Mechanism of Formation of Volatile Organic Compounds from Oxidation of Linseed Oil

The pathways of volatile organic compound (VOC) formation have been investigated through a computational study, employing the Gaussian 03 suite of programs. We optimized geometries and zero-point vibrational energies (ZPVEs) at the B3LYP/6-31G(d) level of theory and improved electronic energies by conducting single-point energy calculations using the large 6-311++G(3df,3pd) basis set. To describe the predominant mechanism of the linseed oil oxidation, the following sequence is proposed: hydrogen abstraction of unsaturated fatty compounds as the initiation reaction followed by the reaction of allylic-type radicals with molecular oxygen to form peroxyl radicals and finally intramolecular rearrangement through four- and five-membered rings. Quantum calculations identified low-energy pathways following cyclization resulting in the formation of major products observed, especially aldehydes and ketones. The overall energy changes taking place through the four- and five-membered rings were found to be 78 and 93 kJ mol(-1) exothermic, respectively. Metal catalysts decompose hydroperoxides based on the Fenton-like mechanism into alkoxyl and peroxyl radicals.