Thioanisole is an organic compound with the formula CH₃SC₆H₅. It is a colorless liquid that is soluble in organic solvents. It is the simplest alkyl-aryl thioether. The name indicates that this compound is the sulfur analogue, the thioether rather than the ether oxygen analogue; it is commonly used as a methylthio donor and as a model substrate in sulfoxidation and sulfone formation studies. Molecular weight is 124.21 g mol-1. Thioanisole undergoes oxidation at sulfur to give the corresponding sulfoxide and sulfone, and the aromatic ring participates in electrophilic aromatic substitution. In analytical and preparative contexts it displays a characteristic 1H NMR methyl singlet near 2.5 ppm and an aromatic multiplet in the 7.0 to 7.5 ppm region. Typical laboratory handling notes include sensitivity to strong oxidants and storage under inert atmosphere to limit formation of oxidation byproducts.
Commercial and laboratory samples of thioanisole are usually specified to high purity with typical assay values at or above 99 percent by gas chromatography. Common related impurities and typical amounts are: methyl phenyl sulfoxide (oxidation product) 0.1 to 0.5 percent, methyl phenyl sulfone <0.05 percent, trace thiophenol <0.01 percent, anisole (oxygen analogue) up to 0.2 percent, dimethyl sulfide and other low-boiling sulfides <0.1 percent, and residual solvents or water typically below 0.1 percent. Acceptable impurity limits may vary by grade; for sensitive synthetic applications or peptide cleavage scavenging, freshly distilled or freshly opened high-purity material is recommended to minimize oxidized sulfur species.
Thioanisole is used as a building block and intermediate in organic synthesis, as a substrate in studies of sulfur oxidation and C-S bond chemistry, and as an acidolysis scavenger in solid-phase peptide synthesis where it protects reactive carbocations; it also serves as a reference compound in analytical methods for sulfides.
Store thioanisole in a cool, dry, well-ventilated area away from strong oxidizers and light, preferably under inert gas for long-term storage; use appropriate personal protective equipment and avoid sources of ignition.
Purity is commonly assessed by gas chromatography with flame ionization detection or mass spectrometry, 1H and 13C NMR spectroscopy to detect oxidation products, and GC headspace or Karl Fischer titration for volatile impurities and water content.
