Episulfide

In organic chemistry, an episulfide is an organic compound that contain a saturated, heterocyclic ring consisting of two carbon atoms and one sulfur atom. It is the sulfur analogue of an epoxide or aziridine. They are also known as thiiranes, olefin sulfides, thioalkylene oxides, and thiacyclopropanes. Episulfides are less common and generally less stable than epoxides. The most common derivative is ethylene sulfide (C2H4S).[1][2]

Structure

According to electron diffraction, the C−C and C−S distances in ethylene sulfide are respectively 1.473 and 1.811 Å. The C−C−S and C−S−C angles are respectively 66.0 and 48.0°.[1]

Preparation

A number of chemists in the early 1900s, including Staudinger and Pfenninger (1916), as well as Delepine (1920) studied episulfides. In 1934 Dachlauer and Jackel devised a general synthesis of episulfides from epoxides using alkali thiocyanates and thiourea.[3]

Episulfides can also be prepared from cyclic carbonates, hydroxyalkylthiols, halohydrins, dihaloalkanes, and chloroalkylthiols.[3] For example, the reaction of ethylene carbonate and KSCN gives ethylene sulfide:[4]

KSCN + C2H4O2CO → KOCN + C2H4S + CO2

Base converts monothiocarbonates to episulfides:[5]

RC2H3OSCO → RC2H3S + CO2

The metal-catalyzed reaction of sulfur with alkenes has been demonstrated but is of little preparative value.[6]

Tetrasubstituted thiiranes form spontaneously from the corresponding thiocarbonyl ylide.[7]

Reactions

Episulfides, due to their innate ring strain, often undergo ring-opening reactions, especially with nucleophiles.[3] For terminal episulfides, nucleophiles attack the primary carbon:

R2C(S)CH2 + NuH → R2CHCH2SNu

Nucleophiles include hydrides, thiolates, alkoxides, amines, and carbanions.

Like ordinary thioethers, episulfides can be oxidized to sulfoxides as in the synthesis of ethylene episulfoxide:

R2C(S)CH2 + H2O2 → R2C(SO)CH2 + H2O

In a related reactivity, episulfides are easily S-alkylated. With methyl bromide, the product is the ring-opened thioether:[8]

R2C(S)CH2 + R'Br → R2C(Br)CH2SR'

Such reactions proceed via episulfonium ions. Episulfonium salts can be prepared using trimethyloxonium tetrafluoroborate:

{{chem2|R2C(S)CH2 + (CH3)3OBF4 -> [[R2C(SCH3)CH2]BF4 + (CH3)2O'}}

Episulfide polymerize, especially in the presence of Lewis acids.[9]

Applications

Thiiranes occur rarely in nature but are found in some pharmaceuticals.[1] They are intermediate in the action of sulfur mustards, a family of chemical weapons.[11]

Dithiiranes consist of three-membered ring containing two sulfur atoms and one carbon. One example was prepared by oxidation of a 1,3-dithietane.[12]

Thiirenes are unsaturated episulfides, the parent having the formula C2H2S formally derived by the formal addition of sulfur atom to an alkyne. They are antiaromatic and rarely observed. S-Alkylthiirenium salts are, however, known.[13][14]

References

  1. ^ a b c Wataru Ando; Nami Choi; Norihiro Tokitoh (1996). "Thiiranes and Thiirenes: Monocyclic". Thiiranes and Thiirenes: Monocyclic. Comprehensive Heterocyclic Chemistry II. Vol. 1A. pp. 173–240. doi:10.1016/B978-008096518-5.00005-8. ISBN 978-0-08-096518-5.
  2. ^ Warren Chew; David N. Harpp (1993). "Recent aspects of thiirane chemistry". Journal of Sulfur Chemistry. 15 (1): 1–39. doi:10.1080/01961779308050628.
  3. ^ a b c Sander, M. Thiiranes. Chem. Rev. 1966, 66(3), 297-339. doi:10.1021/cr60241a004
  4. ^ Searles, S.; Lutz, E. F.; Hays, H. R.; Mortensen, H. E. (1962). "Ethylene Sulfide". Organic Syntheses. 42: 59. doi:10.15227/orgsyn.042.0059.
  5. ^ Reynolds, D. D.; Fields, D. L.; Johnson, D. L. (1961). "Mercaptoethylation. VII. Preparation of Some Cyclic Sulfides". The Journal of Organic Chemistry. 26 (12): 5130–5133. doi:10.1021/jo01070a084.
  6. ^ Adam, Waldemar; Bargon, Rainer M. (2004). "Synthesis of Thiiranes by Direct Sulfur Transfer: The Challenge of Developing Effective Sulfur Donors and Metal Catalysts". Chemical Reviews. 104 (1): 251–262. doi:10.1021/cr030005p. PMID 14719976.
  7. ^ Rolf Huisgen; J. Rapp (1997). "1,3-Dipolar Cycloadditions. 98. The Chemistry of Thiocarbonyl S-Sulfides". Tetrahedron. 53 (3): 950. doi:10.1016/S0040-4020(96)01068-X.
  8. ^ Dittmer, D.C. (1984). "Thiiranes and Thiirenes". Comprehensive Heterocyclic Chemistry. pp. 131–184. doi:10.1016/B978-008096519-2.00112-0. ISBN 978-0-08-096519-2.
  9. ^ Nakano, K.; Tatsumi, G.; Nazaki, K. (2007). "Synthesis of Sulfur-Rich Polymers: Copolymerization of Episulfide with Carbon Disulfide by Using [PPN]Cl/(salph)Cr(III)Cl System". J. Am. Chem. Soc. 129 (49): 15116–15117. Bibcode:2007JAChS.12915116N. doi:10.1021/ja076056b. PMID 17999507.
  10. ^ Elks J (14 November 2014). The Dictionary of Drugs: Chemical Data: Chemical Data, Structures and Bibliographies. Springer. pp. 492–. ISBN 978-1-4757-2085-3.
  11. ^ Mustard agents: description, physical and chemical properties, mechanism of action, symptoms, antidotes and methods of treatment. Organisation for the Prohibition of Chemical Weapons. Accessed June 8, 2010.
  12. ^ a b Ahhiko Ishii; Masamatsu Hoshino; Juzo Nakayama (2009). "Recent Advances in Chemistry of Dithiirane and Small Ring Compounds Containing Two Chalcogen Atoms". Pure Appl. Chem. 68 (4): 869–874. doi:10.1351/pac199668040869. S2CID 55817318.
  13. ^ Vilaivan, T.; Chavasiri, W.; Rashatasakhon, P. (2008). "Thiiranes and Thiirenes: Fused-ring Derivatives". Comprehensive Heterocyclic Chemistry III. pp. 391–431. doi:10.1016/B978-008044992-0.00106-1. ISBN 978-0-08-044992-0.
  14. ^ Poleschner, Helmut; Seppelt, Konrad (2013). "XeF2/Fluoride Acceptors as Versatile One-Electron Oxidants". Angewandte Chemie International Edition. 52 (49): 12838–12842. doi:10.1002/anie.201307161. PMID 24127390.
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