Guaiacol: Difference between revisions

{{short description|Methoxyphenol compound, constituent of plant lignins and essential oils}}

| Watchedfields = changed

| verifiedrevid = 443849411

| Reference =<ref>{{cite book|title=Merck Index|edition=13th|page=4568|title-link=Merck Index}}</ref>

| ImageFileL1 =Guaiacol.png

| ImageFileR1 =Guaiacol 3D spacefill.png

| PIN =2-Methoxyphenol

| 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}}</ref><br> 2-Hydroxyanisole<br> Pyroguaiac acid<br> Pyrocatechol monomethyl ether<br> 1-hydroxy-2-methoxybenzene<br>

|Section1={{Chembox Identifiers

| UNII_Ref = {{fdacite|correct|FDA}}

| CASNo = 90-05-1

| PubChem = 460

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| ChEBI_Ref = {{ebicite|correct|EBI}}

| ChEBI = 28591

}}

|Section2={{Chembox Properties

| C=7|H=8|O=2

| MolarMass =

| Appearance = colorless oil or crystalline solid

| Density = 1.112 g/cm³, liquid<br />1.129 g/cm³, crystals

| MeltingPtC = 26-29

| BoilingPtC = 204–206

| BoilingPt_notes =

| Solubility = 23.3 g/L at 25&nbsp;°C

}}

|Section3={{Chembox Hazards

| MainHazards =

| FlashPt =

| AutoignitionPt =

}}

|Section4={{Chembox Related

| OtherFunction_label = [[methoxyphenol]]s

| OtherFunction = [[Mequinol]]<br /> [[3-Methoxyphenol]]

'''Guaiacol''' ({{IPAc-en|ˈ|ɡ|w|aɪ|ə|k|ɒ|l}}) is an [[organic compound]] with the [[Chemical formula|formula]] C₆H₄(OH)(OCH₃). It is a phenolic compound containing a [[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.<ref name=Ullmann/>

==Occurrence==

Guaiacol is usually derived from [[guaiacum]] or wood [[creosote]].

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 [[celery]] seeds, [[tobacco]] leaves, [[Orange (tree)|orange]] leaves, and [[lemon]] 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 [[smoke]], resulting from the [[pyrolysis]] of [[lignin]]. The compound contributes to the flavor of many substances such as [[whisky|whiskey]]<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 [[roasted coffee]].<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>

The compound was first isolated by [[Otto Unverdorben]] 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 [[methylation]] of ''o''-[[catechol]], for example using [[potash]] and [[dimethyl sulfate]]:<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>

Guaiacol can be prepared by diverse routes in the laboratory. [[o-Anisidine|''o''-Anisidine]], derived in two steps from [[anisole]], can be hydrolyzed via its [[diazonium]] derivative. Guaiacol can be synthesized by the [[methylation|dimethylation]] of [[catechol]] followed by selective mono-[[demethylation]].<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>

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

==Uses and chemical reactions==

===Syringyl/guaiacyl ratio===

[[Lignin]], comprising a major fraction of biomass, is sometimes classified according to the '''guaiacyl''' component. Pyrolysis of lignin from [[gymnosperm]]s gives more guaiacol, resulting from removal of the [[propenyl]] group of [[coniferyl alcohol]]. These lignins are said to have a high guaiacyl (or G) content. In contrast, lignins derived from [[sinapyl alcohol]] affords [[syringol]]. A high syringyl (or S) content is indicative of lignin from [[angiosperm]]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 [[bagasse]] 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>

===Chemical intermediate===

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 [[peroxidase]]s, as in the presence of [[hydrogen peroxide]] 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 [[flavorant]]s, such as [[eugenol]].<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 [[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.<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

| encyclopedia = Kirk–Othmer Encyclopedia of Chemical Technology |edition=4th

| location = New York, NY

| year = 1997}}</ref> 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]].<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>

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

[[Methoxyphenol]]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>

== See also ==

* [[Creosote]]

* [[Guaifenesin]]

== References ==

{{reflist|30em}}

{{Authority control}}

[[Category:Flavors]]

[[Category:Insect pheromones]]

[[Category:O-methylated natural phenols]]

[[Category:Substances discovered in the 19th century]]