Kinetics of the Proton-Transfer Reaction of 4-(2,4-Dihydroxyphenylazo)nitrobenzene in Dioxane–Water Media

Kinetics of proton-transfer reactions in 4 to 50%(v/v) dioxane–water media between hydroxide ion and 4-(2,4-dihydroxyphenylazo)nitrobenzene (Magneson; MAG) having a strong OH···N intramolecular hydrogen-bond are studied by means of the temperature-jump method. The forward and the backward rate constants kf and kr[H2O] for the reaction OH−+HA−2O+A2− are evaluated to be in the range of 9.2×105–1.3×105 mol−1 dm3 s−1 and 5.5×103–1.8×103 s−1, respectively. The dependence of the kf and the acid dissociation constant Kac on the dioxane contents of the medium is interpreted on the basis of solute-solvent interactions.