Organic sulfide

Source: Wikipedia, the free encyclopedia.
(Redirected from
Thioether
)

General structure of a sulfide with the blue marked functional group.

In

organosulfur functional group with the connectivity R−S−R' as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors.[1] A sulfide is similar to an ether except that it contains a sulfur atom in place of the oxygen. The grouping of oxygen and sulfur in the periodic table
suggests that the chemical properties of ethers and sulfides are somewhat similar, though the extent to which this is true in practice varies depending on the application.

Nomenclature

Sulfides are sometimes called thioethers, especially in the old literature. The two organic substituents are indicated by the prefixes. (CH3)2S is called

dimethylsulfide. Some sulfides are named by modifying the common name for the corresponding ether. For example, C6H5SCH3 is methyl phenyl sulfide, but is more commonly called thioanisole, since its structure is related to that for anisole
, C6H5OCH3.

The modern systematic nomenclature in chemistry for the trival name thioether is sulfane.[2]

Structure and properties

Sulfide is an angular functional group, the C–S–C angle approaching 90° The C–S bonds are about 180 

pm
. For the prototype, dimethylsulfide, the C-S-C angles is 99°, which is smaller than the C-O-C angle in ether (~110°). The C-S distance in dimethylsulfide is 1.81 Å.[3]

Sulfides are characterized by their strong odors, which are similar to thiol odor. This odor limits the applications of volatile sulfides. In terms of their physical properties they resemble ethers, but are less volatile, higher melting, and less hydrophilic. These properties follow from the polarizability of the divalent sulfur center, which is greater than that for oxygen in ethers.

Thiophenes

delocalized into the π-system. As a consequence, thiophene exhibits few properties expected for a sulfide – thiophene is non-nucleophilic at sulfur and, in fact, is sweet-smelling. Upon hydrogenation, thiophene gives tetrahydrothiophene
, C4H8S, which indeed does behave as a typical sulfide.

Occurrence and applications

Sulfides are important in biology, notably in the amino acid methionine and the cofactor biotin. Petroleum contains many organosulfur compounds, including sulfides. Polyphenylene sulfide is a useful high temperature plastic. Coenzyme M, CH
3SCH
2CH
2SO−
3, is the precursor to methane (i.e. natural gas) via the process of methanogenesis.

coenzyme-M, the amino acid methionine, the vitamin biotin, and the engineering plastic polyphenylene sulfide
.

Preparation

Sulfides are typically prepared by

Michael acceptors.[4]

RBr + HSR' → RSR' + HBr

Such reactions are usually conducted in the presence of a base, which converts the thiol into the more nucleophilic thiolate.[5] Analogously, the reaction of disulfides with organolithium reagents produces thioethers:

R3CLi + R1S-SR2 → R3CSR1 + R2SLi

Analogous reactions are known starting with Grignard reagents.

Alternatively, sulfides can be synthesized by the addition of a thiol to an alkene in the thiol-ene reaction:

R-CH=CH2 + H-SR' → R-CH2-CH2-S-R'

This reaction is often catalysed by

free radicals produced from a photoinitiator.[6]

Sulfides can also be prepared by many other methods, such as the Pummerer rearrangement. Trialkysulfonium salts react with nucleophiles with a dialkyl sulfide as a leaving group:

Nu− + R3S+ → Nu-R + R2SR1

This reaction is exploited in biological systems as a means of transferring an

alkyl group. For example, S-adenosylmethionine acts as a methylating agent in biological SN2 reactions
.

An unusual but well tested method for the synthesis of thioethers involves addition of alkenes, especially ethylene across the S-Cl bond of sulfur dichloride. This method has been used in the production of bis(2-chloroethyl)sulfide, a mustard gas:[7]

SCl2 + 2 C2H4 → (ClC2H4)2S

Reactions

The

trimethylsulfonium iodide:[8]

S(CH3)2 + CH3I → [S(CH3)3]+I−

Sulfides also oxidize easily to sulfoxides (R−S(=O)−R), which can themselves be further oxidized to sulfones (R−S(=O)2−R). Hydrogen peroxide is a typical oxidant—for example, with dimethyl sulfide (S(CH3)2):[9]

S(CH3)2 + H2O2 → OS(CH3)2 + H2O
OS(CH3)2 + H2O2 → O2S(CH3)2 + H2O

In analogy to their easy alkylation, sulfides bind to metals to form

1,4,7-trithiacyclononane
.

Sulfides undergo hydrogenolysis in the presence of certain metals:

R-S-R' + 2 H2 → RH + R'H + H2S

Raney nickel is useful for stoichiometric reactions in organic synthesis[11] whereas molybdenum-based catalysts are used to "sweeten" petroleum fractions, in the process called hydrodesulfurization.

Unlike

ethers, thioethers are stable in the presence of Grignard reagents.[12] The protons adjacent to the sulfur atom are labile, and can be deprotonated with strong bases.[13]

References

  1. ISBN 0-471-95512-4
    .
  2. ISBN 978-3-64256765-0
    . p. 131: Individual species of the genus thioether can again most uniformly be named as ...sulfane and ...sulfanyl derivatives, respectively (formerly: ...sulfides and ...thio derivatives, respectively). [...] Cyclic sulfides (thioethers) are treated as heterocycles, in the same way as their ether counterparts. Polysulfides substituted at both ends are named substitutively as ...polysulfanes (formerly: ...polysulfides). (230 pages)
  3. doi:10.1246/bcsj.50.2564
    .
  4. doi:10.1021/cr500235v
    .
  5. doi:10.15227/orgsyn.058.0143
    .
  6. PMID 20166107
    .
  7. ISBN 0-7637-2425-4
    .
  8. ^ Brendsma & Arens 1967, p. 596.
  9. ^ Brendsma & Arens 1967, p. 601.
  10. ^ Brendsma & Arens 1967, p. 587.
  11. ^ Brendsma & Arens 1967, pp. 576–578.
  12. ^ Brendsma & Arens 1967, p. 581.
  13. ^ Brendsma & Arens 1967, pp. 555–559.
  • Brendsma, L.; Arens, J. F. (1967). "The chemistry of thioethers; differences and analogies with ethers". In Patai, Saul (ed.). The Chemistry of the Ether Linkage. The Chemistry of Functional Groups. London: Interscience / William Clowes and Sons. pp. 555–559.
    LCCN 66-30401
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Organic_sulfide&oldid=1219069183"