Acetic acid
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Names | |||
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Preferred IUPAC name
Acetic acid[3] | |||
Systematic IUPAC name
Ethanoic acid | |||
Other names | |||
Identifiers | |||
3D model (
JSmol ) |
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3DMet | |||
Abbreviations | AcOH | ||
506007 | |||
ChEBI | |||
ChEMBL | |||
ChemSpider | |||
DrugBank | |||
ECHA InfoCard
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100.000.528 | ||
EC Number |
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E number | E260 (preservatives) | ||
1380 | |||
IUPHAR/BPS |
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KEGG | |||
MeSH | Acetic+acid | ||
PubChem CID
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RTECS number
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UNII | |||
UN number | 2789 | ||
CompTox Dashboard (EPA)
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Properties | |||
CH3COOH | |||
Molar mass | 60.052 g·mol−1 | ||
Appearance | Colourless liquid | ||
Odor | Heavily vinegar-like | ||
Density | 1.049 g/cm3 (liquid); 1.27 g/cm3 (solid) | ||
Melting point | 16 to 17 °C; 61 to 62 °F; 289 to 290 K | ||
Boiling point | 118 to 119 °C; 244 to 246 °F; 391 to 392 K | ||
Miscible | |||
log P | -0.28[4] | ||
Vapor pressure | 1.54653947 kPa (20 °C) 11.6 mmHg (20 °C)[5] | ||
Acidity (pKa) | 4.756 | ||
Conjugate base
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Acetate | ||
-31.54·10−6 cm3/mol | |||
Refractive index (nD)
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1.371 (VD = 18.19) | ||
Viscosity | 1.22 mPa s 1.22 cP | ||
1.74 D | |||
Thermochemistry | |||
Heat capacity (C)
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123.1 J K−1 mol−1 | ||
Std molar
entropy (S⦵298) |
158.0 J K−1 mol−1 | ||
Std enthalpy of (ΔfH⦵298)formation |
-483.88–483.16 kJ/mol | ||
Std enthalpy of (ΔcH⦵298)combustion |
-875.50–874.82 kJ/mol | ||
Pharmacology | |||
G01AD02 (WHO) S02AA10 (WHO) | |||
Legal status |
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Hazards | |||
GHS labelling: | |||
Danger | |||
H226, H314 | |||
P280, P305+P351+P338, P310 | |||
NFPA 704 (fire diamond) | |||
Flash point | 40 °C (104 °F; 313 K) | ||
427 °C (801 °F; 700 K) | |||
Explosive limits
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4–16% | ||
Lethal dose or concentration (LD, LC): | |||
LD50 (median dose)
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3.31 g kg−1, oral (rat) | ||
LC50 (median concentration)
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5620 ppm (mouse, 1 hr) 16000 ppm (rat, 4 hr)[7] | ||
NIOSH (US health exposure limits): | |||
PEL (Permissible)
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TWA 10 ppm (25 mg/m3)[6] | ||
REL (Recommended)
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TWA 10 ppm (25 mg/m3) ST 15 ppm (37 mg/m3)[6] | ||
IDLH (Immediate danger) |
50 ppm[6] | ||
Related compounds | |||
Related carboxylic acids
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Formic acid Propionic acid | ||
Related compounds
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Acetaldehyde Acetamide Acetic anhydride Chloroacetic acid Acetyl chloride Glycolic acid Ethyl acetate Potassium acetate Sodium acetate Thioacetic acid | ||
Supplementary data page | |||
Acetic acid (data page) | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Clinical data | |
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ECHA InfoCard | 100.000.528 |
Data page | |
Acetic acid (data page) |
Acetic acid /əˈsiːtɪk/, systematically named ethanoic acid /ˌɛθəˈnoʊɪk/, is an acidic, colourless liquid and organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component of vinegar apart from water. It has been used, as a component of vinegar, throughout history from at least the third century BC.
Acetic acid is the second simplest carboxylic acid (after formic acid). It is an important chemical reagent and industrial chemical across various fields, 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. 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 tonnes per year (t/a), manufactured from methanol.[8] Its production and subsequent industrial use poses health hazards to workers, including incidental skin damage and chronic respiratory injuries from inhalation.[9]
Nomenclature
The
"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 solid ice-like crystals that form with agitation, slightly below room temperature at 16.6 °C (61.9 °F). 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.[11]
A common
History
In the 16th-century German 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.[15][16]
In 1845 German chemist
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 milk of lime, and the resulting calcium acetate was then acidified with sulfuric acid to recover acetic acid. At that time, Germany was producing 10,000 tons of glacial acetic acid, around 30% of which was used for the manufacture of indigo dye.[15][18]
Because both
Interstellar medium
Properties
Acidity
The hydrogen centre in the
- CH3COOH ⇌ CH3CO−2 + H+
Because of this release of the
Structure
In solid acetic acid, the molecules form chains of individual molecules interconnected by
Solvent properties
Biochemistry
At physiological pHs, acetic acid is usually fully ionised to acetate.
The
Acetic acid is produced and
Production
Acetic acid is produced industrially both synthetically and by bacterial
Acetic acid can be purified via fractional freezing using an ice bath. The water and other impurities will remain liquid while the acetic acid will precipitate out. As of 2003–2005, total worldwide production of virgin acetic acid[b] 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.[34][35] Since then, the global production has increased from 10.7 Mt/a in 2010[36] to 17.88 Mt/a in 2023.[37] The two biggest producers of virgin acetic acid are Celanese and BP Chemicals. Other major producers include Millennium Chemicals, Sterling Chemicals, Samsung, Eastman, and Svensk Etanolkemi .[38]
Methanol carbonylation
Most acetic acid is produced by methanol carbonylation. In this process, methanol and carbon monoxide react to produce acetic acid according to the equation:
The process involves iodomethane as an intermediate, and occurs in three steps. A metal carbonyl catalyst is needed for the carbonylation (step 2).[33]
- CH3OH + HI → CH3I + H2O
- CH3I + CO → CH3COI
- CH3COI + H2O → CH3COOH + HI
Two related processes exist for the carbonylation of methanol: the rhodium-catalyzed
By altering the process conditions, acetic anhydride may also be produced in plants using rhodium catalysis.[39]
Acetaldehyde oxidation
Prior to the commercialization of the Monsanto process, most acetic acid was produced by oxidation of
Light
- 2 C4H10 + 5 O2 → 4 CH3CO2H + 2 H2O
Such oxidations require metal catalyst, such as the naphthenate salts of manganese, cobalt, and chromium.
The typical reaction is conducted at temperatures and pressures designed to be as hot as possible while still keeping the butane a liquid. Typical reaction conditions are 150 °C (302 °F) and 55 atm.[41] 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.[42]
Similar conditions and
- 2 CH3CHO + O2 → 2 CH3CO2H
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 boiling points than acetic acid and are readily separated by distillation.[42]
Ethylene oxidation
Acetaldehyde may be prepared from ethylene via the Wacker process, and then oxidised as above.
In more recent times, chemical company
- C2H4 + O2 → CH3CO2H
It is thought to be competitive with methanol carbonylation for smaller plants (100–250 kt/a), depending on the local price of ethylene. The approach will be based on utilizing a novel selective photocatalytic oxidation technology for the selective oxidation of ethylene and ethane to acetic acid. Unlike traditional oxidation catalysts, the selective oxidation process will use UV light to produce acetic acid at ambient temperatures and pressure.
Oxidative fermentation
For most of human history, acetic acid bacteria of the genus Acetobacter have made acetic acid, in the form of vinegar. Given sufficient oxygen, these bacteria can produce vinegar from a variety of alcoholic foodstuffs. Commonly used feeds include apple cider, wine, and fermented grain, malt, rice, or potato mashes. The overall chemical reaction facilitated by these bacteria is:
- C2H5OH + O2 → CH3COOH + H2O
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.[44]
The first batches of vinegar produced by fermentation probably followed errors in the
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
Nowadays, most vinegar is made in submerged tank culture, first described in 1949 by Otto Hromatka and Heinrich Ebner.[47] 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.[45]
Anaerobic fermentation
Species of
- C6H12O6 → 3 CH3COOH
These acetogenic bacteria produce acetic acid from one-carbon compounds, including methanol, carbon monoxide, or a mixture of carbon dioxide and hydrogen:
- 2 CO2 + 4 H2 → CH3COOH + 2 H2O
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 per cent, 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.[48]
Uses
Acetic acid is a chemical reagent for the production of chemical compounds. The largest single use of acetic acid is in the production of vinyl acetate monomer, closely followed by acetic anhydride and ester production. The volume of acetic acid used in vinegar is comparatively small.[8][34]
Vinyl acetate monomer
The primary use of acetic acid is the production of
- 2 H3C−COOH + 2 C2H4 + O2 → 2 H3C−CO−O−CH=CH2 + 2 H2O
Vinyl acetate can be polymerised to
Ester production
The major
- CH3COO−H + HO−R → CH3COO−R + H2O, R = general alkyl group
For example, acetic acid and ethanol gives ethyl acetate and water.
- CH3COO−H + HO−CH2CH3 → CH3COO−CH2CH3 + H2O
Most acetate
Acetic anhydride
The product of the condensation of two molecules of acetic acid is acetic anhydride. The worldwide production of acetic anhydride is a major application, and uses approximately 25% to 30% of the global production of acetic acid. The main process involves dehydration of acetic acid to give ketene at 700–750 °C. Ketene is thereafter reacted with acetic acid to obtain the anhydride:[50]
- CH3CO2H → CH2=C=O + H2O
- CH3CO2H + CH2=C=O → (CH3CO)2O
Acetic anhydride is an acetylation agent. As such, its major application is for cellulose acetate, a synthetic textile also used for photographic film. Acetic anhydride is also a reagent for the production of heroin and other compounds.[50]
Use as solvent
As a polar protic solvent, acetic acid is frequently used for recrystallization to purify organic compounds. Acetic acid is used as a solvent in the production of terephthalic acid (TPA), the raw material for polyethylene terephthalate (PET). In 2006, about 20% of acetic acid was used for TPA production.[34]
Acetic acid is often used as a solvent for reactions involving
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.[52]
Medical use
Acetic acid injection into a tumor has been used to treat cancer since the 1800s.[53][54]
Acetic acid is used as part of
Acetic acid is an effective antiseptic when used as a 1% solution, with broad spectrum of activity against streptococci, staphylococci, pseudomonas, enterococci and others.[56][57][58] It may be used to treat skin infections caused by pseudomonas strains resistant to typical antibiotics.[59]
While diluted acetic acid is used in iontophoresis, no high quality evidence supports this treatment for rotator cuff disease.[60][61]
As a treatment for otitis externa, it is on the World Health Organization's List of Essential Medicines.[62][63]
Foods
Acetic acid has 349 kcal (1,460 kJ) per 100 g.[64] Vinegar is typically no less than 4% acetic acid by mass.[65][66][67] Legal limits on acetic acid content vary by jurisdiction. Vinegar is used directly as a condiment, and in the pickling of vegetables and other foods. Table vinegar tends to be more diluted (4% to 8% acetic acid), while commercial food pickling employs solutions that are more concentrated. The proportion of acetic acid used worldwide as vinegar is not as large as industrial uses, but it is by far the oldest and best-known application.[68]
Reactions
Organic chemistry
Acetic acid undergoes the typical
- CH3COOH → CH4 + CO2
- CH3COOH → CH2=C=O + H2O
Reactions with inorganic compounds
Acetic acid is mildly corrosive to metals including iron, magnesium, and zinc, forming hydrogen gas and salts called acetates:
- Mg + 2 CH3COOH → (CH3COO)2Mg + H2
Because aluminium forms a passivating acid-resistant film of aluminium oxide, aluminium tanks are used to transport acetic acid. Metal acetates can also be prepared from acetic acid and an appropriate base, as in the popular "baking soda + vinegar" reaction giving off sodium acetate:
- NaHCO3 + CH3COOH → CH3COONa + CO2 + H2O
A
Other derivatives
Organic or inorganic salts are produced from acetic acid. Some commercially significant derivatives:
- Sodium acetate, used in the textile industry and as a food preservative (E262).
- Copper(II) acetate, used as a pigment and a fungicide.
- Aluminium acetate and iron(II) acetate—used as mordants for dyes.
- Palladium(II) acetate, used as a catalyst for organic coupling reactions such as the Heck reaction.
Halogenated acetic acids are produced from acetic acid. Some commercially significant derivatives:
- Chloroacetic acid (monochloroacetic acid, MCA), dichloroacetic acid (considered a by-product), and trichloroacetic acid. MCA is used in the manufacture of indigo dye.
- Bromoacetic acid, which is esterified to produce the reagent ethyl bromoacetate.
- Trifluoroacetic acid, which is a common reagent in organic synthesis.
Amounts of acetic acid used in these other applications together account for another 5–10% of acetic acid use worldwide.[34]
Health and safety
Vapour
Prolonged inhalation exposure (eight hours) to acetic acid vapours at 10 ppm can produce some irritation of eyes, nose, and throat; at 100 ppm marked lung irritation and possible damage to lungs, eyes, and skin may result. Vapour concentrations of 1,000 ppm cause marked irritation of eyes, nose and upper respiratory tract and cannot be tolerated. These predictions were based on animal experiments and industrial exposure.[75]
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 lacrimation and irritation of the eyes, nose, and throat, with pharyngeal oedema and chronic bronchitis. Unacclimatised 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).[9]
Solution
Concentrated acetic acid (≥ 25%) is corrosive to skin.[76] These burns or blisters may not appear until hours after exposure.[77] The hazardous properties of acetic acid are dependent on the concentration of the (typically aqueous) solution, with the most significant increases in hazard levels at thresholds of 25% and 90% acetic acid concentration by weight. The following table summarizes the hazards of acetic acid solutions by concentration:[78]
Concentration by weight |
Molarity | GHS pictograms | H-Phrases
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10–25% | 1.67–4.16 mol/L | H315 | |
25–90% | 4.16–14.99 mol/L | H314 | |
>90% | >14.99 mol/L | H226, H314 |
Concentrated acetic acid can be ignited only with difficulty at standard temperature and pressure, but becomes a flammable risk in temperatures greater than 39 °C (102 °F), and can form explosive mixtures with air at higher temperatures with
See also
Notes
References
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- ^ Acetic Acid Archived 23 April 2022 at the Wayback Machine. SRI Consulting.
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External links
- International Chemical Safety Card 0363
- National Pollutant Inventory – Acetic acid fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- Method for sampling and analysis
- 29 CFR 1910.1000, Table Z-1 (US Permissible exposure limits)
- ChemSub Online: Acetic acid
- Calculation of vapor pressure, liquid density, dynamic liquid viscosity, surface tension of acetic acid
- Acetic acid bound to proteins in the PDB
- Swedish Chemicals Agency. Information sheet – Acetic Acid
- Process Flow sheet of Acetic acid Production by the Carbonylation of Methanol