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{{short description|Methoxyphenol compound, constituent of plant lignins and essential oils}}
{{chembox {{chembox
| Watchedfields = changed
| verifiedrevid = 415511788 | verifiedrevid = 443849411
|Reference=<ref>'']'', 13th Edition, '''4568'''.</ref>
| Reference =<ref>{{cite book|title=Merck Index|edition=13th|page=4568|title-link=Merck Index}}</ref>
|ImageFileL1=Guaiacol.png | ImageFileL1 =Guaiacol.png
|ImageSizeL1=130px
|ImageFileR1=Guaiacol 3D.png | ImageFileR1 =Guaiacol 3D spacefill.png
| PIN =2-Methoxyphenol
|ImageSizeR1 = 120px
| OtherNames =''o''-Methoxyphenol<br>''O''-Methylcatechol<ref>{{cite web|url=http://www.chemindustry.com/chemicals/464173.html|website=Chemindustry|title=List of synonyms for guaiacol|access-date=2009-03-20|archive-date=2016-08-10|archive-url=https://web.archive.org/web/20160810082353/http://www.chemindustry.com/chemicals/464173.html|url-status=dead}}</ref><br> 2-Hydroxyanisole<br> Pyroguaiac acid<br> Pyrocatechol monomethyl ether<br> 1-hydroxy-2-methoxybenzene<br>
|IUPACName=2-methoxyphenol
⚫ |Section1={{Chembox Identifiers
|OtherNames=''o''-Methoxyphenol; Methylcatechol<ref></ref>
⚫ | UNII_Ref = {{fdacite|correct|FDA}}
⚫ |Section1= {{Chembox Identifiers
⚫ | UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 6JKA7MAH9C | UNII = 6JKA7MAH9C
| KEGG_Ref = {{keggcite|correct|kegg}} | KEGG_Ref = {{keggcite|correct|kegg}}
Line 22: Line 22:
| StdInChIKey = LHGVFZTZFXWLCP-UHFFFAOYSA-N | StdInChIKey = LHGVFZTZFXWLCP-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|CAS}} | CASNo_Ref = {{cascite|correct|CAS}}
| CASNo=90-05-1 | CASNo = 90-05-1
| PubChem=460 | PubChem = 460
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 447 | ChemSpiderID = 447
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 28591 | ChEBI = 28591
| SMILES = COc1ccccc1O | SMILES = COc1ccccc1O
}} }}
|Section2= {{Chembox Properties |Section2={{Chembox Properties
| C=7|H=8|O=2
| Formula=C<sub>7</sub>H<sub>8</sub>O<sub>2</sub>
| MolarMass=124.14 g/mol | MolarMass =
| Appearance= | Appearance = colorless oil or crystalline solid
| Density=1.112 g/cm<sup>3</sup>, liquid<br />1.129 g/cm<sup>3</sup>, crystals | Density = 1.112 g/cm<sup>3</sup>, liquid<br />1.129 g/cm<sup>3</sup>, crystals
| MeltingPtC=28 | MeltingPtC = 26-29
| BoilingPtC = 204–206
| BoilingPt=204-206 °C
| BoilingPt_notes =
| Solubility=
| Solubility = 23.3 g/L at 25&nbsp;°C
}} }}
|Section3= {{Chembox Hazards |Section3={{Chembox Hazards
| MainHazards=
| MainHazards =
| FlashPt=
| FlashPt =
| Autoignition=
| AutoignitionPt =
}}
|Section4={{Chembox Related
| OtherFunction_label = ]s
| OtherFunction = ]<br /> ]
}} }}
}} }}


'''Guaiacol''' ({{IPAc-en|ˈ|ɡ|w|aɪ|ə|k|ɒ|l}}) is an ] with the ] C<sub>6</sub>H<sub>4</sub>(OH)(OCH<sub>3</sub>). It is a phenolic compound containing a ] 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 ] of wood.<ref name=Ullmann/>
'''Guaiacol''' is a naturally occurring ] with the ] C<sub>6</sub>H<sub>4</sub>(OH)(OCH<sub>3</sub>). Although it is biosynthesized by a variety of organisms,<ref>See for example, {{cite journal | doi = 10.1016/0305-0491(77)90029-3 | author = Duffey, S. S.; Aldrich, J. R.; Blum, M. S. | title = Biosynthesis of phenol and guaiacol by the hemipteran Leptoglossus phyllopus | journal = Comparative Biochemistry and Physiology, Part B: Biochemistry & Molecular Biology | year = 1977 | volume = 56 | issue = 2B | pages = 101–102}}</ref> this colorless aromatic oil is usually derived from ] or wood ]. Samples darken upon exposure to air and light. Guaiacol is present in wood ], resulting from the ] of ]. The compound contributes to the flavor of many compounds, e.g. roasted coffee.<ref>{{cite journal | doi = 10.1021/jf0341767 | year = 2003 | month = Sep | author = Dorfner, R; Ferge, T; Kettrup, A; Zimmermann, R; Yeretzian, C | title = Real-time monitoring of 4-vinylguaiacol, guaiacol, and phenol during coffee roasting by resonant laser ionization time-of-flight mass spectrometry | volume = 51 | issue = 19 | pages = 5768–5773 | issn = 0021-8561 | pmid = 12952431 | journal = Journal of agricultural and food chemistry}}</ref>

==Occurrence==
Guaiacol is usually derived from ] or wood ].

It is produced by a variety of plants.<ref>{{cite journal | doi = 10.1016/0305-0491(77)90029-3 |pmid=830476 |last1=Duffey |first1=S. S. |last2=Aldrich |first2=J. R. |last3=Blum |first3=M. S. | title = Biosynthesis of phenol and guaiacol by the hemipteran ''Leptoglossus phyllopus'' | journal = Comparative Biochemistry and Physiology B | year = 1977 | volume = 56 | issue = 2B | pages = 101–102}}</ref> It is also found in essential oils from ] seeds, ] leaves, ] leaves, and ] peels.<ref>{{cite book |last=Burdock|first=G. A.|date=1995|title=Encyclopedia of Food and Color Additives|location=Boca Raton, FL|publisher=CRC Press|pages=1244–1245|isbn=978-0849394126}}</ref> The pure substance is colorless, but samples become yellow upon exposure to air and light. The compound is present in wood ], resulting from the ] of ]. The compound contributes to the flavor of many substances such as ]<ref>{{cite news |last=Gallegos |first=Jenna |date=August 17, 2017 |title=The best way to drink whiskey, according to science |newspaper=The Washington Post |url=https://www.washingtonpost.com/news/speaking-of-science/wp/2017/08/17/the-best-way-to-drink-whiskey-according-to-science/ |quote=Guaiacol is what gives whiskey that smoky, spicy, peaty flavor.}}</ref> and ].<ref>{{cite journal |last1=Dorfner |first1=R. |last2=Ferge |first2=T. |last3=Kettrup |first3=A. |last4=Zimmermann |first4=R. |last5=Yeretzian |first5=C. |date=Sep 2003 |title=Real-time monitoring of 4-vinylguaiacol, guaiacol, and phenol during coffee roasting by resonant laser ionization time-of-flight mass spectrometry |journal=Journal of Agricultural and Food Chemistry |issn=0021-8561 |doi=10.1021/jf0341767 |pmid=12952431 |volume=51 |issue=19 |pages=5768–5773}}</ref>


==Preparation== ==Preparation==
In industry, guaiacol is produced by ] of ], e.g. using potash and ]:<ref name=Ullmann>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}}</ref> The compound was first isolated by ] in 1826.<ref>{{cite journal|last1=Stevens |first1=M. E. |last2=Ronan |first2=A. K. |last3=Sourkes |first3=T. S. |first4=Boyd |last4=E. M. | title=On the Expectorant Action of Creosote and the Guaiacols | journal=Canadian Medical Association Journal | year= 1943 | volume= 48 | issue= 2 | pages= 124–127 | pmid=20322688 | pmc=1827660}}</ref> Guaiacol is produced by ] of ''o''-], for example using ] and ]:<ref name=Ullmann>{{Ullmann|first1=Helmut |last1=Fiege |first2=Heinz-Werner |last2=Voges |first3=Toshikazu |last3=Hamamoto |first4=Sumio |last4=Umemura |first5=Tadao |last5=Iwata |first6=Hisaya |last6=Miki |first7=Yasuhiro |last7=Fujita |first8=Hans-Josef |last8=Buysch |first9=Dorothea |last9=Garbe |first10=Wilfried |last10=Paulus |title=Phenol Derivatives|doi=10.1002/14356007.a19_313}}</ref>
:C<sub>6</sub>H<sub>4</sub>(OH)<sub>2</sub> + ] → C<sub>6</sub>H<sub>4</sub>(OH)(OCH<sub>3</sub>) + HO(CH<sub>3</sub>O)SO<sub>2</sub> :C<sub>6</sub>H<sub>4</sub>(OH)<sub>2</sub> + ] → C<sub>6</sub>H<sub>4</sub>(OH)(OCH<sub>3</sub>) + HO(CH<sub>3</sub>O)SO<sub>2</sub>


===Laboratory methods=== ===Laboratory methods===
Guaiacol can be prepared by diverse routes in the laboratory. 2-Aminoanisole, derived in two steps from ], can be hydrolyzed via its diazonium derivative. Guaiacol can be synthesized by the di] of ] followed by selective mono-].<ref>{{OrgSynth | author = R. N. Mirrington and G. I. Feutrill | | year = 1988 | title = Orcinol Monomethyl Ether | collvol = 6 | collvolpages = 859 | prep = cv6p0859}}</ref> Guaiacol can be prepared by diverse routes in the laboratory. ], derived in two steps from ], can be hydrolyzed via its ] derivative. Guaiacol can be synthesized by the ] of ] followed by selective mono-].<ref>{{OrgSynth | first1= R. N. |last1=Mirrington |first2= G. I. |last2=Feutrill | year = 1988 | title = Orcinol Monomethyl Ether | collvol = 6 | collvolpages = 859 | prep = cv6p0859}}</ref>
:C<sub>6</sub>H<sub>4</sub>(OCH<sub>3</sub>)<sub>2</sub> + ] → C<sub>6</sub>H<sub>4</sub>(OCH<sub>3</sub>)(ONa) + C<sub>2</sub>H<sub>5</sub>SCH<sub>3</sub> :C<sub>6</sub>H<sub>4</sub>(OCH<sub>3</sub>)<sub>2</sub> + C<sub>2</sub>H<sub>5</sub>SNa → C<sub>6</sub>H<sub>4</sub>(OCH<sub>3</sub>)(ONa) + C<sub>2</sub>H<sub>5</sub>SCH<sub>3</sub>


==Uses== ==Uses and chemical reactions==
===Syringyl/guaiacyl ratio===
Guaiacol is a precursor to various ]s such as ]<ref>{{OrgSynth | author = C. F. H. Allen and J. W. Gates, Jr. | title = ''o''-Eugenol | collvol = 3 | collvolpages = 418 | year = 1955 | prep = cv30418}}</ref> and ].<ref>{{cite encyclopedia
], comprising a major fraction of biomass, is sometimes classified according to the '''guaiacyl''' component. Pyrolysis of lignin from ]s gives more guaiacol, resulting from removal of the ] group of ]. These lignins are said to have a high guaiacyl (or G) content. In contrast, lignins derived from ] affords ]. A high syringyl (or S) content is indicative of lignin from ]s.<ref name=TPC>{{cite journal |doi=10.1105/tpc.010111|title=The Last Step of Syringyl Monolignol Biosynthesis in Angiosperms is Regulated by a Novel Gene Encoding Sinapyl Alcohol Dehydrogenase |year=2001 |last1=Li |first1=Laigeng |last2=Cheng |first2=Xiao Fei |last3=Leshkevich |first3=Jacqueline |last4=Umezawa |first4=Toshiaki |last5=Harding |first5=Scott A. |last6=Chiang |first6=Vincent L. |journal=The Plant Cell |volume=13 |issue=7 |pages=1567–1586 |pmid=11449052 |pmc=139549 }}</ref> Sugarcane ] is one useful source of guaiacol; pyrolysis of the bagasse lignins yields compounds including guaiacol, 4-methylguaiacol and 4-vinylguaiacol.<ref>{{Cite journal |last1=del Río |first1=José C. |last2=Lino |first2=Alessandro G. |last3=Colodette |first3=Jorge L. |last4=Lima |first4=Claudio F. |last5=Gutiérrez |first5=Ana |last6=Martínez |first6=Ángel T. |last7=Lu |first7=Fachuang |last8=Ralph |first8=John |last9=Rencoret |first9=Jorge |date=2015-10-01 |title=Differences in the chemical structure of the lignins from sugarcane bagasse and straw |journal=Biomass and Bioenergy |language=en |volume=81 |pages=322–338 |doi=10.1016/j.biombioe.2015.07.006 |issn=0961-9534|doi-access=free }}</ref>
⚫ | last = Esposito

⚫ | first = Lawrence J.
===Chemical intermediate===
| coauthors = K. Formanek, G. Kientz, F. Mauger, V. Maureaux, G. Robert, and F. Truchet
Guaiacol is a useful precursor for the synthesis of other compounds.<ref>{{cite journal|doi=10.1351/pac200577071221|title=Masked ''o''-benzoquinone strategy in organic synthesis: Short and efficient construction of ''cis''-decalins and linear triquinanes from 2-methoxyphenols|journal=Pure and Applied Chemistry|volume=77|issue=7|pages=1221–1234|year=2005|last1=Liao|first1=Chun-Chen|doi-access=free}}</ref> Being derived from biomass, it is a potential component or precursor to "green fuels".<ref>{{cite journal|doi=10.1039/C3EE43081B|title=Upgrading of lignin-derived bio-oils by catalytic hydrodeoxygenation|journal=Energy Environ. Sci.|volume=7|pages=103–129|year=2014|last1=Saidi|first1=Majid|last2=Samimi|first2=Fereshteh|last3=Karimipourfard|first3=Dornaz|last4=Nimmanwudipong|first4=Tarit|last5=Gates|first5=Bruce C.|last6=Rahimpour|first6=Mohammad Reza}}</ref>

Guaiacol is also a useful reagent for the quantification of ]s, as in the presence of ] these enzymes will catalyse with it the formation of tetraguaiacol,<ref>{{cite journal | vauthors = Koduri RS, Tien M | journal = Journal of Biological Chemistry | volume = 270 | issue = 38 | pages = 22254–8 | date = 1995 | pmid = 7673205 | doi = 10.1074/jbc.270.38.22254 | title = Oxidation of Guaiacol by Lignin Peroxidase. Role of veratryl alcohol | doi-access = free }}</ref> a coloured compound that can be quantified by its absorbance at 420–470&nbsp;nm, following the equation:

:4 {{chem|guaiacol (colorless)}} + 2 {{chem|H|2|O|2}} → {{chem|tetraguaiacol (colored)}} + 8 {{chem|H|2|O}}.

===Medicinal and food===
Guaiacol is a precursor to various ]s, such as ].<ref>{{OrgSynth | first1= C. F. H. |last1=Allen |first2=J. W. Jr |last2=Gates | title = ''o''-Eugenol | collvol = 3 | collvolpages = 418 | year = 1955 | prep = cv3P0418}}</ref> An estimated 85% of the world's supply of ] 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 ] of ] with guaiacol to give mandelic acid, which is oxidized to produce ]. This acid undergoes a decarboxylation to afford vanillin.<ref>{{cite encyclopedia
⚫ | last1 = Esposito
⚫ | first1 = Lawrence J.
| first2=K. |last2=Formanek |first3=G. |last3=Kientz |first4=F. |last4=Mauger |first5=V. |last5=Maureaux |first6=G. |last6=Robert |first7=F. |last7=Truchet
| title = Vanillin | title = Vanillin
| encyclopedia = Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition | encyclopedia = Kirk–Othmer Encyclopedia of Chemical Technology |edition=4th
| volume = 24 | volume = 24
| pages = 812–825 | pages = 812–825
| publisher = John Wiley & Sons | publisher = John Wiley & Sons
| location = New York | location = New York, NY
| year = 1997}}</ref> Its derivatives are used medicinally as an ], ], and local ]. | year = 1997}}</ref> The crude vanillin product can then be purified with vacuum distillation and recrystallization.
It also can be used as a dye in chemical reactions, as oxygen will turn guaiacol from colorless to brown.


Guaiacol is also used medicinally as an ], ], and local ].<ref>{{cite web |url=https://www.drugbank.ca/drugs/DB11359|title=Guaiacol|author=<!--Not stated--> |date=2019-11-02|website=DrugBank|access-date=2019-11-18}}</ref>
==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|date=October 2007}} The valerianic ester of guaiacol is known as geosote, the benzoic as benzosol, the salicylic as guaiacolsalol, while the glycerin ether is the drug ]. The related derivative, dimethoxybenzene or ], 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.


⚫ Guaiacol is produced in the gut of ]s, ''Schistocerca gregaria'', by the breakdown of plant material. This process is undertaken by the gut bacterium '']'' (''Enterobacter''). It is one of the main components of the pheromones that cause ] ].<ref>{{cite journal|doi=10.1038/35002669|pmid=10706273|title=Pheromones: Exploitation of gut bacteria in the locust|first1=Rod J.|last1=Dillon|first2=Chris T.|last2=Vennard|first3=A. Keith|last3=Charnley|journal=Nature|volume=403|issue=6772|page=851|date=2000-02-24|bibcode=2000Natur.403..851D|s2cid=5207502|doi-access=free}}</ref>
Guaiacol is used as an inducer in Biochemical transformation. It has powerful effect on the fungi culture to incite them for producing the enzyme in their liquid or agar culture.<ref></ref><ref></ref>


==Safety== ==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.<ref></ref> ]s 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.<ref>{{cite web|last=Smith|first=K. R.|date=2005|url=http://ehs.sph.berkeley.edu/krsmith/publications/2005%20pubs/HC%20woodsmoke%20report%20Mar%2031%2005%20%28rev%29.pdf |title=Critical review of the health effects of woodsmoke|publisher=School of Public Health, University of Berkeley|url-status=dead|archive-url=https://web.archive.org/web/20090710235756/http://ehs.sph.berkeley.edu/krsmith/publications/2005%20pubs/HC%20woodsmoke%20report%20Mar%2031%2005%20%28rev%29.pdf|archive-date=2009-07-10}}</ref>


==Locust pheromone== == See also ==
* ]
⚫ Guaiacol is produced in the gut of ], ''Schistocerca gregaria'', by the breakdown of plant material. This process is undertaken by the gut bacterium ] (Enterobacter) agglomerans. Guaiacol is one of the main components of the pheromones that cause locust swarming.<ref></ref>
* ]


==References== == References ==
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