Response surface methodological approach for the synthesis of isobutyl isobutyrate

Immobilized lipase from Rhizomucor miehei (Lipozyme IM-20) was used for the synthesis of isobutyl isobutyrate by direct esterification of isobutyric acid and isobutyl alcohol. Response surface methodology based on a five-variable central composite rotatable design was used to determine the effect of solvent (log P ranging from 0.49 to 4.5), acid concentration (0.05-0.25 M), alcohol to acid ratio (1.25:1), enzyme concentration (25-225 mg), incubation period (24-120 h) and incubation temperature (30-70 degreesC) on the esterification reaction. The extent of esterification was good at all acid concentrations employed in the range 0.05-0.25 M with increase in enzyme concentration. Even with a low enzyme concentration of 25 mg, 50% conversion was observed. The enzyme was active at all the temperatures ranging from 30 to 70 degreesC even up to an incubation period of 120 h. The results obtained show that the yields were higher in solvents having log P > 2, i.e., when solvents of higher non-polarity were employed. Optimum conditions for predicting maximum ester yield were 200 mM using 0.2 M, isobutyric acid; 0.2 M, isobutanol; enzyme concentration, 225 mg; incubation period, 72 h and hexane (log P = 3.5) as reaction media at reaction temperature, 70 degreesC. Under the above mentioned conditions, the experimental yield was 195 mM, which is well matched with the predictive yield. (C) 2001 Elsevier Science Ltd. All rights reserved.