A comparative kinetic study for the oxidation of 2-mercaptoethanol by di-μ-oxo-bis(1,4,7,10-tetraazacyclododecane)-dimanganese(III,IV) and di-μ-oxo-bis(1,4,8,11-tetraazacyclotetradecane)-dimanganese(III,IV) complexes: Influence of copper(II)

✍ Scribed by Sanchita Goswami; Nizamuddin Shaikh; Anangamohan Panja; Pradyot Banerjee

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 114 KB
• Volume: 36
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.10182

✦ Synopsis

Abstract

A comparative kinetic study of the reactions of two mixed valence manganese(III,IV) complexes with macrocyclic ligands, [L^1^Mn^IV^(O)~2~Mn^III^L^1^], 1 (L^1^ = 1,4,7,10‐tetraazacyclododecane) and [L^2^Mn^IV^(O)~2~Mn^III^L^2^], 2 (L^2^ = 1,4,8,11‐tetraazacyclotetradecane) with 2‐mercaptoethanol (RSH) has been carried out by spectrophotometry in aqueous buffer at (30 ± 0.1)°C. Rate of the reactions between the oxidants and the reductant was found to be negligibly slow with no systematic dependence on either redox partners. Externally added copper(II) (usually 5 × 10^−7^ mol dm^−3^), however, increases the rate of the reduction of 1 and 2 significantly. In the presence of catalytic amount of copper(II), the rate of the reaction is nearly proportional to [RSH] at lower concentration of the reductant but follows a saturation kinetics at higher concentration of the latter for the reaction between 1 and the thiol. Reaction rate was found to be strongly influenced by the variation of acidity of the medium and the observed kinetics suggests that the two reductant species ([Cu(RSH)]^2+^ and [Cu(RS)]^+^) are significant for the reaction between 1 and the thiol. The dependence of the rate on [RSH] for the reduction of 2 by the thiol was complex and rationalized considering two equilibria involving the catalyst (Cu^2+^) and the reductant. The pH rate profile suggests that both the μ‐O protonated [Mn^III^(O)(OH)Mn^IV^] and the deprotonated [Mn^III^(O)~2~Mn^IV^] forms of the oxidant 2 become important. The kinetic results presented in this study indicate the domination of outer‐sphere path. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 129–137, 2004