Acid chloride

What is an acid chloride?

Acid chlorides, also known as acyl chlorides, are organic compounds with the general formula R–COCl, where R is an alkyl or aryl group. They are formed by the reaction of carboxylic acids with thionyl chloride (SOCl₂), oxalyl chloride (COCl₂), or phosphorus trichloride (PCl₃). Due to the high reactivity of the C=O and C–Cl bonds, acid chlorides readily undergo nucleophilic acyl substitution reactions, making them valuable intermediates in pharmaceutical, agrochemical, and polymer synthesis.

How are acid chlorides used in industrial and laboratory settings?

In laboratory settings, acid chlorides are commonly used to synthesise amides by reacting with amines, esters by reacting with alcohols, and anhydrides by reacting with carboxylate ions. They are also employed in Friedel–Crafts acylation to introduce acyl groups onto aromatic rings. Industrially, acid chlorides are used in the production of dyes, pharmaceuticals, and polyesters. However, their high reactivity and moisture sensitivity require careful handling under anhydrous conditions and often in inert atmospheres.

What safety and regulatory considerations apply?

Acid chlorides are corrosive and can produce toxic fumes (e.g., hydrogen chloride) when exposed to moisture. They are classified under GHS as corrosive (H314) and hazardous to the environment (H410). Appropriate personal protective equipment (PPE), fume hoods, and proper disposal procedures are essential. Regulatory frameworks such as REACH, TSCA, and ISO standards govern their use, storage, and transport. Safety data sheets (SDS) and certificates of analysis (CoA) are required for procurement and compliance.

Related concepts

Common related compounds include acid anhydrides, esters, amides, and carboxylic acids. Key reagents used in their synthesis include SOCl₂, PCl₃, and oxalyl chloride. Their reactivity is often compared to that of other acylating agents such as trifluoroacetic anhydride.