Guaiacol

Source: Wikipedia, the free encyclopedia.
Guaiacol[1]
Names
Preferred IUPAC name
2-Methoxyphenol
Other names
o-Methoxyphenol
O-Methylcatechol[2]
2-Hydroxyanisole
Pyroguaiac acid
Pyrocatechol monomethyl ether
1-hydroxy-2-methoxybenzene
Identifiers
3D model (
JSmol
)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.001.786 Edit this at Wikidata
KEGG
UNII
  • InChI=1S/C7H8O2/c1-9-7-5-3-2-4-6(7)8/h2-5,8H,1H3 checkY
    Key: LHGVFZTZFXWLCP-UHFFFAOYSA-N checkY
  • InChI=1/C7H8O2/c1-9-7-5-3-2-4-6(7)8/h2-5,8H,1H3
    Key: LHGVFZTZFXWLCP-UHFFFAOYAI
  • COc1ccccc1O
Properties
C7H8O2
Molar mass 124.139 g·mol−1
Appearance colorless oil or crystalline solid
Density 1.112 g/cm3, liquid
1.129 g/cm3, crystals
Melting point 26–29 °C (79–84 °F; 299–302 K)
Boiling point 204–206 °C (399–403 °F; 477–479 K)
23.3 g/L at 25 °C
Related compounds
3-Methoxyphenol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Guaiacol (

methoxy functional group. Guaiacol appears as a viscous colorless oil, although aged or impure samples are often yellowish. It occurs widely in nature and is a common product of the pyrolysis of wood.[3]

Occurrence

Guaiacol is usually derived from guaiacum or wood creosote.

It is produced by a variety of plants.

roasted coffee.[7]

Preparation

The compound was first isolated by Otto Unverdorben in 1826.[8] Guaiacol is produced by methylation of o-catechol, for example using potash and dimethyl sulfate:[3]

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

Laboratory methods

Guaiacol can be prepared by diverse routes in the laboratory.

diazonium derivative. Guaiacol can be synthesized by the dimethylation of catechol followed by selective mono-demethylation.[9]

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

Uses and chemical reactions

Syringyl/guaiacyl ratio

angiosperms.[10] Sugarcane bagasse is one useful source of guaiacol; pyrolysis of the bagasse lignins yields compounds including guaiacol, 4-methylguaiacol and 4-vinylguaiacol.[11]

Chemical intermediate

Guaiacol is a useful precursor for the synthesis of other compounds.[12] Being derived from biomass, it is a potential component or precursor to "green fuels".[13]

Guaiacol is also a useful reagent for the quantification of peroxidases, as in the presence of hydrogen peroxide these enzymes will catalyse with it the formation of tetraguaiacol,[14] a coloured compound that can be quantified by its absorbance at 420–470 nm, following the equation:

4 guaiacol (colorless) + 2 H
2O
2 → tetraguaiacol (colored) + 8 H
2O.

Medicinal and food

Guaiacol is a precursor to various

flavorants, such as eugenol.[15] An estimated 85% of the world's supply of vanillin comes from guaiacol. Because consumers tend to prefer natural vanillin to synthetic vanillin, methods such as microbial fermentation have been adopted. The route entails the condensation reaction of glyoxylic acid with guaiacol to give mandelic acid, which is oxidized to produce phenylglyoxylic acid. This acid undergoes a decarboxylation to afford vanillin.[16]
The crude vanillin product can then be purified with vacuum distillation and recrystallization.

Guaiacol is also used medicinally as an

expectorant, antiseptic, and local anesthetic.[17]

Guaiacol is produced in the gut of

swarming.[18]

Safety

Methoxyphenols are potential biomarkers of biomass smoke exposure, such as from inhalation of woodsmoke. Dietary sources of methoxyphenols overwhelm the contribution from inhalational exposures to woodsmoke.[19]

See also

References

  1. ^ Merck Index (13th ed.). p. 4568.
  2. ^ "List of synonyms for guaiacol". Chemindustry.
  3. ^
    ISBN 978-3527306732
    .
  4. PMID 830476
    .
  5. ISBN 978-0849394126
    .
  6. ^ 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.
  7. PMID 12952431
    .
  8. PMID 20322688
    .
  9. ^ Mirrington, R. N.; Feutrill, G. I. (1988). "Orcinol Monomethyl Ether". Organic Syntheses; Collected Volumes, vol. 6, p. 859.
  10. PMID 11449052
    .
  11. ISSN 0961-9534
    .
  12. doi:10.1351/pac200577071221
    .
  13. doi:10.1039/C3EE43081B
    .
  14. PMID 7673205
    .
  15. ^ Allen, C. F. H.; Gates, J. W. Jr (1955). "o-Eugenol". Organic Syntheses; Collected Volumes, vol. 3, p. 418.
  16. ^ Esposito, Lawrence J.; Formanek, K.; Kientz, G.; Mauger, F.; Maureaux, V.; Robert, G.; Truchet, F. (1997). "Vanillin". Kirk–Othmer Encyclopedia of Chemical Technology. Vol. 24 (4th ed.). New York, NY: John Wiley & Sons. pp. 812–825.
  17. ^ "Guaiacol". DrugBank. 2019-11-02. Retrieved 2019-11-18.
  18. S2CID 5207502
    .
  19. ^ Smith, K. R. (2005). "Critical review of the health effects of woodsmoke" (PDF). School of Public Health, University of Berkeley. Archived from the original (PDF) on 2009-07-10.
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