Sodium tellurite as oxidizing agent for thiols

The reagent is highly selective, as demonstrated by the inertness of several sensitive functionalities such as amino, hydroxyl, azo, hydrazo, phenol, sulphide, disulphide, sulphoxide, aldehyde moieties, and olefmic and acetylenic carbon-carbon bonds. The ability of the reagent to differentiate thiols may be used to prepare unsymmetrical disulphides. 

The cross-coupling reaction proceeds through the initial oxidation of the more reactive thiol, followed by the gradual thiolysis of the formed disulphide by the less reactive thiol. The method is therefore useful for the cross-coupling of the reactive aryl and n-alkyl thiols with the less reactive f-alkylthiols. 

Unsymmetrical disulphide. A solution of Na2Te03x5H20 (0.465 g. 1.49 mmol) and 10% aqueous [Bu4N ]OH (0.28 mol, 0.10 mmol) in H2O (20 mL) is added dropwise to a vigorously stirred solution of phenylmethanetiiiol (0.307 g, 2.47 mmol) and 2-methyl-2-propanethiol (0.251 g, 2.79 mmol) in benzene (20 mL). The resulting mixture is stirred for 36 h at room temperature and then, worked up as described above to give pure benzyl t-butyl disulphide (0.39 g (74% based on phenylmethanethiol)) as an oil (b.p. 97°C/0.9 torr). 

Sodium tellurate (Na2Te04) exhibits similar oxidizing properties towards thiols. 

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