A method of electrochemically reducing nitro-T acids

Abstract

The application discloses a method for electrochemically reducing nitro-T acid. The method is carried out by electrochemical reduction in a divided electrolysis device, wherein the device comprises an electrolytic cell body, a cathode, an anode and an ion film, the ion film divides the electrolytic cell body into an anode tank and a cathode tank, the cathode electrolyte is an acid solution containing nitro-T acid with pH between 1 and 6, and the anode electrolyte is an acid solution; direct current is applied between the cathode and the anode to carry out electrolysis, and nitro-T acid is reduced to generate amino-T acid, and oxygen is discharged at the anode. The application has the advantages of simple nitro-T acid reduction process, recyclable electrolyte, solved problem of difficult treatment of 'three wastes' generated in the nitro-T acid reduction process and reduced production cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dye intermediate synthesis, and particularly relates to a method for electrochemically reducing nitro T acid. BACKGROUND

[0002] There are mainly the following methods for reducing aromatic nitro compounds: (1) iron powder reduction method. In an acid aqueous medium, iron powder is used to reduce the nitro group into an amino group, and Fe3O4 (commonly known as iron mud) which is insoluble in water is produced. This method is suitable for synthesizing water-soluble amino compounds with sulfonic acid groups. After the reaction is completed, the insoluble iron mud can be removed by filtration; the iron powder reduction has been used in industry for many years, but the generated iron mud is difficult to handle, and the production environment is poor. (2) Catalytic hydrogenation reduction method. This method needs to use expensive platinum / palladium / nickel catalysts, and there are problems of recovery and deactivation of noble metal catalysts, and the catalysts are easy to be poisoned and have large loss. In addition, the use of high-pressure conditions and flammable and explosive hydrogen gas also puts forward strict requirements for the equipment, and the operation requirements are strict, which limits its application in industry.

[0003] 1-amino-8-naphthol-3,6-disulfonic acid (referred to as H acid) is an important intermediate for producing reactive dyes. The azo dyes synthesized by using the H acid as a raw material have been widely used in the dyeing of cotton, wool, silk fabrics and the like, and have a large market application amount. The existing production method of the H acid is to use naphthalene as a raw material, first perform sulfonation and nitration to obtain 1-nitro naphthalene-3,6,8-trisulfonic acid (referred to as nitro T acid), then perform alkali neutralization, hydrogenation reduction or iron powder reduction to obtain 1-aminonaphthalene-3,6,8-trisulfonate, then perform acidification and filtration to obtain 1-aminonaphthalene-3,6,8-trisulfonic acid (referred to as amino T acid), and then perform alkali fusion and acidification on the obtained amino T acid to obtain the target product H acid. As can be seen from this, the existing production method of the H acid has a long process, and a large amount of by-products are generated in the production process, causing environmental pollution and three waste emissions. At present, the reduction reaction in the production process of the H acid generally adopts iron powder reduction, and a large amount of wastewater and iron mud are generated in the reaction process, and there is a serious environmental pollution problem.

[0004] As for the catalyst hydrogenation preparation method of H acid, the early Japanese patent JP49127956 discloses using Raney nickel as a catalyst to reduce nitro T acid to amino T acid. The use of palladium-carbon as a catalyst is disclosed in Japanese patent JP50101349, but the catalysts disclosed in the above patents have the disadvantages of poor stability, easy poisoning or high price. In Chinese patents CN1911907A, CN1810779A, CN103739524B, CN101381331B and CN100574877C, modified skeletal nickel is used as a catalyst, and the hydrogenation reaction is carried out in a high-pressure kettle with a stirring device under suitable temperature and pressure. The reaction time is generally 2-10 hours, and the yield of amino T acid can reach 95%-96% (with oily by-products, which affects the product quality). However, mechanical wear of the catalyst occurs during the reaction, resulting in loss of the catalyst in powder form and deactivation of the catalyst. In addition, in order to improve the mass transfer effect in the reaction process, strong stirring is required, which causes strong collision between the catalyst and the stirrer, resulting in deformation of the catalyst skeleton, reduction of the specific surface area, and decrease of the catalyst activity. Therefore, the catalyst needs to be continuously added to maintain the normal progress of the reaction in the batch production process. In Chinese patent CN108129361A, a continuous hydrogenation reduction process of H acid monosodium salt is disclosed. Powdered molecular sieve is used as a catalyst, hydrogen is introduced into a stirring reaction kettle, and the continuous hydrogenation reaction of nitro T acid is completed under the conditions of 140-160℃ and 2.8-3.5 MPa by feeding from the bottom and discharging from the top. The yield can reach 99%. Although the continuous reaction process is used in the patent, the entire catalytic hydrogenation reaction is still carried out in a reaction kettle. In the reaction process, strong stirring is required to ensure sufficient reaction and effective mass and heat transfer, which inevitably causes collision and wear of the catalyst particles or catalyst powder, and loss during the subsequent filtration process. Due to the loss and deactivation of the catalyst, fresh catalyst needs to be continuously added to maintain a high yield. The catalyst consumption is large, and the reaction time is long in the entire reaction process, which is not suitable for large-scale industrial production. SUMMARY

[0005] In order to solve the problems in the existing nitro T acid reduction process, such as the generation of a large amount of "three wastes" in the conventional iron powder reduction method, the increase of post-treatment cost, the high cost and unavailability of noble metal catalysts in the catalytic hydrogenation reduction method, the high process cost and high safety risk under high temperature and high pressure conditions, etc., the present application provides an electrochemical reduction method for preparing amino T acid from nitro T acid in an acidic system. The electrolysis reaction conditions are mild, and the equipment is simple and easy to operate. The method directly uses clean electrons as a reducing agent, effectively avoids the addition of additional catalysts or reducing agents, and utilizes the active H* generated on the cathode surface to react with the reactants in the electrolyte, so that the nitro T acid can be efficiently reduced to the target product amino T acid.

[0006] The application is achieved by the following technical scheme:

[0007] A method for electrochemically reducing nitro-T acid, the method is:

[0008] The electrochemical reduction is carried out in a divided electrolysis device, the divided electrolysis device comprises an electrolytic cell body, a cathode, an anode and an ion membrane, the ion membrane divides the electrolytic cell body into an anode tank and a cathode tank, the cathode electrolyte is an acid solution containing nitro-T acid with a pH of 1-6, and the anode electrolyte is an acid solution; direct current is applied between the cathode and the anode to carry out electrolysis, and nitro-T acid is reduced to generate amino-T acid, and oxygen is discharged at the anode.

[0009] In the above technical scheme, further, the ion membrane is a cation membrane.

[0010] In the above technical scheme, further, the anode material is a platinum electrode, a titanium coating electrode or a graphite electrode, and the cathode material is a foamed copper electrode, a foamed nickel electrode, a zinc electrode or a lead electrode.

[0011] In the above technical scheme, further, the electrolysis is constant current electrolysis, the current density is 20mA / cm 2 ~ 50mA / cm 2 , the electrolysis reaction temperature is 30-70℃, and the reaction time is 4-12h.

[0012] In the above technical scheme, further, the pH of the cathode electrolyte is 1-6, preferably 2.8-3.2. Hydrochloric acid can be added to the cathode electrolyte to adjust the pH. Further, in the cathode electrolyte, the mass fraction of nitro-T acid is 7-8%, and hydrochloric acid is added to adjust the pH of the cathode electrolyte to 2.8-3.2.

[0013] In the above technical scheme, further, the anode electrolyte is a sulfuric acid solution; further, the concentration of the sulfuric acid solution is 1-3M, preferably 2M.

[0014] The cathode and anode reaction processes of the application are as follows:

[0015] Cathode reaction:

[0016]

[0017] Anode reaction: 6OH - → 3 / 2O2 + 3H2O + 6e -

[0018] Advantages of the application:

[0019] 1. The application first proposes a synthesis strategy for preparing amino-T acid from nitro-T acid by electrochemical reduction, and no prior art report is found.

[0020] 2、The existing amino T acid synthesis method generally needs to be carried out under the condition of the presence of a reducing agent and high temperature or precious metal catalysis, and the reaction condition is harsh and the catalyst cost is high. The present application uses a mild and simple condition, uses "electrons" as a reducing agent, and can make the reaction proceed to the predetermined target by changing the current density, reduces pollution, and is green and environmentally friendly.

[0021] 3、Since amino T acid is an important intermediate for the synthesis of H acid, H acid is an important intermediate for the production of reactive dyes, and the azo dyes synthesized therefrom have been widely used for dyeing cotton, wool, silk fabrics and the like, and the market application amount is large. Therefore, the present application has great application value and social and economic effect. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of the separation type electrolysis device used in the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below with examples, and the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not limit the present application.

[0024] The schematic diagram of the separation type electrolysis device used in the embodiment of the present application is shown in Figure 1 , wherein the diaphragm is a cation membrane.

[0025] Example 1

[0026] 5 mL of a 30% mass fraction nitro T acid aqueous solution was added to 24 mL of water, and then 1 mL of a 3M concentrated hydrochloric acid solution was added as a cathode electrolyte, and the pH was 3.02. The cathode electrolyte was added to the cathode chamber.

[0027] 30 mL of a 2M concentrated sulfuric acid solution was added to the anode chamber.

[0028] A foamed copper electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0029] The stirring was started, the power supply was turned on, and the current was passed, under the condition of a current density of 50 mA / cm 2 , a temperature of 30°C, and a stirring speed of 500 r / min under normal pressure for 4.6 h. The current was stopped, and the cathode electrolyte was subjected to diazotization titration, and the yield of amino T acid was 42.14%.

[0030] Example 2

[0031] 5 mL of 30% by mass nitro-T acid aqueous solution was added to 24 mL of water, and 1 mL of 3 M dilute hydrochloric acid solution was further added as a cathode electrolyte, and the pH was 3.08. The cathode electrolyte was added to the cathode chamber.

[0032] 30 mL of 2 M dilute sulfuric acid solution was added to the anode chamber.

[0033] A foamed copper electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0034] Stirring was started, and power was supplied at a current density of 50 mA / cm 2 at 50°C under normal pressure at a stirring speed of 500 r / min, and power was supplied for 4.6 h. Power supply was stopped, and the cathode electrolyte was subjected to diazotization titration, and the yield of amino-T acid was 45.38%.

[0035] Example 3

[0036] 5 mL of 30% by mass nitro-T acid aqueous solution was added to 24 mL of water, and 1 mL of 3 M dilute hydrochloric acid solution was further added as a cathode electrolyte, and the pH was 3.04. The cathode electrolyte was added to the cathode chamber.

[0037] 30 mL of 2 M dilute sulfuric acid solution was added to the anode chamber.

[0038] A foamed copper electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0039] Stirring was started, and power was supplied at a current density of 50 mA / cm 2 at 70°C under normal pressure at a stirring speed of 500 r / min, and power was supplied for 4.6 h. Power supply was stopped, and the cathode electrolyte was subjected to diazotization titration, and the yield of amino-T acid was 46.01%.

[0040] Example 4

[0041] 5 mL of 30% by mass nitro-T acid aqueous solution was added to 24 mL of water, and 1 mL of 3 M dilute hydrochloric acid solution was further added as a cathode electrolyte, and the pH was 3.12. The cathode electrolyte was added to the cathode chamber.

[0042] 30 mL of 2 M dilute sulfuric acid solution was added to the anode chamber.

[0043] A foamed nickel electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0044] Stirring was started, and power was supplied at a current density of 50 mA / cm 2, the stirring speed was 500 r / min at 70 °C under normal pressure, and the current was passed for 7 h. The current was stopped, and the cathode electrolyte was titrated by diazotization to obtain amino T acid with a yield of 44.16%.

[0045] Example 5

[0046] 5 mL of a 30% mass fraction nitro T acid aqueous solution was added to 24 mL of water, and then 1 mL of a 3M concentration dilute hydrochloric acid solution was added as a cathode electrolyte with a pH of 2.94. The cathode electrolyte was added to the cathode chamber.

[0047] 30 mL of a 2M concentration dilute sulfuric acid solution was added to the anode chamber.

[0048] A zinc electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0049] Stirring was started, and the power supply was turned on to pass the current at a current density of 50 mA / cm 2 , the stirring speed was 500 r / min at 50 °C under normal pressure, and the current was passed for 7 h. The current was stopped, and the cathode electrolyte was titrated by diazotization to obtain amino T acid with a yield of 39.59%.

[0050] Example 6

[0051] 5 mL of a 30% mass fraction nitro T acid aqueous solution was added to 24 mL of water, and then 1 mL of a 3M concentration dilute hydrochloric acid solution was added as a cathode electrolyte with a pH of 3.04. The cathode electrolyte was added to the cathode chamber.

[0052] 30 mL of a 2M concentration dilute sulfuric acid solution was added to the anode chamber.

[0053] A lead electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0054] Stirring was started, and the power supply was turned on to pass the current at a current density of 50 mA / cm 2 , the stirring speed was 500 r / min at 50 °C under normal pressure, and the current was passed for 7 h. The current was stopped, and the cathode electrolyte was titrated by diazotization to obtain amino T acid with a yield of 38.09%.

[0055] Example 7

[0056] 5 mL of a 30% mass fraction nitro T acid aqueous solution was added to 24 mL of water, and then 1 mL of a 3M concentration dilute hydrochloric acid solution was added as a cathode electrolyte with a pH of 3.01. The cathode electrolyte was added to the cathode chamber.

[0057] 30 mL of a 2M concentration dilute sulfuric acid solution was added to the anode chamber.

[0058] A foamed copper electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0059] Stirring was started and power was turned on for electrolysis at a current density of 20 mA / cm 2 at a temperature of 50°C, under normal pressure, with a stirring speed of 500 r / min, for 11.5 h. Power was stopped and the cathode electrolyte was titrated for diazotization, and the yield of amino T acid was 48.98%.

[0060] Example 8

[0061] 5 mL of a 30% mass fraction nitro T acid aqueous solution was added to 14 mL of water, and 10 mL of a 3 M concentration dilute hydrochloric acid solution was added as the cathode electrolyte, with a pH of 1.15. The cathode electrolyte was added to the cathode chamber.

[0062] 30 mL of a 2 M concentration dilute sulfuric acid solution was added to the anode chamber.

[0063] A foam copper electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0064] Stirring was started and power was turned on for electrolysis at a current density of 20 mA / cm 2 at a temperature of 50°C, under normal pressure, with a stirring speed of 500 r / min, for 9.2 h. Power was stopped and the cathode electrolyte was titrated for diazotization, and the yield of amino T acid was 42.14%.

[0065] Example 9

[0066] 5 mL of a 30% mass fraction nitro T acid aqueous solution was added to 25 mL of water as the cathode electrolyte, with a pH of 6.21. The cathode electrolyte was added to the cathode chamber.

[0067] 30 mL of a 2 M concentration dilute sulfuric acid solution was added to the anode chamber.

[0068] A foam copper electrode was used as the cathode, and a platinum sheet electrode was used as the anode.

[0069] Stirring was started and power was turned on for electrolysis at a current density of 50 mA / cm 2 at a temperature of 50°C, under normal pressure, with a stirring speed of 500 r / min, for 7 h. Power was stopped and the cathode electrolyte was titrated for diazotization, and the yield of amino T acid was 39.74%.

[0070] Example 10

[0071] 5 mL of a 30% mass fraction nitro T acid aqueous solution was added to 24 mL of water, and 1 mL of a 3 M concentration dilute hydrochloric acid solution was added as the cathode electrolyte, with a pH of 3.00. The cathode electrolyte was added to the cathode chamber.

[0072] 30 mL of 2 M dilute sulfuric acid solution was added to the anode chamber.

[0073] The cathode electrode was a copper foam electrode and the anode electrode was a platinum electrode.

[0074] Stirring was started and power was turned on for electrolysis. The current density was 20 mA / cm 2 , the temperature was 70 °C, the stirring speed was 500 r / min under normal pressure, and the electrolysis time was 11.5 h. The power was turned off and the cathode electrolyte was titrated for diazotization. The yield of amino T acid was 49.68%.

[0075] Example 11

[0076] 5 mL of 30% mass fraction nitro T acid aqueous solution was added to 24 mL of water, and 1 mL of 3 M dilute hydrochloric acid solution was added as the cathode electrolyte, with a pH of 3.07. The cathode electrolyte was added to the cathode chamber.

[0077] 30 mL of 2 M dilute sulfuric acid solution was added to the anode chamber.

[0078] The cathode electrode was a copper foam electrode and the anode electrode was a titanium coated electrode.

[0079] Stirring was started and power was turned on for electrolysis. The current density was 50 mA / cm 2 , the temperature was 50 °C, the stirring speed was 500 r / min under normal pressure, and the electrolysis time was 7.7 h. The power was turned off and the cathode electrolyte was titrated for diazotization. The yield of amino T acid was 46.57%.

[0080] Example 12

[0081] 5 mL of 30% mass fraction nitro T acid aqueous solution was added to 24 mL of water, and 1 mL of 3 M dilute hydrochloric acid solution was added as the cathode electrolyte, with a pH of 3.03. The cathode electrolyte was added to the cathode chamber.

[0082] 30 mL of 2 M dilute sulfuric acid solution was added to the anode chamber.

[0083] The cathode electrode was a copper foam electrode and the anode electrode was a graphite electrode.

[0084] Stirring was started and power was turned on for electrolysis. The current density was 50 mA / cm 2 , the temperature was 50 °C, the stirring speed was 500 r / min under normal pressure, and the electrolysis time was 9.2 h. The power was turned off and the cathode electrolyte was titrated for diazotization. The yield of amino T acid was 33.83%.

Claims

1. A method of electrochemically reducing a nitro-T acid, characterized by: The method is: The electrochemical reduction is carried out in a divided electrolysis device, which comprises an electrolytic cell body, a cathode, an anode and an ion membrane, the anode material is a platinum electrode, a titanium coated electrode or a graphite electrode, the cathode material is a foamed copper electrode, a foamed nickel electrode, a zinc electrode or a lead electrode, the ion membrane is a cation membrane, the ion membrane divides the electrolytic cell body into an anode tank and a cathode tank, the cathode electrolyte is an acid solution containing nitro-T acid, in the cathode electrolyte, the mass fraction of nitro-T acid is 7-8%, hydrochloric acid is added to adjust the pH of the cathode electrolyte to 2.8-3.2; the anode electrolyte is a 1-3M sulfuric acid solution; direct current is applied between the cathode and the anode for electrolysis, the electrolysis is constant current electrolysis, the current density is 20 mA / cm 2 ~50 mA / cm 2 , the electrolysis reaction temperature is 30-70℃, the reaction time is 4-12 h, nitro-T acid is reduced to generate amino-T acid, and oxygen is released at the anode.

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