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A dithiol is a type of organosulfur compound with two thiol functional groups. Their properties are generally similar to those of monothiols in terms of solubility, odor, and volatility. They can be classified according to the relative location of the two thiol group on the organic compound.
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Geminal dithiols
Geminal thiols have the formula RR'C(SH)2. They are derived from aldehydes and ketones by the action of hydrogen sulfide. Their stability contrasts with the rarity of germinal diols. Examples include methanedithiol, 1,1-ethanedithiol, and 1,1-cyclohexanedithiol. Upon heating, gem-dithiols often release hydrogen sulfide, giving the transient thione or thial, which typically convert to oligomers.
1,2-Dithiols
Compounds containing thiol groups on adjacent carbon centers are common. 1,2-Ethanedithiol and benzenedithiol.react aldehydes and ketones to give 1,3-dithiolanes.
1,3-Dithiols
1,3-Propanedithiol is the parent member of this series. It is employed as a reagent in organic chemistry, since it forms 1,3-dithianes upon treatment with ketones and aldehydes. When derived from aldehydes, the methyne C-H group is sufficiently acidic that it can be deprotonated and the resulting anion can be C-alkylated. The process is foundation of the umpolung phenomenon.
Like 1,2-ethanedithiol, propanedithiol forms complexes with metals:
Fe3(CO)12 + C3H6(SH)2 → Fe2(S2C3H6)(CO)6 + H2 + Fe(CO)5 + COA naturally occurring 1,3-dithiol is dihydrolipoic acid.
1,4-Dithiols
A common 1,4-dithiol is dithiothreitol (DTT), HSH2CCH(OH)CH(OH)CH2SH, sometimes called Cleland's reagent for his use of its racemate to reduce protein disulfide links to dithiols. Oxidation of DTT results a stable six-membered heterocyclic ring with an internal disulfide bond.