Salicylic acid is acetylated to form aspirin

In organic chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed acetate esters or simply acetates. Deacetylation is the opposite reaction, the removal of an acetyl group from a chemical compound.

Organic synthesis

Acetate esters^[1] and acetamides^[2] are generally prepared by acetylations. Acetylations are often used in making C-acetyl bonds in Friedel-Crafts reactions.^[3][4] Carbanions and their equivalents are susceptible to acetylations.^[5]

Acetylation reagents

Many acetylations are achieved using these three reagents:

• Acetic anhydride. This reagent is common in the laboratory; its use cogenerates acetic acid.^[3]
• Acetyl chloride. This reagent is also common in the laboratory, but its use cogenerates hydrogen chloride, which can be undesirable.^[4]
• Ketene. At one time acetic anhydride was prepared by the reaction of ketene with acetic acid:^[6]

${\displaystyle {\ce {H2C=C=O + CH3COOH -> (CH3CO)2O}}}$     ${\displaystyle \Delta H=-63{\text{ kJ/mol}}}$

This reagent is common in the laboratory; its use cogenerates acetic acid.^[3]{{}} Acetylations can also be achieved using less electrophilic reagents, such as esters of thioacetic acid.

Acetylation of cellulose

Cellulose is a polyol and thus susceptible to acetylation, which is achieved using acetic anhydride. Acetylation disrupts hydrogen bonding, which otherwise dominates the properties of cellulose. Consequently, the cellulose esters are soluble in organic solvents and can be cast into fibers and films.^[7]

Acetylation/deacetylation in biology

Acetylation is one type of post-translational modification of proteins. The acetylation of the ε-amino group of lysine, which is common, converts a charged side chain to a neutral one.^[8] Acetylation/deacetylation of histones also plays a role in gene expression and cancer.^[9] These modifications are effected by enzymes called histone acetyltransferases (HATs) and histone deacetylases (HDACs).^[10]

See also

• Acetoxy group
• Acylation
• Amide
• Ester
• Organic synthesis

References