Guaiacol
Encyclopedia
Guaiacol is a naturally occurring organic compound
with the formula
C6H4(OH)(OCH3). Although it is biosynthesized by a variety of organisms, 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.
of catechol, e.g. using potash and dimethyl sulfate
:
, can be hydrolyzed via its diazonium derivative. Guaiacol can be synthesized by the dimethylation
of catechol followed by selective mono-demethylation
.
and vanillin
. 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.
. 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.
(Enterobacter) agglomerans. Guaiacol is one of the main components of the pheromones that cause locust swarming.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
C6H4(OH)(OCH3). Although it is biosynthesized by a variety of organisms, this colorless aromatic oil is usually derived from guaiacum
Guaiacum
Guaiacum, sometimes spelled Guajacum, is a genus of flowering plants in the caltrop family Zygophyllaceae. It contains five species of slow-growing shrubs and trees, reaching a height of approximately but are usually less than half of that...
or wood creosote
Creosote
Creosote is the portion of chemical products obtained by the distillation of a tar that remains heavier than water, notably useful for its anti-septic and preservative properties...
. Samples darken upon exposure to air and light. Guaiacol is present in wood smoke
Smoke
Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...
, resulting from the pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
of lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
. The compound contributes to the flavor of many compounds, e.g. roasted coffee.
Preparation
In industry, guaiacol is produced by methylationMethylation
In the chemical sciences, methylation denotes the addition of a methyl group to a substrate or the substitution of an atom or group by a methyl group. Methylation is a form of alkylation with, to be specific, a methyl group, rather than a larger carbon chain, replacing a hydrogen atom...
of catechol, e.g. using potash and dimethyl sulfate
Dimethyl sulfate
Dimethyl sulfate is a chemical compound with formula 2SO2. As the diester of methanol and sulfuric acid, its formula is often written as 2SO4 or even Me2SO4, where CH3 or Me is methyl...
:
- C6H4(OH)2 + (CH3O)2SO2Dimethyl sulfateDimethyl sulfate is a chemical compound with formula 2SO2. As the diester of methanol and sulfuric acid, its formula is often written as 2SO4 or even Me2SO4, where CH3 or Me is methyl...
→ 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 anisoleAnisole
Anisole, or methoxybenzene, is the 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...
, can be hydrolyzed via its diazonium derivative. Guaiacol can be synthesized by the dimethylation
Methylation
In the chemical sciences, methylation denotes the addition of a methyl group to a substrate or the substitution of an atom or group by a methyl group. Methylation is a form of alkylation with, to be specific, a methyl group, rather than a larger carbon chain, replacing a hydrogen atom...
of catechol followed by selective mono-demethylation
Demethylation
Demethylation is the chemical process resulting in the removal a of methyl group from a molecule.A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen atoms....
.
- C6H4(OCH3)2 + C2H5SNaEthanethiolEthanethiol is an organic compound with the formula CH3CH2SH. It consists of an ethyl group, CH3CH2, attached to a thiol group, SH. Its structure parallels that of ethanol, but with S instead of O. The presence of S leads to many different properties, most notably the infamous odour of EtSH...
→ C6H4(OCH3)(ONa) + C2H5SCH3
Uses
Guaiacol is a precursor to various flavorants such as eugenolEugenol
Eugenol is a phenylpropene, an allyl chain-substituted guaiacol. Eugenol is a member of the phenylpropanoids class of chemical compounds. It is a clear to pale yellow oily liquid extracted from certain essential oils especially from clove oil, nutmeg, cinnamon, basil and bay leaf. It is slightly...
and vanillin
Vanillin
Vanillin is a phenolic aldehyde, an organic compound with the molecular formula C8H8O3. Its functional groups include aldehyde, ether, and phenol. It is the primary component of the extract of the vanilla bean. It is also found in Leptotes bicolor, roasted coffee and the Chinese red pine...
. Its derivatives are used medicinally as an expectorant, antiseptic
Antiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...
, 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). The valerianic ester of guaiacol is known as geosote, the benzoic as benzosol, the salicylic as guaiacolsalol, while the glycerin ether is the drug guaifenesinGuaifenesin
Guaifenesin INN or guaiphenesin , also glyceryl guaiacolate, is an expectorant drug sold over the counter and usually taken by mouth to assist the bringing up of phlegm from the airways in acute respiratory tract infections.-History:Similar medicines derived from the guaiac tree were in use as a...
. 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.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 PantoeaPantoea agglomerans
Pantoea agglomerans is a Gram-negative bacterium that belongs to the family Enterobacteriaceae.Formerly called Enterobacter agglomerans, this bacterium is known to be an opportunistic pathogen in the immunocompromised, causing wound, blood, and urinary-tract infections. It is commonly isolated...
(Enterobacter) agglomerans. Guaiacol is one of the main components of the pheromones that cause locust swarming.