Acetylation

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

Salicylic acid is acetylated to form aspirin

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]
H2C=C=O   +   CH3COOH   →   (CH3CO)2O     ΔH = −63 kJ mol−1

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

Acetylation of cellulose
See also: Cellulose acetate

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]

Nomenclature

In IUPAC nomenclature acetylation is called ethanoylation.

See also

References
  1. F. K. Thayer (1925). "Acetylmandelic Acid and Acetylmandelyl Chloride". Organic Syntheses. 4: 1. doi:10.15227/orgsyn.004.0001.
  2. Herbst, R. M.; Shemin, D. (1939). "Acetylglycine". Organic Syntheses. 19: 4. doi:10.15227/orgsyn.019.0004.
  3. F. E. Ray and George Rieveschl, Jr (1948). "2-Acetylfluorene". Organic Syntheses. 28: 3. doi:10.15227/orgsyn.028.0003.
  4. Merritt, Jr., Charles; Braun, Charles E. (1950). "9-Acetylanthracene". Organic Syntheses. 30: 1. doi:10.15227/orgsyn.030.0001.
  5. Denoon, C. E., Jr.; Adkins, Homer; Rainey, James L. (1940). "Acetylacetone". Organic Syntheses. 20: 6. doi:10.15227/orgsyn.020.0006.
  6. Arpe, Hans-Jürgen (2007), Industrielle organische Chemie: Bedeutende vor- und Zwischenprodukte (in German) (6th ed.), Weinheim: Wiley-VCH, pp. 200–1, ISBN 978-3-527-31540-6
  7. Balser, Klaus; Hoppe, Lutz; Eicher, Theo; Wandel, Martin; Astheimer, Hans‐Joachim; Steinmeier, Hans; Allen, John M. (2004). "Cellulose Esters". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a05_419.pub2.
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