Thiophenol

Thiophenol
Skeletal formula	Ball-and-stick model
Names
	Preferred IUPAC name Benzenethiol[1]
	Other names Thiophenol (or phenylthiol); Phenyl mercaptan; Mercaptobenzene;
Identifiers
CAS Number	108-98-5 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	506523
ChEBI	CHEBI:48498 ;
ChEMBL	ChEMBL119405 ;
ChemSpider	7681 ;
ECHA InfoCard	100.003.306
EC Number	203-635-3;
PubChem CID	7969;
RTECS number	DC0525000;
UNII	7K011JR4T0 ;
CompTox Dashboard (EPA)	DTXSID7026811 ;
	InChI InChI=1S/C6H6S/c7-6-4-2-1-3-5-6/h1-5,7H Key: RMVRSNDYEFQCLF-UHFFFAOYSA-N ; InChI=1/C6H6S/c7-6-4-2-1-3-5-6/h1-5,7H Key: RMVRSNDYEFQCLF-UHFFFAOYAL;
	SMILES Sc1ccccc1;
Properties
Chemical formula	C6H6S
Molar mass	110.17 g·mol−1
Appearance	Colorless liquid
Odor	Unpleasant, pungent
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%[2]
Solubility	Most organic solvents; aqueous base
Vapor pressure	1 mmHg (18°C)[2]
Acidity (pKa)	6.62 (H2O)[3]; 10.28 (DMSO)[4];
Magnetic susceptibility (χ)	-70.8·10−6 cm3/mol
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	Toxic
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H226, H300, H310, H314, H315, H330, H410
Precautionary statements	P210, P233, P240, P241, P242, P243, P260, P262, P264, P270, P271, P273, P280, P284, P301+P310, P301+P330+P331, P302+P350, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P320, P321, P322, P330, P332+P313, P361, P362, P363, P370+P378, P391, P403+P233, P403+P235, P405, P501
NFPA 704 (fire diamond)	4 2 1 OX
Flash point	56 °C; 132 °F; 329 K[2]
	NIOSH (US health exposure limits):
PEL (Permissible)	none[2]
REL (Recommended)	C 0.1 ppm (0.5 mg/m3) [15-minute][2]
IDLH (Immediate danger)	N.D.[2]
Related compounds
Related thiols	1,2-Benzenedithiol; Benzenemethanethiol
Related compounds	Phenol; Benzeneselenol; Diphenyl disulfide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Thiophenol is an organosulfur compound with the formula C₆H₅SH, sometimes abbreviated as PhSH. This foul-smelling colorless liquid is the simplest aromatic thiol. The chemical structures of thiophenol and its derivatives are analogous to phenols . An exception is 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. 2 methods are the reduction of benzenesulfonyl chloride with zinc[5] and the action of elemental sulfur on phenyl magnesium halide or phenyllithium followed by acidification.

Via the Newman–Kwart rearrangement, phenols (1) can be converted to the thiophenols (5) by conversion to the O-aryl dialkylthiocarbamates (3), followed by heating to give the isomeric S-aryl derivative (4).[6]

In the Leuckart thiophenol reaction, the starting material is an aniline through the diazonium salt (ArN₂X) and the xanthate (ArS(C=S)OR).[7][8] Alternatively, sodium sulfide and triazene can react in organic solutions and yield thiophenols.[9]

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.[10] The reaction medium is corrosive and requires ceramic or similar reactor lining. Aryl iodides and sulfur in certain conditions may also produce thiophenols.[11]

Applications

Thiophenols are used in the production of pharmaceuticals including of sulfonamides. The antifungal agents butoconazole and merthiolate are derivatives of thiophenols.[9]

Properties and reactions

Acidity

Thiophenol has appreciably greater acidity than does phenol, as is shown by their pK_a values (6.62 for thiophenol and 9.95 for phenol). A similar pattern is seen for H₂S versus H₂O, and all thiols versus 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.[12] Thus, treatment of C₆H₅SH with methyl iodide in the presence of a base gives methyl phenyl sulfide, C₆H₅SCH₃, a thioether often referred to as thioanisole. 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:

4 C₆H₅SH + O₂ → 2 C₆H₅S-SC₆H₅ + 2 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).[13]

Coordination to metals

Metal cations form thiophenolates, some of which are polymeric. One example is "C₆H₅SCu," obtained by treating copper(I) chloride with thiophenol.[14]

Safety

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 m⁻³), and exposures not greater than 15 minutes.[15]

References

"Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. P001–P004. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
NIOSH Pocket Guide to Chemical Hazards. "#0050". National Institute for Occupational Safety and Health (NIOSH).
Cox, Brian G. Acids and Bases: Solvent Effects on Acid-base Strength. 1st ed. Oxford, UK: Oxford UP, 2013.
Bordwell, Frederick G.; Hughes, David L. (1982). "Thiol acidities and thiolate ion reactivities toward butyl chloride in dimethyl sulfoxide solution. The question of curvature in Broensted plots". The Journal of Organic Chemistry. 47 (17): 3224–3232. doi:10.1021/jo00138a005.
Adams, R.; C. S. Marvel, C. S. "Thiophenol". Organic Syntheses.{{cite journal}}: CS1 maint: multiple names: authors list (link); Collective Volume, vol. 1, p. 504.
Melvin S. Newman and Frederick W. Hetzel (1971). "Thiophenols from Phenols: 2-Naphthalenethiol". Organic Syntheses. 51: 139. doi:10.15227/orgsyn.051.0139.
Leuckart, J. prakt. Chem., [2] 41, 189 (1890).
Tarbell, D. S.; Fukushima, D. K. (1947). "m-Thiocresol". Organic Syntheses. 27: 81. doi:10.15227/orgsyn.027.0081.; Collective Volume, vol. 3, p. 809
Kazem-Rostami, Masoud; Khazaei, Ardeshir; Moosavi-Zare, Ahmad; Bayat, Mohammad; Saednia, Shahnaz (2012). "One-pot synthesis of thiophenols". Synlett. 23 (13): 1893–1896. doi:10.1055/s-0032-1316557. S2CID 196805424.
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.
Jiang, Y.; Qin, Y.; Xie, S.; Zhang, X.; Dong, J.; Ma, D., A (2009). "General and Efficient Approach to Aryl Thiols: CuI-Catalyzed Coupling of Aryl Iodides with Sulfur and Subsequent Reduction". Organic Letters. 22 (1): 52–56. doi:10.1021/acs.orglett.9b03866. PMID 31833778. S2CID 209341111.{{cite journal}}: CS1 maint: multiple names: authors list (link)
Campopiano, O. (2004). "Thiophenol". Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons. doi:10.1002/047084289X. hdl:10261/236866. ISBN 9780471936237..
Barrett, A. G. M.; Dhanak, D.; Graboski, G. G.; Taylor, S. J. (1993). "(Phenylthio)nitromethane". Organic Syntheses.{{cite journal}}: CS1 maint: multiple names: authors list (link); Collective Volume, vol. 8, p. 550
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". Organic Syntheses.{{cite journal}}: CS1 maint: multiple names: authors list (link); Collective Volume, vol. 6, p. 248
CDC - NIOSH Pocket Guide to Chemical Hazards

External links

Thiophenol, Toxicology Data Network

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[IUPAC2013-1] "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. P001–P004. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.

[PGCH-2] NIOSH Pocket Guide to Chemical Hazards. "#0050". National Institute for Occupational Safety and Health (NIOSH).

[3] Cox, Brian G. Acids and Bases: Solvent Effects on Acid-base Strength. 1st ed. Oxford, UK: Oxford UP, 2013.

[4] Bordwell, Frederick G.; Hughes, David L. (1982). "Thiol acidities and thiolate ion reactivities toward butyl chloride in dimethyl sulfoxide solution. The question of curvature in Broensted plots". The Journal of Organic Chemistry. 47 (17): 3224–3232. doi:10.1021/jo00138a005.

[5] Adams, R.; C. S. Marvel, C. S. "Thiophenol". Organic Syntheses.{{cite journal}}: CS1 maint: multiple names: authors list (link); Collective Volume, vol. 1, p. 504.

[6] Melvin S. Newman and Frederick W. Hetzel (1971). "Thiophenols from Phenols: 2-Naphthalenethiol". Organic Syntheses. 51: 139. doi:10.15227/orgsyn.051.0139.

[7] Leuckart, J. prakt. Chem., [2] 41, 189 (1890).

[8] Tarbell, D. S.; Fukushima, D. K. (1947). "m-Thiocresol". Organic Syntheses. 27: 81. doi:10.15227/orgsyn.027.0081.; Collective Volume, vol. 3, p. 809

[:0-9] Kazem-Rostami, Masoud; Khazaei, Ardeshir; Moosavi-Zare, Ahmad; Bayat, Mohammad; Saednia, Shahnaz (2012). "One-pot synthesis of thiophenols". Synlett. 23 (13): 1893–1896. doi:10.1055/s-0032-1316557. S2CID 196805424.

[10] 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.

[11] Jiang, Y.; Qin, Y.; Xie, S.; Zhang, X.; Dong, J.; Ma, D., A (2009). "General and Efficient Approach to Aryl Thiols: CuI-Catalyzed Coupling of Aryl Iodides with Sulfur and Subsequent Reduction". Organic Letters. 22 (1): 52–56. doi:10.1021/acs.orglett.9b03866. PMID 31833778. S2CID 209341111.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[12] Campopiano, O. (2004). "Thiophenol". Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons. doi:10.1002/047084289X. hdl:10261/236866. ISBN 9780471936237..

[13] Barrett, A. G. M.; Dhanak, D.; Graboski, G. G.; Taylor, S. J. (1993). "(Phenylthio)nitromethane". Organic Syntheses.{{cite journal}}: CS1 maint: multiple names: authors list (link); Collective Volume, vol. 8, p. 550

[14] 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". Organic Syntheses.{{cite journal}}: CS1 maint: multiple names: authors list (link); Collective Volume, vol. 6, p. 248

[15] CDC - NIOSH Pocket Guide to Chemical Hazards