Oxidation and oligomerization of ethyl linoleate under the influence of the combination of ascorbic acid 6-palmitate/iron-2-ethylhexanoate

In this paper we report the oxidation and oligomerization of ethyl linoleate (EL), a model compound for alkyd resins, under the influence of iron-2-ethylhexanoate (Fe-eh) in combination with ascorbic acid 6-palmitate (AsA6p) at different AsA6p/Fe-eh molar ratios (0/1-4/1). Reactions were studied in time by FT-IR, NMR, size exclusion chromatography (SEC) and peroxide amount determination. The oxidation and oligomerization of EL were accelerated by the combination of AsA6p and Fe-eh, and the catalytic properties of the catalysts were strongly dependent on the molar ratio AsA6p/Fe-eh. The molar ratio of 2/1 appeared to be optimal, at which both the oxidation and oligomerization of EL were the fastest. At molar ratio smaller than 2/1, or only in the presence of Fe-eh, the EL oxidation showed a time lag of up to 100 h; above the ratio 2/1 the rates of both EL oxidation and oligomerization decreased. Results are explained in terms of the multi-facet role played by AsA6p: its pro-oxidant or anti-oxidant properties, depending on the ratio of AsA6p/Fe-eh, and its effect on the Fe-eh complex.