Selective Hydrogenation of Cyclooctadienes Using Colloidal Palladium in Poly(<i>N</i>-vinyl-2-pyrrolidone)

Abstract

Abstract Selective hydrogenation of 1,3-, 1,4-, and 1,5-cyclooctadiene to cyclooctene was carried out at 30 °C under atmospheric hydrogen pressure using colloidal palladium which was prepared by reducing palladium(II) chloride with refluxing methanol in the presence of poly(N-vinyl-2-pyrrolidone). The yields of cyclooctene were 99.9% and 97.8% for hydrogenation of 1,3- and 1,5-cyclooctadiene, respectively at the point that an equimolar hydrogen was uptaken by cyclooctadienes. The hydrogenation rate of 1,3- and 1,4-cyclooctadiene (R1) is expressed as R1=k1[H2][Pd], and that of 1,5-cyclooctadiene (R2) is expressed as R2=k2[H2]0.7[Pd], where k1 and k2 are the rate constants. Alcohols were found to be good solvents for hydrogenation. In particular the fastest rate and the highest selectivity for monoene were observed in methanol among the solvents examined. Effect of bases on the monoene selectivity has also been investigated.