The base hydrolysis of homologous amino acid esters co-ordinated to cobalt (III). kinetics and product analysis

Abstract

Ester containing chloropentammine cobalt(III) complexes of the type cis-[Co(en)2(NH2(CH2)nCO2CH3)Cl]Cl2 (where n=2, 3 and 5) have been prepared, with the cis-configuration being assigned on the basis of spectral characteristics. Their base hydrolysis has been studied by pH-stat and spectrophotometrically at 25.0° and I=0.10M (KCl). Loss of co-ordinated chloride is faster than "dangling" ester hydrolysis by a factor which is dependent on the value of n. Both reactions independently follow the rate law v = k2[Complex][OH-] and lead to the formation of [Co(en)2(NH2(CH2)n CO2)OH]+. For the (β-alanine derivative (n=2), [Co(en)2(NH2(CH2)CO2)CH3)]3+ and [Co(en)2(NH2(CH2)2C02CH3)OH]2+ are produced following chloride loss, the former resulting in rapid ester hydrolysis and intramolecular hydrolysis by bound OH- partially occurring for the latter, both yielding [Co(en)2(NH2(CH2)2C02CH3)]2+.