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

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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%.