Part I. Enzymatic synthesis of lactate and glycolate esters of fatty alcohols

Abstract

Optimum conditions were determined for the esterification reactions of lactic and glycolic acids with fatty alcohols (C8–C16) in the presence of a lipase from Candida antarctica. This synthetic method gives nearly complete conversion to the desired ester in a relatively short time with high volumetric productivity. In acetonitrile the maximum yields of dodecyl lactate (95% in 48 h) and glycolate (87% in 24 h) were obtained in the presence of a desiccant and 0.28% (w/w) added water, respectively. The procedure permits one to increase substrate concentrations without significant adverse effects on the yield of lactate ester for lactic acid concentrations of 0.25 to 1 M. Similar yields of lactate ester (94–96%) were obtained for alcohol chain lengths from C8 to C16. Although esterification of lactic acid with fatty alcohols is not favored in apolar solvents (e.g. n-hexane), esterification of glycolic acid in n-hexane produces high yields of the glycolate ester (96% in 4 h). In the solvent-free system, esterification of lactic acid with a fatty alcohol requires the presence of desiccant from the beginning of the process (yield of 70% in 48 h). For the reactions of glycolic acid, a strategy in which a desiccant is added after 24 h of reaction gives the maximum yield of the glycolate ester (91%) in a shorter time (48 h of total reaction time). Alternatively, transesterification between the alcohol of interest and ethyl lactate increases the maximum yield of dodecyl lactate (87% in 24 h).