Optimization of lipase-catalyzed enantioselective esterification of (±)-menthol in ionic liquid.

Response surface methodology was successfully applied to optimize lipase-catalyzed enantioselective esterification of (±)-menthol. The effects of various reaction conditions, including reaction time, temperature, enzyme loading, substrate molar ratio and water activity, were investigated. A Central Composite Rotatable Design was employed to search for the optimal conversion of (±)-menthol and enantiomeric excess. A quadratic polynomial regression model was used to analyze the experimental data at a 95% confidence level (p<0.05). The analysis confirmed that reaction temperature, enzyme loading and reaction time were the significant factors affecting the conversion of (±)-menthol. Moreover, reaction temperature, enzyme loading, substrate molar ratio and reaction time were found to affect the enantiomeric excess significantly. The coefficient of determination of these two models was found to be 0.980 and 0.967, respectively. Two sets of optimum reaction conditions were established and the verified experimental trials were performed for validating the optimum points. Under the optimum conditions, the conversion of (±)-menthol and the enantiomeric ratio exceeded 53% and 40%, respectively.