Green Catalytic Oxidation of Vanillyl Alcohol to Vanillin by Furoic Hydrazide-Derived Molybdenum Complexes

The selective oxidation of alcohols to aldehydes and ketones is one of the most fundamental transformations in synthetic organic chemistry, particularly for the production of high-value fine chemicals. Among these reactions, the oxidation of vanillyl alcohol to vanillin is of significant industrial interest because vanillin is widely used in the food, fragrance, cosmetic, and pharmaceutical industries. However, achieving high selectivity toward vanillin remains challenging due to the tendency of aldehydes to undergo further oxidation to carboxylic acids and other undesired by-products. Therefore, the development of efficient and sustainable catalytic systems capable of promoting selective oxidation under mild conditions is highly desirable.

In this work, molybdenum complexes were synthesized using a hydrazide-based Schiff base ligand derived from 2-furoic hydrazide and 2-hydroxy-3-methoxybenzaldehyde in methanol, both in the presence and absence of hydrogen peroxide (H₂O₂). The synthesized complexes were investigated as catalysts for the oxidation of vanillyl alcohol using H₂O₂ as a green oxidant at 70 °C. Compared with conventional oxidation methods that often employ toxic oxidants, harsh conditions, and generate hazardous waste, the use of H₂O₂ provides a more environmentally friendly approach because water is produced as the only by-product.

The catalytic activity was evaluated using different catalyst loadings to study their influence on conversion and selectivity toward vanillin. The results demonstrate that subtle structural variations in the molybdenum complexes influence catalytic performance, affecting both substrate conversion and product selectivity. The optimized catalytic system showed efficient oxidation activity with improved selectivity toward vanillin while minimizing overoxidation products.

This study demonstrates the potential of furoic hydrazide-based molybdenum complexes as promising catalysts for green oxidation processes and provides valuable insight into the relationship between catalyst structure and catalytic behaviour for the sustainable production of high-value aromatic aldehydes.