Thiol



 

In hydrogen atom (-SH). Being the sulfur analogue of an alcohol group (-OH), this functional group is referred to either as a thiol group or a sulfhydryl group. More traditionally, thiols are often referred to as mercaptans.

Nomenclature

When a thiol group is a alkane, there are several ways of naming the resulting thiol:

  • The preferred method (used by the IUPAC) is to add the suffix -thiol to the name of the alkane. The method is nearly identical to naming an alcohol. Example: CH3SH would be methanethiol.
  • An older method, the word mercaptan replaces alcohol in the name of the equivalent alcohol compound. Example: CH3SH would be methyl alcohol)
  • As a prefix, the terms sulfanyl or mercapto are used. Example: mercaptopurine.

Etymology

The term mercaptan comes from the Latin mercurius captans, meaning 'laying hold of mercury,' because the –SH group binds tightly to the element mercury.

Physical Properties

Odor

Many thiols are colorless monoterpenoid thiol, is responsible for the characteristic scent of grapefruit.

Boiling points and solubility

Due to the small polar solvents than alcohols of similar molecular weight. Thiols are as soluble and have similar boiling points to isomeric sulfides.

Chemical Properties

Synthesis

The methods used in making thiols are analogous to those used to make alcohols and ethers. The reactions are quicker and higher yielding because sulfur anions are better nucleophiles than oxygen atoms.

Thiols are formed when a halogenoalkane is heated with a solution of sodium hydrosulfide

CH3CH2Br + NaSH heated in ethanol(aq) → CH3CH2SH + NaBr

In addition, disulfides can be readily reduced by reducing agents such as lithium aluminium hydride in dry ether to form two thiols.

R-S-S-R' → R-SH + R'-SH

Reactions

The thiol group is the sulfur analog of the hydroxyl group (-OH) found in alcohols. Since bonding properties. Like alcohol, in general, the deprotonated form RS− (called a thiolate) is more chemically reactive than the protonated thiol form RSH

The chemistry of thiols is thus related to the chemistry of alcohols: thiols form vinyl groups to form a thioether linkage.)

Acidity

The sulfur atom of a thiol is quite disulfide (R-S-S-R).

2R-SH + Br2 → R-S-S-R + 2HBr

Oxidation by more powerful reagents such as sulfonic acids (RSO3H).

R-SH + 3H2O2 → RSO3H + 3H2O

Biological importance

As the functional group of the cysteine proteases.

Examples of thiols

See also

  • Thial
  • Thiol-disulfide exchange
v • d • e
Thioether • Thiol
 
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