Oxalyl chloride
chemical compound
Oxalyl chloride is an organic chemical compound with the formula Cl−C(=O)−C(=O)−Cl. This colorless, sharp-smelling liquid, the diacyl chloride of oxalic acid, is a useful reagent in organic synthesis.
Preparation
Oxalyl chloride was first prepared in 1892 by the French chemist Adrien Fauconnier, who treated diethyl oxalate with phosphorus pentachloride. It can also be prepared by treating oxalic acid with phosphorus pentachloride.
Oxalyl chloride is produced commercially from ethylene carbonate. Photochlorination gives the perchloroethylene carbonate C2Cl4O2CO and hydrogen chloride HCl, which is subsequently degraded to oxalyl chloride and phosgene COCl2:
C2H4O2CO + 4 Cl2 → C2Cl4O2CO + 4 HCl
C2Cl4O2CO → C2O2Cl2 + COCl2
Reactions
As originally determined by Staudinger, oxalyl chloride reacts with water giving off gaseous products only: hydrogen chloride (HCl), carbon dioxide (CO2), and carbon monoxide (CO).
(COCl)2 + H2O → 2 HCl + CO2 + CO
Other acyl chlorides hydrolyze with formation of hydrogen chloride and the original carboxylic acid.
Applications in organic synthesis
Oxidation of alcohols
Addition of a primary or secondary alcohol to a solution of oxalyl chloride in DMSO, followed by quenching with an organic base such as triethylamine converts alcohols to the corresponding aldehydes and ketones via the process known as the Swern oxidation.
Synthesis of acyl chlorides
Oxalyl chloride is mainly used together with a N,N-dimethylformamide catalyst in organic synthesis for the preparation of acyl chlorides from the corresponding carboxylic acids. Like thionyl chloride, the reagent degrades into volatile side products in this application, which simplifies workup.
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