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

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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 (http://dx.doi.org/10.1016/j.cej.2004.09.004)

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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.

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