Acetic acid , systematically named ethanoic acid , is an organic compound with the chemical formula CH3COOH (also written as CH3CO2H or C2H4O2). It is a colourless liquid that when undiluted is also called ''glacial acetic acid''. Vinegar is roughly 3–9% acetic acid by volume, making acetic acid the main component of vinegar apart from water. Acetic acid has a distinctive sour taste and pungent smell. Besides its production as household vinegar, it is mainly produced as a precursor to polyvinylacetate and cellulose acetate. Although it is classified as a weak acid, concentrated acetic acid is corrosive and can attack the skin.
Acetic acid is the second simplest carboxylic acid (after formic acid) and is an important chemical reagent and industrial chemical, mainly used in the production of cellulose acetate for photographic film and polyvinyl acetate for wood glue, as well as synthetic fibres and fabrics. In households, diluted acetic acid is often used in descaling agents. In the food industry, acetic acid is used under the food additive code E260 as an acidity regulator and as a condiment. As a food additive it is approved for usage in many countries, including Canada, the European Union,〔UK Food Standards Agency: (【引用サイトリンク】title=Current EU approved additives and their E Numbers )〕 the United States,〔US Food and Drug Administration: (【引用サイトリンク】title=Listing of Food Additives Status Part I )〕 and Australia and New Zealand.〔Australia New Zealand Food Standards Code(【引用サイトリンク】title=Standard 1.2.4 – Labeling of ingredients )〕
The global demand for acetic acid is around 6.5 million tonnes per year (Mt/a), of which approximately 1.5 Mt/a is met by recycling; the remainder is manufactured from petrochemical feedstock.〔 As a chemical reagent, biological sources of acetic acid are of interest, but generally uncompetitive. Vinegar is dilute acetic acid, often produced by fermentation and subsequent oxidation of ethanol.
The trivial name ''acetic acid'' is the most commonly used and preferred IUPAC name. The systematic name ''ethanoic acid'', a valid IUPAC name, is constructed according to the substitutive nomenclature.〔IUPAC Provisional Recommendations 2004 (Chapter P-12.1; page 4 )〕 The name ''acetic acid'' derives from ''acetum'', the Latin word for vinegar, and is related to the word acid itself.
Glacial acetic acid is a name for water-free (anhydrous) acetic acid. Similar to the German name ''Eisessig'' (''ice-vinegar''), the name comes from the ice-like crystals that form slightly below room temperature at (the presence of 0.1% water lowers its melting point by 0.2 °C).
A common abbreviation for acetic acid is ''AcOH'', where ''Ac'' stands for the acetyl group CH3−C(=O)−. Acetate (CH3COO−) is abbreviated ''AcO−''. The ''Ac'' is not to be confused with the abbreviation for the chemical element actinium. To better reflect its structure, acetic acid is often written as CH3–C(O)OH, CH3–C(=O)OH, CH3COOH, and CH3CO2H. In the context of acid-base reactions, the abbreviation ''HAc'' is sometimes used, where ''Ac'' instead stands for acetate. Acetate is the ion resulting from loss of H+ from acetic acid. The name ''acetate'' can also refer to a salt containing this anion, or an ester of acetic acid.
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