Thioacyl chloride

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

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

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m 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.
^ Hermann Staudinger; Siegwart, J. (1920). "Ueber Thiobenzoylchlorid" [Thiobenzoyl chloride]. Helvetica Chimica Acta. 3: 824–833. doi:10.1002/hlca.19200030177.
^ 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.
^ 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.

[Patai-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m 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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