DD236520A5 - PROCESS FOR THE PREPARATION OF CHLORO-O-NITROANILINES - Google Patents

Abstract

A process for the preparation of chloro-o-nitroanilines of the formula (1), wherein R 1 and R 2 are hydrogen or chlorine atoms, by reacting chloronitrobenzenes of the formula (2), wherein R 1 and R 2 have the meanings given above, with ammonia at elevated temperature by carrying out the reaction with anhydrous ammonia in the presence of aromatic hydrocarbons of the formula (3) in which R3 represents an alkylC1-C4 group and R4 and R5 denote hydrogen atoms or alkylC1-C4 group, at temperatures of about 120 to 200C.

Description

65 708/18

Process for the preparation of chloro-o-nitroanilines

Field of application of the invention

The invention provides a process for preparing chloro-o-nitroanilines in high purity and yield without additional purification operations by reacting chloronitrobenzenes, for example of 2,4-dichloronitrobenzene, with anhydrous ammonia.

Ghlornitroanilines are known to be valuable precursors and intermediates for the production of dyes, pharmaceuticals and pesticides.

Characteristic of the known technical solutions

It is known, for example, to prepare 5-chloro-2-nitroaniline by reacting 2,4-dichloronitrobenzene in ethanolic solution with ammonia (A. 182 (1876) 94, 109; Recueil 72, 44 et seq. (1953)) However, it is associated with such significant deficiencies, in particular because of the unlimited miscibility of the ethanol with water and with the ammonia always present in excess, that a technical use of this method is not considered. An analogous procedure with a solution of ammonia in other water-soluble low molecular weight alkanols or glycol ethers, such as methanol, isopropanol, tert. Butanol or diethylene glycol dimethyl ether, which are to be mixed with water in the work-up of the reaction mixture incurred and also mix unlimited with water, is technically also out of the question for the reasons mentioned.

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In addition, in the preparation of 5-chloro-2-nitroaniline by ammoniaysis in aqueous systems (Recueil 22, 44 ff. (1953)), a considerable amount 1 of 3-chloro-4-nitroaniline is always formed, largely independently of the reaction conditions and 5-amino-2-nitroaniline (diamine), wherein, in the case of a very gentle reaction procedure, unreacted starting product may also be present.

The purification of such mixtures is technically carried out only with considerable effort and with a reduction in the yield, also associated with significant environmental problems. In addition, in comparison to pure 5-chloro-2-nitroaniline reaction mixtures obtained in this way have greatly reduced thermal stabilities, so that safety problems arise when carrying out such processes on an industrial scale.

Bach, US Pat. No. 4,421,694, gives 5-chloro-2-nitroaniline by reacting 2,4-dichloronitrobenzene in chlorinated aromatic hydrocarbons with ammonia in yields of up to about 95% and purities of up to 96 % Although there are increased but not yet satisfactory selectivity with respect to the known processes mentioned, there are also concerns regarding the use of chlorinated hydrocarbons from a commercial hygiene point of view. For example, the maximum workplace concentration values for chlorobenzene and the dichlorobenzenes at 50 ppm are remarkably low. There is a general tendency to limit the use of chlorinated hydrocarbons to an indispensable minimum for lower health reasons.

Object of the invention

The aim of the invention is the preparation of chloro-o-nitroanilines

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I in high purity and yield without additional purification operations and without the use of chlorinated hydrocarbons as solvent.

Explanation of the essence of the invention

The invention has for its object to develop a process for the preparation of chloro-o-nitroanilines by reacting Chlornitrobenzolen with ammonia in a solvent at elevated temperature.

According to the invention, it has been found that chloro-o-nitroanilines of the general formula (1)

(D

R ₂

Cl

in which R 1 and R _{2 are} hydrogen atoms or chlorine atoms, can be prepared in almost quantitative yield and almost 100% purity by reacting chloronitrobenzenes of the general formula (2)

Cl

(2)

I U

₂ y Cl

in v / elcher R ^ and R _{2 have} the meanings mentioned above, with anhydrous ammonia in the presence of aromatic Kon

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Hydrocarbons of the general formula (3)

(3)

which R 1 is an alkyl group, such as the

Methyl, ethyl, η-butyl, iso-butyl, tert. Butyl, propyl or iso-propyl group, and R, and Rj- represent hydrogen atoms or Alky 'groups, at temperatures of about 120 to 200 ⁰ C, preferably 150 to 180 ⁰ C, reacted.

Examples of chloronitrobenzenes of said general formula (2) are 2,3,4- and 2,4,5-trichloronitrobenzo, 2,3,3,5-tetrachloronitrobenzene and, more particularly, 2,4-dichloronitrobenzene.

The p-constant and, as is known, likewise activated chlorine atom, which in each case belongs to the uitro group, virtually does not enter into the reaction under the conditions of the process according to the invention.

Examples of aromatic hydrocarbons of said general formula (3) include toluene, ethylbenzene, xylenes and mesithylene, toluene and xylenes being preferably used.

It is also possible to use mixtures of hydrocarbons of the said general formula (3).

The aromatic hydrocarbons of the general formula (3) which are preferably used in accordance with the process are generally

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commonly available, inexpensive and, from a commercial hygiene point of view, less problematic than the chlorinated aromatic hydrocarbons.

According to the invention, both the ammonia and the aromatic hydrocarbons to be used must be largely anhydrous, since with increasing presence of water, the selective exchange of the activated ghloron atoms, which are ortho to the nitro group, by the amino group in the starting products of said general formula (2)

However, the amounts of water which remain dissolved in the working up of the resulting reaction mixture in the aromatic hydrocarbons, are harmless to the .findfindungsgemäße process.

The amount of aromatic hydrocarbons can be varied within wide limits. Advantageously, the proportions are chosen so that after cooling the resulting reaction mixture still good stirrable and flowable suspensions are obtained.

Crucial parameters for the speed and completeness of the conversion are the reaction temperature and the amount of ammonia used. Although in principle the stoichiometric amount of 2 moles of ifflL per mole of chloronitrobenzene of the formula (2) is sufficient, it is expedient to use an amount in excess of this ratio. The molar ratio of starting material to ammonia can vary from about 1: 3 to 1:12, it being advantageous to choose a molar ratio of 1: 6 to 1: 8. Unused ammonia can be recovered and reused by conventional methods.

The reaction temperature can vary within a wide range of

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Reich ". scroll Zweckmäßigeiweise be selected temperatures between about 120 and 200 ⁰ G," is preferred, the reaction "at temperatures of 150-180 ⁰ C performed together give a correspondingly high excess of ammonia then reaction times of about 3-6. The very high selectivity is neither significantly influenced by the level of the temperature nor by the amount of ammonia used. The combination of these parameters only determines the completeness of the conversion or the required reaction time.

The process according to the invention can be carried out in detail by initially charging the starting product (chloronitrobenzene of the general formula (2)) together with the aromatic hydrocarbon of the formula (3) in an autoclave and adding the anhydrous ammonia at once or in portions.

The isolation of the reaction product 'is carried out according to customary. Methods. Thus, for example, after the autoclave has been expanded-the excess ammonia can be recovered and fed to another batch-and the reaction mixture cooled, the product is filtered off from the resulting crystal suspension and the ammonium chloride which has precipitated out is washed out with water. The filtrate, which consists of the aromatic hydrocarbon, can be used again without further measures. Working up is particularly advantageous by removing the aromatic hydrocarbon by steam distillation and filtering off the product from the aqueous suspension. Again, the hydrocarbon after separation from the water used directly for subsequent batches v / earth. The traces of water dissolved in the hydrocarbon do not interfere with the process according to the invention.

Particularly advantageous over the prior art

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In the process according to the invention, the lenden process is the high selectivity with which the reaction proceeds. With almost quantitative conversion, diamination does not take place practically, so that expensive purification operations can be omitted. The reaction is not critical over wide temperature and concentration ranges and requires only generally accessible and inexpensive aromatic hydrocarbons as the reaction medium. By avoiding the formation of diaminonitrobenzenes, a greatly increased thermal stability is achieved and the tendency to uncontrolled decomposition reactions suppressed in the mixtures obtained by the known processes is suppressed.

In the following examples, the method according to the invention is illustrated, without being limited thereto. Percentages are by weight. ^:

example 1

In a steel autoclave, 192 g (1 mol) of 2,4-dichloronitrobenzene and 400 g of xylene are introduced. After closing the autoclave is pressed 136 g (8 mol) of ammonia gas and heated for 5 hours at 170 ⁰ C, wherein a pressure of about 70 bar sets. It is then cooled, relaxed and the xylene is driven off with steam. From the aqueous crystal suspension, the product is obtained by filtration and washed with V / asser chloride-free.

This gives 171 g of 5-chloro-2-nitroaniline of melting point 124.2 ⁰ C, which corresponds to a yield of 99 % of theory. According to gas chromatographic analysis, the content of 5-chloro-2-nitroaniline is 98.8 % (diamine content < 0.2 %) .

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Example 2

Is heated instead of 5 hours at 170 ⁰ C for 3 hours at 18O ⁰ G and the rest proceeds as described in Example 1, we obtain the 5-chloro-2-nitroaniline in the same yield and purity as in Example 1. ,

Example 3,

192 g (1 mol) of 2,4-dichloronitrobenzene are placed in a steel autoclave together with 300 g of toluene. After pressing 102 g (6 mol) of ammonia is heated to 170 ⁰ G for 6 hours. According to the workup of the reaction mixture obtained in Example 1, the 5-chloro-2-nitroaniline is obtained in the same yield and purity as in Example 1.

Claims (5)

invention claim 1 Process for the preparation of chloro-o-nitroanilines of the general formula (1) (D in which R and Rp are hydrogen atoms or chlorine atoms, by reacting chloronitrobenzenes of the general formula (2) HO, 2. Method-after. Item 1, characterized in that one carries out the reaction at temperatures of 150 to 1SO ⁰ G. (2) in v / elcher R and Rp have the abovementioned meanings, with ammonia at elevated temperature, characterized in that the reaction with anhydrous ammonia in the presence of aromatic hydrocarbons of the general formula (3) 3 · Method according to item 1, characterized in that one uses the Chlornitrobenzole of said formula (2) and the ammonia in a molar ratio of 1: 3 to 1: 12. (3) - 10 - 65 708/18 in which R _{0 represents} an alkyl-! rr group and R ₁ and -> ^U 1 ~ ^υ 4 ⁴ Rr-hydrogen atoms or alkyl----r groups mean "at 5 G ₁ -G ₄ Temperatures of about 120 to 200 C makes. 4. The method according to item 1 and 3 », characterized in that one uses the Chlornitrobenzole of said formula (2) and the ammonia, preferably in a molar ratio 1: β to 1: 8. 5. The method according to item 1, characterized in that one carries out the reaction in the presence of toluene or xylenes.