Acyl chloride

Acyl chlorides are organic compounds containing the functional group -C(=O)Cl, with the general formula R-COCl, where R is a side chain.

General properties

Acyl chlorides are volatile fuming liquids that react with water to form hydrogen chloride and the carboxylic acid of the respective acyl chloride. Due to the Cl substituent, acyl chlorides do not form hydrogen bonds, which causes them to have have lower boiling and melting points than their corresponding carboxylic acid.

Acyl chlorides readily hydrolyze in water to give the corresponding carboxylic acid and hydrochloric acid.

RCOCl + H₂O → RCO₂H + HCl

Acyl chlorides can react with the salt of the corresponding carboxylic acid to give the anhydride of the said acid.

For example, acetyl chloride will react with sodium acetate to give acetic anhydride:

CH₃COCl + CH₃COONa → (CH₃CO)₂O + NaCl

Availability

Due to their hazards, acyl chlorides are difficult if not impossible to get by the amateur chemist.

Some acyl chlorides, such as benzyl chloride are classified as List II in US due to its use in the production of illegal amphetamines, while others, such as acetyl chloride, may be monitored due to its use in the production of acetic anhydride, another List II substance.

Preparation

Acyl chlorides can be prepared by reacting a carboxylic acid or its salt with a chlorodehydrating agent, such as PCl₃, PCl₅ or SOCl₂. Phosgene can also be used, but its great toxicity makes this route dangerous.

Safety

Acyl chlorides are corrosive and very toxic. Wear proper protection when working with them.

See also

• Thionyl chloride

References

Relevant Sciencemadness threads

• Preparation of Acyl Chlorides: TCT Redux
• Can Acyl Chlorides be prepared with Alkalai Hypochlorites (bleach)?
• Acyl chloride on TLC