A diketone is a molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 containing two ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

 groups

Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

. The simpliest diketone is diacetyl

Diacetyl

Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone with the molecular formula C4H6O2...

, also known as 2,3-butanedione. Diacetyl, acetylacetone

Acetylacetone

Acetylacetone is an organic compound that famously exists in two tautomeric forms that rapidly interconvert. The less stable tautomer is a diketone formally named pentane-2,4-dione. The more common tautomer is the enol form. The pair of tautomers rapidly interconvert and are treated as a single...

, and hexane-2,5-dione

Hexane-2,5-dione

Hexane-2,5-dione, C6H10O2, is a diketone and a toxic metabolite of hexane.-Symptoms:The initial symptoms of chronic hexane toxicity, attributable to hexane-2,5-dione, are tingling and cramps in the arms and legs, followed by general muscular weakness...

 are examples of 1,2-, 1,3-, and 1,4-diketones, respectively. Dimedone

Dimedone

Dimedone is a cyclic diketone used in organic chemistry to determine whether a compound contains an aldehyde group. Cyclohexanediones in general can be used as catalysts in the formation of transition-metal complexes. Other uses include applications in colourimetry, crystallography, luminescence...

 is an example of a cyclic diketone.

Reactions

1,3-Diketones, such as acetylacetone, are particularly prone to form stable enols or enolates because of conjugation

Conjugated system

In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the...

 of the enol or enolate with the other carbonyl group, and the stability gained in forming a six-membered ring, (hydrogen bonded in the case of the enol or containing the counter ion in the case of the enolate).

The conjugate base derived from 1,3-ketones form complexes with metal ions.

Diketones with one or two methylene groups separating the carbonyl groups typically coexist with their enol tautomer

Tautomer

Tautomers are isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization. This reaction commonly results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond...

s. The reactions of such dicarbonyls are very similar to those of simple ketones.

In the DeMayo reaction

DeMayo reaction

The DeMayo reaction is a photochemical reaction in which the enol of a 1,3-diketone reacts with an alkene and the resulting cyclobutane ring undergoes a retro-aldol reaction to yield a 1,5-diketone :...

 1,3-diketones react with alkenes in a photochemical pericyclic reaction

Pericyclic reaction

In organic chemistry, a pericyclic reaction is a type of organic reaction wherein the transition state of the molecule has a cyclic geometry, and the reaction progresses in a concerted fashion. Pericyclic reactions are usually rearrangement reactions...

 to form (substituted) 1,5-diketones.

EU Regulation 

In 2004, the EU conducted an examination of certain flavoring additives

Food additive

Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

 grouped together as "Flavouring Group Evaluation FGE.11". This group included diketones. As part of that study, the EU found that acetylacetone (pentane-2,4-dione) (FL 07.191) was genotoxic

Genotoxic

In genetics, genotoxicity describes a deleterious action on a cell's genetic material affecting its integrity. This includes both certain chemical compounds and certain types of radiation....

in vivo and in vitro, and deleted it from the register of permitted flavoring substances. The register of permitted flavoring substances was adopted in 1999.