10.1002/hlca.201900154
Helvetica Chimica Acta
HELVETICA
reflux chloroform. Although benzoic acid or imidazole alone did not
promote the trans-esterification, the mixture of benzoic acid and
imidazole effectively catalyzed the trans-esterification.
A solution of decane, benzoic acid (8 mmol), octan-1-ol (8 mmol), and
imidazole in xylene (8 mL) was refluxed with removing water by Dean-
Stark apparatus. The conversion of octan-1-ol was monitored by GC
analysis using decane as an internal standard.
Table 2. Trans-esterification catalyzed by the mixture of benzoic acid and imidazole.
Equation (2) was used for the kinetic analysis. The integral of equation (2)
catalyst
gives equation (5).
AcOR + C4H9OH
AcOC4H9 + ROH
!
!
−
= 2ꢀ!ꢀ
(5)
1
2
3
!
!
[!"#$%$"]
!"#$%$"
!
a: R = benzyl
, where initial concentration of octan-1-ol [alcohol]0 = 1.00 mol L-1. The
relative concentration of octan-1-ol was used as [alcohol]. [Alcohol]-2 was
plotted against the time (t), and k1 was determined from the slope (2k1) of
the plot.
b: R = 4-nitrophenyl
Catalyst[a]
Yield of 3[b]/%
1a[c]
1b[d]
Trans-esterification of benzyl acetate with butan-1-ol (general
method)
none
< 1
15
6
0
PhCOOH
0
Imidazole
0
A mixture of octadecane, benzyl acetate (2 mmol), butan-1-ol (20 mmol),
and a mentioned additive was refluxed for 24 h. The yield of benzyl
alcohol was determined by GC analysis using octadecane as an internal
standard.
PhCOOH + imidazole
16
49
[a] 10 mol % each was used. [b] GC yield. The range of error was less than 3% ( 1%
for 33% yield). [c] reflux with 10 equivalent of BuOH for 24 h. [d] reflux in
chloroform with 10 equivalent of BuOH for 24 h.
Trans-esterification of 4-nitrophenyl acetate with butan-1-ol
(general method)
Conclusions
A solution of hexadecane, 4-nitrophenyl acetate (2 mmol), and butan-1-ol
(20 mmol) and a mentioned additive in chloroform (5 mL) was refluxed
for 24 h. The yield of 4-nitrophenol was determined by GC analysis using
hexadecane as an internal standard.
This work demonstrates that the dual activation mechanism works even
in the homogeneous mixture of acid and base. Thus, the stronger acid is
not always the more effective catalyst. It should be pointed out that the
carboxylic acid and imidazole moieties play important role in the enzyme
as the acidic and basic moieties, respectively. Although it has been
believed that both functional groups were spatially separated by the
protein backbone to work separately, this work demonstrates that spatial
separation is not essential for the cooperative work.
Author Contribution Statement
YM and ST carried out the experimental work supervised by NK, who
summarized all works.
References
Experimental Section
[1]
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Chemicals and Instruments
All chemicals and solvents were reagent grade, and were used without
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octadecane was used as an internal standard to determine the
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3
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