Sustainable oxidation of cyclohexane catalyzed by a VO(acac)2-oxalic acid tandem: the electrochemical motive of the process efficiency

Abstract

Cyclohexane oxidation by H₂O₂ to cyclohexanol, cyclohexanone, and cyclohexylhydroperoxide under mild (40 °C, 1 atm) conditions is significantly enhanced in the system composed of VO(acac)₂ (starting catalyst) and small additives of oxalic acid (process promoter). In corroboration of this, several times higher yield of the desired products was obtained compared to that obtained in the acid-free process. The revealed advantage was addressed to elevate the electrical conductance G (or vice versa, decreasing the resistance, 1/G) of the reaction medium. On the other hand, the content of oxalic acid (20–30 mM) was compulsory to optimize the process parameters. The last value of concentration affords, besides the lowest 1/G, the utmost impact on pH, redox potential, and current–voltage relationships. Exceeding this level leads to an increase in 1/G of the reaction solution, ceases the impact on pH, ORP, and CV profiles, and is detrimental for the product yield. The putative mechanism of the revealed effects has been envisaged.