MXPA97009816A - Continuous process for the dinitration of aromati substrates - Google Patents

Abstract

A continuous process for the dinitration of the phenol and aniline derivatives that have been replaced by alkyl groups and in which nitric acid is used substantially free of sulfuric acid, which is characterized because the dinitration is carried out in a single stage in a tubular reactor in the presence of a catalytically effective amount of a catalyst capable of reacting with the nitric acid for nitrous form in.

Description

Continuous process for the dinitration of aromatic substrates DESCRIPTION OF THE INVENTION The present invention concerns a continuous process for the dinitration of aromatic compounds, especially of the substituted dinitrable derivatives of phenol and aniline.

More especially, the invention concerns a method for the dinitration of N-al-3-yl-dimethyl-benzenamine, wherein the alkyl group is preferably 1-ethylpropyl, 1-methylbutyl or secbutyl, and as nitrating agent is used nitric acid substantially free of sulfuric acid.

The continuous dinitration of aromatic substrates is known in the technical literature. U.S. Pat. No. 2,951,746 describes continuous nitration in a tubular reactor, but only in relation to tuluene as a substrate and using a sulfonitrile mixture.

With reference to the nitration of substrates that are active toward substitutions in electrophilic aromatics, such as anilines and phenols, U.S. Pat. No. 4,621,157 describes a continuous process carried out in conventional stirred tank reactors, particularly for the production of N-alkyl-2,6-dinitro-3,4-dimethylbenzenamine, commercially known as Pendimethalin.

The process described in said patent is carried out in two stages: in the first stage, the phenol derivative or the aniline which has been replaced by alkyl groups is reacted with relatively dilute nitric acid in REF: 26393 presence of an organic liquid solvent immiscible in water to obtain the mononitro derivative or a nitric acid salt of the start aniline. In the second stage, the product of the first stage is further reacted with relatively concentrated nitric acid to retain the corresponding dinitro derivative. Both stages are carried out in continuous reactors with agitation tank and, in the second, the stage of the dinitration, the time of presence is approximately one hour.

According to the present invention, it has been discovered that the dinitration of the aforementioned active aromatic substrates using nitric acid can be achieved in a single stage in a tubular reactor, with times of presence of the order of several seconds and extraordinarily high yields being obtained.

In view of this discovery, the object of the invention is the continuous dinitration of the dinitrable derivatives of phenol or aniline to which H has been substituted by alkyl groups using nitric acid as a nitrating agent, characterized in that the reaction is carried in a single-stage tubular reactor, a catalytically effective amount of a catalyst capable of reacting with nitric acid to form nitrous acid in situ being supplied to the reactor.

It is known that nitrous acid has an anticatalytic activity in the nitration of aromatic substrates that are not active to promote electrophilic attack, although it has a positive catalytic activity in the case of strongly active substrates such as aniline or phenol. However, in the technical literature relating to the stepless or continuous nitration of these strongly active substrates, the presence of nitrous acid as a catalyst, or compounds capable of generating nitrous acid in situ, is not considered necessary.

While, according to the present invention, it is evident that the presence of the above-mentioned catalysts is essential for the success of the dinitration, because if the substrate and nitric acid are supplied only in the absence of a catalyst, there is no appreciable evidence of nitration. in the mass recovered from the reactor outlet. In this invention, the inorganic salts of nitrous acid are preferably used as catalysts, in particular the salts of the alkali metals or reducing substances which are easily oxidized by nitric acid, such as, for example, aliphatic or aromatic aldehydes, which allow the production, in situ of the necessary nitrous acid.

The aliphatic aldehydes comprise aldehydes having a linear or branched alkyl chain with 1 to 12 carbon atoms, preferably 1 to 3 carbon atoms. Acetaldehyde is preferred; the aromatic aldehydes comprise benzaldehyde, to which the aromatic ring has optionally been substituted with aliphatic groups CPC3 or halogens.

The presence of the catalyst causes the immediate start of the reaction, with the result that the substrate is converted quantitatively into the dinitration products even in a very short presence time within the reactor.

The catalytically effective amount used can vary within a wide range and is generally between 0.01 and 1.5 parts by weight relative to 100 parts of aqueous nitric acid. & The dinitration reaction can be carried out in the presence or absence of a solvent. In the case of a reaction with solvent, the water-immiscible organic solvents in which the solvent is dissolved are preferably used. .- aromatic substrate; the preferred solvent, especially for the production of dinitroaniline Pendimethalin, is dichloroethane. The concentration of this aromatic substrate in the solvent may vary within an ampl. interval and is generally between 15 and 50 percent by weight. The concentrated nitric acid that is substantially free of ^ 'Sulfuric acid is used as a dinitrant agent, generally at a concentration of between 20 and 100 weight percent; Concentrated nitric acid is preferably used at 45-70 weight percent. Nitric acid is preferably used in stoichiometric excesses with respect to the dinitration reaction. twenty As is known, dinitration reactions are strongly exothermic and for this reason they are potentially at risk of thermal explosion (thermal) leakage. Notwithstanding this, the method according to the invention, carried out in a tubular reactor, allows an accurate and effective thermal control. Actually, the reactor can be immersed in a thermostatic bath, or enclosed in a shell, the same result can be achieved by performing the reaction in a tubular heat exchanger used as a reactor.

In the preferred embodiment, the nitric acid and aromatic substrate supplies comprising the catalyst and the solvent, if used, after having passed through a first section of the tubular reactor, are passed through a tubular mixing device. , static, able to achieve the intimate mixture of the flows and thereby allow the rapid completion of the reaction. Static mixers are known and available commercially; for example, static mixers that have an internal lft structure such as those manufactured by Sulzer Chemtech Limited, or the Kenics Static Mixer sold by Chemineer Limited can be used for the invention. The preferred static mixer is a tubular device having a helical internal structure including back-mixing sections, such as the aforementioned Kenics static mixer. In the preferred incorporation of the process, specifically for the production of Pendimethalin, the dinitration stage is carried out at a temperature between 50 and 90 ° C with times of presence in the tubular reactor and in the mixer from 10 to 20 seconds. The reactor outlet stream is passed to a phase separator to separate the aqueous phase, containing dilute nitric acid, from the immiscible organic phase, which contains or is constituted by the crude dinitration product. The aqueous phase can be fed to a concentration stage for azeotropic distillation in order to obtain nitric acid at the desired concentration, which can then directly feed the dinitration stage.

The advantages of the process according to the invention are: very short presence times and, consequently, a limited shutdown of the reactor (more than 200 times less than that of a reactor with stirred tank of equal productivity); the easy and precise control of the reaction temperature by virtue of the in-line heat exchange, the favorable volume / surface ratio, the high linear speeds and the high heat exchange capacity; a low content of N-nitroso and N-nitro derivatives in the dinitroanilines produced, the derivatives of which are inevitably co-produced during the synthesis of dinitroaniline. Acting correctly and continuing with the rapid separation of the organic phase from the acid phase, reaction masses are obtained in which the said N-nitroso derivatives do not exceed 6 to 7 percent of the total weight of the dinitro derivatives, while the The content of N-nitro derivatives does not exceed 50 to 100 ppm by weight with respect to the total weight of the dinitro derivatives.

The advantages described above also mean that the risk of leakage (thermal) is considerably reduced and, consequently, the handling of the industrial installation is much safer.

In addition, there is greater investment economy, less need for maintenance and reduced energy consumption.

The method, according to the invention, is illustrated below with the following non-limiting examples, in which a reaction product is subjected to dinitration according to the method described in U.S. Pat. No. 4 874 895.

Example 1 The dinitration of N- (1-ethylpropyl) -3,4-dimethyl-benzenamine is carried out within an experimental installation in a tubular reactor having a static mixer; The tubular reactor is composed of a coil in three joined sections, each of 5,000 mm in length with an internal diameter of 4 mm, with temperature sensors coupled at the junction between them. The Kenics Static Mixer has a 190 mm long tubular body inserted between the second and third section. The reactor is submerged in a thermostat bath. 67 percent nitric acid supplemented with 5,000 ppm by weight NaN02 is fed to the reactor at a rate of 15 1 / hr at the same time as a 39 percent by weight solution of N-1-ethylpropyl) -3,4 dimethyl -benzenamine in dichloroethane; this solution is fed at a speed of 21 1 / h (liters hour). After a period of 15 minutes, during which the system reaches operating conditions, approximately 6 kg of reaction mass was collected in a separator. After the separation of the acid phase from the organic phase, the latter, which - apart from the solvent - is composed of 95 weight percent dinitration products and contains 6.8 weight percent N-nitroso- N- (1-ethylpropyl) -2,6-dinitro-3,4-dimethylbenzenamine and 54 ppm by weight of N-nitro-N- (1-ethylproyl) -2,6-dinitro-3,4-dimethylbenzenamine , it is washed and subjected to denitrosation by treatment with aqueous hydrobromic acid and sulfamic acid to transform its N-nitroso derivatives co-produced in the course of the reaction resulting in N- (1-ethylpropyl) -2,6-dinitro-, -dimethylbenzenamine. Once the solvent was evaporated, 1.78 kg of crude N- (1-ethylpropyl) -2,6-dinitro-3, -dimethylbenzenamine was obtained with a titer of 94.2 percent.

Example 2 As in Example 1, except that 1,500 ppm of benzaldehyde is added to the solution of N- (1-ethylpropyl) -3,4, -dimethyl-benzenamine in dichloroethane instead of adding sodium nitrite to nitric acid, 1 is obtained. , 77 kg of crude product, being 94.3 weight percent dinitration products and containing 7.3 weight percent of N-nitroso-N- (1-ethylpropyl) -2,6-dinitro-3, 4-dimethylbenzenamine and 38 ppm by weight of N-nitro-N- (1-ethylpropyl) -2,6-dinitro-3,4-di-ethylbenzenamine. At the end of the treatment, a product having a title of 93.9 percent in N- (1-ethylpropyl) -2,6-dinitro-3,4-dimethyl-benzenamine is obtained.

Example 3 Nitric acid 60 percent supplemented with 1,600 ppm of NaN02 is fed to the reactor at a rate of 28 1 / h, along with N- (1-ethylpropyl) -3, -dimethyl-benzenamine at a rate of 7.5 1 / h . After a period of 20 minutes during which the system reaches the conditions of use, approximately 5 kg of reaction mass is collected in a separator provided with a thermostat at 70 ° C containing 13 kg of water at the same temperature. After discarding the aqueous acid phase, the condensed organic phase is washed twice with 6 liters of water heated to 70 ° C and analyzed. It contains 5.9 weight percent of N-nitroso-N- (1-ethylpropyl) -2,6-dinitro-3, -dimethyl-benzenamine.

Subject to denitrosation by treatment with aqueous hydrobromic acid and sulfamic acid, the resulting mass contains 96.3 percent Pendimethalin. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (9)

1. A process for the continuous dinitration of the phenol and aniline derivatives that have been replaced by alkyl groups, using nitric acid substantially free of sulfuric acid, which is characterized by the fact that the dinitration is carried out in a single stage in a tubular reactor in the presence of a catalytically effective amount of a catalyst capable of reacting with nitric acid to form nitrous acid in situ.

2. A process according to Claim 1, characterized in that said catalyst is selected from alkali metal nitrites and aldehydes.

A process according to claim 1 or 2, characterized in that the catalyst is used at a concentration of 50-10,000 ppm by weight with respect to nitric acid in the case of alkaline nitrites, or with respect to N- (1-) ethylpropyl) -3,4-dimethyl-benzonamine in the case of aldehydes.

4. A process according to any of claims 1 to 3, characterized in that the reaction is carried out in a water-immiscible organic solvent for said phenol or aniline.

5. A process according to any of claims 1 to 3, characterized in that the reaction is carried out in the absence of a solvent.

6. A process according to any of claims 1 to 5, characterized in that the nitric acid is used at a concentration of 20 to 100 weight percent.

7 A process according to claim 6, characterized in that the nitric acid is at a concentration of 45 to 70 per cent by weight.

8 A process according to any of the preceding claims, characterized by a static tubular mixer located at the beginning of the tubular reactor or between two consecutive sections thereof.

9. A process according to any of the preceding claims, characterized in that said aniline has been replaced by the group alkyl is N- (1-ethylpropyl) -3,4-dimethyl-benzenamine.