Furfural is an organic compound with the formula C4H3OCHO. It is a colorless liquid, although commercial samples are often brown. It has an aldehyde group attached to the 2-position of furan. It is a product of the dehydration of sugars, as occurs in a variety of agricultural byproducts, including corncobs, oat, wheatbran, and sawdust. The name furfural comes from the Latin word furfur, meaning bran, 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, acetic acid and sugar it is one of the oldest renewable chemicals. It is also found in many processed foods and beverages.
Furfural was first isolated in 1821 (published in 1832) by the GermanchemistJohann Wolfgang Döbereiner, who produced a small sample as a byproduct of formic acid synthesis. In 1840, the Scottish chemist John Stenhouse 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; he also determined furfural's empirical formula (C5H4O2).George Fownes named this oil "furfurol" in 1845 (from furfur (bran), and oleum (oil)). In 1848, the French chemist Auguste Cahours determined that furfural was an aldehyde. Determining the structure of furfural required some time: the furfural molecule contains a cyclic ether (furan), which tends to break open when it's treated with harsh reagents. In 1870, German chemist Adolf von Baeyer speculated (correctly) about the structure of the chemically similar compounds furan and 2-furoic acid. 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 had inferred that some derivatives of furfural contained a furan nucleus. In 1901, the German chemist Carl Harries determined furan's structure by synthesizing it from succindialdehyde, thereby also confirming furfural's proposed structure.
Furfural remained relatively obscure until 1922, when the Quaker Oats Company 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.
Furfural dissolves readily in most polar organic solvents, but it is only slightly soluble in either water or alkanes.
Furfural participates in the same kinds of reactions as other aldehydes and other aromatic compounds. It exhibits less aromatic character than benzene, as can be seen from the fact that furfural is readily hydrogenated to tetrahydrofurfuryl alcohol. When heated in the presence of acids, furfural irreversibly polymerizes, acting as a thermosetting polymer.
Furfural may be obtained by the acid catalyzed dehydration of 5-carbon sugars (pentoses), particularly xylose.
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 in the Republic of South Africa and Central Romana in the Dominican Republic 
In the laboratory, furfural can be synthesized from plant material by heating with sulfuric acid 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.
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 found in many foods: coffee (55-255 mg/kg) and whole grain bread (26 mg/kg).
Furfural is an important renewable, non-petroleum based, chemical feedstock. It can be converted into a variety of solvents, polymers, fuels and other useful chemicals by a range of catalyticreduction.
^J. W. Döbereiner (1832). "Ueber die medicinische und chemische Anwendung und die vortheilhafte Darstellung der Ameisensäure" [On the medical and chemical application and the profitable preparation of formic acid]. Annalen der Pharmacie (in German). 3 (2): 141-146. doi:10.1002/jlac.18320030206. From p. 141: "Ich verbinde mit diese Bitte noch die Bemerkung, ... Bittermandelöl riechende Materie enthält, ... " (I join to this request also the observation that the formic acid which is formed by the simultaneous reaction of sulfuric acid and manganese peroxide with sugar and which contains a volatile material that appears oily in an isolated condition and that smells like a mixture of cassia and bitter almond oil ... )
^George Fownes (1845). "An Account of the Artificial Formation of a Vegeto-Alkali". Philosophical Transactions of the Royal Society of London. 135: 253-262. doi:10.1098/rstl.1845.0008. JSTOR108270. From p. 261: "Under the circumstances, perhaps the name "Furfurol" (from furfur, bran, and oleum [oil]) might be applied provisionally, and I am informed that this is the name which was proposed by the party [viz, Thomas Newborn Robert Morson (1800-1874)] who several years ago prepared a considerable quantity of the oil (a portion of which came into my hands, as mentioned at the commencement of this paper), and endeavoured to discover for it economical applications."
^Cahours, Auguste (1848). "Note sur le furfurol" [Note on furfurol]. Annales de Chimie et de Physique. 3rd series (in French). 24: 277-285. From p. 285: "S'il ne m'a pas été jusqu'à présent possible de réaliser la formation de dérivés analogues à ceux que forment d'ordinaire les aldéhydes, cela tient à la facile altération de la molécule du furfurol de la part d'agent un peu énergiques." (If it hasn't been possible for me until now to make derivatives [that are] analogous to those which aldehydes normally form, this due to the easy alteration of the furfurol molecule by a slightly energetic reagent.)
^Baeyer, A.; Emmerling, A. (1870). "Reduction des Istatins zu Indigblau" [Reduction of istatin to indigo blue]. Berichte der Deutschen Chemischen Gesellschaft (in German). 3: 514-517. doi:10.1002/cber.187000301169. On p. 517, Baeyer proposed structures for furan (German: Tetraphenol) and 2-furoic acid (German: Brenzschleimsäure).
^In 1877, Baeyer published a series of papers on furfural, as he tried to determine its structure.
^In 1870, the German chemist Heinrich Limpricht prepared furan by heating salts of 2-furoic acid (pyromucic acid ; German: Pyroschleimsäure or Brenzschleimsäure), thereby decarboxylating it. Limpricht apparently thought that furan was cyclobutadiene to which a hydroxyl (OH) group was attached. Hence he named furan "tetraphenol" (i.e., an analog of phenol but with 4 carbon atoms instead of 6).
Limpricht, H. (1870). "Ueber das Tetraphenol C4H4O" [On tetraphenol C4H4O]. Berichte der Deutschen Chemischen Gesellschaft (in German). 3: 90-91. doi:10.1002/cber.18700030129. From p. 90: "Die Ansicht, dass die Pyroschleimsäure eine der Salicylsäure ähnliche Constitution besitzt, macht das Auftreten des Tetraphenols bei der Destillation der pyroschleimsauren Salze wahrscheinlich." (The belief that 2-furoic acid has a structure similar to salicylic acid makes probable the presence of tetraphenol [furan] during the distillation of salts of 2-furoic acid.) That is, just as heating salts of salicylic acid produces phenol, so heating salts of 2-furoic acid should produce an analog of phenol containing 4 carbon atoms.
See also (Tilden, 1886), p. 380.
^Tilden, William A., ed. (1886). Watts' Manual of Chemistry: Theoretical and Practical. vol. II: Chemistry of Carbon-Compounds or, Organic Chemistry (2nd ed.). Philadelphia, Pennsylvania, USA: P. Blakiston, Son, & Co. pp. 379-380. |volume= has extra text (help) The proposed structure for furfural appears on p. 380.
^Cai, Charles M.; Zhang, Taiying; Kumar, Rajeev; Wyman, Charles E. (2014). "Integrated furfural production as a renewable fuel and chemical platform from lignocellulosic biomass". Journal of Chemical Technology & Biotechnology. 89: 2-10. doi:10.1002/jctb.4168.
^Bonomi, Antonio; Cavalett, Otavio; Cunha, Marcelo Pereira da; Lima, Marco A. P. (2015-12-09). Virtual biorefinery : an optimization strategy for renewable carbon valorization. Bonomi, Antonio,, Cavalett, Otávio,, Cunha, Marcelo Pereira da,, Lima, Marco A. P. Cham. ISBN9783319260457. OCLC932064033.