MXPA99007091A - Method for isolating 3-[2-chloro-4-(trifluoromethyl)-phenoxy]-benzoic acid - Google Patents

Abstract

The invention relates to a method for isolating 3-[2-chloro-4-(trifluoromethyl)-phenoxy]-benzoic acid of the formula (I) from an aqueous solution of its metallic salt, by a) reacting the metallic salt of the 3-[2-chloro-4-(trifluoromethyl)-phenoxy]-benzoic acid with an organic or inorganic acid;b) heating the reaction mixture until a liquid two-phase system has formed comprising an organic and aqueous phase;and c) separating the organic phase from the aqueousphase.

Description

ISOLATION OF ACID 3- [2-CHLORINE-4- (TRIFLUOROMETIL) FENOXX] BENZOIC The present invention relates to a process for the isolation of 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid of the formula I from an aqueous solution of its metal salt, which consists of: a) reacting the metal salt of 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid with an organic or inorganic acid; b) heating the reaction mixture until it forms a liquid system in two phases of organic and aqueous phase; And c) separating the organic phase from the aqueous phase.

The 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid of the formula I is an intermediate for the preparation of the herbicides acifluorfen, fluoroglycofen and lactofen, which are prepared in DE-A 23 11 638, EP- A 20 052, DE-A 30 29 728 and US 4 031 131. According to US 4 031 131, the benzoic acid derivative of the formula I is precipitated from its saline solution in crystalline form by neutralization with an inorganic acid, it is isolated by filtration, washed with water and dried. This process has several disadvantages: the handling of the solids leads to the formation of crusts during the crystallization, causing the crystals to absorb significantly more water. During drying, this causes bottlenecks and bottlenecks in the process. It is an object of the present invention to provide a process for the isolation of the benzoic acid derivative of the formula I which does not have these disadvantages. We have found that this object is achieved by the process described at the beginning. In US 4 031 131, the preparation of the benzoic acid derivative of the formula I is carried out according to the following scheme: II III IV The trifluoromethylbenzene derivative of the formula II is reacted with the 3-hydroxybenzoic acid dimethalic acid salt to give the metallic salt IV of the benzoic acid derivative. In the process according to the invention, the separation of the free acid from the benzoic acid derivative of the general formula I is carried out in three steps. In step a), the aqueous solution of the metal salt of the benzoic acid derivative of the formula I is reacted with an organic or inorganic acid. In principle, any monovalent or polyvalent metal salt of the compound of the formula IV can be used as starting material. Preference is given to the use of metal salts soluble in water. Among the metal salts soluble in water, preference is given to the alkali metal salts. Particular preference is given to the sodium and potassium salts. All the clauses [sic] and inorganic acids are suitable for the neutralization of the metal salts of the formula IV. Examples of suitable organic acids are formic acid, acetic acid, propionic acid and mixtures thereof. Preference is given to the use of acetic acid. Suitable inorganic acids are hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and mixtures thereof. The organic or inorganic acid is added to the aqueous solution of the metal salt of formula IV with stirring at a temperature of from 29 to 127 ° C, preferably until a pH of less than 5, preferably less than 4.5, is obtained. This corresponds to approximately 1 to 6 times the molar amount of acid per mole of a metal salt of formula IV, preferably 1 to 5 times the molar amount of acid. If the temperature is less than about 90 ° C, the benzoic acid derivative I precipitates. In step b) the reaction mixture is heated until the benzoic acid derivative melts and a two-phase liquid, organic phase and aqueous phase system is formed. The lower organic phase contains the derivative I of the molten benzoic acid. The temperatures in step b) are from 90 to 127 ° C, preferably from 95 to 115 ° C. It is also possible to carry out steps a) and b) in a single reaction step by the addition of the acid at a temperature from 90 to 127 ° C, preferably from 95 to 120 ° C. If the reaction is carried out in this way, a two-phase liquid system is formed directly which is separated into a lower organic phase and an upper aqueous phase. In step c), the organic phase is separated from the aqueous phase. The organic phase comprises the benzoic acid derivative, water and, if used, organic acid. The organic phase can be used directly for other processing. However, the organic phase can be dehydrated in step d) before further processing. The dehydration is carried out by distillation of the water and the remaining organic acid. If acetic acid is used as the organic acid in step a) of neutralization, the water can also be removed by distillation of some or all of the acetic acid. The process according to the invention can be carried out continuously and in batches and at atmospheric pressure, superatmospheric pressure and reduced pressure. In the process according to the invention, the yield of 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid in the organic phase is very high. The aqueous phase that has been repaired contains less than 3%, preferably less than 2%, of this compound.

In this separation process solids handling is dispensed with and the dehydrated melt of 3- [2-chloro-4- (trifluoromethyl) phenoxy] enzoic acid can be used directly to prepare acifluorfen, 5- [2-chloro-4-acid] (trifluoromethyl) -phenoxy] -2-nitrobenzoic acid, by nitration.

Example 1: 2500 parts of a solution of 20% concentration (by weight, according to the free acid) of the potassium salt of 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid (1.58 mol) of pH 8.8 was diluted in a 3 liter glass container, heatable, with stirring, with 498 parts of water and heated to 50 ° C. At this temperature 370 parts (6.17 mol) of acetic acid were added during 90 minutes with stirring, causing the precipitation of 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid. The pH of the resulting suspension is 4.3. The suspension is then heated to 96 ° C at which the solid melts and a two phase liquid mixture is formed. After the agitation has been interrupted, the phases are separated; the organic phase, brown fused, below weighs, after the aqueous phase has been separated, 594 parts and contains in addition to 84.0 parts of 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid 12.9 parts of water and 2.33 acetate parts as free acid or as potassium salt. The aqueous phase only contained < 0.1% 3- [2-Chloro-4- (trifluoromethyl) phenoxy] benzoic acid.

Example 2: 2500 parts of a solution of 20% concentration (by weight, based on the free acid) of the sodium salt of 3- [2-chloro-4- (trifluoromethyl) phenoxy] enzoic acid (1.58 mol) of pH 8.8 were diluted in a 3 liter glass vessel, heatable with stirring, with 498 parts of water and heated to 50 ° C. At this temperature, 360 parts (6.0 mol) of acetic acid were added for 90 minutes by stirring, causing the precipitation of 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid. The pH of the resulting suspension is 4.3. The suspension is then heated to 100 ° C at which the solid melts and a mixture of two liquid phases is formed. After the stirring has been interrupted, the phases are separated; the weight of the molten, organic, brown, lower phase, after the aqueous phase has been removed, is 485 parts and also contains 82.5% by weight of 3- [2-chloro-4- (trifluoromethyl) phenoxy) ] benzoic acid 14.5% by weight of water and 2.5% by weight of acetate as free acid or as a sodium salt. The aqueous phase only contained < 0.1% 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid.

Claims (4)

2. A process for the isolation of 3- [2-chloro-4- (trifluoromethyl) phenoxy] benzoic acid of the formula I from an aqueous solution to its metal salt, which consists of: a) reacting the metal salt of
3. 3- [2-chloro-
4. 4- (trifluoromethyl) phenoxy] enzoic acid with an organic or inorganic acid; b) heating the reaction mixture until it forms a liquid system in two phases of organic and aqueous phase; and c) separating the organic phase from the aqueous phase. The process, as mentioned in claim 1, wherein in steps a) and b) are combined in a reaction step. The process, as mentioned in claim 1 or 2, wherein the organic phase of step c) is dehydrated in an additional step d). The process, as mentioned in any of claims 1 to 3, wherein the metal salt used is a sodium or potassium salt. The process, as mentioned in any of claims 1 to 4, wherein the organic acid used is formic acid, acetic acid, propionic acid or mixtures thereof. The process, as mentioned in claim 5, wherein the organic acid used is acetic acid. The process, as mentioned in any of claims 1 to 4, wherein the organic acid used is hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid or mixtures thereof. The process, as mentioned in any of claims 1 to 7, wherein sufficient organic or inorganic acid is added in step a) to obtain a pH of less than 5. The process, as mentioned in any of claims 1 to 8, wherein the reaction mixture in step b) is heated to at least 90 ° C. The process, as mentioned in claim 9, wherein the reaction mixture is heated to at least 96 ° C. The process, as mentioned in any of claims 3 to 10, wherein the organic phase is dehydrated in step d) by distillation of the water. The process, as mentioned in claim 6, wherein the organic phase is dehydrated in step d) by distillation of the acetic acid.