VARIABLE STOICHIOMETRY IN THE DECOMPOSITION OF AROMATIC DISULFIDES IN ALKALINE SOLUTION. ON THE PROPERTIES OF 3-CARBOXYLATE-4-NITROBENZENE SULFENATE ION

Abstract

The alkaline hydrolysis of low concentrations of the aromatic disulfide 5,5′-dithiobis(2-nitrobenzoic acid) in 3.0 M NaOH, quantitatively forms 3-carboxylate-4-nitrobenzenesulfenate ion as expected for a simple displacement of the thiophenoxide ion by hydroxide ion. In the absence of residual disulfide, the sulfenate ion is stable, apart from slow oxidation to the corresponding sulfinate ion. The red sulfenate ion has an absorption maximum at 492 ± 2 nm with a molar absorption coefficient (∊) of 10,600 M⁻¹ cm⁻¹ at 490 nm. At high initial concentrations of disulfide or at lower concentrations of hydroxide ion, appreciable amounts of the sulfenate ion react with unreacted disulfide to form a transient sulfinic acid thiolester intermediate which decomposes to form the corresponding sulfinate ion and the thiophenoxide ion. This work constitutes the first unambiguous description of the mechanism and variable stoichiometry of the alkaline decomposition of an aromatic disulfide.