The kinetics of oxidation of doxycycline hyclate (DCH) by periodate ion in aqueous medium was monitored spectrophotometrically. 1 mol of DCH reacts with 2 moles of periodate in the initial part of the reaction. The reaction follows second order behaviour. Results under pseudo first order conditions, are in agreement with the rate law: Reaction Rate = kKKw [DCH] [IO4 -]0 [H+] /{K2 Kw + (Kw + Kb K2) [H+] + Kb [H+]2} where kK is the empirical composite rate constant, Kw is ionic product of water, K2 is acid dissociation constant of H4IO6 -, Kb is base dissociation constant of DCH and [IO4 -]0 represents the concentration of periodate that has been taken in excess. The rate-pH profile shows a maximum at pH 6.0. The validity of rate law is tested by matching the experimental and calculated pH value corresponding to the rate-pH profile maximum. Increase in dielectric constant has a positive effect on arte of reaction. Free radical scavengers do not affect the reaction rate. Various thermodynamic parameters are reported. High negative value of entropy of activation and the effect of dielectric constant suggest the involvement of salvation effects in mechanism of the reaction particularly the chances of solvated transition state.
