Studies on the Catalytic Synthesis of Aromatic Nitriles (Part 3)

Dehydrogenation Reaction of Various Hydrocarbons Using SO₂ as a Hydrogen Acceptor

Abstract

Vapor phase catalytic dehydrogenation reactions of various hydrocarbons using SO₂ as a hydrogen acceptor were investigated in order to elucidate the mechanism of the ammoxidation reaction.
(1) The dehydrogenation of ethylbenzene to styrene was promoted over Alundum, Diatomaceous earth, MnO₂, ZnO, TiO₂, CaSO₄, MgO, etc.; however, Pumice, Silicagel and CuO were not active or little active for this reaction. The same phenomenon was observed for the dehydrogenation reactions of cumene to α-methylstyrene and ethylcyclohexane to ethylbeazene and styrene.
Benzylamine was dehydrogenated more readily to benzonitrile than cumene and ethylcyclohexane. From these experimental results, it was inferred that the dehydrogenation reaction took place by abstraction of hydrogen atom with active species containing sulfur and that the catalyst promoted the formation of these active species and the abstraction of hydrogen atom with the active species.
(2) The effect of temperature on the dehydrogenation of ethylbenzene was studied over Alundum catalyst. Therefore, characteristic Arrhenius plot was obtained from this experiment. The plot was composed of two straight lines divided by a bending point at 425°C. The plots of similar pattern were obtained in the case of cumene, cyclohexane and methylcyclohexane.
It was infered that the bending point resulted from the difference in the rate determining process or a state of the active species between the higher and the lower temperature regions.