IE922191A1

IE922191A1 - Alkoxyphenoxybenzoic acid esters, their preparation and use¹in the preparation of (hydroxyphenoxy) benzoic acids

Info

Publication number: IE922191A1
Application number: IE219192A
Authority: IE
Inventors: Jean-Philippe Gillet
Original assignee: Atochem Elf Sa
Priority date: 1991-07-05
Filing date: 1992-07-03
Publication date: 1993-01-13
Also published as: NO922640L; FR2678608A1; EP0521796A1; NO922640D0; CA2073075A1; JPH05208937A; FI923095A; FI923095A0

Abstract

The subject of the present invention is a process for the preparation of esters of (alkoxyphenoxy)benzoic acids, characterised in that an alkyl ester of a hydroxybenzoic acid, in which the alkyl has at least three carbon atoms, is brought into contact with a haloanisole derivative, preferably in excess, in the presence of copper or of one of its derivatives, of a base and optionally of a phase transfer agent, and in that the compound is recovered. Another subject of it is the new esters obtained and their use for preparing the corresponding (hydroxyphenoxy)benzoic acids.

Description

The present invention relates to a process for preparing (alkoxyphenoxy)benzoic acid esters and the employment of the latter in preparing the corresponding (hydroxyphenoxy)benzoic acids.

It also relates to the (alkoxyphenoxy) benzoic acid esters as a new product.

Finally, it relates to a process for preparing (alkoxyphenoxy)benzoic acids.

The preparation of 4-(4'-alkoxyphenoxy) benzoic 10 acid was described by Harington in Biochem. J., 1926, 20, 300. This preparation was then repeated by J. Walker in J. Chem. Soc. (1942) p. 347-53. The principle of the reaction is to react bromoanisole with ethyl parahydroxybenzoate in the presence of neutral potassium carbonate (K2CO3) and of copper. The intermediate is then treated with potassium hydroxide and demethylated in acetic and hydrobromic acid medium. However, this process requires a large amount of copper (14 %) and generates a significant amount of effluents. For this reason, large amounts of acetic acid and of hydrobromic acid are lost as a result of their dilution in water.

A related preparation process was also proposed by Ungnade et al. in J. Org. Chem. 16, 1311-26 (1951) in which bromoanisole is reacted with potassium hydroxyben25 zoate, the product obtained being then demethylated in various ways, especially by potassium hydroxide, hydriodic acid or aluminum trichloride. The yields according to this process are nevertheless quite low.

More recently, US Patent 3,763,210 described a preparation process starting from p-methoxyphenol and ethyl p-fluorobenzoate in the presence of sodium hydroxide. The condensation product is isolated, saponified and demethylated. This process however requires a more expensive starting material and three stages.

The Patents JP 63.099036 and JP 63.104945 describe a process starting from 4,4'-diododiphenyl ether by monocarbonylation and splitting of the remaining iodide - 2 with sodium hydroxide. This process is accompanied by a recycling of the iodine. Such a process seems very difficult to use due to the iodine which easily sublimes.

Another technique was described in the Patent 5 EP-A-321,857. It involves starting from 4-(4'-hydroxyphenoxy)acetophenone which is successively protected by acetylation, oxidized in air and then deprotected with sodium hydroxide. This preparation process has the disadvantage of a long synthesis (three stages) and of start10 ing from a fairly complex compound.

Recently, the Patents US 4,945,450 and US 4,946,926 described a preparation process starting from 4-methoxyphenol and 4-chlorobenzonitrile. The intermediate product is then treated with acetic and hydro15 bromic acids. In this case, the operation is also difficult as a result of the reaction times, which are long, and from the fact that the final product requires a difficult purification.

Finally, Yeager et al. in Synthesis, page 63-68 (1991) described a means of access starting from 4-methoxyphenol which is reacted with 4-fluorobenzaldehyde in the presence of neutral potassium carbonate in DMAC. The intermediate leads, via the Baeyer-Villiger reaction, to the hydroxy ester which can give the hydroxy acid by saponification.

A particular object of the invention is to improve the process such as was described in Walker, mentioned above.

It particularly proposes a process which offers better reaction yields, requires only two reaction stages and avoids laborious acid/base treatments in order to isolate the methoxy acid.

The invention relates in the first place to a process for preparing (alkoxyphenoxy)benzoic acid esters of formula: COO R1 - 3 in which Rj is an alkyl radical having at least three carbon atoms, R2 is an alkyl radical, preferably C1-Cs alkyl, wherein an ester of a hydroxybenzoic acid of formula: HO COOR II is brought into contact with a haloanisole derivative, of formula: III in which: X is a halogen atom chosen from chlorine, bromine, fluorine or iodine, in the presence of copper or of one of its derivatives, of a base and optionally of a phase transfer agent, and in that the compound of formula I is recovered.

In the present description, the term alkyl signifies that the radicals may be either linear or branched. Among the alkyl radicals, there may be mentioned methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or n-pentyl.

Preferably, the hydroxyl radical of the ester of formula (II) is in the meta or para position in relation 20 to the radical COORi· Likewise, the haloanisoles of formula III will be preferred in which the alkoxy radical is in the meta or para position in relation to the halogen atom. The para position for the two compounds leads to the most advantageous results.

Preferably again, the radical Rx is chosen from the linear or branched C3-C6 alkyl radicals; Rx will be advantageously chosen from n-propyl or n-butyl.

Preferably again, X is chosen from the bromine or chlorine atom and/or 0R2 is the methoxy radical.

The reaction temperature will be advantageously between 140 and 220°C, preferably between 180 and 210°C.

The reaction is preferably carried out with an excess of haloanisole of formula III. Generally, the molar ratio of the compound of formula III in relation to the compound of formula II will be between 1.05 and 2 and it will be preferably less than 1.4, particularly for purposes of industrial operation.

The copper derivatives are chosen from metallic copper, cuprous and cupric oxides, cupric and cuprous halides (particularly Cl, Br, I) or copper acetate. These compounds can be used alone or as mixtures.

Preferably, the molar ratio of copper or of one of its derivatives in relation to the compound of formula II is between 0.001 and 0.07, advantageously between 0.01 and 0.05.

Among the bases which are suitable in the context of the present invention, there may be mentioned the alkali metal carbonates, particularly neutral potassium carbonate.

Advantageously, the molar ratio of the base in relation to the compound of formula II is between 0.5 and 1.2, preferably less than 0.75.

Phase transfer agents which can be used in the context of this process are well known to those skilled in the art.

A phase transfer agent means preferably a long30 chain polyethoxylated compound of the Antarox CO 990 type (oxyethylenated nonylphenol containing, on average, 100 ethylene oxide units).

It was found that it was advantageous according to another variant of the present invention to use the process in the presence of a copper ligand. This, in fact, allows a noticeable improvement in the yield of the condensation through an improved conversion and a higher selectivity. - 5 Among these ligands, there may be mentioned 8-hydroxyquinoline, picolinic acid or quinaldic acid or one of their derivatives.

Without wishing to be limited by any scientific 5 interpretation, the Applicant thinks that these compounds act as a ligand for the active species which is Cu1.

Moreover, the use of a ligand makes it possible to reduce the amount of catalyst. Preferably, a molar ratio of ligand/compound of formula II of between 0.001 and 0.07, preferentially between 0.01 and 0.05, will be used.

A further subject of the invention is a process for preparing propyl or butyl 4-(4 ' -methoxyphenoxy) benzoate, which comprises bringing propyl or butyl 4-hydroxy15 benzoate (Ila) into contact with 4-bromoanisole (Ilia) in a molar ratio Ila/IIIa of between 1.05 and 2, preferably less than 1.4, in the presence of neutral potassium carbonate in a molar ratio in relation to Ila of between 0.5 and 1.2, preferably less than 0.75, of metallic copper or of one of its derivatives in a molar ratio in relation to Ila of between 0.001 and 0.07, preferably between 0.01 and 0.05, optionally in the presence of a phase transfer agent and/or of a copper ligand.

An advantageous means of recovering the product of formula I consists, at the end of the reaction, in adding a solvent in order to facilitate the filtration of the salts formed. Among the solvents which may be suitable, there may be mentioned the polar solvents, such as dimethylformamide or dimethyl sulfoxide.

The organic filtrate is then distilled in order to recover, on the one hand, the product of formula I and, on the other hand, the reactants which have not reacted but which can be recycled such as the haloanisole of formula III, which was present in excess in the reaction, or the unreacted starting ccmpound of formula II.

Among the salts formed which were recovered by filtration as indicated above, the salt form of the - 6 compound of formula I is recovered by acidification of the salt of the acid in an aqueous medium. During the reaction according to the invention, in fact, an often low proportion of the ester of formula I was hydrolyzed and converted to the corresponding salt (this will be the alkali metal salt, such as potassium, if neutral potassium carbonate was used as base).

When a neutral alkali metal carbonate was used as base, the alkali metal halide solution resulting from this treatment can lead to a recycling of the halide by chlorine. In the case where X is the bromine atom, recycling by Cl2 is very advantageous.

The subject of the invention is also the (alkoxyphenoxy) benzoic acid esters of formula: in which: Rx is an alkyl radical having at least three carbon atoms, R2 is an alkyl radical, preferably C^-Cg alkyl.

Preferably, the compounds are chosen from propyl 4-(4'-methoxyphenoxy)benzoate or butyl 4-(4'-methoxy20 phenoxy)benzoate.

The compounds of formula I as defined above make it possible to prepare, with great ease and in a single stage, the (hydroxyphenoxy)benzoic acids of formula: These hydroxy acids are used especially as 25 monomers in the synthesis of thermotropic polyesters.

The compounds of formula IV are obtained by simultaneous deprotection, that is to say hydrolysis, of the ether and ester functional groups of the compound of formula I. - 7 Consequently, it is to be noted that, in relation to the prior art previously discussed, the compounds of formula I make it possible to obtain the corresponding acids of formula IV in a single stage.

This hydrolysis is generally carried out in the presence of hydrobromic acid and acetic acid at a temperature generally of between 80 and 130 °C, preferably between 100 and 120°C.

According to an advantageous variant, the alkyl 10 halides and the corresponding esters arising from the hydrolysis are continuously distilled, through a column, in the form of an azeotrope with water.

The acid of formula IV, which crystallizes at the end of the reaction, can be used as such without it being necessary to subject it to a purification operation.

According to a particular embodiment of the process according to the invention, the acids of the reaction medium can be recycled after readjusting their respective concentrations.

Advantageously, the molar ratio of acetic acid in relation to the ester of formula I is between 3 and 18, preferably between 6 and 12.

Preferably, the molar ratio of the compound of formula I in relation to hydrobromic acid is between 1 and 10, and preferably between 3 and 7.

Other acids will make it possible, under the same conditions as those mentioned above, to hydrolyze the ester of formula I in order to lead to the acid of formula IV. Among these acids, there may be mentioned mixtures of hydrobromic acid with another organic acid chosen from formic acid and propionic acid.

Another subject of the invention is a process for preparing hydroxyphenoxybenzoic acid of formula IV mentioned above, wherein, in a first stage, the ester of formula I described above is prepared according to the procedure mentioned previously, together with the different variants mentioned and, in a second stage, the ester of formula I is hydrolyzed as mentioned in the - 8 description above. Preferably, prior to the second stage, the ester of formula I will be isolated with the aim of obtaining the derivative of formula IV with a very high purity. In the contrary case, the reaction can nevertheless take place, but requires an additional purification stage of the final product of formula IV, for example by recrystallization. This variant has the additional disadvantage of leading to a medium, which has to be recycled, which is full of impurities.

The intermediacy of the ester of formula II limits the side reactions, gives better stability and a more fluid medium. It also means that difficult acid/base treatments in order to isolate the alkoxy acid are avoided.

In the light of the above account, it will be understood that the teaching provided by the present invention is not limited to the literal reading of the description. Other variants, particularly the use of equivalent starting compounds, can be used without departing from the scope of the said invention.

The invention will now be described with the help of the following examples: Preparation of butyl and propyl hydroxybenzoate Example 1 These esters are prepared in the conventional way from 4-hydroxybenzoic acid (PHB) and the corresponding alcohols by azeotropic distillation catalyzed by PTSA. The yields are practically quantitative.

HoXQ COOPr M.P.»98*C HO-/QV- COOBu M.P. ,67*C - 9 Preparation of propyl 4-f4'-methoxyphenoxy)benzoate Example 2 g (0.25 mol) of propyl 4-hydroxybenzoate, 52.4 g (0.28 mol) of 4-bromoanisole, 20.7 g (0.15 mol) of potassium carbonate and 0.8 g of Cu are placed in a stirred reactor equipped with a Dean and Stark apparatus. The reaction mixture is brought to 200°C with stirring for 2 h 30. At the end of the reaction, the reaction mixture is cooled and 150 cm3 of DMF are added. The salts formed are isolated by filtration. The filtrate contains 0.167 mol of propyl 4-(4'-methoxyphenoxy) benzoate (VPC determination). This product is isolated by distillation under reduced pressure. The salts isolated are dissolved in water and then acidified. The 4-(4 methoxyphenoxy) benzoic acid which precipitates is isolated by filtration, namely 0.043 mol, with a purity of 96.2 % (HPLC). The overall yield is 84 % of which 67 % is in the ester form. The ester distils at 175°C at 1 mm Hg.

IR HC=0) = 1715 cm'1, i/(C-0) = 1275 cm'1, i/(C-O-C) = 1232 cm'1. 13C NMR: £(C=0) 165.7 ppm, S(CH3O) = 55.1 ppm, £(CH2O) = 65.9 ppm.

Example 3 - with 8-hydroxvouinoline 45 g (0.25 mol) of propyl 4-hydroxybenzoate, 60.7 g (0.325 mol) of 4-bromoanisole, 20.7 g (0.15 mol) of potassium carbonate and 0.4 g of Cu and 0.9 g of 8-hydroxyquinoline are placed in a stirred reactor equipped with a Dean and Stark apparatus. The reaction mixture is brought to 198°C for 2 h 30. At the end of the reaction, the mixture is cooled and 125 cm3 of DMF are added. The salts formed are isolated by filtration. The filtrate contains 0.201 mol of propyl 4-(4'-methoxyphenoxy ) benzoate (VPC determination) . This product is isolated by distillation under reduced pressure. The salts isolated are dissolved in water and then acidified.

The 4-(4'-methoxyphenoxy)benzoic acid which precipitates is isolated by filtration, namely 0.024 mol of 98.1 % purity (HPLC). The overall yield is 90 % of which 80.4 % is in the ester form.

Example 4 - identical to Example 3 without 8-hydroxyquinoline The overall yield is 82 % of which 69 % is in the ester form.

Preparation of butyl 4-(4'-methoxyphenoxy)benzoate Example 5 8.5 g (0.25 mol) of butyl 4-hydroxybenzoate, 52.4 g (0.28 mol) of 4-bromoanisole, 20.7 g (0.15 mol) of potassium carbonate and 0.8 g of Cu are charged into an assembly identical to the previous one. The reaction mixture is brought to 198°C for 2 h 30 with stirring. At the end of the reaction, the reaction mixture is cooled and 175 cm3 of DMF are added. The salts formed are isolated by filtration. The filtrate contains 0.164 mol of butyl 4-(4'-methoxyphenoxy)benzoate (VPC determination). This product is isolated by distillation under reduced pressure. The salts isolated are dissolved in water and then acidified. The 4-(4'-methoxyphenoxy) benzoic acid which precipitates is isolated by filtration, namely 0.029 mol of 91 % purity (HPLC). The overall yield is 77 % of which 65 % is in the ester form. The ester distills at 184°C at 1 mm Hg.

IR j/(C=O) = 1715 cm'1, v(C-O) = 1277 cm'1, ^(C-O-C) = 1232 cm1, 13C NMR: S (C=O) 165.8 ppm, £(CH3O) = 55.2 ppm, 5(CH2O) = 64.3 ppm.

Example 6 - with phase transfer agent The procedure is carried out as in Example 5 but adding 5 g of Antarox 990*. The overall yield is 75 % of which 60 % is in the ester form.

Preparation of methyl 4-(4'-methoxyphenoxy)benzoate with phase transfer agent (comparison test) Example 7 The procedure is carried out as in Example 6 but 5 starting from methyl 4-hydroxybenzoate and from CuBr as catalyst. The overall yield is 49 % of which 35 % is in the ester form.

Working under the general conditions of Example 5, in the presence of Cu and without phase transfer agent, but using methyl hydroxybenzoate, the following results are obtained: the overall yield is 58 % of which 43 % is in the ester form.

Preparation of 4-(4'-hydroxyphenoxy)benzoic acid Example 8 60 g (0.2 mol) of butyl 4-(4'-methoxyphenoxy) benzoate, 120 g (2 mol) of acetic acid and 207 g (1.2 mol) of 47 % hydrobromic acid are placed in a round bottom flask equipped with a distillation column. The two-phase reaction mixture is brought to 120°C. When reflux has become established in the column, removal of the reaction byproducts is begun at the column head. Methyl bromide is cold trapped while butyl bromide, methyl and butyl acetates and water are recovered in the two-phase form. The reaction lasts 2 h 30. After cooling the mixture, the hydroxy acid precipitates. It is filtered, washed and dried. The yield is 96.7 %.

M.P. = 194°-195°C.

Example 9 The same technique is used as in Example 8, but 0 starting from propyl 4-(4'-methoxyphenoxy) benzoate. The reaction is faster, 1 h 45. After cooling, washing and filtering, pure hydroxy acid is recovered with a yield of 96.4 %.

M.P. = 194-195°C. - 12 Example 10 48.8 g (0.2 mol) of 4-(4'-methoxyphenoxy)benzoic acid obtained by acid treatment according to Examples 2 or 3, 207 g (1.2 mol) of 47 % hydrobromic acid and 120 g (2 mol) of acetic acid are placed in a round bottom flask equipped with a distillation column. The reaction mixture is brought to 115e-118°C for 2 h 15. Methyl bromide is cold trapped while methyl acetate is removed at the column head. The reaction mixture is cooled. The hydroxy10 acid which precipitates is filtered, washed and dried. A yield of 96 % is obtained.

M.P. = 194-195°C.

Example 11 This example illustrates the demethylation of 4-(4'-methoxyphenoxy)benzoic acid when carried out at total reflux. 63.4 g (0.26 mol) of 4-(4'-methoxyphenoxy) benzoic acid, 268.9 g (1.56 mol) of 47 % HBr and 110 g (1.83 mol) of acetic acid are charged into the same assembly as previously, equipped for total reflux. The mixture is brought to reflux for 7 h 30. The mixture is then cooled, filtered and the precipitate is washed. 55.9 g of dry product are thus obtained containing 86.8 % of 4-(4'hydroxyphenoxy)benzoic acid and 8.9 % of starting mater25 ial.

Example 12 This example illustrates the preparation of 4-(4'-hydroxyphenoxy) benzoic acid from butyl 4-(4'methoxyphenoxy)benzoate using the total reflux method. 6 g (0.02 mol) of butyl 4-(4'-methoxyphenoxy) benzoate with 7.2 g (0.12 mol) of acetic acid and 20.7 g (0.12 mol) of 47 % HBr are charged into an assembly equipped for total reflux. The reaction mixture is brought to reflux for 8 h 45. At the end of the reaction, the mixture is cooled, filtered and washed with water. 4 g of dry product are obtained containing 73.5 % of -134-(4'-hydroxyphenoxy) benzoic acid and 26% of 4-(4'methoxyphenoxy)benzoic acid.

It will be noted that in the examples carried out in a round bottom flask equipped with a distillation column, the reaction kinetics are markedly improved in relation to a procedure using total reflux. In the latter case, on the one hand, the reaction is much longer and, on the other hand, it often remains incomplete because residual amounts of the starting material are found in the reaction mixture.

Consequently, it is advantageous to use the process according to the invention while removing the reaction byproducts by distillation. These are principally acetates which are formed in the reaction mixture, especially methyl acetate and propyl acetate, as well as the corresponding bromides.

It will also be noted that the acetate removed distills in the form of an azeotrope and consequently water which is not bound up with the hydrobromic acid escapes from the reaction mixture, which constitutes an additional advantage linked to this particular embodiment.

Claims

1. An (alkoxyphenoxy) benzoic acid ester of formula: R 2 Q COO R 1 10 in which: R, represents an alkyl radical containing at least three carbon atoms, and R 2 represents an alkyl radical.

2. An ester according to claim 1 wherein R 2 represents a C 1 - C 6 alkyl radical. 15

3. Propyl 4-(4'-methoxyphenoxy)benzoate or butyl 4(4*-methoxyphenoxy)benzoate.

4. A process for preparing an (alkoxyphenoxy)benzoic acid ester of formula: r 2 o coo Rt X 25 (in which R, represents an alkyl radical containing at least three carbon atoms, and R 2 is an alkyl radical), which process comprises bringing an ester of a hydroxybenzoic acid of formula: KO COOR τ ΤΓ (in which Rt is as defined above) into contact with a compound of formula: ΤΓΓ (in which X represents a halogen atom chosen from chlorine, 10 bromine, fluorine or iodine, and R 2 is as defined above) in the presence of copper or a derivative thereof, of a base and optionally of a phase transfer agent.

5. A process according to claim 4, wherein the hydroxyl radical of the ester of formula II is in the meta or 15 para position relative to the COOR 1 radical.

6. A process according to claim 4 or 5 wherein the alkoxy radical OR 2 of the compound of formula III is in the meta or para position relative to the halogen atom.

7. A process according to any of claims 4 to 6 wherein 20 R, is a linear or branched (C 3 - C 6 ) alkyl radical.

8. A process according to claim 7 wherein R 1 is npropyl or n-butyl.

9. A process according to any of claims 4 to 8 wherein R 2 represents a C, - C 6 alkyl radical. 25 10. A process according to any of claims 4 to 9, wherein X is a bromine or chlorine atom and/or 0R 2 is a methoxy radical. 11. A process according to any of claims 4 to 10 wherein the compound of formula III is used in excess. 30 12. A process according to any of claims 4 to 10, wherein the molar ratio of compound of formula III to compound of formula II is between 1.05 and 2. 13. A process according to claim 12 wherein the molar ratio of compound of formula III to compound of formula II is 35 less than 1.4. 14. A process according to any of claims 4 to 13, wherein the copper or copper derivative is chosen from metallic copper, cuprous and cupric oxides, cupric and cuprous halides (Cl, Br, I) or copper acetate, alone or as mixtures. - 16 15. A process according to any of claims 4 to 14, wherein the molar ratio of copper or copper derivative to compound of formula II is between 0.001 and 0.07 16. A process according to any of claims 4 to 14 5 wherein the molar ratio of copper or copper derivative to compound of formula II is between 0.01 and 0.05. 17. A process according to any of claims 4 to 16, wherein the base is an alkali metal carbonate. 18. A process according to any of claims 4 to 16

10. Wherein the base is neutral potassium carbonate. 19. A process according to any of claims 4 to 18, wherein the molar ratio of the base to compound of formula II is between 0.5 and 1.2. 20. A process according to claim 19 wherein the molar

11. 15 ratio of the base to compound of formula II is less than 0.75. 21. A process for preparing propyl or butyl 4-(4'methoxyphenoxy)benzoate, which process comprises bringing propyl or butyl 4-hydroxybenzoate (Ila) into contact with 4bromoanisole (Ilia) in a molar ratio Ila/IIIa of between 1.05

12. 20 and 2, in the presence of neutral potassium carbonate in a molar ratio relative to Ila of between 0.5 and 1.2, of metallic copper or a derivative thereof in a molar ratio relative to Ila of between 0.001 and 0.07, optionally in the presence of a phase transfer agent. 25 22. A process according to claim 21 wherein the molar ratio Ila/IIIa is less than 1.4.

13. 23. A process according to claim 21 or 22 wherein the molar ratio of neutral potassium carbonate to Ila is less than 0.75. 30

14. 24. A process according to any of claims 21 to 23 wherein the molar ratio of metallic copper or derivative thereof to Ila is between 0.01 and 0.05.

15. 25. A process according to any of claims 4 to 24 which is carried out in the presence of a copper ligand. 35

16. 26. A process according to claim 25 wherein the copper ligand is 8-hydroxy-quinoline.

17. 27. A process according to claim 25 or 26, wherein the molar ratio of ligand to compound of formula II is between 0.001 and 0.07. - 17

18. 28. A process according to claim 25 or 26 wherein the molar ratio of ligand to compound of formula II is between 0.01 and 0.05.

19. 29. A process according to any of claims 4 to 28 wherein reaction byproducts are removed from the reaction medium by distillation.

20. 30. A process for preparing a compound as claimed in claim 1 substantially as described in any of Examples 2 to 7.

21. 31. A compound as claimed in claim 1 prepared by the process claimed in any one of claims 4 to 30.

22. 32. Use of a compound as claimed in any of claims 1 to 3 and 31 in the preparation, by hydrolysis, of a hydroxyphenoxybenzoic acid of formula IV HO COOH 20

23. 33. A process for preparing a hydroxyphenoxybenzoic acid of formula IV HO COOH IY which process comprises hydrolysing a compound as claimed in any of claims 1 to 3 and 31.

24. 34. A process according to claim 33 wherein the 30 hydrolysis is carried out by a hydrobromic acid/acetic acid mixture.

25. 35. A process according to Class 33 substantially as described in any of Examples 8 to 12.

26. 36. A compound of formula IV as defined in claim 33 35 prepared by the process claimed in any of claims 33 to 35.