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Acetic anhydrides

Acetic anhydride
Acetic anhydride
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
3D model (Jmol)
ChEBI
ChemSpider
ECHA InfoCard 100.003.241
EC Number 203-564-8
PubChem CID
RTECS number AK1925000
UNII
Properties
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)
2.6 g/100 mL, see text
Vapor pressure 4 mmHg (20 °C)
-52.8·10−6 cm3/mol
1.3901
Pharmacology
Legal status
Hazards
Safety data sheet ICSC 0209
Corrosive (C)
R-phrases (outdated) R10, R20/22, R34
S-phrases (outdated) (S1/2), S26, S36/37/39, S45
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuel Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Flash point 49 °C (120 °F; 322 K)
316 °C (601 °F; 589 K)
Explosive limits 2.7–10.3%
Lethal dose or concentration (LD, LC):
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
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).
YesY  (what is YesYN ?)
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.


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Wikipedia

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