Tetrahydrofuran (THF), or oxolane, 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.[8] Being polar and having a wide liquid range, THF is a versatile solvent. It is an isomer of another solvent, butanone.
THF can also be synthesized by catalytic hydrogenation of furan.[11][12] This allows certain sugars to be converted to THF via acid-catalyzed digestion to furfural and decarbonylation to furan,[13] although this method is not widely practiced. THF is thus derivable from renewable resources.
The other main application of THF is as an industrial solvent for polyvinyl chloride (PVC) and in varnishes.[8] It is an aproticsolvent 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.[15] THF is water-miscible and can form solid clathrate hydrate structures with water at low temperatures.[16]
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.[17] 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 solvent in 3D printing when printing with PLA, PETG and substantially similar filaments. It can be used to clean clogged 3D printer parts, to remove extruder lines and add a shine to the finished product as well as to solvent weld printed parts.
Laboratory use
In the laboratory, THF is a popular solvent when its water miscibility is not an issue. It is more basic than diethyl ether[18] 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.[19] 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.
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 such as elemental sodium, molecular sieves have been shown to be superior water scavengers.[20]
THF is a relatively acutely nontoxic solvent, with the median lethal dose (LD50) comparable to that for acetone. However, chronic exposure is suspected of causing cancer.[5][25] Reflecting its remarkable solvent properties, it penetrates the skin, causing rapid dehydration. THF readily dissolves latex and thus should be handled with nitrile rubber gloves. It is highly flammable.
One danger posed by THF is its tendency to form the explosive compound 2-hydroperoxytetrahydrofuran upon reaction with air:
To minimize this problem, commercial supplies of THF are often stabilized with butylated hydroxytoluene (BHT). Distillation of THF to dryness is unsafe because the explosive peroxides can concentrate in the residue.
The tetrahydrofuran ring is found in diverse natural products including lignans, acetogenins, and polyketide natural products.[26] Diverse methodology has been developed for the synthesis of substituted THFs.[27]
Oxolanes
Tetrahydrofuran is one of the class of pentic cyclic ethers called oxolanes. There are seven possible structures, namely,[28]
Monoxolane, the root of the group, synonymous with tetrahydrofuran
^Hoydonckx, H. E.; Rhijn, W. M. Van; Rhijn, W. Van; Vos, D. E. De; Jacobs, P. A. (2007), "Furfural and Derivatives", Ullmann's Encyclopedia of Industrial Chemistry, American Cancer Society, doi:10.1002/14356007.a12_119.pub2, ISBN978-3-527-30673-2
^Pruckmayr, Gerfried; Dreyfuss, P.; Dreyfuss, M. P. (1996). "Polyethers, Tetrahydrofuran and Oxetane Polymers". Kirk‑Othmer Encyclopedia of Chemical Technology. John Wiley & Sons.
^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 (11): 3140–3145. doi:10.1039/C3GC41214H.
^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 (12): 1035–1042. doi:10.1021/ar960300e.
^Elschenbroich, C.; Salzer, A. (1992). Organometallics: A Concise Introduction (2nd ed.). Weinheim: Wiley-VCH. ISBN3-527-28165-7.
^Williams, D. B. G.; Lawton, M. (2010). "Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants". Journal of Organic Chemistry. 75 (24): 8351–4. doi:10.1021/jo101589h. PMID20945830. S2CID17801540.
^Lorente, Adriana; Lamariano-Merketegi, Janire; Albericio, Fernando; Álvarez, Mercedes (2013). "Tetrahydrofuran-Containing Macrolides: A Fascinating Gift from the Deep Sea". Chemical Reviews. 113 (7): 4567–4610. doi:10.1021/cr3004778. PMID23506053.
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