Furan
[CAS# 110-00-9]

Identification

• Classification: Organic raw materials >> Heterocyclic compound
• Name: Furan
• Synonyms: 1,4-Epoxy-1,3-butadiene
• Molecular Formula: C₄H₄O
• Molecular Weight: 68.07
• CAS Registry Number: 110-00-9
• EC Number: 203-727-3
• SMILES: C1=COC=C1

Properties

• Density: 0.9±0.1 g/cm³ Calc.^*, 0.936 g/mL (Expl.)
• Melting point: -86 °C (Expl.)
• Boiling point: 31.4±9.0 °C 760 mmHg (Calc.)^*, 32.1 °C (Expl.)
• Flash point: -35.6 °C (Calc.)^*, -35 °C (Expl.)
• Solubility: water: insoluble (Expl.)
• Index of refraction: 1.427 (Calc.)^*, 1.421 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS02;GHS07;GHS08 Danger
• Risk Statements: H224-H302:-H315:-H332:-H341:-H350:-H373-H412:
• Safety Statements: P203-P210-P233-P240-P241-P242-P243-P260-P261-P264-P270-P271-P273-P280-P301+P317-P302+P352-P303+P361+P353-P304+P340-P317-P318-P319-P321-P330-P332+P317-P362+P364-P370+P378-P403+P235-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Flammable liquids	Flam. Liq.	1	H224
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Carcinogenicity	Carc.	1B	H350
Germ cell mutagenicity	Muta.	2	H341
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	1	H330
Acute toxicity	Acute Tox.	3	H332
Acute toxicity	Acute Tox.	3	H302
Specific target organ toxicity - repeated exposure	STOT RE	2	H372

• Transport Information: UN 2389

Discovery and Applications

Furan is a heterocyclic organic compound with the molecular formula C₄H₄O. It consists of a five-membered aromatic ring containing four carbon atoms and one oxygen atom. The structure of furan is planar and features two double bonds, making it an aromatic system with six π electrons, in accordance with Hückel's rule. Furan is a colorless, volatile liquid at room temperature with a boiling point of approximately 31 °C and a characteristic ether-like odor.

The compound was first identified in the 19th century. Its discovery is attributed to Carl Wilhelm Scheele and later substantiated through the work of several chemists, including Heinrich Limpricht, who first isolated it by dry distillation of mucic acid in 1870. Limpricht named it “furan” based on its derivation from furfural, a compound obtained from agricultural byproducts such as oat hulls and corncobs.

Furan is primarily produced via decarbonylation of furfural, itself derived from biomass. This process involves catalytic hydrogenation and subsequent deoxygenation. Industrial synthesis of furan has also been achieved through the Paal–Knorr synthesis, in which 1,4-diketones are cyclized under acidic conditions to form furan derivatives.

Furan and its derivatives serve as important intermediates in organic chemistry. One of the most significant applications of furan is in the synthesis of pharmaceuticals, agrochemicals, and fine chemicals. For example, substituted furans are commonly found in drugs with anti-inflammatory, anti-bacterial, and anti-cancer properties. Specific derivatives such as nitrofurantoin and furazolidone are well-known antibacterial agents.

In polymer chemistry, furan compounds such as furfuryl alcohol are used to produce furan resins. These thermosetting polymers have good thermal stability and chemical resistance and are employed in foundry sand binders, corrosion-resistant coatings, and carbon-carbon composites.

Furan is also of interest in materials science and green chemistry. It is a platform molecule in the development of bio-based chemicals, as it can be derived from renewable resources like hemicellulose. Compounds such as 2,5-furandicarboxylic acid (FDCA), obtained by oxidation of hydroxymethylfurfural (HMF), are considered potential replacements for petroleum-derived terephthalic acid in the production of polyesters and plastics.

In analytical chemistry, furan is often used as a building block or reference compound for the synthesis of more complex heterocyclic systems. Its chemical reactivity includes electrophilic substitution, Diels–Alder reactions, and metal-catalyzed cross-couplings. Due to the high electron density of the ring, furan undergoes substitution more readily than benzene, making it a versatile intermediate in organic synthesis.

Despite its utility, furan has raised health concerns. Studies have shown that it is a potential hepatotoxic and carcinogenic compound in animal models. Furan can form during the thermal processing of foods, particularly those rich in carbohydrates, such as canned or jarred foods. It is created through the degradation of ascorbic acid, polyunsaturated fatty acids, and certain amino acids during heating. As a result, regulatory agencies including the U.S. FDA and EFSA have conducted risk assessments and continue to monitor furan levels in commercial food products.

Laboratory handling of furan requires caution due to its flammability and toxicity. It is classified as a hazardous chemical, with exposure limits recommended for workplace safety. It should be stored in tightly sealed containers under an inert atmosphere to prevent oxidation and peroxide formation, which may lead to explosive decomposition.

In summary, furan is a foundational heterocyclic compound with a wide range of applications in synthetic chemistry, pharmaceuticals, and materials science. Its aromatic nature and reactive properties make it valuable in the creation of complex molecules. At the same time, its toxicological profile has led to increased attention to its occurrence in consumer products and environmental contexts.

References

2005. Comparative genotoxic evaluation of 2-furylethylenes and 5-nitrofurans by using the comet assay in TK6 cells. Mutagenesis, 20(4).
DOI: 10.1093/mutage/gei026

2003. A survey of dioxin and furan compounds in sediments of Florida Panhandle Bay systems. Marine Pollution Bulletin, 46(4).
DOI: 10.1016/s0025-326x(03)00002-x

2003. Selective adduct formation by furan chemical ionization reagent in gas chromatography ion trap mass spectrometry. Journal of Mass Spectrometry, 38(2).
DOI: 10.1002/jms.452