1,2-Benzenedithiol

1,2-Benzenedithiol is the organosulfur compound with the formula C6H4(SH)2. This colourless viscous liquid consists of a benzene ring with a pair of adjacent thiol groups. The conjugate base of this diprotic compound serves as chelating agent in coordination chemistry and a building block for the synthesis of other organosulfur compounds.[1]

1,2-Benzenedithiol
Names
Preferred IUPAC name
Benzene-1,2-dithiol
Other names
1,2-Dimercaptobenzene
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.037.740
Properties
C6H6S2
Molar mass 142.24 g/mol
Appearance colourless liquid
Density 1.236 g/mL
Melting point 22 to 24 °C (72 to 75 °F; 295 to 297 K)
Boiling point 119 to 120 °C (246 to 248 °F; 392 to 393 K) at 17 mmHg
Soluble in basic water
Hazards
Main hazards stench
Flash point 104.0 °C; 219.2 °F; 377.1 K
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis

The compound is prepared by ortho-lithiation of benzenethiol using butyl lithium (BuLi) followed by sulfidation:[2]

C6H5SH + 2 BuLi → C6H4SLi-2-Li + 2 BuH
C6H4SLi-2-Li + S → C6H4(SLi)2
C6H4(SLi)2 + 2 HCl → C6H4(SH)2 + 2 LiCl

The compound was first prepared from 2-aminobenzenethiol via diazotization.[3] Alternatively, it forms from 1,2-dibromobenzene.[4]

Reactions

Oxidation mainly affords the polymeric disulfide. Reaction with metal dihalides and metal oxides gives the dithiolate complexes of the formula LnM(S2C6H4) where LnM represents a variety of metal centers, e.g. (C5H5)2Ti. Ketones and aldehydes condense to give the heterocycles called dithianes:

C6H4(SH)2 + RR’CO → C6H4(S)2CRR’ + H2O

3,4-Toluenedithiol, also called dimercaptotoluene (CAS#496-74-2), behaves similarly to 1,2-benzenedithiol but is a solid at ambient temperatures (m.p. 135-137 °C).

Alkene-1,2-dithiols are unstable, although metal complexes of alkene-1,2-dithiolates, called dithiolene complexes, are well known.[1]

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References
  1. Karlin, K. D.; Stiefel, E. I., Eds. “Progress in Inorganic Chemistry, Dithiolene Chemistry: Synthesis, Properties, and Applications” Wiley-Interscience: New York, 2003. ISBN 0-471-37829-1
  2. D. M. Giolando; K. Kirschbaum (1992). "An efficient one-pot synthesis of 1,2-benzenedithiol from benzenethiol". Synthesis. 1992 (5): 451–452. doi:10.1055/s-1992-26132.
  3. P. C. Guha; M. N. Chakladar (1925). "Dithiocatechol". J. Indian Chem. Soc. 2: 318.
  4. Aldo Ferretti. "1,2-Dimercaptobenzene". Organic Syntheses.; Collective Volume, 5, p. 419
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