First Metal- and Base-Free Selective Oxidative Coupling of Thiols in Neat Ionic Liquids: NMR Probed 'Ambiphilic' Character of Neutral [hmim]Br towards Atom-Efficient Synthesis of Disulfides

摘要

The selective oxidative coupling of thiols has been studied in several imidazolium-based ionic liquids in the absence of any base/metal catalysts. Disulfides were obtained from the corresponding thiols in good to excellent yields in l-hexyl-3-meth-ylimidazolium bromide ([hmimjBr). Furthermore, a ~1H NMR-based mechanistic study of the S-S bond formation demonstrated the cooperative role of halide anion and imidazolium cation of [hmim]Br as an "ambiphile" - a character found to be imperative for the efficient syntheses of disulfides. The developed methodology is simple, selective and green that utilises molecular oxygen as an oxidant and produces water as the only by-product.