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A carboxylic acid is an
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
, or other group. Carboxylic acids occur widely. Important examples include the
. Deprotonation of a carboxylic acid gives a
Examples and nomenclature[
Carboxylic acids are commonly identified by their
. They often have the suffix -ic acid.
-recommended names also exist; in this system, carboxylic acids have an -oic acid suffix.
(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
even if there are other
, such as
. Alternately, it can be named as a “carboxy” or “carboxylic acid” substituent on another parent structure, such as
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
and its conjugate base, respectively. For example, the conjugate base of
, which occurs in
bicarbonate buffer systems
in nature, is not generally classed as one of the carboxylic acids, despite that it has a
that looks like a COOH group.
|Common Name||IUPAC Name||Chemical formula||Common location or use|
|Propanoic acid||CH3CH2COOH||Preservative for stored grains,
, milk, butter, cheese
Palm kernel oil
|Undecanoic acid||CH3(CH2)9COOH||Anti-fungal agent|
and hand wash soaps
|Tridecanoic acid||CH3(CH2)11COOH||Plant metabolite|
|Pentadecanoic acid||CH3(CH2)13COOH||Milk fat|
|Heptadecanoic acid||CH3(CH2)15COOH||Pheromone in various animals|
, waxes, soaps, and oils
|Nonadecanoic acid||CH3(CH2)17COOH||Fats, vegetable oils,
|unsaturated monocarboxylic acids||
(2-propenoic acid) – CH2=CHCOOH, used in polymer synthesis
|medium to long-chain saturated and unsaturated monocarboxylic acids, with even number of carbons, examples:
|the building-blocks of
|acids of biochemical significance that contain a
|containing at least one aromatic ring, examples:
– the sodium salt of benzoic acid is used as a food preservative,
– a beta-hydroxy type found in many skin-care products,
phenyl alkanoic acids
– the class of compounds where a phenyl group is attached to a carboxylic acid
|containing two carboxyl groups, examples:
the monomer used to produce
– a family of sugar acids
|containing three carboxyl groups, examples:
– found in
Alpha hydroxy acids
|containing a hydroxy group, examples:
(2-hydroxypropanoic acid) – found in sour milk,
– found in wine
Divinylether fatty acids
|containing a doubly unsaturated carbon chain attached via an ether bond to a fatty acid, found in some plants|
Carboxylic acids are
. Because they are both hydrogen-bond acceptors (the carbonyl –C=O) and hydrogen-bond donors (the hydroxyl –OH), they also participate in
. 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,
has a low solubility in water (0.2 g/L), but its sodium salt is very soluble in water.
Carboxylic acids tend to have higher boiling points than water, because of their greater surface areas and their tendency to form stabilised dimers through
. For boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporised, increasing the
enthalpy of vaporization
Carboxylic acids are
because they are proton (H+) donors. They are the most common type of
Carboxylic acids are typically
, meaning that they only partially
solution. For example, at room temperature, in a 1-
, only 0.4% of the acid are dissociated. Electron-withdrawing substituents, such as
, give stronger acids (the pKa of formic acid is 3.75 whereas trifluoroacetic acid, with a
, 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
, has a pKa of 4.76)
of carboxylic acids gives carboxylate anions; these are
, 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.
Carboxylic acids often have strong sour odours.
of carboxylic acids tend to have pleasant odours, and many are used in
Carboxylic acids are readily identified as such by
. They exhibit a sharp band associated with vibration of the C–O vibration bond (νC=O) between 1680 and 1725 cm−1. A characteristic νO–H band appears as a broad peak in the 2500 to 3000 cm−1 region.
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
Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives. Industrially important carboxylic acids include
(component of vinegar, precursor to solvents and coatings),
acrylic and methacrylic acids
(precursors to polymers, adhesives),
(a flavor and preservative in food and beverages),
(polymers). Important carboxylate salts are soaps.
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
for the production of acetic acid. Formic acid is prepared by a different carbonylation pathway, also starting from methanol.
- Oxidation of
with air using cobalt and manganese catalysts. The required aldehydes are readily obtained from alkenes by
- 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.
are illustrative large-scale conversions.
is generated from
- Oxidation of ethene using
- 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
. In the
, 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 “
- HCCH + CO + H2O → CH2=CHCO2H
- Hydrolysis of
obtained from plant or animal oils. These methods of synthesizing some long-chain carboxylic acids are related to
of ethanol. This method is used in the production of
provides a route to
, precursor to
Preparative methods for small scale reactions for research or for production of fine chemicals often employ expensive consumable reagents.
Oxidation of primary alcohols
. 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
- Hydrolysis of
, usually with acid- or base-catalysis.
- Carbonation of a
- RLi + CO2 → RCO2Li
- RCO2Li + HCl → RCO2H + LiCl
followed by hydrolysis of
- Base-catalyzed cleavage of non-enolizable ketones, especially aryl ketones:
- RC(O)Ar + H2O → RCO2H + ArH
Many reactions produce carboxylic acids but are used only in specific cases or are mainly of academic interest.
- Disproportionation of an
- Rearrangement of diketones in the
benzilic acid rearrangement
involving the generation of benzoic acids are the
von Richter reaction
from nitrobenzenes and the
The most widely practiced reactions convert carboxylic acids into esters, amides, carboxylate salts, acid chlorides, and alcohols. Carboxylic acids react with
to form carboxylate salts, in which the hydrogen of the hydroxyl (–OH) group is replaced with a metal
. For example, acetic acid found in vinegar reacts with
(baking soda) to form sodium acetate,
, and water:
- CH3COOH + NaHCO3 → CH3COO−Na+ + CO2 + H2O
Carboxylic acids also react with
. This process is widely used, e.g. in the production of
. Likewise, carboxylic acids are converted into
, 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
is a significant biochemical process that requires
The hydroxyl group on carboxylic acids may be replaced with a chlorine atom using
. In nature, carboxylic acids are converted to
, most of carboxylic acid can be
to alcohols by
or using hydride or alkyl transferring agents (since they will deprotonate the acids instead[
further explanation needed
] without transfer) such as
lithium aluminium hydride
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.
- As with all carbonyl compounds, the protons on the
are labile due to
. Thus, the α-carbon is easily halogenated in the
converts carboxylic acids to
- Carboxylic acids are decarboxylated in the
converts an amino acid to the corresponding amino ketone.
- In the
, an carboxylic acid on an aliphatic chain having a simple the
at the alpha position can have the chain shortened by one carbon. The inverse procedure is the
, where an acid is converted into acyl halide, which is then reacted with
to give one additional methylene in the aliphatic chain.
- Many acids undergo
that catalyze these reactions are known as
- Carboxylic acids are reduced to
, via the acid chloride in the
and via the thioester in the
carboxylic acids are converted to ketones.
- Organolithium reagents (>2 equiv) react with carboxylic acids to give a dilithium 1,1-diolate, a stable
which decomposes to give a ketone upon acidic workup.
is an electrolytic, decarboxylative dimerization reaction. It gets rid of the carboxyl groups of two acid molecules, and joins the remaining fragments together.
, •COOH, only exists briefly.
acid dissociation constant
of •COOH has been measured using
electron paramagnetic resonance
The carboxyl group tends to dimerise to form
|Wikimedia Commons has media related to
|Wikiquote has quotations related to:
List of carboxylic acids
Polyhydroxy carboxylic acid
Compendium of Chemical Terminology
, 2nd ed. (the “Gold Book”) (1997). Online corrected version: (2006–) “
. Organic Chemistry IUPAC Nomenclature. Rules C-4 Carboxylic Acids and Their Derivatives.
- Morrison, R.T.; Boyd, R.N. (1992). Organic Chemistry (6th ed.).
- Haynes, William M., ed. (2011).
CRC Handbook of Chemistry and Physics
. pp. 5–94 to 5–98.
- Riemenschneider, Wilhelm (2002). “Carboxylic Acids, Aliphatic”. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH.
- Perry C. Reeves (1977). “Carboxylation Of Aromatic Compounds: Ferrocenecarboxylic Acid”. Org. Synth. 56: 28.
- Fujisawa, Tamotsu; Sato, Toshio.
“Reduction of carboxylic acids to aldehydes: 6-Ooxdecanal”
. 66: 121.
.; Collective Volume, 8, p. 498
- Milligan, D. E.; Jacox, M. E. (1971). “Infrared Spectrum and Structure of Intermediates in Reaction of OH with CO”. Journal of Chemical Physics. 54 (3): 927–942.
- The value is pKa = −0.2 ± 0.1. Jeevarajan, A. S.; Carmichael, I.; Fessenden, R. W. (1990). “ESR Measurement of the pKa of Carboxyl Radical and Ab Initio Calculation of the Carbon-13 Hyperfine Constant”. Journal of Physical Chemistry. 94 (4): 1372–1376.
in Wiktionary, the free dictionary.
- Carboxylic acids pH and titration
– freeware for calculations, data analysis, simulation, and distribution diagram generation
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