エステルの自動酸化反応：ポリオールエステル系潤滑油の酸化劣化反応機構の解明に向けて

Abstract

The liquid phase oxidation of a series of neopentyl esters, chosen to model the more complex polyol esters used as lubricants, has been studied in two ways. In one, detailed product analyses, following reaction with oxygen in a closed reactor at elevated temperatures, allows for mechanisms to be proposed. In the second, the esters were reacted with two different alkoxyl radicals, the results leading to valuable information about the relative rates of attack on the various C-H bonds. For example, it was found that attack could take place readily on both the alkyl and acyl groups in the ester and that the β-acyl C-H bonds are more susceptible to attack than α-C-H bonds. To support the proposals for the mechanisms, details are given of experiments in which reactions of specific peroxyl radicals derived from esters were studied in detail and compared with similar experiments with alkylperoxyl radicals. The reactions of peroxyl radicals formed from esters are similar to those derived from alkanes and it is possible to use rate constants for reactions of alkylperoxyl and related oxygenated radicals to model successfully the reactions of the esterperoxyl radicals. Overall the mechanisms for the autoxidation of the esters can be explained in terms of well-established mechanisms associated with the autoxidation of alkanes, as would be expected from the similarity of the peroxyl radical chemistry of the two systems. However, care has to be taken in accounting for the influence of the functional group which has a profound effect on the point of attack in the case of the autoxidation of the esters.