Perbenzoylation

Perbenzoylation is the chemical modification in which benzoyl groups are introduced onto all suitable reactive sites in a substrate, most commonly converting free hydroxyl groups into benzoate esters. The term is widely used in carbohydrate chemistry to describe the fully benzoylated derivative of sugars and polyols, but it can apply to other alcohols and amines.

Standard procedures employ benzoyl chloride or benzoic anhydride as benzoyl donors in a basic solvent such as pyridine or with catalytic DMAP. Substrates are stirred at typically 0–25 °C until esterification is complete. The reaction yields per-O-benzoylated products where all hydroxyl groups are protected as benzoates; amines can be benzoylated to amide derivatives under appropriate conditions.

Advantages include high protection efficiency and straightforward workup, with benzoate esters being relatively robust under many reaction conditions—useful for planning multi-step syntheses. Deprotection generally requires basic hydrolysis (for example, methoxide in methanol) or transesterification under suitable conditions.

Limitations include slowed reaction at hindered sites due to steric effects, potential formation of mixtures if sites have differing reactivity, and the bulky nature of benzoyl groups which can impede downstream transformations. Perbenzoylation is especially common in carbohydrate synthesis to enable selective deprotection and further functionalization after protecting strategy is employed.

See also: benzoylation, protecting groups, carbohydrate chemistry.