thioketene
{{Short description|1=Organic compounds with the structure >C=C=S}}
File:Thioketenes General Structure.png
In organic chemistry, thioketenes are organosulfur compounds analogous to ketenes with the general formula {{chem2|R2C\dC\dS}}, where R is alkyl or aryl. The parent thioketene (ethenthione) has the formula {{chem2|CH2\dC\dS}}. It is the simplest thioketene.{{cite journal |doi=10.1080/01961779208046190|title=Thio-, Seleno-, and Telluroketenes |year=1992 |last1=Nørkjær |first1=Kim |last2=Senning |first2=Aexander |journal=Sulfur Reports |volume=11 |issue=2 |pages=361–384 }} 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.Otto-Albrecht Neuman (Editor). Rompps Encyclopedia of Chemistry, Frank'sche Publishing House, Stuttgart, 1983, 8. Edition, p. 4242, {{ISBN|3-440-04513-7}}. It has been suggested that thioketenes could be involved in cell damage processes.{{cite journal |last1=Dekant |first1=Wolfgang |last2=Urban |first2=Gudrun |last3=Goersmann |first3=Claus |last4=Anders |first4=M.W. |year=1991 |title=Thioketene formation from α-haloalkenyl 2-nitrophenyl disulfides: models for biological reactive intermediates of cytotoxic S-conjugates |journal=J. Am. Chem. Soc. |volume=113 |issue=13 |pages=5120–5122 |doi=10.1021/ja00013a090}}
Isolable thioketenes
Thioketenes can be stabilized by either steric protection or by electronic effects. Thus, di-tert-butylthioketene is easily isolated and air-stable.{{cite journal |doi=10.1021/jo01271a027|title=Di-tert-Butylthioketene |year=1968 |last1=Elam |first1=E. U. |last2=Rash |first2=F. H. |last3=Dougherty |first3=J. T. |last4=Goodlett |first4=V. W. |last5=Brannock |first5=K. C. |journal=The Journal of Organic Chemistry |volume=33 |issue=7 |pages=2738–2741 }} 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.{{cite journal |doi=10.1002/cber.19791120738|title=Kristall‐ und Molekülstruktur eines Ketens, eines Thioketens und eines Thioketen‐S‐oxids |year=1979 |last1=Schaumann |first1=Ernst |last2=Harto |first2=Surya |last3=Adiwidjaja |first3=Gunadi |journal=Chemische Berichte |volume=112 |issue=7 |pages=2698–2708 }} These compound are prepared by treatment of the acid chloride with phosphorus pentasulfide as described by the following idealized equation:
:{{chem2|1=RCH2COCl + P4S10 -> RCH=C=S + HCl + "P4S9O"}}
Bis(trifluoromethyl)thioketene ({{chem2|(CF3)2C\dC\dS}}) is an example of an electronically stabilized thioketene.{{cite journal | last1 = Raasch | first1 = Maynard S. | year = 1970 | title = Bis(trifluoromethyl)thioketene. I. Synthesis and Cycloaddition Reactions | journal = J. Org. Chem. | volume = 35 | issue = 10 | pages = 3470–3483 | doi = 10.1021/jo00835a064 }}
Reactions
Thioketenes are electrophilic. They add amines to give thioamides:
:{{chem2|R2C\dC\dS + HNR'2 -> R2CH\sC(S)\sNR'2}}
With peroxyacids, they produce thioketene-S-oxides:
:{{chem2|R2C\dC\dS + R'CO3H -> R2C\dC\dS\dO + R'CO2H}}
Thioketenes bind to metal carbonyls giving adducts.{{cite journal |doi=10.1016/0022-328x(89)88030-1|title=Übergangsmetall-heteroallen-komplexe |year=1989 |last1=Seitz |first1=Karsten |last2=Benecke |first2=Jörg |last3=Behrens |first3=Ulrich |journal=Journal of Organometallic Chemistry |volume=371 |issue=2 |pages=247–256 }}
Related compounds
- carbon subsulfide ({{chem2|S\dC\dC\dC\dS}}).