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Kinetics of oxidation of hydroquinone by polymer-supported hypervalent iodine oxidant, iodoxybenzoic acid

Jegasothy, S. and Slater, N.K.H. and Denecker, C. and Sherrington, D.C. and Lei, Z. and Sutherland, A.J. (2004) Kinetics of oxidation of hydroquinone by polymer-supported hypervalent iodine oxidant, iodoxybenzoic acid. Chemical Engineering Journal, 105 (1-2). pp. 1-10. ISSN 1385-8947

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Abstract

lodoxybenzoic acid has been covalently attached to polystyrene-co-divinylbenzene beads at different capacities and the hydroquinone oxidation kinetics have been studied in a stirred batch reactor. An initial rate analysis yielded a first order dependence on the concentration of the substrate hydroquinone and the supported IBX reagent implying chemical reaction is rate limiting. An observed second order rate constant of 1.3 (+/-0.3) M-1 s(-1) was obtained for the initial rate of oxidation using the supported reagent. The activation energy was halved at later stages of reaction (greater than 50% conversion of the reagent), suggesting that intraparticle diffusion then become rate limiting as the conversion of the reagent in the bead proceeded. Unreacted shrinking core and pseudo-homogeneous diffusion-reaction models have been used to analyse the experimental data to yield values for the effective diffusivity of hydroquinone in the polymer matrix of (1.0-1.2) x 10(-11) m(2)/s. The performance of the supported reagent in a packed bed has also been studied by continuous flow of a solution of hydroquinone. The product quinone concentration profile at the reactor exit showed limited dependence on the flow-rates studied. Pronounced tailing of the product concentration was obtained for more highly loaded beads, which was attributed to hindered diffusion limiting access to the residual reactive sites.