Guaiacol

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Guaiacol[1]
Guaiacol.png
Guaiacol 3D.png
Names
IUPAC name
2-methoxyphenol
Other names
o-methoxyphenol; O-methylcatechol;[2] 2-hydroxyanisole
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.001.786
KEGG
UNII
Properties
C7H8O2
Molar mass 124.14 g/mol
Density 1.112 g/cm3, liquid
1.129 g/cm3, crystals
Melting point 28 °C (82 °F; 301 K)
Boiling point 204–206 °C (399–403 °F; 477–479 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

Guaiacol is a naturally occurring organic compound with the formula C6H4(OH)(OCH3), first isolated by Otto Unverdorben in 1826.[3] Although it is biosynthesized by a variety of organisms,[4] this yellowish aromatic oil is usually derived from guaiacum or wood creosote. Samples darken upon exposure to air and light. Guaiacol is present in wood smoke, resulting from the pyrolysis of lignin. The compound contributes to the flavor of many compounds; e.g., whiskey[5] and roasted coffee.[6]

Preparation[edit]

Guaiacol is produced by methylation of catechol; e.g., using potash and dimethyl sulfate:[7]

C6H4(OH)2 + (CH3O)2SO2 → C6H4(OH)(OCH3) + HO(CH3O)SO2

Laboratory methods[edit]

Guaiacol can be prepared by diverse routes in the laboratory. 2-Aminoanisole, derived in two steps from anisole, can be hydrolyzed via its diazonium derivative. Guaiacol can be synthesized by the dimethylation of catechol followed by selective mono-demethylation.[8]

C6H4(OCH3)2 + C2H5SNa[9] → C6H4(OCH3)(ONa) + C2H5SCH3

Uses and chemical reactions[edit]

Guaiacol is a precursor to various flavorants, such as eugenol[10] and vanillin.[11] An estimated 85% of the worlds supply of vanillin comes from guaiacol. The route entails condensation of glyoxylic acid with guaiacol to give mandelic acid, which is oxidized to produce a phenylglyoxylic acid. This acid undergoes a decarboxylation to afford vanillin.[12]

Safety[edit]

Methoxyphenols are potential biomarkers of biomass smoke exposure; e.g., from inhalation of woodsmoke. Dietary sources of methoxyphenols overwhelm the contribution from inhalational exposures to woodsmoke.[13]

Locust pheromone[edit]

Guaiacol is produced in the gut of desert locusts, Schistocerca gregaria, by the breakdown of plant material. This process is undertaken by the gut bacterium Pantoea agglomeransa (Enterobacter). It is one of the main components of the pheromones that cause locust swarming.[14]

See also[edit]

References[edit]

  1. ^ Merck Index, 13th Edition, 4568.
  2. ^ Chemindustry list of synonyms for guaiacol
  3. ^ Stevens ME, Ronan AK, Sourkes TS, Boyd EM (1943). "On the Expectorant Action of Creosote and the Guaiacols.". Can Med Assoc J. 48 (2): 124–7. PMC 1827660Freely accessible. PMID 20322688. 
  4. ^ See for example, Duffey, S. S.; Aldrich, J. R.; Blum, M. S. (1977). "Biosynthesis of phenol and guaiacol by the hemipteran Leptoglossus phyllopus". Comparative Biochemistry and Physiology B: Biochemistry & Molecular Biology. 56 (2B): 101–102. doi:10.1016/0305-0491(77)90029-3. 
  5. ^ Gallegos, Jenna (August 17, 2017). "The best way to drink whiskey, according to science". The Washington Post. Guaiacol is what gives whiskey that smoky, spicy, peaty flavor. 
  6. ^ Dorfner, R.; Ferge, T.; Kettrup, A.; Zimmermann, R.; Yeretzian, C. (Sep 2003). "Real-time monitoring of 4-vinylguaiacol, guaiacol, and phenol during coffee roasting by resonant laser ionization time-of-flight mass spectrometry". Journal of Agricultural and Food Chemistry. 51 (19): 5768–5773. ISSN 0021-8561. PMID 12952431. doi:10.1021/jf0341767. 
  7. ^ Helmut Fiege, Heinz-Werner Voges, Toshikazu Hamamoto, Sumio Umemura, Tadao Iwata, Hisaya Miki, Yasuhiro Fujita, Hans-Josef Buysch, Dorothea Garbe, Wilfried Paulus "Phenol Derivatives" Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a19_313
  8. ^ R. N. Mirrington and G. I. Feutrill (1988). "Orcinol Monomethyl Ether". Org. Synth. ; Coll. Vol., 6, p. 859 
  9. ^ Sodium ethanethiolate
  10. ^ C. F. H. Allen and J. W. Gates, Jr. (1955). "o-Eugenol". Org. Synth. ; Coll. Vol., 3, p. 418 
  11. ^ Esposito, Lawrence J.; K. Formanek; G. Kientz; F. Mauger; V. Maureaux; G. Robert; F. Truchet (1997). "Vanillin". Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition. 24. New York: John Wiley & Sons. pp. 812–825. 
  12. ^ Vidal, J (2007). "Vanillin". Kirk-Othmer Encyclopedia of Chemical Technology (PDF). 25 (5th ed.). Hoboken, NJ: Wiley-Interscience. pp. 544–556. ISBN 9780471238966. 
  13. ^ CRITICAL REVIEW OF THE HEALTH EFFECTS OF WOODSMOKE
  14. ^ Nature, Pheromones: Exploitation of gut bacteria in the locust