4-(Methylthio)benzyl chloride is a moisture-sensitive, low-melting aromatic benzyl chloride that carries a lipophilic methylthio group at the para-position. It is commercially supplied as a yellow to brown semi-solid that liquefies on gentle warming; the melt is a clear, refractive liquid with a penetrating mercaptan-like odour.
Key physical data: density 1.170 g mL⁻¹ (25 °C); refractive index n²⁰/D 1.6020; flash point >110 °C; boiling point 116 °C / 8 mmHg. The substance is stable for months when stored under nitrogen at –20 °C in amber glass; prolonged exposure to moisture leads to slow hydrolysis back to the parent benzyl alcohol.
Typical uses:
Versile C₁ electrophile for the installation of the 4-methylthiobenzyl (MTB) protecting group onto alcohols, phenols and carboxylic acids; the MTB ether/ester is orthogonal to many acid-/base-labile motifs and is readily removed with soft nucleophiles or mild Lewis acids.
Key intermediate for the synthesis of 4-methylthiophenylacetonitrile, a precursor to the COX-2 inhibitor etoricoxib, via nucleophilic substitution with NaCN .
Reagent for convergent routes to agrochemicals, UV-absorbers and liquid-crystalline materials that require a lipophilic benzylthio handle.
Storage/shipping: 2–8 °C under nitrogen; avoid contact with water or protic solvents.
Hazard statement: Causes severe skin burns and eye damage; harmful if inhaled. Classified as Skin Corr. 1B / Eye Dam. 1. Handle only in a fume hood with face shield, butyl gloves and impervious clothing. SDS available on request.
