A ketene is an organic compound of the form R2C=C=O. Hermann Staudinger pioneered the research of ketenes. Ketene also refers to ethenone, the specific compound of this class in which both Rs are hydrogen.
Ethenone is colourless and has a sharp odour, and exposure to concentrated levels causes humans to experience irritation of body parts such as the eye
, and lung
. Pulmonary edema
has also been noted if these levels are experienced for an extended period of time. It has a melting
point of -150.5 °C (-239 °F) and a boiling
point of -56.1 °C (-69 °F).
- A base, usually triethylamine, removes the acidic proton alpha to the carbonyl group, inducing the formation of the carbon-carbon double bond and the loss of chloride ion.
- Ketenes are formed in the Wolff rearrangement from α-diazoketones
- Phenylacetic acid in the presence of base will lose water to produce phenylketene due to the high acidity of the alpha proton.
- Ethenone (CH2=C=O) can be prepared in the laboratory by pyrolysis of acetone vapor:
- CH3−CO−CH3 + Δ → CH2=C=O + CH4
Ketene is very reactive, tending to attach itself to other molecules in the form of an acetyl group
. It will react with itself to form cyclic dimers
known as diketenes
(oxetanones). It will also undergo [2+2] cycloaddition
reactions to electron-rich alkynes
to form cyclobutenones.
Reactions between diols (HO-R-OH) and bis-ketenes (O=C=CH-R'-CH=C=O) yield polyesters with a repeat unit of (-O-R-O-CO-R'-CO-).
Ethenone reacts with acetic acid to form acetic anhydride.