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)

Abstract

A comparative kinetic study of the reactions of two mixed valence manganese(III,IV) complexes with macrocyclic ligands, [L 1 Mn IV ,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.

Catalytic System for Aerobic Oxidation That Simultaneously Functions as Its Own Redox Buffer

“…Our group and those of Matveev, Kozhevnikov, ,, and Neumann − reviewed organic substrate oxidations, including ones based on O 2 as the terminal oxidant, catalyzed by POMs, including PV n Mo 12– n O 40 /Pd systems, while Misono and Mizuno − reviewed industrial POM-catalyzed oxidations some time ago. Thiol oxidations are also important in organic chemistry, physiological processes, and environmental science. − Numerous catalytic and stoichiometric systems are known to selectively oxidize thiols in context with either deodorization or synthesis, including nanoparticle systems, , POMs, ,,− metal–organic frameworks (MOFs), ,, strong stoichiometric oxidants, − and noble metals. − Most of these systems do not use O 2 as the terminal oxidant. In addition, most are slow, require elevated temperatures, and form side products.…”

Kinetics and Mechanism of Oxidation of 2‐Mercaptoethanol by the Heteropolyoxovanadate [MnV13O38]7−

“…The 1 H NMR spectral study shows that complex 1 oxidizes 2‐mercaptoethanol to 2‐hydroxyethyldisulfide . We observed that the two triplet peaks at 2.68 ppm and 3.70 ppm, a representative of two –CH2 groups in 2‐mercaptoethanol (data not shown), shift to a higher δ value (Fig.…”

26 Mechanisms of reactions in solution

“…The former also reacts with 2-mercaptoethanol, but only in the presence of Cu(II), with [Cu(RSH)] 2+ and [Cu(RS)] + being reactive species. 41 Autoxidation of the copper(II)glycine complex has a very long induction period of up to 5 h in the absence of trace amounts of Ni(II) or Co(II) ions. 42 A dramatic decrease in induction period down 0.5s occurs when these ions are present.…”