CS202124B1 - Process for preparing primary aromatic amines containing halogen - Google Patents

Description

The invention relates to a process for the preparation of halogenated aromatic primary amines of the following general formula (I) by reducing the corresponding Bechamp nitro compound.

It is generally known that the reduction of halogenated aromatic nitro compounds is accompanied by a loss of chlorine to produce aromatic primary amines with less halogen than desired or dehalogenated at all. These then form impurities that accompany the major component of the crude product, reduce the yield of the process and must be removed predominantly by fractional distillation.

Dehalogenation can affect the molecule in the reduction of the incoming nitro compound, whose - NO2 group in ortho or para position to chlorine increases the reactivity of chlorine and makes it mobile, but also the molecule by reducing the amine formed.

It has therefore been expedient to focus on suppressing dehalogenation, which performs the main process of Béchamp reduction of aromatic halogenated nitro compounds with an inhibitor of this undesired reaction. A number of substances are known as dechlorination inhibitors, of which dicyandiamide according to U.S. Pat. No. 196 476.

We have now found a process for the preparation of halogenated aromatic primary amines of the formula I nu.

where x is chloro and y is hydrogen or chloro, by Bechamp reduction using iron of the corresponding nitro compounds of formula II

NO *

Wherein x and y are as defined above, which according to the invention consists in using cast iron with a maximum nickel content of 0.1% by weight as reducing iron.

It has been found by a series of experiments that one of the causes of dehalogenation of the reduced nitro compound or the resulting amine is the cleavage of chlorine by nickel-catalyzed hydrogenation.

Nickel is not a rare element in the Béchamp reduction system. It is a very frequent admixture of reducing sawdust prepared from waste cast iron contaminated with stainless, nickel-containing particles. Nickel may also contain its own reducing iron if alloyed iron pulp was used for the reduction. In all these cases, the reduction of the halogenated nitro compounds results in an amine accompanied by the products of the dechlorination process. Dechlorination, or nickel-catalyzed hydrogenation, can be considered negligible when nickel is present in the reducing iron in an amount of the order of hundredths of a percentage at most.

It is therefore advisable to select only those types of reducing iron in the operational application of Béchamp reduction of halogen nitro compounds, their nickel content being practically zero.

Example 1

A Béchamp reduction of 2,5-dichloronitrobenzene was carried out in a system containing 60 g of water, 0.816 g of formic acid and 120 g of cast iron sawdust contaminated with stainless steel particles, so that the Ni content of the average reducing iron sample was 0.3%. The reduction was carried out at the boiling point of the system for about 3 hours to give a product containing 3.5 wt. % Of 3-chloroaniline and 2.0 wt. aniline.

Example 2

Under the same conditions as Example 1, the Bechamp reduction of 2,5-dichloronitrobenzene gave a product with virtually zero 3-chloroaniline content only because cast iron containing 0.031 wt% Ni was used for the reduction.

Example 3

A Béchamp reduction was carried out in a system containing 1800 kg of water, 50 kg of formic acid, 3000 kg of cast iron sawdust (Ni content 0.07% by weight) and 3000 kg of technical 2,5-dichloronitrobenzene for about 20 h at the boiling point of the system. The crude product contained:

99.4 wt. 2,5-dichloroaniline 0.1 wt. 3-chloroaniline 0.07 wt. 2-chloroaniline 0.08 wt. Of 4-chloroaniline

0.25 wt. 3,4-dichloroaniline 0.10 wt. 2,4-dichloroaniline.

The reduction was carried out under the same conditions using a reducing iron of 0.18% by weight. Ni gave a product containing 3-chloroaniline as the main dechlorination product in an amount of 2.2 wt.

Example 4

The Béchamp reduction was carried out in a system containing 60 g of water, 60 g of cast iron sawdust (Ni content 0.03% w / w), 7.9 g of HCl and 120 g of o-chloronitrobenzene. The product obtained after the reduction contained only 0.2 wt. % p-chloroaniline and 0.2 wt. aniline.

The experiment using cast iron sawdust with 0.3% Ni content then showed only 98.1% by weight. % o-chloroaniline and in addition to 0.2 wt. % p-chloroaniline i 1.7 wt. aniline.

Claims (1)

A process for the preparation of halogenated aromatic primary amines of formula (I) NH (I) wherein x is chloro and y is hydrogen or chloro. Bechamp reduction using iron of the corresponding nitro compounds of formula II N0 _} O '(II), wherein x and y are as defined above, characterized in that cast iron with a maximum nickel content of 0.1% by weight is used as reducing iron.