Lipae-catalyzed synthesis of isoamyl isobutyrate - optimization using a central composite rotatable design

Rhizomucor miehei lipase, Lipozyme IM-20, was used to catalyze the esterifi cation reaction between isobutyric acid and isoamyl alcohol to synthesize i soamyl isobutyrate in n-hexane. Response surface methodology (RSM) based on a five-level, four-variable central composite rotatable design (CCRD) was employed for optimization with respect to four important reaction variables enzyme/substrate (E/S) ratio, substrate concentration, reaction time, and temperature. Conversion was efficient in an acid concentration range of 0.5 -2.5 M, even when a very low E/S ratio (5 g/mol) was employed. Although an increase in temperature resulted in improved reaction rates, overall conver sions remained practically unchanged, as the yields obtained at lower tempe ratures (30-40 degreesC) were higher. Reaction time also exhibited a less s ignificant effect on ester yields at higher E/S ratios. The optimum conditi ons predicted for achieving maximum ester yield (2.2 M) are: E/S ratio, 19. 6 g/mol; substrate concentration, 2.5 M; reaction time, 18 h and temperatur e, 26.5 degreesC. (C) 2001 Elsevier Science Ltd. All rights reserved.