SU533590A1 - The method of obtaining 4,4-azobenzene dicarboxylic acid - Google Patents

Description

one

The invention relates to an improved process for the preparation of 4.4 azobenzene dicarboxylic acid, used as a monomer for the synthesis of polymeric materials with a number of valuable physicomechanical properties, to obtain heat-resistant fiber-forming polymers.

A known method for producing 4,4-azobenzo-dicarboxylic acid by electrochemical reduction of T1-nitrobenzoic acid in a batch mode to 4.4 - hydrazo-benzo-benzoic dicarboxylic acid, followed by its oxidation to the target product by chemical methods.

Also known is an uninterrupted method for the synthesis of 4.4. Azobenzene dicarboxylic acid, according to which T1 -nitrobenzoic acid is first electrically reduced in an alkali solution, in the presence of lead ions on solid cathodes, in an electrolyte duct in a cascade of electrolytic cells with a diaphragm from ion-exchange material, and then an electrolyte coming out of the third electrolytic cell is purged with air to oxidize the resulting 4,4-hydrazobene

4,4-azobenzene dicarboxylic acid zoldicarboxylic acid, the kotor is separated by acidification of the solution with hydrochloric acid followed by separation of the precipitated precipitate and drying it.

The disadvantages of the electrolytic method for producing 4,4 -azobenzene dicarboxylic acid are the complex design of the electrolyzer, the use of an ion-exchange membrane for separating the cathode and anode spaces, and the need for its frequent replacement, and the use of sulfuric acid as the anolyte. In addition, during the synthesis of 4,4-azobenzene dicarboxylic acid, the final product of the electrolysis stage is 4,4-hydrazobenzene dicarboxylic acid, which must be chemically oxidized at the next stage of the process to the desired product, for example, air oxygen at 70-80 ° C in an aqueous alkaline medium.

The aim of the invention is to simplify the process of electrosynthesis of 4,4 -azobenzene dicarboxylic acid. For this, reduction and oxidation are carried out electrochemically in two diaphragm-free

electrolysis cells in which the flow of electrolyte is directed as follows. In the first electrolytic cell from the anode to the cathode, and in the second - vice versa, in addition, the electrolyte 4,4-hydrazobenzene dicarboxylic acid is carried out on anodes made of platinum, nickel or other corrosion-resistant material at 20–90 ° С and anode current density 5 -50 a / dm

To obtain 4,4 -azobenzene-dicarbonate-BATY acid And -nitrobenzoic acid, are electrochemically reduced on solid cathodes using an aqueous alkali solution as an electrolyte in the absence of lead ions, followed by electro-oxidation of the resulting 4,4-hydrazo benzenedicarboxylic acid, using a cascade of two without diaphragragragragmes using two electrolyzers in the electrolyte duct according to the following scheme.

The initial electrolyte containing Tl-nitrobenzoic acid enters the anodic zone of the first electrolyzer, from which it goes into the cathode zone of the same electrolyzer, where partially -n-nitrobenzoic acid is partially reduced, the electrolyte coming out of the first electrolyte cell of the second electrolyzer, where 1i-nitrobenzoic acid and all intermediates are reduced to 4.4-hydrazobenzene dicarboxylic

acid. Thereafter, the electrolyte enters the anode zone of the same electrolyzer, in which 4,4-hydrazobenzene dicarboxylic acid is oxidized to 4.41 zobenzene dicarboxylic acid.

The first electrolytic cell is filled with a solution of the original electrolyte, then an electric current is started to flow, and at the same time continuously feed the initial electrolyte solution into the anode zone of this electrolytic cell. The second electrolyzer is not filled before the start of the synthesis. The electrolysis in the second electrolyzer begins p: after filling it with electrolyte from the first electrolyzer. The electrolysis time is calculated from the start of the release of the solution of 4,4 -azobenzene dicarboxylic acid from the second electrolyzer. The desired product from the solution is isolated by known methods, the yield reaches 97%; the content of the basic substance (purity of the target product) is 10%.

The table shows the results of the synthesis of 4,4-azobenzene dicarboxylic acid in a continuous manner in the ‑ cascade of two non-diffracted electrolyzers under the following conditions: the volume of each electrolyzer is 700 ml, the flow rate of the electrolyte is 250 ml / hour, the temperature in the electrolyzers is 80–3 ° C, force current 5 a, cathode and anode current density of 2O a / dm.

where P is NBK-T1 - nitrobenzoic acid;

ABDC - 4,4 zobenzene dicarboxylic acid.

Example. In the first electrolytic cell of a cascade of 2 electrolysers, an electrolyte of the composition of 0.14 m / l of TJ-nitrobenzoic acid and 0.008 m / l in an aqueous solution of a 2% alkaline NolOH solution is poured. The electrolyzer is a cylindrical horizontally arranged 700 ml thermostatted vessel.

equipped with agitators in the cathode and anode zones, an inert gas bubbler, a cathode of 0.25 dm steel, and an anode of

platinum 0,25 dm.

Claims (1)

After the electrolyzer is filled, a direct current of 5 a current is started to flow, and the initial electrolyte is fed into the anode space at a rate of 250 ml / hour. The solution leaving the first cell is fed to the cathode space of the second cell. After filling the second electrolyzer, a current of 5 a is also started to flow. Temperature in electrolyzers 8О ± 3 ° С 7 hours after the start of electrolyte output from the second electrolyzer, the isolated product consists of 100% 4,4-az benzenedicarboxylic acid. The yield is 97.0%. Example2. Under conditions similar to those described in Example 1, the flow rate is maintained at 300 ml / hour. After 9 hours of electrolysis, the isolated product consists of 10O% 4.41-azobenzene dicarboxylic acid with a yield of 96.5%. Example Z.V conditions similar to those described in example 1, the electrolysis is carried out with a current of 7 a. After 5 hours, the product consists of a 100% 4.4 gobenzene dicarboxylic acid with a yield of 96.8%. 6 Claims I Method of obtaining 4,4-zobenzene dicarboxylic acid by electrochemical reduction of N-nitrobenzoic acid in a cascade of electrolyzers on solid cathodes using an alkali aqueous solution as electrolyte, in the presence of lead ions, in an electrolyte duct, followed by oxidation of the resulting 4,4 hydrazobenzene dicarboxylic acids, in order to simplify the process, reduction and oxidation are carried out electrochemically in two electrolyzer-free electrolyzers, in which to the direction: in the first electrolytic cell from the anode to the cathode, and in the second - vice versa, and the electro-oxidation of 4,4-hydrazobenzene dicarboxylic acid is carried out on anodes of platinum, nickel or another corrosion-resistant material at a temperature of 20-90 ° C and anode current density of 5- 50 a / dm