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Acetic anhydride, like most acid anhydrides, is a flexible molecule with a nonplanar structure. The pi system linkage through the central oxygen offers very weak resonance stabilization compared to the dipole-dipole repulsion between the two carbonyl oxygens. The energy barriers to bond rotation between each of the optimal aplanar conformations are quite low.
Like most acid anhydrides, the carbonyl carbon atom of acetic anhydride has electrophilic character, as the leaving group is carboxylate. The internal asymmetry may contribute to acetic anhydride's potent electrophilicity as the asymmetric geometry makes one side of a carbonyl carbon atom more reactive than the other, and in doing so tends to consolidate the electropositivity of a carbonyl carbon atom to one side (see electron density diagram).
Often a base such as pyridine is added to function as catalyst. In specialized applications, Lewis acidicscandium salts have also proven effective catalysts.
Acetylation of aromatic rings
Aromatic rings are acetylated by acetic anhydride. Usually acid catalysts are used to accelerate the reaction. Illustrative are the conversions of benzene to acetophenone and ferrocene to acetylferrocene:
Acetic anhydride dissolves in water to approximately 2.6% by weight. Aqueous solutions have limited stability because, like most acid anhydrides, acetic anhydride hydrolyses to give carboxylic acids. In this case, acetic acid is formed, this reaction product being fully water miscible:
(CH3CO)2O + H2O -> 2 CH3CO2H
As indicated by its organic chemistry, acetic anhydride is mainly used for acetylations leading to commercially significant materials. Its largest application is for the conversion of cellulose to cellulose acetate, which is a component of photographic film and other coated materials, and is used in the manufacture of cigarette filters. Similarly it is used in the production of aspirin (acetylsalicylic acid), which is prepared by the acetylation of salicylic acid. It is also used as a wood preservative via autoclave impregnation to make a longer-lasting timber.
In starch industry, acetic anhydride is a common acetylation compound, used for the production of modified starches (E1414, E1420, E1422)
Because of its use for the synthesis of heroin by the diacetylation of morphine, acetic anhydride is listed as a U.S. DEA List II precursor, and restricted in many other countries.
Acetic anhydride is an irritant and combustible liquid. Because of its reactivity toward water, alcohol foam or carbon dioxide are preferred for fire suppression. The vapour of acetic anhydride is harmful.
^Seidel, R. W.; Goddard, R.; Nöthling, N.; Lehmann, C. W. (2016), "Acetic anhydride at 100 K: the first crystal structure determination", Acta Crystallographica Section C, 72 (10): 753-757, doi:10.1107/S2053229616015047.
^Wu, Guang; Van Alsenoy, C.; Geise, H. J.; Sluyts, E.; Van Der Veken, B. J.; Shishkov, I. F.; Khristenko (2000), "Acetic Anhydride in the Gas Phase, Studied by Electron Diffraction and Infrared Spectroscopy, Supplemented with ab Initio Calculations of Geometries and Force Fields", The Journal of Physical Chemistry A, 104 (7): 1576-1587, doi:10.1021/jp993131z.
^Zoeller, J. R.; Agreda, V. H.; Cook, S. L.; Lafferty, N. L.; Polichnowski, S. W.; Pond, D. M. (1992), "Eastman Chemical Company Acetic Anhydride Process", Catal. Today, 13 (1): 73-91, doi:10.1016/0920-5861(92)80188-S