Lipase-catalyzed acetylation of 2-alkanol with vinyl acetate has been studied kinetically using
Burkholderia cepacia lipase (BCL), enantiomerically pure (
R)- and (
S)-2-alkanols and different organic solvents. The rate equation was derived by the steady state method for the simplified mechanism. The second order rate constants (
kR and
kS) for (
R)- and (
S)-2-alkanols were evaluated from the slopes of the double reciprocal plots,
v-1 vs. [2-alkanol]
-1, where
v is the initial rate of the reaction. The log
kR value increased with the solvent hydrophobicity log
P, where
P is a partition coefficient of a given solvent between octanol and water. The log
kS value also increased with log
P except the bulky solvents such as 1,4-dioxane and cyclohexane, in which the rates were faster than those expected from the log
kS vs. log
P plot. The slope of log
kS vs. log
P plot was larger than that for (
R)-2-alkanol. Thus, log
E (
E=
kR/
kS: enantioselectivity) decreased with log
P except the bulky solvents. The rate constants and the enantioselectivity were different depending on the structure (carbon number CN) of 2-alkanol. The log
E vs. CN plot was minimized at CN=8 and 10 and the log
kS vs. CN plot maximized at CN=8 and 10. In contrast the log
kR vs. CN plot showed a different feature from the log
E vs. CN plot. These facts suggest that dependence of
E on CN is more strongly affected by the reactivity of (
S)-2-alkanol than that of (
R) isomer in this acetylation.
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