CS217896B1 - A method for partial reduction of di- and polynitro compounds - Google Patents

Abstract

The process of partial reduction of di- and polynitro compounds by the action of green silica is protected.

Description

The invention relates to a method for the partial reduction of di- and polynitro compounds. The partial reduction of di- and polynitro compounds is mainly carried out by means of inorganic simulants, e.g. Na ₂ S, NaHS, (NH ₄ ) ₂ S, (NH^HS, Na ₂ S ₂ , higher polysulfides, etc. The partial reduction with sodium sulfide can be characterized as a stepwise reaction by the following summary scheme:

.NO, .HH.

Ar< ² + 6 Na,S + 7 H _o 0—> 4 Ar< + 3 Na_S,O, + 6 NaOH ^NO ₂ ^{2 2} ^ ^N0 2 ^ZJ where Ar denotes the residue of the aromatic hydrocarbon. When polysulfides are used, elemental sulfur also appears in the reaction products.

Examples of the use of partial reductions in simics include the preparation of a friction machine,

3.4-diamino-5-nitrobenzamide, 4-amino-4'-nitrodiphenyl, 4-amino-2,6-dinitrotoluene,

2.4-diamino-6-nitrotoluene, 4-amino-4'-nitro-2,2'-stilbenedisulfonic acid, 1-amino-5-nitronaphthalene and 2-amino-6-nitronaphthalene, 2,2'-dinitrobenzidine from 2,2',4,4'-trinitrodiphenyl, 4-amino-2-nitrobenzenesulfonic acid and a number of other aminonitro compounds. Despite the considerable attractiveness of partial sulfide reductions, their technical implementation is accompanied by the risk of poisoning of the operator and contamination of the air and water waste with hydrogen sulfide, sulfides, sulfides, or possibly sulfur.

The use of green lye in the partial reduction of di- and polynitro compounds has not yet been used in technical practice. If reductions of nitro compounds with green lye are described, then it is a total conversion of all -NOg to -NH,. For example, o-aminobenzaldehyde can be prepared from o-nitrobenzaldehyde, or 2,7-diamino-9-(4 '-nitrophenyl)-1O-methylphenanthridium chloride can be reduced to the corresponding triamino derivative, and 2-amino-4-acetylaminobenzoic acid, 2-aminoveratric acid, 2-aminobenzothiazole and a number of other amines can be prepared.

The subject of this invention is a method for the partial reduction of aromatic di- or polynitro compounds, the essence of which according to the invention consists in the interaction of aromatic di- or polynitro compounds and green silicate in an amount of 6 to 7 molecules of green silicate per nitro group and an inorganic basic agent, for example hydroxides or carbonates of alkali metals or ammonium, which are added to the pH value of the solution >6.5. It is also possible to add a solvent completely or to a limited extent miscible with water to the reaction medium, for example alcohols, hydrocarbons, halogenated hydrocarbons and glycols.

The new procedure can be used with surprising ease to carry out partial reduction of di- and polynitro compounds, while the proportion of impurities of a higher reduction degree in the reaction mixture is relatively very low and after isolation of aminonitro products, the content of impurities usually decreases for a longer time. The advantage of the new procedure is also the easy separation of iron oxides from other products, either by sedimentation or mechanical separation, and the toxic harmlessness of the sulfates formed after alkaline conversion of the original green slag. When working with starting nitro compounds or resulting aminonitro compounds soluble in water, the isolation is carried out by salting out, acidification, distillation concentration, etc., while the choice of separation procedure depends on the number of amino groups and solubility-inducing groups in the molecule. For example, in cases of partial reductions of aromatic dl-nitromonosulfonic acids or their salts, the aqueous solution, freed from solid iron oxides after the reaction, is acidified with mineral acid to a pH lower than 5 and the precipitated solid inner salt of aminonitrosulfonic acid (Zwitterion) is mechanically separated from the mother liquors. In cases of partial reductions of water-insoluble dl- and polynitro compounds, a solvent can be added to the reaction mixture, such as methanol, ethanol, acetone, glycols, but 1-butanol, methyl ethyl ketone, etc. in an amount sufficient to completely or only partially dissolve the nitro compounds; after reduction, it is then advantageous to heat the reaction mixture to a temperature at which the aminonitro products are completely dissolved, the solid iron oxides are separated while hot, and the precipitated product is separated from the mother liquors, optionally after distillation of the auxiliary solvent. However, any of the methods of product separation that are currently used in sulfide reduction, with iron according to Béchamp, or after hydrogenation can be chosen.

Partial reduction of di- and polynitro compounds with green silicate in an alkaline environment takes place at temperatures above 5 °C, but in technical practice it is advantageous to work at higher temperatures, where not only does the rate of conversion of the nitro to the amino group increase, but the higher temperature also has a positive effect on simultaneously occurring processes, such as the precipitation of ferrous hydroxide, and also affects the modification and grain size of the precipitated ferric oxide, the miscibility of the system and the homogeneity of the reaction mixture during the partial reduction of less soluble nitro compounds.

The following alkalis are suitable for influencing the pH of the reaction medium: soda, potash, sodium hydroxide, potassium hydroxide, ammonia, water saturated with ammonia, calcium hydroxide, trisodium or tripotassium phosphates and all substances that exhibit an alkaline reaction when mixed with water.

The new procedure has a number of advantages over previous sim reductions:

a) The reagents used do not produce volatile toxic products. Sulphides release highly toxic hydrogen sulphide in water and mineral acids, which endangers operators and pollutes the air.

b) Waste from the new method of partial reduction with green lime is - after the isolation of nitroamino compounds - practically harmless (iron oxides and sulfates of alkali metals, caustic earths, or ammonium). Excess sulfides, sulfates, and possibly even elemental sulfur are released from the aimitic reductions, all of which are unacceptable compounds in waste.

c) In many cases, the new method allows for easier isolation, especially where acidification of the reaction mixture precipitates the desired product; acidification of simic reductions is excluded due to the possibility of the release of toxic exhalations.

d) Partial reduction with green scale is also advantageous from an economic point of view, because a significant amount of scale is wasted, for example, from the production of titanium white and from pickling of sheets in metallurgy, and the quality of this scale is suitable for reduction.

Example 1

0.2 mol of 1,3-dinitrobenzene-4-sulfonic acid is dissolved in 500 ml of water, the solution is heated to 55 °C, after which a total of 90 ml of 25% aqueous ammonia and 166.8 g of FeSO^, 7 HgO (0.6 mol) are added simultaneously so that the pH of the reaction mixture is in the range of 7.5 to 8.5 and the temperature is up to 60 °C. The resulting reaction mixture is then kept for 30 min. at 65 °C, solid iron oxides are filtered off, washed with 200 ml of hot water and the filtrate combined with the washing water is analyzed. The yield of nitro-aminobenzenesulfonic acids is 92% and according to chromatographic analysis, a mixture of 1-amino-3-nitrobenzene-4-sulfonic acid and 1-nitro-3-aminobenzene-4-sulfonic acid in a molar ratio of 2:1 is obtained.

Example 2

0.1 mol of 4,4'-dinitrostilbene-2,2'-disulfonic acid is dissolved in 430 ml of water, heated to 50 °C, after which a total of 45 ml of 25% aqueous ammonia solution and 83.4 g of FeSO^, 7 HgO (0.3 mol) are added simultaneously, while the pH of the reaction mixture is maintained at 8 ± 0.5 units and the temperature up to 60 °C by choosing the doses of both reagents. The resulting reaction mixture is then maintained for 30 min. at 65 °C, iron oxides are filtered off, washed with 150 ml of hot water and the filtrate combined with the washing water is analyzed. The yield of 4-amino-4'-nitrostilbene-2,2'-disulfonic acid ranges between 85 and 90% th. Impurities identified by chromatographic analysis consist of 4,4'-diaminostilbene-2,2'-disulfonic acid and higher molecular weight compounds, probably azoxycondensates from the starting dinitro compound.

Instead of the compounds mentioned in Examples 1 and 2, equimolar amounts of, for example, 4,4'-dinitrodibenzyl-2,2'-disulfonic acid, dinitrodiphenylmethanesulfonic acid, m-dinitrobenzene, 2j4-dinitrotoluene, 2,4-dinitrobenzoic acid, 3,5-dinitrobenzoic acid, 3,7-dinitrocarbazole-4-sulfonic acid, 2,7-dinitronaphthalene-1,5-disulfonic acid, 2,4,6-trinitrotoluene, tetranitrocarbazole, etc. can be used.

In place of NH^OH, NaOH, KOH, NagCO-j, KgCO-j, Na ₃ P0 ₄ , K ₃ PO ₄ , CaCOp NaHCO-p KHCOp MgCOp MgO, CaO, and other inorganic agents characterized by blunting the resulting acidity can be used.

Claims (2)

1. A process for the partial reduction of aromatic di- or polynitro compounds, characterized in that they interact with aromatic di- or polynitro compounds and green vitriol in an amount of 6 to 7 green vitriol molecules per nitro group and an inorganic base such as alkali metal or ammonium hydroxides or carbonates. are added to a solution pH > 6.5. 2. Process according to claim 1, characterized in that a solvent which is totally or limitedly miscible with water, for example alcohols, hydrocarbons, halogenated hydrocarbons and glycols, is added to the reaction medium.