Density functional theory study of selective aerobic oxidation of cyclohexane: the roles of acetic acid and cobalt ion

Abstract

AbstractA computational study of cyclohexane autoxidation and catalytic oxidation to a cyclohexyl hydroperoxide intermediate (CyOOH), cyclohexanol, and cyclohexanone has been conducted using a hybrid density functional theory method. The activation of cyclohexane and O2 is the rate-determining step in the formation of CyOOH due to its relatively high energy barrier of 41.2\xa0kcal/mol, and the subsequent reaction behavior of CyOOH controls whether the production of cyclohexanol or cyclohexanone is favored. Using CH3COOH or (CH3COO)2Co as a catalyst reduces the energy barriers required to activate cyclohexane and O2 by 4.1 or 7.9\xa0kcal/mol, respectively. Employing CH3COOH improves the CyOOH intramolecular dehydration process, which favors the formation of cyclohexanone. The energy barrier to the decomposition of CyOOH to CyO·, an important precursor of cyclohexanol, decreases from 35.5\xa0kcal/mol for autoxidation to 25.9\xa0kcal/mol for (CH3COO)2Co catalysis. (CH3COO)2Co promotes the autoxidation process via a radical chain mechanism. The computational results agree with experimental observations quite well, revealing the underlying role of CH3COOH and Co ion in cyclohexane oxidation.\n Graphical abstractThrough DFT analysis of cyclohexane autoxidation and catalytic oxidation, we reveal the mechanism of the effects of CH3COOH and Co2+ on the reaction routes