What Is Oxalyl Chloride?
Oxalyl chloride is a colorless, fuming liquid with a pungent odor. Its chemical formula is (COCl)2, with a molecular weight of 126.93, and its CAS number is 79-37-8. Structurally similar to phosgene, with an additional carbonyl group, its acute toxicity and other properties significantly differ.
French chemist Adrien Fauconnier first prepared oxalyl chloride in 1892 by reacting diethyl oxalate with phosphorus pentachloride.
Uses of Oxalyl Chloride
Oxalyl chloride, akin to thionyl chloride, generates volatile by-products such as hydrochloric acid, making it a milder and more selective reagent. It is widely used in organic synthesis, particularly for converting carboxylic acids to acyl chlorides, often with dimethylformamide as a catalyst.
RCOOH + (COCl)2 → RCOCl + CO2 + CO
Key applications include the synthesis of acid chlorides, acylation of aromatic compounds, diester formation, and alcohol oxidation. Notably, it facilitates the Friedel-Crafts acylation of aromatic compounds, with hydrolysis of the resulting acyl chloride producing carboxylic acids. Oxalyl chloride can also react with alcohols to form esters.
2RCH2OH + (COCl)2 → RCH2OC(O)C(O)OCH2R + 2HCl
Properties of Oxalyl Chloride
With a melting point of -12°C and a boiling point of 65°C, oxalyl chloride’s density is 1.48 g/mL. It dissolves in ether, benzene, and chloroform but reacts explosively with water, producing hydrogen chloride gas.
As a chlorinating agent, it decomposes into phosgene and carbon monoxide upon heating. Although toxic by inhalation, its acute toxicity is significantly lower than phosgene.
Other Information on Oxalyl Chloride
1. Manufacturing Process of Oxalyl Chloride
Oxalyl chloride can be synthesized by treating oxalic anhydride with phosphorus pentachloride. It is commercially produced by decomposing tetrachloride obtained through the chlorination of ethylene carbonate.
C2H4O2CO + 4Cl2 → C2Cl4O2CO + 4HCl
C2Cl4O2CO → C2O2Cl2 + COCl2
2. Reaction of Oxalyl Chloride
Oxalyl chloride reacts with water, releasing gaseous products such as hydrogen chloride, carbon dioxide, and carbon monoxide, different from other acyl chlorides which hydrolyze to carboxylic acids. In the presence of DMSO and triethylamine, it can facilitate Swern oxidation, converting alcohols into aldehydes and ketones. It also undergoes Friedel-Crafts acylation with aromatic compounds in the presence of aluminum chloride.
3. Regulatory Information
Oxalyl chloride is not specifically regulated under major laws relating to safety and fire.
4. Handling and Storage Precautions
- Store in refrigerated conditions (2-10°C) under inert gas.
- Use containers made of or lined with corrosion-resistant materials.
- Handle only in well-ventilated areas or outdoors.
- Wear appropriate protective gear including gloves, eye protection, and masks.
- Avoid contact with water, strong oxidizers, alcohols, and metals.
- Wash hands thoroughly after handling. Move to fresh air if inhaled and rest comfortably for breathing.
- In case of skin or eye contact, rinse immediately with plenty of water and soap, and seek medical attention for eyes.