Tetrahydrofuran

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Structural formula
Structural formula of tetrahydrofuran
General
Surname Tetrahydrofuran
other names
  • Oxolane ( IUPAC )
  • Tetramethylene oxide
  • 1,4-epoxybutane
  • Oxacyclopentane
  • THF
Molecular formula C 4 H 8 O
Brief description

colorless, ethereal-smelling liquid

External identifiers / databases
CAS number 109-99-9
EC number 203-726-8
ECHA InfoCard 100.003.389
PubChem 8028
Wikidata Q278332
properties
Molar mass 72.11 g mol −1
Physical state

liquid

density

0.8892 g cm −3 (20 ° C)

Melting point

−108.39 ° C

boiling point

65.81 ° C

Vapor pressure
  • 173 h Pa (20 ° C)
  • 268 hPa (30 ° C)
  • 402 hPa (40 ° C)
  • 586 hPa (50 ° C)
solubility

miscible with water, ethanol , acetone and diethyl ether

Dipole moment

1.63 D

Refractive index

1.4070

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
02 - Highly / extremely flammable 07 - Warning 08 - Dangerous to health

danger

H and P phrases H: 225-302-319-335-351
EUH: 019
P: 210-280-301 + 312 + 330-305 + 351 + 338-370 + 378-403 + 235
MAK

DFG / Switzerland: 50 ml m −3 or 150 mg m −3

Toxicological data

1650 mg kg −1 ( LD 50 ,  rat ,  oral )

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

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

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 .

Synthesis of tetrahydrofuran

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.

Synthesis of tetrahydrofuran 2

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 .

properties

Physical Properties

Fig. 1: Binary vapor-liquid equilibrium of THF with water
Fig. 2: Binary vapor-liquid equilibria of THF with methanol, ethanol, 1-propanol and 2-propanol
Fig. 3: Excess volumes of THF / water mixtures
Fig. 4: THF vapor pressure curve
Fig. 5: Temperature dependence of the heat of vaporization of THF

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
Standard entropy 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)
Triple point T triple
p triple 		164.76 K
101.33 kPa
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.

Safety-related parameters

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).

Chemical properties

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.

Peroxide formation with THF

When heated in the presence of hydrochloric acid , the ether is easily cleaved with formation of 4-chlorobutanol and later 1,4-dichlorobutane .

Cleavage of THF to 1,4-dichlorobutane

use

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 .

Risk assessment

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.

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m Entry on tetrahydrofuran in the GESTIS substance database of the IFA , accessed on July 31, 2017(JavaScript required) .
  2. ↑ a b The Merck Index . An Encyclopaedia of Chemicals, Drugs and Biologicals. 14th edition. 2006, ISBN 0-911910-00-X , p. 1585.
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  4. ↑ a b c d Yoshio Yoshikawa, Akira Takagi, Masahiro Kato: Indirect Determination of Vapor-Liquid Equilibria by a Small Ebulliometer. Tetrahydrofuran-Alcohol Binary Systems. In: J. Chem. Eng. Data . 25 (4), 1980, pp. 344-346. doi: 10.1021 / je60087a017 .
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  16. ↑ Dortmund database .
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  18. ↑ E. Brunner, AGR Scholz: Isobaric vapor-liquid equilibria of the tetrahydrofuran / ethanol system at 25, 50, and 100 kPa. In: J. Chem. Eng. Data 29 (1), 1984, pp. 28-31. doi: 10.1021 / je00035a011 .
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  23. ^ GA Clegg: Thermodynamics of Polymerization of Heterocyclic Compounds. II. The heat capacity, entropy, enthalpy and free energy of polytetrahydrofuran. In: polymer . 9, 1968, pp. 501-511. doi: 10.1016 / 0032-3861 (68) 90060-8 .
  24. ↑ RC Cass, SE Fletcher, CT Mortimer, HD Springall, TR White: Heats of combustion and molecular structure. Part V. The mean bond energy term for the CO bond in ethers, and the structures of some cyclic ethers. In: J. Chem. Soc. 1958, pp. 1406-1410. doi: 10.1039 / JR9580001406 .
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  29. ↑ JB Fenn: Lean flammability limit and minimum spark ignition energy. In: Ind. Eng. Chem. 43, 1951, pp. 2865-2869.
  30. ↑ HF Calcote, CA Gregory, CM Barnett, RB Gilmer: Spark Ignition - Effect of Molecular Structure. In: Ind. Eng. Chem. 44, 1952, pp. 2656-2662.
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  32. ↑ Technical rule for hazardous substances TRGS 727, BG RCI leaflet T033 Avoidance of ignition hazards due to electrostatic charges , status August 2016, Jedermann-Verlag Heidelberg, ISBN 978-3-86825-103-6 .
  33. ^ Author collective: Organikum . 22nd edition. Wiley-VCH, 2004, ISBN 3-527-31148-3 .
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  35. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): Tetrahydrofuran , accessed on March 26, 2019.
  36. ↑ Yann Grosse, Dana Loomis, Kathryn Z Guyton, Fatiha El Ghissassi, Véronique Bouvard, Lamia Benbrahim-Tallaa, Heidi Mattock, Kurt Straif: Some chemicals that cause tumors of the urinary tract in rodents. In: The Lancet Oncology . 18, 2017, pp. 1003-1004. doi: 10.1016 / S1470-2045 (17) 30505-3 .