JPS6042230B2 - Purification method for aromatic amines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying aromatic amines, and particularly to a method for removing coloring impurities contained in aromatic amines.

Aromatic amines are generally produced by hydrogenation of aromatic nitro compounds, but in this reaction, various by-products are produced in addition to the desired product.

Among these by-products are impurities that are the main cause of coloring of the product over time and significantly color the amines. Aromatic amines, especially m- and p-phenylenediamine, which are used as raw materials for heat-resistant polymers are strongly required to have little coloration, but it is difficult to obtain products with such excellent hue using conventional purification methods. It's not easy. In other words, conventional purification methods to remove colored impurities include decolorizing an alkaline (or acidic) aqueous solution of these amines with activated carbon and then precipitating crystals as neutral, and removing zinc and acid chlorides during distillation. There are known methods of adding it, but if it is stored for a long period of more than 3 months, it will become noticeably discolored. Although there are methods for preventing coloration using various additives, the addition of a third component often causes industrial disadvantages and cannot be said to be an appropriate method.

In addition, there are improved stabilization methods using reducing sulfur compounds (Japanese Patent Application Laid-Open No. 49-31628) and distillation under a stream of sulfur dioxide gas (Japanese Patent Application Laid-open No. 51-11722), but the additives themselves are unstable. However, it is not a sufficient method because it is complicated to operate and requires additional equipment due to problems such as pollution, environment, and equipment corrosion. The present inventors conducted intensive studies to improve these and found that aromatic amines with good long-term stability can be obtained by distilling aromatic amines in contact with an inorganic zinc salt or after heat treatment. I found out.

The effects of these inorganic zinc salts were completely unknown. Examples of the aromatic diamines applicable to the present invention include O-, m- or p-phenylenediamine and tolylenediamine.

Further, particularly preferred inorganic zinc salts are zinc sulfate and zinc chloride, and these may also be added in the form of sulfuric acid (or hydrochloric acid) and without zinc. Furthermore, after adding these, 200°C
Purification can be carried out more effectively by distilling after heat treatment at a temperature above, preferably 250° C. or above, for one hour or more, preferably two hours or more. The amines obtained by the method of the present invention did not undergo any change over time during long-term storage for more than 3 months.

The present invention will be specifically described below with reference to Examples. Example 1 Crude m obtained by catalytic hydrogenation of m-dinitrobenzene
- 0.25 y of zinc sulfate was added to 50 y of phenylenediamine, heated at 250° C. for 2 hours, and then distilled under reduced pressure to obtain 45.3 g of an almost colorless fraction.

This fraction remained light brown even after being stored for 3 months in a room under a nitrogen seal. Comparative Example 1 Fraction 47.6y obtained by distillation without adding zinc sulfate in Example 1 was almost colorless immediately after distillation, but turned dark brown after being stored for 3 months under a nitrogen seal.

Examples 2-4 Comparative Examples 2-3 In Example 1, various inorganic zinc salts were used instead of zinc sulfate.
25y (however, in the case of treatment with sulfuric acid and without zinc, each is 0
．． The fraction obtained by adding 13f) and distilling it under reduced pressure after contact or heat treatment was stored indoors under a nitrogen seal for 3 months. As a result of measuring the transmittance, the results shown in Table 1 were obtained.

Example 5 0.25y of zinc sulfate was added to 50f1 of crude p-phenylenediamine obtained by catalytic hydrogenation of p-nitroalinine, heated at 230°C for 2 hours, and then distilled under reduced pressure to obtain 43.7y of an almost colorless fraction. I got it.

Even after this fraction was stored for one year at room temperature in a glass bottle surrounded by air, no change in hue was observed over time. Comparative Example 4 The fraction 48.2 Da obtained by distilling without adding zinc sulfate in Example 5 was almost colorless immediately after distillation. After being stored for 3 months at room temperature in a glass bottle surrounded by air, it took on a coppery red color.

Claims (1)

[Claims] 1. A method for purifying aromatic amines, which comprises distilling aromatic amines or a mixture containing them in contact with an inorganic zinc salt or after heat treatment.