In organic chemistry, thioketenes are organosulfur compounds analogous to ketenes with the general formula , where R is alkyl or aryl. The parent thioketene (ethenthione) 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.
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 HOMOâÂÂLUMO gap. These compound are prepared by treatment of the acid chloride with phosphorus pentasulfide as described by the following idealized equation:
Bis(trifluoromethyl)thioketene () is an example of an electronically stabilized thioketene.
Thioketenes are electrophilic. They add amines to give thioamides:
With peroxyacids, they produce thioketene-S-oxides:
Thioketenes bind to metal carbonyls giving adducts.