furfural or furfuraldehyde [Lat.,=bran], C₄H₃OCHO, viscous, colorless liquid that has a pleasant aromatic odor; upon exposure to air it turns dark brown or black. It boils at about 160°C;. It is commonly used as a solvent; it is soluble in ethanol and ether and somewhat soluble in water. Furfural is the aldehyde of pyromucic acid; it has properties similar to those of benzaldehyde. A derivative of furan, it is prepared commercially by dehydration of pentose sugars obtained from cornstalks and corncobs, husks of oat and peanut, and other waste products. It is used in the manufacture of pesticides, phenolfurfural resins, and tetrahydrofuran. Tetrahydrofuran is used as a commercial solvent and is converted in starting materials for the preparation of nylon.

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.

History

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 of C₅H₄O₂. 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.

Properties

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 or alkanes.

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.

Production

Many plant materials contain the polysaccharide hemicellulose, a polymer of sugars 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 .

Uses

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.

Safety

When ingested or inhaled, furfural can cause intoxication, including euphoria, headache, dizziness, nausea, 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.

References