Kinetic studies on the liquid‐phase catalytic oxidation of 4‐methyl guaiacol to vanillin

Kinetic studies on the catalytic oxidation of 4-methyl guaiacol using an ether intermediate towards vanillin in an agitator bubbling reactor were presented. The reaction was catalyzed by N,N′-ethylenebis(acetylacetoniminato)-cobalt(II) hexafluorophosphoric pyridinium (Co-[Salen-Py][PF6]2) under strong alkaline conditions with molecular oxygen as the terminal oxidant. The reaction scheme was demonstrated by a detailed analysis of the products distribution and control experiments. The intrinsic kinetics were explored based on our proposed p-benzoquinone methide mechanism, which revealed that the oxidation rate was determined by the oxidation of phenoxyl anion to phenoxyl radical catalyzed by LCo3+(O2 · ) (L = [Salen-Py][PF6]2). The kinetic experiments were performed under a mass transfer-reaction condition due to the inevitable mass transfer resistance involved. Pseudo-first order fast reactions were observed for both steps of the consecutive reactions based on the calculated physical and mass transfer parameters. The intrinsic kinetic equations for the first and second steps can be written as RA=5.98×105exp−31950RTCcat.CACO2 and RF=1.02×106exp−29770RTCcat.CECO2, respectively, which are well in accordance with the mechanism. These conclusions are expected to give a clue for the mechanistic study, kinetic investigation, reaction optimization, and catalyst design for the oxidation of various p-cresols. This article is protected by copyright. All rights reserved