Oxalyl chloride, (COCl)₂, as an inexpensive commercially available chemical is one of the most versatile applicable organic reagents in chemical transformations. It is also employed extensively in various chemical industries.

It is employed in various chemical transformations such as chlorination, oxidation, reduction, dehydration, decarboxylation, and formylation reactions as well as ring cleavage of epoxides. During the past decades, numerous procedures using (COCl)₂ as reagent have been developed and published.

Applications in organic synthesis

Oxidation of alcohols

The solution comprising DMSO and oxalyl chloride, followed by quenching with triethylamine converts alcohols to the corresponding aldehydes and ketones via the process known as the Swern oxidation.

Synthesis

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. One of the minor byproducts from the N,N-dimethylformamide catalyzed reaction is a potent carcinogen, stemming from the N,N-dimethylformamide decomposition. Relative to thionyl chloride, oxalyl chloride tends to be a milder, more selective reagent. It is also more expensive than thionyl chloride so it tends to be used on a smaller scale.

The action of oxalyl chloride on an aromatic hydrocarbon in the presence of anhydrous aluminium chloride and in a solvent (for example, carbon disulphide) can lead to the production of the aromatic acid as the chief reaction product. This may provide, too, a general method for the synthesis of p-alkylbenzoic acids.