An acetate is a
salt
In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
formed by the combination of
acetic acid
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 compone ...
with a base (e.g.
alkaline
In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...
,
earthy,
metallic,
nonmetallic, or radical
base). "Acetate" also describes the
conjugate base or
ion (specifically, the negatively charged ion called an
anion) typically found in
aqueous solution and written with the chemical formula . The neutral molecules formed by the combination of the acetate ion and a ''positive'' ion (called a
cation) are also commonly called "acetates" (hence, ''acetate of lead'', ''acetate of aluminium'', etc.). The simplest of these is hydrogen acetate (called
acetic acid
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 compone ...
) with corresponding salts,
ester
In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
s, and the
polyatomic anion , or .
Most of the approximately 5 million tonnes of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of
polymers. In nature, acetate is the most common building block for
biosynthesis
Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...
.
Nomenclature and common formula
When part of a
salt
In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
, the formula of the acetate ion is written as , , or . Chemists often represent acetate as OAc
− or, less commonly, AcO
−. Thus, HOAc is the symbol for acetic acid, NaOAc for
sodium acetate, and EtOAc for
ethyl acetate[Zumdahl, S. S. “Chemistry” Heath, 1986: Lexington, MA. .] (as Ac is common symbol for
acetyl group CH
3CO). The
pseudoelement symbol "Ac" is also sometimes encountered in chemical formulas as indicating the entire acetate ion (). It is not to be confused with the symbol of
actinium
Actinium is a chemical element; it has chemical symbol, symbol Ac and atomic number 89. It was discovered by Friedrich Oskar Giesel in 1902, who gave it the name ''emanium''; the element got its name by being wrongly identified with a substa ...
, the first element of the
actinide series; context guides disambiguation. For example, the formula for sodium acetate might be abbreviated as "NaOAc", rather than "NaC
2H
3O
2". Care should also be taken to avoid confusion with
peracetic acid when using the OAc abbreviation; for clarity and to avoid errors when translated, HOAc should be avoided in literature mentioning both compounds.
Although its
systematic name is ''ethanoate'' (), the common ''acetate'' remains the
preferred IUPAC name.
Salts
The acetate
anion,
3COO">H3COOsup>−,(or
2H3O2">2H3O2sup>−) is one of the
carboxylate family. It is the
conjugate base of
acetic acid
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 compone ...
. Above a pH of 5.5, acetic acid converts to acetate:
[
:CH3COOH ⇌ CH3COO− + H+
Many acetate salts are ionic, indicated by their tendency to dissolve well in water. A commonly encountered acetate in the home is sodium acetate, a white solid that can be prepared by combining vinegar and sodium bicarbonate ("bicarbonate of soda"):
:CH3COOH + NaHCO3 → CH3COO−Na+ + H2O + CO2
Transition metals can be complexed by acetate. Examples of acetate complexes include ]chromium(II) acetate
Chromium(II) acetate hydrate, also known as chromous acetate, is the coordination compound with the chemical formula, formula Cr2(CH3CO2)4(H2O)2. This formula is commonly abbreviated Cr2(OAc)4(H2O)2. This red-coloured compound features a quadruple ...
and basic zinc acetate.
Commercially important acetate salts are aluminium acetate, used in dyeing, ammonium acetate, a precursor to acetamide, and potassium acetate, used as a diuretic. All three salts are colourless and highly soluble in water.[Hosea Cheung, Robin S. Tanke, G. Paul Torrence "Acetic acid" in ''Ullmann's Encyclopedia of Industrial Chemistry'' Weinheim, Germany: Wiley-VCH, 2005. ]
Esters
Acetate ester
In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
s have the general formula CH3CO2R, where R is an organyl group. The esters are the dominant forms of acetate in the marketplace. Unlike the acetate salts, acetate esters are often liquids, lipophilic, and sometimes volatile. They are popular because they have inoffensive, often sweet odors, they are inexpensive, and they are usually of low toxicity.
Almost half of acetic acid production is consumed in the production of vinyl acetate, precursor to polyvinyl alcohol, which is a component of many paints. The second largest use of acetic acid is consumed in the production of cellulose acetate
In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and ...
. In fact, "acetate" is jargon for cellulose acetate, which is used in the production of fibres or diverse products, e.g. the acetate discs used in audio record production. Cellulose acetate can be found in many household products. Many industrial solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
s are acetates, including methyl acetate, ethyl acetate, isopropyl acetate, and ethylhexyl acetate. Butyl acetate is a fragrance used in food products.[
]
Acetate in biology
Acetate is a common anion in biology. It is mainly utilized by organisms in the form of acetyl coenzyme A.
Intraperitoneal injection of sodium acetate (20 or 60 mg per kg body mass) was found to induce headache in sensitized rats, and it has been proposed that acetate resulting from oxidation of ethanol
Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
is a major factor in causing hangover
A hangover is the experience of various unpleasant physiological and psychological effects usually following the consumption of alcohol (beverage), alcohol, such as wine, beer, and liquor. Hangovers can last for several hours or for more than ...
s. Increased serum acetate levels lead to accumulation of adenosine in many tissues including the brain, and administration of the adenosine receptor antagonist caffeine
Caffeine is a central nervous system (CNS) stimulant of the methylxanthine chemical classification, class and is the most commonly consumed Psychoactive drug, psychoactive substance globally. It is mainly used for its eugeroic (wakefulness pr ...
to rats after ethanol was found to decrease nociceptive behavior.
Acetate has known immunomodulatory properties and can affect the innate immune response to pathogenic bacteria such as the respiratory pathogen ''Haemophilus influenzae''.
Fermentation of acetyl CoA to acetate
Pyruvate is converted into acetyl-coenzyme A (acetyl-CoA) by the enzyme pyruvate dehydrogenase. This acetyl-CoA is then converted into acetate in ''E. coli'', whilst producing ATP by substrate-level phosphorylation
Substrate-level phosphorylation is a metabolism reaction that results in the production of ATP or GTP supported by the energy released from another high-energy bond that leads to phosphorylation of ADP or GDP to ATP or GTP (note that the rea ...
. Acetate formation requires two enzymes: phosphate acetyltransferase and acetate kinase.
acetyl-CoA + phosphate → acetyl-phosphate + CoA
acetyl-phosphate + ADP → acetate + ATP
Fermentation of acetate
Acetic acid can also undergo a dismutation reaction to produce methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
and carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
:
:CH3COO− + H+ → CH4 + CO2 Δ''G''° = −36 kJ/mol
This disproportionation reaction is catalysed by methanogen archaea
Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...
in their fermentative metabolism. One electron is transferred from the carbonyl function ( e− donor) of the carboxylic
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl group (e. ...
group to the methyl group ( e− acceptor) of acetic acid to respectively produce CO2 and methane gas.
Structures
Image:Acetate-anion-3D-vdW.png,
Image:Acetate-anion-resonance-hybrid-2D-skeletal.png,
Image:Acetate-resonance-2D-skeletal.png,
See also
* Acetic acid
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 compone ...
* Acetoxy group
* Acetyl chloride
* Acetylation
* Cellulose acetate
In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and ...
* Copper(II) acetate
* Fermentation (biochemistry)
* Mixed acid fermentation
* Sodium acetate
* Zinc acetate
References
External links
{{Authority control
Carboxylate anions
Leaving groups