Hydrogenolysis of C-O Bond of the Alkoxy Group in the Catalytic Reduction of Oleyl Oleate

Abstract

In the catalytic reduction of oleyl oleate by palladium on carbon catalyst, it has been found that hydrogenolysis of C-O bond of alkoxy group is occurred besides the hydrogenation of double bonds. The hydrogenolysis is occurred only when the esters being reduced possess unsaturated alkoxy group. The whole reactions occurred are illustrated below :
in which A¹B¹=oleyl oleate, A¹B¹=stearyloleate, A⁰B¹=oleyl stearate, A⁰B⁰=stearyl stearate, A¹H=oleic acid, A⁰H=stearic acid, B'H=n-octadecene and B⁰H=n-octadecane.
Rate equation of the hydrogenolysis is seemed to be expressed as first order with respect to the reactants :
d/dt ([A¹H] + [A⁰H]) =k₆ [A¹B¹] +k₇ [A⁰B¹]
in which the rate constant k₇ seems to be greater than k₆. The reaction temperature has a marked effect on the hydrogenolysis, the higher the temperature the greater the extent of hydrogenolysis.
Besides the palladium catalyst, rhodium, platinum, ruthenium and nickel catalysts have also tried for the catalytic reductions of oleyloleate. Of all these catalysts, palladium has an excellent hydrogenolytic activity as shown below :
palladium>>rhodium>platinum>rutheniumnickel
The activity of ruthenium and nickel are almost nil. The order of the activities is identical with that of the doudle bond migration in the general catalytic reduction of olefins.