Acetic Acid

Acetic acid is an organic acid with the chemical formula CH₃COOH. It is found most commonly in vinegar.

In the form of vinegar, acetic acid is one of the earliest chemical compounds known to and used by humans. It is mentioned in the Bible as a condiment and was used even earlier in the manufacture of white lead and the extraction of mercury metal from its ores. The first reasonably precise chemical description of the acid was provided by the German natural philosopher Johann Rudolf Glauber in about 1648.

Acetic acid is a colorless liquid with a sharp, distinctive odor and the characteristic taste associated with vinegar. In its pure form it is referred to as glacial acetic acid because of its tendency to crystallize as it is cooled. Glacial acetic acid has a melting point of 62°F (16.7°C) and a boiling point of 244.4°F (118°C). The acid mixes readily with water, ethyl alcohol, and many other liquids. Its water solutions display typical acid behaviors such as neutralization of oxides and bases and reactions with carbonates. Glacial acetic acid is an extremely caustic substance with a tendency to burn the skin. This tendency is utilized by the medical profession for wart removal.

Originally acetic acid was manufactured from pyroligneous acid which, in turn, was obtained from the destructive distillation of wood. Today the compound is produced commercially by the oxidation of butane, ethylene, or methanol (wood alcohol). Acetic acid forms naturally during the aerobic fermentation of sugar or alcoholic solutions such as beer, cider, fruit juice, and wine. This process is catalyzed by the bacterium Acetobacter, a process from which the species gets its name.

Although acetic acid is best known to the average person in the form of vinegar, its primary commercial use is in the production of cellulose acetate, vinyl acetate, and terephthalic acid. The first of these compounds is widely used as a rubber substitute and in photographic and cinematic film, while the latter two compounds are starting points for the production of polymers such as adhesives, latex paints, and plastic film and sheeting.

A promising new use for acetic acid is in the manufacture of calcium-magnesium acetate (CMA), a highly effective and biodegradable deicer. CMA has had limited use in the past because it is 50 times more expensive than salt. In 1992, however, Shang-Tian Yang, an engineer at Ohio State University, announced a new method for making acetic acid from wastes produced during cheese making.

Most commonly vinegar is prepared commercially by the fermentation of apple cider, malt, or barley. The fermentation product is a brownish or yellow liquid consisting of 4-8% acetic acid. It is then distilled to produce a clear colorless liquid known as white vinegar.