Synthesis,characterization, and mechanism of trans-dichlorido-bis-(ethylenediamine)cobalt(III) with L-cystine in the presence of chloride

Substitution reactions of trans-CoCl₂(en)₂]Cl (where en?=?ethylenediamine) with L-cystine has been studied in 1.0?×?10^?1?mol?dm^?3 aqueous perchlorate at various temperatures (303–323?K) and pH (4.45–3.30) using UV-Vis spectrophotometer on various Cl^?] from 0.05 to 0.01?mol?L^?1. The products have been characterized by their physico-chemical and spectroscopic data. Trans-CoCl(en)₂(H₂O)]²⁺, from the hydrolysis of trans-CoCl₂(en)₂]⁺ in the presence of Cl^?, formed a complex with L-cystine at all temperatures in 1?:?1 molar ratio. L-cystine is bidentate to Co(III) through Co–N and Co–S bonds. Product formation and reversible reaction rate constants have been evaluated. The rate constants for SN_i mechanism have been evaluated and activation parameters E _a, ΔH ^#, and ΔS ^# are determined.