Guaiacol

Guaiacol[1]
IUPAC name 2-methoxyphenol
Other names o-Methoxyphenol; Methylcatechol[2]
Identifiers
CAS number	90-05-1 Y
PubChem	460
ChemSpider	447 Y
UNII	6JKA7MAH9C Y
KEGG	D00117 Y
ChEBI	CHEBI:28591 Y
ChEMBL	CHEMBL13766 Y
Jmol-3D images	Image 1
SMILES COc1ccccc1O
InChI InChI=1S/C7H8O2/c1-9-7-5-3-2-4-6(7)8/h2-5,8H,1H3 Y Key: LHGVFZTZFXWLCP-UHFFFAOYSA-N Y InChI=1/C7H8O2/c1-9-7-5-3-2-4-6(7)8/h2-5,8H,1H3 Key: LHGVFZTZFXWLCP-UHFFFAOYAI
Properties
Molecular formula	C7H8O2
Molar mass	124.14 g/mol
Density	1.112 g/cm3, liquid 1.129 g/cm3, crystals
Melting point	28 °C, 301 K, 82 °F
Boiling point	204-206 °C
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Guaiacol is a naturally occurring organic compound with the formula C₆H₄(OH)(OCH₃). Although it is biosynthesized by a variety of organisms,^[3] this colorless 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.^[4]

Preparation

In industry, guaiacol is produced by methylation of catechol, e.g. using potash and dimethyl sulfate:^[5]

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.^[6]

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

Uses

Guaiacol is a precursor to various flavorants such as eugenol^[7] and vanillin.^[8] Its derivatives are used medicinally as an expectorant, antiseptic, and local anesthetic. It also can be used as a dye in chemical reactions, as oxygen will turn guaiacol from colorless to brown.

Related compounds

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).^{[citation needed]} 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.^[9]

Locust pheromone

Guaiacol is produced in the gut of locusts, Schistocerca gregaria, by the breakdown of plant material. This process is undertaken by the gut bacterium Pantoea (Enterobacter) agglomerans. Guaiacol is one of the main components of the pheromones that cause locust swarming.^[10]

References

1. ^ Merck Index, 13th Edition, 4568.
2. ^ Chemindustry list of synonyms for guaiacol
3. ^ 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, Part B: Biochemistry & Molecular Biology 56 (2B): 101–102. doi:10.1016/0305-0491(77)90029-3. 
4. ^ 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. 
5. ^ 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
6. ^ R. N. Mirrington and G. I. Feutrill (1988), "Orcinol Monomethyl Ether", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6p0859 ; Coll. Vol. 6: 859 
7. ^ C. F. H. Allen and J. W. Gates, Jr. (1955), "o-Eugenol", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv30418 ; Coll. Vol. 3: 418 
8. ^ Esposito, Lawrence J.; K. Formanek, G. Kientz, F. Mauger, V. Maureaux, G. Robert, and F. Truchet (1997). "Vanillin". Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition. 24. New York: John Wiley & Sons. pp. 812–825. 
9. ^ CRITICAL REVIEW OF THE HEALTH EFFECTS OF WOODSMOKE
10. ^ Nature, Pheromones: Exploitation of gut bacteria in the locust