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

Iodoxybenzoic 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 ^-1S^-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) × 10^-11 m²/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.