Tetrahydrofuran
Properties
| State | Liquid |
| Color | Colorless |
| Solubility | Miscible with water and most organic solvents |
| Melting Point | -108.4°C |
| Boiling Point | 66°C |
About Tetrahydrofuran
Tetrahydrofuran (THF, C4H8O, 72.106 g/mol) is a five-membered cyclic ether with one oxygen and four carbons in the ring — the saturated analog of furan and the workhorse polar aprotic-ish solvent of organometallic chemistry. It boils at 66°C, mixes with water in any ratio, smells faintly ethereal, and dissolves nearly everything an organic chemist might want to dissolve, which is why a 4-L bottle sits within arm's reach of every synthesis hood in the world. The oxygen lone pairs coordinate to electropositive metals — Li, Mg, Na, K — well enough to dissolve and stabilize organolithium reagents, Grignard reagents, and lithium aluminum hydride into solutions that actually react. The THF molecule typically donates two solvent molecules to each Li⁺ in solution, breaking up the aggregated tetramers that organolithiums form in hydrocarbon solvents. Compared to diethyl ether, THF wins on three fronts: higher boiling point (66 vs 35°C, so reactions can be run hotter), water miscibility for easy aqueous workups, and stronger Lewis basicity for difficult metallations. The tradeoff is peroxide formation. THF reacts with atmospheric oxygen via radical chain initiation at the α-position to oxygen, generating 2-hydroperoxytetrahydrofuran and related species that concentrate as the solvent evaporates and detonate when distilled to dryness. Every chemistry department keeps a peroxide-test kit (KI/starch paper or Quantofix strips) by the THF bottle for exactly this reason.
Where you'll encounter it
If you've ever run a Grignard reaction in undergraduate organic lab and been told to use freshly opened anhydrous THF rather than the older bottle in the back, the older bottle was the peroxide-risk one. In a process-chemistry plant making polyurethane prepolymers, THF is the monomer for polytetramethylene glycol (PTMG): cation-initiated ring-opening polymerization of THF with BF3 or trifluoromethanesulfonic acid gives the linear ether-diol that is the soft segment of Spandex, Lycra, and high-performance polyurethane elastomers. INVISTA and BASF are the dominant PTMG producers. PVC pipe joints get glued together with PVC cement that's mostly THF dissolving the surface of two pipe ends so they fuse into a continuous polymer matrix on solvent evaporation. The deuterated form, THF-d8, is one of the standard NMR solvents for metallocenes and air-sensitive organometallic complexes that other deuterated solvents would attack.
Common Uses
- Solvent for Grignard, organolithium, and LiAlH4 reductions in synthesis
- Monomer for polytetramethylene glycol (PTMG) used in Spandex/Lycra fibers
- Solvent for PVC cement and ABS adhesive formulations
- Pharmaceutical manufacturing solvent for API isolation and recrystallization
- Deuterated NMR solvent (THF-d8) for air-sensitive organometallic spectroscopy
- Co-solvent in lithium-ion electrolyte formulations and electrochemistry research
- Reaction medium for hydroboration with BH3·THF complex
Safety Information
GHS: Flammable Liquid Category 2 (H225, flash point -14°C closed cup), Acute Toxicity Category 4 (oral, H302), Eye Irritation Category 2A (H319), STOT-SE Category 3 (H335, H336). Exposure limits carry both an 8-hr TWA and a short-term ceiling, and the advisory limit is set several times below the enforceable one. The defining hazard is peroxide formation. THF reacts with atmospheric O2 to form 2-hydroperoxy-THF, which concentrates as the solvent evaporates and can detonate when distilled to dryness. Test with KI/starch paper or Quantofix strips before distilling, especially from bottles older than three months or containing residue. Stored with 250 ppm BHT (2,6-di-tert-butyl-4-methylphenol) as inhibitor in commercial bottles — anhydrous/inhibitor-free grades for reactive chemistry have shorter shelf life and need stricter inventory control. Causes CNS depression on inhalation; ingestion is hazardous. Treat all spills as flammable liquid emergencies.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.