The catalytic hydrogenation of methyl elaeostearate, and of mixtures of elaeostearic with other polyethenoid long-chain esters

Abstract

The hydrogenation (using Raney nickel catalyst at 110 and 170° C) of the conjugated triene system present in methyl elaeostearate (octadeea-9, 11, 13-trienoate) has been compared with that of the pentadiene systems —CH: CH. CH₂. CH: CH— present in methyl linolenate and methyl linoleate. The course of the hydrogenation action in methyl elaeostearate itself has been followed spectrophotometrically, and it has been established that, for the most part, the primary action is the simultaneous addition of two molecules of hydrogen to one molecule of elaeostearate and formation of very large proportions of octadeca-11-enoic esters. Production of stearate does not occur to any marked extent until over 80 % of elaeostearate has been converted to mono-ethenoid ester. The selectivity of the hydrogenation process has been studied in the cases of equimolecular binary mixtures of methyl elaeostearate with, respectively, methyl'oleate, linoleate or linolenate. In a mixture of methyl elaeostearate and oleate, hydrogenation of the latter does not set in until nearly all the elaeostearate has been converted to octadecenoate. With a mixture of methyl elaeostearate and linoleate, the diene ester remains almost unattacked until 50% or more of the conjugated triene ester present has been converted into monoethenoid ester, after which it also commences to be transformed into mono-ethenoid esters. In a mixture of methyl elaeostearate and linoleaate, both esters undergo hydrogenation from the outset, but conjugated triene ester disappears about twice as rapidly as the non-conjugated isomer. The activity to hydrogen of the double pentadiene system —CH:CH.CH₂.CH:CH.CH₂.CH:CH— is thus comparable with that of the conjugated triene group in the elaeostearate molecule. The hydrogenation of methyl linoleate in presence of Raney nickel either at 110 or 170° C is extremely selective, no methyl stearate being produced until over 90 % of the linoleate has been transformed into octadecenoates.