Department of Chemistry, Osmania University, Hyderabad-500 007 Manuscript received 26 February 1985, revised 8 October 1985, accepted 9 March 1987 A study of IrIII catalysed oxidation of diacetone alcohol (DAA) by CeIV in H2SO4 and HCIO4 media was undertaken to understand the mechanism of catalysis. The change in reactive species of CeIV in tnese media produces a marked effect on the relative rates of catalysed and uncatalysed reactions. The catalysis was found to be more pronounced in H2SO4

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... ium. The order in [CuIV] was found to be unity and that in [IrIII] fractional in both the media studied. The order in [substrate] changed from unity in the uncatalysed reaction to fractional in the catalysed reaction in H2SO4 medium However, in HCl4 medium, the order in [DAA] was found to be fractional both in Latabsed as well as uncatalysed reaction. A mechanism involving formation of IrIII-DAA complex in a fast step followed by its reaction with CeIV in the slow step to give [IrIV complex] which decomposes to give lull and first stage intermediate products is proposed to explain the kinetic data.