Ketenes can also be formed from α-diazoketones by Wolff rearrangement.
Phenylacetic acid in the presence of a base will lose water to produce phenylketene due to the high acidity of the alpha proton.
- CH3−CO−CH3 + ΔT → CH2=C=O + CH4
Ketenes are generally very reactive, and participate in various cycloadditions. They will also undergo [2+2] cycloaddition reactions with electron-rich alkynes to form cyclobutenones, or carbonyl groups to form beta-lactones. With imines beta-lactams are formed. This is the Staudinger synthesis, a facile route to this important class of compounds.
Ethyl acetoacetate, a very 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 good; this method is therefore used industrially.
- Hermann Staudinger (1905). "Ketene, eine neue Körperklasse". Berichte der deutschen chemischen Gesellschaft 38 (2): 1735–1739. doi:10.1002/cber.19050380283.
- Ketene in Organic Syntheses Organic Syntheses, Submitted by C. D. Hurd Checked by Oliver Kamm Coll. Vol. 1, p.330 (1941); Vol. 4, p.39 (1925).Link
- Schmidlin and Bergmann, Ber. 43, 2881 (1910);