An acetate is a salt 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 component ...

with a base (e.g.

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

, earthy, metallic,

nonmetal In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite). The electrons in nonmetals behave differentl ...

lic or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called an anion) typically found in

aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...

and written with the chemical formula . The neutral molecules formed by the combination of the acetate ion and a ''positive'' ion (called a

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

) are also commonly called "acetates" (hence, ''acetate of lead'', ''acetate of aluminum'', etc.). The simplest of these is hydrogen acetate (called

) with corresponding salts, esters, and the polyatomic anion , or . Most of the approximately 5 billion kilograms 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 is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...

Nomenclature and common formula

When part of a salt, 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 acetateZumdahl, S. S. “Chemistry” Heath, 1986: Lexington, MA. . (as Ac is common symbol for

acetyl In organic chemistry, acetyl is a functional group with the chemical formula and the structure . It is sometimes represented by the symbol Ac (not to be confused with the element actinium). In IUPAC nomenclature, acetyl is called ethanoyl, ...

group CH₃CO).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, the first element of the actinide series; context guides disambiguation. For example, the formula for sodium acetate might be abbreviated as "NaOAc", rather than "NaC₂H₃O₂". 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, H₃COOsup>−,(or ₂H₃O₂sup>−) is one of the carboxylate family. It is the conjugate base of

. 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 Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3−) ...

("bicarbonate of soda"): :CH₃COOH + NaHCO₃ → CH₃COO⁻Na⁺ + H₂O + CO₂ Transition metals can be complexed by acetate. Examples of acetate complexes include chromium(II) acetate 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 esters 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

paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...

s. The second largest use of acetic acid is consumed in the production of cellulose acetate. 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 solvents are acetates, including methyl acetate, ethyl acetate, isopropyl acetate, 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 is a major factor in causing hangovers. Increased serum acetate levels lead to accumulation of

adenosine Adenosine ( symbol A) is an organic compound that occurs widely in nature in the form of diverse derivatives. The molecule consists of an adenine attached to a ribose via a β-N9-glycosidic bond. Adenosine is one of the four nucleoside building ...

in many tissues including the brain, and administration of the

receptor antagonist caffeine to rats after ethanol was found to decrease nociceptive behavior. Acetate has known immunomodulatory properties and can affect the innate immune response to

pathogenic In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

bacteria such as the respiratory pathogen ''Haemophilus influenzae''.

Fermentation 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 by the transfer of a phosphate group from a substrate directly to ADP or GDP. Transferring from a higher energy (whether phosphate group atta ...

. Acetate formation requires two enzymes: phosphate acetyltransferase and acetate kinase. EscherichiaColi NIAID

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 and carbon dioxide: :CH₃COO⁻ + H⁺ → CH₄ + CO₂ Δ''G''° = −36 kJ/mol This disproportionation reaction is catalysed by

methanogen Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens are com ...

archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

in their fermentative metabolism. One electron is transferred from the carbonyl function ( e⁻ donor) of the carboxylic group to the

methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...

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,

References

External links

{{Authority control Carboxylate anions Leaving groups