Kinetic Analysis of Hydroxide-Catalyzed, Aerobic Oxidation of 2-Mercaptoethanol

Experiments and mechanistic kinetic analyses are conducted for the hydroxide-catalyzed, aerobic oxidation of the thiol 2-mercaptoethanol (2-ME) to water and the corresponding disulfide at 22°C and 1 atm total pressure in tetrahydrofuran. The experiments are performed in an isothermal, bench-scale reactor with a maintained O2 partial pressure. The 2-ME concentrations are measured using gas chromatograph/flame ionization detector (GC/FID). The mixture includes a small amount of aqueous NaOH required to activate the thiol (RSH) to thiolate (RS−). The observed 2-ME conversion is first order in 2-ME concentration. A multistep mechanism is proposed consistent with the observed kinetics. The rate-determining step is the coupling of RS− to dissolved O2, with an estimated rate constant k = 1.93 × 10−6 liter/mmol h.

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