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Tetrahydrofuran

[te-truh-hahy-druh-fyoor-an]

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"THF" redirects here. For other uses, see THF (disambiguation).

Tetrahydrofuran, also known as THF, is a heterocyclic organic compound with the formula (CH₂)₄O). It is a colorless low-viscosity liquid with a smell similar to diethyl ether. It is one of the most polar ethers. THF is the fully hydrogenated analog of the aromatic compound furan.

Solvent properties

THF is an aprotic solvent with a dielectric constant of 7.6. It is a moderately polar, aprotic solvent that dissolves a wide range of nonpolar and polar compounds.

Diethyl ether can often be substituted by THF when a higher-boiling solvent is required. Thus THF, like diethyl ether, is often used for hydroborations used to synthesize primary alcohols. Both ethers have an oxygen atom which can coordinate to the electron-deficient boron atom, forming an adduct. Similarly, THF or diethyl ether are often used as solvents for Grignard reagents because of the oxygen atom's ability to coordinate to the magnesium ion component of the Grignard reagent. In addition, the oxygen atom has no acidic hydrogen that can undergo an acid-base reaction with the Grignard reagent. 2-methyltetrahydrofuran has become a popular THF alternative based on its similar properties to THF; its lower melting point makes it useful for lower temperature reactions, and its higher boiling point allows procedures under reflux at higher temperatures.

THF is often used in polymer science. For example, it can be used to dissolve rubber prior to determining its molecular mass using gel permeation chromatography. THF dissolves PVC as well, and is the main ingredient in PVC adhesives. It can be used to liquefy old PVC cement.

THF can be polymerized by strong acids to give a linear polymer called poly(tetramethylene ether) glycol (PTMEG), CAS Registry Number [25190-06-1], also known as PTMO, polytetramethylene oxide. The primary use of this polymer is to make elastomeric polyurethane fibers like Spandex.

It is often used industrially to degrease metal parts.

Preparation

THF can be synthesized by catalytic hydrogenation of furan.

The major industrial process for making THF is the acid-catalyzed dehydration of 1,4-butanediol. Du Pont developed a process for producing THF by oxidizing n-butane to crude maleic anhydride, followed by catalytic hydrogenation of maleic anhydride to THF.

Precautions

THF tends to form peroxides on storage in air. As a result, THF should not be distilled to dryness, which can leave a residue of highly-explosive peroxides. Commercial THF is therefore often inhibited with BHT.