|Jmol-3D images||Image 1|
|Molar mass||72.11 g mol−1|
|Density||0.8892 g/cm3 @ 20 °C, liquid|
|Melting point||−108.4 °C (−163.1 °F; 164.8 K)|
|Boiling point||66 °C (151 °F; 339 K)|
|Solubility in water||Miscible|
|Viscosity||0.48 cP at 25 °C|
|Dipole moment||1.63 D (gas)|
|EU classification||Flammable (F)
|R-phrases||R11, R19, R20/21/22, R36/37|
|S-phrases||S16, S29, S33|
|Flash point||−14 °C (7 °F; 259 K)|
|Related compounds||Diethyl ether|
|Supplementary data page|
|n, εr, etc.|
Solid, liquid, gas
|Spectral data||UV, IR, NMR, MS|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Tetrahydrofuran (THF) is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. THF has an odor similar to acetone. It is mainly used as a precursor to polymers. Being polar and having a wide liquid range, THF is a versatile solvent.
About two hundred thousand tonnes of tetrahydrofuran are produced annually. The most widely used industrial process involves the acid-catalyzed dehydration of 1,4-butanediol, akin to the production of diethyl ether from ethanol. The butanediol is derived from condensation of acetylene with formaldehyde followed by hydrogenation. Du Pont developed a process for producing THF by oxidizing n-butane to crude maleic anhydride followed by catalytic hydrogenation. A third major industrial route entails hydroformylation of allyl alcohol followed by hydrogenation to the butanediol.
THF can also be synthesized by catalytic hydrogenation of furan. Certain sugars can be converted to THF although this method is not a widely practiced. Furan is thus derivable from renewable resources.
- n C4H8O → -(CH2CH2CH2CH2O)n-
As a solvent
The other main application of THF is as an industrial solvent for PVC and in varnishes. It is an aprotic solvent with a dielectric constant of 7.6. It is a moderately polar solvent and can dissolve a wide range of nonpolar and polar chemical compounds. THF is water-miscible, and can form solid clathrate hydrate structures with water at low temperatures.
THF is a popular solvent in the laboratory when a moderately higher-boiling ethereal solvent is required and its water miscibility is not an issue. The oxygen center of ethers can coordinate to Lewis acids such as Li+, Mg2+, and boranes, forming adducts. Hence, like diethyl ether, THF can be used in hydroboration reactions to synthesize primary alcohols, and as a solvent for organometallic compounds such as organolithium and Grignard reagents. Although similar to diethyl ether, THF is a stronger base. Thus, while diethyl ether remains the solvent of choice for some reactions (e.g., Grignard reactions), THF fills that role in many others where strong coordination is desirable, and the precise properties of ethereal solvents such as these (alone and in mixtures and at various temperatures) allows for fine-tuning modern chemical reactions. Commercial THF contains substantial water that must be removed for sensitive operations, e.g. those involving organometallic compounds. Although THF is traditionally dried by distillation from an aggressive desiccant, molecular sieves are far superior.
|Drying agent||Duration of drying||water content|
|none||0 hours||108 ppm|
|Sodium/benzophenone||48 h||43 ppm|
|3 A molecular sieves (20% by volume)||72 h||4 ppm|
THF is often used in polymer science. For example, it can be used to dissolve polymers prior to determining their molecular mass using gel permeation chromatography. THF dissolves PVC as well, and thus it is the main ingredient in PVC adhesives. It can be used to liquefy old PVC cement, and is often used industrially to degrease metal parts.
THF is used as a component in mobile phases for reversed-phase liquid chromatography. It has a greater elution strength than methanol or acetonitrile, but is less commonly used than these solvents.
2-Methyltetrahydrofuran (2MeTHF) has been promoted as an ecologically friendler alternative to THF. Whereas 2-MeTHF is more expensive, it may provide for greater overall process economy. 2MeTHF has solvating properties that are intermediate between diethyl ether and THF, has limited water-miscibility, and forms an azeotrope with water on distillation. Its lower melting point makes it useful for lower temperature reactions, and its higher boiling point allows procedures under reflux at higher temperatures (relative to THF).
THF is considered a relatively nontoxic solvent, with the median lethal dose (LD50) comparable to that for acetone. Reflecting its remarkable solvent properties, it penetrates the skin causing rapid dehydration. THF readily dissolves latex and is typically handled with nitrile or neoprene rubber gloves. It is highly flammable.
One danger posed by THF follows from its tendency to form highly-explosive peroxides on storage in air. To minimize this problem, commercial samples of THF are often inhibited with BHT. THF should not be distilled to dryness, because the explosive peroxides concentrate in the residue.
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