Catalysis of Cumene Oxidation by 2-Ethylhexanoates of the 12 Group of Metals: Experiment and Quantum Chemical Modeling

In the radical-chain oxidation of cumene by molecular oxygen in the presence of Zn, Cd, and Hg 2-ethylhexanoates (hereinafter Me(EH)2), Cd 2-ethylhexanoate exhibits the highest catalytic activity. The structure and catalytic activity of Cd 2-ethylhexanoate adducts with cumene hydroperoxide (ROOH) were investigated by using density functional theory (IEF-PCM + B3PW91-GD3/x2c-TZVPall). Thermodynamic parameters indicated the formation of intermediate 1:1 and 1:2 adducts of Cd 2-ethylhexanoate with ROOH and dimethylphenylcarbinol (ROH), including a mixed ROH···ROOH·Cd(EH)2 adduct. The formation of 1:2 adducts is thermodynamically more favorable due to a more stable octahedral environment around the Cd atom. Modeling of ROOH radical decomposition in these adducts showed that ROOH in the associated ROH···α-ROOH·Cd(EH)2 adduct decomposes faster into free radicals compared with the free ROOH molecule. This ensures effective ROOH decomposition at the degenerate chain branching stage, leading to a general acceleration of cumene oxidation. Based on these quantum chemical modeling results, a mechanism for the catalytic effect of Cd 2-ethylhexanoate in the radical-chain oxidation of cumene by molecular oxygen has been proposed. The results of this study will allow for the construction of a complete and reliable kinetic scheme for the process, aiming at its optimization.