Reaction characteristics of the dynamic kinetic resolution of 1-phenylethanol over Ru complexes immobilized on PTA-modified gamma-alumina and Novozym 435 (R)

Abstract

Homogeneous Ru catalysts, [RuCl2(p-cymene)](2) (Ru-p-cymene) and (eta(5)-C5Ph4O)(2)HRu2H(CO)(4) (Shvo's catalyst), were immobilized on phosphotungstic acid (PTA)-modified gamma-alumina (Augustine's method) and applied to the dynamic kinetic resolution (DKR) of 1-phenylethanol (1-PE) with an enzyme (Novozym 435 (R)). The immobilized catalysts showed rates similar to those of homogeneous catalysts in conventional reaction conditions and the immobilized Shvo's catalyst showed no leaching during reaction. The yield to the ester of the immobilized catalysts was found to be dependent on the solvent and alkali additive. When the DKR of 1-PE was performed in n-octane, the reaction proceeded well without an alkali additive over Ru-p-cymene, which is a new observation. Furthermore, the reaction yields with the immobilized catalysts were greater than those with the corresponding homogeneous catalysts at that condition. The main factors influencing the process carried out in the DKR mode over the Ru complexes are the solvent, the support, the alkali additive and the catalyst type. The effects of the reaction temperature, type of acyl donor and catalyst/enzyme amount were further investigated in order to find the optimum process condition of the DKR using immobilized catalysts without alkali additive in n-octane. (C) 2013 Elsevier B.V. All rights reserved.