# Diketene

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**Diketene** is an [organic compound](/source/Organic_compound) with the [molecular formula](/source/Molecular_formula) C4H4O2, and which is sometimes written as (CH2CO)2. It is formed by [dimerization](/source/Dimerization_(chemistry)) of [ketene](/source/Ethenone), H2C\dC\dO. Diketene is a member of the [oxetane](/source/Oxetane) family. It is used as a [reagent](/source/Reagent) in [organic chemistry](/source/Organic_chemistry).[1] It is a colorless liquid.

## Production

Diketene is produced on commercial scale by dimerization of [ketene](/source/Ethenone).[2]

## Reactions

Heating or irradiation with UV light[3] regenerates the ketene monomer:

- (C2H2O)2 <→ 2 CH2CO

Alkylated ketenes also dimerize with ease and form substituted diketenes.

Diketene readily hydrolyzes in water forming [acetoacetic acid](/source/Acetoacetic_acid). Its [half-life](/source/Half-life) in water is approximately 45 min. a 25 °C at 2 < [pH](/source/PH) < 7.[4]

Certain diketenes with two [aliphatic chains](/source/Aliphatic_compound), such as [alkyl ketene dimers](/source/Alkyl_ketene_dimer) (AKDs), are used industrially to improve [hydrophobicity](/source/Hydrophobe) in [paper](/source/Paper).

At one time acetic anhydride was prepared by the reaction of ketene with acetic acid:[5]

- H2C\dC\dO + CH3COOH → (CH3CO)2O ΔH = −63 kJ/mol

### Acetoacetylation

Diketene also reacts with [alcohols](/source/Alcohol_(chemistry)) and [amines](/source/Amine) to the corresponding acetoacetic acid derivatives. The process is sometimes called **acetoacetylation**. An example is the reaction with [2-aminoindane](/source/Indane):[6]

Diketene is an important industrial intermediate used for the production of acetoacetate esters and amides as well as substituted 1-phenyl-3-methylpyrazolones. The latter are used in the manufacture of dyestuffs and pigments.[7] A typical reaction is:

- ArNH2 + (CH2CO)2 → ArNHC(O)CH2C(O)CH3

These acetoacetamides are precursors to [arylide yellow](/source/Arylide_yellow) and [diarylide pigments](/source/Diarylide_pigment).[8]

## Use

Diketenes with two alkyl chains are used in the manufacture of paper for [sizing](/source/Sizing) of paper in order to improve their printability (by [hydrophobization](/source/Hydrophobization)). Besides the rosin resins with about 60% share of world consumption, long chain diketenes called alkylketene dimers (AKD) are with 16% share the most important synthetic paper sizes, they are usually used in concentrations of 0.15%, meaning 1.5 kg solid AKD/[t](/source/Ton) paper.

The preparation of AKD is carried out by chlorination of long chain fatty acids (such as [stearic acid](/source/Stearic_acid), using chlorinating agents such as [thionyl chloride](/source/Thionyl_chloride)) to give the corresponding acid chlorides and subsequent elimination of HCl by amines (for example [triethylamine](/source/Triethylamine)) in [toluene](/source/Toluene) or other solvents:[9]

Furthermore, diketenes are used as [intermediates](/source/Chemical_intermediate) in the manufacture of [pharmaceuticals](/source/Pharmaceuticals), [insecticides](/source/Insecticide) and [dyes](/source/Dye). For example [pyrazolones](/source/Pyrazolone) are formed from substituted [phenylhydrazines](/source/Phenylhydrazine), they were used as [analgetics](/source/Analgesics) but are now largely obsolete. With [methylamine](/source/Methylamine) diketene reacts to give [*N*,*N'*-dimethylacetoacetamide](/source/N,N'-dimethylacetoacetamide), a precursor to the (controversial) insecticide [monocrotophos](/source/Monocrotophos). Diketenes react with substituted aromatic amines to [acetoacetanilides](/source/Acetoacetanilide), which are important [precursors](/source/Precursor_(chemistry)) for many yellow, orange, and red [azo dyes](/source/Azo_dye) and [azo pigments](/source/Arylide_yellow).

Exemplary for the synthesis of arylides by the reaction of diketenes with aromatic amines is:

The product undergoes aromatic diazonium coupling with arylides to form azo dyes, such as [Pigment Yellow 74](/source/Pigment_Yellow_74).

The industrial synthesis of the sweetener acesulfam-K is based on the reaction of diketene with sulfamic acid and cyclization by [sulfur trioxide](/source/Sulfur_trioxide) (SO3).[10]

Drugs made from Diketene include:

1. [Lercanidipine](/source/Lercanidipine)
1. [Manidipine](/source/Manidipine)
1. [Olaquindox](/source/Olaquindox)
1. [Butoctamide](/source/Butoctamide)
1. [Ketazolam](/source/Ketazolam)
1. [Carboxin](/source/Carboxin)
1. [Ipramidil](/source/Ipramidil)

## Safety

Despite its high reactivity as an [alkylating agent](/source/Alkylating_agent), and unlike analogue β-lactones [propiolactone](/source/Beta-Propiolactone) and [β-butyrolactone](/source/%CE%92-butyrolactone), diketene is inactive as a carcinogen, possibly due to the instability of its [DNA adducts](/source/DNA_adduct).[11]

## References

1. [Beilstein](/source/Friedrich_Konrad_Beilstein) E III/IV 17: 4297.

1. Miller, Raimund; Abaecherli, Claudio; Said, Adel; Jackson, Barry (2001). "Ketenes". *Ullmann's Encyclopedia of Industrial Chemistry*. [doi:10.1002/14356007.a15_063](https://doi.org/10.1002/14356007.a15_063). ISBN 978-3-527-30385-4.

1. Susana Breda; Igor Reva; Rui Fausto (2012). "UV Induced Unimolecular Photochemistry of Diketene Isolated in Cryogenic Inert Matrices". *[J. Phys. Chem. A](/source/J._Phys._Chem._A)*. **116** (9): 2131–2140. [Bibcode:2012JPCA..116.2131B](https://ui.adsabs.harvard.edu/abs/2012JPCA..116.2131B). [doi:10.1021/jp211249k](https://doi.org/10.1021/jp211249k). [PMID 22273010](https://pubmed.ncbi.nlm.nih.gov/22273010)

1. Rafael Gómez-Bombarelli; Marina González-Pérez; María Teresa Pérez-Prior; José A. Manso; Emilio Calle; Julio Casado (2008). "Kinetic Study of the Neutral and Base Hydrolysis of Diketene". *[J. Phys. Org. Chem.](/source/J._Phys._Org._Chem.)*. **22** (5): 438–442. [doi:10.1002/poc.1483](https://doi.org/10.1002/poc.1483)

1. Arpe, Hans-Jürgen (2007), [*Industrielle organische Chemie: Bedeutende vor- und Zwischenprodukte*](https://books.google.com/books?id=36kHHvzx6M8C&q=wacker+verfahren+essigs%C3%A4ureanhydrid&pg=PA200) (in German), 6th ed., Weinheim: [Wiley-VCH](/source/Wiley-VCH), pp. 200–1, ISBN 978-3-527-31540-6[dead link]

1. Kiran Kumar Solingapuram Sai; Thomas M. Gilbert; Douglas A. Klumpp (2007). "Knorr Cyclizations and Distonic Superelectrophiles". *[J. Org. Chem.](/source/J._Org._Chem.)*. **72** (25): 9761–9764. [doi:10.1021/jo7013092](https://doi.org/10.1021/jo7013092). [PMID 17999519](https://pubmed.ncbi.nlm.nih.gov/17999519)

1. Ashford's Dictionary of Industrial Chemicals, Third Edition, 2011, pages 3241-2.

1. Hunger, K. & Herbst, W. (2012). "Pigments, Organic". *[Ullmann's Encyclopedia of Industrial Chemistry](/source/Ullmann's_Encyclopedia_of_Industrial_Chemistry)*. Weinheim: [Wiley-VCH](/source/Wiley-VCH). [doi:10.1002/14356007.a20_371](https://doi.org/10.1002/14356007.a20_371). ISBN 978-3527306732.

1. Wolf S. Schultz: [*Sizing Agents in Fine Paper*](http://www.tappi.org/Downloads/Conference-Papers/PM99813.aspx)[dead link] Retrieved 1 March 2012.

1. Rafael Gómez-Bombarelli; Marina González-Pérez; María Teresa Pérez-Prior; José A. Manso; Emilio Calle; Julio Casado (2008). "Chemical Reactivity and Biological Activity of Diketene". *[Chem. Res. Toxicol.](/source/Chem._Res._Toxicol.)*. **21** (10): 1964–1969. [doi:10.1021/tx800153j](https://doi.org/10.1021/tx800153j). [PMID 18759502](https://pubmed.ncbi.nlm.nih.gov/18759502)

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Adapted from the Wikipedia article [Diketene](https://en.wikipedia.org/wiki/Diketene) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Diketene?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.