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Acetic acid (Updated in 2013)

CAS no 64-19-7

Synonym
Ethanic acid

Physical data
Melting point:  16.6░C
Boiling point: 118░C
Vapour pressure: 15.7 kPa (20░C)
Water solubility: infinite

Pure acetic acid, containing 1% water or less is called glacial acetic acid because it is solid at temperatures below 16║C, but then melts at room temperature. Glacial acetic acid readily absorbs water, and most grades on the market contain water. Vinegar contains 4-6%, pickling vinegar about 5% and pyro-acetic spirit (or vinegar essence) 12% acetic acid. The acetic acid molecules amalgamate to form dimers, both in solution and as a gas which gives acetic acid fumes a greater density than one might expect. Acetic acid has a penetrating smell, the olfactory threshold is in the region of one millionth part acetic acid in air.

Acetic acid is included in many biological processes, and it is a central substance in all biological systems for energy turnover. A human being secretes about 70 mg of acetic acid daily through exhalation air and perspiration.

Acetic acid plays the same central role in organic chemistry as sulphuric acid in inorganic. Changes in the use of acetic acid reflect changes in progress in industry.

The main part of all acetic acid is made from methanol and carbon monoxide, and another part by oxidation of acetaldehyde (from ethanol). Smaller quantities for food use are produced by fermentation to ethanol, which is then left to react with atmospheric oxygen, forming vinegar.

Annual production in the world of acetic acid is approximately 6.5 million tonnes. About 1 million tonnes are produced in Europe and in USA 2.5 mlllion tonnes are produced. It is difficult to gauge total world output of acetic acid because a great deal occurs as a bi-product of many processes and large quantities are recirculated.

Most of all acetic acid is used for synthesis to other substances: acetic acid anhydride for use in the production of cellulose acetate (fibres for adhesives and textiles), vinyl acetate for polyvinyl acetate in latex (adhesive, paint, paper coating) chloroacetic acid for cellulose ethers like CMC (thickening agent), surfactants and phenoxyacetic acids (pesticides). Short acetic acid esters like ethylacetate and butylacetate are widely used solvents.

The most widespread use of acetic acid as an acid is in foodstuffs, both for its flavour and its preservative properties. Its acidic properties are also used in products for the treatment of metallic surfaces and photographic chemicals.

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