EPR Measurement of the Reaction of Atomic Hydrogen with Periodate and Iodate in Aqueous Solution

Abstract

Electron paramagnetic resonance free induction decay (FID) attenuation measurements have been used to determine Arrhenius parameters for the reaction of hydrogen atoms with IO[sub 4][sup [minus]] and IO[sub 3][sup +] in aqueous solution at pH 4.6. At 25[degree]C, scavenging rate constants of (7.31 [+-] 0.12) x 10[sup 8] and (1.22 [+-] 0.04) x 10[sup 7] dm[sup 3] mol[sup [minus]1] s[sup [minus]1] were obtained for IO[sub 4][sup [minus]] and IO[sub 3][sup [minus]], respectively, with corresponding activation energies, measured over the temperature range 6-75[degree]C, of 22.35 and 27.46 kJ mol[sup [minus]1]. From kinetic measurements in 0.10 and 1.00 M HClO[sub 4] over the same temperature range, the rate constants for hydrogen atom reaction with the acid forms of these species, H[sub 5]IO[sub 6] and HIO[sub 3], were calculated to be 3.5 x 10[sup 8] and 6.0 x 10[sup 6] dm[sup 3] mol[sup [minus]1] s[sup [minus]1] (25[degree]C), with activation energies of 53.00 and 36.55 kJ mol[sup [minus]1], respectively. We suggest that all of these reactions involve oxygen atom transfer to the hydrogen atom, giving OH and a reduced iodine complex as product. 32 refs., 5 figs., 2 tabs.