Synthesis of benzoates by enzymatic catalysis in heterogeneous medium

Abstract

The enzyme-catalyzed synthesis of methyl and 1-butyl benzoates is reported. Direct esterification is performed with good yields by lipase from Candida rugosa suspended in a hexane/toluene mixture. Influence of substrates concentration, water content and toluene ratio are examined. Methanol and 1-butanol are lipase-inhibitors: they interact with the water adsorbed on lipase and on the enzyme as well. Increasing benzoic acid concentration in the system partially eliminates the alcohol inhibition. Water content greatly affects reaction kinetics and must be optimized to both activate the lipase and reach good conversion yields. Toluene, used to solubilize benzoic acid, negatively acts on reaction kinetics, mostly by increasing the partition of benzoic acid for the organic phase. The kinetic modelisation of 1-butyl benzoate synthesis agrees with a ping-pong Bi–Bi mechanism with 1-butanol inhibition. Apparent reaction coefficients are then determined.