Hydrogenation and deuteration of conjugated isomers of linoleate and linolenate with palladium, platinum, nickel and lindlar catalysts

Abstract

AbstractConjugated isomers of methyl linoleate and linolenate were reduced with palladium, platinum, nickel and Lindlar catalysts at atmospheric hydrogen or deuterium pressure. After the products were separated, positions of their double bonds were determined by ozonolysis. Palladium and platinum catalysts reduced β‐eleostearate directly to monoene. Nickel reduced β‐eleostearate to dienes chiefly by 1,2‐addition and to a lesser extent by 1,4‐ and 1,6‐addition, whereas Lindlar catalyst reduced by 1,2‐and 1,6‐addition only. All catalysts reduced conjugated linoleate isomers by both 1,2‐ and 1,4‐addition, with nickel being somewhat preferential for 1,2‐addition. Selectivity for the catalytic reduction of dienes to monoenes decreased in the order: nickel, palladium and platinum. Lindlar catalyst did not isomerize or reduce monoenes that formed during reduction. Palladium and platinum did not isomerize conjugated dienes and trienes during their reduction, whereas nickel and Lindlar catalysts isomerized them slightly. Some deuterium was found in unreacted conjugated diene and triene with nickel and Lindlar catalysts, but none with palladium or platinum. Deuterated products contained a wide range of isotopic isomers with some products having up to 31 deuterium atoms. This wide deuterium distribution resulted from (a) exchange followed by addition, (b) addition followed by exchange and (c) exchange‐addition‐exchange reactions.