KINETICS AND MECHANISM OF THE OXIDATION OF 1-PROPANETHIOL AND 2-PROPANETHIOL BY 2,6-DICHLOROPHENOLINDOPHENOL IN METHANOL-WATER MEDIUM

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Abstract
The oxidative cleavage of 1-propanethiol and 2-propanethiol (1-PT and 2-PT respectively) by 2,6-dichloro-phenolindophenol have been studied in methanol-water medium and the thiol-disulphide conversion has been studied kinetically in presence of hydroxyl ion at 30°C. The reaction follows a second order kinetics in indophenol in both cases. The order of reaction is one in 1-propanethiol while in 2-propanethiol, the order shows a transition from zero to one at higher concentrations of alkali. The rate constant shows a direct proportionality with [OH−] in case of 1-propanethiol but in the oxidation of 2-propanethiol, an inverse linear proportionality has been noticed. Again in the oxidation of 2-PT, the rate is indifferent to [OH−] at higher concentrations of sodium hydroxide (ca. < 2.5 × 10−4M). The rate of oxidation of 1-PT increases on increasing the dielectric constant of the medium while a decrease in the rate of oxidation of 2-PT has been observed in these studies. Variation of ionic strength and the addition of reaction products do not influence the rate in both the cases. The reaction has been studied at different temperatures and activation parameters have been evaluated. Mechanisms consistent with kinetic data have been proposed and the diversity in kinetic results has been interpreted in terms of the difference in the mode of addition of thiol molecule to indophenol dimer.