Thionyl chloride is mainly used in the industrial production of organochlorine compounds, which are often intermediates in pharmaceuticals and agrichemicals. It usually is preferred over other reagents, such as phosphorus pentachloride, as its by-products (HCl and ) are gaseous, which simplifies purification of the product.
Many of the products of thionyl chloride are themselves highly reactive and as such it is involved in a wide range of reactions.