Mechanistic investigations of the reaction network in chemobiocatalyzed synthesis of R1Phenylethyl Acetate

• The kinetics and reaction network of the onepot synthesis of R1phenylethyl acetate was investigated at 70°C in toluene over a combination of three different catalysts: PdZn/Al2O3 as a catalyst for acetophenone hydrogenation, lipase as an enzymatic catalyst for R1phenylethanol acylation with ethyl acetate and Ru/Al2O3 as a racemization catalyst for S1phenylethanol. In addition to the desired reactions, other reactions, namely hydrogenolysis and dehydration of (R, S)1phenylethanol and debenzylation of (R, S)1phenylethyl acetate also occurred. The kinetic results revealed that ethylbenzene formation was enhancedwith higher amounts of PdZn/Al2O3, whereas lipase did not catalyze ethylbenzene formation. Furthermore, ethylbenzene was formed in the hydrogenolysis of (R, S)phenylethanol and in the debenzylation of (R, S)1phenylethylacetate over Pd/Al2O3 catalyst. The presence of Ru/Al2O3 catalyst, in which Ru was in the oxidation state of 3+, enhanced the formation of R1phenylethyl acetate, although no clear racemization of S1phenylethanol during the onepot synthesis of  R1phenylethyl acetate was observed. Dynamic kinetic resolution of (R, S)1phenylethanol in toluene, was, however, demonstrated over Ru/Al2O3 and lipase.

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