Since the classical work of Harcourt and Essona the kinetics of the reaction between permanganate and oxalate ions in acid solution have been studied by several investigator^.^^^^^ The development of a sound theory of kinetic salt effect by Bronsted6 offers another method of investigating the mechanism of this reaction. Lamersa has shown that a positive salt effect is found when the reaction occurs in the presence of relatively large concentrations of oxalate and of added manganous ion.A mechanism for the reaction is presented here as a basis for discussion. rMn04-$. yMn++ + 8xH+ + (Sum of series of rapid reactions) Mn++++ -b Mn++ Mn+++ + 3c~o4' Mn++ + 2CzOh Mn++++ -k c 2 0 4 ' --f Mn+++ 4-(20% + Cog-Mn++++ 4-COz-+ Mn+++ f COa (rapid) Mn+++ + Mn+++ + CG-+ Mn++ + COa zMn++++ + [ (x 4y)z]Mn+++ + 4xHz0 (1) 2Mn++* (rapid, reversible) Mn(GO&' (rapid, reversible) (rapid, slower than (6)) (8) + Mn++ + COS + C0,-If the reduction of the permanganate ion to the intermediate valences occurs in a series of rapid bi-molecular reactions, as seems probable to the authors, both Mnf+++ and Mn+++ ions are produced. Due to the existence of the equilibrium represented by equation (2), this point is not easily demonstrated and is not essential to the rest of the mechanism.The formula of the manganic oxalate complex ion in equation (3) differs from that proposed by Evidence for the formula Mn(Ca0,)p will be presented in another paper. The existence(1) The material in this paper is taken from a thesis submitted by Bryan C. Redmon to the Graduate School of the Massachusetts State College in partial fulfilment of the requirements for the degree of (6) Bronstcd, Z. physik. Cham., 10%. 169 (1922); 118. 337 (l92K). Yost, ibid., 66,2K71 (1934). of the equilibrium represented in equation (4) is shown by the work of Scholder and Linstrom.' Equations (5), (6), (7) and (8) are those proposed by Launer and Yost.6b The existence of reaction (7) is ditficult to prove because of the existence of the equilibrium represented by equation (2) and reaction (5).From an inspection of the mechanism it is evident that, if the rate-determining equation is either (5) or (7), the salt effect should be negative according to the Bronsted theory. LauneP in his investigation of the salt effect used a relatively high concentration of the oxalate ion and added manganous ion. Under these conditions, the reactions from left to right in the equilibria represented by equations (2) and (3) are favored, and the rate of reaction becomes inversely proportional to the concentration of the manganic oxalate complex ion. The effect of added salts on this equilibrium would be to increase the dissociation of the manganic oxalate complex ion and so increase the rate of reaction. From these considerations the positive salt effect found by Launer is apparently not a kinetic salt effect, but a salt effect on the equilibrium represented by equation (3) or a secondary salt effect according to the Bronsted theory.If the reaction is carried out in the presence of relatively low concentr...
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