For synthesis.

Thionyl chloride is an inorganic acid chloride mainly used as a reagent to prepare carboxylic acid chlorides from carboxylic acids.

Thionyl chloride may be used in the following processes:
- To facilitate the synthesis of indenones from 3-hydroxyindanones via dehydroxylation
- To functionalize silica gel for thioacetalization of aldehydes
- Conversion of tert-butyl esters to acid chlorides
- Conversion of aliphatic and aromatic sulfoxides to sulfides in the presence of triphenylphosphine