Degradation of Multiply-Chlorinated Hydrocarbons on Cu(100)

Dechlorination and hydrodechlorination of multiply-chlorinated ethanes and propanes on a clean Cu(100) surface have been studied by Auger electron spectroscopy, temperature-programmed desorption, and chemical displacement measurements. The rate-limiting step in degradation is dissociation of the first C−Cl bond in the molecule, and this process is more facile in CCl2 groups than in CCl groups. The activation energies for C−Cl bond scission on Cu(100) are 12−20% of the gas phase bond dissociation energies, and the extent of dissociation by the physisorbed molecules is a sensitive function of the relative rates of C−Cl bond scission and molecular desorption. The chlorinated hydrocarbon fragments generated on the surface by C−Cl bond cleavage undergo facile α- or β-chlorine elimination while all C−H bonds remain intact. β-Chlorine elimination dominates in cases where chlorine is present at both the α- and β-positions, and as a result of β-chlorine elimination, alkenes are generated and evolved to the gas pha...