Kinetics of the Proton-Transfer Reactions of Some ortho-Hydroxy Derivatives of Azo and Azomethine Compounds in Dioxane-Water Medium

The kinetics of the proton-transfer reactions between hydroxide ion and o-hydroxy azo and o-hydroxy azomethine compounds having a strong O–H···N or an O–H···π intramolecular hydrogen-bond are studied in 50% (v/v) dioxane-water by means of temperature-jump method. The forward and the backward rate constant kf and kr for the overall reactions OH−+HA2O+A− are evaluated to be in the range between 4.4×104 and 6.1×108 M−1 s−1 and between 1.5×103 and 6.2×104 s−1 respectively. The values of the kf for the azomethines are by several orders of magnitude higher than those of the corresponding azo compounds. The values of kf and kr in dioxane-water are found to be smaller than those in aqueous medium.