The chemical compound furfural is an industrial chemical derived from a variety of agricultural byproducts, including corncobs, oat and wheat bran, and sawdust. The name furfural comes from the Latin word furfur, meaning bran, referring to its usual source.
Furfural is an aromatic aldehyde, with the ring structure shown at right. Its chemical formula is C5 H4 O2. In its pure state, it is a colorless oily liquid with the odor of almonds, but upon exposure to air it quickly becomes yellow.
Furfural was first isolated in 1832 by the German chemist Johann Wolfgang Döbereiner
, who formed a very small quantity of it as a byproduct of formic acid
synthesis. At the time, formic acid was formed by the distillation
of dead ants
, and Döbereiner's ant bodies probably contained some plant matter. 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
, and he determined that this chemical had an empirical formula
. In 1901, the German chemist Carl Harries
deduced furfural's structure.
Except for occasional use in perfume, furfural remained a relatively obscure chemical 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.
Furfural's physical properties are summarized in the table at right. Furfural dissolves readily in most polar organic
solvents, but is only slightly soluble in either water
Chemically, furfural participates in the same kinds of reactions as other aldehydes and other aromatic compounds. The aromatic stability of furfural is not as great as in benzene, and furfural participates in hydrogenation and other addition reactions more readily than many other aromatics.
When heated above 250 °C, furfural decomposes into furan and carbon monoxide, sometimes explosively.
When heated in the presence of acids, furfural irreversibly solidifies into a hard thermosetting resin.
Many plant materials contain the polysaccharide hemicellulose
, a polymer
containing five carbon atoms each. When heated with sulfuric acid, hemicellulose undergoes hydrolysis
to yield these sugars, principally xylose
. Under the same conditions of heat and acid, xylose and other five carbon sugars undergo dehydration, losing three water molecules to become furfural:
- C5H10O5 → C5H4O2 + 3 H2O
For crop residue feedstocks, about 10% of the mass of the original plant matter can be recovered as furfural. Furfural and water evaporate together from the reaction mixture, and separate upon condensation.
Global total capacity of production is about 450,000 ton. China is the biggest supplier of this product and they have about a half of global capacity.
In the laboratory, synthesis of furfural from corn cobs takes place by reflux with dilute sulfuric acid .
Furfural is used as a solvent
in petrochemical refining
to extract dienes
(which are used to make synthetic rubber
) from other hydrocarbons
Furfural, as well as its derivative furfuryl alcohol, can be used either by themselves or in together with phenol, acetone, or urea to make solid resins. Such resins are used in making fiberglass, some aircraft components, and automotive brakes.
Furfural is also used as a chemical intermediate in the production of the solvents furan and tetrahydrofuran. Hydroxymethylfurfural has been identified in a wide variety of heat processed foods.
When ingested or inhaled, furfural can cause intoxication
, including euphoria
, and eventual unconsciousness and death due to respiratory failure. Contact with furfural irritates the skin
and respiratory tract
and can cause the lungs
to fill with fluid.
Chronic skin exposure can lead to a skin allergy to the substance, as well as an unusual susceptibility to sunburn. In toxicity studies, furfural has led to tumors, mutations, and liver and kidney damage in animals.