Selective homogeneous hydrogenation of triunsaturated fats catalyzed by tricarbonyl chromium complexes

The need for a selective catalyst to hydrogenate linolenate in soybean oil has prompted our continuing study of various model triunsaturated fats. Hydrogenation of methylβ-eleostearate (methyltrans,trans,trans-9,11,13-octadecatrienoate) with Cr(CO)₃ complexes yielded diene products expected from 1,4-addition (trans-9,cis-12- andcis-10,trans-13-octadecadienoates). Withα-eleostearate (cis,trans,trans-9,11,13-octadecatrienoate), stereoselective 1,4-reduction of thetrans,trans-diene portion yielded linoleate (cis,cis-9,12-octadecadienoate). However,cis,trans-1,4-dienes were also formed from the apparent isomerization ofα- toβ-eleostearate. Hydrogenation of methyl linolenate (methylcis,cis,cis-9,12,15-octadecatrienoate) produced a mixture of isomeric dienes and monoenes attributed to conjugation occurring as an intermediate step. The hydrogenation ofα-eleostearin in tung oil was more stereoselective in forming thecis,cis-diene than the corresponding methyl ester. Hydrogenation of linseed oil yielded a mixture of dienes and monoenes containing 7%trans unsaturation. We have suggested how the mechanism of stereoselective hydrogenation with Cr(CO)₃ catalysts can be applied to the problem of selective hydrogenation of linolenate in soybean oil. No. Market. Nutr. Res. Div., ARS, USDA.