Kinetics and Mechanism of Oxidation of 2‐Mercaptoethanol by the Heteropolyoxovanadate [MnV 13 O 38 ] 7−

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 V V O 6 units (in total 13 in number) are reduced to VO 2+ 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 Mn IV 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.