IL124483A - Process for the preparation of para-fluorophenol - Google Patents

Abstract

Process for the preparation of p-fluorophenol, which comprises hydrolyzing p-bromofluorobenzene with a mixture of NaOH and Na2CO3 in the presence of a copper catalyst.

Description

3347/np2/94+ ■71] 9Π1ΝΤ79-ΝΊΝ9 ΤΗΏ ΪΟ "Γ^ΠΠ PROCESS FOR THE PREPARATION OF para-FLUOROPHENOL PROCESS FOR THE PREPARATION OF pgrg-FLUOROPHENOL Field of the Invention This invention relates to a process for the preparation of p-fluorophenol by the hydrolysis of p-bromofluorobenzene. It particularly refers to a process which yields highly pure p-fluorophenol, obtained from a crude p-fLuorophenol reaction product, which has an extremely low content of phenol and a low content of heavy by-products.

Background of the Invention Aromatic fluorine compounds based on fluorobenzene are important intermediates for the manufacture of agrochemicals, pharmaceuticals and speciality polymers. One such fluorine compound is p-fluorophenol (hereinafter PFP). Various processes for the preparation of PFP are known in the art. Among them the foHowing may be cited: direct fluorination of phenol, fluori ation of p-aminophenol, hydroxylation of fluorobenzene, diazotization of p-fluoroaxdline followed by hydrolysis of the diazonium salt, alkylation of fluoroanisole or fluorophenetole, and hydrolysis of p-chlorofluorobenzene. A process whic has received considerable attention in the art is the hydrolysis of p-bromofhiorobenzene (hereinafter PBFB). Said hydrolysis has been carried out under basic conditions, under pressure, with or without a catalyst. The problems inherent in the preparation of PFP by the hydrolysis of PBFB are the low selectivity regarding PFP and the formation, of phenol by-product. Phenol is not the only by-product formed; other by-products are, for instance, 4,4'-difluorodiphenyl ether (hereinafter DFDPE) and 4-fluoro-4'-hydroxydiphenyl ether (hereinafter FHDPE). Phenol, however, is a particularly undesirable byproduct, because it is practically impossible to remove by distillation, and other methods known for its removal, such as melt crystallization or treatment with phthalic anhydride/H2S04, require an extra process step, which is detrimental to the economics of the process. Therefore considerable attention has been devoted in the art to the reduction of the amount of phenol formed, but the results have not been completely satisfactory.

Thus, USP 2,934,569 and GB 850888 disclose the hydrolysis of PBFB with Ca(OH)2 as a base, and in the presence of a catalyst, whereby it is attempted to reduce the formation of phenol, but PFP is obtained in yields of only 50-70% and large amounts of DFDPE (10-15%) are formed.

Russian Patent 143404 describes the hydrolysis of PBFB using an alkali fluoride, such as NaHF2 or KOAc, as a base and 0¾0 as the catalyst. The reaction takes place at 250°C for 4 hours with a PFP yield of 73%.

DE 3430554 discloses the hydrolysis of PBFB in the presence of Ba(OH)2 with Cu powder as a catalyst and a quaternary ammonium cocatalyst. Yields of up to 94.6% are mentioned. ? USP 2,950,325 describes the basic hydrolysis of PBFB with alkaline earth metal oxides or hydroxides, which are said to avoid the formation of byproducts such as phenol, "which are frequently formed when the stronger alkaline agent, e.g., potassium hydroxide or sodium hydroxide, is employed in the reaction".

In conclusion, the prior art teaches that the best way of carrying out the basic hydrolysis of PBFB comprises using a copper compound catalyst, and calcium or barium hydroxide as a base. Stronger bases, such as in particular sodium hydroxide, are said to produce bad results. The combined use of calcium hydroxide and copper catalysts, according to prior art, provides yields that may reach 70-75%.

It is a purpose of this invention to provide a process for the production of PFP which gives this product in high yields and a very low amount of phenol byproduct.

It is a particular purpose of this invention to provide such a process which comprises the hydrolysis of PBFB and permits a reduction in the formation of phenol to amounts in the order of 0.1% and even below that amount.

It is a further purpose of this invention to provide such a process which does not involve the production of large amounts of heavy by-products, such as DFDPE and FHDPE. Any such heavy by-products are easily removed during the work-up, which includes extraction with an organic solvent, followed by fractional distillation.

It is a still further purpose of this invention to achieve the aforesaid' purposes by a simple and economical process, which does not involve the use of expensive reagents. .

It is a still further purpose of this invention to provide a process for the production of PFP having increased productivity together with high selectivity.

Other purposes and advantages of this invention will appear as the description proceeds. ..

Summary of the Invention The process accord ng to the invention is characterized in that PBFB is hydrolyzed with a mixture of NaOH and Na^Ou as the base, and using a copper catalyst.

It is known that the use of NaOH alone as base produces PFP with a phenol content of -0.7%. We have found that under the preferred conditions, the hydrolysis with NaOH together with Na2CO3 as the base, succeeded in producing PFP with a lower amount of phenol and a relatively low amount of heavy by-products relative to the prior art processes.

The hydrolysis is carried out on pure PBFB at temperatures from 180 to 240°C, and preferably at a temperature of 200-210°C. An increase in the temperature leads to an increase in the rate of the reaction, but also to an increase in the amount of phenol formed and the amount of F~ in the reaction mixture. A lower temperature increases the reaction time.

The molar ratio NaOH PBFB is comprised between 0.8 and 2.6, and preferably between 1.4 and 2.4. The NagCOa/PBFB molar ratio is comprised between 0.25 and 1.6, and preferably between 0.25 and 1.2. . The copper catalyst is chosen from among 0¾Ο, CuO and CuSO «5H2O, and is preferably an oxide, C112O or CuO. The molar ratio of PBFB to Ο¾Ο is from 4 to 16 and the molar ratio of PBFB to CuO is from 2 to 8.

Detailed Description of Preferred Embodiments When the reaction is carried out in a batch process, the NaOH and Na2CO3 are used in aqueous solution and the total base concentration (NaOH + Na2C03) in said solution varies from 10 to 30% and preferably from 20 to 25% w/w. The preferred molar ratio NaOH PBFB is comprised between 1.4 and 1.6. The preferred Na^Oa/PBFB molar ratio is comprised between 1.1 and 1.2. The bases are charged together with the PBFB and the catalyst into a reactor, which is sealed and heated to reaction temperature for the required period of time. The use of a higher concentration of base raises the efficiency of the reactor, but as the base concentration increases, more phenol and heavy byproducts (DFDPE and FHDPE) are formed. Thus, NaOH/PBFB in a molar ratio of -1.4, together with Na2C03PBFB in a molar ratio of -1.1, gave a product with a low amount of phenol (-0.1%) and relatively low amounts of heavy byproducts (-6-8%).

The preferred molar ratio of PBFB to 0¾Ο is between 6 and 12, and the preferred molar ratio of PBFB to CuO is between 3 and 6. The larger amounts of catalyst accelerate the reaction and reduce the formation of phenol byproduct.

The reaction time is about four hours at 205±5°C. Under the ' aforesaid conditions, low amounts of phenol and heavy by-products are obtained, with high conversions of PBFB (>99.5%). PFP yields of 85-90%, before distillation, are achieved.

The reaction product is subjected to work-up, comprising filtration of the reaction rnixture, addification to pH 3-7 with concentrated aqueous HC1, then extraction with an "organic solvent. The solvent is chosen from among toluene, n-butyl acetate (n-BuAc) and methyl isobutyl ketone (MIBE). - The organic phases from the extraction are combined and subjected to. fractional distillation. The fractional distillation is carried out with about 5-10 theoretical stages and the pure PFP comes off at 123-125°C at 100 mm Hg.

The foregoing advantages of the invention may be better understood through the following illustrative and non-limitative examples.

Examples 1 to 23 illustrate embodiments in which the invention is carried out in a batch process.

Example 1 Preparation of PFP using a mixture of Na^CO^ and NaOH as the base A one liter autoclave was charged with 620 g water, 50.6 g NaOH (1.26 mol), 105.2 g Na2C03 (0.99 mol), 157.5 g pure PBFB (0.9 mol) and 11 g Cu2O (0.076 mol). The autoclave was sealed and heated to 205°C over 45 minutes, the maintained "at 205°C for 4 hrs. The contents of the autoclave were cooled to room temperature and filtered. The composition of the reaction mixture was determined by GC and GC/MS.

The conversion of the PBFB, determined by titratin the filtrate for Br", was >99.5%. The filtrate was carefully acidified with 188 g 32% HC1 to pH 3-7 and extracted with 2 x 250 g toluene.

Four experiments were carried out under these conditions. The extraction was performed counter-current; i.e. organic phase from the second extraction served as the extractant for the first extraction of the following batch.

All the organic phases were combined and then distilled in a laboratory column, 1" diameter, about 5 theoretical stages. The solvent was distilled at atmospheric pressure, and can be recycled. Fractional distillation was then performed. The pure PFP was obtained at 123-125°C at 100 mm Eg. The main fraction contained 320 g PFP in a purity of 99.5% and a phenol content of 0.1%. Off-spec fractions containing ~25 g PFP can be transferred to the next distillation.

Based on these results, the yield of PFP is -85%, based on starting PBFB.

Examples 2 and 3 The preparation of PFP was carried out as described in Example 1, but under the following conditions and with the results shown in Table I: aq. (NaOH + NasCOa) 20% aOH/PBFB molar-ratio 1.4 NazCO-j/PBFB molar ratio 1.1 PBFB/Cu2O molar ratio 6.0 Temperature 205±5°C Time 4 hours Table I *PhOH n.<L <0.1% It should be pointed out that under said conditions, the level of F" in the reaction mixture is ~700-800 ppm, whic is lower than obtained with the use of NaOH alone. The yield of PFP in the crude reaction mixture is 85% or more.

Pure PFP is obtained by filtration of the reaction mixture, acidification to pH 3- 7 by aqueous HC1, followed by extraction with one of the following solvents: n-BuAc, EBK, toluene, then fractional distillation.

Examples 4 and 5 The preparation of PFP was carried out as described in Example 1, but using CuO as catalyst and under the following conditions and with the results shown in Table Π: aq. (NaOH + Na2CO.$) 20% NaOH/PBFB molar ratio 1.4 NaaCOa PBFB molar ratio 1.1 PBFB/CuO molar ratio 3.2 Temperature 205±5°C Time 4 hours Table Π *PhOH n-d. <0.1% Examples 6 to 11 The comparative behavior of different catalysts is illustrated by the following hydrolyses shown in Table ΠΙ: aq. (NaOH + NaaCOa) - 23% Temperature - 205±5°C Time - 4 hours Table ΠΊ Examples 12, 13 and 14 The following examples, carried out under the following conditions and with the results shown in Table IV, illustrate the effect of temperature variations within the range 205±5°C. aq. (NaOH + N zCO-j) NaOH PBFB molar ratio Na2CO3/PBFB molar ratio PBFB/CuO molar ratio Table IV The reaction can be carried out at lower and higher temperatures, e.g. from 180 to 220°C. However, as the temperature is lowered, the reaction proceeds more slowly; and as it is increased, more phenol by-product tends- to form.

Examples 15 and 16 The amounts of bases used can var within relatively wide limits and still produce satisfactory results, as shown by the following examples in Table V: aq. (NaOH + Na2CO;j) - 20% w/w PBFB/Cu20 molar ratio - 13 Temperature - 205±5°C Table V The use of Na^COs alone would give small amounts of phenol, but at the expense of large amounts of DFDPE and FHDPE.

Examples 17 to 20 The total concentration of the bases in their aqueous solution can also be varied considerably. Non-limitative examples are given in the following examples, shown in Table VL " · NaOH/PBFB molar ratio 1.4 Na2C03/PBFB molar ratio 1.1 Temperature 205±5°C Time 4 hours Table VI The use of a higher concentration of. base raises.. he. efficiency of the reactor, but the results show that the higher the base concentration, the lower the selectivity of the hydrolysis for PFP. Higher base concentrations led to the formation of more phenol and heavies (DFDPE and FHDPE). .

Examples 21 to 23 The ratio of PBFB to catalyst has an influence on the results of the reaction. Examples 21 to 23, shown in Table VII, relate to hydrolyses carried out under the following conditions: aq. (NaOH + Na2CO3) NaOH/PBFB molar ratio Na2CO3/PBFB molar ratio Temperature Time Table VII A large amount of catalyst produces a faster reaction and less phenol byproduct, as shown by the tabulated results.

The following examples illustrate embodiments wherei the invention is carried out in a semi-batch process. By semi-batch process is meant a process in which the NaOH is slowly added to the reaction mass during the course of the reaction.

In the semi-batch process, the water, the Na2CO3, the PBFB and the catalyst are charged into a reactor, which is sealed and, heated to reaction temperature. NaOH solution is then added at a constant flow rate over a few, preferably 3 to RECTIFIED SHEET (RULE 91,) , hours, whereafter the temperature is maintained for an additional time, e.g. about one hour, to permit the reaction to be completed. When the reaction is carried out in this manner, the preferred catalyst is 0¾Ο and the preferred molar ratio of PBFB to CU2O is from 4 to 6.3. The reaction temperature is from 200° to 220°C, preferably about 210°C. The preferred molar ratio Na2C03 PBFB is 0.25-0.50 and the preferred molar ratio NaOH/PBFB is 1.8-2.2.

Example 24 An 8-litre reactor was loaded with 1919 g H20, 283 g Na2C03, 1847 g PBFB and 369 g CU2O. The mixture was heated to 210°C. 1738 g of 48% NaOH was then slowly added to the reactor by means of a diaphragm pump, the temperature in the reactor being maintained at 210°C. The NaOH was added at a constant flow rate over 5 hours. The temperature was maintained for an additional hour. During this hour, a drop in the pressure of about 1 atm from -20 to 19 atm was observed, which indicated elimination of the vapor pressure of the PBFB and completion of the reaction.

The roixture was then cooled to 70eC. The mixture was filtered1 ©- remove the catalyst and the filtration line washed with 1000 g water . The mixture was acidified to pH=6.5 and cooled to ambient temperature. The product was ' extracted with 1850 g butyl-acetate. A second extraction was then done with 927 g butyl-acetate. The two extracts were mixed together. The total weight of the two extracts was 4017 g. 3941 g of this extract was distilled in two fractions, in a water-heated rotavapor and then in an oil-heated rptavapor. The first distilled fraction, weighed 3680 g and had the followin composition (GC area %): BuAc: 72.2%, PFP: 27.4%, DFDFE: 0.4%. The PFP assay as determined by acid titration was 26.0%. 85 g of a two-phase mixture of BuAc and water was collected in the trap. "i The second distilled fraction weighed 28.6 and had the following concentration: BuAc: 1.3%, PFP: 81.4%, DFDFE: 16%. The PFP assay was of 84.5%.

The recovered PFP in the two distillation fractions gave a yield of 83%, relative to the PBFB feed- The residue of distillation represents 85.3 g. The balance on the distillation was 98%.

Examples 25-29 The same operations of Example 24 were carried out in the following Examples, but with the amount of reagents and catalyst and the composition of the final product set forth in the following Table VUL Table VIII Detailed reaulta of semi-batch reaction in the 81 reactor Example Feed Tamp. Compoalti No. PBFB Molar ratio CuiO (daB. C) (molaa) PBFB NaOII NaiCOi FB OFP PBFB PhOH Θ.6Θ 1 2.4 0.25 20 210 0:7 0.08 0.01 0.088 28 Θ.5Θ 1 2.3 0.26 20 220 0.5 0.08 0.07 0.120 27 . 9.69 1 2.4 0.6 20 210 0.1 1.44 nd 0.240 28 10.56 1 2 0.25 20 210 n.d. 0.05 n.d. 0.082 29 13.4 1 2.2 0.25 13 210 0.2 0.08 n.d. 0.128 The productivity of the process is increased by the semi-batch operation. In Examples 24 to 29 the PBFB loading of the reactor, calculated on the basis of its fina content, after NaOH addition, free of catalyst, varied from 16 to .38 wt%.

The process can be carried out, if desired, in a continuous manner.

While ' embodiments of the invention have been described by way of ilLustration, it will be apparent that the invention may be carried out by persons skilled in the art with many, modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the daims.

WO 97/26235 Γ (~ PCT/IL97/00019

Claims (17)

1. Process for the preparation of p-fluorophenol, which comprises hydrolyzing p-bromoflTiorobenzene with a mixture of NaOH and Ν¾0Ο3 in the presence of a copper catalyst.

2. Process according to claim 1, wherein the copper catalyst is chosen from among Ο¾0, CuO and CuSCySEfcO.

3. Process according to claim 1, wherein the hydrolysis is carried out at temperatures from 180 and 240"C .

4. Process according to daim 1, wherein the hydrolysis is carried out at temperatures of 200-210°C.

5. Process according to daim 1, wherein the molar ratio of sodium hydroxide to p-bromofLuorobenzene is comprised between 0.8 and 2.6.

6. Process according to claim 1, wherein the molar ratio of sodium hydroxide to p-bromofluorobenzene is comprised between 1.4 and 2.4.

7. Process according to claim 1, wherein the molar ratio of sodium carbonate to p-bromofluorobenzene is comprised between 0.25 and 1.6.

8. Process according to claim 1, wherein the molar ratio of sodium carbonate to p-bromofluorobeiizene is comprised between 0.25 and 1.2. 124483/2 -17-

9. Process according to claim 1, wherein the sodium hydroxide and the sodium carbonate are used in aqueous solution with a total concentration from 10 to 30% w/w.

10. Process according to claim 9, wherein the sodium hydroxide and the sodium carbonate are used in aqueous solution with a total concentration of 20 to 25% w/w.

11. Process according to claim 2, carried out in batch, wherein the copper catalyst is used in such an amount that the molar ratio of p-bromofluorobenzene to Cu20 is from 6 to 12 and the molar ratio of p-bromofLuorobenzene to CuO is from 3 to 6.

12. Process according to claim 2, carried out in semi-batch, wherein the copper catalyst is CU2O and used in such an amount that the molar ratio of p-bromofluorobenzene to Cu20 is from 4 to 6.3.

13. Process according to claim 1, carried out in semi-batch, wherein the molar ratio of sodium hydroxide to p-bromofluorobenzene is comprised between 1.8 and 2.2 and the molar ratio of sodium carbonate to p-bromofluorobenzene is comprised between 0.25 and 0.5.

14. Process according to claim 1, carried out in semi-batch, wherein the sodium hydroxide is slowly added to a mixture of p-bromofluorobenzene, sodium carbonate and catalyst, at the reaction temperature and at such a flow rate that the addition lasts from 3 to 5 hours.

15. Process according to daim 14, wherein the reaction mixture is kept at the' reaction temperature, after the addition of sodium hydroxide, until the reaction is completed.

16. Process according to claim 1, further comprising subjecting the reaction product to work-up, extraction with a suitable solvent and distillation.

17. Process according to daim 16, wherein the solvent for extraction is chosen from among toluene, n-butyi acetate and methyl isobutyl ketone. a,.. RECTIFIED SHEET (RULE 91) ISA/EP