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.

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.

Safety

When ingested or inhaled, furfural can cause symptoms similar to those of 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.more