The Synthesis of Alpha-Methylbenzyl Acetate
July Kelley
Cochise College
Spring 2004
Alpha-methylbenzyl acetate was successfully synthesized from the
simpler compound, styrene.
The styrene was brominated, then
dehydrobrominated to yield phenylacetylene. The phenylacetylene was
hydrated to acetophenone. The acetophenone was reduced via NaBH4.
The resulting alpha-methylbenzyl alcohol was esterfied to the final
product, alpha-methylbenzyl acetate.
Introduction
Starting at the end of the Fall 2003 semester, the organic chemistry class started a multistep synthesis project to make alpha-methylbenzyl acetate (6). This is a benzyl acetate
compound reported to smell like gardenias. It is used to make scented products1. This
project applied the material learned during lecture to actual laboratory experiments. Lab
techniques learned during the first part of this course are used during this synthesis. We
also learned how to write up experiments in a lab notebook.
Results and Discussion
I had good results for this series of experiments with the only mishap being spilling some
of the desired product during recrystalliation in G-0 resulting in a 12% yield for that
particular experiment. All of my IRs supported that I had obtained the desired products.
The percent purity of my final products was determined by either GC chromatography or
from examining the final tlc plate. The final product was a slightly yellow, viscose
liquid.
(1) Bauer, K.; Garbe, D. Common Fragrance and Flavor Materials. VCH. 1985, 76.
Br
b
a
Br
1
2 (12%)
O
d
c
3 (48%)
O
4 (57%)
OH
O
e
5 (82%)
6 (81%)
Key for drawing
A. (nBu)4N+Br3-, CH2Cl2, RT
B. 50% NaOH, pentane, (nBu)4N+HSO4C. 88% HCO2H, reflux
D. 1) NaBH4, 95% EtOH
2) H3O+
E. Acid chloride, pyridine, CH2Cl2
Conclusion
My overall percent yield was 2.18 %. I believe this yield could be improved by
concentrating on the first part of this synthesis. I liked the continuity of the experiment;
how the product for one experiment was the starting material for the next. I wish we
could have used our actual product for staring material but understand that time
constraints do not allow us to purify each product. The final product did smell like
gardenias, but not until diluted with EtOH.
Experimental Section
General Section. Melting point was determined with the melting point apparatus. IRs
was taken of the pure compounds with a Thermo Nicolet IR 200 Spectometer. H-NMR
data was provided by Mr. Cox setting was 500 Hz and done in CDCl3 unless otherwise
noted. All tlcs were eluted in CH2Cl2.
Styrene dibromide (2). A 25 ml Erlenmeyer flask equipped with a stir bar was charged
with 500 l styrene (1) and 5 ml CH2Cl2. Dropwise 3.16 g (nBu)4N+Br3 - was added
over 3 minutes. At ambient temperature, reaction was mixed for 30 minutes. The
reaction mixture was a clear yellow color. After 30 minutes, a tlc indicated the reaction
was over the mixture was worked up. The work up was washing the reaction mixture
with 3 ml distilled water, then 2 times with 5% sodium thiosulfate, and again with
distilled water. After drying (anhydrous Na2SO4), the excess solvent was removed with a
rotary evaporator. The resulting yellow solid was recrystallized with hot 95% ethanol to
give 0.14 g of clear crystals. The percent yield was 12.2 %. Mp: 50 C. H-NMR
(CDCl3), (500 MHz):  3.89 (multiplet, 1 H),  4.09 (singlet, 1 H),  5.10 (multiplet, 1
H), and  7.31 (singlet, 5 H). IR (KBr) = 1456.52, 1753.41, 2375.11, 2958.00, 3031.11
cm-1. Rf (20/80 ethyl acetate/hexanes): 0.83.
Phenylacetylene (3). A 25 ml Erlenmeyer flask equipped with a stir bar was charged
with 0.6g styrene dibromide and 5 ml of hexanes and then 2.32 g of PTC. Dropwise 1.45
ml of 50% NaOH was added over 4 minutes. At ambient temperature, reaction was
mixed for 45 minutes. The reaction mixture was a clear yellow color with a white
precipitate. After 45 minutes, a tlc indicated the reaction was over the mixture was
worked up. The work up consisted of decanting the reaction mixture and then washing 3
times with hexanes and then with distilled water. After drying (anhydrous Na2SO4), the
excess solvent was removed with a rotary evaporator. The resulting water white liquid
weighed 0.11 g. The percent yield was 47.8%. H-NMR (CDCl3):  3.00 (singlet, 1 H), 
7.5 (multiplet, 5 H). IR = 2856.44, 2952.61, 2955.72, 3031.57, 3079.85, 3292.47 cm-1.
Rf (10/90 CH2Cl2/ hexanes): 0.86.
Acetophenone (4). A 10 ml round bottom flask equipped with a stir bar was charged
with 500 l of phenylacetylene and 5 ml of 88% HCO2H. A water condenser was
attached to the flask. The reaction mixture refluxed for 75 minutes. The reaction mixture
was a clear black liquid. After 75 minutes, a tlc indicated the reaction was over the
mixture was worked up. The work up consisted washing with distilled water, extracting
twice with CH2Cl2, twice with Na2CO3, and twice with distilled water. Reaction mixture
is an opaque yellow liquid. After drying (anhydrous Na2SO4), the excess solvent was
removed from the clear reaction mixture with a rotary evaporator. The resulting clear
yellow liquid weighed 0.3 g. The percent yield was 57.41%. H-NMR (CCl4):  2.5
(singlet, 3 H),  7.3 (multiplet, 3 H),  7.75 (multiplet, 2 H). IR = 1681.1, 2923.2,
3004.88, 3062.51, 3352.2 cm-1. Rf (30/70 hexanes/ CH2Cl2): 0.6.
Alpha-methyl benzyl-alcohol (5). A 10 ml round bottomed flask equipped with a stir
bar was charged with 500 l acetophenone dissolved in 95% EtOH. Dropwise 0.163
NaBH4 was added over 3 minutes. Reaction mixture was cloudy white. At ambient
temperature, reaction was mixed for 30 minutes. The reaction mixture was a cloudy white
color. After 30 minutes, a tlc indicated the reaction was over the mixture was worked up.
Reaction mixture was cooled in ice water bath. Dropwise 2 ml HCl was added over 5
minutes. Reaction mixture was washed three times with CH2Cl2 and once with distilled
water. After drying (anhydrous Na2SO4), the excess solvent was removed with a rotary
evaporator. The resulting yellow liquid weighed 0.43 g. The percent yield was 81.9%.
H-NMR  1.5 (doublet, 2 H), 1.9 (singlet, 1 H),  4.75 (quadruplet, 3 H),  7.2
(multiplet, 5 H). IR = 1493.39,2973.38,3352.42 cm-1. Rf (CH2Cl2): 0.5.
Alpha-methylbenzyl acetate (6). A 30 ml Erlenmeyer flask equipped with a stir bar was
charged with 500 l alpha-methylbenzylalcohol and 5 ml dichloromethane. 0.36 g of
pyridine was added. Dropwise 1.29 g of acid chloride dissolved in 3 ml of
dichloromethane was added over 3 minutes. Reaction mixture formed to two layers; the
top layer was cloudy white with white precipitate. Two ml of dichloromethane was
added to make one layer. At ambient temperature, reaction was mixed for 15minutes. The
reaction mixture was a cloudy white color. After 15 minutes, a tlc indicated the reaction
was over the mixture was worked up. Reaction mixture was cooled in ice water bath.
Yellow precipitate formed. Quenched with distilled water. Washed 2x with 3M HCl, 2x
distilled water and 2x with saturated sodium bicarbonate. Reaction mixture was water
white. After drying (anhydrous Na2SO4), the excess solvent was removed with a rotary
evaporator. The resulting yellow liquid weighed 0.55 g. The percent yield was 80.8%.
H-NMR (CDCl3): δ 1.53 (doublet, 3 H), δ 2.03 (singlet, 3 H) δ 5.9 (multiplet, 1 H) δ 7.32
(singlet, 5 H). IR = 1729.81, 1826.34, 2934.88, 2982.74, 3034.32, 3064.71 cm-1. Rf
(CH2Cl2): 0.75.