Comparative DFT study of triplet and singlet elementary oxidation acts of the cyclohexane and 1,3-cyclohexadiene initiated by primary interaction with 3O2 under SCF conditions

Abstract

The primary stages of the oxidation of model cyclohexane and 1,3-cyclohexadiene by triplet molecular oxygen and subsequent transformations involving triplet and singlet states were studied for the first time by the DFT method with the density functional B3LYP with the basis set 6-311++g(df,p). It was shown that, ceteris paribus, cyclohexane and 1,3-cyclohexadiene will be orders of magnitude more reactive compared to the activity of acyclic saturated hydrocarbons under SCF conditions when the oxidation process is initiated by the primary reaction with 3O2, which allows the propane-butane mixture to be effectively used as SCF conditions of heavy oils and use air purge to activate this process. The triplet associate complexes resulting from the oxidative cleavage of the secondary C–H bond of cyclohexane and 1,3-cyclohexadiene consist of hydrogen-bonded hydroperoxyl radical and cyclohexyl radical or 1,3-cyclohexadiene radical, respectively. These complexes can dissociate into unbound pairs of radicals, and therefore further reactions can proceed in the triplet or singlet direction. The singlet direction is characterized by hydrate-induced hydroperoxide-carbonyl transformation, as well as other hydrate-induced rearrangements. The triplet direction is characterized by the occurrence of triplet rearrangement, which in its essence is a triplet recombination of associated radicals. Associate triplet complexes can be agents of radical hydroperoxyl and alkyl activity, as well as agents of radical hydroxyl and alkoxyl activity. Most oxidative dehydrogenation reactions are absolutely real under a number of conditions, namely, they must take place under SCF conditions, as well as in the presence of an excess of SCF solvent necessary for the effective shift of thermodynamic equilibrium towards the target products in accordance with the Le Chatelier principle.