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A lipase catalysed enantioselective hydrolysis process under in situ racemization of the remaining (R)-ibuprofen ester substrate with sodium hydroxide as the catalyst was developed for the production of S-ibuprofen from (R,S)-ibuprofen ester in isooctane. Detailed investigations on parameters study indicated that 0.5 M NaOH, addition of 20% (v/v) co-solvent (dimethyl sulphoxide), operating temperature of 45 degrees C, and 40 mmol/L substrate gave 86% conversion and 99.4% optical purity of S-ibuprofen in dynamic kinetic resolution. Meanwhile, in common enzymatic kinetic resolution process, only 42% conversion of the racemate and 93% enantiomeric excess of the product was obtained which are of lower values as compared to dynamic kinetic resolution. The S-ibuprofen produced during each process was evaluated and approximately 50% increment in concentration of S-acid product was produced when dynamic kinetic resolution was applied into the process.

The aim of this study is to review on mechanism of ultrasonic irradiation in enzymatic esterification reaction, the effect on enzyme activity and stability and also rate of reaction in ultrasonic assisted enzymatic reaction. Conventional enzymatic esterification system using immobilized enzyme generally have a limitation in internal mass transfer that might plausible to reduce rate of ester formation. However, this obstacle can be overcome using ultrasonic system that offers different movement of the molecule. The mechanism of ultrasonic is based on the high energy waves that create cavitations in the liquid solution. Better cavitations are attained at high amplitudes, nucleation sites, lower temperature, external pressure and dissolved gas. While for the activity and stability of the enzyme during ultrasonic irradiation process, appropriate wave duty cycles, acoustic power, prolong of exposure and support materials are required in order to retain the stability and activity of the enzyme. Application of ultrasonic irradiation in enzymatic esterification reaction enhanced mass transfer and diffusion of substrate and product within the reaction medium. This factor results in higher reaction rate as compared to the mechanical agitation.

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