Peculiarities of Obtaining Alkyl-Substituted 1,4-Benzoquinones in Two-Phase Systems in the Presence of Mo-V-P Heteropoly Acid Solutions
In the present study, aqueous solutions of Mo-V-phosphoric heteropoly acids H3+xPMo12-xVxO40 with high and low vanadium content were applied as homogeneous catalysts for oxidation of 2,3,6-trimethylphenol and 2,6-dimethylphenol into corresponding 1,4-benzoquinones. The reaction was performed in two-phase system. Different reaction parameters such as substrate concentration, organic solvent, temperature, catalyst composition etc. were analysed in terms of product selectivity. The quinone yield was found to depend strongly on the catalyst redox potential which determines the rate of electron transfer. The results obtained enabled to establish the optimal reaction conditions and to prepare 2,3,5-trimethyl-1,4-benzoquinone and 2,6-dimethyl-1,4-benzoquinone with selectivities of 99 and 85%, respectively. The catalyst used is rapidly regenerated in separate stage under oxygen pressure and reused.