Effect of Solvent Hydrogen‐Bonding and Catalyst Pore Size on Catalytic Oxidation of Benzylic Alcohols

Control over selective oxidation rates remain a key challenge in industrial chemicals production. Here, we demonstrate how liquid phase alcohol oxidation is a complex interplay among solvent, reactant, catalyst porosity, and local active site environment. Specifically, we study the impact of sulfolane versus acetonitrile solvents on rates of catalytic oxidation of benzylic alcohols to the corresponding ketone using hydrogen peroxide (H ₂ O ₂ ) over Ti‐based heterogeneous catalysts of different local steric environments. The polar, H‐bonding sulfolane enhances the reaction rate in wide pore materials, presumably by promoting hydrogen transfer steps. However, in sulfolane, the reaction rate also decreases as the local environment around the Ti active site becomes more sterically congested, either by decreasing catalyst pore size or by increasing reactant bulk. This is assigned to an effect of the bulky hydrogen‐bonding complex formed between reactant alcohol and sulfolane that introduces transport limitations. Finally, large‐pore Ti–SiO ₂ catalysts modified with additional SiO ₂ near the active sites were able to further tune reaction rates in these two solvents by a combination of effects induced in the immediate pore environment. Better understanding of size‐ and solvent‐dependent transport and kinetic effects should allow for improved control over the rate of selective oxidation reactions.