Kinetics of acid-catalysed hydrolysis of the α and β Carbonato(4,7-dimethyltriethylenetetramine) cobalt(III) ions

Abstract

The synthesis and separation of the complexes α-[Co(dmtr)CO₃] ClO₄ and β-[Co(dmtr)CO₃] C1O₄,H₂O (dmtr = 4,7-dimethyltriethylenetetramine or N,N'-bis(2-aminoethyl)-N,N'-dimethylethane-1,2-diamine) are described. The kinetics of the acid hydrolysis of both complexes, studied in perchloric acid at 25ºC and μ = 1.0M (LiC1O₄), follow rate laws of form -d[complex]dt=(k₀ + k₁[H⁺I)[complex] The values of k_o and k₁ for the K-complex are 1.0 x 10^-3 s^-1 and 1.8 x 10^-2 1. mol^-1 s^-1 respectively, while for the β-complex the corresponding values are 3.6 x 10^-5 s^-1 and 5.6 x 10^-4 1. mol^-1 s^-1. Comparisons of these rate constants with the values for similar carbonato(tetramine)cobalt(111) complexes previously studied suggest that the k_o path could involve O-C bond cleavage in the present dmtr complexes. The values of the acid dissociation constants of dmtr,4HCl, determined by potentiometric titration, are 1.61, 5.86, 8.18 and 9.95.