|Molecular formula||C 4 H 8 O|
colorless, ethereal-smelling liquid
|External identifiers / databases|
|Molar mass||72.11 g mol −1|
0.8892 g cm −3 (20 ° C)
−108.39 ° C
65.81 ° C
DFG / Switzerland: 50 ml m −3 or 150 mg m −3
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C|
Presentation and extraction
There are various production processes for the manufacture of tetrahydrofuran. The most frequently used process is the Reppe process , which was developed in the 1930s . Starting from acetylene 1 and formaldehyde , 2-butyne-1,4-diol ( 2 ) is initially formed. After its hydrogenation to 1,4-butanediol ( 3 ), the THF 4 is obtained by an acid-catalyzed cyclization .
Another production process starts from 1,3-butadiene ( 5 ). This is oxidatively at 80 ° C and 3 MPa with acetic acid over a palladium - tellurium - catalyst to 2-butene-1,4-diol diacetate ( 6 implemented). After hydrogenation to 1,4-butanediol diacetate ( 7 ) and targeted hydrolysis of the ester 8 , the THF 4 is formed. Alternatively, the process can lead to 1,4-butanediol as the end product.
THF can also be obtained by hydrogenating furan . A more recent synthesis is based on the gas phase hydrogenation of maleic acid dimethyl ester . A reaction sequence runs through the intermediate stages dimethyl succinate , γ-butyrolactone and 1,4-butanediol .
Tetrahydrofuran is a colorless, flammable liquid with an ethereal odor. It is fully miscible with water up to a temperature of 71.8 ° C, above this temperature a small forms a miscibility gap , which joins at 137.1 ° C again. Mixing with water takes place with a contraction in volume . THF is infinitely miscible with alcohols, ketones and ethers.
With a water content of 19.9 mol%, an azeotropic boiling point of 63.8 ° C. is observed at atmospheric pressure . In the case of alcohols, azeotropic phase diagrams are only observed with methanol and ethanol at atmospheric pressure. The phase diagrams with higher alcohols such as 1-propanol and 2-propanol are zeotropic . The azeotropic boiling points at atmospheric pressure are 60.7 ° C. for methanol with a THF content of 49.7 mol% and 65.7 ° C. for ethanol with a THF content of 85 mol%. These azeotropes are clearly pressure-dependent and disappear for ethanol at lower pressures. Further azeotropes are made with the solvents n-hexane at 63 ° C. with a THF content of 50% by mass , with cyclohexane at 60 ° C. with a THF content of 97% by mass and with acetone at 64 ° C. with a THF content formed by 8 Ma%.
The vapor pressure curve (Fig. 4) can be calculated in the temperature range from 296 K to 373 K with the Antoine equation as log 10 ( p ) = A - ( B / ( T + C )) ( p in bar, T in K) Describe A = 4.12118, B = 1202.942 and C = −46.818.
The temperature dependency of the enthalpy of vaporization (Fig. 5) results from the equation Δ V H 0 = A exp (−β T r ) (1 − T r ) β (Δ V H 0 in kJ / mol, T r = ( T / T c ) reduced temperature) with A = 46.11 kJ / mol, β = 0.2699 and T c = 540.2 K in the temperature range between 302 K and 339 K.
The most important thermodynamic properties are listed in the following table:
|property||Formula symbol||Value (remark)|
|Standard enthalpy of formation||Δ f H 0 (g)||−184.2 kJ mol −1|
S 0 (l)
S 0 (g)
|203.9 J mol −1 K −1 (liquid)
301.7 J mol −1 K −1 (gas)
|Enthalpy of combustion||Δ c H 0 (l)||−2505.8 kJ mol −1|
|Heat capacity||c p||124.1 J mol −1 K −1 (as a liquid at 25 ° C)
1.72 J g −1 K −1 (as a liquid at 25 ° C)
|Enthalpy of fusion||Δ f H 0||8.540 kJ mol −1 (at the melting point)|
|Entropy of fusion||Δ f S 0||51.8 kJ mol −1 (at the melting point)|
|Enthalpy of evaporation||Δ v H 0||29.8 kJ mol −1 (at normal pressure boiling point)|
|Critical temperature||T c||268 ° C|
|Critical pressure||p c||51.9 bar|
|Critical volume||V c||0.225 l mol −1|
|Acentric factor||ω c||0.22535|
Tetrahydrofuran forms a solid hydrate with water with the composition THF · 16.9H 2 O, which melts at 5 ° C.
Tetrahydrofuran forms highly flammable vapor-air mixtures. The compound has a flash point of −20 ° C. The explosion range is between 1.5% by volume (46 g / m 3 ) as the lower explosion limit (LEL) and 12.4% by volume (370 g / m 3 ) as the upper explosion limit (UEL). A correlation of the explosion limits with the vapor pressure function results in a lower explosion point of −23 ° C and an upper explosion point of 13 ° C. The limit gap width was determined to be 0.83 mm. This results in an assignment to explosion group IIB. With a minimum ignition energy of 0.54 mJ, the tetrahydrofuran vapor-air mixtures are extremely ignitable. The ignition temperature is 230 ° C. The substance therefore falls into temperature class T3. The electrical conductivity is rather low at 4.6 · 10 −8 S · m −1 .
According to the dangerous goods regulations , tetrahydrofuran is assigned to class 3 (flammable liquids) with packaging group II (medium hazard) (label: 3).
Like many ethers, THF also forms a peroxide through autoxidation when left to stand in air for a long time and when exposed to light . This can remain as a highly explosive residue when the THF is distilled off. It is therefore advisable to carry out a peroxide test before each distillation of THF . THF mixed with peroxide should be disposed of for safety reasons.
Tetrahydrofuran is used as a solvent for PVC , polystyrene , polyurethanes , cellulose nitrate , adhesives and paints ; it is an intermediate in the manufacture of polyamides , polyester and polyurethane, and it is used to produce tetrahydrothiophene and pyrrolidine . It is an important precursor for polytetrahydrofuran . Due to its donor effect , it is used as a solvent in numerous organic reactions .
In addition to diethyl ether , tetrahydrofuran is one of the most important solvents for reactions with basic and neutral reactants , as it has good dissolving properties and is largely inert. In reactions with strongly ( Lewis ) acidic reactants, one must expect ether cleavage. Tetrahydrofuran often forms acid-base adducts with weaker (Lewis) acidic reactants.
A related cyclic ether is 1,4-dioxane .
Tetrahydrofuran was included in the EU's ongoing action plan ( CoRAP ) in 2012 in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation . The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. Tetrahydrofuran uptake was caused by concerns about its classification as a CMR substance, consumer use , worker exposure , high (aggregated) tonnage and widespread use. The reassessment took place from 2013 and was carried out by Germany . A final report was then published.
The International Agency for Research on Cancer (IARC) classified tetrahydrofuran as possibly carcinogenic in 2017.
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