Diketene

Diketene

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Names
IUPAC name 4-methylideneoxetan-2-one
Other names γ-methylenebutyrolactone
Identifiers
CAS Number	674-82-8 Y
ChemSpider	12140 Y
Jmol 3D model	Interactive image
InChI InChI=1S/C4H4O2/c1-3-2-4(5)6-3/h1-2H2 Y Key: WASQWSOJHCZDFK-UHFFFAOYSA-N Y InChI=1/C4H4O2/c1-3-2-4(5)6-3/h1-2H2 Key: WASQWSOJHCZDFK-UHFFFAOYAM
SMILES O=C1OC(=C)C1
Properties
Chemical formula	C4H4O2
Molar mass	84.08 g mol−1
Density	1.09 g cm−3
Melting point	−7 °C (19 °F; 266 K)
Boiling point	127 °C (261 °F; 400 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Diketene is an organic compound with the formula (CH₂CO)₂. It is formed by dimerization of ketene (IUPAC name: ethenone). Diketene is a member of the oxetane family. It is used as a reagent in organic chemistry. It is a colorless liquid.

Production

Ketene is generated by dehydrating acetic acid at 700–750 °C in the presence of triethyl phosphate as a catalyst or (in Switzerland and the CIS) by the thermolysis of acetone at 600–700 °C in the presence of carbon disulfide as a catalyst.

CH₃CO₂H → H₂C=C=O + H₂O (ΔH = +147 kJ/mol)

CH₃COCH₃ → H₂C=C=O + CH₄

Reactions

Heating or irradiation with UV light regenerates the ketene monomer:

(CH₂CO)₂ $\overrightarrow{\leftarrow}$ 2 CH₂CO

Alkylated ketenes also dimerize with ease and form substituted diketenes.

Diketene readily hydrolyses in water forming acetoacetic acid, its half-life in pure water is approximately 45 minutes a 25 °C at 2<pH<7.

Certain diketenes with two aliphatic chains, such as alkyl ketene dimer (AKD), are used industrially to improve hydrophobicity in paper.

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

H₂C=C=O + CH₃COOH → (CH₃CO)₂O (ΔH = −63 kJ/mol)

Acetoacetylation

Diketene also reacts with alcohols and amines to the corresponding acetoacetic acid derivatives. The process is sometimes called acetoacetylation. An example is the reaction with 2-aminoindane:

Diketene reaction Sai 2007

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. A typical reaction is:

ArNH₂ + (CH₂CO)₂ → ArNHC(O)CH₂C(O)CH₃

These acetoacetamides are precursors to arylide yellow and diarylide pigments.

Safety

Despite its high reactivity as an alkylating agent, and unlike analogue β-lactones propiolactone and β-butyrolactone, diketene is inactive as a carcinogen, possibly due to the instability of its DNA adducts.