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The copper-catalysed oxidation of hydrazine by peroxydisulphate in acid solution follows the rate law (i) where K,is the hydrolysisconstant of Cu2+, k was found to be 8.8 f 0-8 min.-l, 13.1 f 1.4 min.-l, and 17.2 f 1 a 3 min.-1 at 35,40. and 45" C respectively and , U = 0.2M. The composition of theactivated complex is Cua+, CuOH+,N2.H4,H+ or 2Cua+,N,H,.Ally1 acetate inhibits the reaction and Mnn and CIare without any effect in contrast with the other copper-catalysed peroxydisulphate oxidations. Perhaps several hydrazine complexes of CuT1 participate in the reaction and one of them isolated was Cu(NaH4),,(HS04),. An oxidation study of this complex also was in conformity with the above rate law and the rate constants in the two cases were comparable.CATALYSIS by copper (11) in peroxydisulphate oxidations has been reported for thiosulphate,1*2 ~x a l a t e , ~ AsIII,~ and in a few other cases. It appears that CuII catalysis is characteristic in cases where it can form a complex with the reducing substance or where the oxidation involves multielectron-transfer change. The possibility for both the processes also exists. The above conclusion is supported by the fact that CuI1 does not catalyse the oxidations of MnII, CeIII, vanadyl, and other ions and molecules involving one-electron change and also by the fact that it does not form complexes with these reducing substances. CuII does form complexes with thiosulphate,5 oxalate,6 and AsIII.' Recently a kinetic study of the CuII catalysed oxidations of AsI1I8 and SbI1I9 has been made and mechanisms involving Asm and SbIV have been suggested. Kinetic evidence for a complex has been obtained in case of AsnI, but not in

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Permanganate oxidises small amounts of iodide to iodite in the presence of malonic, citric or malic acid. The colourless reaction mixtures always have an oxidising capacity equivalent to four times the concentration of the iodide originally taken. In mixtures of permanganate and one of these acids, iodate is reduced to its 2/3 oxidising capacity, showing the formation of iodite. A mechanism for this has been suggested. Iodine is the product in the first stage of the oxidation of iodide, which is further oxidised to iodite or iodate or which may react with the oxidation products of the organic acids. Citric acid probably gives a number of such iodinated products, one of which is solid.