GB1582427A

GB1582427A - Aromatic fluorine compounds

Info

Publication number: GB1582427A
Application number: GB4331176A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1977-10-17
Filing date: 1977-10-17
Publication date: 1981-01-07

Description

(54) AROMATIC FLUORINE COMPOUNDS (71) We, IMPERIAL CHEMICAL INDUS TRIES LIMITED, Imperial Chemical House, Milibank, London SWlP 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the preparation of aromatic fluorine compounds and in particular to a method of preparing fluorobenzenes.

The introduction of fluorine into an aromatic ring presents particular problems.

Aromatic fluorine compounds have generally been prepared by reaction of a source of fluorine with an aromatic starting material having a reactive substituent. For example fluorobenzene is commonly prepared by the decomposition of diazonium salts of complex fluorides such as fluoroborate. Such reactions involve a number of stages and are expensive to operate; There is thus a need for a method of manufacture of aromatic fluorine compounds Which involves the direct reaction of a source of fluorine with a commonly available and relatively inexpensive starting material.

According to the present invention there is provided a method of manufacturing an optionally substituted, fluorobenzene which comprises contacting a corresponding phenol at an elevated temperature with hydrogen fluoride.

The method of the present invention is especially suitable for -the preparation -of fluorobenzene from- phenol itself (unsub- stituted phenol). IIoweVe'r', - the phenol may be substituted - in the aromatic nucleus with suitable substituents' which are' not affected under the reaction 'conditions, and the product is then the - correspondingly substituted' fluorobenzene.' ' ' '-Preferably the hydrogen fluonde' - is present in a molar excess. For example it is pre"fe'rred. that 'tli'e olar --'ratid' of hydrogen fluoride to phenol is at least 2 to 1 and especially preferred that the molar ratio is at least 5 to 1. There is no particular upper limit to the proportion of hydrogen fluoride, but there is little advantage in employing a molar ratio of hydrogen fluoride to phenol of greater than 50 to 1.

The reaction preferably takes place at superatmospheric pressure, and typical pressures range from 100 to 1500 psig; autogenous pressure is conveniently employed.

The reaction may take place in the presence of a liquid medium comprising hydrogen fluoride. For example the reaction may take place below the critical temperature of hydrogen fluoride for a given reaction pressure.

Thus according to a further aspect of the present invention there is provided a method of manufacturing an, optionally substituted, fluorobenzene which comprises contacting a corresponding phenol at an elevated temperature with a liquid medium comprising hydrogen fluoride.

When autogenous pressure is used; the critical temperature of hydrogen fluoride is 1800C. When it is desired to maintain a liquid medium comprising hydrogen fluoride, a suitable reaction temperature is front 1300C to 1600C, the pressure being either autogenous or at' least sufficient to ensure the presence of a liquid phase.

However, we have found that our invention is not limited to reactions which take place in the presence of a liquid medium comprising hydrogen fluoride. The reaction may take place entirely in the liquid phase; partly in the liquid phase and partly in the vapour "phase; 'or entirely in the vapour phase; - Thus the reaction temperature is suitably within the range loQ0C to 3000 C, and is preferably 'within the range 130 C t6 2500C, for example 1500C to ,200?C. -' Reaction times vary typically from, 3 hours to 3 'days," and the appropriate reaction time to 'ensure that the desired degree ref reaction has been obtained is readily ascer tained for given reaction conditions.

The hydrogen fluoride and the phenol are preferably substantially anhydrous. Water is produced during the course of the reaction of the phenol and hydrogen fluoride, 'and it may be advantageous to include a water 'scavenger, for example thionyl fluoride, in the'reaction mixture.

Preferably the reaction takes place in the presence of a catalyst. Suitable catalysts include'Lewis acids (fluoride ion acceptors), for example Lewis acids having a Hammet constant (Ho) in hydrogen fluoride of from - 10 to -20. Examples of suitable catalysts include boron trifluoride (Ho in hydrogen fluoride approximately - 15). The concentration of the catalyst is suitably from 0.5 to 25% w/w based on hydrogen fluoride and preferably from 0.5 to l0% w/w based on hydrogen fluoride.

The desired product may be separated from the reaction mixture by conventional techniques, for example solvent extraction and fractional distillation. Any unreacted phenol is conveniently recycled.

The invention is illustrated by the following Examples.

EXAMPLE I A nickel-lined autoclave of '500 ml capacity was charged with 47g (0.5 mole) of phenol and 150g (7.5 moles) of anhydrous liquid hydrogen fluoride. The' vessel was heated with stirring at 1500C for 24 hours giving a gauge pressure of approximately 440 psig. The autoclave was then cooled to 0 C and volatile material vented off. The contents of the autoclave were poured onto an ice/water mixture when a brown oil separated. The oil layer was extracted with the methylene chloride and analysis of the methylene chloride solution showed fluorobenzene and diphenyl ether in addition to unreacted phenol. No other impurities were detected.

Quantitative analysis indicated that 5.5g of fluorobenzene and lg of diphenyl ether had been formed. This corresponds to an efficiency of 11.5% to 2.4% respectively based on phenol fed to the reactor.

EXAMPLE 2 The procedure of Example 1 was repeated except that the vessel was heated at 1500C for 66 hours.

6.6g of fluorobenzene and 1.9g diphenyl ether were formed with essentially no other impurities. This corresponds to an efficiency of formation of fluorobenzene of 1.2% based on phenol fed to the reactor.

EXAMPLE 3 The procedure of Example 1 was repeated except that the vessel was heated at 1500C for 6 hours.

1.6g of fluorobenzene was formed, corresponding to an efficiency of 3.3% based on phenol fed to the reactor.

EXAMPLE 4 The procedure of Example 1 was repeated except that 4g (3% wjw based on hydrogen fluoride) of boron ' trifluoride were added as catalyst and the reaction vessel was heated at 1500C for 6 hours.

7.4g of fluorobenzene and 0.06 of diphenyl ether were formed with essentially no other impurities. This corresponds to an efficiency of formation of fluorobenzene of 15.4% based on phenol fed to the reactor.

EXAMPLE 5 The procedure of Example 1 was repeated except that 4g (3% w/w based on hydrogen fluoride) of boron trifluoride were added as catalyst, and the reaction vessel was heated at 2000C for 6 hours. The autoclave pressure was approximately 850 psig.

11.0g fluorobenzene and 0.24g of diphenyl ether were formed with essentially no other ingredients. This corresponds to an efficiency of formation of fluorobenzene of 23% based on phenol fed to the reactor.

EXAMPLE 6 The procedure of Example 1 was repeated except that 4g (3% w/w based on hydrogen fluoride) of antimony pentafluoride were added as catalyst, and the reaction vessel was heated at 2000C for 6 hours.

11.0g of fluorobenzene and 0.5g of diphenyl ether were formed with essentially no other impurities. This corresponds to an efficiency of formation -of fluorobenzene of 23% based on phenol fed to the reactor.

WHAT WE CLAIM IS : - 1. A method of manufacturing an, optionally substituted, fluorobenzene which comprises contacting a corresponding phenol at an elevated temperature with hydrogen fluoride.

2. A method of manufacturing fluorobenzene which comprises contacting phenol at an elevated temperature with hydrogen fluoride.

3. A method according to claim 1 or 2, wherein the hydrogen fluoride is present in a molar excess relative to the phenol.

4. A method according to claim 3 wherein the molar ratio of hydrogen fluoride to phenol is at least 2 to 1.

5. A method according to claim 4 wherein the molar ratio of hydrogen fluoride to phenol is at least 5 to 1.

6. A method according to any of the preceding claims wherein the molar ratio of hydrogen fluoride to phenol is not more than 50 to 1.

7. A method according to any of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The hydrogen fluoride and the phenol are preferably substantially anhydrous. Water is produced during the course of the reaction of the phenol and hydrogen fluoride, 'and it may be advantageous to include a water 'scavenger, for example thionyl fluoride, in the'reaction mixture. Preferably the reaction takes place in the presence of a catalyst. Suitable catalysts include'Lewis acids (fluoride ion acceptors), for example Lewis acids having a Hammet constant (Ho) in hydrogen fluoride of from - 10 to -20. Examples of suitable catalysts include boron trifluoride (Ho in hydrogen fluoride approximately - 15). The concentration of the catalyst is suitably from 0.5 to 25% w/w based on hydrogen fluoride and preferably from 0.5 to l0% w/w based on hydrogen fluoride. The desired product may be separated from the reaction mixture by conventional techniques, for example solvent extraction and fractional distillation. Any unreacted phenol is conveniently recycled. The invention is illustrated by the following Examples. EXAMPLE I A nickel-lined autoclave of '500 ml capacity was charged with 47g (0.5 mole) of phenol and 150g (7.5 moles) of anhydrous liquid hydrogen fluoride. The' vessel was heated with stirring at 1500C for 24 hours giving a gauge pressure of approximately 440 psig. The autoclave was then cooled to 0 C and volatile material vented off. The contents of the autoclave were poured onto an ice/water mixture when a brown oil separated. The oil layer was extracted with the methylene chloride and analysis of the methylene chloride solution showed fluorobenzene and diphenyl ether in addition to unreacted phenol. No other impurities were detected. Quantitative analysis indicated that 5.5g of fluorobenzene and lg of diphenyl ether had been formed. This corresponds to an efficiency of 11.5% to 2.4% respectively based on phenol fed to the reactor. EXAMPLE 2 The procedure of Example 1 was repeated except that the vessel was heated at 1500C for 66 hours. 6.6g of fluorobenzene and 1.9g diphenyl ether were formed with essentially no other impurities. This corresponds to an efficiency of formation of fluorobenzene of 1.2% based on phenol fed to the reactor. EXAMPLE 3 The procedure of Example 1 was repeated except that the vessel was heated at 1500C for 6 hours. 1.6g of fluorobenzene was formed, corresponding to an efficiency of 3.3% based on phenol fed to the reactor. EXAMPLE 4 The procedure of Example 1 was repeated except that 4g (3% wjw based on hydrogen fluoride) of boron ' trifluoride were added as catalyst and the reaction vessel was heated at 1500C for 6 hours. 7.4g of fluorobenzene and 0.06 of diphenyl ether were formed with essentially no other impurities. This corresponds to an efficiency of formation of fluorobenzene of 15.4% based on phenol fed to the reactor. EXAMPLE 5 The procedure of Example 1 was repeated except that 4g (3% w/w based on hydrogen fluoride) of boron trifluoride were added as catalyst, and the reaction vessel was heated at 2000C for 6 hours. The autoclave pressure was approximately 850 psig. 11.0g fluorobenzene and 0.24g of diphenyl ether were formed with essentially no other ingredients. This corresponds to an efficiency of formation of fluorobenzene of 23% based on phenol fed to the reactor. EXAMPLE 6 The procedure of Example 1 was repeated except that 4g (3% w/w based on hydrogen fluoride) of antimony pentafluoride were added as catalyst, and the reaction vessel was heated at 2000C for 6 hours. 11.0g of fluorobenzene and 0.5g of diphenyl ether were formed with essentially no other impurities. This corresponds to an efficiency of formation -of fluorobenzene of 23% based on phenol fed to the reactor. WHAT WE CLAIM IS : -

1. A method of manufacturing an, optionally substituted, fluorobenzene which comprises contacting a corresponding phenol at an elevated temperature with hydrogen fluoride.

7. A method according to any of the

preceding claims wherein superatmospheric pressure is employed.

8. A method according to claim 7 wherein autogenous pressure is employed.

9. A method according to any of the preceding claims wherein the temperature is from 100 to 300"C.

10. A method according to claim 8 wherein the temperature is from 1300C to 250"C.

11. A method according to claim 8 wherein the temperature is from 1500C to 200"C.

12. A method according to any of the preceding claims wherein the reaction takes place in the presence of a Lewis acid catalyst.

13. A method according to claim 17 wherein the Lewis acid has a Hammet constant in hydrogen fluoride of from '-10 to -20.

14. A method according to claim 13 wherein the catalyst is boron trifluoride or antimony pentafluoride.

15. A method according to any of claims 12 to 14 wherein the concentration of the catalyst is from 0.5 to 25 parts by weight per 100 parts by weight of hydrogen fluoride.

16. A method according to claim 15 wherein the concentration of the catalyst is from 0.5 to 10 parts by weight per 100 parts by weight of hydrogen fluoride.

17. A method according to claim 1 substantially as described with reference to any of Examples 1 to 6.

18. A fluorobenzene whenever manufactured by a method according to any of claims 1 to 17.

19. A method of manufacturing an, optionally substituted, fluorobenzene which comprises contacting the corresponding phenol at an elevated temperature with a liquid medium comprising hydrogen fluoride.

20. A method of manufacturing fluorobenzene which comprises contacting phenol at an elevated temperature with a liquid medium comprising hydrogen fluoride.

21. A method according to claim 19 or 20 wherein the hydrogen fluoride is present in a molar excess relative to the phenol.

22. A method according to claim 21 wherein the molar ratio of hydrogen fluoride to phenol is at least 2 to 1.

23. A method according to claim 22 wherein the molar ratio of hydrogen fluoride to phenol is at least 5 to 1.

24. A method according to any of claims 19 to 23 wherein the molar ratio of hydrogen fluoride to phenol is not more than 50 to 1.

25. A method according to any of claims 19 to 24 wherein superatmospheric pressure is employed.

26. A method according to claim 25 wherein autogenous pressure is employed.

27. A method according to any of claims 19 to 26 wherein the temperature is from 1300C to 1600C.

28. A method according to claim 19 substantially as described with reference to Example 1.

29. A fluorobenzene whenever manufactured by a method according to any of claims 19 to 28.