GERANYL ACETATE SYNTHESIS BY LIPASE-CATALYZED TRANSESTERIFICATION IN SUPERCRITICAL CARBON-DIOXIDE

The synthesis of geranyl acetate by transesterification catalyzed by i mmobilized lipase from Mucor miehei was studied in supercritical carbo n dioxide (SCCO2) and compared with n-hexane. The influence of water c ontent on the thermostability of the enzyme was investigated in SCCO2. The increase of water content and increase of temperature diminished enzyme stability. The half-life of the dry enzyme in SCCO2 at 100-degr ees-C was about 24 h. The effect of ester chain length on the rate of reaction was investigated. Propyl acetate was found to be the best sub strate for geranyl acetate synthesis in both media. In order to define the optimal conditions of the reaction, optimization of water content was carried out. The water content of the solid phase seemed to be th e most important factor for the activity of the enzyme. The same optim um, 8-10% (w/w) water content, was determined in both media. The kinet ics of the reaction are suggested to fit a Ping-Pong Bi Bi mechanism i n which inhibition by excess of geraniol has been identified. The valu es of all apparent kinetic parameters which were not affected by the e xternal diffusional limitations were calculated. The differences betwe en the kinetic constants in both media were discussed. Considering the reaction rates and the maximum velocity of the reaction, the SCCO2 is not better than the conventional organic solvents, such as hexane, fo r the reaction of transesterification between geraniol and propyl acet ate.