Impact of Fluorinated Cobalt(II) Phthalocyanine Catalysts on Aerobic Thiol Oxidation Kinetics

Abstract

Kinetic studies were conducted for the aerobic oxidation of 2-mercaptoethanol (2-ME) and 4-fluorobenzenethiol (4-FBT) catalyzed by cobalt(II) phthalocyanines: H16PcCo, F16PcCo, and F64PcCo, each exhibiting a metal center subject to increasing Lewis acidity and steric hindrance. The experiments were performed in a reaction-limited, isothermal, bench-scale, batch reactor, with thiol concentrations measured using GC/FID. Conversions of 2-ME to 2-hydroxyethyl disulfide and 4-FBT to 4-fluorophenyl disulfide in excess of 90% were achieved. Kinetic analyses suggest that the substrate binding and electron transfer are directly related to the Lewis acidity and steric bulkiness of catalyst molecules. Substrate binding was found to be the slow step for thiol oxidations catalyzed by H16PcCo. The rate-determining step for thiol oxidations, catalyzed by F16PcCo and F64PcCo, is the expulsion of the thiyl radical (RS•) from the catalyst molecule.