The Selectivity of Catalysts in the Hydrogen Exchange Reaction of p-Xylene with Deuterium Oxide

Abstract

The isotopic exchange reaction of p-xylene with deuterium oxide was studied using rhodium, silver, and nickel-alumina as catalysts at 100 deg C, and the results were compared with those of previous studies. The reaction products were analyzed by infrared and mass-spectrometric methods. On rhodium catalyst, the exchange occurred at both hydrogen atoms of methyl groups and benzene ring of p-xylene, but on silver the exchange did not take place under the same experimental condition. The following order of the selectivity for benzene ring was found to exist among the metals studied: Pt > Pd > Rh > Ni, a new relation between the selectivity and the geometric factor of catalysts. When the surface of nickel-alumina had been previously exposed to diethylsulfide at room temperature, the exchange at methyl groups was more retarded than at the benzene ring. Furthermore, selectivity for the demethylation of p-xylene, low as it was, was confirmed only in the case of nickelalumina under similar experimental conditions. The results suggest that the mechanism of the exchange of benzene ring is not the same for the cases of palladium and nickel-alumina catalysts. (auth)