Allylic oxidation of cycloalkenes, represented by cyclohexene, is a promising process for the obtention of α,β-unsaturated alcohols and ketones which are valuable intermediates in manufacturing a variety of chemicals. However, during the oxidation of cycloalkenes, allylic oxidation and epoxidation are often competitive processes and occur simultaneously. To verify the reaction pathways of cyclohexene oxidation in the presence of transition-metal-substituted phosphotungstates [PW11M(L)O39]m- (PW11M, M = CoII, CuII, FeIII, NiII, MnII, L = H2O or absence) and hydrogen peroxide (H2O2), homogeneous catalytic oxidations in acetonitrile were experimentally studied. The catalytic activities of allylic oxidation were found to strongly depend on the transition metals, and PW11Co showed the highest activity. The product distribution and the catalyst stability were dominated by the H2O2-to-PW11M mole ratio, whereby low or high led to stable structure of PW11M and predominant formation of allylic oxidation products or decomposition of PW11M (M = Co, Cu, Ni and Mn), respectively. The decomposition behaviors of PW11M in the presence of H2O2 were investigated by nuclear magnetic resonance (NMR), ultraviolet visible (UV-Vis) and Fourier transform infrared (FT-IR) spectroscopy. Different from the activation of allylic C–H bond by free radicals, the oxidation of C=C double bond was based on tungsten-peroxo species. A reaction mechanism composed of radical and non-radical processes was proposed from the selective inhibiting effect of a radical scavenger, electron paramagnetic resonance (EPR) spectra and kinetic data, to describe the reaction pathways of cyclohexene oxidation.

Reaction pathways of cyclohexene oxidation in the presence of transition-metal-substituted phosphotungstates and hydrogen peroxide

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.