Acetic anhydrides

Acetic anhydride

Names
Preferred IUPAC name Acetic anhydride
Systematic IUPAC name Ethanoic anhydride
Other names Ethanoyl ethanoate Acetic acid anhydride Acetyl acetate Acetyl oxide Acetic oxide
Identifiers
CAS Number	108-24-7 Y
3D model (Jmol)	Interactive image Interactive image
ChEBI	CHEBI:36610 Y
ChemSpider	7630 Y
ECHA InfoCard	100.003.241
EC Number	203-564-8
PubChem CID	7918
RTECS number	AK1925000
UNII	2E48G1QI9Q Y
InChI InChI=1S/C4H6O3/c1-3(5)7-4(2)6/h1-2H3 Y Key: WFDIJRYMOXRFFG-UHFFFAOYSA-N Y InChI=1/C4H6O3/c1-3(5)7-4(2)6/h1-2H3 Key: WFDIJRYMOXRFFG-UHFFFAOYAH
SMILES O=C(OC(=O)C)C CC(=O)OC(=O)C
Properties
Chemical formula	C4H6O3
Molar mass	102.09 g·mol−1
Appearance	colorless liquid
Density	1.082 g cm−3, liquid
Melting point	−73.1 °C (−99.6 °F; 200.1 K)
Boiling point	139.8 °C (283.6 °F; 412.9 K)
Solubility in water	2.6 g/100 mL, see text
Vapor pressure	4 mmHg (20 °C)
Magnetic susceptibility (χ)	-52.8·10−6 cm3/mol
Refractive index (nD)	1.3901
Pharmacology
Legal status	AU: S6 (Poison) CA: Schedule VI
Hazards
Safety data sheet	ICSC 0209
EU classification (DSD) (outdated)	Corrosive (C)
R-phrases (outdated)	R10, R20/22, R34
S-phrases (outdated)	(S1/2), S26, S36/37/39, S45
NFPA 704	2 3 1 W
Flash point	49 °C (120 °F; 322 K)
Autoignition temperature	316 °C (601 °F; 589 K)
Explosive limits	2.7–10.3%
Lethal dose or concentration (LD, LC):
LC50 (median concentration)	1000 ppm (rat, 4 hr)
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 5 ppm (20 mg/m3)
REL (Recommended)	C 5 ppm (20 mg/m3)
IDLH (Immediate danger)	200 ppm
Related compounds
Related acid anhydrides	Propionic anhydride
Related compounds	Acetic acid Acetyl chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH₃CO)₂O. Commonly abbreviated Ac₂O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a colorless liquid that smells strongly of acetic acid, which is formed by its reaction with moisture in the air.

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 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 more reactive than the other, and in doing so tends to consolidate the electropositivity of a carbonyl carbon to one side (see electron density diagram).

Acetic anhydride was first synthesized in 1852 by the French chemist Charles Frédéric Gerhardt (1816-1856) by heating potassium acetate with benzoyl chloride.

Acetic anhydride is produced by carbonylation of methyl acetate:

The Tennessee Eastman acetic anhydride process involves the conversion of methyl acetate to methyl iodide and an acetate salt. Carbonylation of the methyl iodide in turn affords acetyl iodide, which reacts with acetate salts or acetic acid to give the product. Rhodium chloride in the presence of lithium iodide is employed as catalysts. Because acetic anhydride is not stable in water, the conversion is conducted under anhydrous conditions.