Oxalyl chloride with the formula (COCl)2, is one of the most versatile applicable organic reagents in chemical transformations. It is a colorless and sharp smelling liquid belonging to the family of diacetyl chloride. Oxalyl chloride can be produced by treating oxalic acid with PCl5.

Oxalyl chloride is sensitive to moisture. It is employed in various chemical transformations such as chlorination, oxidation, reduction, dehydration, decarboxylation, and formylation reactions as well as ring cleavage of epoxides. 

Oxalyl chloride is a highly toxic chemical compound that can cause severe health problems if improperly handled. Its toxicity is mainly due to its ability to produce hydrochloric acid, carbon monoxide, and oxalic acid when it reacts with water or moisture in the air. These compounds can cause severe damage to the respiratory system, eyes, skin, and other organs if inhaled, ingested, or exposed to the skin. Due to its highly reactive nature and potential to cause severe health problems, proper safety measures must be taken when handling oxalyl chloride.