Acetic anhydride
From Wikipedia, the free encyclopedia
| Acetic anhydride | |
|---|---|
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| General | |
| Systematic name | Ethanoyl ethanoate |
| Other names | Acetic anhydride Acetic acid anhydride Acetylacetate Acetyl oxide Acetic oxide Ethanoic anhydride |
| Molecular formula | C4H6O3 |
| SMILES | CC(=O)OC(=O)C |
| Molar mass | 102.1 g/mol |
| Appearance | clear liquid |
| CAS number | [108-24-7] |
| Properties | |
| Density and phase | 1.08 g/cm³, liquid |
| Solubility in water | 2.6% by weight; rapidly reacts to form acetic acid |
| Melting point | −73.1 °C |
| Boiling point | 139.9 °C |
| Dipole moment | ? D |
| Hazards | |
| MSDS | External MSDS |
| EU classification | Corrosive (C) |
| NFPA 704 |
2
2
1
|
| R-phrases | R10, R20/22, R34 |
| S-phrases | S1/2, S26, S36/37/39, S45 |
| Flash point | 54 °C |
| RTECS number | AK1925000 |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related acid anhydrides | Propionic anhydride |
| Related compounds | Acetic acid Acetyl chloride |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Acetic anhydride, formally known as ethanoic anhydride and commonly abbreviated Ac2O, is one of the simplest of acid anhydrides. With the chemical formula (CH3CO)2O, it is a widely used reagent in organic synthesis. This a colourless liquid smells strongly of vinegar (acetic acid) due to its reaction with the moisture in the air.
Contents |
[edit] Properties
Acetic anhydride dissolves in water to approximately 2.6% by weight[1]; however, it is not possible to keep a solution of acetic anhydride because it decomposes within a few minutes (the exact time being dependent upon the temperature) into a solution of acetic acid[2].
[edit] Production
Acetic anhydride is produced by condensation of acetic acid. In 2006, ca. 25%of the global production of acetic acid was consumed for this process.[3] 
Acetic anhydride can also be prepared by the reaction of acetyl chloride with sodium acetate:
- H3C-C(=O)Cl + H3C-COO− Na+ → Na+Cl− + H3C-CO-O-CO-CH3
[edit] Uses
Ac2O is widely used for acetylation of alcohols and amines. [4] Illustrative applications include the production of cellulose acetate, which is used for clothing. Aspirin, acetyl salicylic acid, is prepared by the acetylation of salicylic acid. Heroin, diacetylmorphine, is prepared by the acetylation of morphine.
[edit] Reactions
Hydrolysis of acetic anhydride produces acetic acid slowly at room temperature:
- (CH3CO)2O + H2O → 2CH3COOH
Acetic anhydride also reacts under gentle heating with alcohols to form acetic acid and an ester. [5] For example, the reaction of acetic anhydride with ethanol is:
- (CH3CO)2O + CH3CH2OH → CH3COOCH2CH3 + CH3COOH
Here, the ester produced is ethyl acetate. Often a base such as pyridine is added to function as catalyst.
[edit] Safety
Acetic anhydride is corrosive, an irritant, and flammable. Because of its reactivity toward water, alcohol foam or carbon dioxide are preferred for fire suppresion. [6]
The vapour of acetic anhydride is harmful, potentially necessitating cardiopulmonary resuscitation (CPR).[7]
[edit] Notes and references
- ^ British Petroleum. Acetic Anhydride: Frequently Asked Questions (PDF). Retrieved on 2006-05-03.
- ^ Celanese. Acetic Anhydride: Material Safety Data Sheet (PDF). Retrieved on 2006-05-03.
- ^ Greener Industry. Ethanoic Acid – Major Uses. Retrieved on 2006-03-25.
- ^ Science is Fun…. Chemical of the Week. Retrieved on 2006-03-25.
- ^ ChemGuide. Acid Anhydrides. Retrieved on 2006-03-25.
- ^ Data Sheets. International Occupational Safety and Health Information Centre. Retrieved on 2006-04-13.
- ^ NIOSH. Pocket Guide to Chemical Hazards. Retrieved on 2006-04-13.
