Guaiacol

Guaiacol[1]
Names
IUPAC name
2-methoxyphenol
Other names
o-methoxyphenol; O-methylcatechol;[2] 2-hydroxyanisole
Identifiers
90-05-1 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:28591 YesY
ChEMBL ChEMBL13766 YesY
ChemSpider 447 YesY
ECHA InfoCard 100.001.786
KEGG D00117 YesY
PubChem 460
UNII 6JKA7MAH9C YesY
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 to 206 °C (399 to 403 °F; 477 to 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., roasted coffee.[5]

Preparation

Guaiacol is produced by methylation of catechol, e.g., using potash and dimethyl sulfate:[6]

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

Laboratory methods

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.[7]

C6H4(OCH3)2 + C2H5SNa → C6H4(OCH3)(ONa) + C2H5SCH3

Uses and chemical reactions

Guaiacol is a precursor to various flavorants, such as eugenol[8] and vanillin.[9] 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.[10]

In basic solution, it is readily oxidized, giving yellowish brown and absorbs light maximally at about 470 nm.

Its derivatives are used medicinally as an expectorant, antiseptic, and local anesthetic.

Guaiacol carbonate is known as duotal, the phosphate as phosphatol, the phosphite as guaiaco-phosphal (phosphotal is a mixture of the phosphites of creosote phenols). The valerianic ester of guaiacol is known as geosote, the benzoic as benzosol, the salicylic as guaiacolsalol, while the glycerin ether is the drug guaifenesin. The related derivative, dimethoxybenzene or veratrole, is also useful. In preparation of food by smoking, guaiacol is the main chemical responsible for the smoky taste, whereas syringol is responsible for the smoky aroma.

Safety

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.[11]

Locust pheromone

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.[12]

References

  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. 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. ↑ 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. doi:10.1021/jf0341767. ISSN 0021-8561. PMID 12952431.
  6. ↑ 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
  7. ↑ R. N. Mirrington and G. I. Feutrill (1988). "Orcinol Monomethyl Ether". Org. Synth.; Coll. Vol., 6, p. 859
  8. ↑ C. F. H. Allen and J. W. Gates, Jr. (1955). "o-Eugenol". Org. Synth.; Coll. Vol., 3, p. 418
  9. ↑ 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.
  10. ↑ Vidal, J (2007). "Vanillin". Kirk-Othmer Encyclopedia of Chemical Technology (PDF). 25 (5th ed.). Hoboken, NJ: Wiley-Interscience. pp. 544–556. ISBN 9780471238966.
  11. ↑ CRITICAL REVIEW OF THE HEALTH EFFECTS OF WOODSMOKE
  12. ↑ Nature, Pheromones: Exploitation of gut bacteria in the locust
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