Download Exp`t 88 - Chemistry Courses

Exp't 88
The Acid-Catalyzed Reaction of Acetic Anhydride and
Isopropyl Alcohol
by Robert Minard and Kurt Rublein, Organic Instructional Laboratories, Revision 3/21/02
Ester syntheses are one of the more enjoyable experiments in organic chemistry, as one can't help
but notice the special odors associated with esters - some fruity, some more like nail polish. In contrast,
the acids which are used in their syntheses usually have a rotten odor. The reverse reaction, hydrolysis
of the ester, gives the alcohol and the acid from which it was synthesized. Because the hydrolysis can
occur in the presence of sweat, esters are not used as perfumes.
OH
+
CH
H3C
CH 3
H3C
O
O
C
C
O
H+
?
(two organic products)
CH 3
In this experiment, you should predict the product(s) of the reaction above and interpret your
analysis data to confirm or negate your prediction. You may need to refer to your Organic textbook to
review the reactions of acid derivatives (i.e., acetic anhydride, and acid anhydride) with alcohols.
PreLab
Be sure to include all sections that accompany the PreLab for Synthetic Experiments. Be sure to
include an entry in the Chemical Data Table for the predicted product. Properly named, the product can
be found in Aldrich. Use the formula index if you are not sure about the name.
Include answers to the following questions in your PreLab:
1. The same experiment could be performed using acetic acid, isopropyl alcohol, and sulfuric acid; in
this particular experiment, what advantage could acetic anhydride have over acetic acid? (Hint:
consider what by-product is formed if acetic acid were used, and how this could affect the
equilibrium between reagent and products.)
2. In developing this experiment, precautions were taken to ensure that acetic anhydride and sulfuric
acid were mixed together before the isopropyl alcohol was added. What reaction is likely to take
place if concentrated sulfuric acid was added directly to the isopropyl alcohol? (Hint: Look up acid
catalyzed reactions of alcohols.)
Precautions
Concentrated sulfuric acid is very reactive and corrosive - it will eat holes in your clothes. Acetic
anhydride is also very reactive and will react vigorously with water to give acetic acid and heat. Wear
gloves when handling these chemicals or when handling solutions that contain these. Remember that
the sulfuric acid is a catalyst, so when the reaction is complete, it is still present until after the work up
and neutralization with sodium bicarbonate solution. Also, when water is added to the reaction, this
hydrolyzes the acetic anhydride to acetic acid, which is also neutralized by sodium bicarbonate.
1
Exp't 88
Procedure
Wear gloves while mixing the reactants. Measure 1.6 mL of acetic anhydride into the short-neck
round-bottomed flask from your microscale kit. Clamp the flask upright using the three-finger
microclamp. Using a glass Pasteur pipet, cautiously add 3 drops of concentrated sulfuric acid, one drop
at a time, letting the sulfuric acid run down the inside wall of the flask neck. Add 4 boiling chips and
gently swirl the liquids so that they are thoroughly mixed. Now slowly add 1.3 mL of isopropyl alcohol.
Caution--the flask will get very warm at this point--which is why the flask should already be clamped
upright. Connect the air-cooled condenser column to the flask. Heat the mixture gently, just to the point
that it begins to reflux. Be careful to observe that condensed vapors are returning to the reaction flask
and that the reaction product is not distilling out of the top of the condenser.
Reflux the mixture for 25 min. After the reflux period, let the mixture cool to room temperature.
Once the solution is cool, add 2 mL of 5% sodium bicarbonate solution to the flask DROPWISE.
Initially the bubbling will be very strong. Once the bubbling has subsided, transfer the mixture to one of
your 13 X 100 mm test tubes. Notice that there are two layers of immiscible liquids. (Which layer is
which?--you should be able to say from the density data in your Chemical Data Table, but you can do a
drop test to be sure!) Remove the aqueous layer and add another 2 mL of 5% sodium bicarbonate
solution. Gently mix the two layers by pipet mixing, and again remove the aqueous layer. Make sure all
of the acid has been neutralized by adding a few more test drops of sodium bicarbonate; if there is still
bubbling, add another 1 to 2 mL of sodium bicarbonate, mix, let separate, and discard the aqueous layer.
In the last rinse, remove as much of the aqueous layer as possible. Add a small amount of sodium
sulfate to remove traces of moisture, let stand for 5 min, then remove the organic layer by pipet
filtration, leaving the drying agent in the tube. Transfer the organic liquid into the long-neck roundbottom flask from the microscale kit. Distill the liquid using simple distillation, being sure to record the
temperature range over which distillate is collected, and transfer the distillate to a tared shorty vial.
Cleaning Up
The aqueous layers from the sodium bicarbonate washings can go down the drain with flushing
water. The distillation residue should be discarded in the organic waste container.
Analyses
The product can be analyzed by NMR, GC, GC-MS, IR, or by refractometry. See your assignment
strip for your assigned analysis.
Questions
Answers to the following should be included in your Final Report
1. Write balanced equations for all neutralization reactions that take place when the sodium
bicarbonate solution was used to wash the reaction mixture.
2. At what step of the purification would unreacted isopropyl alcohol be removed from the product?
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Synthetic Experiment PreLab Grading Sheet
Name(s):
TA:
Date:
PreLab For Exp't #: 88
Title: Mystery Product: The Acid-catalyzed Reaction of Acetic Anhydride and
Isoopropyl Alcohol
Possible
Points
Date, Name, Desk #, Experiment # & Title(abbreviated after 1st pg), Section &
TA Name
8
Summary
10
Goals
10
Reactions, structures, diagrams
16
Completeness of Chemical Data Table(s)
14
PreLab Exercise
16
Spectral Features Comparison (NMR, GC, RI)
14
Work-up - Explanation of the product isolation and purification process
12
TOTAL FOR PRELAB
100
Missed
Points
Date Handed in:
Total Points:
General Comments:
3
Synthetic Experiment Final Report Grading Sheet
Name:
TA:
Date:
Final Report For Exp't #: 88
Title: Mystery Product: The Acid-catalyzed Reaction of Acetic Anhydride and
Isoopropyl Alcohol
Possible
Points
Name, Date, Experiment Title (abbreviated after 1st page) and every page
numbered
4
OBSERVATION and DATA - Overall organization, readability, completeness
8
Data: Weighing data, molecular weights, moles, density, volumes, analysis
conditions. (Examples: NMR solvent, IR – KBr and sample weight, GC
analysis conditions sheet)
12
Yield: Show % yield calculations with limiting reagent clearly stated.
12
Missed
Points
Purity: boiling point, color, or other indicators of purity.
RESULTS AND DISCUSSION - Overall organization, readability, completeness
8
16
Results; Achievement of goals, discussion of product
Product Analysis Data: Quality and Interpretation – Structure(s) drawn on
each Spectrum or Chromatogram and peaks interpreted.
24
Assignment and discussion of all NMR peaks, or major IR peaks, or GC peaks
or RI.
Unknown Determination: Correct ID of the “Mystery” Product
See Lab Guide Chapter 3, Section 3.4 for guidelines in annotating spectra and
Ch 11 for help with interpretation.
POSTLAB PROBLEMS
16
TOTAL POINTS
100
Date Handed in:
Total Points:
General Comments:
4