MXPA01006142A - Method for preparing polyhalogenated paratrifluoromethylanilines - Google Patents

Abstract

The invention concerns a novel method for preparing polyhalogenated paratrifluoromethylanilines particularly useful as reaction intermediates for preparing compositions used as insecticides. The products of the inventive method are obtained by the action of ammonia on polyhalogenated para-trifuoromethylbenzene at a temperature ranging between 150 and 350°C. The inventive reaction can be carried out in the presence of an alkaline halide.

Description

PROCEDURE FOR THE PREPARATION OF PARA-TRIFLUOROMETI POLYHALOGENATED ANILINES DESCRIPTION OF THE INVENTION The present invention has as its object a new process for the preparation of polyhalogenated para-trifluoromethylanilines, more particularly dihalogen-para-trifluoromethylanilines. The processes that allow the preparation of anilines substituted with a halogen atom have been the subject of numerous works as well as numerous patents or publications. Thus, U.S. Pat. No. 4,096,185 relates to an aminating process of halogenated aromatic compounds, such as para-trifluoromethylaniline, from para-chloro-trifluoromethylbenzene and using a particular catalytic combination in order to improve the yield of the reaction. The process of U.S. Pat. No. 4,197,259 describes the preparation of monohalogenated anilines using difficult reaction conditions associated with the use of an alkaline amide as the amination agent; the reaction conditions REF: 129934 as the use of said alkaline amide, in effect requiring the reaction to be carried out in the absence of any traces of water in the reaction medium, makes the industrialization of said process quite problematic; said reaction conditions also involve important difficulties related to the dissipation of the heat of reaction. The patent of the former German Democratic Republic 292,238 concerns the preparation of nitrated and monohalogenated anilines. 'European patent application 173,202 describes the preparation of 5-chloro-2-nitroanilines. Japanese Patent 5,255,206 and European Patent Application 543,633 have as their object the preparation, respectively, of monofluorinated onofluoroanilines and trifluoromethylanilines. Thus, and in spite of the importance of the number of works carried out for the development of new synthetic routes, mainly in order to improve the known procedures for the preparation of halogenated anilines, almost all the methods known today do not refer to more than the only monohalogenated anilines. Furthermore, and although a process for preparing polyhalogenated nitroanilines is known from Japanese Patent 7,025,834, the application of these reactions to compounds substituted with a trifluoromethyl group is not often transportable due, among other things, to the low reactivity conferred to the reactants for this trifluoromethyl group. One of the objects of the present invention is to provide a method of preparing polyhalogenated para-trifluoromethylanilines. Another object of the invention is to solve the problems related to the preparation of 2,6-dihalogenated and 4-trifluoromethylated anilines avoiding the formation of polyation products as well as hydrogenation products of the aromatic moiety. A further object of the process of the invention is to promote the formation of polyhalogenated para-trifluoromethylanilines with respect to the meta-trifluoromethylated isomers. It has now been found that these objectives can be achieved in whole or in part thanks to the method according to the invention. It is a process for the preparation of polyhalogenated derivatives of trifluoromethylaniline by the reaction of polyhalogenated trifluoromethylbenzenes, in particular 3,4,5-trihalogen-trifluoromethylbenzenes, for example 4-bromo-3,5-dichloro-trifluoroethylbenzene or 3, 4 , 5-trichloro-trifluoromethylbenzene, with ammonia.

The reaction of the process according to the invention is carried out at a temperature comprised between 150 and 350 ° C, more particularly between 180 and 278 ° C and, advantageously in a polar organic solvent.

The reaction of the invention can be carried out, in addition to ammonia, in the presence of an alkali halide.

Thus, the process according to the invention allows the preparation of the products of formula (I): X1, X2 = F, Cl, Br, I (I) from the reactants of formula (II) X1, X2, X3 = F, Cl, Br, I (II) When present, the alkali halide is in catalytic amount, particularly in an amount comprised between 1 and 50% of the amount of reactant of formula (II) used, more particularly an amount comprised between 5 and 20%. The alkali halide is advantageously a fluoride or an alkali metal bromide, preferably a lithium halide. The process according to the invention is advantageously carried out with a water content in the reaction medium such that the H2O / NH3 ratio is less than 80/100, preferably less than 20/100, more preferably less than 2/100. The organic solvent optionally employed in the invention is preferably a polar organic solvent, more preferably a non-ionic polar organic solvent, for example an N-alkyl-pyrrolidone whose alkyl radical preferably has from 1 to 12 carbon atoms. The use of N-methyl-pyrrolidone is preferred. The pressure prevailing in the medium during the reaction according to the invention is an autogenous pressure resulting from the use of a closed system, for example an autoclave, in order to better control the amount of ammonia present. The product obtained by the reaction according to the invention is separated from the reaction medium by any conventional means, for example by distillation, extraction or extraction followed by distillation or even by isolation of the salts obtained by the action of hydrochloric acid. In order to isolate the obtained aniline derivative, unreacted polyhalogenated para-trifluoromethylbenzene is separated from the reaction medium. In the case where the benzene derivative used is present only in small quantities, this step can be omitted. By carrying out the reaction of the process according to the invention in a reactor equipped with a distillation apparatus, the desired aniline derivative and the unreacted benzene derivative are separated directly from the reaction medium by distillation.

To isolate the desired reaction product by extraction, water and a low-boiling organic solvent, for example ether, dichloromethane or hexane, are added to the reaction medium. After separation of the aqueous phase, the organic phase is distilled in order to separate the desired aniline derivative from the unreacted benzene derivative. The thus separated benzene derivative is then recycled as reactant for the process of the invention. Another mode of separation of the reaction product of the invention is its salification by the action of hydrochloric acid. For this, the reaction mixture is diluted in a solvent in which the salified derivative of the desired aniline is poorly soluble, it is then reacted with a flow of hydrochloric acid in the reaction medium in order to precipitate the derivative of desired aniline so salified. The precipitate obtained is then filtered. The process of the invention allows the preparation of the desired aniline derivatives with a particularly advantageous conversion rate of the reactants. The results of the process of the invention, however, vary according to the particular reaction conditions chosen; those skilled in the art can easily find optimal reaction conditions following the indications of the present disclosure. Another advantage of the process of the invention is to allow the transformation of polyhalogenated trifluoromethylbenzenes into aniline derivatives in a high yield. This process is also particularly advantageous because it provides a high selectivity which favors the formation of the polyhalogenated para-trifluoromethylanilines in relation to the polyhalogenated meta-trifluoromethylanilines. A further advantage of the method of the invention is that it allows reaction times that can be short; for example, reaction times of less than 10 hours and even reaction times of less than 5 hours can be used. Among the polyhalogenated trifluoromethylanilines which can be prepared by the process according to the invention, 2,6-dichloro-4-trifluoromethylaniline is particularly interesting as an intermediate reaction product for the preparation of compounds used as insecticides. The different examples that follow will make it possible to better illustrate the method of the invention as well as the advantages that accompany it; however, these examples do not limit the scope of the invention at all.

Example 1: In an autoclave, 3, 4, 5-trichloro-trifluoromethylbenzene (0.681 g, 2.73 mmol), lithium fluoride (7.1 mg, 0.273 mmol) and N-methyl-pyrrolidone (1) were mixed. , 8 mi). It was cooled to -95 ° C and then ammonia (1.3 g, 76.4 mmol) was added. It was then heated to 250 ° C with stirring for 4 hours and then allowed to return to room temperature. The reaction product was extracted by washing with water and dichloromethane and then evaporated after the organic phase had dried. There were obtained 0.453 g (1.97 mmol) of 2,6-dichloro-4-trifluoromethylaniline with a conversion rate of 3,4,5-trichloro-trifluoromethylbenzene of 97%, a ratio equal to 83/17 for the selectivity of 2,6-dichloro-para-trifluoromethyl-aniline in relation to 2,6-dichloro-meta-trifluoromethyl-aniline and an 87% yield of 2,6-dichloro-para-trifluoromethylaniline.

Example 2: In an autoclave, 4-bromo-3,5-dichloro-trifluoromethylbenzene (0.802 g, 2.73 mmol) and N-methyl-pyrrolidone (1.8 ml) were mixed. It was cooled to -95 ° C and then ammonia (1.3 g, 76.4 mmol) was added. It was then heated to 200 ° C and with stirring for 4 h, then it was allowed to return to room temperature. The reaction product was extracted by washing with water and dichloromethane and then evaporated after the organic phase had dried. There were obtained 0.428 g (1.86 mmol) of 2,6-dichloro-4-trifluoromethylaniline with a conversion rate of 4-bromo-3,5-dichloro trifluoromethylbenzene of 91%, a total selectivity of 2,6-dichloro- para-trifluoromethylaniline and a 68% yield of 2,6-dichloro-para-trifluoromethylaniline.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims (7)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. Procedure for the preparation of products of formula (I): X, X r == F, Cl, Br, I (I) from the reactants of formula (II) X1, X2, X3 = F, Cl, Br, I (II) in the presence of ammonia and at a temperature comprised between 150 and 350 ° C, preferably between 180 and 270 ° C.

2. Procedure for the preparation of products of formula (I): X1, X1 = F, Cl, Br, I (I) from the reactants of formula (II) X1, X2, X3 = F, Cl, Br, I (II) in the presence of ammonia, an alkaline halide and at a temperature between 150 and 350 ° C, preferably between 180 and 270 ° C.

3. Process according to claim 2, characterized in that the alkali halide is present in a catalytic amount.

4. Method according to claim 2, characterized in that the alkali halide is present in an amount comprised between 1 and 50%, preferably between 5 and 20%, of the molar amount of the reactant of formula (II). Method according to any one of claims 1 to 4, characterized in that the water content in the reaction medium is such that the ratio H2O / NH3 is less than 80/100, preferably less than 20/100, more preferably lower to 2/100. 6. Process according to any of claims 1 to 5, wherein a polar organic solvent is used, preferably a non-ionic polar organic solvent. 7. Process according to any of claims 1 to 6, characterized in that the solvent used is an N-alkyl-pyrrolidone whose alkyl radical preferably has 1 to 12 carbon atoms, more preferably N-methyl-pyrrolidone.