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°C) 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°C 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°C. Under the above mentioned conditions, the experimental yield was 195 mM, which is well matched with the predictive yield.