Abstract
Relaxation spectra have been obtained for the formation and decomposition of H2I2O104– at 25.0 ± 0.2 °C and I= 0.25 ± 0.01 mol dm–3(Na2[SO4]) in the pH range 9.1–9.6 by the temperature-jump method. The observed relaxation times (in the range 50–200 µs, depending on concentration and pH) could be fitted to a scheme involving dimerisation reactions of H3IO62– with itself (kf), and with H2IO63–(kf′). The values (dm2 mol–1 s–1) determined by least-squares analysis of the pH dependence are: for 2H3IO62–, kf=(1.54 ± 0.04)× 105; and for H3IO62–+ H2IO63–, kf′⩽(6.94 ± 0.50)× 106. The value of kf′ is close to the diffusion-control limit. The results are interpreted in terms of a nucleophilic mechanism in which there is attack on the iodine by –O– followed by elimination.