The Mercury Photosensitized Hydrogenation of Ethylene, Ethylene-d4 and Partially Deuterized Ethylenes

Abstract

The hydrogenation of ethylene, ethylene‐d₄ and partially deuterized ethylene photosensitized by excited mercury to λ = 2537A has been studied. It has been found that the rate of hydrogenation of the deutero‐compound is more rapid than that of ethylene under comparable conditions. With excess hydrogen, the rate is independent of the ethylene pressure. The data obtained indicate that butane is the important product together with small amounts of ethane relatively more abundant in the case of ethylene‐d₄. Negligible amounts of methane are formed. The suggested mechanism involves the reactions H+C₂H₄ = C₂H₅ followed by C₂H₅+C₂H₅ = C₄H₁₀ and to a lesser degree, C₂H₅+C₂H₅ = C₂H₆+C₂H₄. At low hydrogen concentrations, or in absence of hydrogen, a photosensitized polymerization occurs, faster with ethylene than with ethylene‐d₄. The slower rate of polymerization of the deutero‐compound may be explained on the basis of zero‐point energy differences between C₂H₄ and C₂D₄ in their reactions with free radicals to yield more complex radicals.