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

Abstract

In aqueous acetate buffer (pH 3.25–4.30) 2‐mercaptoethanol is oxidized to 2‐hydroxyethyldisulfide by 13‐vanadomanganate(IV) (1). Each mole of 1 consumes 15 mol of 2‐mercaptoethanol, and in this process all of their VVO6 units (in total 13 in number) are reduced to VO2+ in a multistep process. In the first step, 1 is converted to a one‐electron–reduced product (2), comparable to heteropolyblue. Its kinetics has been measured for the first time. The extra electron in 2 is most possibly trapped (in electron paramagnetic resonance spectroscopic timescale) on the 13th vanadium atom, which shares one oxygen with the central MnIV atom in 1. Complex 2 being metastable in the studied pH range decompose further into smaller oligomers, which are further reduced to free vanadyl ions. We found that in the presence of ≥10 fold [2‐mercaptoethanol] over [1], the kinetics of the first step is first order with respect to [1], [2‐mercaptoethanol], and [H+]. Monoprotonated 1 seems kinetically more active than 1. A plausible mechanism has been suggested.

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.…”

Decavanadate Toxicology and Pharmacological Activities: V10 or V1, Both or None?

“…Therefore, GSH is an important cellular antioxidant defense system and directly or indirectly regulates the levels of ROS [ 19 , 20 ]. However, it is proposed that the mechanism for decavanadate detoxification is not the same, as it was suggested for the mechanism of thiol compounds oxidation by similar POMs [ 21 ]. Eventually, vanadate reduction by GSH may be delayed if decavanadate species are present.…”

Kinetics and Mechanism of 13-Vanadomanganate(IV) Catalyzed Oxidation of Benzoic Acid Hydrazide by Bromatein Buffer Solution of pH 4.0

“…7used in the present study has two redox centers Mn IV within the vanadium polyoxometalate cage and V V as the addenda ion. The reduction of both the ions is possible in presence of a strong reductant 17 . Reduction of Mn IV center results after the reduction of all the thirteen V V since it is buried within the polyoxometalate structure.…”

“…It has also been proposed that after the reduction of all the V V ions in the outer cage the polyoxometalate structure will be totally dismantled thus making possible the interaction between the Mn IV and the reductant. During such reduction of both the hetero atom (Mn IV ) and the addenda atom (V V ), formation of a heteropoly blue is expected 17 . In order to understand the type of interaction between the catalyst and the hydrazides the spectrophotometric examination of a mixture of catalyst and the hydrazide was examined.…”