Synthetic access to thiols: A review

Thiols are ubiquitous compounds found in almost all spheres of life, viz: from simple matter to complex human body. It has widespread applications in diverse domains such as pharmaceuticals, materials, agricultural science, fire science, laser science, catalytic systems, reagent systems, and industry. Although all sulphur compounds encompass one or the other significant properties. However, thiols containing –SH bond are vital as they act as starting substrates for many chemical reactions, are directly present in the biological systems, are abundantly found in natural products, and exhibit profound chemical and biotechnological properties. For example, the –SH group can be easily manipulated to a range of other potent functionalities such as –S–S, –SO₂Cl₂, –SOCH₃, –SOCl₂, –SONH₂, –Cl, –NH₂, –OH, etc. In this view, this review focuses on reporting detailed synthetic methodologies giving access to thiols (–SH). For interesting reading, it has been categorised as follows: (i) via isothiouronium salts; (ii) catalytic preparation of thiols using H₂S; (iii) using silanethiol/disilathiane; (iv) using thiolacetic acid/thioacetates; (v) from xanthates; (vi) reaction of sodium thiocyanate; (vii) using sodium trithiocarbonates; (viii) using Lawesson’s reagent; (ix) using phosphorus decasulfide; (x) enzymatic method; and the rest of a methods are classified under miscellaneous section.

Synthetic methodologies to form terminal –SH bonds using various reagent systems, viz; (i) isothiouronium salts; (ii) catalytic preparation using H₂S; (iii) silanethiol/disilathiane; (iv) thiolacetic acid/thioacetates; (v) xanthates; (vi) reaction of sodium thiocyanate; (vii) sodium trithiocarbonates; (viii) Lawesson’s reagent; (ix) phosphorus decasulfide and (x) few enzymatic methods.