Thiophenol

Thiophenol

Names
IUPAC name Thiophenol
Other names Benzenethiol, Phenyl mercaptan, Mercaptobenzene
Identifiers
CAS Registry Number	108-98-5 Y
ChEBI	CHEBI:48498 Y
ChEMBL	ChEMBL119405 Y
ChemSpider	7681 Y
InChI InChI=1S/C6H6S/c7-6-4-2-1-3-5-6/h1-5,7H Y Key: RMVRSNDYEFQCLF-UHFFFAOYSA-N Y InChI=1/C6H6S/c7-6-4-2-1-3-5-6/h1-5,7H Key: RMVRSNDYEFQCLF-UHFFFAOYAL
Jmol-3D images	Image
PubChem	7969
RTECS number	DC0525000
SMILES Sc1ccccc1
UNII	7K011JR4T0 Y
Properties
Chemical formula	C6H6S
Molar mass	110.19 g/mol
Appearance	colorless liquid, with unpleasant odour.
Density	1.0766 g/mL
Melting point	−15 °C (5 °F; 258 K)
Boiling point	169 °C (336 °F; 442 K)
Solubility in water	0.08% in water, 25°C[1]
Solubility	Most organic solvents; aqueous base
Vapor pressure	1 mmHg (18°C)[1]
Acidity (pKa)	6.62 (H2O),[2] 10 (DMSO)[3]
Hazards
Main hazards	Toxic
R-phrases	R10 R24/25 R26 R41
S-phrases	S23 S26 S28 S36/37/39 S45
Flash point	56 °C; 132 °F; 329 K[1]
US health exposure limits (NIOSH):
PEL (Permissible)	none[1]
REL (Recommended)	C 0.1 ppm (0.5 mg/m3) [15-minute][1]
IDLH (Immediate danger)	N.D.[1]
Related compounds
Related thiols	1,2-Benzenedithiol Benzenemethanethiol
Related compounds	Phenol Benzeneselenol Diphenyl disulfide
Except where noted otherwise, data is 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

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.^[4] 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.^[5] In the Leuckart thiophenol reaction the starting material is an aniline through the diazonium salt (ArN₂X) and the xanthate (ArS(C=S)OR) ^[6][7]

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.^[8] The process is quite corrosive and requires ceramic or similar reactor lining.

Properties

Acidity

Thiophenol has appreciably greater acidity than does phenol. Thiophenol has a pK_a 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

The thiophenolate is highly nucleophilic, which translates to a high rate of alkylation.^[9] 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

Thiophenols, especially in the presence of base are 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

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).^[10]

Coordination to metals

Metal cations form thiophenolates, some of which are polymeric. One example is "C₆H₅SCu," obtained by treating copper(I) chloride with thiophenol.^[11]

Safety

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.^[12]

References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 "NIOSH Pocket Guide to Chemical Hazards #0050". National Institute for Occupational Safety and Health (NIOSH). 
2. ↑ Cox, Brian G. Acids and Bases: Solvent Effects on Acid-base Strength. 1st ed. Oxford, UK: Oxford UP, 2013.
3. ↑ Arnett, E.M., Venkatasubremanian, K.G., J. Org. Chem., 1983, 48, 1569.
4. ↑ Adams, R.; C. S. Marvel, C. S. "Thiophenol". Org. Synth. ; Coll. Vol. 1, p. 504 
5. ↑ Melvin S. Newman and Frederick W. Hetzel (1990). "Thiophenols from Phenols: 2-Naphthalenethiol". Org. Synth. ; Coll. Vol. 6, p. 824 
6. ↑ Leuckart, J. prakt. Chem., [2] 41, 189 (1890).
7. ↑ Organic Syntheses, Coll. Vol. 3, p.809 (1955); Vol. 27, p.81 (1947).Link
8. ↑ 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. 
9. ↑ Campopiano, O. "Thiophenol" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289.
10. ↑ Barrett, A. G. M.; Dhanak, D.; Graboski, G. G.; Taylor, S. J. (1993). "(Phenylthio)nitromethane". Org. Synth. ; Coll. Vol. 8, p. 550 
11. ↑ 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, p. 248 
12. ↑ CDC - NIOSH Pocket Guide to Chemical Hazards