Benzyl mercaptan

Benzyl mercaptan is an organosulfur compound with the formula C6H5CH2SH. It is a common laboratory alkylthiol that occurs in trace amounts naturally. It is a colorless, malodorous liquid.

Benzyl mercaptan
Names
Preferred IUPAC name
Phenylmethanethiol
Other names
alpha-Toluenethiol
Benzylthiol
Thiobenzyl alcohol
Benzyl mercaptan
alpha-Toluolthiol
Benzylhydrosulfide
Benzyl hydrosulfide
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.002.602
UNII
Properties
C7H8S
Molar mass 124.20 g/mol
Appearance colourless liquid
Odor leek or garlic-like
Density 1.058 g/mL
Melting point −30 °C (−22 °F; 243 K)
Boiling point 195 °C (383 °F; 468 K)
low
Solubility very soluble in ethanol, ether
soluble in CS2
slightly soluble in CCl4
Acidity (pKa) 9.43 (H2O)[1]
1.5751 (20 °C)
Hazards
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
2
0
Flash point 70 °C (158 °F; 343 K)
Lethal dose or concentration (LD, LC):
493 mg/kg (rat, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Preparation and occurrence

Benzyl mercaptan can be prepared by the reaction of benzyl chloride and thiourea. The initially formed isothiouronium salt must be subjected to alkaline hydrolysis to obtain the thiol.

It has been identified in boxwood (Buxus sempervirens L.) and is known to contribute to the smoky aroma of certain wines.[2] It also occurs naturally in coffee.

Use in organic synthesis

Benzyl mercaptan is used for S-alkylation to give benzylthioethers.[3]

It has been used as a source of the thiol functional group in organic synthesis. Debenzylation can be effected by dissolving metal reduction:[4]

RSCH2C6H5 + 2 H+ + 2 e− → RSH + CH3C6H5

Condensed tannins undergo acid-catalyzed cleavage in the presence of benzyl mercaptan.

Methoxy-substituted benzyl mercaptans have been developed that cleave easily, are recyclable, and are odorless.[5]

References
  1. Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. pp. 5–89. ISBN 978-1498754286.
  2. Tominaga, Takatoshi; Guimbertau, Guy; Dubourdieu, Denis (2003). "Contribution of Benzenemethanethiol to Smoky Aroma of Certain Vitis vinifera L. Wines". Journal of Agricultural and Food Chemistry. 51 (5): 1373–1376. doi:10.1021/jf020756c.
  3. Norman Kharasch, Robert B. Langford (1964). "2,4-Dinitrobenzenesulfenyl Chloride". Org. Synth. 44: 47. doi:10.15227/orgsyn.044.0047.CS1 maint: uses authors parameter (link)
  4. Wuts, Peter G. M. (2014). Greene's Protective Groups in Organic Synthesis (5th ed.). Hoboken, NJ: Wiley. p. 842. ISBN 9781118057483.
  5. Matoba, Manabu; Kajimoto, Tetsuya; Node, Manabu (2007). "Development of a Novel Benzyl Mercaptan as a Recyclable Odorless Substitute of Hydrogen Sulfide". Synlett. 2007 (12): 1930–1934. doi:10.1055/s-2007-984524.
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