Tetrahydrofuran

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

Production

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

THF can also be synthesized by catalytic hydrogenation of furan. This allows certain sugars to be converted to THF via acid-catalyzed digestion to furfural and decarbonylation to furan, although this method is not widely practiced. THF is thus derivable from renewable resources.

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.

Precautions

ТHF is 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 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.