Thionyl chloride (or thionyl dichloride) is an inorganic compound with the formula SOCl2. It is a reactive chemical reagent used in chlorination reactions. It is a liquid at room temperature and pressure. It is odorous, toxic, corrosive, lachrymatory, and a skin and inhalation hazard. It decomposes when heated above 140°C.
Reactions
Thionyl chloride is used both on a laboratory and an industrial scale. It reacts with water to release hydrogen chloride (HCl) and sulfur dioxide (SO2), and it is not found in nature.
- HO + O=SCl2 → SO2 + 2 HCl
Thionyl chloride reacts with carboxylic acids to produce acyl chlorides,
R-CO-OH + O=SCl2 → R-CO-Cl + SO2 + HCl
and with alcohols to produce alkyl chlorides.
R-OH + O=SCl2 → R-Cl + SO2 + HCl
Uses
Thionyl chloride is used inside lithium-thionyl chloride batteries as the positive active material with lithium as the negative active material. It is also used as a reagant for the production of other chemical compounds or materials. A major application is in the preparation of acid chlorides from carboxylic acids, including the important organic reactant acetyl chloride made via the following reaction:
H3C-COO-H + O=SCl2 → H3C-COCl + SO2 + H-Cl
Synthesis of Thionyl Chloride
The major industrial process is from the reaction of sulfur trioxide and sulfur dichloride [1]:
SO3 + SCl2 → SOCl2 + SO2
Other methods include:
SO2 + PCl5 → SOCl2 + POCl3
SO2 + Cl2 + SCl2 → 2 SOCl2
SO3 + Cl2 + 2 SCl2 → 3 SOCl2
References
- N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.