would activation parameters for the other reactions with an apparent substitution-controlled mechanism.It is possible that the rapid manganese(II1) oxidation of thiocyanate is also substitution controlled, as found in the analogous reaction with ~o b a l t ( I I I ) .~ If the trends observed in complexation reactions of Fe3taq 14,15,24 and substitution-controlled redox reactions of C O~+~~~,~~ are maintained in the rnanganese(II1) series (24) D. Seewald and E. Sutin, Inorg. Chem., 2, 643 (1963).then the rate of the Mn3+,,-SCN-reaction might be expected to be somewhat higher than those for complexation by Br-and C1-, the rate constants of which are presumably a t least lo6 M-l sec-I a t 25°.The rate of oxidation of V(I1) with Cr(V1) to form V(II1) in perchloric acid solution was studied a t lo", primarily under second-order conditions and with V(I1) in excess. The observed rate law for the reaction in 1.00 M NaC104 is -d[Cr(VI)]/ dt = (k1 + kz[H+] + k3[V(II)])[HCr04-] [V(II)] where kl = (1.02 i 0.01) X 1oj iM-' sec-l, k2 = (7.9 i 0.26) x 104 M-2 sec-', and ka = (1.27 + 0.09) X lo7 M -2 sec-l. The first step in the reaction results in the direct formation of V(II1)by means of a one-electron redox process. Evidence is presented for the absence of the direct formation of vanadium(1S') under the conditions of these experiments. A mechanism is proposed based on the observed rate law, IntroductionThe net reaction between chromium(V1) and vanadium(I1) in acid solution when V(I1) is in excess can be represented by the equation

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Die Oxidationsgeschwindigkeit in perchlorsaurer Lösung von V(II) zu V(III) durch Cr(VI) wird bei 10°C und V(II)‐Überschuß untersucht.