[Oxidative degradation of linoleic acid methyl ester in suspensions of inorganic excipients. 1. Auto-oxidation in the presence of silicic acid products and aluminum oxide].

Linoleic acid methyl ester (LME) was selected as a model to study the autoxidation of unsaturated compounds at the surfaces of inorganic excipients. From IR spectra of LME-silica adsorbates it was concluded that the interaction between LME and the silica surface is mainly due to hydrogen bonds, established between the ester carbonyl and the silica silanol groups. The autoxidation was continuously monitored by measuring the oxygen consumption of LME under UV light exposure and isobaric conditions, and, in parallel, by determining the carbonyl and peroxide values of LME. The oxidative degradation of LME is enhanced by porous and colloidal silicas as well as by colloidal aluminium oxide. From the oxygen consumption and the ratio of intermediates (carbonyls, peroxides) formed during the degradation of LME it was concluded that the prooxidative effect of the inorganic excipients can be attributed to an accelerated reaction of the peroxides of LME.