Substituent Effects on Regioselectivity in the Autoxidation of Nonconjugated Dienes

Citations Over TimeTop 17% of 2009 papers

Abstract

Free radical oxidation of several 1,4-dienes was carried out in the presence of variable concentrations of alpha-tocopherol to investigate the effect of diene structure on product distribution. Oxidations carried out at low tocopherol concentration gave only C-1 and C-5 conjugated diene hydroperoxides, while higher concentrations of the antioxidant resulted in formation of substantial amounts of the nonconjugated C-3 diene hydroperoxide. Increasing size of the substituents at C-1 and C-5 of the diene favors kinetic products arising from oxygen addition at the nonconjugated position, C-3, of the pentadienyl radical intermediate. Substituents at C-1 or C-5 of the pentadienyl radical also have a significant effect on the regioselectivity of the conjugated diene hydroperoxides formed, larger substituents directing oxygen addition to the pentadienyl radical at the site of least steric hindrance. This trend is also observed in oxidations of omega-3 and omega-6 linolenate fatty acid esters. Groups at C-1 and C-5 of the diene can influence product distribution based upon (a) steric demand in the oxygen-radical reaction and (b) the influence of substituents on the rearrangement of the C-3 peroxyl radical to give conjugated diene products.

Related Papers

• → Autoxidation of methyl linolenate and methyl linoleate: The effect of α‐tocopherol(1981)74 cited
• → Effect of Droplet Size on Autoxidation Rates of Methyl Linoleate and ^|^alpha;-Linolenate in an Oil-in-Water Emulsion(2013)12 cited
• → A hydroperoxy-epidioxide from the autoxidation of a hydroperoxide of methyl linolenate(1980)41 cited
• → The oxidation of α-tocopherol during the autoxidation of ethyl oleate, linoleate, linolenate, and arachidonate(1969)33 cited
• → The resistance of cyclo-octa-1,5-diene to liquid-phase metal-centered autoxidation(1978)2 cited