Editing Ketene (section)

==Reactions and applications==
Due to their [[cumulated double bond]]s, ketenes are very reactive.<ref name=":1">{{citation|surname1=Siegfried Hauptmann|title=Organische Chemie: mit 65 Tabellen|publisher=Deutscher Verlag für Grundstoffindustrie|location=Leipzig|at=pp.&nbsp;410–412|isbn=3871449024|date=1985|language=de
}}</ref>

=== Formation of carboxylic acid esters ===
By reaction with alcohols, [[carboxylic acid ester]]s are formed:

:[[File:Ketene_Reaktion1_V1.svg|380x380px|none]]

=== Formation of carboxylic anhydrides ===
Ketenes react with a carboxylic acids to form [[carboxylic acid anhydride]]s:

:[[File:Ketene_Reaktion2_V1.svg|450x450px|none]]

=== Formation of amides ===
Ketenes react with [[ammonia]] and [[amine]]s to give the corresponding [[amide]]s:
:[[File: Ketene Reaktion4 V1.svg|frameless|none|380x380px]]

=== Hydrolysis ===
By reaction with water, carboxylic acids are formed from ketenes:

:[[File: Ketene Reaktion6 V1.svg|frameless|none|350x350px]]

=== Formation of enol esters ===
Enol esters are formed from ketenes with [[enol]]isable [[carbonyl compounds]]. The following example shows the reaction of [[ethenone]] with [[acetone]] to form a propen-2-yl acetate:

:[[File: Ketene Reaktion7 V3 unlabeled.svg|frameless|none|480x480px]]

=== Dimerisation ===
At room temperature, ketene quickly dimerizes to [[diketene]], but the ketene can be recovered by heating:

:[[File:Dimerisation of ketene.png|frameless|Dimerisation of ketene|500px]]

=== [2+2]-cycloaddition ===
Ketenes can react with [[alkenes]], carbonyl compounds, [[carbodiimides]] and imines in a [[Enone–alkene cycloadditions|[2+2] cycloaddition]]. The example shows the synthesis of a [[β-lactam]] by the reaction of a ketene with an imine (see [[Staudinger synthesis]]):<ref name=":2">{{citation|surname1=Jie Jack Li|title=Name reactions. A collection of detailed reaction mechanisms|edition=3|publisher=Springer-Verlag|location=Berlin|at=pp.&nbsp;561-562|isbn=9783540300304|date=2006|language=de|doi=10.1007/3-540-30031-7
}}</ref><ref name=":3">{{citation|surname1=Hermann Staudinger|periodical=[[Justus Liebigs Annalen der Chemie]]|title=Zur Kenntnis der Ketene. Diphenylketen|volume=356|issue=1–2|publisher=John Wiley & Sons, Inc.|at=pp.&nbsp;51–123|date=1907|language=de|doi=10.1002/jlac.19073560106
|url=https://zenodo.org/record/1427571}}</ref>
:[[File:Staudinger-Synthese ÜV6.svg|frameless|none|450x450px]]

===Applications===
Ketenes are generally very reactive, and participate in various [[ketene cycloaddition]]s. One important process is the dimerization to give [[beta-propiolactone|propiolactone]]s. A specific example is the dimerization of the ketene of [[stearic acid]] to afford [[alkyl ketene dimer]]s, which are widely used in the paper industry.<ref name="Ullmann" /> AKD's react with the hydroxyl groups on the cellulose via [[esterification]] reaction.

They will also undergo [2+2] cycloaddition reactions with electron-rich [[alkyne]]s to form [[cyclobutenone]]s, or carbonyl groups to form beta-[[lactone]]s. With [[imine]]s, beta-lactams are formed. This is the Staudinger synthesis, a facile route to this important class of compounds. With [[acetone]], ketene reacts to give [[isopropenyl acetate]].<ref name="Ullmann" />

A variety of [[hydroxyl group|hydroxylic]] compounds can add as nucleophiles, forming either [[enol]] or [[ester]] products. As examples, a water molecule easily adds to ketene to give [[1,1-dihydroxyethene]] and [[acetic anhydride]] is produced by the reaction of [[acetic acid]] with ketene. Reactions between [[diol]]s ({{chem2|HO\sR\sOH}}) and bis-ketenes ({{chem2|O\dC\dCH\sR'\sCH\dC\dO}}) yield [[polyester]]s with a repeat unit of ({{chem2|\sO\sR\sO\sCO\sR'\sCO}}).

[[Ethyl acetoacetate]], an important starting material in organic synthesis, can be prepared using a [[diketene]] in reaction with [[ethanol]]. They directly form ethyl acetoacetate, and the yield is high when carried out under controlled circumstances; this method is therefore used industrially.