Acetic acid /əˈsiːtᵻk/, systematically named ethanoic acid /ˌɛθəˈnoʊᵻk/, is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H or C2H4O2). When undiluted, it is sometimes 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. In addition to household vinegar, it is mainly produced as a precursor to polyvinyl acetate 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 consists of two small functional groups, an acetyl group (sometimes symbolized as Ac) and a hydroxyl group (AcOH); it can also be viewed as a methyl group and a carboxyl group linked. It is an important chemical reagent and industrial chemical, used primarily in the production of cellulose acetate for photographic film, polyvinyl acetate for wood glue, and synthetic fibres and fabrics. In households, diluted acetic acid is often used in descaling agents. In the food industry, acetic acid is controlled by 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, the United States, Australia and New Zealand. In biochemistry, the acetyl group, derived from acetic acid, is fundamental to all forms of life. When bound to coenzyme A, it is central to the metabolism of carbohydrates and fats.
The global demand for acetic acid is about 6.5 million metric tons 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 cannot compete economically. Vinegar is mostly dilute acetic acid, often produced by fermentation and subsequent oxidation of ethanol.
Acetic acid is used to treat an outer ear infection (external otitis). It works by stopping the growth of bacteria and fungus. Treating the infection reduces pain and swelling in the ear. Wetness in the ear canal can help bacteria and fungus to grow. This medication may also contain drying ingredients such as glycerin or alcohol. Drying of the ear canal helps to cure the infection.