Activation of molecular oxygen for the oxidation of 2-mercaptoethanol: A kinetic and mechanistic approach

• Molecular oxygen reduction by 2-mercaptoethanol in presence of cobalt(II)histidine.
• Molecular oxygen react in the form of an adduct with cobalt(II)histidine.
• Decrease in absorbance of dioxygen complex was monitored spectrophotometrically.

Reduction of molecular oxygen by 2-mercaptoethanol in the presence of cobalt(II)histidine is described. Cobalt(II)histidine complex forms dinuclear 2:1 (Co:O2) complex with molecular oxygen (μ-dioxytetrakis(histidinato)dicobalt(II)). The molecular oxygen did not directly react with 2-mercaptoethanol, but, reacted in the form of an adduct with cobalt(II)histidine complex. During the course of the reaction the molecular oxygen is reduced to hydroxide ion while the cobalt(II)histidine complex was oxidized to cobalt(III)histidine while 2-mercaptoethanol is reduced into 2,2′-dithiodiethanol. The decrease in absorbance for the dioxygen complex was monitored spectrophotometrically and was observed that the values of rate constant increased with the increase in [2-mercaptoethanol]. The values of kobs also increased with increasing [NaOH]. Thus, from the results of these studies, mechanism of the reaction has been proposed. In addition, the values of various equilibrium constants and rate constants were also determined using nonlinear least square techniques.

Repetitive scans of absorption spectra of solution containing [CoL2] = 2.0 × 10−3 mol dm−3, [2-mercaptoethanol] = 2.0 × 10−2 mol dm−3 and [NaOH] = 5.0 × 10−4 mol dm−3 at 5.0 ± 0.1 °C. The scans were recorded at the intervals of 120 s. The arrow indicates that the values of absorbance decreases with the progress of reaction with the increase in time.Figure optionsDownload as PowerPoint slide