Synthesis of salicylaldehyde through oxidation of o-cresol: Evaluation of activity and selectivity of different metals supported on OMS-2 nanorods and kinetics

Abstract

Octahedral molecular sieve (OMS-2) was synthesized by the hydrothermal method and modified by the impregnation of different metals to give M/OMS-2 catalysts (where M = V, Cr, Fe, Co, and Mo). All these catalysts were tested in the oxidation of o-cresol to 2-hydroxybenzaldehyde (or salicylaldehyde, SAL). Among all M/OMS-2 catalysts, 5% Co/OMS-2 was found to be the most active catalyst for selective oxidation of o-cresol to SAL. Effect of several oxygen sources such as air, hydrogen peroxide (H2O2), molecular oxygen (O2), and tert-butyl hydroperoxide (TBHP) was studied for the oxidation of o-cresol. There was a complete conversion of o-cresol with 98% yield of SAL at 5 atm O2 pressure and 80 °C in 2 h. Additionally, the catalysts (virgin as well as reused forms) were characterized by FESEM, EDS, HR-TEM, XRD, CO2-TPD, TPR, Raman Spectra, BET surface area analysis, XPS, and DSC-TGA. The reaction kinetic model was developed using Mars van Krevelen mechanism. The catalyst was found to be inexpensive, robust, active, and showed very good reusability of 4 cycles, which makes it an attractive choice for o-cresol oxidation to SAL. The atom economy of the oxidation process is 98.15%. Thus, this process is an example of the synthesis of a vital chemical entity, salicylaldehyde, at mild reaction condition by a novel clean and green route.