Thionyl chloride is a major inorganic intermediate used in the chemical industry. The most important reaction of thionyl chloride is the selective substitution of OH-groups for the production of carbonic acid chlorides from carbonic acids or of aromatic sulfonyl chlorides. Thionyl chloride is also used in the synthesis of alkyl chlorides from aliphatic alcohols. These substance classes are frequently used as intermediates for the preparation of crop protecting agents, dyestuffs and pharmaceutical active ingredients.
Advantages of thionyl chloride in the substitution of OH-groups:
- Other functional groups and double bonds are not attacked by thionyl chloride.
- Secondary products HCl and SO2 are gaseous and therefore easy to separate.
- The yields are usually very high (also with optically active molecules).
Chemical and physical properties:
Thionyl chloride is a clear, colourless to light yellow, low-viscosity liquid. Thionyl chloride is miscible with nearly all organic solvents and a good solvent for most organic compounds itself. Thionyl chloride is not combustible and does not form explosive mixtures with air.