Acylering

Acylering, also spelled acylation, is a chemical reaction in which an acyl group (R-CO-) is introduced into a molecule. This transformation is central to organic synthesis because it converts nucleophiles such as amines, alcohols, or aromatic rings into higher-molar-mass products such as amides, esters, or ketones, and it can serve to modify reactivity, polarity, or protection status.

There are several common forms of acylering. N-acylation refers to the transfer of an acyl group to nitrogen, forming amides from amines or amino groups. O-acylation involves attaching an acyl group to oxygen, producing esters from alcohols or phenols. Friedel-Crafts acylation is a distinct procedure in which an acyl group is appended to an aromatic ring via electrophilic aromatic substitution, typically using an acyl chloride or acid anhydride in the presence of a Lewis acid such as aluminum chloride, generating an acylium ion (R-CO+) that reacts with the arene to yield an aryl ketone after workup.

Common acylating agents include acid chlorides, acid anhydrides, and activated esters. Catalysts and conditions vary with the substrate; for Friedel-Crafts reactions, Lewis acids are essential, while N- and O-acylations often proceed with these reagents under basic or neutral conditions. Mechanistically, acyl transfer proceeds through nucleophilic attack on the carbonyl carbon, with different pathways depending on whether the site is nitrogen, oxygen, or an arene.

Applications of acylering include protection of functional groups (for example, acetylation of amines or alcohols), formation of amides in pharmaceuticals and peptides, and synthesis of esters and aryl ketones. Typical examples include acetylation of aniline to acetanilide, formation of ethyl acetate from ethanol, and Friedel-Crafts acetylation of benzene to acetophenone.