Bioorganic & Medicinal Chemistry Letters 16 (2006) 4041–4044
Lipase catalyzed synthesis of benzyl acetate in solvent-free
medium using vinyl acetate as acyl donor
Abir B. Majumder, Bhupender Singh, Debjit Dutta,
Sushabhan Sadhukhan and Munishwar N. Gupta*
Department of Chemistry, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, India
Received 23 February 2006; accepted 2 May 2006
Available online 22 May 2006
Abstract—Use of vinyl acetate as acyl donor in transesterification of benzyl alcohol catalyzed by a commercially available lipase
Lipozyme RM IM) gave 100% conversion in 10 min. The excess acyl donor and the enzyme could be recovered and reused. Unlike
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(
the chemical catalytic processes, it produced no undesirable side product.
2006 Elsevier Ltd. All rights reserved.
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9
,10
The chemical synthesis of benzyl acetate is carried out
by acetoxylation of toluene by using inorganic cata-
esterification and transesterification reactions.
Hence, Lipozyme RM IM was used in the present
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1
,2
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lysts. This chemical synthesis produces unwanted side
3
work. The solvent-free medium (i.e., using reactants
as such as medium) was employed. Some advantages
of employing solvent-free medium have been discussed
,4
product and it also has an associated problem of cat-
5
alyst deactivation. There has been some work on the
6
,7
12
formation of benzyl esters using enzymes. However,
no work seems to have been carried out on the lipase
catalyzed synthesis of benzyl acetate.
previously. It was seen that for efficient and fast
conversion, it was necessary to operate with high
amount of enzyme (10% of the mass of the two
reactants) and excess acyl donor (6· benzyl alcohol on
a molar basis) (Table 1 and Fig. 1). It may be added that
Benzyl acetate finds extensive uses in perfumery, food,
3
and chemical industries. The present work shows that
a commercially available lipase (Lipozyme RM IM),
similar high level of enzyme load has been generally
9,13,14
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reported to be required in such reactions.
Conversion in enzyme catalyzed reactions has been
100%
under optimized conditions, in solvent-free medium,
can be a very efficient biocatalyst for conversion of
benzyl alcohol to benzyl acetate.
9
,15–17
reported earlier,
however, the 100% conversion
obtained in 10 min is among the fastest reported for
enzyme catalyzed transesterification reactions.
For enzyme catalyzed esterification and transesterifica-
tion reactions in non-aqueous media vinyl acetate is
considered a very good choice for acyl donor. Isomeri-
Figure 2a shows further optimization to reduce the
required amount of enzyme and the acyl donor. With
vinyl acetate just at 1:1 molar ratio (with respect to
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zation of the unstable vinyl alcohol to acetaldehyde as
the product drives the reaction in this forward direction.
Lipases have proven to be versatile catalysts for such
1
8
the benzyl alcohol), 10% enzyme (w/w, reactants)
was necessary to obtain 100% conversion (as monitored
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19
reactions. Lipozyme RM IM, a commercially available
lipase, is among the more economical industrial level
catalysts which has been extensively employed in several
by GC) ; although with the reduced concentration of
acyl donor, it required 180 min (96% conversion though
could be obtained in 60 min) (Fig. 2a). With vinyl ace-
tate at 1:6 molar excess, even 5% enzyme (w/w, reac-
tants) could also produce 100% conversion (Fig. 2b).
Again the reaction time was greater than 60 min and
Keywords: Benzyl acetate; Mucor miehei lipase; Lipozyme RM-IM;
Solvent-free media; Low water system.
180 min was adequate. Thus, a combination of high
*
level of enzyme and excess acyl donor was required to
obtain 100% conversion in a short period of 10 min.
There is obviously a trade off behavior of enzyme
2
These authors have contributed equally to the work described in this
manuscript.
0
960-894X/$ - see front matter ꢁ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.05.006