Large-scale preparation of (Z)-3-hexen-1-yl acetate using Candida antarctica immobilized lipase in hexane

A kilogram-scale synthesis of (Z)-3-hexen-1-yl acetate, in hexane, on direct esterification of (Z)-3-hexen-1-ol with acetic acid in the presence of 2% (w/w reactants) of an immobilized lipase from Candida antarctica (Novozym 435) is reported. Conversion yields ranging from 92 to 96% were obtained after optimization of various parameters. In that respect, elimination of the water proved crucial. Using at both the laboratory large scale (preparation of 200-400 g of ester) and the pilot scale (1-5 kg) a "reflux" rotary evaporator equipped with a graduated decantation flask, we were able to trap the water evolved during esterification while at the same time monitor the time course of the reaction. As a consequence of both an efficient water trapping and of a gentle dispersion of the immobilized lipase into the reaction medium, the lifetime of the enzyme was significantly prolonged. At the laboratory large scale (LLS), the yield was still greater than or equal to 90% after seven consecutive utilizations whereas at the pilot scale (PS), it reached 93% after reusing the enzyme four times. In those conditions, the amount of immobilized enzyme necessary to produce 1 kg of (Z)-3-hexen-1-yl acetate was 18 g (1.8%) and 60 g (6%) at the LLS and the PS, respectively. (C) 1998 John Wiley & Sons, Inc.