4-Fluorothioanisole is a low-melting (≈ –20 °C), high-boiling (184–185 °C @ 760 mm Hg) liquid that combines a strongly electron-withdrawing fluorine para to the methylthio group, rendering the sulfur centre mildly electrophilic and the ring activated toward nucleophilic substitution. The material is employed in four main areas:
Pharmaceutical & agro-chemical intermediate – Serves as the key precursor to the anti-inflammatory agent flurbiprofen and to the fungicide flusulfamide after further fluorination or nitration steps.
OLED & opto-electronic materials – Palladium-catalysed C–S or C–N cross-coupling converts the methylthio group into diaryl-sulfides or diaryl-amines that function as electron-transport or hole-blocking layers in small-molecule OLED devices.
Flavour & fragrance building block – FEMA-GRAS 4693, used at 0.1–5 mg kg⁻¹ to impart a spicy, woody, sawdust note to meat seasonings and oriental perfumes.
Photoredox probe – Recently utilised as a model substrate for visible-light-driven, catalyst-free photo-oxidation of sulfides to sulfoxides under UVA irradiation in aqueous acetonitrile, providing a green route to sulfoxide libraries.
Store under nitrogen at 2–8 °C; the liquid is air-sensitive and slowly oxidises to the disulfide. It is harmful if swallowed (rat oral LD₅₀ 560 mg kg⁻¹) and is irritating to skin and eyes; handle with gloves and local exhaust ventilation.
