Reactions of Propyne and Propadiene on Magnesium Films Part 1.—Self-hydrogenation

Abstract

The self-hydrogenation of propyne and propadiene to propene on evaporated magnesium films has been studied at 373 and 423 K. The species retained in the solid state in the course of the reaction were then desorbed by deuterium oxide and characterized as deuterated hydrocarbons. The structures of these hydrocarbons (mainly propyne and propene) and the variations in their deuterium distributions with temperature and contact time of the previous self-hydrogenation reaction are consistent with a mechanism involving two parallel processes: (a) dehydrogenation of propyne and propadiene into metalated propyne CH3—C[triple bond, length as m-dash]C—Mg—(deuterolysed to [2H1]propyne), stable at 373 K but rapidly further dehydrogenated at 423 K to the magnesium carbide Mg2C3(deuterolysed to [2H4]propyne); (b) two-step hydrogenation of the reagent to propene, via half-hydrogenated intermediates, stable at 373 K and deuterolysed to [2H1]propene.