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Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component of vinegar apart from water. Historically, vinegar was produced from the third century BC and was likely the first acid to be produced in large quantities.
Acetic acid is the second simplest carboxylic acid (after formic acid). It is an important Reagent and industrial chemical across various fields, used primarily in the production of cellulose acetate for photographic film, polyvinyl acetate for wood Adhesive, and synthetic fibres and fabrics. In households, diluted acetic acid is often used in . In the food industry, acetic acid is controlled by the E number E260 as an acidity regulator and as a condiment. 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 and .
The global demand for acetic acid as of 2023 is about 17.88 million Tonne per year (t/a). Most of the world's acetic acid is produced via the carbonylation of methanol. Its production and subsequent industrial use poses health hazards to workers, including incidental skin damage and chronic respiratory injuries from inhalation.
"Glacial acetic acid" is a name for water-free (anhydrous) acetic acid. Similar to the German language name "Eisessig" ("ice vinegar"), the name comes from the solid ice-like crystals that form with agitation, slightly below room temperature at . Acetic acid can never be truly water-free in an atmosphere that contains water, so the presence of 0.1% water in glacial acetic acid lowers its melting point by 0.2 °C. (2025). 9781856175678, Butterworth-Heinemann. ISBN 9781856175678
A common symbol for acetic acid is AcOH (or HOAc), where Ac is the pseudoelement symbol representing the acetyl functional group ; the conjugate acid, acetate (), is thus represented as . (2010). 9781439811665, CRC Press. ISBN 9781439811665 Acetate is the ion resulting from loss of from acetic acid. The name "acetate" can also refer to a salt containing this anion, or an ester of acetic acid. (The symbol Ac for the acetyl functional group is not to be confused with the symbol Ac for the element actinium; context prevents confusion among organic chemists). To better reflect its structure, acetic acid is often written as , , , and . In the context of acid–base reactions, the abbreviation HAc is sometimes used, where Ac in this case is a symbol for acetate (rather than acetyl).
The carboxymethyl functional group derived from removing one hydrogen from the methyl group of acetic acid has the chemical formula .
In the 16th-century Germany alchemist Andreas Libavius described the production of acetone from the dry distillation of lead acetate, ketonic decarboxylation. The presence of water in vinegar has such a profound effect on acetic acid's properties that for centuries chemists believed that glacial acetic acid and the acid found in vinegar were two different substances. French chemist Pierre Adet proved them identical. In 1845 German chemist Hermann Kolbe synthesized acetic acid from inorganic compounds for the first time. This reaction sequence consisted of chlorination of carbon disulfide to carbon tetrachloride, followed by pyrolysis to tetrachloroethylene and aqueous chlorination to trichloroacetic acid, and concluded with electrolysis reduction to acetic acid.
By 1910, most glacial acetic acid was obtained from the pyroligneous liquor, a product of the distillation of wood. The acetic acid was isolated by treatment with limewater, and the resulting calcium acetate was then acidified with sulfuric acid to recover acetic acid. At that time, Germany was producing 10,000 of glacial acetic acid, around 30% of which was used for the manufacture of indigo dye.
Because both methanol and carbon monoxide are commodity raw materials, methanol carbonylation long appeared to be attractive precursors to acetic acid. Henri Dreyfus at British Celanese developed a methanol carbonylation pilot plant as early as 1925. However, a lack of practical materials that could contain the corrosive reaction mixture at the high needed (200 atm or more) discouraged commercialization of these routes. The first commercial methanol carbonylation process, which used a cobalt catalyst, was developed by German chemical company BASF in 1963. In 1968, a rhodium-based catalyst ( cis−) was discovered that could operate efficiently at lower pressure with almost no by-products. US chemical company Monsanto Company built the first plant using this catalyst in 1970, and rhodium-catalyzed methanol carbonylation became the dominant method of acetic acid production (see Monsanto process). In the late 1990s, BP Chemicals commercialized the Cativa catalyst (), which is promoted by iridium for greater efficiency. Industrial Organic Chemicals, Harold A. Wittcoff, Bryan G. Reuben, Jeffery S. Plotkin Known as the Cativa process, the iridium-catalyzed production of glacial acetic acid is Green chemistry, and has largely supplanted the Monsanto process, often in the same production plants.
The acetyl functional group, formally derived from acetic acid, is fundamental to all forms of life. Typically, it is bound to coenzyme A by acetyl-CoA synthetase enzymes, where it is central to the metabolism of and . Unlike longer-chain carboxylic acids (the fatty acids), acetic acid does not occur in natural . Most of the acetate generated in cells for use in acetyl-CoA is synthesized directly from ethanol or Pyruvic acid. However, the artificial triglyceride triacetin (glycerine triacetate) is a common food additive and is found in cosmetics and topical medicines; this additive is metabolized to glycerol and acetic acid in the body.
Acetic acid is produced and Excretion by acetic acid bacteria, notably the genus Acetobacter and Clostridium acetobutylicum. These bacteria are found universally in , water, and soil, and acetic acid is produced naturally as fruits and other foods spoil. Acetic acid is also a component of the vaginal lubrication of and other , where it appears to serve as a mild antibacterial agent. (1996). 9780412540905, Chapman & Hall. ISBN 9780412540905
Acetic acid can be purified via fractional freezing using an ice bath. The water and other Impurity will remain liquid while the acetic acid will precipitate out. As of 2003–2005, total worldwide production of virgin acetic acid was estimated at 5 Mt/a (million tonnes per year), approximately half of which was produced in the United States. European production was approximately 1 Mt/a and declining, while Japanese production was 0.7 Mt/a. Another 1.5 Mt were recycled each year, bringing the total world market to 6.5 Mt/a. Since then, the global production has increased from 10.7 Mt/a in 2010 Acetic Acid . SRI Consulting. to 17.88 Mt/a in 2023. The two biggest producers of virgin acetic acid are Celanese and BP Chemicals. Other major producers include Millennium Chemicals, Sterling Chemicals, Samsung, Eastman, and .
The process involves iodomethane as an intermediate, and occurs in three steps. A metal carbonyl Catalysis is needed for the carbonylation (step 2).
Two related processes exist for the carbonylation of methanol: the rhodium-catalyzed Monsanto process, and the iridium-catalyzed Cativa process. The latter process is Green chemistry and more efficient and has largely supplanted the former process. Catalytic amounts of water are used in both processes, but the Cativa process requires less, so the water-gas shift reaction is suppressed, and fewer by-products are formed.
By altering the process conditions, acetic anhydride may also be produced in plants using rhodium catalysis.
Light naphtha components are readily oxidized by oxygen or even air to give organic peroxide, which decompose to produce acetic acid according to the chemical equation, illustrated with butane:
The typical reaction is conducted at and pressures designed to be as hot as possible while still keeping the butane a liquid. Typical reaction conditions are and 55 atm. (2025). 9780306472466, Springer. ISBN 9780306472466 Side-products may also form, including butanone, ethyl acetate, formic acid, and propionic acid. These side-products are also commercially valuable, and the reaction conditions may be altered to produce more of them where needed. However, the separation of acetic acid from these by-products adds to the cost of the process.
Similar conditions and are used for butane oxidation, the oxygen in air to produce acetic acid can oxidize acetaldehyde.
Using modern catalysts, this reaction can have an acetic acid yield greater than 95%. The major side-products are ethyl acetate, formic acid, and formaldehyde, all of which have lower than acetic acid and are readily separated by distillation.
In more recent times, chemical company Showa Denko, which opened an ethylene oxidation plant in Ōita, Japan, in 1997, commercialized a cheaper single-stage conversion of ethylene to acetic acid. The process is catalyzed by a palladium metal catalyst supported on a heteropoly acid such as silicotungstic acid. A similar process uses the same metal catalyst on silicotungstic acid and silica:
It is thought to be competitive with methanol carbonylation for smaller plants (100–250 kt/a), depending on the local price of ethylene.
A dilute alcohol solution inoculated with Acetobacter and kept in a warm, airy place will become vinegar over the course of a few months. Industrial vinegar-making methods accelerate this process by improving the supply of oxygen to the bacteria. (2025). 9780387278421, Springer. ISBN 9780387278421
One of the first modern commercial processes was the "fast method" or "German method", first practised in Germany in 1823. In this process, fermentation takes place in a tower packed with wood shavings or charcoal. The alcohol-containing feed is trickled into the top of the tower, and fresh air supplied from the bottom by either natural or forced convection. The improved air supply in this process cut the time to prepare vinegar from months to weeks.
Nowadays, most vinegar is made in submerged tank culture, first described in 1949 by Otto Hromatka and Heinrich Ebner. In this method, alcohol is fermented to vinegar in a continuously stirred tank, and oxygen is supplied by bubbling air through the solution. Using modern applications of this method, vinegar of 15% acetic acid can be prepared in only 24 hours in batch process, even 20% in 60-hour fed-batch process.
These bacteria produce acetic acid from one-carbon compounds, including methanol, carbon monoxide, or a mixture of carbon dioxide and hydrogen:
This ability of Clostridium to metabolize sugars directly, or to produce acetic acid from less costly inputs, suggests that these bacteria could produce acetic acid more efficiently than ethanol-oxidizers like Acetobacter. However, Clostridium bacteria are less acid-tolerant than Acetobacter. Even the most acid-tolerant Clostridium strains can produce vinegar in concentrations of only a few percent, compared to Acetobacter strains that can produce vinegar in concentrations up to 20%. At present, it remains more cost-effective to produce vinegar using Acetobacter, rather than using Clostridium and concentrating it. As a result, although acetogenic bacteria have been known since 1940, their industrial use is confined to a few niche applications.
Most acetate esters, however, are produced from acetaldehyde using the Tishchenko reaction. In addition, ether acetates are used as solvents for nitrocellulose, , varnish removers, and wood stains. First, glycol monoethers are produced from ethylene oxide or propylene oxide with alcohol, which are then esterified with acetic acid. The three major products are ethylene glycol monoethyl ether acetate (EEA), ethylene glycol monobutyl ether acetate (EBA), and propylene glycol monomethyl ether acetate (PMA, more commonly known as PGMEA in semiconductor manufacturing processes, where it is used as a resist solvent). This application consumes about 15% to 20% of worldwide acetic acid. Ether acetates, for example EEA, have been shown to be harmful to human reproduction.
Acetic anhydride is an acetylation agent. As such, its major application is for cellulose acetate, a synthetic textile also used for photographic film, which is produced by reacting cellulose with acetic acid and acetic anhydride in the presence of sulfuric acid. Acetic anhydride is also a reagent for the production of heroin and other compounds.
Acetic acid is often used as a solvent for reactions involving , such as Friedel-Crafts alkylation. For example, one stage in the commercial manufacture of synthetic camphor involves a Wagner-Meerwein rearrangement of camphene to isobornyl acetate; here acetic acid acts both as a solvent and as a nucleophile to trap the rearranged carbocation. (2025). 9780854048243, Royal Society of Chemistry. ISBN 9780854048243
Glacial acetic acid is used in analytical chemistry for the estimation of weakly alkaline substances such as organic amides. Glacial acetic acid is a much weaker base than water, so the amide behaves as a strong base in this medium. It then can be titrated using a solution in glacial acetic acid of a very strong acid, such as perchloric acid.
Acetic acid is used as part of cervical cancer screening in many areas in the developing world. The acid is applied to the cervix and if an area of white appears after about a minute the test is positive.
Acetic acid is an effective antiseptic when used as a 1% solution, with broad spectrum of activity against streptococci, staphylococci, pseudomonas, enterococci and others. It may be used to treat skin infections caused by pseudomonas strains resistant to typical antibiotics.
While diluted acetic acid is used in iontophoresis, no high quality evidence supports this treatment for rotator cuff disease.
As a treatment for otitis externa, it is on the World Health Organization's List of Essential Medicines.
A colour reaction for salts of acetic acid is iron(III) chloride solution, which results in a deeply red colour that disappears after acidification. A more sensitive test uses lanthanum nitrate with iodine and ammonia to give a blue solution. Acetates when heated with arsenic trioxide form cacodyl oxide, which can be detected by its odour vapours.
Halogenated acetic acids are produced from acetic acid. Some commercially significant derivatives:
Amounts of acetic acid used in these other applications together account for another 5–10% of acetic acid use worldwide.
In 12 workers exposed for two or more years to an airborne average concentration of 51 ppm acetic acid (estimated), symptoms of conjunctive irritation, upper respiratory tract irritation, and hyperkeratotic dermatitis were produced. Exposure to 50 ppm or more is intolerable to most persons and results in intensive Tears and irritation of the eyes, nose, and throat, with pharyngeal oedema and chronic bronchitis. Unacclimatized humans experience extreme eye and nasal irritation at concentrations in excess of 25 ppm, and conjunctivitis from concentrations below 10 ppm has been reported. In a study of five workers exposed for seven to 12 years to concentrations of 80 to 200 ppm at peaks, the principal findings were blackening and hyperkeratosis of the skin of the hands, conjunctivitis (but no corneal damage), bronchitis and pharyngitis, and erosion of the exposed teeth (incisors and canines).
| 10–25% | 1.67–4.16 mol/L | ||
| 25–90% | 4.16–14.99 mol/L | ||
| >90% | >14.99 mol/L |
Concentrated acetic acid can be ignited only with difficulty at standard temperature and pressure, but becomes a flammable risk in temperatures greater than , and can form explosive mixtures with air at higher temperatures with of 5.4–16% concentration.
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