IE903547A1 - Process for the hydrogenation of halogeno-nitroaromatic¹derivatives in the presence of catalysts based on noble¹metals - Google Patents

Abstract

Process for the hydrogenation of aromatic nitro and halogen compounds. The invention relates more particularly to the preparation of halogenated amines. The present invention is capable, by starting from platinum or palladium, of depositing it on an alumina-based support, and this makes this hydrogenation catalyst easily separable and therefore recyclable, and endows it with all the qualities required for hydrogenation of nitroaromatic halogen derivatives.

Description

PROCESS FOR THE HYDROGENATION OF HALOGENONITRQAROMATIC DERIVATIVES IN THE PRESENCE OF CATALYSTS BASED ON NOBLE METALS The present invention relates to a process for 5 the hydrogenation of aromatic nitrated and halogenated compounds. It relates more especially to the preparation of halogenated amines.

When a hydrogenation process is carried out on a nitrated aromatic derivative carrying halogen atoms linked to the aromatic nucleus, a dehalogenation phenomenon, with loss of halogen atoms in the form of hydrogen halides, occurs at the same time as the conversion of the nitro group to an amine group.

This phenomenon has been known for a very long time, because it was described in 1904 by P. Sabatier and A. Mailhe.

Numerous patents have been filed for avoiding this side-reaction whilst making it possible to preserve correct activity of the catalyst.

These patents can be divided into two groups: those which use Raney nickel as the hydrogenation catalyst and those which use platinum or palladium.

All these patents describe the use of a modified catalyst.

In the first group of patents, describing the use of Raney nickel, there may be mentioned U.S. Patent 3,067,253/ British Patent 1,191,610, Japanese Patent 73-49,728, British Patent 1,498,722 and French Patent 2,245,615.

U.S. Patent 3,067,253 describes the use of Raney nickel to which calcium hydroxide or magnesium hydroxide is added. The reaction temperatures are however always low (25 to 60°C), so as to avoid the dehalogenation, and this does not allow these processes to be used industrially.

British Patent 1,191,610 describes the use of Raney nickel in the presence of a thiocyanate. This process only allows slow hydrogenation (4 hours to 8 hours) and the catalyst is modified during the hydrogenation, which does not make it possible to consider a continuous process.

Japanese Patent 73-49,728 describes the use of Raney nickel in the presence of an alkylamine, an alkan15 olamine or a heterocyclic base. In this patent, the hydrogenation temperature is limited to 60°C, as in the U.S. patent mentioned above.

This temperature does not permit satisfactory industrial exploitation because the productivity of the process at these temperatures is inadequate. French Patent 2,245,615 even states that the process of Japanese Patent 73-49,728 does not make it possible to avoid dehalogenation satisfactorily, because at least 5% of the aniline obtained is dehalogenated.

British Patent 1,498,722 describes the use of Raney nickel with a trialkyl phosphite. The reaction temperature is about 100’C but the proportion of dehalogenation is very high, since it varies between 2 - 3 and 8%. This process can thus not be considered industrially.

The last patent describing the use of Raney nickel is French Patent 2,245,615, which combines it with a dehalogenation inhibitor chosen from among dicyandiamide, cyanamide and calcium cyanamide. The hydrogenation temperature is between 50 and 130eC and the proportion of dehalogenation is always less than 0.15%.

Among the second group of patents describing the 10 use of metals of the platinum group there may be mentioned French Patents 2,330,669 and 2,127,092.

French Patent 2,330,669 describes the use, as a catalyst for the hydrogenation of chlorinated nitroaromatic compounds, of platinum deposited on charcoal and inhibited by the presence of a sulphur derivative chosen from among the thioethers and the disulphides. The proportion of dehalogenation is very low (0.01 to 0.08%), this being largely attributable to the platinum, which even in the absence of a sulphur derivative does not cause dehalogenation.

French Patent 2,127,092 describes the preparation of a platinum catalyst deposited on charcoal which is sulphurized. The preparation of this catalyst consists of first carrying out a hydrogenation of the catalyst and then sulphurizing the latter by addition of hydrogen sulphide in an amount varying between 0.45 and 0.55 mole of hydrogen sulphide per mole of hydrogen absorbed.

On the one hand, the preparation of the catalyst is difficult and, on the other hand, the use of a catalyst deposited on charcoal does not allow the catalytic mass to be separated out easily and thus makes it very difficult to exploit the process in a continuous version.

The use of platinum, which is a very expensive catalyst, has caused the industry to be reluctant to use such a process industrially? The present invention starts from platinum or palladium and deposits it on an alumina-based carrier, which makes this hydrogenation catalyst easy to separate off and hence enables it to be recycled, and which gives it all the properties required for the hydrogenation of halogenonitroaromatic derivatives .

It consists of bringing the halogenonitroaromatic derivative or polyhalogenonitroaromatic derivative together with the hydrogenation catalyst consisting of platinum or palladium deposited on an alumina-based carrier.

The halogenonitroaromatic derivatives which can be hydrogenated in accordance with the process of the present invention correspond to the following formula: (Z)q (Y)p (X)n - Ar — NO2 in which: Ar represents a monocyclic, polycyclic or hetero25 cyclic radical which is optionally substituted by an alkyl group containing 1 to 4 carbon atoms, X, i and Z each represent a halogen chosen from among fluorine, chlorine and bromine, and - 5 η, p and q each represent an integer greater than or equal to 0 and less than or equal to 5, the sum of n + p + q being greater than or equal to 1.

It is preferred to use a monocyclic halogeno5 nitroaromatic compound containing one to three halogen atoms chosen from among chlorine and fluorine attached to the nucleus, and the invention is very particularly applicable to the following derivatives: chloronitrobenzenes, fluoronitrobenzenes, dichloronitrobenzenes, monochloromonofluoronitrobenzenes, trichloronitrobenzenes, chloronitromethylbenzenes and fluoronitromethylbenzenes.

The hydrogenation of the halogenonitroaromatic derivatives with the aid of the catalyst according to the invention is carried out under the usual hydrogenation conditions. Because of the high non-dehalogenation power which the alumina confers, it is entirely possible to carry out the hydrogenation at a temperature of between 60°C and 150°C. It is even carried out preferably between 70eC and 110°C, which makes it possible to achieve productivities (amount of amine formed per hour and per volume of reaction mixture) which are comparable with the productivities of the processes aimed at the preparation of non-halogenated amines.

A further advantage of the catalyst according to the invention, which the catalysts deposited on charcoal do not provide, is the ease with which it can be used in processes carried out continuously. In fact, the catalysts based on metals deposited on alumina are markedly easier to separate off than are catalysts deposited on charcoal.

A last advantage of the catalyst according to the 5 invention is the ease with which it can be used; no prior treatment of the catalyst - as in French Patent 2,127,092 which describes hydrogenation of the catalyst, followed by its sulphurization - is necessary. In the present process, it is only necessary to introduce all the reactants, namely the metal deposited on alumina, the halogenonitroaromatic derivative and the solvent, into the hydrogenation reactor and then to pressurize the reactor with hydrogen.

The process of the invention can be carried out in the absence of a solvent or in any solvent which is inert under the reaction conditions, such as, for example: water, alcohols such as methanol, ethanol and isopropanol and aromatic solvents such as toluene and xylene. The use of methanol is preferred.

For better performance of the invention, it is preferred to use an amount by weight of catalyst (platinum or palladium deposited on alumina) of between 1 g and 20 g per litre of reaction medium. In the catalyst, the calculated amount by weight of metal per 100 grams of alumina is generally between 0.1 g and 1 g.

The process can be carried out continuously, the amount of halogenonitroaromatic derivative not being set up in a static manner but in the form of a stream. Thus a feed rate of about 1 to 3 moles per litre of reaction medium per hour is entirely recommended.

The hydrogen pressure is advantageously between 1 bar (0.1 MPa) and 100 bars (10 MPa) and preferably between 5 bars (0.5 MPa) and 25 bars (2.5 MPa).

The present invention will be described more completely with the aid of the examples which follow and which must in no case be regarded as limiting the invention.

Examples 1 and 2: Hydrogenation of 3,4-dichloronitrobenzene ml of methanol, 10 ml of water and the amount of catalyst shown in Table 1 are charged into a stainless steel autoclave. After it has been closed, the reactor is purged repeatedly with nitrogen and then with hydrogen.

The pressure is set at 18 bars (1.8 MPa). The reaction mixture is heated to 75°C. When this temperature has been reached, the substrate (25 g of dichloronitrobenzene dissolved in 135 ml of methanol) is injected over minutes.

At the end of the reaction, the reactor is cooled to ambient temperature and the gas is then released.

The reaction mass is filtered and the filtrate is analysed by gas phase chromatography.

The chloride ions (C1‘) present in the filtrate are determined with silver nitrate; these chloride ions represent the hydrodechlorination of the 3,4-dichloronitrobenzene which has occurred during the hydrogenation.

TABLE 1 Catalyst DC % 3,4-DCNB RY % Cl' Mol.% of DCNB Ex. Nature and amount of metal in % mass (g) 3,4-DCA 3-CA A 1 0.5 Pt/A12Q3 0.7 100 99.5 0.25 <0.1 1.1 10 2 0.1 Pt/Al^Oj 1.4 100 99.5 0.2 <0.1 0.5 DC = degree of conversion RY = yield relative to the substrate (3,4-DCNB) employed 3,4-DCNB = 3,4-dichloronitrobenzene 3,4-DCA. = 3,4-dichloroaniline 3-CA = 3-chloroaniline A = aniline For degrees of conversion of 100%, very little hydrodechlorination relative to the 3,4-DCNB employed is observed.

Examples 3 to 13 270 ml of methanol and 30 ml of water are introduced into a 750 cm3 stainless steel reactor. The amount of catalyst based on 0.5% of platinum deposited on alumina is shown in Tables 2, 3 and 4.

The reactor is purged with nitrogen and hydrogen and is then pressurized with hydrogen under a pressure of 18 bars (1.8 MPa). It is heated to 60 eC (Table 2), 80°C (Table 3) or 100’C (Table 4). ml of a mixture of 182.2 mmol of 3-chloro-4fluoronitrobenzene (CFNB) and 72.8 mmol of 4-fluoronitrobenzene (pFNB) are injected over 16 minutes.

The various compounds, namely CFNB, pFNB, CFA (3chloro-4-fluoroaniline), pFA (parafluoroaniline) and A (aniline) are determined by gas phase chromatography.

The chloride ions are determined with silver nitrate.

TABLE 2 Effect of the amount of catalyst at 60°C TESTS CATALYST (g) DC % HDCL % HDF % CFNB pFNB 3 0.5 18 18 0 0 4 1.0 100 100 0 0 5 2.0 100 100 0 0 6 4.0 100 100 0 0 20 HDCL = hydrodechlorination expressed in mol.% relative to the CFNB introduced HDF = hydrodefluorination expressed in mol.% relative to the pFNB introduced TABLE 3 Effect of the amount of catalyst at 80°C TESTS CATALYST DC % HDCL HDF 5 (g) CFNB pFNB % % 7 0.5 100 100 0.5 0 8 1.0 98.5 100 1.2 0 9 2.0 99 100 1.2 0 10 10 4.0 100 100 1.2 0.2 TABLE 4 Effect of the amount of catalyst at 100°C TESTS CATALYST (g) DC % HDCL % HDF % CFNB pFNB 11 0.5 100 100 0.1 0 12 1.0 100 100 1.1 0 20 13 4.0 100 100 1.0 0.5 Example 14 250 ml of methanol containing 10% by volume of water and 1.25 g of a catalyst of 0.5% of Pd on Al2O3 are introduced into the reactor used to carry out Examples 3 to 13 .

The temperature of the reaction mixture is raised (after purging with nitrogen and then with hydrogen) to - 11 110’C and the hydrogen pressure to 18 bars.

When these conditions have been reached and stabilized, a solution consisting of 12.5 g of a 70/30 molar mixture of parafluoronitrobenzene (pFNB) + ortho5 fluoronitrobenzene (oFNB) and 12.5 g of a 35/5 by volume mixture of methanol and water is injected at the rate of 25 g/h.

The duration of injection is 15 hours. In order to maintain the activity of the catalytic mass at the initial level, it is necessary to add 0.125 g of catalyst twice, after 5 and 10 hours' reaction.

The degree of conversion of the nitrofluorobenzenes is complete and the yields determined by analysis and relative to each of the fluoronitrobenzenes are: parafluoroaniline : 99.8% orthofluoroaniline : 99.8%.

The formation of 0.2% of aniline is detected.

Claims (10)

1. Process for the preparation of halogenoaminoaromatic derivatives characterized in that a halogenonitroaromatic derivative is brought together with a catalyst consisting of a metal chosen from among platinum and palladium deposited on an alumina-based carrier, and with hydrogen.

2. Process according to Claim 1, characterized in that the halogenonitroaromatic derivative corresponds to the formula (I) (Z), (Y) p (X) n - Ar - N0 2 in which: Ar represents a monocyclic, polycyclic or heterocyclic radical which is optionally substituted by an alkyl group containing 1 to 4 carbon atoms, X, Y and Z each represent a halogen chosen from among fluorine, chlorine and bromine, and η, p and q each represent an integer greater than or equal to 0 and less than or equal to 5, the sum of n + p + q being an integer greater than or equal to 1.

3. Process according to Claim 2, characterized in that Ar represents a monocyclic aromatic radical and X and Y represent chlorine and/or fluorine.

4. Process according to Claim 1, characterized in that the reaction is carried out in a solvent chosen from among alcohols and aromatic derivatives.

5. Process according to Claim 4, characterized in that the solvent is methanol. - 13

6. Process according to Claim 1, characterized in that the amount of catalyst used is between 1 and 20 g per litre of reaction medium.

7. Process according to Claim 1, characterized in that the amount by weight of metal used in the catalyst, relative to the alumina-based carrier, is between 0.1 and 1%.

8. Process according to Claim 1, characterized in that the reaction temperature is between 70°C and 150 e C and preferably between 70 e C and 100°C.

9. A process according to Claim 1 for the preparation of a halogenoaminoaromatic derivative, substantially as hereinbefore described and exemplified.

10. A halogenoaminoaromatic derivative , whenever prepared by a process claimed in a preceding claim.