Thioalcohols

Thioalcohols, more commonly called thiols, are organic compounds that contain a sulfhydryl group (−SH) bonded to a carbon atom. They are the sulfur analogs of alcohols, in which the hydroxyl group (−OH) is replaced by the sulfhydryl group. Like alcohols, thiols can be primary, secondary, or tertiary, depending on the substitution around the carbon bearing the −SH group.

Thiols are notable for their distinct and often strong odors. They generally have higher acidity than alcohols; for simple aliphatic thiols, the pKa is typically around 10, with aryl thiols tending to be more acidic due to resonance stabilization. The sulfur atom makes thiols good nucleophiles, especially when deprotonated to thiolate anions (RS−). They readily oxidize to disulfides (R−S−S−R), and they can react with alkylating agents to form thioethers (R−S−R′). These reactivities underpin many uses in organic synthesis and biochemistry.

Common examples include ethanethiol (ethyl mercaptan), benzene thiol, and 2-mercaptoethanol. Thiols occur in nature and play important roles in biology, most notably through cysteine residues in proteins, which can form disulfide bonds that stabilize structure. In industry, thiols contribute to flavors and odors (for example, certain thiols are added to natural gas as warning odorants). They also serve as ligands in coordination chemistry and as precursors for various sulfur-containing compounds.

Preparation methods for thiols often involve converting alkyl halides to thiols via thiourea-mediated processes, followed by hydrolysis, or the reduction of thioesters and related precursors. Safety considerations include strong odors, flammability, and potential toxicity, necessitating careful handling and ventilation.