Relative hydrogenation rates of normal and conjugated linolenic and linoleic acid glycerides

Summary A mixture of 50% tung oil and 50% linseed oil was hydrogenated and samples withdrawn at approximately 10 I.V. intervals during the course of the reaction were analyzed for fatty acid composition. Reactivity ratios for the various fatty acids were calculated. Because of the limitations of the analytical methods, particularly the spectrophotometric methods used for linolein, conjugated linolein, and linolenin, and the arbitrary procedures of arriving at corrected values for these constituents, the composition data and reactivity ratios derived therefrom must be regarded as only approximations. However it seems safe to conclude that during the initial stages of the hydrogenation the eleostearin was many times more reactive than normal linolenin for equivalent concentrations but as the eleostearin was reduced in concentration, its reactivity decreased until, at a 1% to 2% level, it was only slightly more reactive than the normal linolenin, again for equivalent concentration. Likewise the conjugated linolein formed from the eleostearin was many times as reactive as the normal linolein when present in considerable amounts, but the reactivity ratio of conjugated linolein to normal linolein dropped markedly in the latter stages of the process. Normal linolenin and normal linolein had similar reactivities. It is suggested that the amount of conjugation and unsaturation in the glyceride rather than in the individual fatty acid may be the controlling factor in hydrogenation selectivity.