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Furfural is an
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 C4H3OCHO. It is a colorless liquid, although commercial samples are often brown. It has an
aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
group attached to the 2-position of
furan Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans. Furan is a colorless, flammable, highly ...
. It is a product of the
dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
of sugars, as occurs in a variety of
agricultural Agriculture or farming is the practice of cultivating Plant, plants and livestock. Agriculture was the key development in the rise of Sedentism, sedentary human civilization, whereby farming of Domestication, domesticated species created food ...
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 g ...
,
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, unlike other cereals and pseudocereals). While oats are suitable for human con ...
,
wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
bran Bran, also known as miller's bran, is the hard outer layers of Cereal, cereal grain. It consists of the combined aleurone and pericarp. Corn (maize) bran also includes the pedicel (tip cap). Along with cereal germ, germ, it is an integral pa ...
, and
sawdust Sawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sanding, milling, planing, and routing. It is composed of small chippings of wood. These operations can be performed by woodworking machinery, ...
. The name ''furfural'' comes from the
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
word , meaning
bran Bran, also known as miller's bran, is the hard outer layers of Cereal, cereal grain. It consists of the combined aleurone and pericarp. Corn (maize) bran also includes the pedicel (tip cap). Along with cereal germ, germ, it is an integral pa ...
, referring to its usual source. Furfural is only derived from lignocellulosic biomass, i.e., its origin is non-food or non-coal/oil based. Aside from
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
,
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 component ...
, 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, fructose, and galactose. Compound sugars, also called disaccharides or double ...
, it is one of the oldest renewable chemicals. It is also found in many processed foods and beverages.


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 best known for work that foreshadowed the periodic law for the chemical elements, and for inventing the first lighter, which was known as the Döberei ...
, who produced a small sample as a byproduct of
formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Es ...
synthesis. In 1840, the Scottish chemist
John Stenhouse John Stenhouse FRS FRSE FIC FCS (21 October 1809 – 31 December 1880) was a Scottish 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 ...
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 ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
; 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, would simply be SO, as is th ...
(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 Gr ...
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). Ole ...
'' (oil)). In 1848, the French chemist Auguste Cahours determined that furfural was an
aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
. 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—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...
(
furan Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans. Furan is a colorless, flammable, highly ...
), 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 and developed a nomenclature for cyclic compounds (that was subsequently extended and adopted as part of the IUPAC org ...
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 extraor ...
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, Jakobskirch, Germany – 1942, Rolândia, Brazil) was a German chemist. He was nominated for the Nobel Prize in Chemistry in 1922 by Gustav Tammann and again in 1929 by Niels Bohr, Dirk Coster and George de Hevesy. Biograp ...
had inferred that some derivatives of furfural contained a furan nucleus. In 1901, the German chemist Carl Harries 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 based in Chicago. It has been owned by PepsiCo since 2001. History Precursor miller companies In the 1850s, Ferdinand Schumacher and Robert Stuart founded oat mills. S ...
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 which ...
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 chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
, 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 organic co ...
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 ( grc, ξύλον, , "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 gro ...
. : → + 3 These sugars may be obtained from
pentosan Pentosans are polymers composed of pentoses. In contrast to cellulose, which is composed of hexose (glucose) monomers, pentosans are derived from five-carbon sugars such as xylose. Pentosan-rich biomass is the precursor to furfural. The pentosan co ...
s obtained from
hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls.Scheller HV, Ulvskov H ...
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 a ...
. 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 ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
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). 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 that are feedstock for future finished products. As feedst ...
. It can be converted into a variety of solvents, polymers, fuels and other useful chemicals by a range of
catalytic Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
reduction.
Hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a Catalysis, catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or S ...
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. Th ...
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 * Analgesic ...
to help
herbicides Herbicides (, ), also commonly known as weedkillers, 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 fo ...
penetrate the leaf structure. In another application as a feedstock,
palladium Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...
-catalyzed
decarbonylation Decarbonylation is a type of organic reaction that involves loss of CO. It is often an undesirable reaction since it represents a degradation. In the chemistry of metal carbonyls, decarbonylation describes a substitution process, whereby a CO lig ...
on furfural manufactures industrially
furan Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans. Furan is a colorless, flammable, highly ...
. Another important solvent made from furfural is methyltetrahydrofuran. Furfural is used to make other
furan Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans. Furan is a colorless, flammable, highly ...
derivatives, such as furoic acid, via oxidation, and furan itself via
palladium Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...
catalyzed vapor phase
decarbonylation Decarbonylation is a type of organic reaction that involves loss of CO. It is often an undesirable reaction since it represents a degradation. In the chemistry of metal carbonyls, decarbonylation describes a substitution process, whereby a CO lig ...
. Furfural is also a specialized chemical solvent. There is a good market for value added chemicals that can be obtained from furfural.


Safety

Furfural is
carcinogenic A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substan ...
in
lab animal Animal testing, also known as animal experimentation, animal research, and ''in vivo'' testing, is the use of non-human animals in experiments that seek to control the variables that affect the behavior or biological system under study. This ...
s 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 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 is a cause of acute and chronic liver disease caused specifically by medications and the most common reason for a drug to be withdrawn fro ...
. 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 toxin, radiation, or pathogen. The value of LD50 for a substance is the ...
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 large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...
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 agent such as high level noise. Permissible exposure limits are established by the Occupational S ...
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 The aniline acetate test is a chemical test for the presence of certain carbohydrates, in which they are converted to furfural with hydrochloric acid, which reacts with aniline acetate to produce a bright pink color. Pentoses give a strong reactio ...
*
Bial's test Bial's test is a chemical test for the presence of pentoses. It is named after Manfred Bial, a German physician. The components include orcinol, hydrochloric acid, and ferric chloride. A pentose, if present, will be dehydrated to form furfural ...
*
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 ni ...


References


External links

* {{Authority control Conjugated dienes Monomers Flavors Solvents Fuel dyes Resins 2-Furyl compounds