Tetrahydrofuran

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"THF" redirects here. For other uses, see THF (disambiguation).
Tetrahydrofuran
Tetrahydrofuran.svg Space-filling model of the THF molecule
Tetrahydrofuran sample.jpg
Identifiers
CAS number 109-99-9 YesY
PubChem 8028
ChemSpider 7737 YesY
ChEBI CHEBI:26911 N
ChEMBL CHEMBL276521 YesY
RTECS number LU5950000
Jmol-3D images Image 1
Properties
Molecular formula C4H8O
Molar mass 72.11 g mol−1
Appearance colorless liquid
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
Structure
Molecular shape envelope
Dipole moment 1.63 D (gas)
Hazards
MSDS External MSDS
EU classification Flammable (F)
Irritant (Xi)
R-phrases R11, R19, R20/21/22, R36/37
S-phrases S16, S29, S33
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point −14 °C (7 °F; 259 K)
Related compounds
Related heterocycles Furan
Pyrrolidine
Dioxane
Related compounds Diethyl ether
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
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)
 N (verify) (what is: YesY/N?)
Infobox references

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.[1] Being polar and having a wide liquid range, THF is a versatile solvent.

Production[edit]

About two hundred thousand tonnes of tetrahydrofuran are produced annually.[2] The most widely used industrial process involves the acid-catalyzed dehydration of 1,4-butanediol. The method is similar to the production of diethyl ether from ethanol. The butanediol is derived from condensation of acetylene with formaldehyde followed by hydrogenation.[1] Du Pont developed a process for producing THF by oxidizing n-butane to crude maleic anhydride followed by catalytic hydrogenation.[3] A third major industrial route entails hydroformylation of allyl alcohol followed by hydrogenation to the butanediol.

Other methods[edit]

THF can also be synthesized by catalytic hydrogenation of furan.[4][5] Certain sugars can be converted to THF although this method is not a widely practiced. Furan is thus derivable from renewable resources.

Applications[edit]

In the presence of strong acids, THF converts to a linear polymer called poly(tetramethylene ether) glycol (PTMEG), also known as PTMO, polytetramethylene oxide:

n C4H8O → -(CH2CH2CH2CH2O)n-

This polymer is primarily used to make elastomeric polyurethane fibers like Spandex.[6]

As a solvent[edit]

The other main application of THF is as an industrial solvent for PVC and in varnishes.[1] 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.[7] THF is water-miscible, and can form solid clathrate hydrate structures with water at low temperatures.[8]

In the laboratory, THF is a popular solvent when its water miscibility is not an issue. It is more basic than diethyl ether and forms stronger complexes with Li+, Mg2+, and boranes. It is a popular solvent for hydroboration reactions and for organometallic compounds such as organolithium and Grignard reagents.[9] Although similar to diethyl ether, THF is a stronger base.[10] 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.

Purification[edit]

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.[11]

Drying of THF
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

Potential uses and research[edit]

THF has been explored as a miscible co-solvent in aqueous solution to aid in the liquefaction and delignification of plant lignocellulosic biomass for production of renewable platform chemicals and sugars as potential precursors to biofuels.[12] Aqueous THF augments the hydrolysis of glycans from biomass and dissolves the majority of biomass lignin making it a suitable solvent for biomass pretreatment.

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.

Other uses[edit]

THF is also a starting material for the preparation of tetrahydrothiophene. In the presence of a solid acid catalyst, it reacts with hydrogen sulfide.[13]

2-MethylTHF[edit]

2-Methyltetrahydrofuran (2MeTHF) has been promoted as an ecologically friendler alternative to THF.[14] 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).

Precautions[edit]

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.

Tetrahydrofuran peroxide formation.svg

See also[edit]

References[edit]

  1. ^ a b c Herbert Müller, "Tetrahydrofuran" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a26_221
  2. ^ "Ethers, by Lawrence Karas and W. J. Piel". Kirk‑Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. 2004. 
  3. ^ Merck Index of Chemicals and Drugs, 9th ed.
  4. ^ Morrison, Robert Thornton; Boyd, Robert Neilson: Organic Chemistry, 2nd ed., Allyn and Bacon 1972, p. 569
  5. ^ Donald Starr and R. M. Hixon (1943), Tetrahydrofuran, Org. Synth. ; Coll. Vol. 2: 566 
  6. ^ "Polyethers, Tetrahydrofuran and Oxetane Polymers by Gerfried Pruckmayr, P. Dreyfuss, M. P. Dreyfuss". Kirk‑Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. 1996. 
  7. ^ "Chemical Reactivity". Cem.msu.edu. Retrieved 2010-02-15. 
  8. ^ "FileAve.com". Gashydrate.fileave.com. Retrieved 2010-02-15. 
  9. ^ Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) Wiley-VCH: Weinheim. ISBN 3-527-28165-7
  10. ^ E.g., B.L. Lucht, D.B. Collum "Lithium Hexamethyldisilazide: A View of Lithium Ion Solvation through a Glass-Bottom Boat" Accounts of Chemical Research, 1999, volume 32, 1035–1042 doi:10.1021/ar960300e, and references therein.
  11. ^ Williams, D. B. G., Lawton, M., "Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants", The Journal of Organic Chemistry 2010, vol. 75, 8351. doi: 10.1021/jo101589h
  12. ^ Cai, Charles; Zhang, Taiying; Kumar, Rajeev; Wyman, Charles (13 August 2013). "THF co-solvent enhances hydrocarbon fuel precursor yields from lignocellulosic biomass". Green Chemistry 15: 3140–3145. doi:10.1039/C3GC41214H. 
  13. ^ Jonathan Swanston “Thiophene” in Ullmann’s Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2006. doi:10.1002/14356007.a26_793.pub2.
  14. ^ "Greener Solvent Alternatives – Brochure" (PDF). Retrieved 2010-02-15. 

General reference[edit]

External links[edit]