FORMATION, ISOMERIZATION, AND CYCLIZATION REACTIONS OF HYDROPEROXYALKYL RADICALS IN HEXADECANE AUTOXIDATION AT 160-190-DEGREES-C

Kinetic and mechanistic investigations of the effects of oxygen pressure on liquid-phase autoxidation reactions in hydrocarbons at elevated temperatures were carried out with hexadecane at 160-190-degrees-C and at oxygen pressures from 4 to 120 kPa using a stirred-flow reactor. Results of studies of formation of primary oxidation products showed that the intramolecular alpha,gamma and alpha,delta hydrogen abstraction reactions of peroxy radicals (reactions 4) are highly reversible and that the intermediate hydroperoxyalkyl radicals formed from these abstractions, besides addition of oxygen and reverse intramolecular hydrogen abstraction (isomerization) reactions (reactions -4) undergo cyclization reactions leading to formation of cyclic ether products (reaction 10). Kinetic analyses based on the proposed reaction scheme allowed derivation of the absolute rate constants for reactions 4, -4, and 10 of the intermediate alpha,gamma- and alpha,delta-hydroperoxyhexadecyl radicals, HOOR.. The derived rate constants are in good agreement with published values from gas-phase oxidations.