Reactions of methyl chloride and of methylene chloride at metal surfaces: II. Reactions over evaporated films of titanium and other metals

Abstract

The reaction of methyl chloride and hydrogen, and of methylene chloride and hydrogen has been studied at the surface of a number of evaporated metal films in a static system. Adsorption of alkyl chloride resulted in rupture of all carbon-chlorine bonds before any carbon-hydrogen bonds were broken; thus in the reaction with deuterium, virtually no deuteroparent was formed. By the use of 13C and 35Cl it was shown that in the adsorption of methyl chloride on titanium, carbon-chlorine bond rupture was totally irreversible. Over nickel, tungsten, copper, platinum, cobalt, manganese, aluminum and silver, methane was the only hydrocarbon product. Over palladium and titanium higher hydrocarbons were formed. In the reaction of methylene chloride over titanium, polymer was also formed, and olefins were the main C 2 and C 3 products. The reaction of methyl chloride on titanium was shown to be first order in both methyl chloride and hydrogen pressures. Adsorption measurements with the alkyl chlorides on the above metals gave surface hydrogen/carbon ratios which, in most cases, suggested the average surface hydrocarbon residue to be more extensively dehydrogenated than the group in the original alkyl chloride: the extent of dehydrogenation increased with increasing temperature. The exception to this was titanium where adsorption of methyl chloride and methylene chloride gave approximately CH 3 and CH 2 surfaces residues, respectively. From the influence of hydrogen on the reaction product distribution, and from the results from reactions with deuterium it has been concluded that on palladium, chemisorbed hydrogen was directly involved in the process of product desorption, but on titanium this was not so, and inter-residue hydrogen transfer occurred in desorption. Evidence has been adduced that carbon-carbon bond formation probably occurred by reaction of an alkyl chloride molecule with a surface CH 2 group. Activation energies and frequency factors have been evaluated for the reactions of both alkyl chlorides on titanium.