Furfural

Furfural
IUPAC name Furan-2-carbaldehyde
Other names furfural, furan-2-carboxaldehyde, fural, furfuraldehyde, 2-furaldehyde, pyromucic aldehyde
Identifiers
CAS number	98-01-1 Y
PubChem	7362
ChemSpider	13863629 Y
UNII	DJ1HGI319P Y
KEGG	C14279 Y
ChEMBL	CHEMBL189362 Y
Jmol-3D images	Image 1
SMILES c1cc(oc1)C=O
InChI InChI=1S/C5H4O2/c6-4-5-2-1-3-7-5/h1-4H Y Key: HYBBIBNJHNGZAN-UHFFFAOYSA-N Y InChI=1/C5H4O2/c6-4-5-2-1-3-7-5/h1-4H Key: HYBBIBNJHNGZAN-UHFFFAOYAD
Properties
Molecular formula	C5H4O2
Molar mass	96.08 g mol−1
Appearance	Colorless oil
Density	1.16 g/mL (20 °C)
Melting point	-37 °C, 236 K, -35 °F ()
Boiling point	162 °C, 435 K, 324 °F ()
Solubility in water	83 g/L
Hazards
Flash point	62 °C (144 °F)
LD50	300–500 mg/kg (oral, mice)
Related compounds
Related furan-2-carbaldehydes	Hydroxymethylfurfural Methoxymethylfurfural
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Furfural is an organic compound derived from a variety of agricultural byproducts, including corncobs, oat, wheat bran, and sawdust. The name furfural comes from the Latin word furfur, meaning bran, referring to its usual source.

Furfural is an heterocyclic aldehyde, with the ring structure shown at right. Its chemical formula is OC₄H₃CHO. It is a colorless oily liquid with the odor of almonds, but upon exposure to air samples quickly become yellow.

History

Furfural was first isolated in 1821 (published in 1832) by the German chemist Johann Wolfgang Döbereiner, who produced a small sample 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 the empirical formula (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. The main countries producing furfural today are South Africa and China.

Properties

Furfural's physical properties are summarized in the table at top 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. Indicating its diminished aromaticity relative to benzene, furfural is readily hydrogenated to the corresponding tetrahydrofuran derivatives. 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. The global production capacity is about 450,000 tons as of 2004. China is the biggest supplier of furfural, and accounts for around half of global capacity. The other major commercial producer is SASOL in the Republic of South Africa.

In the laboratory, synthesis of furfural from corn cobs takes place by reflux with dilute sulfuric acid.

The lignocellulosic residue that remains after the removal of the furfural is used to generate all the steam requirements 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.. It also has been used as a glue extender in the North American board industry.

Uses

Furfural is an important renewable, non-petroleum based, chemical feedstock. Hydrogenation of furfural provides furfuryl alcohol (FA), which is a useful chemical intermediate and which may be further hydrogenated to tetrahydrofurfuryl alcohol (THFA). THFA is used as a nonhazardous solvent in agricultural formulations and as an adjuvant to help herbicides penetrate the leaf structure. Furfural is used to make other furan chemicals, such as furoic acid, via oxidation, and furan itself via palladium catalyzed vapor phase decarbonylation. Furfural is also an important chemical solvent.

Safety

Although it occurs in many foods and flavorants, furfural is toxic with an LD₅₀ of 65 mg/kg (oral, rat). It is a skin irritant and chronic skin exposure can lead to a skin allergy as well as an unusual susceptibility to sunburn.

See also

• Bial's test
• Aniline acetate test
• Tollens test