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

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)-O-center dot) were preferred to be formed in CH3CN and responsible for the formation of carbonyl compounds, while superoxide ion radicals (O-center dot(2)-) 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.