ohmeter)
UV-VIS spectrometer
Blueberries
Blackberries
TiO2 (anatase)
Iodine tablets
Vinegar
Binder clips
hot plate
mortar/pestle
variable resistors
Procedure
Caution: Ethanol and rubbing alcohol are flammable and hazardous. Iodine is an oxidizer.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
1. Prepare a solution of the fruit dye.
Raspberry tea: Immerse a few tea bags in ~100 mL of boiling water after it was removed from the heat source.
Dip and steep the bags several times to make a dark red colored solution.
Cool the dye solution to room temperature.
Blackberries or Blueberries: blend or crush fresh or frozen blackberries or blueberries in a blender or by hand, adding a
tablespoon (15 ml) of water for every 10 blackberries.
Or take the juice from the bottom of frozen berries after they have thawed.
Tomato: filter tomato juice and use the filtrate (should not have any solid).
Anode preparation.
1. ID and clean the conductive glass slide.
a. Identify the conducting side of the glass slide.
Check the resistance of each side of the glass slide with a multimeter operated in the resistance mode.
The conducting side will have the ___ (higher or lower?) resistance, typically 10-40 Ω.
b. Clean the conducting side by swabbing with alcohol and drying in air.
Care should be taken, once cleaned, not to touch the conducting slide.
Use tweezers or hold the slide by the edges. Finger grease can increase resistance hence wearing gloves is
recommended.
2. Deposit TiO2 onto a conductive glass slide
a. Place a few grams of TiO2 into a mortar. Add a small amount of vinegar, a few mL’s at a time, to the TiO2 and use the
pestle to grind the mixture into a uniform paste. (It should be smooth and free of lumps.)
The final ratio of vinegar to TiO2 is approximately 5 mL to 3 g.
b. Cast (drop) a few drops of this slurry onto ~25 mm of the conducting side of the ITO plate.
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21
Deposit (distribute) a thin film of the TiO2 slurry uniformly by “painting” with a glass rod (a paint brush may also be used).
(See Reference 4 for pictures.)
o
c. Allow the anode to dry. You can expedite this process by using a hotplate at 80 C for about 10 min.
3. Staining the Anode
Fresh or frozen fruit or tea can be used as the dye to sensitize the anode. Dye pigments in fruits, such as blackberries,
4+
raspberries, or pomegranate, that contain several =O or –OH groups are capable of chelating the Ti sites on the titania
surface are desirable. Although several colored fruits, e.g., strawberries, and leaves contain anthocyanins, they may not
chelate to the titania surface if they do not possess the aforementioned functional groups.
We will test different dyes. Your instructor will assign your group to use a specific fruit.
After you have prepared your organic dye solution,
o
a. Drop cast the dye onto the titania-coated glass plates and allow the dye to dry over a hot plate at ~80 C.
Repeat this procedure several times until the white TiO2 is visibly red on the reverse side of the glass plate.
b. Store your dye filmed conductive glass slide in the dark until you are ready to use it.
c. Measure the UV-VIS spectrum of your leftover dye solution.
Record the wavelength(s) of light absorbed by your fruit pigment dye. λ = _____ nm.
Identify the chromophore (the substance that gives the fruit its color).
Draw the structure of the chromophore.
Apply the Woodward-Feiser or Feiser-Kuhn rules to determine the peak wavelength. Does this wavelength match the
experimental wavelength?
Alternate Method: Soak the anode in the dye solution until the white TiO2 is visibly colored on the reverse side of the glass
plate.
4. Counter electrode preparation
Prepare the counter electrode can be prepared while the drying the dye in the staining process of the titania anode
(previous step).
a. With another clean ITO glass plate (cleaned by swabbing alcohol), use a pencil or graphite rod to apply a light carbon
film on the entire conducting side of the ITO plate. Do not remove the ITO from the conductive glass slide!
o
b. A heat treatment can be carried out for a more stable electrode (350 C for 30 min in air), but this step is not critical.
Alternate method: hold the ITO glass slide above a candle flame until it is coated black.
5. Assemble the device
A schematic of the device assembly is given in Figure 1 (from Reference 3).
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22
Figure 1. The scheme explaining the steps in assembling the DSSC: (1) lay the parafilm/tape with an aperture on top of the TiO2dye/ITO plate; (2) place the carbon/ITO plate with the carbon side facing the TiO2-dye/ITO with the slides slightly offset; (3) attach
binder clips to the edges of the assembly; (4) add a few drops of the iodine mixture (electrolyte) to the side, gently working out any air
bubbles.
a. Prior to assembly, take a piece of parafilm or wax paper or folded tape ~20 x 20 mm. This serves as a separator
between the anode and cathode of the solar cell. Cut an aperture or window in the middle of the separator to an arbitrary
size and note the area.
b. Next, lay the TiO2-dye/ITO plate flat with the TiO2-dye facing up. Overlay the parafilm/wax paper/tape separator
followed by the carbon/ITO plate facing down.
c. “Sandwich” the assembly together using two binder clips on the long edge of the plates. The plates will need to be
slightly offset as shown in Figure 1 for contact point for the positive and negative electrodes of a potentiostat or
multimeter.
d. A solution prepared with a few iodine tablets in ethanol or water serves as the electrolyte. One to a few drops of this
solution can be placed at the edges of the plates. Opening each binder clip, alternately, will ensure the electrolyte fills the
void via capillary action. Once the device is assembled, it is ready to be tested.
6. Test the device
Test the device either inside (simulated light) or outside (direct/diffuse sunlight).
a. Connect an alligator clip and wire to each slide and to a multimeter.
b. Place the DSSC under light.
c. Measure the voltage and current.
d. Turn off or remove the DSSC from the light.
What happens to the voltage?
e. Repeat the dark/light cycle.
Does the voltage change with each cycle?
Note: During prolonged or continuous operation, the electrolyte may dry up; add few drops to the edge of the cell to
“revive” the device.
f. Share your data and results with the class.
g. Summarize the class data and results in Table 2.
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23
Table 2. DSSC data and results. Tomato, raspberry, blueberry, blackberry. Try 3 light/dark cycles.
Voltage,
Calculated
Chromophore Voltage,
Group Fruit
Color
Experimental
st
nd
2 cycle
1 cycle
λmax, nm
λmax, nm
Voltage,
rd
3 cycle
Optional: Additional testing of solar cell properties.
Plot I-V curve using potentiostat to vary resistance (or use fixed resistors in circuit)
Measure Power = I x V.
Fill factor
Power conversion efficiency
Waste Disposal: fruit juice – in sink.
Recycle the cell: Disassemble the cell.
TiO2 coated glass slide: If the TiO2 film is undamaged, wash the electrolyte off the glass slides with ethanol. Burn the old
o
dye off the TiO2 coated slide by sintering (heating) for 30 minutes at 450 C. Cool to room temperature and store in a
cellophane (glassine) envelope to prevent scratching or damage.
If the TiO2 film is damaged, wipe off the TiO2 off the glass slide with a tissue dampened with isopropanol or ethanol.
Carbon coated glass slide: wash the carbon coated slide with ethanol, then dry and store in the cellophane (glassine)
envelope.
TiO2 and vinegar suspension: save in a labelled and sealed bottle for reuse.
Electrolyte: keep free of water and seal the electrolyte bottle using wax paper.
Pipettes: recycle by rinsing in water and then isopropanol or ethanol.
Questions
1. a. Summarize the class data and results in a table (fruit, color, λmax, Voltage)
b. Identify the fruit dye that produced the highest voltage. Rank the fruit dyes by voltage.
c. UV-VIS spectroscopy gives information about conjugated π electron systems. Rank the fruits by absorption wavelength.
Is this ranking the same as the ranking in Report Question 1b?
d. What is the relationship if any, between λmax and the voltage produced?
2. A DSSC is a type of electrochemical cell. Describe how sunlight produces an electron. Then, describe the path of this
electron as it goes through your DSSC.
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24
Lab 5. Ring Around: Electrophilic Aromatic Substitution Reactions
How does a side group affect the rate of EAS? Does a pi bond in benzene react the same way as a pi bond in an alkene?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. a. Compare 1,3-cyclohexadiene to benzene. Which compound is aromatic? Give reasons. (Hint: see criteria for
aromaticity.)
b. What structural feature does each substance in the Materials section have in common?
c. What color is bromine? When Br2 reacts with a pi bond, what experimental observation tells you Br2 has reacted?
Table 1. Chemical Properties of Lab 5 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
b.p./m.p.,
o
C
Polar
or nonpolar?
Objectives
1. Name and classify arenes; identify their physical and chemical properties, especially reactivity trends.
2. Measure rate of EAS reactions
3. Determine which groups make EAS go faster. Propose a reaction mechanism.
4. Determine which groups make EAS go slower. Propose a reaction mechanism.
5. Predict EAS product of monosubstituted benzene.
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014, Ch. 18 and 19
2. Schoffstall, et al., “Microscale and Miniscale Organic Chemistry Laboratory Experiments”, McGraw-Hill, 2000 p. 289294.
3. S. Tantayanon, “Small Scale Laboratory: Organic Chemistry at University Level”, p. 73
(http://www.unesco.org/science/doc/Organi_chem_220709_FINAL.pdf)
Introduction
Alkenes and conjugated dienes undergo addition reactions. Aromatic compounds undergo electrophilic aromatic
substitution reactions (EAS). The rate of a EAS reaction depends on the substituent on the aromatic ring. Electrondonating substituents donate electron density to the benzene ring making the pi electrons more nucleophilic, thus
activating the ring and speeding up the rate of an EAS reaction. Electron-withdrawing substituents withdraw electron
density from the benzene ring making the pi electrons less nucleophilic, thus de-activating the ring and slowing down the
rate of an EAS reaction.
Materials
Part 1.
toluene
aniline
benzonitrile
chlorobenzene
phenol
acetanilide
anisole
biphenyl
ethylbenzene
phenyl acetate
acetophenone
benzoic acid
bromobenzene
methyl benzoate
0.05 M bromine in acetic acid
15 M acetic acid
Part 2.
Acetanilide
Potassium bromate, KBrO3
(or sodium bromate)
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glacial acetic acid
48% HBr
10% NaHSO3
25
Procedure
Caution: The organic compounds in this experiment are flammable. Some are toxic and are irritants.
Bromine is an oxidizing agent. Be careful handling the Br2 in acetic acid.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
Part 1. Use reaction rate to determine whether a group activates or deactivates the aromatic ring in EAS (adapted from
Reference 2).
1. a. Using the substituted benzene compounds assigned to your group, do a microscale bromination of substituted
benzene derivatives. You will measure the time elapsed for each bromination reaction to determine the relative EAS rate.
(i) For the liquid aromatic compounds, prepare 1 ml of 0.1 M solution using glacial acetic acid as the solvent.
Sample calculation: volume of liquid aromatic compound = 0.1 M x 0.001 l x molar mass / density
Measure this volume of liquid aromatic compound and add enough glacial acetic acid to make 1 ml of solution.
(ii) For the solid aromatic compounds, prepare 1 ml of 0.1 M solution using glacial acetic acid as the solvent.
Sample calculation: mass of liquid aromatic compound = 0.1 M x 0.001 l x molar mass
Measure this mass of liquid aromatic compound and add enough glacial acetic acid to make 1 ml of solution.
(iii) Calculate the moles of reactants, determine the limiting reactant, and calculate the theoretical yield of product.
o
b. Prepare a 40 C water bath.
Should the temperature of this bath be constant?
c. Obtain the number of test tubes equal to the number of substituted benzene compounds assigned to your group plus
one.
To your first test tube, add 1.0 ml of 0.1 M toluene.
To the other test tubes, add 1.0 ml of 0.1 M solution of each assigned substituted benzene compound.
o
d. Place each test tube in the 40 C water bath. Allow the solutions to reach thermal equilibrium.
2. a. Add 1.5 ml of 0.05 M Br2 in acetic acid all at once (not dropwise) to the test tube with the 0.1 M toluene.
Swirl the contents of the test tubes to mix.
Start timing.
When the red Br2 color disappears (the solution turns colorless or light yellow), record the _____.
b. Repeat this process with the other substituted benzene compounds.
Note: we want to determine how fast or slow each reaction is relative to toluene, e.g., reaction is faster than toluene or
slower than toluene.
3. a. The class will combine their data.
Which substituted benzene compound undergoes bromination the fastest?
Slowest?
Rank the substituted benzene compounds in order of fastest to slowest.
Based on the data and results, identify the groups that activates the ring. Identify the groups that deactivates the ring.
b. Summarize your data and results in Table 2.
Table 2. EAS data and results.
Compound
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time
Activating or Deactivating?
26
Waste Disposal: Bromine is a halogen so any solution that contains bromine – in halogenated waste.
Questions
1. a. Show your Table 2.
b. Rank of each compound from fastest (best electon donating group or activators) to slowest (best electron withdrawing
group or deactivators).
st
c. Compare your ranking to Klein, “Organic Chemistry,” 1 ed., Wiley, p. 883, Table 19.1 A List of Activators and
Deactivators by Category. How close does your ranking match Table 19.1?
2. Your group will present one reaction to the class. Relate your results to the mechanism of the reaction.
Part 2. Bromination of acetanilide (adapated from Reference 3).
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. a. Using Lewis structures, write a chemical equation that represents the synthesis of _____ from acetanilide and
bromine.
b. Identify the functional group(s) in each reactant and product.
c. Which reactant is chiral? Identify the chirality center(s).
d. Which reactant is an acid? Identify the acidic H. State the pKa of this acid.
e. Which reactant is a base? Identify the basic atom. Draw the conjugate acid of this base. State the pKa of this acid.
f. Identify the nucleophile(s) and electrophile(s). If there is more than one nucleophile or electrophile, identify the best
nucleophile/electrophile. Use curved arrows to show how the nucleophile reacts with the electrophile.
g. This reaction is a ____ reaction.
o
o
o
i. Identify the alpha carbon. Is this carbon 1 , 2 , or 3 ?
h. Identify the leaving group. Is this leaving group a good or poor leaving group?
i. Identify the beta carbon. Is there a H bonded to this C?
j. Calculate the moles of each reactant in each reaction. Identify the limiting reactant. Calculate the theoretical yield of
product.
k. What property of the product distinguishes it from the reactant? How will you characterize the product?
Procedure
Caution: Acetanilide is toxic and an irritant. Avoid skin and eye contact. HBr is corrosive and causes burns.
-
Note: instead of using concentrated Br2 solution, which is very corrosive, you will generate Br2 in situ from HBr and BrO3 :
+
6 H + 5 Br + BrO3 ---> 3 Br2 + 3 H2O
1. Synthesis
a. Weigh 200 mg (1.5 mmol) of acetanilide, 85 mg (0.5 mmol) of potassium bromate in the appropriate microscale round
bottom flask and 2 mL of glacial acetic acid to the flask and swirl the mixture until all the solid has dissolved.
b. Add 0.3 mL of 48% HBr and stir the mixture at room temperature for 30 minutes.
How many moles of Br2 are produced?
Which reactant is the limiting reactant?
While your reaction is occurring, go to Step 4.
2. Workup
a. Pour the mixture into a 100-mL beaker containing 25 mL of (ethanol or water?) and stir the mixture rapidly for 15
minutes.
b. Collect the solid product by _________ filtration.
What is this solid?
Wash the precipitate with several drops of 10% NaHSO3 and water to rem ove any residualbrom ine.
c. Recrystallize the crude product from ethanol.
d. After crystallization is complete, collect the crystals by ________.
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27
Wash the product with cold (ethanol or water?) and continue suction to dry.
e. Weigh the dry product. Determine % yield.
f. Measure the melting point.
3. Summarize your data and results in Table 3.
Table 3. Bromination of acetanilide reaction data and results.
Run 1
Method
reflux
Mass of acetanilide
Moles of acetanilide
Mass of potassium bromate
Moles of potassium bromate
Volume of 48% HBr
Moles of HBr
Moles of Br2
Limiting reactant
Moles of product
Theoretical yield of product, g
Actual yield of product, g
% yield of product
o
Experimental melting point range, C
o
True melting point, C
Run 2
microwave
4. Repeat the experiment except this time use the microwave oven to heat your reaction mixture instead of doing a stirring
at room temperature for 30 minutes.
Waste Disposal: Treat the filtrate with 10% NaHSO3 to destroy the left over HBr – in halogenated waste.
Solids – in solid waste.
Allternate Procedure (use Br2 in glacial acetic acid)
Caution: Acetanilide is toxic and an irritant. Avoid skin and eye contact. Br2 is corrosive and causes burns.
1. Synthesis
a. Weigh 200 mg (1.5 mmol) of acetanilide in the appropriate microscale round bottom flask.
Add 1 mL of glacial acetic acid to the flask and swirl the mixture until all the solid has dissolved.
b. Slowly add 1.8 mL of 1 M Br2 in glacial acetic acid and stir the mixture at room temperature for 30 minutes.
How many moles of Br2 are produced?
Which reactant is the limiting reactant?
2. Workup
a. Pour the mixture into a 100-mL beaker containing 15 mL of (ethanol or water?) and stir the mixture rapidly for 15
minutes.
b. Collect the solid product by _________ filtration.
What is this solid?
Wash the precipitate with several drops of 10% NaHSO3 and water to remove any residual bromine.
c. Recrystallize the crude product from ethanol.
d. After crystallization is complete, collect the crystals by ________.
Wash the product with cold (ethanol or water?) and continue suction to dry.
e. Weigh the dry product. Determine % yield.
f. Measure the melting point.
Waste Disposal: Treat the filtrate with 10% NaHSO3 to destroy the left over Br2 – in halogenated waste.
Solids – in solid waste.
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28
Questions
1. a. Report your Table 3.
b. Describe how you characterized the product. How do you know you made the desired product?
2. a. Write the mechanism of the bromination of acetanilide.
b. In Step 2a, you poured your reaction mixture in water. What solid formed? Why is water needed?
c. What is the purpose of adding 10% NaHSO3 to the solution? Write the equation of this reaction.
3. a. Bromination of aniline usually produces the trisubstituted tribromoaniline as the product. Explain why it is difficult to
control the number of substitutions when aniline undergoes EAS.
b. Why is an acetamido group less reactive toward electrophilic aromatic substitution at o- and p-positions than an amino
group? Explain by using resonance structures.
c. What product would you expect for the bromination of anisole? Would you expect difficulty controlling the number of
substitutions when anisole undergoes EAS? Give reasons.
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29
Lab 6. Making Big from Small: Grignard(-like) Reaction
What happens when a carbonyl carbon reacts with a base? What functional group is produced?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. a. Using Lewis structures, write a chemical equation that represents the reaction of benzaldehyde with allyl bromide
and Mg.
b. Identify the functional group(s) in each reactant and product.
c. Which reactant is chiral? Identify the chirality center(s).
d. Which reactant is an acid? Identify the acidic H. State the pKa of this acid.
e. Which reactant is a base? Identify the basic atom. Draw the conjugate acid of this base. State the pKa of this acid.
f. Identify the nucleophile(s) and electrophile(s). If there is more than one nucleophile or electrophile, identify the best
nucleophile/electrophile. Use curved arrows to show how the nucleophile reacts with the electrophile.
g. This reaction is a ____ reaction.
o
o
o
i. Identify the alpha carbon. Is this carbon 1 , 2 , or 3 ?
h. Identify the leaving group. Is this leaving group a good or poor leaving group?
i. Identify the beta carbon. Is there a H bonded to this C?
j. Calculate the moles of each reactant in each reaction. Identify the limiting reactant. Calculate the theoretical yield of
product.
k. What property of the product distinguishes it from the reactant? How will you characterize the product?
Table 1. Chemical Properties of Lab 6 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
b.p./m.p.,
o
C
Polar
or nonpolar?
Objectives: Name and classify carbonyl compounds; identify their physical and chemical properties, especially reactivity
trends.
1. synthesize an alcohol from a carbonyl compound using a Grignard-like reaction.
2. Make a big molecule from a small molecule and form a C-C bond.
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014, Ch. 20
2. “A Grignard-like Organic Reaction in Water,” G.W. Breton and C. A. Hughey, J. Chem. Educ. 1998, 75, 85.
3. “Small Scale Laboratory: Organic Chemistry at University Level,” Supawan Tantayanon, p. 101
(http://www.unesco.org/science/doc/Organi_chem_220709_FINAL.pdf )
Introduction
The Grignard reaction is a very common synthetic method to make a C-C bond. This reaction requires
scrupulously dry conditions. Any water present reacts with ___ and stops the reaction.
In this lab, you will perform a reaction that is similar to the Grignard reaction but can be done in aqueous
conditions. In this reaction, benzaldehyde reacts with allyl bromide in the presence of Zn to form a ___. A C-C bond forms
to make a bigger molecule from smaller molecules.
This Grignard-like reaction is “green” and hopefully more reproducible.
Materials
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30
Zn powder
Benzaldehyde
THF
Na2SO4
saturated NH4Cl (aq)
allyl bromide
diethyl ether
Procedure
Caution: Benzaldehyde is considered a hazardous substance by the US EPA.
Allyl bromide has an intense, acrid, and persistent smell – use in the fume hood.
THF and diethyl ether are flammable.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
1. Synthesis
a. Mix 0.256 g of zinc powder with 2 mL of a saturated aqueous NH4Cl solution.
b. To a 25-mL round-bottomed flask fitted with a condenser, add 2 mL of THF and 0.21 mL of benzaldehyde.
c. Add the Zn/NH4Cl mixture to the benzaldhyde/THF solution.
d. While stirring this mixture vigorously, dropwise add 0.21 mL of allyl bromide using a calibrated pipet through the
condenser. Make sure each drop is falls directly into the stirring mixture. (Your % yield will be lower if the allyl bromide
runs down the side of the condenser.)
What reacts with the allyl bromide?
What is the limiting reactant?
b. Stir the mixture for 30 minutes.
While your reaction is going, consider doing this reaction in a microwave. Go to Step 4.
2. Workup
a. Add 2 mL of ether to the reaction mixture.
b. Filter this mixture through a plug of glass wool to remove excess zinc and any precipitate (zinc salts) that may have
formed.
(Here’s a quick way: Wrap the Pasteur pipette tip with a small piece of cotton wool. Immerse the pipette into the solution
until the pipette tip reaches the bottom of the flask while squeezing the rubber bulb. Draw the solution up into the pipette
by releasing the rubber bulb. Take off the cotton wool and expel the solution in the pipette into the proper container).
If any precipitate is present, rinse the precipitate is with 1 mL of fresh ether.
Which should you do with the rinse ether?
c. Separate the two phases.
Which layer is the organic phase?
Which layer is the aqueous phase?
In which phase is the desired product?
d. Wash the aqueous phase once with a 2 mL of ether.
Separate the layers.
Combine the ether layer with the ___ layer from the previous step.
e. Dry the combined organic phases over Na2SO4.
Then, _____ to separate the solid from liquid.
f. At this point, the organic phase contains ___ and ___.
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31
How will you remove the ___ to obtain the product, which is a colorless liquid?
g. Measure the yield of product.
h. Characterize your product by IR and NMR.
3. Summarize your data and results in Table 2.
Table 2. Grignard-like reaction data and results. What else goes in Table 2?
Run 1
Run 2
Method
reflux
microwave
Mass of _____, g
Limiting reactant
% yield
4. Repeat the experiment except this time use the microwave oven to heat your reaction mixture instead of doing a reflux.
Waste Disposal: any liquid containing zinc without Br – in heavy metals waste.
Liquid containing Br – in halogenated waste.
3. Draw a flowchart of the procedure. Describe the purpose of each reagent or step. In other words, determine or explain
why you do each step in the procedure. The Flow Chart is not a rewrite of the procedure in boxes.
Questions
1. a. Report the % yield of your product.
b. Report your product characterization. Did you make the desired product?
2. Show your flowchart of the procedure.
3. a. Use your flowchart to answer these questions. Compare this reaction to the Grignard reaction.
a. What substance in the Grignard reaction serves the same as Zn?
b. Draw the structure of the Grignard-like reagent. Is this compound a nucleophile or electrophile? Identify the nucleophilic
or electrophilic atom in this compound. What compound does the Grignard-like reagent react with? Use curved arrows to
show bonds breaking and forming in this reaction.
c. In Step 2a-c, you added ether and did an ex_____ (finish this word). What substance(s) is/are in the top layer? What
substance(s) is/are in the bottom layer?
d. In Step 2d, you washed the aqueous layer with ether. For what reason did you do this step?
e. In Step 2f, the organic phase contains ___ and ___. How did you remove the ___ to obtain the product, which is a
colorless liquid?
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32
Lab 7. The Most Practiced Reaction in the World! Maillard Reaction
What happens when a carbonyl carbon reacts with a base? What functional group is produced?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. a. Using Lewis structures, write a chemical equation that represents the reaction of an amino acid, e.g., glycine, with a
sugar, e.g., glucose.
b. Identify the functional group(s) in each reactant and product.
c. Which reactant is chiral? Identify the chirality center(s).
d. Which reactant is an acid? Identify the acidic H. State the pKa of this acid.
e. Which reactant is a base? Identify the basic atom. Draw the conjugate acid of this base. State the pKa of this acid.
f. Identify the nucleophile(s) and electrophile(s). If there is more than one nucleophile or electrophile, identify the best
nucleophile/electrophile. Use curved arrows to show how the nucleophile reacts with the electrophile.
g. This reaction is a ____ reaction.
o
o
o
i. Identify the alpha carbon. Is this carbon 1 , 2 , or 3 ?
h. Identify the leaving group. Is this leaving group a good or poor leaving group?
i. Identify the beta carbon. Is there a H bonded to this C?
j. Calculate the moles of each reactant in each reaction. Identify the limiting reactant. Calculate the theoretical yield of
product.
k. What property of the product distinguishes it from the reactant? How will you characterize the product?
Table 1. Chemical Properties of Lab 7 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
o
b.p., C
Polar
or nonpolar?
2. An imine is produced by reacting a ___ with a ____. Pancakes are made from flour, sugar, a leavening agent, and
milk/water.
a. Flour is the source of ____? (What functional group?)
b. Sugar is the source of ___? (What functional group?)
c. Milk is a source of ___? (What component of milk? What functional group?)
Objectives
1. Name and classify carbonyl compounds; identify their physical and chemical properties, especially reactivity trends.
2. synthesize an imine from a carbonyl compound.
3. Make a big molecule from a small molecule. (And then make small molecules that smell and taste good from big
molecules.)
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014, Ch. 20
2. “Favorite Chemical Reactions” http://cen.acs.org/articles/89/i47/Maillard-Reaction.html and http://sciencegeist.net/themaillard-reaction/
3. “The Maillard Reaction Turns 100” http://cen.acs.org/articles/90/i40/Maillard-Reaction-Turns-100.html
Introduction
One way to brown food and product wonderful flavors and tastes is to use the Maillard reaction. This reaction is
the most practiced reaction in the world although it is done mainly in kitchens rather than in the lab. (Pictures credit:
Shutterstock)
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33
An overview of this reaction and reactions that produce flavor and aromas is shown in Figure 1.
In this lab, you will practice the Maillard reaction by making pancakes. You will determine the optimum pH at
which this reaction occurs. You will determine how well this reaction occurs by observing the brown-ness of your
pancakes.
Materials
Students: bring flour (not cake flour or pancake mix), baking powder, baking soda, sugar, milk, a pan, spatula, fork, a
measuring spoon (1/4 tsp is ideal), mixing bowl, and plate.
Procedure
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
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34
Figure 1. Overview of Maillard reaction and products (from http://sciencegeist.net/the-maillard-reaction/).
A simple recipe to make one average size pancake is:
¼ cup of flour,
¼ tsp baking powder,
___ tsp sugar, and
¼ cup liquid (milk or water).
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35
Some recipes add a small amount of baking soda.
If you like thicker pancakes, use less liquid. For thinner pancakes, use more liquid.
Mixing the solid ingredients into the liquid will make a difference in making your pancakes “cakey” or “rubbery”. Mix the
solid into the liquid until they are just mixed if you want “cakey” pancakes.
Reaction variables:
1. The temperature of the reaction (temperature of the pan) ____ reaction rate and ____ color development.
2. The time of the reaction (cooking time of the pancake) ____ color development.
3. Sugar type (reducing/non-reducing or pentose/hexose) affects the reaction.
4. Amino acid type affects the reaction.
5. pH affects the reaction.
We will look at the ratio of protein to sugar.
What is the source of protein?
What is the source of sugar?
What should you do about the other variables?
1. Design experiments to test the effect of the amount of sugar on the food browning reaction.
2. a. Do your experiment.
b. Make sure you record your observations.
c. Summarize your data and results in Table 2.
Table 2. Maillard reaction data and results. What else goes in Table 2?
Trial
Mass of ____, g
Browning (1-5 scale)
Waste Disposal: pancakes – in your mouth.
Questions
1. Prepare a 5 minute presentation of your data and results to the class.
2. The description below is from Reference 2 and accompanies Figure 1.
“The set of reactions that take place under the general description of the Maillard reaction can be generalized as follows.
(Please refer to the figure for more detail.) A sugar (1) combines with an amine (in this case, NHn-AminoAcid) to
form 2. 2 rearranges into a glycosylamine (3), which is unstable in these conditions. The glycosylamine rearranges into an
aminoketose (5) through an aminoenol (4) intermediate. The aminoketose is one of the main products of the Maillard
reaction. It is called the Amadori component because, well, Amadori isolated these compounds from Maillard reaction
products in the 1930s. And, while this is a primary component, it really isn’t very interesting. The tasty parts of the Maillard
reaction come about when 4 is converted into a deoxy-hexosulose (7) or the Amadori product rearranges into an enediol
(6), which is further converted into a deoxy-hexodiulose (8). 7 and 8 are the intermediates that ultimately lead to the smallmolecule aroma, flavor, and color compounds that our senses recognize as the products of the Maillard reaction. The
exact mechanism by which 7 and 8 are converted into these small molecules is still not fully understood. I imagine that
ANY number of reasonable or creative electron pushing descriptions have been used.
Before the reaction starts producing 7 and 8 (up to the point when the sugar is attached to a protein through an amino
acid), the Maillard reaction isn’t making any molecules beneficial for humans. The protein is actually less nutritious than
before the reaction. While our bodies recycle the amino acids that we consume, modified amino acids, like the Amadori
product, contain little nutritional value. Because the Amadori product (5) is produced in higher amounts than other
molecules, evolutionary arguments would suggest that humans should shy away from foods that have undergone the
Maillard reaction. But our personal observations tells us that this is not the case. We recognize and hunger for the
aroma/flavor/color molecules that the Maillard reaction produces in relatively low amounts. The simplistic argument is that
we have developed the ability to sense these molecules in cooked food because cooking kills bacteria. And food with less
bacteria is less likely to make us ill.”
a. Is Compound 1 a sugar or amino acid?
b. Compound 3 is called a glycosylamine. What is this compound called, e.g., diol, acetal, eneamine, according to CHM
12B lecture?
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36
c. How does high pH, e.g., a base, affect the formation of Compound 3? In other words, how does a base react with
Compound 1? Will Compound 3 form? Relate your answer to your experimental observations.
d. How does low pH, e.g., an acid, affect the formation of Compound 3? In other words, how does an acid react with
Compound 1? Will Compound 3 form?
e. How is the formation of Compound 3 from Compound 1 related to the Grignard reaction?
f. We looked at enols in CHM 12. What compound(s) is/are an enol? What does an enol form?
g. Glucose, C6H12O6, exists as a ring or chain. Which form of glucose, the chain or ring, reacts with an amino acid in the
Maillard reaction? Give reasons. Draw the structures of the chain and ring forms of glucose to support your answer.
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Lab 8. Lifesavers: Wintergreen from Salicylic Acid
How do I make wintergreen? Which functional groups react? What functional group is produced?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. a. Draw the structure of wintergreen (methyl salicylate). Identify the functional group(s) in wintergreen.
b. What functional groups are used to make the functional group in methyl salicylate? What type of reaction occurs
between these two functional groups.
c. Which reactant is chiral? Identify the chirality center(s).
d. Which reactant is an acid? Identify the acidic H. State the pKa of this acid.
e. Which reactant is a base? Identify the basic atom. Draw the conjugate acid of this base. State the pKa of this acid.
f. Identify the nucleophile(s) and electrophile(s). If there is more than one nucleophile or electrophile, identify the best
nucleophile/electrophile. Use curved arrows to show how the nucleophile reacts with the electrophile.
g. This reaction is a ____ reaction.
o
o
o
i. Identify the alpha carbon. Is this carbon 1 , 2 , or 3 ?
h. Identify the leaving group. Is this leaving group a good or poor leaving group?
i. Identify the beta carbon. Is there a H bonded to this C?
j. Calculate the moles of each reactant in each reaction. Identify the limiting reactant. Calculate the theoretical yield of
product.
k. What property of the product distinguishes it from the reactant? How will you characterize the product?
Table 1. Chemical Properties of Lab 8 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
b.p./m.p.,
o
C
Polar
or nonpolar?
Objectives
1. Name and classify acids and acid derivatives; identify their physical and chemical properties, especially reactivity
trends.
2. synthesize an ester from an acid and alcohol
3. hydrolyze an ester to make an acid and alcohol
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014, Ch. 21
2. “Synthesis of Methyl Salicylate” http://www.uccs.edu/Documents/chemistry/nsf/WintergreenExperiment.pdf
Introduction
The wintergreen taste in Wintergreen Lifesavers is methyl salicylate. It is produced naturally by certain plants to
defend agains bug attack and in the lab for use as a fragrance and flavoring agent in gum and mints, in liniments
(Bengay) as a rubefacient and analgesic, as an antiseptic in Listerine mouthwash, and other uses. You may have done
this before - when a Wintergreen Lifesaver is mechanically crushed, it emits blue-green light – a phenomena called
triboluminescence – very cool!
Materials
Salicylic acid
H2SO4 (conc.)
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methanol
NaOH (s)
38
CH2Cl2
10% NaHCO3 (aq)
Procedure
Caution: H2SO4 and NaOH are corrosive. CH2Cl2 is volatile, flammable, and may be a carcinogen.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
Part 1. Synthesis of methyl salicylate from salicylic acid.
1. a. Mix 250 mg of salicylic acid with 4 ml of methanol. Carefully add 8 drops of concentrated H2SO4.
o
b. Heat and stir this mixture in a 60 C hot water bath on a hot plate/stirrer.
c. After 20 minutes, remove the reaction mixture from the heating source and carefully smell (waft) the mixture. Does it
smell like wintergreen?
While you are heating your reaction, go to Step 4.
d. Continue heating for another 10 minutes. Carefully smell the reaction mixture again. Does it still smell like wintergreen?
Is the smell stronger or weaker or the same as before? Decide whether to continue heating or to go to step e.
e. Cool to room temperature.
2. Workup – after Step 1, your reaction mixture should contain wintergreen and ______. How will you separate and isolate
the wintergreen? Choose one of the three Methods.
Method A: distillation
What is the boiling point of methyl salicylate?
What is the boiling point of the other substances in this mixture?
Determine the actual and % yield of methyl salicylate.
Method B: extraction using CH2Cl2
a. Transfer the reaction mixture to a test tube.
b. Add 4 ml of CH2Cl2 to the reaction mixture. Then, add 4 ml of water.
How many layers form?
In which layer is the methyl salicylate?
How do you separate the layers?
Does the layer that has methyl salicylate have leftover H2SO4? If so, how do you neutralize it?
Is the layer that contains the methyl salicylate dry? If not, how do you dry it?
In the layer that contains the methyl salicylate, how do you separate the methyl salicylate from whatever else is in the
layer?
c. Once you have isolated the pure methyl salicylate, determine the % yield.
Method C: extraction using H2O
a. Add the reaction mixture to ___ ml of water in a test tube. Cap, invert, shake, and vent. (Why?)
How many layers form?
In which layer is the methyl salicylate?
How do you separate the layers?
Does the layer that has methyl salicylate have leftover H2SO4? If so, how do you neutralize it?
Is the layer that contains the methyl salicylate dry? If not, how do you dry it?
In the layer that contains the methyl salicylate, how do you separate the methyl salicylate from whatever else is in the
layer?
b. Once you have isolated the pure methyl salicylate, determine the % yield.
3. a. Characterize your product by ___.
b. Summarize your data and results in Table 2.
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39
Table 2. Wintergreen synthesis data and results.
Run 1
Method
reflux
Mass of ___, g
Run 2
microwave
% yield
4. Repeat the experiment except this time use the microwave oven to heat your reaction mixture instead of doing a reflux.
Waste Disposal: any liquid that contains CH2Cl2 – in halogenated waste.
Salicylic acid or methyl salicylate solution – in non-halogenated waste.
H2SO4– dilute with water and neutralize with NaOH – in sink.
4. Draw a flowchart of the procedure. Describe the purpose of each reagent or step. In other words, determine or explain
why you do each step in the procedure. The Flow Chart is not a rewrite of the procedure in boxes.
Part 2. Synthesis of salicylic acid from methyl salicylate.
1. a. Identify the reaction conditions to convert methyl salicylate to salicylic acid. Explain the purpose of each step.
b. Draw a flowchart of the procedure. Describe the purpose of each reagent or step. In other words, determine or explain
why you do each step in the procedure. The Flow Chart is not a rewrite of the procedure in boxes.
2. a. Do your experiment.
b. Characterize your product.
Waste Disposal:
Questions
1. a. Show your data and results for each synthesis.
b. Report your product characterization for each synthesis. Did you make the desired product?
2. a. Propose a reaction mechanism for the wintergreen synthesis reaction (Part 1) and wintergreen hydrolysis reaction
(Part 2). Use curved arrows to show bonds breaking and forming.
b. Identify the common intermediate in each mechanism. Once this intermediate forms, what makes the reaction go in one
direction or the other? (This reaction is reversible.)
c. How is this reaction similar to the Grignard reaction and imine formation reaction?
3. Use your flowcharts to answer these questions:
a. What is sulfuric acid used for in the synthesis of methyl salicylate?
b. For Extraction Method B or C (the one you used),
i.
in which layer is the methyl salicylate?
ii.
How do you separate the layers?
iii.
Does the layer that has methyl salicylate have leftover H2SO4? If so, how do you neutralize it?
iv.
Is the layer that contains the methyl salicylate dry? If not, how do you dry it?
v.
In the layer that contains the methyl salicylate, how do you separate the methyl salicylate from whatever else is in
the layer?
4. Salicylic acid is used to make aspirin (acetylsalicylic acid). Look up the structure of aspirin.
a. Acetic anhydride is usually used to react with salicylic acid to make aspirin. Name another reagent that reacts with
salicylic acid to make aspirin. Draw the structure of this reagent. Identify the functional group in this reagent that reacts
with salicylic acid.
b. Compare the reaction of salicylic acid with acetic anhydride to the reagent you found in part a. Why do you think acetic
anhydride is usually used instead of the other reagent? (Hint: one reaction is exothermic; the other is endothermic. This
also tells you the relative reactivity of these two reagents.)
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40
Lab 9. Biodiesel from Vegetable Oil
What is biodiesel? How do I make biodiesel? Which functional groups react? What functional group is produced?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
Your instructor will discuss various vegetable oils to use. Bring corn oil, vegetable oil, canola oil, olive oil, or used
cooking oil.
1. What is biodiesel?
2. a. Using Lewis structures, write a chemical equation that represents the synthesis of biodiesel from vegetable oil.
Which vegetable oil is used? Cite the reference where you found this information.
b. Identify the functional group(s) in each reactant and product.
c. Which reactant is chiral? Identify the chirality center(s).
d. Which reactant is an acid? Identify the acidic H. State the pKa of this acid.
e. Which reactant is a base? Identify the basic atom. Draw the conjugate acid of this base. State the pKa of this acid.
f. Identify the nucleophile(s) and electrophile(s). If there is more than one nucleophile or electrophile, identify the best
nucleophile/electrophile. Use curved arrows to show how the nucleophile reacts with the electrophile.
g. This reaction is a ____ reaction.
o
o
o
i. Identify the alpha carbon. Is this carbon 1 , 2 , or 3 ?
h. Identify the leaving group. Is this leaving group a good or poor leaving group?
i. Identify the beta carbon. Is there a H bonded to this C?
j. Calculate the moles of each reactant in each reaction. Identify the limiting reactant. Calculate the theoretical yield of
product.
k. What property of the product distinguishes it from the reactant? How will you characterize the product?
Table 1. Chemical Properties of Lab 9 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
b.p./m.p.,
o
C
Polar
or nonpolar?
Objectives: Name and classify alcohols, acids, and esters; identify their physical and chemical properties, especially
reactivity trends.
1. make biodiesel from vegetable oil
2. analyze biodiesel by HPLC or GC
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014, Ch. 21
2. “A Simple, Safe Method for Preparation of Biodiesel,” M.S. Behnia, D. W. Emerson, S.M. Steinberg, R.M. Alwis, J.A.
Duenas, J.O. Serafino, J. Chem. Educ. 2011, 88, 1290-1292.
3. “Synthesis and Determination of Biodiesel: An Experiment for High School Chemistry Laboratory,” J. Yang, C. Xu, B. Li,
G. Ren, L. Wang, J. Chem. Educ. 2013, 90, 1362-1364.
Introduction
The U.S. was the second largest energy consumer in 2010
(http://en.wikipedia.org/wiki/Energy_in_the_United_States). In 2009, 37% of our country’s energy came from petroleum,
21% from coal, 25% from natural gas, 9% from nuclear power, 8% from renewable energy (mainly hydroelectric dams;
wind power, geothermal and solar energy contribute about 2%). This energy is used for industrial, transportation,
residential, and commercial purposes.
An alternative source of energy is biofuels. Biofuels include ethanol (from corn, switchgrass, cellulose), biodiesel,
and straight vegetable oil. Biodiesel is a fatty acid methyl ester (FAME). In this lab, you will make biodiesel from vegetable
oil in a trans-esterification reaction (carbonyl carbon is involved).
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41
Materials
Students: bring either corn oil, vegetable oil, canola oil, olive oil, or used cooking oil
Methanol
1.2 M acetic acid or vinegar
solid Na2SO4
powdered, anhydrous K2CO3 solid
Procedure
Caution: methanol is flammable.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes.
Your instructor will assign a different vegetable oil, e.g., soybean, olive, canola, for each group to use.
1. Synthesis
Make biodiesel from cooking oil (adapted from Reference 3). Visual determination and NMR and HPLC.
We will assume the molar mass of the oil is 880 g/mole. We will use a 6:1 mole ratio of methanol to triglycerides in the oil.
a. Add 2.0 g of your cooking oil to a round bottom flask.
b. Add 0.12 g of powdered, anhydrous K2CO3 to the oil in your reaction container. (What is the function of the K2CO3?)
c. Based on the amount of triglcerides in 2.0 g of your oil, calculate the amount of methanol to use. Add this amount of
methanol to the reaction container. (What does the methanol react with?)
o
d. Attach a condenser to your reaction container. Heat (reflux) and stir (vigorously) your reaction mixture at 60-65 C for
20-25 minutes. As the reaction proceeds, the reaction mixture will become clearer.
While your reaction undergoes reflux, go to Step 4.
2. Workup
a. When the reaction is finished, slowly add 1-1.5 ml of 1.2 M acetic acid or 2 ml of vinegar. You should see gas form.
b. Stir this mixture vigorously for a few minutes. Then, let stand. You should see two _____ form.
c. The top ____ contains the biodiesel. Remove the top layer. (What is in the bottom layer?)
d. Dry the top layer.
One way to dry the top layer: Prepare a drying tube consisting of a Pasteur pipet with a small cotton plug in the narrow
part and add about 1 cm of anhydrous sodium sulfate (Na2SO4). Clamp the tube vertically and place a tared vial under the
drying tube. Add the top layer to the drying tube and let the contents run through the drying tube. When the flow stops, put
a bulb on the top of the drying tube and squeeze out a few drops more of product.
e. Weigh your dried liquid. This liquid is ____. Determine the % yield.
3. a. Characterize your biodiesel. IR and HPLC is used to analyze biodiesel samples.
b. Since biodiesel is a fuel, carefully try the ignition test on your biodiesel sample.
Caution: Make very sure no other flammable materials are close by.
(i) Pour about 1 ml of your biodiesel on the lab bench.
Use a match or lit splint to light the biodiesel.
(ii) The letter below was published in Chemical & Engineering News, 5/18/15, p. 4:
“Fuming Over Foam” details the problems of recycling polystyrene (C&EN, March 23, page 23). New York City’s recyclers
could avoid the use of densifiers and avoid washing the food service Styrofoam products (without risk of putrefaction) by
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42
simply dissolving all the food service Styrofoam products in fatty acid methyl ester, such as biodiesel made from soybean
oil. Enhanced-energy-content biodiesel can be used as a fuel in waste-to-energy plants or other industrial boilers.
Kimball Nill
Chesterfield, Mo.
Take 1 ml of your biodiesel. Add a small amount of styrofoam.
Does the styrofoam dissolve in the biodiesel?
Use a match or lit splint to light the enhanced biodiesel.
Does it burn better than biodiesel?
c. Summarize your data and results in Table 2.
Table 2. Biodiesel synthesis data and results.
Oil source
Method
Run 1
reflux
Run 2
microwave
4. Repeat the experiment except this time use the microwave oven to heat your reaction mixture instead of doing a reflux.
Waste Disposal: Bottom layer from Step 2c – in sink. Biodiesel – in sink.
5. Draw a flow chart of the procedure. Describe the purpose of each reagent or step. In other words, determine or explain
why you do each step in the procedure. The Flow Chart is not a rewrite of the procedure in boxes.
Questions
1. a. Show your Table 2. Show how you calculated the amount of methanol to use based on 2.0 g of oil.
b. Report your product characterization. How do you know you made biodiesel?
c. Get the results of other oils from other groups. Compare the class results of the biodiesel synthesis from the different
oils. Which oil produced the “best” biodiesel?
2. a. Describe the mechanism of the trans-esterification reaction. Use curved arrows to show bonds breaking and forming.
b. How is the intermediate in this mechanism similar to the mechanism of the salicylic acid to methyl salicylate reaction in
the previous lab?
c. How is this reaction similar to the Wintergreen synthesis reaction?
3. Use your flowchart to answer these questions:
a. What compound forms when methanol reacts with K2CO3? Why is this compound more soluble in methanol than
KHCO3?
o
b. If you reflux the reaction mixture at a higher temperature than 65 C, your biodiesel yield wil be lower. Explain.
c. When the reaction was finished, you added 1-1.5 ml of 1.2 M acetic acid or 2 ml of vinegar. You should see gas form.
What is the gas? The acetic acid neutralizes ____ and ___.
d. In what layer is the biodiesel? Give reasons.
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43
Lab 10. Multistep Synthesis of a Sunscreen
How do I make sunscreen? Is the sunscreen effective? Which functional groups react in each step? What functional group
is produced?
Prelab Activity
Spend 5 minutes on the following activity. Assign a notetaker. Report to the class.
1. For each step in this multistep synthesis:
a. Using Lewis structures, write a chemical equation that represents the reaction.
b. Identify the functional group(s) in each reactant and product.
c. Which reactant is chiral? Identify the chirality center(s).
d. Which reactant is an acid? Identify the acidic H. State the pKa of this acid.
e. Which reactant is a base? Identify the basic atom. Draw the conjugate acid of this base. State the pKa of this acid.
f. Identify the nucleophile(s) and electrophile(s). If there is more than one nucleophile or electrophile, identify the best
nucleophile/electrophile. Use curved arrows to show how the nucleophile reacts with the electrophile.
g. This reaction is a ____ reaction.
o
o
o
i. Identify the alpha carbon. Is this carbon 1 , 2 , or 3 ?
h. Identify the leaving group. Is this leaving group a good or poor leaving group?
i. Identify the beta carbon. Is there a H bonded to this C?
j. Calculate the moles of each reactant in each reaction. Identify the limiting reactant. Calculate the theoretical yield of
product.
k. What property of the product distinguishes it from the reactant? How will you characterize the product?
Table 1. Chemical Properties of Lab 10 Compounds.
Compound
Structure
Functional
Acid/Base/
Group(s)
pKa
-
+
Nu: /E
Molar
mass
density
o
b.p., C
Polar
or nonpolar?
Objectives: Name and classify acids, acid derivatives, and amines; identify their physical and chemical properties,
especially reactivity trends.
1. make PABA from p-toluidine
2. make a PABA derivative
3. measure the UV-VIS spectrum of PABA and the derivative to determine their effectiveness as a sunscreen
nd
References: 1. D. Klein, "Organic Chemistry", 2 ed., 2014
2. Schoffstall, et al., “Microscale and Miniscale Organic Chemistry Laboratory Experiments”, McGraw-Hill, 2000 p. 419427.
Introduction
Synthesis is the heart of chemistry. Chemists have designed and created molecules with different and unique
properties for a variety of uses and applications. Usually, substances are not synthesized in one or two steps, as you have
done in most of the experiments in this course, but often require several or many steps to make. The raw materials or
feedstocks to make these substances are usually readily available and cheap. Many raw materials are based on
petroleum. As you have seen from this course so far, there are many organic reactions that can be used to make new
substances.
In this lab, you will make a common sunscreen p-aminobenzoic acid (PABA) starting from p-toluidine (paminotoluene) in three steps as shown in Figure 1. From PABA, you will make benzocaine or a benzocaine analog. You
will test the effectiveness of this substance and PABA as a sunscreen.
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Figure 1. Sunscreen synthesis overview. 1 = p-toluidine, 2 = p-methylacetanilide (p-acetotoluidide), 3 = pacetamidobenzoic acid, 4 = p-aminobenzoic acid, 5 = benzocaine.
Materials
Part A. p-toluidine
Part B. KMnO4 (s)
Part C. HCl (6 M)
Part D. ethanol
NaC2H3O2  3H2O (s)
MgSO4  7H2O (s)
NH3 (aq, 6 M)
H2SO4 (conc.)
HCl (conc.)
ethanol
acetic acid (glacial)
Na2CO3 (10%)
acetic anhydride
H2SO4 (20%)
CH2Cl2
Procedure
Caution: the inorganic acids and bases and acetic anhydride are corrosive.
KMnO4 is a strong oxidizer.
CH2Cl2 is volatile, flammable, and may be a carcinogen.
Ethanol is flammable.
While you are doing this experiment, try to determine the purpose of each step in the procedure, e.g.,
• Is this reagent reacting with one of the acid, base, or neutral? If so, write a chemical equation that represents the
reaction. Is this reagent the limiting reactant or excess reactant?
• If the solvent I just added formed two layers, is the solvent extracting something? Which substance is being
extracted?
• What is the reason for heating or cooling?
Record the purpose of each step in your notes. After each Part, draw a flow chart of the procedure. The Flow Chart is not
a rewrite of the procedure in boxes.
Part A. Synthesis of p-methylacetanilide (p-acetotoluidide) from p-toluidine.
1. Synthesis
a. Prepare a solution of sodium acetate by combining 2.15 g of sodium acetate trihydrate (CH3CO2Na  3 H2O) and 5-6
mL of water in a 10-mL Erlenmeyer flask. Swirl vigorously to dissolve. Set the sodium acetate solution aside.
b. In a 125-mL Erlenmeyer flask, dissolve 1.61 g of p-toluidine in 40 mL of water. With stirring (use a stir bar), add 1.3 mL
of concentrated HCl. Stir for 2 minutes.
c. With stirring, add 2.1 mL of acetic anhydride and immediately add the sodium acetate solution. (Which reactant reacts
with the p-toluidine? Which reactant is limiting?) Stir vigorously to mix the reagents. Cool the solution in an ice bath and
continue to stir vigorously while the product crystallizes.
2. Workup
a. Isolate the product by vacuum filtration, washing the crystals with several small portions of ice-cold water.
b. Let the crystals air dry or place in a warm drying oven.
c. Weigh the product. Save at least 25 mg of the product for characterization and spectral analysis. The remainder may be
used without purification in the next step.
d. Summarize your data and results in Table 2.
Table 2. Multistep synthesis data and results.
Run 1
Method
reflux
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Run 2
microwave
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Part B. Synthesis of p-acetamidobenzoic acid from p-methylacetanilide.
This procedure is designed for use of 1 g of p-methylacetanilide.
1. Synthesis
a. Dissolve 2.6 g KMnO4 in 14 mL of boiling water. Set this solution aside. (What do you want KMnO4 to do?)
b. To a 250-mL Erlenmeyer flask fitted with a stir bar, add 1 g of dry p-methylacetanilide (or all of the remaining solid from
part A), 2.6 g of MgSO4  7H2O, and 64 mL of water.
o
c. Heat to 85 C on a steam bath or water bath. While vigorously stirring the solution of p-methylacetanilide, slowly add via
pipet a hot solution of potassium permanganate. The addition should take approximately 30 minutes. It is important to add
the permanganate solution slowly and uniformly to avoid local build up of the oxidant.
d. After all of the oxidant has been added, add 2 mL of ethanol, stir vigorously, and bring to a boil. (What does the ethanol
do?) Check to make certain that no purple color remains, then filter over a pad of Celite using vacuum filtration, washing
with water to dissolve any adsorbed product.
2. Workup
a. Transfer the clear solution to an Erlenmeyer flask. Cool the filtrate in an ice bath and acidify with 20% sulfuric acid until
the pH is 3-4. (For what reason do you want to lower the pH?)
b. Collect the product using vacuum filtration, rinsing the crystals with small amounts of ice-cold water.
c. Dry the crystals as much as possible by continuing suction. The product does not need to be completely dry for the next
step. Measure the yield. Save at least 25 mg of the product and let it dry thoroughly for characterization and spectral
analysis.
d. Summarize your data and results in Table 2.
Part C. Synthesis of p-aminobenzoic acid from p-acetamidobenzoic acid.
1. Synthesis
a. Add 1.0 g of p-acetamidobenzoic acid and 5 mL of 6M HCl to a 10-mL round-bottom flask containing a stir bar. (Which
group in p-acetamidobenzoic acid reacts with HCl?)
b. Attach a reflux condenser to the round-bottom flask and reflux gently, with stirring, for 30 minutes.
c. After the heating time is over, let cool to room temperature. Transfer the contents of the flask to a 50-mL Erlenmeyer
flask, rinsing with 2.5 mL of cold water. Add the rinses to the flask.
2. Workup
a. Add concentrated (15 M) ammonia dropwise until the pH is between 7 and 8. Do not go beyond pH 8. During the
addition, precipitates will form and redissolve. (What is the reason for adding ammonia?)
b. Estimate the volume of the solution: then add 1 mL of glacial acetic acid for every 30 mL of solution to induce
crystallization. Stir vigorously and cool the solution in an ice bath. It may be necessary to add more glacial acetic acid, to
add a seed crystal or to scratch the inside surface of the flask with a glass rod.
c. Suction filter the product and let air dry until the next lab period. Measure the yield. Save 25 mg of product for analysis
and use the remainder in Part D.
d. Summarize your data and results in Table 2.
Part D. Synthesis of benzocaine from p-aminobenzoic acid.
1. Synthesis
a. To a 10-mL round bottom flask fitted with a stir bar, add 0.33 g of dry p-aminobenzoic acid and 2.5 mL of the assigned
alcohol.
b. While stirring, add 0.25 mL of concentrated H2SO4 dropwise. The precipitate that forms upon the addition of sulfuric
acid should dissolve when the solution is heated.
c. Reflux, with stirring, for 1 hour.
d. Cool to room temperature, then transfer the solution into a centrifuge tube.
2. Workup
a. Neutralize cautiously with dropwise addition of 10% Na2CO3 until the pH is approximately 8. (Gas evolution will be
vigorous. What is the gas? What reacts with Na2CO3 to form this gas?)
b. Extract with two 3-mL portions of methylene chloride. (What substance are you extracting?)
c. Wash the combined methylene chloride layers with two 8-mL portions of water. (What does the water wash out?)
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d. Dry the methylene chloride solution over anhydrous sodium sulfate.
e. Gravity filter into a clean Erlenmeyer flask containing a boiling stone.
f. Evaporate the methylene chloride under the hood on low heat.
g. Recrystallize the whitish residue using as a solvent pair, the assigned alcohol and water. Suction filter the product, and
let air dry.
h. Measure the yield.
d. Summarize your data and results in Table 2.
Part E. Sunscreen effectiveness. Measure the UV-VIS spectrum of:
a. PABA
b. PABA derivative
Prepare a Table that summarizes your data and results.
Waste Disposal: halogenated compounds – in halogenated waste.
Solids – in solids waste.
Acids and bases – neutralize with base or acid – in sink.
KMnO4 – if oxidizing agent solution is still purple, add ethanol until no purple color remains – in heavy metals waste.
Questions
1. a. For each step, report the % yield of product. Report the overall % yield of benzocaine or the benzocaine analog.
Which synthesis step limited your overall yield?
b. Report your product characterization for each step.
2. a. Summarize your data and results of your tests of the effectiveness of PABA and benzocaine or the benzocaine
analog in a table.
b. Show your UV/Vis absorption spectrum for each substance.
c. Compare the UV-VIS spectra. Which compound is the more effective sunscreen? Give reasons.
3. Use your flowcharts to answer these questions:
a. In the first step of the synthesis, why does the amine group react in p-toluidine and not the methyl group or pi bonds?
b. In the third step, why does the amide group in p-acetamidobenzoic acid react and not the acid group?
c. When you converted PABA to benzocaine, why does the acid group react and not the amine group?
d. Is there a reagent that reacts with the amine group in PABA and not the acid group? If so, give an example.
4. a. Propose a reaction mechanism for each Part. Identify the reaction type, e.g., substitution, elimination, for each Part.
Note: you don’t have to propose a mechanism for the KMnO4 oxidation.
b. Discuss the order of the synthesis steps. Could you have made PABA from p-toluidine in a different sequence of steps?
For example, could you make PABA by doing Part A followed by Part C followed by Part B? Would your yield improve?
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