Enzymatic synthesis of caffeic acid phenethyl ester

Caffeic acid phenethyl ester was successfully synthesized from caffeic acid and phenethyl alcohol catalyzed by Novozym 435. Caffeic acid was found to yield much higher conversion in non-polar solvents than in polar ones, albeit its low solubility in non-polar solvents. Among all solvents tested, isooctane gave the highest conversion and was chosen as the solvent in this study. A reaction temperature of 70 °C was chosen to give high solubility of caffeic acid and hence high conversion. The optimum molar ratio of acid to alcohol was found to be 1:92. More alcohol resulted in the inactivation of enzyme. An acid to enzyme ratio of 1:15 (w/w) gave nearly a 100% conversion in 48 h. The conversion was found to be independent of stirring speed. Low stirrer speed of 50 rpm was enough and necessary to provide good mixing. Results from batch reuse stability study show that Novozym 435 could maintain more than 90% of its original activity up to the third batch. The enzyme lost its activity faster under higher stirring speed. Reactions carried out without stirring gave better enzyme batch stability, however, the conversions were always less than 90%.