Redox transfer. Part V. Elementary steps. The oxidation of ferrous and cuprous chloride by carbon tetrachloride

Abstract

The oxidation of ferrous chloride by carbon tetrachloride has been studied spectrophotometrically by initial-rate measurements of FeCl₄^– formation in acetonitrile as solvent and in the presence of an excess of chloride ion. A transient violet intermediate appears upon mixing of the reagents, considered to be a charge-transfer complex between ferrous chloride and carbon tetrachloride, which decomposes into FeCl₄^– and a trichloromethyl radical. This decomposition is the rate-determining step in the overall oxidation to ferric chloride. Trichloromethyl radicals are captured by ferrous chloride in a subsequent fast reaction, giving a carbenoid complex which decomposes bimolecularly into ferric chloride and tetrachloroethylene. in the presence of an olefin, dichlorocyclopropanes are also formed. The overall reaction is first-order in ferrous chloride and has a rate constant of 2·10^–4l. mole^–1 sec.^–1 at 22°. The fast interaction of ferrous chloride and trichloromethyl radicals, and the subsequent reactions of the complex formed, are recognized as the main mode of termination in the radical-chain addition of carbon tetrachloride to olefins in a redox transfer-system. The rate constant of the reaction between cuprous chloride and carbon tetrachloride (CCl₄+ CuCl[graphic omitted]CuCl₂+·CCl₃) is about 40 times smaller than the corresponding constant for the ferrous chloride reaction. The reaction reaches a quasi-equilibrium already at conversions into cupric chloride as low as 1·5%.