1,2-diketone
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In
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, a dicarbonyl is a
molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
containing two
carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...
()
groups A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...
. Although this term could refer to any
organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
containing two carbonyl groups, it is used more specifically to describe molecules in which both carbonyls are in close enough proximity that their reactivity is changed, such as 1,2-, 1,3-, and 1,4-dicarbonyls. Their properties often differ from those of monocarbonyls, and so they are usually considered functional groups of their own. These compounds can have symmetrical or unsymmetrical
substituent In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...
s on each carbonyl, and may also be functionally symmetrical (di
aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
s, di
ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
s, di
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, ''etc.'') or unsymmetrical (keto-esters,
keto-acid In organic chemistry, keto acids or ketoacids (also called oxo acids or oxoacids) are organic compounds that contain a carboxylic acid group () and a ketone group ().Franz Dietrich Klingler, Wolfgang Ebertz "Oxocarboxylic Acids" in Ullmann's En ...
s, ''etc.'').


1,2-Dicarbonyls


1,2-Dialdehyde

The only 1,2-dialdehyde is
glyoxal Glyoxal is an organic compound with the chemical formula OCHCHO. It is the smallest dialdehyde (a compound with two aldehyde groups). It is a crystalline solid, white at low temperatures and yellow near the melting point (15 °C). The liquid ...
, . Like many alkyldialdehydes, glyoxal is encountered almost exclusively as its hydrate and oligomers thereof. These derivatives often behave equivalently to the
aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
s since hydration is reversible. Glyoxal condenses readily with
amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...
s. Via such reactions, it is a precursor to many heterocycles, e.g.
imidazole Imidazole (ImH) is an organic compound with the formula . It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. It can be classified as a heterocycle, specifically as a diazole. Many natural products, ...
s.


1,2-Diketones

The principal diketone is
diacetyl Diacetyl ( ; IUPAC systematic name: butanedione or butane-2,3-dione) is an organic compound with the chemical formula (CH3CO)2. It is a yellow liquid with an intensely buttery flavor. It is a vicinal diketone (two C=O groups, side-by-side). Di ...
, also known as 2,3-butanedione, . 1,2-Diketones are often generated by oxidation (dehydrogenation) of the
diol A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol may also be called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting gro ...
s: :RCH(OH)CH(OH)R -> RC(O)C(O)R + 2 H2 2,3-Butanedione,
2,3-pentanedione Acetylpropionyl, also known as acetyl propionyl or 2,3-pentanedione, is an organic compound, specifically a diketone.Hardo Siegel, Manfred Eggersdorfer "Ketones" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. Uses f ...
, and 2,3-hexanedione are found in small amounts in various foods. They are used as aroma components in alcohol-free beverages and in baked goods.
Benzil Benzil (i.e. Bz2, systematically known as 1,2-diphenylethane-1,2-dione) is the organic compound with the formula ( C6H5 CO)2, generally abbreviated ( PhCO)2. This yellow solid is one of the most common diketones. Its main use is as a photoinitiat ...
, , is the corresponding diphenyl derivative. A distinctive feature of 1,2-diketones is the long C-C bond linking the carbonyl groups. This bond distance is about 1.54 Å, compared to 1.45 Å for the corresponding bond in
1,3-butadiene 1,3-Butadiene () is the organic compound with the formula CH2=CH-CH=CH2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two ...
. The effect is attributed to repulsion between the partial positive charges of the carbonyl carbon atoms. 1,2-Diketones condense with many bifunctional nucleophiles, such as
urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...
and
thiourea Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), with the oxygen atom replaced by sulfur atom (as implied by the '' thio-'' prefix). The properties of urea and thiourea differ s ...
to give heterocycles. Condensation with aromatic amines gives diketimine (). In the cases of
1,2-cyclohexanedione 1,2-Cyclohexanedione is an organic compound with the formula . It is one of three isomeric cyclohexanediones. It is a colorless compound that is soluble in a variety of organic solvents. It can be prepared by oxidation of cyclohexanone by sel ...
and
1,2-cyclopentanedione 1,2-Cyclopentanedione is the organic compound with the formula (CH2)3(CO)2. It is one of two isomeric cyclopentanediones, the other being 1,3-cyclopentanedione. It was first prepared by base-induced condensation of di ethylglutarate with dieth ...
, the
enol In organic chemistry, enols are a type of functional group or intermediate in organic chemistry containing a group with the formula (R = many substituents). The term ''enol'' is an abbreviation of ''alkenol'', a portmanteau deriving from "-ene ...
is about 1-3 kcal/mol more stable than the diketo form. ortho-Quinone, , is the parent of a large family of 1,2-diketones.


1,2-Ketoaldehydes

A well-known compound of this class is
methylglyoxal Methylglyoxal (MGO) is the organic compound with the formula CH3C(O)CHO. It is a reduced derivative of pyruvic acid. It is a reactive compound that is implicated in the biology of diabetes. Methylglyoxal is produced industrially by degradation ...
, , also known as pyruvaldehyde. These compounds are also known as 2-oxoaldehydes or α-ketoaldehydes.


1,2-Diesters and diacids

Oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...
and its esters define this family of compounds. The diacid is produced industrially by oxidation of waste sugars. It occurs naturally (as the conjugate base), notably in members of the plant species ''Oxalis''. Condensation of the diesters with
diamine A diamine is an amine with two amino groups. Diamines are used as monomers to prepare polyamides, polyimides, and polyureas. The term ''diamine'' refers mostly to Primary (chemistry), primary diamines, as those are the most reactive. In terms of ...
s gives cyclic diamides.


α-Keto- and formylcarboxylic acids

α-Keto-acids and -esters are well known.
Pyruvic acid Pyruvic acid (CH3COCOOH) is the simplest of the keto acids, alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is an metabolic intermediate, intermediate in several m ...
() is the parent α-ketoacid. Its conjugate base, pyruvate (), is a component of the
citric acid cycle The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of chemical reaction, biochemical reactions that release the energy stored in nutrients through acetyl-Co ...
and product of glucose metabolism (
glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvic acid, pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The Thermodynamic free energy, free energy released in this process is used to form ...
). The corresponding aldehyde-acid is
glyoxalic acid Glyoxylic acid or oxoacetic acid is an organic compound. Together with acetic acid, glycolic acid, and oxalic acid, glyoxylic acid is one of the C2 carboxylic acids. It is a colourless solid that occurs naturally and is useful industrially. Str ...
().


1,3-Dicarbonyls


1,3-Dialdehydes

The parent 1,3-dialdehyde is
malondialdehyde Malondialdehyde belong to the class of β-dicarbonyls. A colorless solid, malondialdehyde is a highly reactive compound that occurs as the enol. It is a physiological metabolite, and a marker for oxidative stress. Structure and synthesis Malon ...
(), a β-dicarbonyl. Like most dialdehydes, it is rarely encountered as such. Instead it is handled almost exclusively as its hydrate, methyl acetal, and oligomers thereof. These derivatives often behave like the parent. Many 2-substituted derivatives are known. They are often prepared by alkylation of the
enolate In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the Organic synthesis, synthesis of organic compounds. Bonding and structure Enolate ...
of malondialdehyde.


1,3-Diketones

1,3-Diketones are also called β-diketones. An important member is
acetylacetone Acetylacetone is an organic compound with the chemical formula . It is classified as a 1,3-diketone. It exists in equilibrium with a tautomer . The mixture is a colorless liquid. These tautomers interconvert so rapidly under most conditions that ...
, .
Dimedone Dimedone is an organic compound with the formula . Classified as a cyclic diketone, it is a derivative of 1,3-Cyclohexanedione, 1,3-cyclohexanedione. It is a white solid that is soluble in water, as well as ethanol and methanol. It once was used a ...
is a cyclic 1,3-diketone. 1,3-Indandione is the cyclic 1,3-diketone fused to a benzene ring. Acetylacetone is prepared industrially by the thermal rearrangement of isopropenylacetate. Another cyclic 1,3-diketone is
2,2,4,4-tetramethylcyclobutanedione 2,2,4,4-Tetramethylcyclobutanedione is the organic compound with the formula (CH3)4C4O2. The compound is a diketone of cyclobutane, bearing four methyl groups. It is a white solid that is used as a precursor to diverse industrial products. Synth ...
, which is a precursor to a useful
diol A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol may also be called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting gro ...
. :CH2(CH3)COC(O)Me -> MeC(O)CH2C(O)Me 1,3-Diketones often
tautomer In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...
ize to an
enol In organic chemistry, enols are a type of functional group or intermediate in organic chemistry containing a group with the formula (R = many substituents). The term ''enol'' is an abbreviation of ''alkenol'', a portmanteau deriving from "-ene ...
and ketol. They usually exist predominantly in the enol form . The percent enol in
acetylacetone Acetylacetone is an organic compound with the chemical formula . It is classified as a 1,3-diketone. It exists in equilibrium with a tautomer . The mixture is a colorless liquid. These tautomers interconvert so rapidly under most conditions that ...
,
trifluoroacetylacetone 1,1,1-Trifluoroacetylacetone is the organofluorine compound with the formula CFC(O)CHC(O)CH. It is a colorless liquid. Like other 1,3-diketones, it is used as a precursor to heterocycles, e.g. pyrazoles, and metal chelates. It is prepared by conde ...
, and
hexafluoroacetylacetone Hexafluoroacetylacetone is the chemical compound with the nominal formula CF3C(O)CH2C(O)CF3 (often abbreviated as hfacH). This colourless liquid is a ligand precursor and a reagent used in MOCVD. The compound exists exclusively as the enol CF3C( ...
are 85, 97, and 100%, respectively (neat, 33 °C). Cyclic 1,3-diketones, such as
1,3-cyclohexanedione 1,3-Cyclohexanedione is an organic compound with the formula (CH2)4(CO)2. It is one of three isomeric cyclohexanediones. It is a colorless compound that occurs naturally. It is the substrate for cyclohexanedione hydrolase. The compound exist ...
and
dimedone Dimedone is an organic compound with the formula . Classified as a cyclic diketone, it is a derivative of 1,3-Cyclohexanedione, 1,3-cyclohexanedione. It is a white solid that is soluble in water, as well as ethanol and methanol. It once was used a ...
, similarly exist significantly in the enol form. : Like other diketones, 1,3-diketones are versatile precursors to heterocycles. The conjugate base derived from 1,3-ketones can serve as
ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...
s to form metal acetylacetonate coordination complexes. In the
DeMayo reaction The DeMayo reaction is a photochemical reaction in which the enol of a 1,3-diketone reacts with an alkene (or another species with a C=C bond) and the resulting cyclobutane ring undergoes a retro-aldol reaction to yield a 1,5-diketone: The net e ...
1,3-diketones react with alkenes in a photochemical
pericyclic reaction In organic chemistry, a pericyclic reaction is the type of organic reaction wherein the transition state of the molecule has a cyclic geometry, the reaction progresses in a concerted fashion, and the bond orbitals involved in the reaction overl ...
to form (substituted) 1,5-diketones. Classically, 1,3-diketones are prepared by the
Claisen condensation The Claisen condensation is a carbon–carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base. The reaction produces a β-keto ester or a β- diketone. It is named ...
of a ketone with an ester.


1,3-Diesters and diacids

Malonic acid Malonic acid is a dicarboxylic acid with structure CH2(COOH)2. The ionized form of malonic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is malonic acid's diethyl ester. The name originates from ...
and its esters are the parent members of this class of dicarbonyls. Also common are the 2-substituted derivatives with the formula , which arise by C-alkylation of the conjugate base (the enolate) .


β-Keto-esters

β-Keto-esters arise readily by the condensation of a pair of esters. A well known example is
ethyl acetoacetate The organic compound ethyl acetoacetate (EAA) is the ethyl ester of acetoacetic acid. It is a colorless liquid. It is widely used as a chemical intermediate in the production of a wide variety of compounds. Preparation At large scale, ethyl ac ...
(although it is prepared by ethanolysis of
ketene In organic chemistry, a ketene is an organic compound of the form , where R and R' are two arbitrary valence (chemistry), monovalent functional group, chemical groups (or two separate Substituent, substitution sites in the same molecule). The na ...
).


1,4-Dicarbonyls


1,4-Dialdehydes

Succinaldehyde Succinaldehyde or Butanedial is an organic compound with the formula . It is a colorless viscous liquid. Typical of some other saturated dialdehydes, succinaldehyde is handled as the hydrates or methanol-derived acetal. It is a precursor to tropi ...
(CH2CHO)2 is the simplest and parent 1,4-dialdehyde. The aromatic derivative is
phthalaldehyde Phthalaldehyde (sometimes also ''o''-phthalaldehyde or ''ortho''-phthalaldehyde, OPA) is the chemical compound with the formula C6H4(CHO)2. It is one of three isomers of benzene dicarbaldehyde, related to phthalic acid. This pale yellow solid is ...
.


1,4-Diketones

Diketones with two methylene groups separating the carbonyl groups, also called γ-diketones, typically coexist with their
enol In organic chemistry, enols are a type of functional group or intermediate in organic chemistry containing a group with the formula (R = many substituents). The term ''enol'' is an abbreviation of ''alkenol'', a portmanteau deriving from "-ene ...
tautomer In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...
s. The preeminent member is
acetonylacetone 2,5-Hexanedione (Acetonylacetone) is an aliphatic diketone. It is a colorless liquid. In humans, it is a toxic metabolite of hexane and of 2-hexanone. Symptoms of poisoning The chronic toxicity of hexane is attributed to hexane-2,5-dione. The ...
. 1,4-Diketones are useful precursors to heterocycles via the
Paal–Knorr synthesis The Paal–Knorr synthesis is a reaction used to synthesize substituted furans, pyrroles, or thiophenes from diketone, 1,4-diketones. It is a synthetically valuable method for obtaining substituted furans and pyrroles, which are common structural ...
, which gives
pyrrole Pyrrole is a heterocyclic, aromatic, organic compound, a five-membered ring with the formula . It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-methylpyrrol ...
s: : This reactivity is the basis of the
neurotoxicity Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specifical ...
of γ-diketones. 1,4-Diketones are also precursor to
furan Furan is a Heterocyclic compound, heterocyclic organic compound, consisting of a five-membered aromatic Ring (chemistry), ring with four carbon Atom, atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as f ...
s and
thiophene Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a planar five-membered ring, it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its reacti ...
s. The condensation of 1,4-diketones (and related substrates) with
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly hazardous unless handled in solution as, for example, hydraz ...
s afford dihydropyridazines, which can be converted to
pyridazine Pyridazine is an aromatic, heterocyclic, organic compound with the molecular formula . It contains a six-membered ring with two adjacent nitrogen atoms. It is a colorless liquid with a boiling point of 208 °C. It is isomeric with two other ...
s. ''para''-quinone, C4H4(CO)2, is the parent of a large family of 1,4-diketones.


1,4-Diesters and diacids

Succinic acid Succinic acid () is a dicarboxylic acid with the chemical formula (CH2)2(CO2H)2. In living organisms, succinic acid takes the form of an anion, succinate, which has multiple biological roles as a metabolic intermediate being converted into fum ...
and its esters are the parent members of this family of 1,4-dicarbonyls. Succinic acid is notable as a component in the
citric acid cycle The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of chemical reaction, biochemical reactions that release the energy stored in nutrients through acetyl-Co ...
. It forms a cyclic acid anhydride,
succinic anhydride Succinic anhydride, is an organic compound with the molecular formula (CH2CO)2O. This colorless solid is the acid anhydride of succinic acid. Preparation In the laboratory, this material can be prepared by dehydration of succinic acid. Such dehy ...
. Unsaturated members include maleic and
fumaric acid Fumaric acid or ''trans''-butenedioic acid is an organic compound with the formula HO2CCH=CHCO2H. A white solid, fumaric acid occurs widely in nature. It has a fruit-like taste and has been used as a food additive. Its E number is E297. The sa ...
s and their esters.


1,5-Dicarbonyls


1,5-Dialdehydes

Glutaraldehyde Glutaraldehyde is an organic compound with the formula . The molecule consists of a five carbon chain doubly terminated with formyl (CHO) groups. It is usually used as a solution in water, and such solutions exists as a collection of hydrates, ...
(CH2)3(CHO)2 is the simplest and parent 1,5-dialdehyde. It hydrates readily. The aromatic analogue is
isophthalaldehyde Isophthalaldehyde is an organic compound with the formula C6H4(CHO)2. It is one of three isomers of benzene di carbaldehyde, a reduced analog of phthalic acid. It is a colorless solid, although commercial samples often appear yellowish. One prepa ...
.


1,5-Diketones

These diketones have three methylene groups separating the carbonyl groups.


1,5-Diesters and diacids

Glutaric acid Glutaric acid is the organic compound with the formula C3H6(COOH)2. Although the related "linear" dicarboxylic acids adipic and succinic acids are water-soluble only to a few percent at room temperature, the water-solubility of glutaric acid is o ...
(CH2)3(CO2H)2 is the parent 1,5-diacid.


Hydration and cyclization

Small aldehydes tend to hydrate. Hydration is prevalent for dialdehydes. Glyoxal forms a series of cyclic hydrates.
Succinaldehyde Succinaldehyde or Butanedial is an organic compound with the formula . It is a colorless viscous liquid. Typical of some other saturated dialdehydes, succinaldehyde is handled as the hydrates or methanol-derived acetal. It is a precursor to tropi ...
hydrates readily to give 2,5-dihydroxy­tetrahydro­furan. The aromatic
phthalaldehyde Phthalaldehyde (sometimes also ''o''-phthalaldehyde or ''ortho''-phthalaldehyde, OPA) is the chemical compound with the formula C6H4(CHO)2. It is one of three isomers of benzene dicarbaldehyde, related to phthalic acid. This pale yellow solid is ...
also forms hydrated. Similar hydration and cyclization equilibria apply to maleic dialdehyde,
glutaraldehyde Glutaraldehyde is an organic compound with the formula . The molecule consists of a five carbon chain doubly terminated with formyl (CHO) groups. It is usually used as a solution in water, and such solutions exists as a collection of hydrates, ...
, and adipaldehyde.


Safety

A number of dicarbonyl compounds are bioactive. Diacetyl is known to cause the lung disease
bronchiolitis obliterans Bronchiolitis obliterans (BO), also known as obliterative bronchiolitis, constrictive bronchiolitis and popcorn lung, is a disease that results in obstruction of the smallest airways of the lungs (bronchioles) due to inflammation. Symptoms inclu ...
in those individuals exposed to it in an occupational setting. Dialdehydes, e.g. glutaraldehyde and malonaldehyde, are fixatives or sterilizers.


See also

* Triketone


References

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