Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes (50,000 short tons) per year being produced during the early 1990s,[5] but is occasionally also used as a solvent.

[11] Thionyl chloride has a long shelf life, however "aged" samples develop a yellow hue, possibly due to the formation of disulfur dichloride.

[13] Samples showing signs of ageing can be purified by distillation under reduced pressure, to give a colourless liquid.

If the alcohol is chiral the reaction generally proceeds via an SNi mechanism with retention of stereochemistry;[15] however, depending on the exact conditions employed, stereo-inversion can also be achieved.

Reactions with an excess of alcohol produce sulfite esters, which can be powerful methylation, alkylation and hydroxyalkylation reagents.

These species are highly reactive and can be used to catalyse the conversion of carboxylic acids to acyl chlorides;[24] they are also exploited in the Bischler–Napieralski reaction as a means of forming isoquinolines.

It is for this type of reaction that thionyl chloride is listed as a Schedule 3 compound, as it can be used in the "di-di" method of producing G-series nerve agents.

The contents of the batteries are highly toxic and require special disposal procedures; additionally, they may explode if shorted.

In 1857, the German-Italian chemist Hugo Schiff subjected crude thionyl chloride to repeated fractional distillations and obtained a liquid which boiled at 82 °C and which he called Thionylchlorid.