%0 Journal Article
%T Synergistic Effect of [Ru(III) + Ir(III)] in N-Bromosuccinimide Reaction with Certain Aliphatic Ketones: A Kinetic Study
%A P. Giridhar Reddy
%A K. Ramesh
%A S. Shylaja
%A K. C. Rajanna
%A S. Kandlikar
%J Advances in Physical Chemistry
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/292908
%X Dramatic rate enhancements have been observed in the oxidation of acetone (MMK), ethyl methyl ketone (EMK), and isobutyl methyl ketone (IBMK) by N-bromosuccinimide (NBS) in the presence of a mixture of metal ions [Ru(III) + Ir(III)]. The rate of oxidation in the the [Ru(III) + Ir(III)] system is much faster than either in the Ru(III) or in Ir(III) catalyzed system. The order in [NBS] was found to be zero both in catalyzed as well as uncatalyzed reactions. However, the order in [ketone] changed from unity to a fractional one in metal ion catalyzed systems. On the basis of kinetic features, the most plausible mechanism involving the oxidation of [Ir(III)-ketone] by Ru(III) to give [Ir(V)-ketone] and Ru(I) in the rate limiting step is proposed. Ru(I) thus formed is oxidized by NBS to Ru(III) in a fast step is discussed and individual rate parameters were evaluated. 1. Introduction Bimetallic catalysts often exhibit improved properties than either of the single metal catalysts. This is generally called the synergistic effect. The presence of the synergistic activity of platinum and rhodium in bimetallic catalysts and possible reasons for the effects has been discussed in the literature [1¨C10]. The synergistic activity of certain mixed catalyst systems, namely, [Ag(I) + Mn(II)], [Ag(I) + Cu(II)], [Ru(III) + Mn(II)], [Ir(III) + Mn(II)] and [Ru(III) + Os(VIII)], and so forth, has been the subject of interest in the field of homogenous redox reactions by several workers [4¨C10] in recent years. N-bromosuccinimide (NBS) has been used as a versatile oxidizing agent and analytical reagent in acid and alkaline media [11¨C24]. In recent past microconcentrations (10£¿6 to 10£¿5£¿M) of Ru(III) and Ir(III) have been employed as an efficient catalyst in N-bromosuccinimide (NBS) oxidations and other redox systems [25¨C31]. Recently we have reported that Ru(III) 34 catalyzed the oxidation of aliphatic ketones by NBS in aqueous acetic acid [27], wherein trace amount of Ru(III) is used as a catalyst. However, kinetic studies involving the mixture of metal ions as a catalyst also appeared to be scanty in NBS oxidations. Preliminary experiments involving the mixture of Ru(III) and Ir(III) as a catalyst in NBS-aliphatic ketone redox system in aqueous acetic acid medium containing H2SO4 indicated that the reaction rate is much greater than the sum of the reaction rates when metal ions such as Ru(III) and Ir(III) are separately employed as a catalyst. These striking features have become stimulus for us to take up a systematic kinetic study comprising the catalytic oxidation of certain
%U http://www.hindawi.com/journals/apc/2012/292908/