Oxalyl chloride
[CAS# 79-37-8]

Identification

• Classification: Chemical pesticide >> Insecticide intermediate
• Name: Oxalyl chloride
• Synonyms: Oxalyl dichloride; Ethanedioyl dichloride
• Molecular Formula: C₂Cl₂O₂
• Molecular Weight: 126.93
• CAS Registry Number: 79-37-8
• EC Number: 201-200-2
• SMILES: C(=O)(C(=O)Cl)Cl

Properties

• Density: 1.6±0.1 g/cm³ Calc.^*, 1.5 g/mL (Expl.)
• Melting point: -10 - -8 °C (Expl.)
• Boiling point: 63.5±9.0 °C 760 mmHg (Calc.)^*, 62 - 65 °C (Expl.)
• Flash point: 4.5±19.3 °C (Calc.)^*
• Solubility: reacts (Expl.)
• Index of refraction: 1.449 (Calc.)^*, 1.429 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS02;GHS05;GHS06;GHS07 Danger
• Risk Statements: H260-H301-H314-H318-H331-H335
• Safety Statements: P223-P231+P232-P260-P261-P264-P264+P265-P270-P271-P280-P301+P316-P301+P330+P331-P302+P335+P334-P302+P361+P354-P304+P340-P305+P354+P338-P316-P317-P319-P321-P330-P363-P370+P378-P402+P404-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H331
Serious eye damage	Eye Dam.	1	H318
Skin corrosion	Skin Corr.	1B	H314
Substances or mixtures which in contact with water emit flammable gases	Water-react.	1	H260
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin corrosion	Skin Corr.	1C	H314
Acute toxicity	Acute Tox.	3	H301
Skin corrosion	Skin Corr.	1A	H314
Acute toxicity	Acute Tox.	2	H330
Acute toxicity	Acute Tox.	4	H302
Hazardous for the ozone layer	Ozone 99	1	H420
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H312
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Acute toxicity	Acute Tox.	1	H330

• Transport Information: UN 2922

Discovery and Applications

Oxalyl chloride is an acyl chloride with the molecular formula C₂Cl₂O₂. Structurally, it consists of a central carbon–carbon bond flanked by two carbonyl groups, each bonded to a chlorine atom, giving the formula (COCl)₂. It is a colorless to pale yellow liquid with a pungent odor and is highly reactive, particularly toward nucleophiles and moisture. The compound reacts vigorously with water, producing carbon dioxide, carbon monoxide, and hydrochloric acid, and must therefore be handled under anhydrous conditions.

Oxalyl chloride is primarily used as a reagent in organic synthesis. Its most common application is the conversion of carboxylic acids into acyl chlorides, which are highly reactive intermediates for forming esters, amides, and other carbonyl-containing compounds. This transformation is widely employed in both laboratory-scale and industrial chemical synthesis.

The compound is also used in the synthesis of oxalate esters and other functionalized carbonyl compounds. Its ability to introduce reactive acyl chloride groups allows for sequential reactions in multistep organic syntheses. In combination with catalysts such as dimethylformamide (DMF), oxalyl chloride can efficiently convert carboxylic acids under mild conditions.

Oxalyl chloride is typically prepared by the chlorination of oxalic acid or oxalates using phosphorus pentachloride or thionyl chloride. Due to its high reactivity and corrosive nature, handling requires strict adherence to safety protocols, including use of gloves, eye protection, and well-ventilated fume hoods. It is also highly flammable and should be stored away from moisture and heat.

Overall, oxalyl chloride is a highly reactive acyl chloride widely used in organic synthesis for the preparation of acyl chlorides, esters, amides, and other carbonyl derivatives. Its structural simplicity, high electrophilicity, and ability to activate carboxylic acids make it an indispensable reagent in both academic and industrial chemistry.

References

2010. Novel tricyclic pyrazole BRAF inhibitors with imidazole or furan central scaffolds. Bioorganic & Medicinal Chemistry, 18(18).
DOI: 10.1016/j.bmc.2010.06.031

2005. Polymer-supported and polymeric chiral guanidines: Preparation and application to the asymmetric Michael reaction of iminoacetate with methyl vinyl ketone. Molecular Diversity, 9(4).
DOI: 10.1007/s11030-005-8116-z