Tetrahydrofuran

Tetrahydrofuran
Names
Preferred IUPAC name
Oxolane
Other names
Tetrahydrofuran
1,4-Epoxybutane
Butylene oxide
Cyclotetramethylene oxide
Oxacyclopentane
Diethylene oxide
Tetra-methylene oxide
Identifiers
3D model (JSmol)
Abbreviations THF
ChEBI
ChemSpider
ECHA InfoCard 100.003.389
RTECS number LU5950000
Properties
C4H8O
Molar mass 72.11 g·mol−1
Appearance colorless liquid
Odor ether-like[1]
Density 0.8892 g/cm3 at 20 °C, liquid
Melting point −108.4 °C (−163.1 °F; 164.8 K)
Boiling point 66 °C (151 °F; 339 K)
Miscible
Vapor pressure 132 mmHg (20 °C)[1]
Viscosity 0.48 cP at 25 °C
Structure
envelope
1.63 D (gas)
Hazards
Safety data sheet See: data page
Flammable (F)
Irritant (Xi)
R-phrases (outdated) R11, R19, R20/21/22, R36/37
S-phrases (outdated) S16, S29, S33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
3
2
1
Flash point −14 °C (7 °F; 259 K)
Explosive limits 2%–11.8%[1]
Lethal dose or concentration (LD, LC):
1650 mg/kg (rat, oral)
2300 mg/kg (mouse, oral)
2300 mg/kg (guinea pig, oral)[2]
21000 ppm (rat, 3 hr)[2]
US health exposure limits (NIOSH):
PEL (Permissible)
 TWA 200 ppm (590 mg/m3)[1]
REL (Recommended)
 TWA 200 ppm (590 mg/m3) ST 250 ppm (735 mg/m3)[1]
IDLH (Immediate danger)
 2000 ppm[1]
Related compounds
Related heterocycles
 Furan
Pyrrolidine
Dioxane
Related compounds
 Diethyl ether
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Tetrahydrofuran (THF), whose preferred IUPAC name was changed in 2013 to oxolane,[3] 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. It is mainly used as a precursor to polymers.[4] Being polar and having a wide liquid range, THF is a versatile solvent.

Production

About 200,000 tonnes of tetrahydrofuran are produced annually.[5] The most widely used industrial process involves the acid-catalyzed dehydration of 1,4-butanediol. Ashland/ISP is one the biggest producers of this chemical route. 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.[4] DuPont developed a process for producing THF by oxidizing n-butane to crude maleic anhydride, followed by catalytic hydrogenation.[6] A third major industrial route entails hydroformylation of allyl alcohol followed by hydrogenation to the butanediol.

Other methods

THF can also be synthesized by catalytic hydrogenation of furan.[7][8] Certain sugars can be converted to THF, although this method is not widely practiced. Furan is thus derivable from renewable resources.

Applications

Polymerization

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

n C4H8O → −(CH2CH2CH2CH2O)n−

This polymer is primarily used to make elastomeric polyurethane fibers like Spandex.[9]

As a solvent

The other main application of THF is as an industrial solvent for polyvinyl chloride (PVC) and in varnishes.[4] 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.[10] THF is water-miscible and can form solid clathrate hydrate structures with water at low temperatures.[11]

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.[12] Although similar to diethyl ether, THF is a stronger base.[13] 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 fine-tuning modern chemical reactions.

Purification

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.[14]

Drying of THF
Drying agent Duration of drying Water content
None 0 hours 108 ppm
Sodium/benzophenone 48 hours 43 ppm
3 Å molecular sieves (20% by volume) 72 hours 4 ppm

Potential uses and research

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.[15] 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

THF is also a starting material for the preparation of tetrahydrothiophene. In the presence of a solid acid catalyst, it reacts with hydrogen sulfide.[16]

THF is used as a solvent in 3D printing when using PLA plastics. It can be used to clean clogged 3D printer parts, as well as when finishing prints to remove extruder lines and add a shine to the finished product.

2-MethylTHF

2-Methyltetrahydrofuran (2-MeTHF) has been promoted as a more ecologically-friendly alternative to THF.[17] Whereas 2-MeTHF is more expensive, it may provide for greater overall process economy. 2-MeTHF 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

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 butylated hydroxytoluene (BHT). THF should not be distilled to dryness, because the explosive peroxides concentrate in the residue.

See also

References

  1. 1 2 3 4 5 6 "NIOSH Pocket Guide to Chemical Hazards #0602". National Institute for Occupational Safety and Health (NIOSH).
  2. 1 2 "Tetrahydrofuran". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
  3. ↑ "New IUPAC Organic Nomenclature - Chemical Information BULLETIN" (PDF).
  4. 1 2 3 Müller, Herbert (2005), "Tetrahydrofuran", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a26_221
  5. ↑ Karas, Lawrence; Piel, W. J. (2004). "Ethers". Kirk‑Othmer Encyclopedia of Chemical Technology. John Wiley & Sons.
  6. ↑ Budavari, Susan, ed. (2001), The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (13th ed.), Merck, ISBN 0911910131
  7. ↑ Morrison, Robert Thornton; Boyd, Robert Neilson (1972). Organic Chemistry (2nd ed.). Allyn and Bacon. p. 569.
  8. ↑ Starr, Donald; Hixon, R. M. (1943). "Tetrahydrofuran". Org. Synth.; Coll. Vol., 2, p. 566
  9. ↑ Pruckmayr, Gerfried; Dreyfuss, P.; Dreyfuss, M. P. (1996). "Polyethers, Tetrahydrofuran and Oxetane Polymers". Kirk‑Othmer Encyclopedia of Chemical Technology. John Wiley & Sons.
  10. ↑ "Chemical Reactivity". Michigan State University. Retrieved 2010-02-15.
  11. ↑ "NMR–MRI study of clathrate hydrate mechanisms" (PDF). Fileave.com. Retrieved 2010-02-15.
  12. ↑ Elschenbroich, C.; Salzer, A. (1992). Organometallics: A Concise Introduction (2nd ed.). Weinheim: Wiley-VCH. ISBN 3-527-28165-7.
  13. ↑ Lucht, B. L.; Collum, D. B. (1999). "Lithium Hexamethyldisilazide: A View of Lithium Ion Solvation through a Glass-Bottom Boat". Accounts of Chemical Research. 32: 1035–1042. doi:10.1021/ar960300e.
  14. ↑ Williams, D. B. G.; Lawton, M. (2010). "Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants". Journal of Organic Chemistry. 75: 8351. PMID 20945830. doi:10.1021/jo101589h.
  15. ↑ 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.
  16. ↑ Swanston, Jonathan (2005), "Thiophene", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a26_793.pub2
  17. ↑ "Greener Solvent Alternatives – Brochure" (PDF). Sigmaaldrich.com. Retrieved 2010-02-15.

General reference

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