Thionyl chloride is an inorganic compound with the chemical formula SOCl2. It is a moderately volatile colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tons per year being produced during the early 1990s. It is toxic and will react violently with water to produce toxic gases, it is also listed as a Schedule 3 compound as it may be used for the production of chemical weapons.
Thionyl Chloride is sometimes confused with sulfuryl chloride, SO2Cl2, but the properties of these compounds differ significantly. Sulfuryl chloride is a source of chlorine whereas Thionyl chloride is a source of chloride ions.