This colorless, sharp-smelling liquid, the diacyl chloride of oxalic acid, is a useful reagent in organic synthesis.

[4] Oxalyl chloride was first prepared in 1892 by the French chemist Adrien Fauconnier, who treated diethyl oxalate with phosphorus pentachloride.

[citation needed] Like thionyl chloride, the reagent degrades into volatile side products in this application, which simplifies workup.

The diester derived from phenol, phenyl oxalate ester, is Cyalume, the active ingredient in glow sticks.

[citation needed] A similar reaction occurs with amines to give substituted oxalamides:[17] Oxalyl chloride was reportedly used in the first synthesis of dioxane tetraketone (C4O6), an oxide of carbon.