Thioketene
In organic chemistry, thioketenes are organosulfur compounds analogous to ketenes with the general formula R2C=C=S, where R is alkyl or aryl. The parent thioketene (ethenethione) has the formula CH2=C=S. It is the simplest thioketene.[1] Ethenethione is stable as a gas, but like most thioketenes, it polymerizes upon condensation.
Synthesis
[edit]Thioketones may be prepared by treatment of acid chlorides with phosphorus pentasulfide as described by the following idealized equation:
- RR'CHC(O)Cl + P4S10 → RR'C=C=S + HCl + "P4S9O"
Some thioketenes are produced as transient species upon pyrolysis of 1,2,3-thiadiazoles.[2] Elimination from α-chloroalkenyl thiolates RR'C=C(Cl)S− also yields thioketenes.[3] These intermediates are believed to be responsible for the cytotoxicity and mutagenicity of trichloroethylene, as well as certain other polyhalogenated alkenes, with toxication occurring via conjugation with glutathione.[4][5]
Isolable thioketenes
[edit]Thioketenes can be stabilized by either steric protection or by electronic effects. Thus, di-tert-butyl thioketene is easily isolated and air-stable.[6] 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.[7]
Bis(trifluoromethyl)thioketene ((CF3)2C=C=S) is an example of an electronically stabilized thioketene.[8]
Reactions
[edit]Thioketenes are electrophilic. They add amines to give thioamides:[6]
- R2C=C=S + HNR'2 → R2CH−C(S)−NR'2
With peroxyacids, they produce thioketene-S-oxides:[7]
- R2C=C=S + R'CO3H → R2C=C=S=O + R'CO2H
Thioketenes bind to metal carbonyls giving adducts.[9]
Related compounds
[edit]- carbon subsulfide (S=C=C=C=S).
References
[edit]- ↑ Nørkjær, Kim; Senning, Aexander (1992). "Thio-, Seleno-, and Telluroketenes". Sulfur Reports. 11 (2): 361–384. doi:10.1080/01961779208046190.
- ↑ Neumüller, Otto-Albrecht; Römpp, Hermann [in German] (1988). Römpps Chemie-Lexikon. Bd. 6., T–Z [Römpp's Chemistry Lexicon] (in German). Vol. 6, T–Z (8, revised and expanded ed.). Stuttgart: Franckh. p. 4242. ISBN 3-440-04516-1. OCLC 1200574101.
- ↑ Dekant, Wolfgang; Urban, Gudrun; Goersmann, Claus; Anders, M.W. (1991). "Thioketene formation from α-haloalkenyl 2-nitrophenyl disulfides: models for biological reactive intermediates of cytotoxic S-conjugates". J. Am. Chem. Soc. 113 (13): 5120–5122. doi:10.1021/ja00013a090.
- ↑ Anders, M. W.; Lash, Lawrence; Dekant, Wolfgang; Elfarra, Adnan A.; Dohn, David R.; Reed, Donald J. (January 1988). "Biosynthesis and Biotransformation of Glutathione S-Conjugates to Toxic Metabolites". CRC Critical Reviews in Toxicology. 18 (4): 311–341. doi:10.3109/10408448809037470.
- ↑ Dekant, Wolfgang; Lash, Lawrence H.; Anders, M. W. (1988). "Fate of Glutathione Conjugates and Bioactivation of Cysteine S-Conjugates by Cysteine Conjugate β-Lyase". In Sies, Helmut; Ketterer, Brian (eds.). Glutathione Conjugation: Mechanisms and Biological Significance. London; New York: Academic Press. p. 429. ISBN 9780126427554.
- 1 2 Elam, E. U.; Rash, F. H.; Dougherty, J. T.; Goodlett, V. W.; Brannock, K. C. (1968). "Di-t-Butylthioketene". J. Org. Chem. 33 (7): 2738–2741. doi:10.1021/jo01271a027.
- 1 2 Schaumann, Ernst; Harto, Surya; Adiwidjaja, Gunadi (1979). "Kristall‐ und Molekülstruktur eines Ketens, eines Thioketens und eines Thioketen‐S‐oxids" [Crystal and Molecular Structures of a Ketene, a Thioketene, and a Thioketene S-Oxide]. Chemische Berichte (in German). 112 (7): 2698–2708. doi:10.1002/cber.19791120738.
- ↑ Raasch, Maynard S. (1970). "Bis(trifluoromethyl)thioketene. I. Synthesis and Cycloaddition Reactions". J. Org. Chem. 35 (10): 3470–3483. doi:10.1021/jo00835a064.
- ↑ Seitz, Karsten; Benecke, Jörg; Behrens, Ulrich (1989). "Übergangsmetall-heteroallen-komplexe: XXII. Zweikernige cobalt- und eisen-komplexe mit bis(trifluormethyl)- und bis(ethoxycarbonyl)thioketen als liganden" [Transition metal heteroallene complexes: XXII. Dinuclear cobalt and iron complexes with bis(trifluoromethyl) and bis(ethoxycarbonyl)thioketene as ligands]. Journal of Organometallic Chemistry (in German). 371 (2): 247–256. doi:10.1016/0022-328x(89)88030-1.