acylchloride

An acyl chloride, or acid chloride, is an organic compound containing the functional group R-COCl, where a carbonyl carbon is bonded to chlorine. The acyl chloride group is highly reactive due to the polarized carbonyl and the good leaving group chloride, making these compounds versatile acylating agents in organic synthesis. They are typically colorless liquids or low-melting solids and are sensitive to moisture, hydrolyzing readily to the corresponding carboxylic acid and hydrogen chloride.

Preparation and sources: Most acyl chlorides are prepared from carboxylic acids by treatment with reagents such as thionyl chloride (SOCl2), oxalyl chloride ((COCl)2), or phosphorus trichloride (PCl3) or phosphorus pentachloride (PCl5). The reactions often release byproducts such as sulfur dioxide, carbon dioxide, or hydrogen chloride, and are commonly carried out under anhydrous conditions with catalysts like catalytic DMF in some routes.

Reactions and reactivity: Acyl chlorides undergo nucleophilic acyl substitution where the chloride is displaced by nucleophiles. Reactions with water yield the parent carboxylic acid and HCl; with alcohols they form esters; with amines they form amides. They also react with organomagnesium or organolithium reagents to form ketones or tertiary alcohols after workup, and with carboxylates to form anhydrides under suitable conditions. These attributes make acyl chlorides among the most reactive carboxylic derivatives.

Uses: They are widely used as acylating agents in the synthesis of amides, esters, and anhydrides, as intermediates in pharmaceutical and polymer chemistry, and in the preparation of other acyl compounds. Common examples include acetyl chloride and benzoyl chloride.

Safety and handling: Acyl chlorides are corrosive, lachrymatory, and react violently with water. They are handled under strictly dry and vented conditions to avoid hydrolysis and release of HCl gas, with appropriate protective equipment and fume hood usage.