Kinetics of acid and base hydrolysis of azido[(RR)-1,11-diamino-3,6,9-triazaundecane]cobalt(III)

Abstract

The kinetics of hydrolysis of the ion [Co(Hdtu)N₃]²⁺[Hdtu =(RR)-1,11-diamino-3,6,9-triazaundecane] in perchloric acid solutions has been investigated spectrophotometrically and by N₃^– release. Over the range 0·05–0·52M-HClO₄[I= 1·00M(NaClO₄)] the reaction follows a rate law of the form –dln[Co(Hdtu)N₃²⁺]/dt=k_a, where k_a=k₁+k₂[H⁺]. Over the range 0·006–0·03M-HClO₄[I= 1·00M(NaClO₄)] the reaction follows a rate expression for opposed first- and second-order reactions. The pseudo-first-order rate constant for the forward reaction has an inverse hydrogen-ion dependence of the form k_b=k₁′+(k₃/[H⁺]), while the second-order rate constant for the reverse reaction shows a complex dependence on [H⁺], of the form k_c=(k₄/[H⁺])+(k₅/[H⁺]²). Activation parameters and a mechanism for the overall reaction are given.