Cyclic voltammetry has been exploited to reinvestigate discrepancies in the reported rate constant for the reaction: k f cr(bipy):+ + 2H20 + ~r ( b i~~)~(~~~) : + + bipy which follows electrode reduction of the substitution inert cr(bipy):'. It is shown that the problems arise from oversimplified treatment of residual currents when estimating the anodic peak current, i,. A "two scan" procedure for estimating the background currents is introduced which appears to resolve discrepancies. The kinetic studies were extended to a methylsubstituted bipyridine. Since ring methylation has very little effect on kf, it appears that the aquation reaction is initiated by a rate-determining step which requires a minimum of bipyridine rearrangement. SHACHAR D. NADLER, JAMES G. DICK et COOPER H. LANGFORD. Can. J. Chem. 63, 2732Chem. 63, (1985.Utilisant la voltamttrie cyclique, on a reexamine les divergences rapporttes au sujet de la vitesse de la rkaction:Cette mtthode permet de suivre 1'Cvolution de la rduction 2i 17Clectrode du cr(bipy):' qui est inerte 2i la substitution. On dCmontre que les probBmes proviennent d'une trop grande simplification des courants rksiduels lorsqu'on tvalue le courant anodique maximal, i,. On introduit une mCthode 2i double balayage pour Cvaluer les courants rCsiduels et cette mCthode semble Climiner les irrCgularitCs. On a Ctendu les ttudes cinCtiques h une bipyridine substituCe par un mtthyle. Puisque la mCthylation du cycle n'a qu'un minime effet sur kf, il semble que la rkaction reprtsentte par 1'Cquation est initik par une Ctape determinant la vitesse qui nkcessite un minimum de transposition de la part de la bipyridine.[Traduit par le journal] IntroductionThe behaviour of the tris-(2,2-bipyridine) chromium(111) has been the subject of several electrochemical studies which have challenged the capacity of various electrochemical techniques to extract chemical kinetic information. The system has been reinvestigated in order to resolve discrepancies and refine the procedures for accurate extraction of kinetic parameters. Sato and Tanaka (1) have demonstrated that in aprotic solvents, [Cr(bipy),13+ is reduced in four, one electron steps to the [Cr(bipy),ll-anion. The aqueous behaviour of this chromium complex has been shown to be somewhat more complicated, notably because of solvolytic ligand exchange. Using conventional polarographic techniques, Tucker et al. (2) and Baker and Metha (3) obtained four polarographic waves for the reduction of aqueous [Cr(bipy),13+. They observed that the nature of these waves (size and shape) was a function of pH and temperature. From the behaviour of the first two polarographic waves Baker suggested the following reactions:

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