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

A 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 O is the rate-determining step in the formation of CyOOH due to its relatively high energy barrier of 41.2 kcal/mol, and the subsequent reaction behavior of CyOOH controls whether the production of cyclohexanol or cyclohexanone is favored. Using CHCOOH or (CHCOO)Co as a catalyst reduces the energy barriers required to activate cyclohexane and O by 4.1 or 7.9 kcal/mol, respectively. Employing CHCOOH 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 kcal/mol for autoxidation to 25.9 kcal/mol for (CHCOO)Co catalysis. (CHCOO)Co promotes the autoxidation process via a radical chain mechanism. The computational results agree with experimental observations quite well, revealing the underlying role of CHCOOH and Co ion in cyclohexane oxidation. Graphical abstract Through DFT analysis of cyclohexane autoxidation and catalytic oxidation, we reveal the mechanism of the effects of CHCOOH and Co on the reaction routes.