Thioacyl chloride

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General structure of the thioacyl chloride functional group Thioacyl chloride.png
General structure of the thioacyl chloride functional group

In organic chemistry, a thioacyl chloride is an organic compound containing the functional group −C(=S)Cl. Their formula is usually written R−C(S)Cl, where R is a side chain. Thioacyl chlorides are analogous to acyl chlorides, but much rarer and less robust. Indeed, one of the simplest, thioacetyl chloride (c.f. acetyl chloride), remained unknown as of 1972. [1] : 350 

Contents

Most thioacyl halides are "highly coloured, labile oils with pronounced pungent odours". [1] : 358  Simple alkyl derivatives are volatile. [1] : 359 

The best studied thioacyl chloride is thiobenzoyl chloride, a purple oil first prepared by chlorination of dithiobenzoic acid with a combination of chlorine and thionyl chloride. [2] [1] : 350–351  A more modern preparation employs phosgene as the chlorinating agent, [3] by-producing carbonyl sulfide:

PhCS2H + COCl2 → PhC(S)Cl + HCl + COS

One example of a thioacyl chloride has been crystallized. [4]

In general, thioacyl chlorides are produced from passing halocarbons through phosphorus pentasulfide or boiling sulfur. Such is the case for the simplest thioacyl chloride, thiophosgene. [1] : 351–352, 354  Thiocarbamyl and -carbonyl chlorides are prepared from the corresponding amines and alcohols by careful thiophosgenation. [1] : 356–358 

Reactions

Thioacyl chlorides are electrophilic at the carbon atom. Amines, alcohols, and thiols displace the chloride to form (respectively) thioamides, thionoesters, and dithioesters. [1] : 362–365  Friedel-Crafts reaction thioacylate arenes. [1] : 369–370 

Cyanide reacts with thioacyl chlorides to form thioacyl cyanides. These thioacyl cyanides are known to dimerize to dicyanoalkenes, eliminating sulfur. [1] : 365  Likewise thioacyl azide cyclizes to a thiatriazole, and diazo compounds and tetrazoles react to thiadiazoles. [1] : 366–368 

Like other unstabilized thiocarbonyls, thioacyl chlorides undergo a variety of dimerization and cycloaddition reactions. "Simple thiocarbonyl halides all show a tendency to dimerize to some degree, especially fluoro­thio­acyl fluorides," the only exception being trifluorothioacetyl fluoride. [1] : 370–371  Carbenes attack the double bond to form episulfides, and the double-bond in general is an extremely active dienophile. [1] : 371–372 

Safety

Thioacyl chlorides are toxic. [1] : 359 

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 Potts KT, Sapino C (1972). "Thiocarbonyl halides". In Saul Patai (ed.). Acyl Halides. PATAI'S Chemistry of Functional Groups. pp. 349–380. doi:10.1002/9780470771273.ch11. ISBN   9780470771273.
  2. ↑ Hermann Staudinger; Siegwart, J. (1920). "Ueber Thiobenzoylchlorid" [Thiobenzoyl chloride]. Helvetica Chimica Acta. 3: 824–833. doi:10.1002/hlca.19200030177.
  3. ↑ Viola H, Mayer R (1975). "Eine neue Darstellungsmethode für aromatische Thiocarbonsäurechloride" [A New Preparation Route for Aromatic Thiocarboxylic Acid Chlorides]. Z. Chem. 15 (9): 348. doi:10.1002/zfch.19750150904.
  4. ↑ Ogurtsov, Vladimir A.; Rakitin, Oleg A.; Rees, Charles W.; Smolentsev, Alexey A.; Belyakov, Pavel A.; Golovanov, Denis G.; Lyssenko, Konstantin A. (2005). "Synthesis of Thienothiopyranthiones by a New Molecular Rearrangement". Organic Letters. 7 (5): 791–794. doi:10.1021/ol0476669. PMID   15727442.
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