Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1999-07-28
2000-05-23
Richter, Johann
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C07C 6521
Patent
active
060667613
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the isolation of 3-[2-chloro-4-(trifluoromethyl)pehnoxy]benzoic acid of the formula I ##STR2## from an aqueous solution of its metal salt, which comprises a) reacting the metal salt of 3-[2-chloro-4-(trifluoromethyl)-phenoxy]benzoic acid with an organic or inorganic acid; and aqueous phase has formed; and
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 U.S. Pat. No. 4,031,131.
According to U.S. Pat. No. 4,031,131, the benzoic acid derivative of the formula I is precipitated from its salt solution in crystalline form by neutralization with an inorganic acid, isolated by filtration, washed with water and dried.
This process has a number of disadvantages: the handling of solids leads to the formation of crusts during the crystallization, causing the crystals to absorb significantly more water. During drying, this leads to clogging and to 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 outset.
In U.S. Pat. No. 4,031,131, the preparation of the benzoic acid derivative of the formula I is carried out according to the following scheme: ##STR3##
The trifluoromethylbenzene derivative of the formula II is reacted with the dimetal salt of 3-hydroxybenzoic acid to give the metal salt IV of the benzoic acid derivative.
In the process according to the invention, the isolation of the free acid of 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 Me.sup.+ of the compound of the formula IV can be used as starting material. Preference is given to water-soluble metal salts.
Among the water-soluble metal salts, preference is given to the alkali metal salts. Particular preference is given to potassium and sodium salts.
All organic and inorganic acids are suitable for neutralizing 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 using 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 the formula IV with stirring at a temperature from 20 to 127.degree. C., preferably 20 to 115.degree. C., 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 the formula IV, preferably 1 to 5 times the molar amount of acid. If the temperature is below about 90.degree. C., the benzoic acid derivative I precipitates.
In step b) the reaction mixture is heated until the benzoic acid derivative I is molten and a liquid two-phase system of organic phase and aqueous phase has formed. The lower organic phase contains the molten benzoic acid derivative I. The temperatures in step b) are from 90 to 127.degree. C., preferably from 95 to 115.degree. C.
It is also possible to carry out steps a) and b) in a single reaction step by carrying out the addition of the acid at a temperature from 90 to 127.degree. C., preferably from 95 to 115.degree. C. If the reaction is carried out in this way, a liquid two-phase system which separates into a lower organic phase and an upper aqueous phase is formed directly.
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 f
REFERENCES:
patent: 4031131 (1977-06-01), Johnson
patent: 4076741 (1978-02-01), Bayer et al.
patent: 4400530 (1983-08-01), Grove
Eva Ronald R.
Franke Dirk
Jones Simon A.
Mattmann Wolfgang
Merkle Hans Rupert
BASF - Aktiengesellschaft
Davis Brian J.
Richter Johann
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