2-Methyltetrahydrofuran

2-Methyltetrahydrofuran (2-MeTHF) is an organic compound with the molecular formula C5H10O. It is a highly flammable, mobile liquid. It is mainly used as a replacement for Tetrahydrofuran (THF) in specialized applications for its better performance, such as to obtain higher reaction temperatures, or easier separations (as, unlike THF, it is not miscible with water). It is derived from sugars via furfural and is occasionally touted as a biofuel.[2]

2-Methyltetrahydrofuran
Names
Preferred IUPAC name
2-Methyloxolane
Other names
2-Methyltetrahydrofuran, 2-Methyl-THF
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.002.281
EC Number
UNII
UN number 2536
  • InChI=1S/C5H10O/c1-5-3-2-4-6-5/h5H,2-4H2,1H3 checkY
    Key: JWUJQDFVADABEY-UHFFFAOYSA-N checkY
  • (Racemic): InChI=1/C5H10O/c1-5-3-2-4-6-5/h5H,2-4H2,1H3
    Key: JWUJQDFVADABEY-UHFFFAOYAM
Properties
C5H10O
Molar mass 86.134 g·mol−1
Density 0.854 g/mL
Melting point −136 °C (−213 °F; 137 K)[1]
Boiling point 80.2 °C (176.4 °F; 353.3 K)[1]
Hazards
GHS labelling:
GHS02: FlammableGHS05: CorrosiveGHS07: Exclamation mark
Warning
H225, H302, H315, H318, H319, H335, H336
P210, P233, P240, P241, P242, P243, P261, P264, P270, P271, P280, P301+P312, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P330, P332+P313, P337+P313, P362, P370+P378, P403+P233, P403+P235, P405, P501
Safety data sheet (SDS) External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Infobox references

Structures and properties

2-Methyltetrahydrofuran is "inversely soluble" in water. That is, its solubility decreases with increasing temperature, which is a rare property.[3] Much like tetrahydrofuran, 2-methyltetrahydrofuran can act as a Lewis base in organometallic reactions.[1] 2-Methyltetrahydrofuran is usually produced as a racemic mixture.

Preparation

2-Methyltetrahydrofuran is usually synthesized by catalytic hydrogenation of furfural.[4]

OC4H3CHO + 4 H2 → OC4H7CH3 + H2O

Furfural is produced by the acid-catalyzed digestion of pentosan sugars, C5 polysaccharides, in biomass. Thus, the raw materials of 2-methyltetrahydrofuran are renewable biomass rich with cellulose, hemicelluloses, and lignin, such as corncobs or bagasse and other plant and agricultural waste.[5]

2-Methyltetrahydrofuran can also be produced starting from levulinic acid. Cyclization and reduction gives γ-valerolactone:

γ-Valerolactone can be hydrogenated to 1,4-pentanediol, which can then be dehydrated to give 2-methyltetrahydrofuran:

Applications

2-Methyltetrahydrofuran is mainly used as a higher boiling substitute for tetrahydrofuran as a specialty solvent. It also is used in the electrolyte formulation for secondary lithium electrodes and as a component in alternative fuels. It is a valued solvent for low-temperature reactions. 2-Methyltetrahydrofuran forms a glass, which does not crystallize, and is frequently used as a solvent for spectroscopic studies at −196 °C.[1]

Other common uses of 2-methyltetrahydrofuran is as a solvent for Grignard reagents used in organometallic and biphasic chemical processes, because of the oxygen atom's ability to coordinate to the magnesium ion component of the Grignard reagent, or to azeotropically dry products. The use of 2-methyltetrahydrofuran provides very clean organic water phase separations. It is a popular, but costlier substitute for tetrahydrofuran.

2-Methyltetrahydrofuran is approved by the United States Department of Energy as an additive to gasoline. Furfural and other furyl compounds (furfuryl alcohol, methylfuran, tetrahydrofufuryl alcohol) have a tendency to polymerize and are quite volatile. 2-Methyltetrahydrofuran itself, however, is more stable and less volatile, and thus is suitable for use as a motor fuel.

2-Methyltetrahydrofuran has been promoted as an ecologically-friendly alternative to THF.[6] 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).

References
  1. Aycock, David F. (2007). "Solvent Applications of 2-Methyltetrahydrofuran in Organometallic and Biphasic Reactions". Org. Process Res. Dev. 11: 156–159. doi:10.1021/op060155c.
  2. Leal Silva, Jean Felipe; Mariano, Adriano Pinto; Maciel Filho, Rubens (2018). "Economic potential of 2-methyltetrahydrofuran (MTHF) and ethyl levulinate (EL) produced from hemicelluloses-derived furfural". Biomass and Bioenergy. 119 (December 2018): 492–502. doi:10.1016/j.biombioe.2018.10.008. S2CID 104836889.
  3. Sicaire, Anne-Gaëlle; Vian, Maryline Abert; Filly, Aurore; Li, Ying; Bily, Antoine; Chemat, Farid (2014), Chemat, Farid; Vian, Maryline Abert (eds.), "2-Methyltetrahydrofuran: Main Properties, Production Processes, and Application in Extraction of Natural Products", Alternative Solvents for Natural Products Extraction, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 253–268, doi:10.1007/978-3-662-43628-8_12, ISBN 978-3-662-43627-1
  4. Huber, GW; Iborra, S; Corma, A (September 2006). "Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering". Chem. Rev. 106 (9): 4044–98. doi:10.1021/cr068360d. PMID 16967928. ref 306
  5. Hoydonckx, H. E.; Van Rhijn, W. M.; Van Rhijn, W.; De Vos, D. E.; Jacobs, P. A. "Furfural and Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a12_119.pub2.
  6. "Greener Solvent Alternatives – Brochure" (PDF). Sigmaaldrich.com. Retrieved 2010-02-15.

Further reading
  • Zheng, Hong-Yan; Zhu, Yu-Lei; Teng, Bo-Tao; Bai, Zong-Qing; Zhang, Cheng-Hua; Xiang, Hong-Wei; Li, Yong-Wang (2006). "Towards understanding the reaction pathway in vapour phase hydrogenation of furfural to 2-methylfuran". Journal of Molecular Catalysis A: Chemical. 246 (1–2): 18–23. doi:10.1016/j.molcata.2005.10.003.
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