Carboxylic acid
In
Examples and nomenclature
Carboxylic acids are commonly identified by their
The carboxylate anion (R−COO− or R−CO−2) of a carboxylic acid is usually named with the suffix -ate, in keeping with the general pattern of -ic acid and -ate for a
Carbonic acid, which occurs in bicarbonate buffer systems in nature, is not generally classed as one of the carboxylic acids, despite that it has a moiety that looks like a COOH group.
Carbon atoms |
Common Name | IUPAC Name | Chemical formula | Common location or use |
---|---|---|---|---|
1 | Formic acid | Methanoic acid | HCOOH | Insect stings
|
2 | Acetic acid | Ethanoic acid | CH3COOH | Vinegar |
3 | Propionic acid | Propanoic acid | CH3CH2COOH | Preservative for stored grains, body odour , milk, butter, cheese
|
4 | Butyric acid | Butanoic acid | CH3(CH2)2COOH | Butter |
5 | Valeric acid | Pentanoic acid | CH3(CH2)3COOH | Valerian plant |
6 | Caproic acid | Hexanoic acid | CH3(CH2)4COOH | Goat fat |
7 | Enanthic acid | Heptanoic acid | CH3(CH2)5COOH | Fragrance |
8 | Caprylic acid | Octanoic acid | CH3(CH2)6COOH | Coconuts
|
9 | Pelargonic acid | Nonanoic acid | CH3(CH2)7COOH | Pelargonium plant |
10 | Capric acid | Decanoic acid | CH3(CH2)8COOH | Coconut and Palm kernel oil |
11 | Undecylic acid | Undecanoic acid | CH3(CH2)9COOH | Anti-fungal agent |
12 | Lauric acid | Dodecanoic acid | CH3(CH2)10COOH | Coconut oil and hand wash soaps |
13 | Tridecylic acid | Tridecanoic acid | CH3(CH2)11COOH | Plant metabolite |
14 | Myristic acid | Tetradecanoic acid | CH3(CH2)12COOH | Nutmeg |
15 | Pentadecylic acid | Pentadecanoic acid | CH3(CH2)13COOH | Milk fat |
16 | Palmitic acid | Hexadecanoic acid | CH3(CH2)14COOH | Palm oil |
17 | Margaric acid | Heptadecanoic acid | CH3(CH2)15COOH | Pheromone in various animals |
18 | Stearic acid | Octadecanoic acid | CH3(CH2)16COOH | Chocolate, waxes, soaps, and oils |
19 | Nonadecylic acid | Nonadecanoic acid | CH3(CH2)17COOH | Fats, vegetable oils, pheromone |
20 | Arachidic acid | Icosanoic acid | CH3(CH2)18COOH | Peanut oil |
Compound class | Members |
---|---|
unsaturated monocarboxylic acids | acrylic acid (2-propenoic acid) – CH2=CH−COOH, used in polymer synthesis |
Fatty acids | medium to long-chain saturated and unsaturated monocarboxylic acids, with even number of carbons; examples: docosahexaenoic acid and eicosapentaenoic acid (nutritional supplements) |
Amino acids | the building-blocks of proteins |
Keto acids | acids of biochemical significance that contain a ketone group; examples: acetoacetic acid and pyruvic acid |
Aromatic carboxylic acids | containing at least one aromatic ring; examples: benzoic acid – the sodium salt of benzoic acid is used as a food preservative; salicylic acid – 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 |
Dicarboxylic acids | containing two carboxyl groups; examples: adipic acid the monomer used to produce nylon and aldaric acid – a family of sugar acids |
Tricarboxylic acids | containing three carboxyl groups; examples: citrus fruits and isocitric acid
|
Alpha hydroxy acids |
containing a hydroxy group in the first position; examples: glyceric acid, glycolic acid and lactic acid (2-hydroxypropanoic acid) – found in sour milk, tartaric acid – found in wine |
Beta hydroxy acids |
containing a hydroxy group in the second position |
Omega hydroxy acids | containing a hydroxy group beyond the first or second position |
Divinylether fatty acids | containing a doubly unsaturated carbon chain attached via an ether bond to a fatty acid, found in some plants |
Physical properties
Solubility
Carboxylic acids are
Boiling points
Carboxylic acids tend to have higher boiling points than water, because of their greater surface areas and their tendency to form stabilized dimers through hydrogen bonds. For boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporized, increasing the enthalpy of vaporization requirements significantly.
Acidity
Carboxylic acids are Brønsted–Lowry acids because they are proton (H+) donors. They are the most common type of organic acid.
Carboxylic acids are typically
Carboxylic acid[4] | pKa |
---|---|
Formic acid (HCO2H) | 3.75 |
Chloroformic acid (ClCO2H) | 0.27[5] |
Acetic acid (CH3CO2H) | 4.76 |
Glycine (NH2CH2CO2H) | 2.34 |
Fluoroacetic acid (FCH2CO2H) | 2.586 |
Difluoroacetic acid (F2CHCO2H) | 1.33 |
Trifluoroacetic acid (CF3CO2H) | 0.23 |
Chloroacetic acid (ClCH2CO2H) | 2.86 |
Dichloroacetic acid (Cl2CHCO2H) | 1.29 |
Trichloroacetic acid (CCl3CO2H) | 0.65 |
Benzoic acid (C6H5−CO2H) | 4.2 |
2-Nitrobenzoic acid (ortho-C6H4(NO2)CO2H) | 2.16 |
Oxalic acid (HO−C(=O)−C(=O)−OH) (first dissociation) | 1.27 |
Hydrogen oxalate (HO−C(=O)−CO−2) (second dissociation of oxalic acid) | 4.14 |
Odour
Carboxylic acids often have strong sour odours.
Characterization
Carboxylic acids are readily identified as such by
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 aminocarboxylic acids are the main components of proteins.
Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives. Industrially important carboxylic acids include acetic acid (component of vinegar, precursor to solvents and coatings), acrylic and methacrylic acids (precursors to polymers, adhesives), adipic acid (polymers), citric acid (a flavor and preservative in food and beverages), ethylenediaminetetraacetic acid (chelating agent), fatty acids (coatings), maleic acid (polymers), propionic acid (food preservative), 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 for the production of acetic acid. Formic acid is prepared by a different carbonylation pathway, also starting from methanol.
- Oxidation of aldehydes 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. propene.[7]
- Oxidation of ethene using silicotungstic acid 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 alkynes is catalyzed by strong acids. Hydrocarboxylations involve the simultaneous addition of water and CO. Such reactions are sometimes called "Reppe chemistry."
- HC≡CH + CO + H2O → CH2=CH−CO2H
- Hydrolysis of soap making.
- Fermentation of ethanol. This method is used in the production of vinegar.
- The Kolbe–Schmitt reaction provides a route to salicylic acid, precursor to aspirin.
Laboratory methods
Preparative methods for small scale reactions for research or for production of fine chemicals often employ expensive consumable reagents.
- Jones reagent, potassium permanganate, or sodium chlorite. 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.[citation needed]
- Oxidative cleavage of .
- Hydrolysis of nitriles, esters, or amides, usually with acid- or base-catalysis.
- Carbonation of a organolithiumreagents:
- methyl ketones in the haloform reaction
- Base-catalyzed cleavage of non-enolizable ketones, especially aryl ketones:[8]
- R−C(=O)−Ar+ H2O → R−CO2H + 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 in the Cannizzaro reaction
- Rearrangement of diketones in the benzilic acid rearrangement
- Involving the generation of benzoic acids are the von Richter reaction from nitrobenzenes and the Kolbe–Schmitt reaction from phenols.
Reactions
The most widely practiced reactions convert carboxylic acids into
- CH3COOH + NaHCO3 → CH3COO−Na+ + CO2 + H2O
Carboxylic acids also react with alcohols to give esters. This process is widely used, e.g. in the production of polyesters. Likewise, carboxylic acids are converted into amides, 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 acids into peptides is a significant biochemical process that requires ATP.
The hydroxyl group on carboxylic acids may be replaced with a chlorine atom using thionyl chloride to give acyl chlorides. In nature, carboxylic acids are converted to thioesters.
Reduction
Like
Specialized reactions
- As with all carbonyl compounds, the protons on the keto–enol tautomerization. Thus, the α-carbon is easily halogenated in the Hell–Volhard–Zelinsky halogenation.
- The Schmidt reaction converts carboxylic acids to amines.
- Carboxylic acids are decarboxylated in the Hunsdiecker reaction.
- The Dakin–West reaction converts an amino acid to the corresponding amino ketone.
- In the Arndt–Eistert synthesis, where an acid is converted into acyl halide, which is then reacted with diazomethaneto give one additional methylene in the aliphatic chain.
- Many acids undergo decarboxylases(EC 4.1.1).
- Carboxylic acids are reduced to aldehydes via the ester and 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 intermediatewhich 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
See also
- Acid anhydride
- Acid chloride
- Amide
- Amino acid
- Ester
- List of carboxylic acids
- Dicarboxylic acid
- Pseudoacid
- Thiocarboxy
- Carbon dioxide (CO2)
References
- ^ Recommendations 1979. Organic Chemistry IUPAC Nomenclature. Rules C-4 Carboxylic Acids and Their Derivatives.
- ^ ISBN 0-13-643669-2.
- ISBN 978-1439855119.
- ^ "Chlorocarbonic acid". Human Metabolome Database.
- ^ Smith, Brian. "The C=O Bond, Part VIII: Review". Spectroscopy. Retrieved 12 February 2024.
- ISBN 3527306730..
- .
- ; Collected Volumes, vol. 8, p. 498.
- .
- .
External links
- Carboxylic acids pH and titration – freeware for calculations, data analysis, simulation, and distribution diagram generation
- PHC.