2-furaldehyde
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Furfural is an
organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
with the formula C4H3OCHO. It is a colorless liquid, although commercial samples are often brown. It has an
aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
group attached to the 2-position of
furan Furan is a Heterocyclic compound, heterocyclic organic compound, consisting of a five-membered aromatic Ring (chemistry), ring with four carbon Atom, atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as f ...
. It is a product of the
dehydration In physiology, dehydration is a lack of total body water that disrupts metabolic processes. It occurs when free water loss exceeds intake, often resulting from excessive sweating, health conditions, or inadequate consumption of water. Mild deh ...
of sugars, as occurs in a variety of
agricultural Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created f ...
byproducts, including
corncobs Corn on the cob is a culinary term for a cooked ear of sweet corn (maize) eaten directly off the cob. The ear is picked while the endosperm is in the "milk stage" so that the kernels are still tender. Ears of corn are steamed, boiled, or gril ...
,
oat The oat (''Avena sativa''), sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural). Oats appear to have been domesticated as a secondary crop, as their seeds ...
,
wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...
bran Bran, also known as miller's bran, is the component of a Cereal, cereal grain consisting of the hard layersthe combined aleurone and Fruit anatomy#Pericarp layers, pericarpsurrounding the endosperm. Maize, Corn (maize) bran also includes the p ...
, and
sawdust Sawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sanding, milling and routing. It is composed of very small chips of wood. These operations can be performed by woodworking machinery, portable p ...
. The name ''furfural'' comes from the
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
word , meaning
bran Bran, also known as miller's bran, is the component of a Cereal, cereal grain consisting of the hard layersthe combined aleurone and Fruit anatomy#Pericarp layers, pericarpsurrounding the endosperm. Maize, Corn (maize) bran also includes the p ...
, referring to its usual source. Furfural is derived only from dried biomass. In addition to
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
,
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...
, and
sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...
, furfural is one of the oldest known organic chemicals available readily purified from natural precursors.


History

Furfural was first isolated in 1821 (published in 1832) by the German chemist
Johann Wolfgang Döbereiner Johann Wolfgang Döbereiner (13 December 1780 – 24 March 1849) was a German chemist who is known best for work that was suggestive of the periodic law for the chemical elements, and for inventing the first lighter, which was known as the Dö ...
, who produced a small sample as a byproduct of
formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid. It has the chemical formula HCOOH and structure . This acid is an important intermediate in chemical synthesis and occurs naturally, most notably in some an ...
synthesis. In 1840, the Scottish chemist
John Stenhouse John Stenhouse FRS FRSE FIC FCS (21 October 1809 – 31 December 1880) was a British chemist. In 1854, he invented one of the first practical respirators. He was a co-founder of the Chemical Society in 1841. Life John Stenhouse was born i ...
found that the same chemical could be produced by distilling a wide variety of crop materials, including corn, oats, bran, and sawdust, with aqueous
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
; he also determined furfural's
empirical formula In chemistry, the empirical formula of a chemical compound is the simplest whole number ratio of atoms present in a compound. A simple example of this concept is that the empirical formula of sulfur monoxide, or SO, is simply SO, as is the empir ...
(C5H4O2).
George Fownes George Fownes, FRS (14 May 1815 in London – 31 January 1849) was a British chemist. He attended the Palace School in Enfield. He obtained his PhD at Giessen, in Germany. From 1842 he was chemistry professor at the Pharmaceutical Society of G ...
named this oil "furfurol" in 1845 (from ''furfur'' (bran), and ''
oleum Oleum (Latin ''oleum'', meaning oil), or fuming sulfuric acid, is a term referring to solutions of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid). Ol ...
'' (oil)). In 1848, the French chemist Auguste Cahours determined that furfural was an
aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
. Determining the structure of furfural required some time: the furfural molecule contains a cyclic
ether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R†...
(
furan Furan is a Heterocyclic compound, heterocyclic organic compound, consisting of a five-membered aromatic Ring (chemistry), ring with four carbon Atom, atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as f ...
), which tends to break open when it's treated with harsh reagents. In 1870, German chemist
Adolf von Baeyer Johann Friedrich Wilhelm Adolf von Baeyer (; 31 October 1835 – 20 August 1917) was a German chemist who synthesised indigo dye, indigo and developed a Von Baeyer nomenclature, nomenclature for cyclic compounds (that was subsequently extended a ...
speculated about the structure of the chemically similar compounds furan and 2-furoic acid. Additional research by German chemist
Heinrich Limpricht Heinrich Limpricht (21 April 1827 – 13 May 1909) was a German chemist. Limpricht was a pupil of Friedrich Wöhler; he worked on the chemistry of furans and pyrroles, discovering furan in 1870. In 1852 he became lecturer and in 1855 extraordi ...
supported this idea. From work published in 1877, Baeyer had confirmed his previous belief on the structure of furfural. By 1886, furfurol was being called "furfural" (short for "furfuraldehyde") and the correct chemical structure for furfural was being proposed. By 1887, the German chemist
Willy Marckwald Willy Marckwald (1864, Radwanice, Polkowice County, Jakobskirch, Kingdom of Prussia – 1942, Rolândia, Brazil) was a German chemist. Biography Marckwald studied at Berlin's Humboldt University of Berlin, Friedrich-Wilhelms-Universität and rec ...
had inferred that some derivatives of furfural contained a furan nucleus. In 1901, the German chemist
Carl Harries Carl Dietrich Harries (5 August 1866 – 3 November 1923) was a German chemist born in Luckenwalde, Brandenburg, Prussia. He received his doctorate in 1892. In 1900, he married Hertha von Siemens, daughter of the electrical genius Werner von Si ...
determined furan's structure through work with succindialdehyde and 2-methylfuran, thereby also confirming furfural's proposed structure. Furfural remained relatively obscure until 1922, when the
Quaker Oats Company The Quaker Oats Company, known as Quaker, is an American food Conglomerate (company), conglomerate based in Chicago, Illinois. As Quaker Mill Company, the company was founded in 1877 in Ravenna, Ohio. In 1881, Henry Crowell bought the company and ...
began mass-producing it from oat hulls. Today, furfural is still produced from agricultural byproducts like sugarcane bagasse and corn cobs. The main countries producing furfural today are the Dominican Republic, South Africa and China.


Properties

Furfural dissolves readily in most polar organic solvents, but it is only slightly soluble in either water or
alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...
s. Furfural participates in the same kinds of reactions as other aldehydes and other aromatic compounds. It exhibits less aromatic character than
benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...
, as can be seen from the fact that furfural is readily
hydrogenated Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organi ...
to
tetrahydrofurfuryl alcohol Tetrahydrofurfuryl alcohol (THFA) is an organic compound with the formula HOCH2C4H7O. In terms of its structure, it consists of a tetrahydrofuran ring substituted in the 2-position with a hydroxymethyl group. It is a colorless liquid that is use ...
. When heated in the presence of acids, furfural irreversibly polymerizes, acting as a
thermosetting polymer In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (" curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and ...
.


Production

Furfural may be obtained by the acid catalyzed dehydration of 5-carbon sugars (
pentose In chemistry, a pentose is a monosaccharide (simple sugar) with five carbon atoms. The chemical formula of many pentoses is , and their molecular weight is 150.13 g/mol.xylose Xylose ( , , "wood") is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional group. It is deriv ...
. : → + 3 These sugars may be obtained from pentosans obtained from
hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls. Cellulose is crystalline, strong, an ...
present in
lignocellulosic biomass Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels. It is composed of two kinds of carbohydrate polymers, cellulose ...
. Between 3% and 10% of the mass of crop residue feedstocks can be recovered as furfural, depending on the type of feedstock. Furfural and water evaporate together from the reaction mixture, and separate upon condensation. The global production capacity is about 800,000 tons as of 2012. China is the biggest supplier of furfural, and accounts for the greater part of global capacity. The other two major commercial producers are
Illovo Sugar Illovo Sugar Africa (Pty) Ltd based in uMhlanga, KwaZulu-Natal, South Africa, is Africa's largest sugar producer. The group produces raw and refined sugar for local, regional African, European Union (EU), United States and world markets from sug ...
in South Africa and Central Romana in the Dominican Republic. In the laboratory, furfural can be synthesized from plant material by heating with
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
or other acids. With the purpose to avoid toxic effluents, an effort to substitute sulfuric acid with easily separable and reusable solid acid catalysts has been studied around the world. The formation and extraction of xylose and subsequently furfural can be favored over the extraction of other sugars with varied conditions, such as acid concentration, temperature, and time. In industrial production, some lignocellulosic residue remains after the removal of the furfural. This residue is dried and burned to provide steam for the operation of the furfural plant. Newer and more energy efficient plants have excess residue, which is or can be used for co-generation of electricity, cattle feed, activated carbon, mulch/fertiliser, etc.


Uses and occurrence

It is commonly found in many cooked or heated foods such as coffee (55–255 mg/kg) and whole grain bread (26 mg/kg). In
petrochemical industry file:Jampilen Petrochemical Co. 02.jpg, 300px, Jampilen Petrochemical co., Asaluyeh, Iran The petrochemical industry is concerned with the production and trade of petrochemicals. A major part is constituted by the plastics industry, plastics (poly ...
, furfural is utilized as a specialized chemical solvent for
diene In organic chemistry, a diene ( ); also diolefin, ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nome ...
extraction. Furfural is an important renewable, non-petroleum based, chemical
feedstock A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials/Intermediate goods that are feedstock for future finishe ...
which can be converted into solvents, polymers, fuels and other useful chemicals by a range of
catalytic Catalysis () is the increase in reaction rate, rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst ...
reduction.
Hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or Saturated ...
of furfural provides
furfuryl alcohol Furfuryl alcohol is an organic compound containing a furan substituted with a hydroxymethyl group. It is a colorless liquid, but aged samples appear amber. It possesses a faint odor of burning and a bitter taste. It is miscible with but unstabl ...
(FA), which is used to produce
furan resin Furan resin refers to polymers produced from various furan compounds, of which the most common starting materials are furfuryl alcohol and furfural. In the resin and in the cured polyfurfurol, the furan rings are not connected by conjugation. T ...
s, which are exploited in
thermoset polymer matrix A thermoset polymer matrix is a synthetic polymer reinforcement where polymers act as binder or matrix to secure in place incorporated particulates, fibres or other reinforcements. They were first developed for structural applications, such as gla ...
composites, cements, adhesives, casting resins and coatings. Further hydrogenation of furfuryl alcohol leads to
tetrahydrofurfuryl alcohol Tetrahydrofurfuryl alcohol (THFA) is an organic compound with the formula HOCH2C4H7O. In terms of its structure, it consists of a tetrahydrofuran ring substituted in the 2-position with a hydroxymethyl group. It is a colorless liquid that is use ...
(THFA), which is used as a solvent in agricultural formulations and as an
adjuvant In pharmacology, an adjuvant is a drug or other substance, or a combination of substances, that is used to increase the efficacy or potency of certain drugs. Specifically, the term can refer to: * Adjuvant therapy in cancer management * Anal ...
to help
herbicides Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...
penetrate the leaf structure.
Palladium Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), ...
-catalyzed
decarbonylation In chemistry, decarbonylation is a type of organic reaction that involves the loss of carbon monoxide (CO). It is often an undesirable reaction, since it represents a degradation. In the chemistry of metal carbonyls, decarbonylation describes a ...
on furfural manufactures industrially
furan Furan is a Heterocyclic compound, heterocyclic organic compound, consisting of a five-membered aromatic Ring (chemistry), ring with four carbon Atom, atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as f ...
. Another important solvent made from furfural is methyltetrahydrofuran. Furfural is used to make other
furan Furan is a Heterocyclic compound, heterocyclic organic compound, consisting of a five-membered aromatic Ring (chemistry), ring with four carbon Atom, atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as f ...
derivatives, such as furoic acid, via oxidation, and furan itself via
palladium Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), ...
catalyzed vapor phase
decarbonylation In chemistry, decarbonylation is a type of organic reaction that involves the loss of carbon monoxide (CO). It is often an undesirable reaction, since it represents a degradation. In the chemistry of metal carbonyls, decarbonylation describes a ...
. There is a good market for value added chemicals that can be obtained from furfural.


Safety

Furfural is
carcinogenic A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and Biological agent, biologic agent ...
in lab animals and
mutagenic In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can cause cancer in ...
in single cell organisms, but there is no data on human subjects. It is classified in
IARC Group 3 IARC group 3 substances, chemical mixtures and exposure circumstances are those that can not be classified in regard to their carcinogenicity to humans by the International Agency for Research on Cancer (IARC). This category is used most commonly ...
due to the lack of data on humans and too few tests on animals to satisfy Group 2A/2B criteria. It is
hepatotoxic Hepatotoxicity (from ''hepatic toxicity'') implies chemical-driven liver damage. Drug-induced liver injury (DILI) is a cause of acute and chronic liver disease caused specifically by medications and the most common reason for a drug to be withdr ...
. The
median lethal dose In toxicology, the median lethal dose, LD50 (abbreviation for " lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a given substance. The value of LD50 for a substance is the dose re ...
is high, 650–900 mg/kg (oral, dogs), consistent with its pervasiveness in foods. The
Occupational Safety and Health Administration The Occupational Safety and Health Administration (OSHA; ) is a regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. The United States Congress established ...
has set a
permissible exposure limit The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agents such as high level noise. Permissible exposure limits were established by the Occupational ...
for furfural at 5ppm over an eight-hour time-weighted average (TWA), and also designates furfural as a risk for skin absorption.


See also

* Aniline acetate test *
Bial's test Bial's test is a chemical test for the presence of pentoses originally developed for the diagnosis of pentosuria. It is named after Manfred Bial, a German physician. The components include orcinol, hydrochloric acid, and ferric chloride. A pentos ...
*
Molisch's test Molisch's test is a sensitive chemical test, named after Austrian botanist Hans Molisch, for the presence of carbohydrates, based on the dehydration of the carbohydrate by sulfuric acid or hydrochloric acid to produce an aldehyde, which condenses ...
*
Tollens' reagent Tollens' reagent (chemical formula Ag(NH3)2OH) is a chemical reagent used to distinguish between aldehydes and ketones along with some alpha-hydroxy ketones which can tautomerize into aldehydes. The reagent consists of a solution of silver n ...


References


External links

* {{Authority control Conjugated dienes Monomers Flavors Solvents Fuel dyes Resins 2-Furyl compounds Substances discovered in the 19th century