Thioketene
In organic chemistry, thioketenes are organosulfur compounds analogous to ketenes with the general formula, where R is alkyl or aryl. The parent thioketene has the formula. It is the simplest thioketene. Ethenthione is stable as a gas, but like most thioketenes, it polymerizes upon condensation.
Some thioketenes are produced as transient species upon pyrolysis of 1,2,3-thiadiazoles. It has been suggested that thioketenes could be involved in cell damage processes.
Isolable thioketenes
Thioketenes can be stabilized by either steric protection or by electronic effects. Thus, di-tert-butylthioketene is easily isolated and air-stable. Several examples have been characterized by X-ray crystallography. The C=S distance is 157 pm and the C=C distance is 124 pm, both bonds being suitable for the C=C=S assignment. The violet color characteristic of thioketenes indicates the small HOMO-LUMO gap. These compound are prepared by treatment of the acid chloride with phosphorus pentasulfide as described by the following idealized equation:Bisthioketene is an example of an electronically stabilized thioketene.
Reactions
Thioketenes are electrophilic. They add amines to give thioamides:With peroxyacids, they produce thioketene-S-oxides:
Thioketenes bind to metal carbonyls giving adducts.