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

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.