SELECTIVE HYDROGENOLYSIS OF CHLOROFLUOROCARBONS BY RHCL(PPH(3))(3)

Factors affecting hydrogenolysis of CFC-113a (CF3CCl3) catalyzed by Rh Cl(PPh(3))(3) were studied to have an insight on the mechanism of the reaction. A slightly polar solvent such as THF is found to be appropri ate for selective hydrogenolysis of fluorochlorocarbons. Kinetic analy sis showed the reaction was first-order with respect to the concentrat ions of catalyst and substrate, respectively, Reaction rates were depe ndent on the concentration of Cl- ions added; the reaction rate increa sed initially but remained constant at the higher Cl- concentration. S triking effect of halide ions were rationalized by increased nucleophi licity of [RhX(2)(PPh(3))(2)](-) (X = Cl, Br, I), a product from the i nitial reaction between catalysts and added halide ions, toward CFC-11 3a. Hydrogenolysis of CFC-113 (CF2ClCFCl2) produced HCFC-123a (CF2ClCH ClF) and chlorotrifluoroethene (CF2=CFCl), a product from beta-elimina tion of HCFC-123a, indicating nucleophilic attack of metal complexes t o more electropositive carbons actually occurred. These results appear s to support the S(N)2 mechanism for the oxidative addition of CFC-113 a. Added amines decreased reaction rates most probably by inhibiting t he formation of more nucleophilic complexes mentioned above. Added pro ton induced decrease in reaction rates, Effect of added phosphines is rather complicated; reaction rates initially decline to the range wher e the ratio of [PPh(3)] to [catalyst] is 6 but increase thereafter, Th is rate enhancement strongly indicates the existence of an independent phosphonium-containing reaction (c)ycle. Light brownish compound was actually isolated and was spectroscopically characterized as [Ph(3)P(C Cl2CF3)]Cl. Plausible reaction cycles are proposed and the rate equati ons for this proposed mechanism are derived.