Solvent effect on the formation of active free radicals from H2O2 catalyzed by Cr-substituted PKU-1 aluminoborate: Spectroscopic investigation and reaction mechanism

Abstract

The nature of a solvent plays an important role in selectively catalytic oxidations, influencing the catalytic activity and product selectivity. Most work attribute such roles to the polarity, acidity/basicity, or coordination ability of the solvent. Here, we systematically investigated the generated active free radicals in five different organic solvents during the catalytic oxidation of styrene by H2O2. Cr-doped PKU-1 aluminoborate was selected as the heterogeneous catalyst in this system. The solvent effect was comprehensively understood along this perspective. Hydroxyl radicals (OH) were preferred to be formed in CH3CN and responsible for the formation of carbonyl compounds, while superoxide ion radicals (O2−) were favored in DMF and beneficial to the epoxide production. The function of Cr3+ was correlated with the solvent effect and a tentative mechanism pathway was proposed accordingly.