Tetrahydrofuran

• Tetramethylene
• 1,4- epoxy butane
• Oxacyclopentane
• Oxolane
• THF

Colorless, ethereal smelling liquid

Liquid

0.89 g · cm -3 ( 20 ° C)

-108.39 ° C

65.81 ° C

173 hPa ( 20 ° C)

Miscible with water, ethanol, acetone and diethyl ether

1.63 D

1.4070

Risk

150 mg · m-3

1650 mg · kg -1 ( LD50, rat, oral)

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Tetrahydrofuran (THF) is an organic solvent and part of the class of the ( cyclic ) ethers.

Representation and extraction

For the production of tetrahydrofuran, there are different production processes. The most commonly used method is developed already in the 1930s, Reppe process. Starting from acetylene and formaldehyde is initially 1, the 2- butyne-1 ,4 -diol ( 2). After the hydrogenation to 1,4-butanediol ( 3), the THF 4 is obtained by an acid catalyzed cyclization.

Another manufacturing process starts from the 1,3-butadiene ( 5). This is converted by oxidation at 80 ° C and 3 MPa, with acetic acid over a palladium -tellurium catalyst for 2-butene -1 ,4- diol diacetate (6). After the hydrogenation to 1,4- butanediol diacetate (7) and selective hydrolysis of the ester 8 4, the THF is formed. Alternatively, the process for 1,4- butanediol can be performed as a final product.

THF can be further obtained by the hydrogenation of furan. A recent synthesis is based on the gas-phase hydrogenation of dimethyl maleate. In this case, through a sequence of reactions through the intermediate stages, dimethyl succinate, γ -butyrolactone and 1,4-butanediol.

Properties

Physical Properties

Tetrahydrofuran is a colorless, flammable liquid with etherartigem odor. It is completely miscible with water up to a temperature of 71.8 ° C, above this temperature, a small miscibility gap is formed, which closes again at 137.1 ° C. The mixture with water is carried out under volume contraction. With alcohols, ketones and ethers THF is completely miscible.

At a water content of 19.9 mol% of an azeotropic boiling point of 63.8 ° C at atmospheric pressure is observed. With alcohols azeotropic phase diagrams can be observed only with methanol and ethanol at atmospheric pressure. Phase diagrams with higher alcohols such as 1- propanol and 2-propanol are zeotropic. The azeotropic boiling points at atmospheric pressure are to methanol at 60.7 ° C in a THF content of 49.7 mol % and for ethanol at 65.7 ° C in a THF content of 85 mol %. These azeotropes are significantly pressure dependent and disappear for ethanol at lower pressures. Other azeotropes are with the solvents n-hexane at 63 ° C and a THF content of 50 % by mass, with cyclohexane at 60 ° C and a THF content of 97 % by mass and with acetone at 64 ° C and a THF content formed by 8 % by mass.

The vapor pressure curve (Fig. 4) can be in the temperature range from 296 K to 373 K with the Antoine equation as log10 (p) = A- ( B / ( T C )) ( p in bar, T in K ) with A = 4.12118, B = 1202.942 and C = -46.818 describe.

The temperature dependence of the enthalpy of vaporization (Fig. 5) can be determined according to equation ΔVH0 = A · exp (- β · Tr ) (1- Tr) β ( ΔVH0 in kJ / mol, Tr = (T / Tc) reduced temperature ) with A = 46.11 kJ / mol, β = 0.2699 and Tc = 540.2 K describe the temperature range between 302 K and 339 K.

The most important thermodynamic properties are listed in the following table:

Tetrahydrofuran with water forms a solid hydrate with the composition 16.9 THF · H2O, which melts at 5 ° C.

Safety characteristics

Tetrahydrofuran forms flammable vapor - air mixtures. The compound has a flash point of -20 ° C. The explosion range is between 1.5 vol % (46 g/m3) as the lower explosive limit ( LEL) and 12.4 % by volume (370 g/m3 ) and upper explosive limit (UEL ). A correlation of explosion limits with the vapor pressure function yields a lower explosion point of -24 ° C and an upper explosion point of 13 ° C. The marginal gap width was determined to be 0.87 mm. The result is thus a mapping in the explosion group IIB. With a minimum ignition energy of 0.54 mJ Tetrahydrofurandampf - air mixtures are extremely flammable. The ignition temperature is 230 ° C. The fabric falls within the temperature class T3. The electrical conductivity is relatively low at 4.6 · 10-8 S · m -1.

According to the Dangerous Goods Regulations is tetrahydrofuran Class 3 ( Flammable liquids ) with the Packing Group II (medium hazard ) associated with ( Label: 3 ).

Chemical Properties

How many ether also forms THF on prolonged standing in air and exposed to light by autoxidation a peroxide. This may remain as highly explosive residue in the distilling off THF. It is therefore recommended before each distillation of THF perform a peroxide and possibly precipitate the peroxide by treatment with solid potassium hydroxide.

Upon heating in the presence of hydrochloric acid, the ether is cleaved easily to give 4 - chlorobutanol and then 1,4- dichlorobutane.

Use

Tetrahydrofuran is used as solvent for PVC, polystyrene, polyurethanes, cellulose nitrate, adhesives, and varnishes; it is an intermediate in the polyamide, polyester and polyurethane production, and it is used for production of tetrahydrothiophene and pyrrolidine. It is an important precursor for Polytetrahydrofuran. In many organic reactions, it is used because of its donor action as a solvent.

Addition of diethyl ether, tetrahydrofuran is a solvent for one of the main reactions with basic and neutral reactants because it possesses good solvent properties and is substantially inert. Reactions with strong ( Lewis ) acidic reactant must reckon with ether cleavage. With weaker ( Lewis ) acid reactants tetrahydrofuran is often an acid-base adducts.

A related cyclic ether is 1,4-dioxane.