Thiophenol

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To be distinguished from benzyl mercaptan.
Thiophenol
Skeletal formula Ball-and-stick model
Identifiers
CAS number 108-98-5 YesY
PubChem 7969
ChemSpider 7681 YesY
UNII 7K011JR4T0 YesY
ChEBI CHEBI:48498 YesY
ChEMBL CHEMBL119405 YesY
RTECS number DC0525000
Jmol-3D images Image 1
Properties
Molecular formula C6H6S
Molar mass 110.19 g/mol
Appearance colorless liquid, with unpleasant odour.
Density 1.0766 g/mL
Melting point -15 °C
Boiling point 169 °C
Solubility Most organic solvents; aqueous base
Acidity (pKa) 8 (H2O),[1] 10 (DMSO)[2]
Hazards
R-phrases R10 R24/25 R26 R41
S-phrases S23 S26 S28 S36/37/39 S45
Main hazards Toxic
Related compounds
Related thiols 1,2-Benzenedithiol
Benzenemethanethiol
Related compounds Phenol
Benzeneselenol
Diphenyl disulfide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Thiophenol is an organosulfur compound with the formula C6H6S, and sometimes abbreviated as PhSH. This foul-smelling colourless liquid is the simplest aromatic thiol. The chemical structures of thiophenols are analogous to phenols except the oxygen atom in the hydroxyl group (-OH) bonded to the aromatic ring is replaced by a sulfur atom. The prefix thio- implies a sulfur-containing compound and when used before a root word name for a compound which would normally contain an oxygen atom, in the case of 'thiol' that the alcohol oxygen atom is replaced by a sulfur atom.

Thiophenols also describes a class of compounds formally derived from thiophenol itself. All have a sulfhydryl group (-SH) covalently bonded to an aromatic ring. The organosulfur ligand in the medicine thiomersal is a thiophenol.

Synthesis[edit]

There are several methods of synthesis for thiophenol and related compounds, although thiophenol itself is usually purchased for laboratory operations. Methods are the reduction of benzenesulfonyl chloride with zinc.[3] and the action of elemental sulfur on phenyl magnesium halide or phenyllithium followed by acidification.

Phenols can be converted to the thiophenols via rearrangement of their O-aryl dialkylthiocarbamates.[4] In the Leuckart thiophenol reaction the starting material is an aniline through the diazonium salt (ArN2X) and the xanthate (ArS(C=S)OR) [5][6]

Thiophenol can be manufactured from chlorobenzene and hydrogen sulfide over alumina at 700 to 1,300 °F (371 to 704 °C). The disulfide is the primary byproduct.[7] The process is quite corrosive and requires ceramic or similar reactor lining.

Properties[edit]

Acidity[edit]

Thiophenol has appreciably greater acidity than does phenol. Thiophenol has a pKa of 6 vs 10 for phenol. A similar pattern is seen for H2S vs. H2O and all thiols vs. the corresponding alcohols. Treatment of PhSH with strong base such as sodium hydroxide (NaOH) or sodium metal affords the salt sodium thiophenolate (PhSNa).

Alkylation[edit]

The thiophenolate is highly nucleophilic, which translates to a high rate of alkylation.[8] Thus, treatment of C6H5SH with methyl iodide in the presence of a base gives methyl phenyl sulfide, C6H5SCH3, a thioether. Such reactions are fairly irreversible. C6H5SH also adds to α,β-unsaturated carbonyls via Michael addition.

Oxidation[edit]

Thiophenols, especially in the presence of base is easily oxidized to diphenyl disulfide:

2 C6H5SH + 1/2 O2 → C6H5S-SC6H5 + H2O

The disulfide can be reduced back the thiol using sodium borohydride followed by acidification. This redox reaction is also exploited in the use of C6H5SH as a source of H atoms.

Chlorination[edit]

Phenylsulfenyl chloride, a blood-red liquid (b.p. 41–42 °C, 1.5 mm Hg), can be prepared by the reaction of thiophenol with chlorine (Cl2).[9]

Coordination to metals[edit]

Metal cations form thiophenolates, some of which are polymeric. One example is "C6H5SCu," obtained by treating copper(I) chloride with thiophenol.[10]

Safety[edit]

Thiophenol is an irritant and toxic by ingestion, absorption through skin, or inhalation. This chemical is also flammable. The US National Institute for Occupational Safety and Health has established a recommended exposure limit at a ceiling of 0.1 ppm (0.5 mg/m3), and exposures not greater than 15 minutes.[11]

References[edit]

  1. ^ Arnett, E.M., Wu, C.Y., J. Am. Chem. Soc.,1960, 82, 5660.
  2. ^ Arnett, E.M., Venkatasubremanian, K.G., J. Org. Chem., 1983, 48, 1569.
  3. ^ Adams, R.; C. S. Marvel, C. S., "Thiophenol", Org. Synth. ; Coll. Vol. 1: 504 
  4. ^ Melvin S. Newman and Frederick W. Hetzel (1990), "Thiophenols from Phenols: 2-Naphthalenethiol", Org. Synth. ; Coll. Vol. 6: 824 
  5. ^ Leuckart, J. prakt. Chem., [2] 41, 189 (1890).
  6. ^ Organic Syntheses, Coll. Vol. 3, p.809 (1955); Vol. 27, p.81 (1947).Link
  7. ^ US Patent 2,490,257, Duncan J. Crowley & Alvin L Kosak, "Mono- and Polyalkyl Mono- and Polynuclear Mercaptans", issued 1949-12-06, assigned to Socony-Vacuum Oil Co. 
  8. ^ Campopiano, O. "Thiophenol" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289.
  9. ^ Barrett, A. G. M.; Dhanak, D.; Graboski, G. G.; Taylor, S. J. (1993), "(Phenylthio)nitromethane", Org. Synth. ; Coll. Vol. 8: 550 
  10. ^ Posner, G. H.; Whitten, C. E., "Secondary and Tertiary Alkyl Ketones from Carboxylic Acid Chlorides and Lithium Phenylthio(alkyl)cuprate Reagents: tert-Butyl Phenyl Ketone", Org. Synth. ; Coll. Vol. 6: 248 
  11. ^ CDC - NIOSH Pocket Guide to Chemical Hazards