View source for Dithiol

{{Short description|Organosulfur compound with two –SH groups}}
{{About|compounds with two SH functional groups||dithiole}}

In [[organic chemistry]], a '''dithiol''' is a type of [[organosulfur compound]] with two [[thiol]] ({{chem2|\sSH}}) [[functional group]]s. Their properties are generally similar to those of monothiols in terms of [[solubility]], odor, and [[Volatile organic compound|volatility]].  They can be classified according to the relative location of the two thiol groups on the organic backbone.

<gallery caption="Structure of some dithiols" widths="120px" heights="100px" >
File:C6H4(SH)2.svg|[[Benzene-1,2-dithiol]], the [[Parent structure|parent]] aromatic dithiol
File:1,3-Propandithiol Structural Formula V1.svg|[[Propane-1,3-dithiol]]
File:Meso-2,3-dimercaptosuccinic-acid-2D-skeletal-A-configurations-labelled.png|The drug meso-2,3-[[dimercaptosuccinic acid]]
File:Dimercaprol.svg|[[Dimercaprol]] ("British anti-Lewisite"), an early antidote for arsenic poisoning
File:Dihydrolipoic-acid-2D-skeletal.png|[[Dihydrolipoic acid]], a vitamin
File:Dithiothreitol.png|[[Dithiothreitol]], a reagent in protein biochemistry
</gallery>

==Geminal dithiols==
[[Geminal dithiol]]s have the formula RR'C(SH)<sub>2</sub>. They are formally derived from aldehydes and ketones by the action of [[hydrogen sulfide]].<ref>{{cite journal |doi=10.3891/acta.chem.scand.17-0273 |title=gem-Dithiols|date=1963 |last1=Magnusson |first1=Bengt |last2=Hassel |first2=O. |last3=Lindheim |first3=A. |last4=Kvande |first4=P. C. |last5=Meisingseth |first5=E. |journal=Acta Chemica Scandinavica |volume=17 |pages=273–275 }}</ref> Their stability contrasts with the rarity of geminal diols. Examples include [[methanedithiol]], [[ethane-1,1-dithiol]], and cyclohexane-1,1-dithiol. Upon heating, gem-dithiols often release hydrogen sulfide, giving the transient [[thioketone]] or [[thial]], which typically convert to [[oligomer]]s.<ref>{{cite journal|title=gem-Dithiols|author1=Cairns, T. L. |author2=Evans, G. L. |author3=Larchar, A. W. |author4=McKusick, B. C. |journal=Journal of the American Chemical Society|year=1952|volume=74|issue=16|pages=3982–9|doi=10.1021/ja01136a004}}</ref>

==1,2-Dithiols==
Compounds containing thiol groups on adjacent carbon centers are common. [[Ethane-1,2-dithiol]] reacts with aldehydes ({{chem2|\sCH\dO}}) and ketones ({{chem2|>C\dO}}) to give 1,3-dithiolanes:
:<chem>(HS)2C2H4 + R-CHO -> R-CHS2C2H4 + H2O</chem>

Some dithiols are used in [[chelation therapy]], i.e. the removal of heavy metal poisons.<ref>{{cite journal |doi=10.1016/j.tox.2007.02.016|title=The role of thiols, dithiols, nutritional factors and interacting ligands in the toxicology of mercury|year=2007|last1=Rooney|first1=James P.K.|journal=Toxicology|volume=234|issue=3|pages=145–156|pmid=17408840}}</ref> Examples include [[2,3-Dimercapto-1-propanesulfonic acid|dimercaptopropanesulfate]] (DMPS), [[dimercaprol]] ("BAL"), and meso-2,3-[[dimercaptosuccinic acid]].

===Enedithiols===
Enedithiols, with the exception of aromatic examples, are rare.  The parent aromatic example is [[1,2-Benzenedithiol|benzenedithiol]]. The dithiol of [[Sodium 1,3-dithiole-2-thione-4,5-dithiolate|1,3-dithiole-2-thione-4,5-dithiolate]]<sup>2-</sup> is also known.

==1,3-Dithiols==
[[Propane-1,3-dithiol]] is the [[Parent structure|parent member]] of this series. It is employed as a reagent in organic chemistry, since it forms 1,3-[[dithiane]]s upon treatment with ketones and [[aldehyde]]s.  When derived from aldehydes, the [[methyne]] ({{chem2|\dCH\s}}) group is sufficiently acidic that it can be deprotonated and the resulting anion can be [[Alkylation|C-alkylated]].  The process is the foundation of the [[Umpolung#Carbonyl umpolung|umpolung]] phenomenon.<ref>{{cite encyclopedia
 |author1=Conrow, R. E. |author2=Le Huérou, Y. | title = 1,3-Propanedithiol
 | encyclopedia=Encyclopedia of Reagents for Organic Synthesis|editor=L. Paquette
 | year = 2004
 | publisher = J. Wiley & Sons, New York
 | doi = 10.1002/047084289X|isbn=9780471936237 | hdl=10261/236866| hdl-access=free}}
</ref>

Like 1,2-ethanedithiol, propanedithiol forms [[Coordination complex|complexes]] with metals, for example with [[triiron dodecacarbonyl]]:
:{{chem2|Fe3(CO)12 +  C3H6(SH)2 -> Fe2(S2C3H6)(CO)6  +  H2  + Fe(CO)5  +  CO}}

A naturally occurring 1,3-dithiol is [[dihydrolipoic acid]].  

1,3-Dithiols oxidize to give 1,2-[[dithiolane]]s.<ref>{{cite journal |doi=10.1021/ja00173a017 |title=Predicting the stability of cyclic disulfides by molecular modeling: Effective concentrations in thiol-disulfide interchange and the design of strongly reducing dithiols |date=1990 |last1=Burns |first1=John A. |last2=Whitesides |first2=George M. |journal=Journal of the American Chemical Society |volume=112 |issue=17 |pages=6296–6303 |bibcode=1990JAChS.112.6296B }}</ref>

==1,4-Dithiols==
A common 1,4-dithiol is [[dithiothreitol]] (DTT), HSCH<sub>2</sub>CH(OH)CH(OH)CH<sub>2</sub>SH, sometimes called [[W. Wallace Cleland|Cleland]]'s reagent, for to [[reducing agent|reduce]] protein [[disulfide bond]]s.  Oxidation of DTT results a stable six-membered [[heterocycle|heterocyclic]] ring with an internal [[disulfide bond]]. 
[[Image:Disulfide reduction by DTT-2.png|left|thumb|400px|Reduction of a typical [[disulfide bond]] by DTT via two sequential [[thiol-disulfide exchange]] reactions.]]{{clear|left}}

==References==
<references />

[[Category:Thiols| ]]
[[Category:Functional groups]]
[[Category:Organosulfur compounds]]