What is Thiol?

Thiols can be defined as a sulfur analog of alcohols that is in simple it is an organic compound consisting of compounds with a sulfur atom. It is also referred as mercaptan. It consists of sulfhydryl group, i.e., Thiol = R-SH.

Alcohols and Thiols share some similarity i.e. sulfur emergers to be a larger element compared to that of oxygen, the length of C–S bond is more than that of C–O bond. The hydrogen bonding between the thiol groups is much weaker in liquids or solids mainly because of the cohesive force. They exhibit low dipole moment than alcohol.

Properties of Thiol

Many thiols consist of odours that are usually strong which may be resembling scent of onions and garlic. Thiols possessing a low molecular weight consists of repulsive and strong smell. For example, consider skunks consisting of the lower molecular weight of thiol and it is easily detectable by humans. It is also responsible for some sort of wine faults that have resulted due to some unintended reactions caused between sulphur and yeast.

Not all kind of thiols holds bad odour; they are many other thiols with a pleasant smell. For example furan-2-yl methanethiol, responsible for the beautiful aroma of roasted coffee, monoterpenoid thiol responsible for the mesmerizing scent of a grapefruit. One can find it only at low concentration levels.

Thiols are less likely soluble in water. Thioether functional groups possess similar boiling points and solubility features, well this does not hold true for alcohols. Volatile thiols can be easily identified due to their distinctive odours.

Reactions of Thiol

Many reactions are exhibited by Thiols similar to that of hydroxyl compounds involving the formation of sulphides and thioesters. Oxidation would affect the sulphur atom in thiols, whereas in alcohol it would lead to the generation of a new product where it changes the oxidation state of a carbon atom.


Thiolates react with carbon disulphide to produce thioxanthate.

Metal ion complexation

Thiolates form transition metal thiolate complexes with metal ions.


Thiols readily oxidize through a reagent iodine, in the presence of a base to produce organic sulphide. The redox reaction of thiol is mentioned below.

2 R–SH + Br2 → R–S–S–R + 2 HBr

Reagents such as hydrogen peroxide or sodium hypochlorite can also produce sulfonic acids.

R–SH + 3 H2O2 → RSO3H + 3 H2O

In the presence of a catalyst, Oxidation can be affected by oxygen.

2 R–SH + 12 O2 → RS–SR + H2O

Participation of Thiols in thiol-disulfide exchange.

RS–SR + 2 R′SH → 2 RSH + R′S–SR′


Thiols are alkylated to give thioethers.

RSH + R′Br + B → RSR′ + [HB]Br


Thiols are more acidic in nature. Thiolate is a conjugate base of thiol. It is obtained from thiol treatment with alkali metal hydroxides.

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