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A carboxylic acid is an
organic acid An organic acid is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, beha ...
that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the
alkyl In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, pr ...

alkyl
,
alkenyl , the simplest alkene. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior ...
,
aryl In the context of organic molecules, aryl is any functional group In organic chemistry, a functional group is a substituent or moiety in a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene mole ...
, or other group. Carboxylic acids occur widely. Important examples include the
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
s and
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s. Deprotonation of a carboxylic acid gives a
carboxylate A carboxylate is the conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory The Brønsted–Lowry theory (also called proton theory of acids and bases) is an acid–base reaction An acid–base reaction is a ...

carboxylate
anion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
.


Examples and nomenclature

Carboxylic acids are commonly identified by their
trivial name In chemistry, a trivial name is a nonsystematic name for a chemical substance. That is, the name is not recognized according to the rules of any formal system of chemical nomenclature such as IUPAC nomenclature of inorganic chemistry, IUPAC inorg ...
s. They often have the suffix ''-ic acid''.
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authoritative power over chemist ...
-recommended names also exist; in this system, carboxylic acids have an ''-oic acid'' suffix. For example,
butyric acid Butyric acid (from grc, βούτῡρον, meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study o ...

butyric acid
(C3H7CO2H) is butanoic acid by IUPAC guidelines. For nomenclature of complex molecules containing a carboxylic acid, the carboxyl can be considered position one of the
parent chain In the IUPAC nomenclature The International Union of Pure and Applied Chemistry (IUPAC) has published four sets of rules to standardize chemical nomenclature. There are two main areas: * IUPAC nomenclature of inorganic chemistry (Red Book) * I ...
even if there are other
substituent A substituent is one or a group of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that ca ...
s, such as 3-chloropropanoic acid. Alternately, it can be named as a "carboxy" or "carboxylic acid" substituent on another parent structure, such as
2-carboxyfuran
2-carboxyfuran
. The carboxylate anion (R–COO or RCO2) of a carboxylic acid is usually named with the suffix ''-ate'', in keeping with the general pattern of ''-ic acid'' and ''-ate'' for a
conjugate acid A conjugate acid, within the Brønsted–Lowry acid–base theory The Brønsted–Lowry theory (also called proton theory of acids and bases) is an acid–base reaction theory which was proposed independently by Johannes Nicolaus Brønsted ...
and its conjugate base, respectively. For example, the conjugate base of
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
is
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetal image:Simple Periodic Table Chart-en.svg, upright=1.75, Nonmetals (and metalloids) in the periodic table: Metalloids are i ...

acetate
.
Carbonic acid In chemistry, carbonic acid is a dibasic acid with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical ...

Carbonic acid
, which occurs in
bicarbonate buffer system The bicarbonate buffer system is an acid-base homeostatic mechanism involving the balance of carbonic acid (H2CO3), bicarbonate ion (HCO), and carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% highe ...
s in nature, is not generally classed as one of the carboxylic acids, despite that it has a
moiety Moiety may refer to: * Moiety (chemistry), a part or functional group of a molecule * Moiety (kinship), either of two groups into which a society is divided * A division of society in the Iroquois government and societal structure * An Australian Ab ...
that looks like a COOH group.


Physical properties


Solubility

Carboxylic acids are
polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the clim ...
. Because they are both hydrogen-bond acceptors (the carbonyl –C=O) and hydrogen-bond donors (the hydroxyl –OH), they also participate in
hydrogen bond A hydrogen bond (or H-bond) is a primarily electrostatic Electrostatics is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department ...

hydrogen bond
ing. Together, the hydroxyl and carbonyl group form the functional group carboxyl. Carboxylic acids usually exist as dimers in nonpolar media due to their tendency to "self-associate". Smaller carboxylic acids (1 to 5 carbons) are soluble in water, whereas bigger carboxylic acids have limited solubility due to the increasing hydrophobic nature of the alkyl chain. These longer chain acids tend to be soluble in less-polar solvents such as ethers and alcohols. Aqueous sodium hydroxide and carboxylic acids, even hydrophobic ones, react to yield water-soluble sodium salts. For example, enathic acid has a low solubility in water (0.2 g/L), but its sodium salt is very soluble in water.


Boiling points

Carboxylic acids tend to have higher boiling points than water, because of their greater surface areas and their tendency to form stabilised dimers through
hydrogen bond A hydrogen bond (or H-bond) is a primarily electrostatic Electrostatics is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department ...

hydrogen bond
s. For boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporised, increasing the
enthalpy of vaporization The enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy ( enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. T ...
requirements significantly.


Acidity

Carboxylic acids are Brønsted–Lowry acids because they are proton (H+) donors. They are the most common type of
organic acid An organic acid is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, beha ...
. Carboxylic acids are typically
weak acids
weak acids
, meaning that they only partially
dissociate Dissociation in chemistry and biochemistry is a general process in which molecules (or ionic compounds such as salt (chemistry), salts, or coordination complex, complexes) separate or split into smaller particles such as atoms, ions, or radical (c ...
into
H3O+
H<sub>3</sub>O<sup>+</sup>
cations An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are u ...
and
RCOO
RCOO<sup>−</sup>
anions An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
in neutral
aqueous An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute and the water the solvent. In chemistry, a solution ...
solution. For example, at room temperature, in a 1- molar solution of
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
, only 0.4% of the acid are dissociated. Electron-withdrawing substituents, such as -CF3 group, give stronger acids (the pKa of formic acid is 3.75 whereas trifluoroacetic acid, with a
trifluoromethyl substituent
trifluoromethyl substituent
, has a pKa of 0.23). Electron-donating substituents give weaker acids (the pKa of formic acid is 3.75 whereas acetic acid, with a
methyl substituent
methyl substituent
, has a pKa of 4.76)
Deprotonation Deprotonation (or dehydronation) is the removal (transfer) of a proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutro ...

Deprotonation
of carboxylic acids gives carboxylate anions; these are
resonance stabilized In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or ''canonical stru ...
, because the negative charge is delocalized over the two oxygen atoms, increasing the stability of the anion. Each of the carbon–oxygen bonds in the carboxylate anion has a partial double-bond character. The carbonyl carbon's partial positive charge is also weakened by the -1/2 negative charges on the 2 oxygen atoms.


Odour

Carboxylic acids often have strong sour odours.
Esters An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical ...

Esters
of carboxylic acids tend to have pleasant odours, and many are used in
perfume Perfume (, ; french: parfum) is a mixture of fragrance, fragrant essential oils or aroma compounds (fragrances), Fixative (perfumery), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and livin ...

perfume
.


Characterization

Carboxylic acids are readily identified as such by
infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption spectroscopy, absorption, emission spectrum, emission, or reflection (physics), reflection. ...

infrared spectroscopy
. They exhibit a sharp band associated with vibration of the C–O vibration bond (''ν''C=O) between 1680 and 1725 cm−1. A characteristic ''ν''O–H band appears as a broad peak in the 2500 to 3000 cm−1 region. By 1H
NMR Nuclear magnetic resonance (NMR) is a physical phenomenon A phenomenon (; plural phenomena) is an observable In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ...
spectrometry, the
hydroxyl A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the ...

hydroxyl
hydrogen appears in the 10–13 ppm region, although it is often either broadened or not observed owing to exchange with traces of water.


Occurrence and applications

Many carboxylic acids are produced industrially on a large scale. They are also frequently found in nature. Esters of fatty acids are the main components of lipids and polyamides of are the main components of
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s. Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives. Industrially important carboxylic acids include
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
(component of vinegar, precursor to solvents and coatings), (precursors to polymers, adhesives),
adipic acid Adipic acid or hexanedioic acid is the organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's abili ...

adipic acid
(polymers),
citric acid Citric acid is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, ...

citric acid
(a flavor and preservative in food and beverages),
ethylenediaminetetraacetic acid Ethylenediaminetetraacetic acid (EDTA) is an aminopolycarboxylic acid with the formula H2N(CH2CO2H)2sub>2. This white, water-soluble solid is widely used to bind to iron and calcium ions. It binds these ions as a hexadentate ("six-toothed") che ...
(chelating agent),
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s (coatings),
maleic acid Maleic acid or ''cis''-butenedioic acid is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of ...

maleic acid
(polymers),
propionic acid Propionic acid (, from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population ...

propionic acid
(food preservative),
terephthalic acid Terephthalic acid is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reaction ...

terephthalic acid
(polymers). Important carboxylate salts are soaps.


Synthesis


Industrial routes

In general, industrial routes to carboxylic acids differ from those used on a smaller scale because they require specialized equipment. *Carbonylation of alcohols as illustrated by the
Cativa process 200px, Space-filling model of the [Ir(CO)2I2sup>− catalyst used in the Cativa process The Cativa process is a method for the production of acetic acid by the carbonylation of methanol. The technology, which is similar to the Monsanto process, wa ...
for the production of acetic acid. Formic acid is prepared by a different carbonylation pathway, also starting from methanol. *Oxidation of
aldehyde Chemically, an aldehyde is a compound containing a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same ...

aldehyde
s with air using cobalt and manganese catalysts. The required aldehydes are readily obtained from alkenes by hydroformylation. *Oxidation of hydrocarbons using air. For simple alkanes, this method is inexpensive but not selective enough to be useful. Allylic and benzylic compounds undergo more selective oxidations. Alkyl groups on a benzene ring are oxidized to the carboxylic acid, regardless of its chain length.
Benzoic acid Benzoic acid is a white (or colorless) solid with the formula C6H5CO2H. It is the simplest aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic ( ...

Benzoic acid
from
toluene Toluene (), also known as toluol (), is an aromatic hydrocarbon. It is a colorless, Water (molecule), water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group ( ...

toluene
,
terephthalic acid Terephthalic acid is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reaction ...

terephthalic acid
from ''para''-
xylene Xylene (from ''xylon'', "wood"), xylol or dimethylbenzene is any one of three s of dimethylbenzene, or a combination thereof. With the formula (CH3)2C6H4, in each of the three compounds two hydrogen atoms in the ring are substituted by two s. ...
, and
phthalic acid Phthalic acid is an aromatic dicarboxylic acid, with formula C6H4(CO2H)2. It is an isomer of isophthalic acid and terephthalic acid. Although phthalic acid is of modest commercial importance, the closely related derivative phthalic anhydride i ...
from ''ortho''-
xylene Xylene (from ''xylon'', "wood"), xylol or dimethylbenzene is any one of three s of dimethylbenzene, or a combination thereof. With the formula (CH3)2C6H4, in each of the three compounds two hydrogen atoms in the ring are substituted by two s. ...
are illustrative large-scale conversions.
Acrylic acid Acrylic acid (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science ...

Acrylic acid
is generated from
propene Propene, also known as propylene, is an unsaturated organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The s ...
. *Oxidation of ethene using
silicotungstic acid Silicotungstic acid (also known as tungstosilicic acid) is a heteropoly acid with the formula H4SiW12O40.nH2O. In freshly prepared samples, n is approximately 29, but after prolonged desiccation, n = 6. It is a white solid although impure sampl ...
catalyst. *Base-catalyzed dehydrogenation of alcohols. *Carbonylation coupled to the addition of water. This method is effective and versatile for alkenes that generate secondary and tertiary
carbocation A carbocation () is an ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday ...
s, e.g.
isobutylene Isobutylene (or 2-methylpropene) is a hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molec ...

isobutylene
to
pivalic acid Pivalic acid is a carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the alkyl, alken ...

pivalic acid
. In the
Koch reaction The Koch reaction is an organic reaction for the synthesis of tertiary carboxylic acids from alcohols or alkenes. The chemical reaction, reaction is a strongly acid-catalysis, catalyzed carbonylation using carbon monoxide, and typically occurs at ...

Koch reaction
, the addition of water and carbon monoxide to alkenes is catalyzed by strong acids. Hydrocarboxylations involve the simultaneous addition of water and . Such reactions are sometimes called "
Reppe chemistry Walter Julius Reppe (29 July 1892 in Göringen – 26 July 1969 in Heidelberg Heidelberg ( , ) is a university town in the German state of Baden-Württemberg Baden-Württemberg (; ) is a States of Germany, state (''Land'') in southwest Ge ...

Reppe chemistry
." :HCCH + CO + H2O → CH2=CHCO2H * Hydrolysis of
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester An ester is a derived from an (organic or inorganic) in which at least one –OH group is replaced by an –O– () group, as in the substitution reaction of a an ...

triglyceride
s obtained from plant or animal oils. These methods of synthesizing some long-chain carboxylic acids are related to . *
Fermentation Fermentation is a metabolism, metabolic process that produces chemical changes in organic Substrate (chemistry), substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in ...
of ethanol. This method is used in the production of
vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation; converting simple sugars to eth ...

vinegar
. *The
Kolbe–Schmitt reaction The Kolbe–Schmitt reaction or Kolbe process (named after Hermann Kolbe and Rudolf Schmitt) is a carboxylation chemical reaction that proceeds by heating sodium phenoxide (the sodium salt of phenol) with carbon dioxide under pressure (100 atmosph ...

Kolbe–Schmitt reaction
provides a route to
salicylic acid Salicylic acid is an organic compound with the formula HOC6H4CO2H. A colorless, bitter-tasting solid, it is a precursor to and a active metabolite, metabolite of aspirin (acetylsalicylic acid). It is a plant hormone, and has been listed by the ...

salicylic acid
, precursor to
aspirin Aspirin, also known as acetylsalicylic acid (ASA), is a medication used to reduce pain, fever, or inflammation. Specific inflammatory conditions which aspirin is used to treat include Kawasaki disease, pericarditis, and rheumatic fever. Aspirin ...

aspirin
.


Laboratory methods

Preparative methods for small scale reactions for research or for production of fine chemicals often employ expensive consumable reagents. * Oxidation of primary alcohols or
aldehyde Chemically, an aldehyde is a compound containing a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same ...

aldehyde
s with strong
oxidants Image:DOT hazmat class 5.1.svg, 125px, Dangerous goods label for oxidizing agents In chemistry, an oxidizing agent (oxidant, oxidizer), or oxidising agent (oxidiser) is a substance that has the ability to oxidize other substances — in other ...

oxidants
such as
potassium dichromate Potassium dichromate, , is a common inorganic compound, inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically ...

potassium dichromate
,
Jones reagent Jones may refer to: People * Jones (surname), a common Welsh and English surname * List of people with surname Jones * Jones (singer), a British singer-songwriter Arts and entertainment * Jones (''Animal Farm''), a human character in George Or ...
,
potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and permanganate, . It is a purplish-black crystalline salt, that dissolves in water to give intensely pink or purple solutions. P ...

potassium permanganate
, or
sodium chlorite Sodium chlorite (NaClO2) is a chemical compound used in the manufacturing of paper Paper is a thin sheet material produced by mechanically and/or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses or ...
. The method is more suitable for laboratory conditions than the industrial use of air, which is "greener" because it yields less inorganic side products such as chromium or manganese oxides. *Oxidative cleavage of
olefin In chemistry, an alkene is a hydrocarbon that contains a carbon–carbon double bond. The term is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, and ...

olefin
s by
ozonolysis Ozonolysis is an organic reaction where the Saturated and unsaturated compounds, unsaturated bonds of alkenes, alkynes, or azo compounds are Bond cleavage, cleaved with ozone. Alkenes and alkynes form organic compounds in which the multiple carbon ...

ozonolysis
,
potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and permanganate, . It is a purplish-black crystalline salt, that dissolves in water to give intensely pink or purple solutions. P ...

potassium permanganate
, or
potassium dichromate Potassium dichromate, , is a common inorganic compound, inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically ...

potassium dichromate
. *Hydrolysis of
nitrile A nitrile is any organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...
s,
ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

ester
s, or
amide In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

amide
s, usually with acid- or base-catalysis. *Carbonation of a
Grignard reagent A Grignard reagent or Grignard Compound is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...
and
organolithium Organolithium reagents are organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkaline, alk ...
reagents: :RLi + CO2 → RCO2Li :RCO2Li + HCl → RCO2H + LiCl *
Halogenation In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, ...

Halogenation
followed by hydrolysis of methyl ketones in the
haloform reaction The haloform reaction is a chemical reaction where a haloform (CHX3, where X is a halogen) is produced by the exhaustive halogenation of a methyl ketone (RCOCH3, where R can be either a hydrogen atom, an alkyl or an aryl group), in the presenc ...
* Base-catalyzed cleavage of non-enolizable ketones, especially aryl ketones: :RC(O)Ar + H2O → RCO2H + ArH


Less-common reactions

Many reactions produce carboxylic acids but are used only in specific cases or are mainly of academic interest. * Disproportionation of an
aldehyde Chemically, an aldehyde is a compound containing a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same ...

aldehyde
in the
Cannizzaro reaction The Cannizzaro reaction, named after its discoverer Stanislao Cannizzaro, is a chemical reaction that involves the base (chemistry), base-induced disproportionation of two molecules of a non-enolizable aldehyde to give a primary alcohol and a carb ...
* Rearrangement of diketones in the
benzilic acid rearrangementThe benzilic acid rearrangement is formally the 1,2-rearrangement of 1,2-diketones to form α-Hydroxyl, hydroxy–carboxylic acids using a Base (chemistry), base. This reaction receives its name from the reaction of benzil with potassium hydroxide to ...
involving the generation of benzoic acids are the von Richter reaction from nitrobenzenes and the
Kolbe–Schmitt reaction The Kolbe–Schmitt reaction or Kolbe process (named after Hermann Kolbe and Rudolf Schmitt) is a carboxylation chemical reaction that proceeds by heating sodium phenoxide (the sodium salt of phenol) with carbon dioxide under pressure (100 atmosph ...

Kolbe–Schmitt reaction
from
phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl Functional group, groups (—Oxygen, OHydrogen, H) Chemical bond, bonded directly to an aromatic hydrocarbon group. The s ...

phenols
.


Reactions

The most widely practiced reactions convert carboxylic acids into esters, amides, carboxylate salts, acid chlorides, and alcohols. Carboxylic acids react with bases to form carboxylate salts, in which the hydrogen of the hydroxyl (–OH) group is replaced with a metal
cation An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are u ...
. For example, acetic acid found in vinegar reacts with
sodium bicarbonate Sodium bicarbonate ( IUPAC name: sodium hydrogen carbonate), 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 ...

sodium bicarbonate
(baking soda) to form sodium acetate,
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, and water: :CH3COOH + NaHCO3 → CH3COONa+ + CO2 + H2O Carboxylic acids also react with
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...

alcohol
s to give
ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

ester
s. This process is widely used, e.g. in the production of
polyester Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...
s. Likewise, carboxylic acids are converted into
amide In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

amide
s, but this conversion typically does not occur by direct reaction of the carboxylic acid and the amine. Instead esters are typical precursors to amides. The conversion of
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
s into
peptide Peptides (from Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the dialects of the Greek language spoken ...
s is a significant biochemical process that requires
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
. The hydroxyl group on carboxylic acids may be replaced with a chlorine atom using
thionyl chloride Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year being pro ...

thionyl chloride
to give
acyl chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group -Carbonyl, COChlorine, Cl. Their formula is usually written RCOCl, where R is a side chain. They are reactive derivatives of carboxylic ac ...
s. In nature, carboxylic acids are converted to
thioester In chemistry thioesters are compounds with the functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functi ...

thioester
s.


Reduction

Like
ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

ester
s, most of carboxylic acid can be reduced to alcohols by
hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant ...

hydrogenation
or using hydride or alkyl transferring agents (since they will deprotonate the acids instead without transfer) such as
lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, ...

lithium aluminium hydride
or
Grignard reagent A Grignard reagent or Grignard Compound is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...
s (
organolithium Organolithium reagents are organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkaline, alk ...
compounds). ''N'',''N''-Dimethyl(chloromethylene)ammonium chloride (ClHC=N+(CH3)2Cl) is a highly chemoselective agent for carboxylic acid reduction. It selectively activates the carboxylic acid to give the carboxymethyleneammonium salt, which can be reduced by a mild reductant like lithium tris(''t''-butoxy)aluminum hydride to afford an aldehyde in a one pot procedure. This procedure is known to tolerate reactive carbonyl functionalities such as ketone as well as moderately reactive ester, olefin, nitrile, and halide moieties.


Specialized reactions

* As with all carbonyl compounds, the protons on the α-carbon are labile due to keto–enol tautomerization. Thus, the α-carbon is easily halogenated in the
Hell–Volhard–Zelinsky halogenation The Hell–Volhard–Zelinsky halogenation reaction halogenates carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R ...
. * The
Schmidt reactionThe Schmidt reaction is an organic reaction in which an azide reacts with a carbonyl derivative, usually a aldehyde, ketone, or carboxylic acid, under acidic conditions to give an amine or amide, with expulsion of nitrogen. It is named after Karl Fri ...

Schmidt reaction
converts carboxylic acids to
amine In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

amine
s. * Carboxylic acids are decarboxylated in the
Hunsdiecker reaction The Hunsdiecker reaction (also called the Borodin reaction or the Hunsdiecker–Borodin reaction) is a name reaction in organic chemistry whereby silver salts of carboxylic acids react with a halogen to produce an organic halide. It is an examp ...
. * The Dakin–West reaction converts an amino acid to the corresponding amino ketone. * In the Barbier–Wieland degradation, an carboxylic acid on an aliphatic chain having a simple the
methylene bridge In organic chemistry, a methylene bridge, methylene spacer, or methanediyl group is any part of a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five c ...
at the alpha position can have the chain shortened by one carbon. The inverse procedure is the Arndt–Eistert synthesis, where an acid is converted into acyl halide, which is then reacted with diazomethane to give one additional methylene in the aliphatic chain. * Many acids undergo oxidative decarboxylation. Enzymes that catalyze these reactions are known as carboxylases (Enzyme Commission number, EC 6.4.1) and decarboxylases (EC 4.1.1). * Carboxylic acids are reduced to
aldehyde Chemically, an aldehyde is a compound containing a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same ...

aldehyde
s via the
ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

ester
and Diisobutylaluminium hydride, DIBAL, via the acid chloride in the Rosenmund reduction and via the thioester in the Fukuyama reduction. * In ketonic decarboxylation carboxylic acids are converted to ketones. * Organolithium reagents (>2 equiv) react with carboxylic acids to give a dilithium 1,1-diolate, a stable tetrahedral intermediate which decomposes to give a ketone upon acidic workup. * The Kolbe electrolysis is an electrolytic, decarboxylative dimerization reaction. It gets rid of the carboxyl groups of two acid molecules, and joins the remaining fragments together.


Carboxyl radical

The carboxyl free radical, radical, •COOH, only exists briefly. The acid dissociation constant of COOH has been measured using electron paramagnetic resonance spectroscopy.The value is p''K''a = −0.2 ± 0.1. The carboxyl group tends to dimerise to form oxalic acid.


See also

* Acid anhydride * Acid chloride * Amide * Amino acid * Ester * List of carboxylic acids * Dicarboxylic acid * Polyhydroxy carboxylic acid (PHC). * Pseudoacid * Thiocarboxy


References


External links

* Carboxylic acids pH and titratio
– freeware for calculations, data analysis, simulation, and distribution diagram generation

PHC.
{{DEFAULTSORT:Carboxylic Acid Carboxylic acids, Functional groups