Diketene

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Diketene
Diketene-2D-skeletal.png
Diketene-from-xtal-3D-balls.png
Names
IUPAC name
4-methylideneoxetan-2-one
Other names
γ-methylenepropiolactone
Identifiers
674-82-8 YesY
ChemSpider 12140 YesY
Jmol 3D model Interactive image
Properties
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.[1] It is a colorless liquid.

Production[edit]

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.[2]

CH3CO2H → H2C=C=O + H2O (ΔH = +147 kJ/mol)
CH3COCH3 → H2C=C=O + CH4

The dimerization to diketene proceeds spontaneously at room temperature.

Reactions[edit]

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

(CH2CO)2 ⇌ 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.[4]

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:[2]

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

Acetoacetylation[edit]

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:[5]

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.[6] A typical reaction is:

ArNH2 + (CH2CO)2 → ArNHC(O)CH2C(O)CH3

These acetoacetamides are precursors to arylide yellow and diarylide pigments.[7]

Use[edit]

Diketenes with two alkyl chains are used in the manufacture of paper for sizing of paper in order to improve their printability (by 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 paper.

The preparation of AKD is carried out by chlorination of long chain fatty acids (such as stearic acid, using chlorinating agents such as thionyl chloride) to give the corresponding acid chlorides and subsequent elimination of HCl by amines (for example triethylamine) in toluene or other solvents:[8]

Synthesis of alkylketene dimers (AKD)

Furthermore, diketenes are used as intermediates in the manufacture of pharmaceuticals, insecticides and dyes. For example pyrazolones are formed from substituted phenylhydrazines, they were used as analgesics but are now largely obsolete. With methylamine diketenes reacts to N,N'-dimethylacetoacetamide which is chlorinated with sulfuryl chloride and reacted with trimethyl phosphite to the highly toxic insecticide monocrotophos (especially toxic to bees). Diketenes react with substituted aromatic amines to acetoacetanilides, which are important precursors for mostly yellow, orange or red azo dyes and azo pigments.

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

Acetoacetanilid aus Diketen - Synthese von Aryliden

Aromatic diazonium coupling with arylides to form azo dyes, such as Pigment Yellow 74:

Synthese von Brilliantgelb.svg

The industrial synthesis of the sweetener acesulfame-K is based on the reaction of diketene with sulfamic acid and cyclization by SO3.[9]

Safety[edit]

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.[10]

References[edit]

  1. ^ Beilstein E III/IV 17: 4297.
  2. ^ a b Arpe, Hans-Jürgen (2007-01-11), Industrielle organische Chemie: Bedeutende vor- und Zwischenprodukte (6th ed.), Weinheim: Wiley-VCH, pp. 200–1, ISBN 3-527-31540-3 .
  3. ^ Susana Breda; Igor Reva; Rui Fausto (2012). "UV Induced Unimolecular Photochemistry of Diketene Isolated in Cryogenic Inert Matrices". J. Phys. Chem. A 116 (9): 2131–2140. doi:10.1021/jp211249k. 
  4. ^ 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". Phys. Org. Chem 22 (5): n/a. doi:10.1002/poc.1483. 
  5. ^ Kiran Kumar Solingapuram Sai; Thomas M. Gilbert; Douglas A. Klumpp (2007). "Knorr Cyclizations and Distonic Superelectrophiles". J. Org. Chem. 72 (25): 9761–9764. doi:10.1021/jo7013092. PMID 17999519. 
  6. ^ Ashford's Dictionary of Industrial Chemicals, Third Edition, 2011, pages 3241-2.
  7. ^ K. Hunger. W. Herbst "Pigments, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012. doi:10.1002/14356007.a20_371
  8. ^ Wolf S. Schultz: Sizing Agents in Fine Paper Abgerufen am 1. März 2012.
  9. ^ EP 0218076  Process for the preparation of the non-toxic salts of 6-methyl-3,4-dihydro-1,2,3-oxathiazin-4-on-2,2-dioxide.
  10. ^ 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. 21 (10): 1964–1969. doi:10.1021/tx800153j. PMID 18759502.