The specific features of the liquid-phase oxidation of saturated esters. Kinetics, reactivity and mechanisms of formation of destruction products

Data on kinetics, reactivity, and mechanisms of formation of destruction products of the liquid-phase oxidation of saturated esters by molecular oxygen have been systematized and discussed. The ester group has both an activating and deactivating effects on the reactivity of the CH bonds of the alkoxyl (α′-, β′-, γ′-, and δ′-) and acyl (α-, β-, and γ-) groups. The activating effect in esters is weaker than in alcohols, ketones, and ethers and extends to the α- and α′-CH bonds. The reactivity of the β-, β′-, and γ′-CH bonds is significantly lower than that of the secondary CH bonds of hydrocarbons. Oxidation of the β-CH bonds of the acyl moieties of esters leads to HOO · radical, α,β-epoxy-, α,β-dihydroxy-, and α,β-unsaturated esters, but not to hydroperoxides. Upon the oxidation of esters, the highly active α-carboxy-alkylperoxy-, α-acyloxyperoxy-, and HOO · -radicals are formed. The recombination reactions involving these radicals occur both with and without chain termination. The specificity of the decomposition of ester hydroperoxides are due to intra- and intermolecular interactions of the hydroperoxide groups with the ester groups. Labile peroxide intermediates (α-hydroxyperoxy-esters, peroxyesters, and peroxylactones) are formed through the corresponding tetrahedral intermediates and decay predominantly by the non-radical pathway. The recombination of the peroxyl radicals and the decay of labile peroxides result in the parallel accumulation of peroxide and non-peroxide products during the oxidation of esters.