Episulfide

Episulfides are a class of organic compounds 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]

General structure of an episulfide

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

History

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

Contemporary methods

Following the lead of Dachlauer and Jackel, contemporary routes to episulfides utilize a two-step method, converting an olefin to an epoxide followed by thiation using thiocyanate or thiourea.[3]

Episulfides can also be prepared from cyclic carbonates, hydroxy mercaptans, hydroxyalkyl halides, dihaloalkanes, and halo mercaptans.[3] The reaction of ethylene carbonate and KSCN gives ethylene sulfide:[4]

KSCN + C₂H₄O₂CO → KOCN + C₂H₄S + CO₂

The metal-catalyzed reaction of sulfur with alkenes has been demonstrated.[5]

alkene + "S" → episulfide

Reactions

Common uses of episulfides in both academic and industrial settings most often involve their use as monomers in polymerization reactions. Episulfides have an innate ring strain due to the nature of three-membered rings. Therefore, most reactions of episulfides involve ring-opening. Most commonly, nucleophiles are employed for the ring-opening process.[3] For terminal episulfide, nucleophiles attack the primary carbon. Nucleophiles include anionic hydride, thiolates, alkoxide, amines, and carbanions.

Applications

Thiiranes occur very rarely in nature and are of no significance medicinally.[1]

Very few commercial applications exist, although the polymerization of episulfide has been reported.[6]

Dithiiranes

Dithiiranes are three membered rings containing two sulfur atoms and one carbon. One example was prepared by oxidation of a 1,3-dithietane.[7]

Structure of a dithiirane.[7]

References

1. Wataru Ando Nami Choi Norihiro Tokitoh (1996). "Thiiranes and Thiirenes: Monocyclic". Comprehensive Heterocyclic Chemistry II. 1A. pp. 173–240. doi:10.1016/B978-008096518-5.00005-8. ISBN 9780080965185.CS1 maint: uses authors parameter (link)
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. 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. 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: 251–262. doi:10.1021/cr030005p. PMID 14719976.
6. 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. doi:10.1021/ja076056b. PMID 17999507.
7. 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.CS1 maint: uses authors parameter (link)