Thioether

In organic chemistry, a thioether (or sulfide) is a compound that contains the functional group formed by a sulfur bridge between two carbon chains (R-S-R&# 39; or R¹-S-R²) as shown on the right. Sulfur being analogous to an ether group (R-O-R'), this functional group is called a thioether group or sulfide group. Like many other sulfur-containing compounds, volatile thioethers have characteristic unpleasant odors.

A thioether is similar to an ether, containing a sulfur atom instead of an oxygen atom. Because oxygen and sulfur belong to the anphigenes in the periodic table, the chemical properties and reactivity of ethers and thioethers have some commonalities.

This functional group is important in biology, especially in the amino acid methionine and the cofactor biotin.

Preparation

• Tioeters are usually prepared for the rental of tioles:

R-Br + HS-R' → R-S-R' + HBr

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

• An alternative synthesis method includes the addition of tiol to an alcheno, typically catalyzed by free radicals:

R-CH=CH₂ + HS-R' → R-CH₂-CH₂-S-R'

• Tioeters can also be prepared via the Pummerer rearrangement.

Reactivity

• While ethers are generally stable, the thyoeters (R-S-R) are easily oxidized to sulfoxides (R-S(=O)-R), which can be further oxidized to sulfones (R-S(=O)₂-R).

For example, 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. As for example methyl and propyl sulfide.

Examples of thioethers

Due to their unpleasant odor, some thioethers are used as an additive to give odor to odorless domestic gases (methane, ethane, butane,...) such as methylthiol (CH₃ -SH).

The characteristic smell of onions and its spicy effect is due to propanethiol (CH₃-CH₂-CH₂-SH).

The characteristic odor of garlic and its spicy effect is due to diethyl sulfide (CH₃-CH₂-S-CH₂ >-CH₃).