Phenylacetaldehyde and Carbon Monoxide as Effective Additives for the Selective Hydrogenation of Cyclooctadienes to Cyclooctene over Palladium Catalysts

Abstract

Abstract Three isomeric cyclooctadienes (1,5-, 1,4-, and 1,3-COD) were hydrogenated with phenylacetaldehyde (PAA)- or carbon monoxide (CO)-treated palladium black in tetrahydrofuran at 25 °C and atmospheric pressure of hydrogen. A complete depression of the hydrogenation of cyclooctene (COE) to cyclooctane (COA) was attained with both of the poisoned catalysts. By PAA the hydrogenation of 1,5-COD to COE was not hindered and the isomerization of 1,5-COD to 1,4-COD was greatly promoted, while the rate of hydrogenation of 1,4- and 1,3-COD decreased in the presence of PAA. By CO the hydrogenation and isomerization of 1,5-COD, as well as the hydrogenation of 1,4- and 1,3-COD, was suppressed. In the hydrogenation of 1,5-COD the PAA-treated palladium was more active and selective than was the CO-treated palladium for the formation of COE. The differences in the effects of these catalyst poisons are discussed on the basis of kinetic data concerning the individual and competitive hydrogenation of the three isomeric cyclooctadienes.