EP0000542B1 - Process for the preparation of trifluoromethyl phenols - Google Patents

Description

The invention relates to a process for the preparation of phenols having a trifluoromethyl group.

It has already become known that numerous trifluoromethyl-nitro-phenols are produced by reacting certain halogenated nitrobenzotrifluorides with an at least equimolar amount of an alkali metal or alkaline earth metal hydroxide in the presence of one or more solvents from the group consisting of dimethyl sulfoxide, dimethylformamide and dimethylacetamide (see U.S. Patent 3,813,446 and J. Org. Chem. 32, 242 (1971)). For example, it is possible to convert 4-chloro-3-nitro-benzotri-fluoride into 2-nitro-4-trifluoromethyl-phenol with sodium hydroxide solution in the presence of dimethyl sulfoxide. However, this known method has several disadvantages. It requires the presence of solvents, which are not only expensive, but are difficult to separate from the desired end product because of their relatively high boiling point. In addition, when using dimethyl sulfoxide, dimethylformamide and / or dimethylacetamide as a solvent, special safety precautions must be taken to avoid unpleasant odors and damage caused by these relatively highly toxic solvents. Finally, the yields in this process often leave much to be desired.

According to another process, trifluoromethylphenols are obtained by cleaving the corresponding methoxy compounds with pyridine hydrochloride at 210 ° C. (J. org. Chem. 27, 4660 (1962): in this process, the methoxy compounds are prepared from chloronitrobenzotrifluorides in a preceding process step.

in der

• X Halogen,
• R¹, R² und R³ Wasserstoff, Trifluormethyl, Nitro, Alkylsulfonyl, Arylsulfon, Carboxyl oder Carbonsäureester und
• Y Wasserstoff, ein Halogen oder Alkoxy

bedeuten,
wobei von den Substituenten R¹, R² und R³ einer eine Trifluormethylgruppe darstellt und mindestens ein weiterer von Wasserstoff verschieden ist, in alkoholischer Lösung mit überschüssigem wäßrigen Alkalihydroxid in Gegenwart von quartären Oniumsalzen umsetzt.A process for the preparation of trifluoromethylphenols has been found, in which compounds of the formula

in the

• X halogen,
• R ¹ , R ² and R ^{3 are} hydrogen, trifluoromethyl, nitro, alkylsulfonyl, arylsulfone, carboxyl or carboxylic acid esters and
• Y is hydrogen, a halogen or alkoxy

mean,
wherein one of the substituents R ¹ , R ² and R ^{3 represents} a trifluoromethyl group and at least one other is different from hydrogen, in alcoholic solution with excess aqueous alkali metal hydroxide in the presence of quaternary onium salts.

Halogens (X) can be fluorine, chlorine, bromine or iodine, preferably fluorine or chlorine.

• die Nitrogruppe, die Alkylsulfonylgruppe, deren Alkylrest bevorzugt ein geradkettiger oder verzweigter niederer Alkylrest mit 1-8 Kohlenstoffatomen sein kann, wie beispielsweise Methyl, Äthyl, Propyl, Isopropyl oder isomeres Butyl, Hexyl oder Octyl, die Arylsulfongruppe, deren Arylrest bevorzugt Phenyl oder ein beispielsweise durch Chlor oder Methyl substituiertes Phenyl sein Kann, die Carboxylgruppe, die Carbonsäureestergruppe, deren Alkoholkomponente ein geradkettiger oder verzweigter niederer aliphatischer Alkohol mit 1-8 Kohlenstoffatomen sein kann, wie beispielsweise Methanol, Äthanol, Propanol, Isopropanol, oder die isomeren Butanole, Hexanole oder Octanole.

In addition to hydrogen and trifluoromethyl, the following may be mentioned as substituents R ¹ , R ² or R ³ :

• the nitro group, the alkylsulfonyl group, the alkyl radical of which can preferably be a straight-chain or branched lower alkyl radical having 1-8 carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl or isomeric butyl, hexyl or octyl, the arylsulfone group, the aryl radical of which is preferably phenyl or an example Phenyl substituted by chlorine or methyl, the carboxyl group, the carboxylic acid ester group, the alcohol component of which can be a straight-chain or branched lower aliphatic alcohol having 1-8 carbon atoms, such as, for example, methanol, ethanol, propanol, isopropanol, or the isomeric butanols, hexanols or octanols .

Halogen atom (Y) may be, for example, fluorine, chlorine, bromine or iodine, preferably chlorine or bromine.

The alkoxy group (Y) preferably contains alkyl radicals having 1 to 4 carbon atoms, for example the methyl, ethyl, propyl, isopropyl, butyl or tert-butyl radical.

in der

• X' ein Fluor- oder ein Chloratom bedeutet und die Reste R¹, R², R³ die obengenannte Bedeutung haben, genannt.

Preferred compounds of the formula (I) are compounds of the formula 11

in the

• X 'represents a fluorine or a chlorine atom and the radicals R ¹ , R ² , R ^{3 have} the abovementioned meaning.

Compounds of formula 1 are known and can be prepared by nitrating chlorotrifluoromethylbenzene with nitric acid / sulfuric acid (J. org. Chem. 26, 2707 (1961)).

• 4-Chlor-3-nitro-benzotrifluorid
• 2-Chlor-5-nitro-benzotrifluorid
• 3,4-Dichlor-5-nitro-benzotrifluorid
• 2,3-Dichlor-5-nitro-benzotrifluorid
• 2,4-Dichlor-5-nitro-benzotrifluorid
• 6-Chlor-3-nitro-5-trifluormethyl-benzoesäure
• 2-Chlor-3-nitro-5-trifluormethyl-benzoesäure
• 4-Brom-3-nitro-benzotrifluorid
• 2-Brom-5-nitro-benzotrifluorid d
• 2-Chlor-3-methoxy-5-nitro-benzotrifluorid
• 2-Methoxy-4-chlor-5-nitro-benzotrifluorid.

The following compounds of the formula (I) may be mentioned, for example:

• 4-chloro-3-nitro-benzotrifluoride
• 2-chloro-5-nitro-benzotrifluoride
• 3,4-dichloro-5-nitro-benzotrifluoride
• 2,3-dichloro-5-nitro-benzotrifluoride
• 2,4-dichloro-5-nitro-benzotrifluoride
• 6-chloro-3-nitro-5-trifluoromethyl-benzoic acid
• 2-chloro-3-nitro-5-trifluoromethyl-benzoic acid
• 4-bromo-3-nitro-benzotrifluoride
• 2-bromo-5-nitro-benzotrifluoride d
• 2-chloro-3-methoxy-5-nitro-benzotrifluoride
• 2-methoxy-4-chloro-5-nitro-benzotrifluoride.

It is extremely surprising that the corresponding trifluoromethylphenols can be prepared from the compounds of the formula (I) in a smooth reaction and with a high yield, since it was assumed based on the known prior art that not only the substituent X would be exchanged for hydroxy, but also a trifluoromethyl group is saponified to a carboxyl group (cf. J. Org. Chem. 26, 2707 (1961)). Contrary to expectations, however, a selective halogen-hydroxyl exchange is possible without simultaneous saponification of the trifluoromethyl group by the process according to the invention.

Alkonols with a lower unbranched or branched alkyl radical can be used as solvents for the process according to the invention. Alcohols whose unbranched or branched alkyl radical has 1 to 4 carbon atoms, such as methanol, ethanol, propanol, isopropanol, the various isomeric butanols, glycol and glycol monomethyl ether, are preferred.

The amount of solvent can vary within wide limits, for example 1 to 20 parts by weight, preferably 2 to 8 parts by weight, of solvent can be used per 1 part by weight of a compound of the formula (I).

Sodium or potassium hydroxide are preferably used as alkali metal hydroxides for the process according to the invention. They are generally used in the form of their aqueous solutions which contain, for example, 30-50% by weight of alkali metal hydroxide. However, the sodium or potassium hydroxide can also be added in solid form to the aqueous alcoholic solution. The alkali metal hydroxides are generally used in excess, the use of about three times the molar amount based on the conversion of the halogen atom to the phenolic hydroxyl group is particularly advantageous.

The water content of the reaction solution can vary within wide limits. In general, it can be about 20 to 25% by weight.

eingesetzt werden, in der

• Z für ein Element der 5. Hauptgruppe des Periodensystems steht,
• R⁴ bis R⁷ gleich oder verschieden sind und gegebenenfalls substituiertes Alkyl, Cycloalkyl, Aralkyl oder Aryl bedeuten oder zwei der Reste R⁴ bis R⁷ zusammen mit dem Zentralatom Z und gegebenenfalls weiteren Heteroatomen einen Heterocyclus bilden, wobei die Reste R⁴ bis R⁷ gemeinsam mindestens 6 Kohlenstoffatome enthalten, und
• A eine unter den Bedingungen des erfindungsgemäßen Verfahrens inertes anorganisches oder organisches Anion bedeutet.

Onium salts of the formula can be used for the process according to the invention

be used in the

• Z represents an element of the 5th main group of the periodic table,
• R ⁴ to R ^{7 are} identical or different and represent optionally substituted alkyl, cycloalkyl, aralkyl or aryl or two of the radicals R ⁴ to R ⁷ together with the central atom Z and optionally further heteroatoms form a heterocycle, the radicals R ⁴ to R ⁷ together contain at least 6 carbon atoms, and
• A is an inorganic or organic anion which is inert under the conditions of the process according to the invention.

As elements of the 5th main group of the periodic table (according to Mendelejeff) are mentioned: nitrogen, phosphorus, arsenic, antimony or bismuth.

The radicals R ⁴ to R ⁷ can be low-molecular or high-molecular organic radicals.

Optionally substituted alkyl radicals, cycloalkyl radicals, aralkyl radicals or aryl radicals may be mentioned as low molecular weight organic radicals. Two of the radicals R ⁴ to R ⁷ can also form a heterocycle together with the central atom Z and optionally further heteroatoms.

The optionally substituted or branched alkyl radicals can especially those with 1-18 Carbon atoms, preferably having 1-12 carbon atoms, such as the methyl, ethyl, isomeric propyl, butyl, octyl, decyl or dodecyl radicals.

The cycloalkyl radicals can be cyclopentyl and in particular cyclohexyl radicals which are optionally substituted by C ₁ -C ₄ -alkyl radicals.

The aralkyl radicals can optionally be benzyl radicals substituted by C _i -c _4- alkyl radicals, methoxy groups or halogen atoms.

The aryl radicals can be phenyl radicals which are optionally substituted by C 1 -C ₄ -alkyl radicals, methoxy groups, ethoxy groups or halogen atoms.

In the case of a heterocycle which two adjacent radicals R ⁴ to R ^{7 can form} together with the central atom Z and optionally with further heteroatoms, oxygen, nitrogen or sulfur are preferred as further heteroatoms.

The 5- and 6-membered heterocycles may be mentioned, for example the pyrrolidine ring, the piperidine ring or the morpholine ring.

An example of a polymeric organic radical in one of the radicals R ⁴ to R ⁷ is a polystyrene which may be crosslinked by divinylbenzene.

The total number of carbon atoms of all radicals R ⁴ to R ⁷ is at least six for the process according to the invention. For example, the maximum number of all carbon atoms in a polymeric organic radical can be very large. The preferred total number of carbon atoms of all low-molecular radicals R ⁴ to R ⁷ is 8 to 25.

Preferred anions A are the chloride, bromide and hydroxide anion.

in der

• Z' Stickstoff oder Phosphor bedeutet und
• R⁴ bis R⁷ und A die oben angegebene Bedeutung haben.

Preferred onium salts for the process according to the invention are quaternary ammonium or phosphonium salts of the formula

in the

• Z 'means nitrogen or phosphorus and
• R ⁴ to R ⁷ and A have the meaning given above.

Examples of the preferred quaternary ammonium or phosphonium salts are: tetraethylammonium chloride, tetrabutylammonium bromide, triethylbenzylammonium hydroxide, benzyldimethyldodecylammonium chloride, dibutylpiperidiniumbromide, methyltrioctylammoniumchloride, dimethylbenzylpidylphenyl-methyldylylphenyl-methylphenyl-methyl-phenyl methyl-piperdinium hydroxide, triethyl-phenyl-ammonium chloride, dodecyl-trimethyl-ammonium hydroxide, cyclohexyldodecyl-dimethyl-ammonium chloride, methyl-ethyl-piperidinium bromide, triphenyl-benzyl-phosphonium bromide, tetrabutyl-phosphonium chloride, tributyl-benzyl-phosphonium chloride.

Quaternary ammonium compounds in which one of the radicals R ⁴ to R ^{7 is} a polymeric radical can be, for example, ion exchangers based on styrene and generally 2 mol% of divinylbenzene as crosslinking agents which carry quaternary ammonium groups.

The amounts of the quaternary onium salt used can vary from 1 to 20% by weight and are generally about 5 to 10% by weight, based on the starting compound.

The quaternary onium salts mentioned are known as phase transition catalysts in multiphase systems and can be prepared by known processes (Houben-Weyl, 4th ed. Stuttgart 1958, volume XI, 2, p. 587 and volume XIV, 2nd p. 750).

The process according to the invention can be carried out in the temperature range from about 0 to about 80 ° C., preferably from about 50 to 75 ° C.

The process according to the invention can be explained by the following reaction equation:

• a) Verbindungen der Formel
  
  in welcher
  • X, Y, R¹, R² und R³ die oben angegebene Bedeutung haben,
  
  in Gegenwart eines als Lösungsmittel dienenden Alkohols mit einem niederen unverzweigten oder verzweigten Alkylrest mit überschüssigem, wäßrigen Alkalihydroxid in Gegenwart von quartären Oniumsalzen bei Temperaturen zwischen 15 und 35°C umsetzt und
• b) die dabei entstehenden Verbindungen der Formel
  
  in welcher
  • Y, R¹, R² und R³ die oben angegebene Bedeutung haben und
  • R¹² für einen niederen unverzweigten oder verzweigten Alkylrest steht,
  
  in alkoholischer Lösung mit überschüssigem, wäßrigem Alkalihydroxid in Gegenwart von quartären Oniumsalzen umsetzt.

In a special variant, the method according to the invention can be carried out in such a way that

• a) Compounds of the formula
  
  in which
  • X, Y, R ¹ , R ² and R ^{3 have} the meaning given above,
  
  in the presence of an alcohol serving as solvent with a lower unbranched or branched alkyl radical with excess, aqueous alkali metal hydroxide in the presence of quaternary onium salts at temperatures between 15 and 35 ° C. and
• b) the resulting compounds of the formula
  
  in which
  • Y, R ¹ , R ² and R ^{3 have} the meaning given above and
  • R ^{12 represents} a lower unbranched or branched alkyl radical,
  
  in alcoholic solution with excess, aqueous alkali hydroxide in the presence of quaternary onium salts.

in der die Reste R¹, R², R³ und Y die oben angegebene Bedeutung haben und

• R¹² ein niederer unverzweigter oder verzweigter Alkylrest ist,

können isoliert werden, sofern man in dem Temperaturbereich zwischen 15 und 35°C arbeitet.The alkoxy compounds of the formula which occur as intermediates in this variant of the process according to the invention

in which the radicals R ¹ , R ² , R ³ and Y have the meaning given above and

• R ^{12 is} a lower unbranched or branched alkyl radical,

can be isolated if you work in the temperature range between 15 and 35 ° C.

The alkyl radicals R ^{12 of} these alkoxy compounds are determined by the alcohol used as solvent; when using methanol, a methoxy compound is obtained.

Such alkoxy compounds are known (J. Org. Chem. 26, 2707 (1961)) and can be prepared, for example, by reacting an organically bonded halogen atom with sodium methylate or with methanolic potassium hydroxide.

• Im Reaktionsgefäß werden die Ausgangsverbindung, das Lösungsmittel und der Katalysator vorgelegt und unter Rühren das Alkalihydroxid, beispielsweise als wäßrige Lösung, zugetropft. Die Temperatur steigt dann an; man reguliert die Zutropfgeschwindigkeit so ein, daß die gewünschte Reaktionstemperatur nicht überschritten wird. Nach dem Ende der Zugabe wird bei der Reaktionstemperatur noch für einige Stunden nachgerührt. Das Phenol liegt in Form seines Alkalisalzes vor und kann in üblicher Weise durch Ansäuern mit einer Mineralsäure erhalten werden. Es kann nun durch Phasentrennung (bei Flüssigkeiten), durch Abfiltrieren (bei Festprodukten), durch Extraktion aus dem Reaktionsgemisch oder durch Wasserdampfdestillation abgetrennt werden.

The method according to the invention can be carried out, for example, as follows:

• The starting compound, the solvent and the catalyst are placed in the reaction vessel and the alkali metal hydroxide, for example as an aqueous solution, is added dropwise with stirring. The temperature then rises; the dropping rate is regulated so that the desired reaction temperature is not exceeded. After the end of the addition, stirring is continued for a few hours at the reaction temperature. The phenol is in the form of its alkali salt and can be obtained in the usual way by acidification with a mineral acid. It can now be separated by phase separation (in the case of liquids), by filtering (in the case of solid products), by extraction from the reaction mixture or by steam distillation.

Compared to the known processes for the preparation of trifluoromethylphenols, the process according to the invention has the advantage of being simple to carry out and of leading to the desired phenols in one step.

The quaternary onium salts of the formula (IV) are known as phase transition catalysts in systems with two immiscible liquid phases (DT-OS 2 634 419).

The method according to the invention, however, is carried out with quaternary onium compounds in a system with only one liquid phase.

in der die Reste R¹, R², R³ und y die oben angegebene Bedeutung haben, hergestellt werden.According to the process of the invention, trifluoromethylphenols of the formula

in which the radicals R ¹ , R ² , R ³ and y have the meaning given above, are prepared.

in der

• R⁸ Trifluormethyl, Chlor oder Wasserstoff,
• R⁹ Trifluormethyl, Nitro oder Chlor,
• R¹⁰ Nitro, Chlor oder Carboxyl,
• R" Methoxy oder Wasserstoff

'bedeuten,
wobei von den Substituenten R⁸ und R⁹ einer eine Trifluormethylgruppe darstellt und von den Substituenten R⁸ und R" höchstens einer Wasserstoff ist, sind neu.The trifluoromethylphenols of the formula

in the

• R ⁸ trifluoromethyl, chlorine or hydrogen,
• R ⁹ trifluoromethyl, nitro or chlorine,
• R ¹⁰ nitro, chlorine or carboxyl,
• R "methoxy or hydrogen

'mean,
wherein one of the substituents R ⁸ and R ^{9 represents} a trifluoromethyl group and of the substituents R ⁸ and R "is at most one hydrogen are new.

• 2-chlor-4-trifluormethyl-6-nitro-phenol
• 2-Chlor-6-trifluormethyl-4-nitro-phenol
• 4-Chlor-2-trifluormethyl-6-nitro-phenol
• 3-Methoxy-4-trifluormethyl-6-nitro-phenol
• 5-Nitro-3-trifluormethyl-salicylsäure

Examples of compounds of the formula (VII) which may be mentioned are:

• 2-chloro-4-trifluoromethyl-6-nitro-phenol
• 2-chloro-6-trifluoromethyl-4-nitro-phenol
• 4-chloro-2-trifluoromethyl-6-nitro-phenol
• 3-methoxy-4-trifluoromethyl-6-nitro-phenol
• 5-nitro-3-trifluoromethyl salicylic acid

The trifluoromethylphenols, in particular the new trifluoromethylphenols, are intermediate products for the production of crop protection agents, in particular herbicides (DT-OS 2311 638, DT-OS 1 944 335).

For example, a trifluoromethylphenol of the formula VI can be reacted with p-nitrochlorobenzene in the presence of potassium m-methylate to give trifluoromethyl-nitrodiphenyl ether.

Herbicides from new trifluoromethylphenols of the formula VII show improved activity compared to the known herbicides.

example 1

400 ml of methanol, 20 g of benzyldimethyldodecylammonium chloride and 180 g of 4-chloro-3-nitrobenzotrifluoride are placed in the reaction flask with stirring and then 400 g of 50% sodium hydroxide solution are added dropwise. The temperature rises to approx. 70 ° C if the addition takes place in approx. 20 minutes. The mixture is then stirred for a further 4 hours at 65 ° C., then cooled by throwing in ice and adjusted to pH 3 with concentrated hydrochloric acid. The phenol is driven over with steam and the phases in the receiver are separated by adding about 50 ml of concentrated hydrochloric acid.

• Siedepunkt: 92-95°C bei 15 mm,np : 1.5020.

There are 156 g of 2-nitro-4-trifluoromethylphenol with a purity of more than 98.5% after gas chromatographic analysis, which corresponds to a yield of 91% of theory.

• Boiling point: 92-95 ° C at 15 mm, np: 1.5020.

Example 2

450 g of 2-chloro-5-nitro-benzotrifluoride are placed in 1250 ml of methanol and 35 g of tetraethylammonium chloride. 1000 g of an aqueous 50% strength potassium hydroxide solution are then added dropwise (1 hour), the temperature being kept at a maximum of 40 ° C. by cooling. About 30 minutes after the end of the addition, the mixture is heated to 80 ° C. for 6 hours, cooled and acidified with concentrated hydrochloric acid. The mixture is extracted several times with 300 ml of methylene chloride, the organic phase is dried with sodium sulfate and the solvent is removed under reduced pressure. About 413 g of crude product, F: 9 fl-95 ° C with a purity of about 95% according to gas chromatographic analysis. After recrystallization from toluene or distillation at 0.5 mm, pure 4-nitro-2-trifluoromethylphenol is obtained, F: 134 ° C.

Example 3

• F: 33-34°C aus Hexan. Ausbeute: 77% der Theorie.

50 g of 3,4-dichloro-5-nitro-benzotrifluoride and 5 g of benzyltriethylammonium bromide are placed in 150 ml of methanol, and 100 g of 50% sodium hydroxide solution are added dropwise at 25 to 30 ° C. The mixture is then stirred for a further 4 hours at 65 ° C., cooled, mixed with 100 ml of water and acidified with sulfuric acid. The crude product is extracted with methylene chloride, the solution is dried and the methylene chloride is distilled off. The residue is fractionally distilled, and 35 g of 2-chloro-4-trifluoromethyl-6-nitrophenol are obtained with a boiling point of 74 to 76 ° C at 0.25 mm.

• F: 33-34 ° C from hexane. Yield: 77% of theory.

Example 4

• Ausbeute: 73% der Theorie.

50 g of 2,3-dichloro-5-nitro-benzotrifluoride in 150 ml of methanol and 5 g of tetrabutylammonium chloride are placed in the reaction vessel and then 100 g of 50% strength sodium hydroxide solution are added dropwise in such a way that the temperature rises to a maximum of 50 ° C. At this temperature the mixture is stirred for 5 more times, then cooled and acidified with hydrochloric acid. The product is taken up in methylene chloride and, after drying, distilled with sodium sulfate. At bp: 110 to 115 ° C 33 g of 2-chloro-6-trifluoromethyl-4-nitrophenol pass over, which has a melting point of 78 to 80 ° C.

• Yield: 73% of theory.

Example 5

104 g of 2,4-dichloro-5-nitrobenzotrifluoride and 7 g of tetrabutylphosphonium chloride are placed in 400 ml of methanol, and 400 g of 50% sodium hydroxide solution are added dropwise. The temperature is kept at a maximum of 70 ° C. and, after the dropping has ended, stirring is continued for 6 hours. The cooled mixture is acidified with hydrochloric acid, then the product is extracted with methylene chloride. After the solvent has been distilled off, the residue is recrystallized from isopropanol. This gives 69 g of 3-methoxy-4-trifluoromethyl-6-nitrophenol with a melting point of 77 to 78 ° C, the yield is 73% of theory.

Example 6

45 g of 4-chloro-3-nitro-benzotrifluoride and 10 ml of a 50% strength aqueous benzyldodecyldimethylammonium chloride are placed in 150 ml of ethylene glycol monomethyl ether and 100 g of 50% strength potassium hydroxide solution are added dropwise in about 30 minutes to a temperature of 65 ° C. Then the mixture is stirred for 6 hours at 65 ° C., then cooled, made with concentrated hydrochloric acid and about 500 ml of distillate are driven over with steam. The organic phase is separated off, washed with 20 ml of dilute hydrochloric acid, separated off again and dried with sodium sulfate. 38 g of 2-nitro-4-trifluoromethylphenol are obtained, which corresponds to a yield of 92% of theory.

Example 7

If example 6 is repeated and 150 ml of ethanol are used instead of ethylene glycol monomethyl ether, 39 g of 2-nitro-4-trifluoromethylphenol are obtained, which corresponds to 94% of theory.

Example 8

27 g of 6-chloro-3-nitro-5-trifluoromethylbenzoic acid are dissolved in 100 ml of methanol, 1 g of trioctylmethylammonium chloride is added, and 70 g of 50% sodium hydroxide solution are then added dropwise, with the temperature not to rise above 65.degree . After stirring for a further 4 hours at 65 ° C, cool and add enough water until everything has dissolved. The mixture is then acidified by dropping concentrated hydrochloric acid at 20 to 30 ° C., whereupon the product precipitates and is suctioned off. The crude 5-nitro-3-trifluoromethyl-salicylic acid is recrystallized from toluene, melting point: 171-173 ° C., yield: 18 g; that corresponds to 72% of theory.

Example 9

27 g of 2-chloro-3-nitro-5-trifluoromethylbenzoic acid and 1 g of tetraethylammonium chloride are placed in 200 ml of methanol and 70 g of 50% sodium hydroxide solution are added dropwise with stirring. The mixture is stirred at 65 ° C. for 5 hours, diluted with 300 ml of H ₂ O and then acidified with hydrochloric acid. The solid product is filtered off and recrystallized from water. 16 g of 2-hydroxy-3-nitro-5-trifluoromethyl-benzoic acid with a melting point of 166 to 168 ° C. are obtained.

Example 10

45 g of 4-chloro-3-nitro-benzotrifluoride are initially dissolved in 150 ml of methanol. Then 80 g of ion exchange resin with quaternary ammonium groups are added, the mixture is stirred for 10 minutes, 100 g of 50% sodium hydroxide solution are added dropwise to a maximum temperature of 70 ° C. and the mixture is stirred at 65 ° C. for 8 hours. After the mixture has cooled, it is acidified with concentrated hydrochloric acid, filtered off from the ion exchanger and the tube product is distilled with steam. 27 g of 2-nitro-4-trifluoromethylphenol are obtained. no: 1,5003.

Example 11 1

• A) 45 g of sodium hydroxide and 10 g of tetraethylammonium chloride are placed in 200 g of methanol and 112.5 g of 2-chloro-5-nitro-benzotrifluoride are added dropwise at 25 to 30 ° C., followed by stirring at 30 ° C. for 5 hours . Then the mixture is poured into 250 ml of water and extracted with methylene chloride. After evaporation of the solvent, the compound is recrystallized from isopropanol. 67 g of 2-methoxy-5-nitro-benzotrifluoride with a melting point of 70 to 74 ° C. are obtained.
• B) 67 g of 2-methoxy-5-nitro-benzotrifluoride are dissolved in 150 ml of methanol, 8 g of tetraethylammonium chloride are first added, and 150 g of 50% strength potassium hydroxide solution are then added dropwise to a temperature of 70.degree. The mixture is stirred at 70 ° C for 8 hours, cooled, acidified and extracted with methylene chloride. After the methylene chloride has evaporated, 52 crude 4-nitro-2-trifluoromethylphenol remain, F: 90 to 94 ° C., which can be purified by distillation.

Claims (11)

1. Process for the preparation of trifluoromethylphenols, characterised in that compounds of the formula

in which

X denotes halogen,

R¹, R² and R³ denote hydrogen, trifluoromethyl, nitro, alkylsulphonyl, arylsulphone, carboxyl or carboxylic acid ester and

Y denotes hydrogen, a halogen or alkoxy, one of the substituents R¹, R² and R³ representing a trifluoromethyl group and at least one other of them being different from hydrogen,

are reacted with excess aqueous alkali metal hydroxide in alcoholic solution in the presence of quaternary onium salts.

2. Process according to Claim 1, characterised in that the reaction is carried out in the presence of a quaternary onium salt of the formula

in which

Z denotes an atom of main group 5 of the periodic system,

R⁴ to R⁷ independently of one another denote optionally substituted alkyl, cycloalkyl, aralkyl or aryl, or two of the radical R⁴ to R⁷, together with the central atom Z and optionally further hetero-atoms, form a heterocyclic ring, the radicals R⁴ to R⁷ together containing at least 6 carbon atoms, and

A denotes a chloride, bromide or hydroxide anion.

3. Process according to Claim 1 and 2, characterised in that the quaternary onium salt is a quaternary ammonium or phosphonium salt, the substituents of which contain a total of 8 to 25 carbon atoms.

4. Process according to Claim 1 and 2, characterised in that an ion exchanger which is based on styrene with 2 mol% of divinylbenzene as a cross-linking agent and which contains quaternary ammonium groups is employed as the quaternary ammonium salt.

5. Process according to Claim 1 to 4, characterised in that the quaternary onium salt is employed in an amount of 1 to 20% by weight, relative to the halogenobenzotrifluoride.

6. Process according to Claim 1 to 5, characterised in that the quaternary onium salt is employed in an amount of 5 to 10% by weight, relative to the halogenobenzotrifluoride.

7. Process according to Claim 1 to 6, characterised in that alcohols with a lower unbranched or branched alkyl radical are employed as the alcoholic solvent.

8. Process according to Claim 1 to 7, characterised in that the alkali metal hydroxide is employed in three times the molar amount, relative to the halogenobenzotrifluoride.

9. Process according to Claim 1 to 8, characterised in that sodium hydroxide or potassium hydroxide is employed as the alkali metal hydroxide.

10. Process according to Claim 1 to 9, characterised in that the reaction is carried out in the temperature range from 0 to 80°C.

11. Process according to Claim 1, characterised in that

a) compounds of the formula

in which

X, Y, R¹, R² and R³ have the meaning indicated above are reacted with excess aqueous alkali metal hydroxide in the presence of an alcohol with a lower unbranched or branched alkyl radical acting as solvent, in the presence of quaternary onium salts at temperatures between 15° and 35°C and

b) the resulting compounds of the formula

in which

Y, R¹, R² and R³ have the abovementioned meaning and

R¹² represents a lower unbranched or branched alkyl radical,

are reacted with excess aqueous alkali metal hydroxide in alcoholic solution in the presence of quaternary onium salts.