The chromium(II)-catalysed dissociation of monochlorochromium(III)

Abstract

The reaction between chromium(II) and monochlorochromium(III) which results in a net dissociation of the chloride from the chromium(III), has been studied in aqueous perchloric acid solutions, ionic strength µ= 2·0H, using conventional spectrophotometric techniques. The kinetics conform to the rate equation Rate =k₁″[CrCl²⁺][Cr²⁺][H⁺]^–1 which is consistent with the formation of a transition complex [Cl Cr OH Cr]³⁺. At 25° the experimental rate constant k₁″ is 2·6 × 10^–4 sec.^–1, and from the temperature dependence ΔH^‡= 21·62 kcal. mole^–1, and ΔS^‡=–2 e.u. Use of literature values for the acid dissociation constant of CrCl²⁺ gives the rate constant for reaction between Cr²⁺ and Cr(Cl)OH⁺ as 20 ± 2·5 I. mole^–1 sec.^–1 at 20°.