Trace Water-Promoted Oxidation of Benzylic Alcohols with Molecular Oxygen Catalyzed by Vanadyl Sulfate and Sodium Nitrite under Mild Conditions

An inexpensive catalytic system consisting of vanadyl sulfate and sodium nitrite was developed for the oxidation of benzylic alcohols with molecular oxygen under mild conditions. Benzyl alcohols with various substitutions were efficiently converted to their corresponding aldehydes with high conversion and selectivity under 80 C (e.g., 4-nitrobenzyl alcohol was smoothly oxidized to 4-nitrobenzyl aldehyde with 94% yield under 0.5 MPa of molecular oxygen). Halogen, noble metals, extra base or complicated ligands were avoided. Addition of a trace of water to this system before the reaction was crucial for the high efficiency.