Ketene

A ketene is an organic compound of the form R′R″C=C=O, where R and R' are two arbitrary monovalent chemical groups (or two separate substitution sites in the same molecule). The name may also refers to the specific compound ethenone H2C=C=O, the simplest ketene. A ketene is an organic compound of the form R′R″C=C=O, where R and R' are two arbitrary monovalent chemical groups (or two separate substitution sites in the same molecule). The name may also refers to the specific compound ethenone H2C=C=O, the simplest ketene. Although they are highly useful, most ketenes are unstable. When used as reagents in a chemical procedure, they are typically generated when needed, and consumed as soon as (or while) they are produced. Ketenes were first studied as a class by Hermann Staudinger before 1905. Ethenone, the simplest ketene can be generated by pyrolysis (thermal cracking) of acetone: This reaction is called the Schmidlin ketene synthesis. Other ketenes can be prepared from acyl chlorides by an elimination reaction in which HCl is lost: In this reaction, 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 a chloride ion. Ketenes can also be formed from α-diazoketones by Wolff rearrangement. Another way to generate ketenes is through flash vacuum thermolysis (FVT) with 2-pyridylamines. Plüg and Wentrup developed a method in 1997 that improved on FVT reactions to produce ketenes with a stable FVT that is moisture insensitive, using mild conditions (480 °C). The N-pyridylamines are prepared via a condensation with R-malonates with N-amino(pyridene) and DCC as the solvent.