organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
C6H4(OH)(OCH3). It is a phenolic compound containing an 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.
Occurrence
Guaiacol is usually derived from
guaiacum
''Guaiacum'' (''OED'' 2nd edition, 1989.Entry "guaiacum" in creosote.
It is produced by a variety of plants. It is also found in essential oils from
celery
Celery (''Apium graveolens'') is a marshland plant in the family Apiaceae that has been cultivated as a vegetable since antiquity. Celery has a long fibrous stalk tapering into leaves. Depending on location and cultivar, either its stalks, lea ...
seeds,
tobacco
Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...
leaves, orange leaves, and lemon peels. 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
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
of
lignin
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
. The compound contributes to the flavor of many substances such as
whiskey
Whisky or whiskey is a type of distilled alcoholic beverage made from fermented grain mash. Various grains (which may be malted) are used for different varieties, including barley, corn, rye, and wheat. Whisky is typically aged in wooden cask ...
Otto Unverdorben
Otto Unverdorben (13 October 1806 – 28 November 1873) was a German chemist and merchant who was born in Dahme/Marke. After completing his schooling in Dresden, he studied chemistry at Halle, Leipzig and Berlin.
In 1826 at the age of 20, Unver ...
in 1826. Guaiacol is produced by
methylation
In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These t ...
potash
Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.
and
dimethyl sulfate
Dimethyl sulfate (DMS) is a chemical compound with formula (CH3O)2SO2. As the diester of methanol and sulfuric acid, its formula is often written as ( CH3)2 SO4 or Me2SO4, where CH3 or Me is methyl. Me2SO4 is mainly used as a methylating agent ...
Guaiacol can be prepared by diverse routes in the laboratory. ''o''-Anisidine, derived in two steps from
anisole
Anisole, or methoxybenzene, is an organic compound with the formula CH3OC6H5. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances. The compound is ...
, can be hydrolyzed via its diazonium derivative. Guaiacol can be synthesized by the dimethylation of catechol followed by selective mono- demethylation.
:C6H4(OCH3)2 + C2H5SNa → C6H4(OCH3)(ONa) + C2H5SCH3
Uses and chemical reactions
Syringyl/guaiacyl ratio
Lignin
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
, comprising a major fraction of biomass, is sometimes classified according to the guaiacyl component. Pyrolysis of lignin from
gymnosperm
The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, Î³Ï…Î¼Î½ÏŒÏ ...
s gives more guaiacol, resulting from removal of the
propenyl In organic chemistry, 1-propenyl (or simply propenyl) has the formula CH=CHCH3 and 2-propenyl (isopropenyl) has the formula CH2=C-CH3. These groups are found in many compounds. Propenyl compounds are isomeric with allyl compounds, which have the f ...
group of
coniferyl alcohol
Coniferyl alcohol is an organic compound with the formula HO(CH3O)C6H3CH=CHCH2OH. A colourless or white solid, it is one of the monolignols, produced via the phenylpropanoid biochemical pathway. When copolymerized with related aromatic compounds, ...
. 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
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s. Sugarcane bagasse is one useful source of guaiacol; pyrolysis of the bagasse lignins yields compounds including guaiacol, 4-methylguaiacol and 4-vinylguaiacol.
Chemical intermediate
Guaiacol is a useful precursor for the synthesis of other compounds. Being derived from biomass, it is a potential component or precursor to "green fuels".
Guaiacol is also a useful reagent for the quantification of peroxidases, as in the presence of
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
these enzymes will catalyse with it the formation of tetraguaiacol, a coloured compound that can be quantified by its absorbance at 420–470 nm, following the equation:
4 + 2 → + 8 .
Medicinal and food
Guaiacol is a precursor to various
flavorant
A flavoring (or flavouring), also known as flavor (or flavour) or flavorant, is a food additive used to improve the taste or smell of food. It changes the perceptual impression of food as determined primarily by the chemoreceptors of the gust ...
s, such as
eugenol
Eugenol is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds. It is a colorless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove, nutmeg, cinnamon, basil ...
. An estimated 85% of the world's supply of
vanillin
Vanillin is an organic compound with the molecular formula . It is a phenolic aldehyde. Its functional groups include aldehyde, hydroxyl, and ether. It is the primary component of the extract of the vanilla bean. Synthetic vanillin is now used ...
comes from guaiacol. Because consumers tend to prefer the taste of natural vanillin to synthetic vanillin, methods such as microbial fermentation have been adopted to chemically simulate the taste of natural vanillin. The route entails the condensation reaction of glyoxylic acid with guaiacol to give mandelic acid, which is oxidized to produce
phenylglyoxylic acid
Phenylglyoxylic acid is the organic compound with the formula C6H5C(O)CO2H. The conjugate base, known as benzoylformate is the substrate of benzoylformate decarboxylase, a thiamine diphosphate-dependent enzyme:
:benzoylformate + H+ benzaldehyde ...
. This acid undergoes a decarboxylation to afford vanillin. 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.
Guaiacol is produced in the gut of
desert locust
The desert locust (''Schistocerca gregaria'') is a species of locust, a periodically swarming, short-horned grasshopper in the family Acrididae. They are found primarily in the deserts and dry areas of northern and eastern Africa, Arabia, and sou ...
s, ''Schistocerca gregaria'', by the breakdown of plant material. This process is undertaken by the gut bacterium ''
Pantoea agglomerans
''Pantoea agglomerans'' is a Gram-negative bacterium that belongs to the family Erwiniaceae.
It was formerly called ''Enterobacter agglomerans'', or ''Erwinia herbicola'' and is a ubiquitous bacterium commonly isolated from plant surfaces, seed ...
'' (''Enterobacter''). It is one of the main components of the pheromones that cause locust
swarming
Swarm behaviour, or swarming, is a collective behaviour exhibited by entities, particularly animals, of similar size which aggregate together, perhaps milling about the same spot or perhaps moving ''en masse'' or migrating in some direction. ...
.
Safety
Methoxyphenol Methoxyphenol or hydroxyanisole may refer to:
* 2-Methoxyphenol (guaiacol, ''o''-methoxyphenol, methylcatechol, 2-hydroxyanisole)
* 3-Methoxyphenol (''m''-methoxyphenol, ''m''-guaiacol, resorcinol monomethyl ether, 3-hydroxyanisole, ''m''-hydroxyan ...
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.
Guaifenesin
Guaifenesin, also known as glyceryl guaiacolate, is an expectorant medication that aids in the elimination of sputum from the respiratory tract. Chemically it is an ether of guaiacol and glycerine. It is often used in combination with other me ...