Kinetics of the Fluorination/Chlorination of 1-Chloro-1,2,2,2-Tetrafluoroethane

Abstract

The kinetics of the catalytic fluorination and chlorination of 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124) by HF and HCl to give pentafluoroethane (HFC-125) and 1,1-dichloro-2,2,-trifluoroethane (HCFC-123), respectively, were examined in order to further define the mechanisms of these reactions. An HF-treated preparation of 2% CoCl2 on Al2O3 was used as a catalyst. Reaction of deuterium-labeled HCFC-124 with HF or HCl showed the deuterium to be retained in both reactant and products. suggesting the absence of carbenoid or olefinic intermediates in these halogenations. Thermodynamic and thermokinetic properties of these halogenations were also determined in order to determine the extent of contributions of reverse reactions to the kinetics of these halogenations. Kinetic studies indicated that these halogenations are consistent with a classical Langmuir-Hinshelwood mechanism where both HX (X = F or Cl) and HCFC-124 are adsorbed on identical active sites of the catalyst in the rate-determining step.