Thioether



A thioether (similar to sulfide) is a functional group in volatile thioethers characteristically have foul odors.[1]

A thioether is similar to an biotin.

Preparation

  • Thioethers are typically prepared by the thiols:
R-Br + HS-R' → R-S-R' + HBr

Such reactions are accelerated in the presence of base, which converts the thiol into the more nucleophilic thiolate.

  • An alternative method of synthesis includes the addition of a thiol to an free radicals:
R-CH=CH2 + HS-R' → R-CH2-CH2-S-R'

Reactions

  • While ethers are generally stable, thioethers (R-S-R) are easily oxidized to the dimethyl sulfide can be oxidized as follows:
S(CH3)2 + O → OS(CH3)2
OS(CH3)2 + O → O2S(CH3)2

Typical oxidants include peroxides.

  • The sulfur-sulfur bond in disulfides is susceptible to cleavage by nucleophiles, and reaction with a carbon nucleophile produces a thioether:
R3C- + R1S-SR2 → R3CSR1 + R2S-
  • Trialkysulfonium salts react with nucleophiles with a dialkyl sulfide as a leaving group:
Nu- + R3S+ → Nu-R + R-S-R

This reaction is exploited in biological systems as a means of transferring an SN2 reactions.

  • Ethers can be alkylated at oxygen only with difficulty to give highly reactive trialkyloxonium salts. In contrast, thioethers are readily alkylated to give stable sulfonium salts, such as trimethylsulfonium:
S(CH3)2 + CH3I → [S(CH3)3]+I-

Thiophenes

The tetrahydrothiophene, C4H8S, which indeed does behave as a typical thioether.

References

  1. ^ R. J. Cremlyn “An Introduction to Organosulfur Chemistry” John Wiley and Sons: Chichester (1996). ISBN 0-471-95512-4.
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