CN100455559C - Method for preparing aromatic amines by reduction of aromatic nitro compounds - Google Patents

Abstract

The invention provides a method for preparing aromatic amines by reduction of aromatic nitro compounds, that is, in supercritical carbon dioxide/water as the reaction medium, metal iron powder or zinc powder is used as the reducing agent to reduce the aromatic nitro compounds to obtain the corresponding of aromatic amines. For example, the mixture of iron powder, water and p-chloronitrobenzene is reacted at a reaction temperature of 120°C and a carbon dioxide pressure of 15 MPa for 12 hours, and the yield of the reduced product p-chloroaniline is 98%. In the method of the present invention, the carbon dioxide, water and unreacted iron powder used can be reused, which not only has the high product yield of the traditional iron powder reduction method, but also has the advantages of being resistant to aromatic nitro groups containing other easily reducible groups on the ring. It has the advantage of being able to selectively reduce the iron powder, and can avoid the problem of a large amount of waste water discharge in the traditional iron powder reduction method.

Description

Method for preparing aromatic amines by reduction of aromatic nitro compounds

technical field

The present invention relates to a method for preparing aromatic amines by reduction of aromatic nitro compounds, especially for the selective reduction of aromatic nitro compounds containing other easily reducible substituent groups (such as halogen, carbonyl, cyano) on the ring, using metal Powder reducing agent combined with supercritical carbon dioxide/water system can reduce aromatic nitro compounds to obtain corresponding aromatic amines. After the reaction, carbon dioxide, water and unreacted iron powder can be reused, avoiding a large amount of waste water in the traditional iron powder reduction method emission problem.

Background technique

Aromatic amines are the main raw materials and intermediates of synthetic rubber, dyes, pigments, chemical reagents, pharmaceuticals and pesticides, and are widely used. The methods for synthesizing aromatic amines from corresponding aromatic nitro compounds usually include iron powder reduction method, alkali sulfide reduction method, catalytic hydrogenation method, etc. The iron powder reduction method has a wide range of applications, and many amines are obtained by reducing their corresponding nitro compounds with iron powder in the presence of electrolytes. The iron powder reduction method has the advantages of simple process, low requirements for equipment, and high product yield. However, a large amount of waste water is produced in the production process, which has brought great pollution problems to the environment. [Zhang Xiucheng, Li Shenhui. Full cycle process treatment of reducing wastewater in the production of 2,4-dimethylaniline [J]. Chemical Environmental Protection. 19, p93-95, 1999, Kirk-Othmer, Encyclopedia of Chemical Technology 3 ^rd Ed.The Interscience Encyclopedia, Inc., 2; p364-373, 1978].

Alkali sulfide reduction method, also known as Qi Ning (Zinin) reduction. The reaction conditions of this method are relatively moderate [Hu Jianli et al., Dyestuff Industry, 1, p36, 1999], the selectivity is good, and the compounds containing C=C, -Cl and other nitro groups can be selectively reduced to make nitroazo dyes The reduction of the nitro group in it does not affect the azo group [Gao Lei, Zhang Qian. Research on the technology of p-aminoanisole [J]. Henan Chemical Industry, 2, p25-28, 1992]. However, the production cost of this method is higher, the yield is lower than that of the iron powder reduction method, and more sulfur-containing wastewater is generated, which pollutes the environment and is difficult to handle. [Zhang Tianyong, You Lanying et al., Research on the preparation method of p-chloroaniline, Dye and Dyeing, 41, p365-366.2004].

The main problem of catalytic hydrogenation is the selectivity of aromatic nitro substrates with other easily reducible groups (such as halogens, carbonyls, nitriles, etc.) on the aromatic ring. Reductive dehalogenation occurs, and the degree of reductive dehalogenation will increase with the increase of reduction reaction temperature and hydrogenation rate [Zhang Tianyong, Yu Lanying, etc., research on the preparation method of p-chloroaniline, dyes and dyeing, 41, p365-366, 2004] ; Although dehalogenation inhibitors can be added to the reaction system or catalyst performance can be improved to solve dehalogenation problems (such as US5554573, US4070401), dehalogenation inhibitors can affect product quality and increase production costs. In addition, the use of hydrogen in catalytic hydrogenation is dangerous, difficult to store and transport, and the cost of the catalyst is relatively high when noble metals are used.

In the traditional iron powder reduction method, the reaction must be carried out in an acidic solution (strong inorganic acid such as hydrochloric acid, sulfuric acid solution or organic acid such as acetic acid). After the reaction is completed and the separated product is processed, a large amount of salty wastewater will be generated, which cannot be reused and causes serious pollution. The environment is difficult and expensive to deal with. However, the iron powder reduction method has the advantages of wide application range, easy production control, less side reactions, high selectivity, and good product quality. Groups (such as halogenated nitro compounds are often prone to dehalogenation reactions in the catalytic hydrogenation process. The selectivity is poor), is still a good way. At the same time, the iron sludge produced by the iron powder method can co-produce iron oxide pigments. German Bayer Company and American Mobay Chemical Company still retain a part of the iron powder method to produce aniline, and by-product iron oxide pigment "M". It is known that in the process of iron powder reducing nitro compounds, the solution must have sufficient acidity to promote the reaction. In pure water medium, iron powder can hardly reduce nitro compounds, Professor Poliakoff et al. (C.Boix, M.Poliakoff; J.Chem.Soc., Perkin Trans 1, p1487-1490, 1999) of the University of Nottingham, UK used The method of increasing the reaction temperature (adopting near-critical water) realizes the iron powder reduction of nitro compounds, and reacts for 2.5 hours at 250° C. (pressure 100 bar), and the nitrobenzene reduction has only 10% aniline yield; at the same temperature , using zinc powder to reduce nitrobenzene can get 90% yield of aniline. It can be seen that the method of only strengthening the reaction conditions is not ideal. Wang Lei et al. (Lei Wang, *Pinhua Li, Zongtao Wu, et al; Synthesis, 13, p2001--2004, 2003) recently reported the reduction of nitro compounds using nano-iron powder in near-critical water (temperature 210°C) , and reacted for 2 hours, the reduction of p-methylnitrobenzene can achieve 95% yield of arylamine. But the raw material cost of nano-iron powder is high.

The purpose of the present invention is to solve the pollution problem in the traditional iron powder-strong acid aqueous solution reduction system, and to provide a method for preparing aromatic nitro compounds without using stronger inorganic acids such as hydrochloric acid, sulfuric acid or organic acids such as acetic acid. A new amine method, which not only has the advantages of the iron powder reduction method, but also avoids the pollution of the saline wastewater to the environment.

Contents of the invention

The invention proposes to realize iron powder reduction of nitro compounds under supercritical CO ₂ -water system. The acidity needed to facilitate the reaction is provided by _CO2 dissolved in water.

It is known that CO ₂ dissolved in water forms carbonic acid (H ₂ CO ₃ ) to increase the acidity of the system, and the solubility in water increases with pressure; the acidity in CO ₂ -water systems increases significantly, and the pH value is easily reduced to Close to 3; equivalent to the acidity of 1M acetic acid aqueous solution; therefore, the iron powder reduction of nitro compounds can be realized in the supercritical CO ₂ -water system, and the acidity provided by the CO ₂ dissolved in water can promote the reaction, and the reaction is completed and eliminated After CO ₂ , the reaction mixture does not contain the salt formed by the strong acid and the product aromatic amine, so the separation of the product amine adds alkali, so that the water phase does not contain salt after the separation of the product amine, and the water phase can be directly recycled for the next reaction In the reaction process, there is no discharge problem of salty waste water; the pollution problem to the environment is avoided.

The technical scheme adopted in the present invention is: in the autoclave, add aromatic nitro compound, reducing agent and water, make the mol ratio of aromatic nitro compound and reducing agent be 1: 0.5-20, tighten the autoclave, Replace the air twice with carbon dioxide, heat up to 60-170°C under stirring, fill in carbon dioxide to a pressure of 1-18MPa, and react for 1-50 hours; the corresponding aromatic amine is obtained.

In the method for the preparation of aromatic nitro compounds by reduction of the above-mentioned aromatic nitro compounds, the preferred reaction conditions are that the molar ratio of the aromatic nitro compounds to the reducing agent is 1: 6-8, the carbon dioxide pressure in the reaction is 12-17MPa, and the reaction temperature is 90- 130°C, the reaction time is 2-20 hours.

In the above method, the aromatic nitro compound used is selected from nitrobenzene, nitrohalobenzene, nitroanthraquinone, nitroacetophenone, nitropropiophenone, nitrobenzonitrile or nitrophenylacetonitrile.

In the above method, the reducing agent used is selected from iron powder or zinc powder.

The main advantage of the method for preparing aromatic amines through the reduction of aromatic nitro compounds in the present invention is that the reaction system has the ability to realize nitrohalogenated benzene, nitroanthraquinone, nitroacetophenone, nitropropiophenone, and nitrate These aromatic nitro compounds of benzonitrile or nitrophenylacetonitrile selectively reduce the nitro group to prepare the corresponding aromatic amine, the reduction reaction yield is high, the cost of the reducing agent is low, and there is no pollution problem caused by the discharge of salty wastewater to the environment. .

Detailed ways

The present invention will be further described below in combination with specific embodiments.

Embodiment 1: the preparation of p-chloroaniline

In a 100ml stainless steel autoclave, add 1.58g of p-chloronitrobenzene, 3.35g of iron powder, and 20ml of water, tighten the reactor, replace the air with CO ₂ for 3 times, start stirring, raise the temperature to 120°C, and fill with carbon dioxide until the pressure reaches 15MPa, react for 12 hours, stop the reaction. The content of each component was analyzed by gas chromatography, and the result showed that the yield of p-chloroaniline was 98.0%.

Embodiment 2-9 is as embodiment 1 mode, and specific operating conditions are shown in Table 1

Embodiment 10-16 provides the reaction that other aromatic nitro compounds are reduced to prepare aromatic amine, and the results are shown in Table 2

*Note A: o-nitrochlorobenzene, B: p-nitroacetophenone, C: o-nitrobenzonitrile, D: p-nitrophenylacetonitrile,

E: 1-nitroanthraquinone

Claims (3)

1, a kind of method of aromatic amines preparation by reducing aromatic nitro-compound, its feature is in autoclave in this method, add aromatic nitro compound, reductive agent and water, the mol ratio that makes aromatic nitro compound and reductive agent is 1: 0.5-20, tighten autoclave, use the carbon dioxide replacement secondary, under agitation, heat temperature raising is to 60-170 ℃, charging into carbonic acid gas to the pressure of reaction system is 7.9-18Mpa, in this supercritical co-water reaction medium, reaction is carried out making corresponding arylamine in 1-50 hour, and wherein reductive agent is selected from iron powder or zinc powder.

2, according to the method for the described aromatic amines preparation by reducing aromatic nitro-compound of claim 1, the reaction conditions that it is characterized in that this method is that the mol ratio of aromatic nitro compound and reductive agent is 1: 6-8, pressure carbon dioxide is 12-17MPa in the reaction, temperature of reaction is 90-130 ℃, and the reaction times is 2-20 hour.

3,, it is characterized in that aromatic nitro compound used in this method is selected from oil of mirbane, the nitro halogeno-benzene according to the method for the described aromatic amines preparation by reducing aromatic nitro-compound of claim 1, nitroanthraquinone, nitro-acetophenone, oil of mirbane acetone, p-nitrile or oil of mirbane acetonitrile.