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155Carboxylic acid esters resulting from the liquid phase oxidation of hydrocarbons and their oxygen derivatives [1,2] can enter into free radical chain pro cesses involving both the acyl and alkoxyl moieties [1,3,4]. The electron withdrawing functional group affects the mechanisms of formation and transforma tion of the intermediates (peroxyl radicals and hydro peroxides) and also the reactivity of the C-H bonds nearest to this functional group [1,3,4]. It was shown for the reactions of tert butylperoxy radicals with cyclohexyl acetate at 333 K [5] that the ester group activates the α C-H bonds and substantially deacti vates the β and γ C-H bonds of the alkoxyl moiety with respect to the peroxyl radicals. Although there have been many works devoted to ester oxidations (see monograph [1] and review [3]), the influence of the functional group on the reactivity of various types of C-H bonds in the acyl moiety remains unclear. The discovery of a new mechanism and new products of the oxidation of carbonyl containing compounds at the β C-H bonds [6-8] makes disputable the results of an earlier study [9] in which the relative reactivity of the C-H bonds of methyl hexanoate were determined from the composition of the alcohols that resulted from the reduction of the oxidation products of this ester with lithium aluminum hydride at 413 K.The purpose of the present work is to determine, using methyl hexanoate as an example, the reactivity of the main types of C-H bonds in the acyl moiety of the ester toward the tert butylperoxy radical at 373 K. EXPERIMENTALMethyl hexanoate (analytical grade) was purified by vacuum distillation in flowing argon. According to GLC data, the product contained 99.5 ± 0.1% methyl hexanoate.tert Butyl hydroperoxide (TBHP) was synthesized and purified by a standard procedure [10]. As deter mined by iodometry, the synthesized compound con tained at least 99.3 ± 0.2% hydroperoxide. Peroxide compounds were quantified by a colorimetric method using a reagent containing Fe 2+ ions and N,N dime thyl para phenylenediamine [11].The reference substances necessary for gas chro matographic identification of methyl hexanoate oxi dation products were synthesized using standard methods. 2 Hydroxyhexanoic acid was obtained by the hydrolysis of 2 bromohexanoic acid [12]. Accord ing to GLC data, the 2 hydroxyhexanoic acid content of the product was 99.3 ± 0.2%. Methyl 6 hydroxy hexanoate was obtained by heating ε caprolactone with water in a sealed tube followed by the esterifica tion of the carboxyl groups with diazomethane. 2 Hexenic acid was synthesized by the Knoevenagel condensation of butanal and propanedioic acid in the presence of pyridine [13] and was purified by consec utive recrystallization from water and an ethanolwater (1 : 1) mixture. The melting point of the product was 32°С (reference value: 32-33°С [13]). 2,3 Epoxy hexanoic acid was obtained by treating 2 hexenic acid with a 30% aqueous solution of hydrogen peroxide in the presence of Na 2 WO 4 [14]. The purity of the result ing acid, according ...

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