Title of Invention

PROCESS FOR SYNTHESIZING 2,4-DIAMINO BENZENE SULFONIC ACID AND SALTS THEREOF

Abstract

A process for synthesizing 2, 4-diamino benzene sulfonic acid, which comprises the following step: reacting m-phenylenediamine and sulfuric acid or oleum in a solvent at the temperature of 140-250°C to obtain 2,4-diamino benzene sulfonic acid, said solvent being one or more solvents selected from inorganic solvent phosphoric acid or polyphosphoric acid and organic solvent having a boiling point above 140°C under the normal pressure. A preparation process of 2,4-diamino benzene sulfonate, which comprises the following steps: obtaining 2, 4-diamino benzene sulfonic acid by the above-mentioned process, then conducting the salt forming reaction to obtain 2, 4-diamino benzene sulfonate. The present invention can effectively resolve the environmental problem caused by large amount of sulfuric acid and high cost problem, together with high yield and quality.

Full Text

Specification Process for Synthesizing 2,4-diaminobenzene Sulfonic Acid And Salts Thereof Technical Field The present invention relates to a process for synthesizing 2,4-diaminobenzene sulfonic acid and salts thereof. Background Art 2,4-diaminobenzene sulfonic acid, also named m-phenylene diamine-4-sulfonic acid, has a structure as follows: 2,4-diaminobenzene sulfonic acid and salts thereof (especially its sodium salt) are used mainly as important intermediates for synthesizing dyes. Their derivative products have been widely used in industrial production and daily life. A conventional method for preparing 2,4-diaminobenzene sulfonic acid comprises reacting 2,4-dinitrochlorobenzene as the starting material with sodium bisulfite, followed by reduction. The drawbacks of this method include low yield, poor product quality and low production efficiency. Another method for preparing 2,4-diaminobenzene sulfonic acid as disclosed in the prior art (e.g. Japanese Patent Publication No. S57-48961 and Japanese Patent Publication No. H4-13657) comprises dissolving m-phenylene diamine as the starting material in sulfuric acid amounting to over 5 times by weight of the amount of m-phenylene diamine, followed by sulfonating m-phenylene diamine with fuming sulfuric acid or S03 gas as the sulfonating agent to obtain 2,4-diaminobenzene sulfonic acid as the final product. One drawback of this method is the need of a large amount of sulfuric acid which is in an amount of at least over 5 times or even more by weight of the amount of m-phenylene diamine. Since the sulfuric acid can only be expelled in the form of waste solution due to can not being subjected to effective recovery, this method leads to serious pollution to the environment while adds to the cost of the production of 2,4-diaminobenzene sulfonic acid. The other drawback of this method is the use of S03 gas as the sulfonating agent. It will render the process more complex to store, transport, utilize and recover the gas source of S03. Furthermore, safety constitutes another concern. Summary of the Invention The object of the invention is to provide a process for preparing 2,4-diaminobenzene sulfonic acid, which can solve the environment pollution problem in the prior art caused by using a large amount of sulfuric acid and the high cost problem. Moreover, the process has the advantages of short reaction route, simple procedure, and higher yield, product quality and manufacturing efficiency. After intensive research, the inventors of the invention have found that when 2,4-diaminobenzene sulfonic acid is prepared by sulfonating m-phenylene diamine with sulfuric acid or fuming sulfuric acid in a given solvent, the problem in the prior art that the use of a large amount of sulfuric acid results in environmental pollution and higher cost can be solved, and higher yield and product quality can be obtained. In the first aspect of the invention, a process for preparing 2,4-diaminobenzene sulfonic acid is provided, which comprises reacting m-phenylene diamine with sulfuric acid or fuming sulfuric acid in a solvent at a temperature in the range of 140-250 °C to give 2,4-diaminobenzene sulfonic acid, wherein the solvent is one or more solvents selected from inorganic solvents such as phosphoric acid, polyphosphoric acid and a combination thereof, and organic solvents having a boiling point of above 140 °C under normal pressure. In the second aspect of the invention, a process for preparing 2,4-diaminobenzene sulfonate is provided, which comprises obtaining 2,4-diaminobenzene sulfonic acid in accordance with the first aspect of the invention, then conducting the salification reaction to give 2,4-diaminobenzene sulfonate. In the forementioned synthesis processes, the organic solvent preferably has a boiling point in the range of 140-300°C under normal pressure. More preferably, the organic solvent is selected from one or more of the group consisting of aromatics or alkylaromatics or arylalkanes containing 8~20 carbon atoms, aromatics or alkylaromatics or arylalkanes containing 6~20 carbon atoms and substituted by halogen and/or nitro-group, acetophenone, saturated alkanes containing 9-30 carbon atoms, saturated alkanes containing 2~30 carbon atoms and substituted by halogen, cyclohexanone, cyclobutyl sulfone, butanedinitrile and adipic dinitrile. Particularly more preferably, the organic solvent is selected from one or more of the group consisting of xylene, trimethyl benzene, isopropyl benzene, isobutyl benzene, tert-butyl benzene, isopropyl biphenyl, naphthalene, methyl naphthalene, tetralin, diphenyl methane, di-p-tolyl methane, dimethylchlorobenzene, trimethylchlorobenzene, dichlorobenzene, trichlorobenzene, bromobenzene, chlorotoluene, dichlorotoluene, bromotoluene, dimethylbromobenzene, nitrobenzene, nitrotoluene, nitroethylbenzene, nitro-xylene, trimethylnitrobenzene, nitrochlorobenzene, acetophenone, nonane, undecane, paraffin, chloroparaffin, high-temperature kerosene, heat-conducting oil, tetrabromoethane, trichloropropane, tetrabromobutane, cyclohexanone, cyclobutyl sulfone, butanedinitrile and adipic dinitrile. In the forementioned methods, the weight ratio between the inorganic solvent and m-phenylene diamine is preferably in the range of 0.1:1-5:1, more preferably in the range of 0.2:1-1:1, still more preferably in the range of 0.3:1-0.8:1, and particularly more preferably in the range of 0.4:1-0.5:1. In the forementioned methods, the weight ratio between the organic solvent and m-phenylene diamine is preferably in the range of 0.1:1-30:1, more preferably in the range of 1:1-10:1, still more preferably in the range of 2:1-6:1, and particularly more preferably in the range of 3:1-5:1. In the forementioned methods, the weight ratio between m-phenylene diamine and sulfuric acid or fuming sulfuric acid is preferably in the range of 1:0.9-1: 4.5 based on 100% sulfuric acid, more preferably in the range of 1:1.2-1:3 based on 100% sulfuric acid, and particularly more preferably in the range of 1:1.5-1:2.4 based on 100% sulfuric acid. In the forementioned methods, the fuming sulfuric acid is preferably selected from those with S03 concentration greater than 0% but not greater than 70%. More preferably, the fuming sulfuric acid is selected from those with S03 concentration greater than 0% but not greater than 10%. Still more preferably, the fuming sulfuric acid is selected from those with S03 concentration greater than 0% but not greater than 5%. Particularly more preferably, the fuming sulfuric acid is selected from those with S03 concentration greater than 0% but not greater than 1%, for example, 0.1-1%. In the forementioned methods, the sulfuric acid is preferably selected from those sulfuric acids with concentration in the range of 0.1-100% or those fuming sulfuric acids with any concentration that may be diluted with water to form 0.1-100% sulfuric acid. More preferably, the sulfuric acid is selected from those with concentration in the range of 60-100%. Still more preferably, the sulfuric acid is selected from those with concentration in the range of 80-100%. Particularly more preferably, the sulfuric acid is selected from those with concentration in the range of 90-100%. In the forementioned processes, m-phenylene diamine and sulfuric acid or fuming sulfuric acid react at a temperature in the range of 160~210°C, wherein the organic solvent has a boiling point of above 160°C at atmospheric pressure(normal pressure). Particularly preferably, m-phenylene diamine and sulfuric acid or fuming sulfuric acid react at a temperature in the range of 170~200°C, wherein the organic solvent has a boiling point of above 170°C at atmospheric pressure. In the second aspect of the invention, the 2,4-diaminobenzene sulfonate is preferably sodium or potassium salt thereof. Detailed Description of the Invention The invention provides a process for preparing 2,4-diaminobenzene sulfonic acid by sulfonating m-phenylene diamine using sulfuric acid or fuming sulfuric acid in a solvent, which comprises reacting m-phenylene diamine and sulfuric acid or fuming sulfuric acid in the solvent at a temperature in the range of 140~250°C to give 2,4-diaminobenzene sulfonic acid, wherein the solvent is one or more solvents selected from inorganic solvents, such as phosphoric acid, polyphosphoric acid and a combination thereof, and organic solvents having a boiling point of above 140°C under normal pressure. The synthesis process may be represented as the reaction formula that follows: The invention also provides a synthesis process for preparing 2,4-diaminobenzene sulfonate, which comprises subjecting 2,4-diaminobenzene sulfonic acid as obtained above to salification reaction to give the desirable 2,4-diaminobenzene sulfonate. The salification reaction may be any reaction that can produce the desirable benzene sulfonate, as long as the reaction has no adverse influence on the invention. The solvents and conditions used for the salification reaction can be determined experientially by those skilled in the art. In the forementioned synthesis processes, the organic solvent preferably has a boiling point in the range of 140~300°C under normal pressure. More preferably, the organic solvent is selected from one or more of the group consisting of aromatics or alkylaromatics or arylalkanes containing 8-20 carbon atoms, aromatics or alkylaromatics or arylalkanes containing 6-20 carbon atoms and substituted by halogen and/or nitro-group, acetophenone, saturated alkanes containing 9-30 carbon atoms, saturated alkanes containing 2-30 carbon atoms and substituted by halogen, cyclohexanone, cyclobutyl sulfone, butanedinitrile and adipic dinitrile. Particularly more preferably, the organic solvent is selected from one or more of the group consisting of xylene, trimethyl benzene, isopropyl benzene, isobutyl benzene, tert-butyl benzene, isopropyl biphenyl, naphthalene, methyl naphthalene, tetralin, diphenyl methane, di-p-tolyl methane, dimethylchlorobenzene, trimethylchlorobenzene, dichlorobenzene, trichlorobenzene, bromobenzene, chlorotoluene, dichlorotoluene, bromotoluene, dimethylbromobenzene, nitrobenzene, nitrotoluene, nitroethylbenzene, nitro-xylene, trimethylnitrobenzene, nitrochlorobenzene, acetophenone, nonane, undecane, paraffin, chloroparaffin, high-temperature kerosene, heat-conducting oil, tetrabromoethane, trichloropropane, tetrabromobutane, cyclohexanone, cyclobutyl sulfone, butanedinitrile and adipic dinitrile. In the forementioned processes, the weight ratio between the inorganic solvent and m-phenylene diamine is preferably in the range of 0.1:1-5:1, more preferably in the range of 0.2:1-1:1, still more preferably in the range of 0.3:1-0.8:1, and particularly more preferably in the range of 0.4:1-0.5:1. In the forementioned processes, the weight ratio between the organic solvent and m-phenylene diamine is preferably in the range of 0.1:1-30:1, more preferably in the range of 1:1-10:1, still more preferably in the range of 2:1-6:1, and particularly more preferably in the range of 3:1-5:1. In the methods according to the invention, the inorganic solvent and the organic solvent may be used separately or as a mixture thereof. When a mixture of an inorganic solvent and an organic solvent is used, their dosages may be determined respectively with reference to the foregoing description concerning the dosages of the inorganic solvent and the organic solvent. For example, for on part by weight of m-phenylene diamine, 0.1-5 parts by weight of the inorganic solvent and 0.1-30 parts by weight of the organic solvent may be used, preferably 0.2-1 parts by weight of the inorganic solvent and 1—10 parts by weight of the organic solvent, still more preferably 0.3-0.8 parts by weight of the inorganic solvent and 2-6 parts by weight of the organic solvent, and particularly more preferably 0.4-0.5 parts by weight of the inorganic solvent and 3-5 parts by weight of the organic solvent. In the processes according to the invention, the sulfonating reaction is carried out at a temperature in the range of 140-250 °C, preferably in the range of 160-210 °C, and particularly more preferably in the range of 170-200 °C. The sulfuric acid used in herein refers to a sulfuric acid of any concentration or a fuming sulfuric acid of any concentration that is diluted to form a sulfuric acid of any concentration. For example, The sulfuric acid used in the invention may be a sulfuric acid having a concentration in the range of 0.1-100% or a fuming sulfuric acid having any concentration that is diluted to form a sulfuric acid having a concentration in the range of 0.1-100%. The sulfuric acid is more preferably a sulfuric acid having a concentration in the range of 60-100%, still more preferably in the range of 80-100%, and particularly more preferably in the range of 90-100%. The fuming sulfuric acid used in the processes according to the invention is preferably a fuming sulfuric acid with S03 concentration greater than 0% but not greater than 70%, for example, 0.1-70%. More preferably, the fuming sulfuric acid is selected from those with S03 concentration greater than 0% but not greater than 10%, for example, 0.1-10%. Still more preferably, the fuming sulfuric acid is selected from those with SO3 concentration greater than 0% but not greater than 5%, for example, 0.1-5%. Particularly more preferably, the fuming sulfuric acid is selected from those with S03 concentration greater than 0% but not greater than 1%, for example, 0.1-1%. As for the dosages of the reactants used in the invention, the weight ratio between m-phenylene diamine and sulfuric acid or fuming sulfuric acid is in the range of 1:0.9-1: 4.5 based on 100% sulfuric acid, more preferably in the range of 1:1.2-1:3 based on 100% sulfuric acid, and particularly more preferably in the range of 1:1.5-1:2.4 based on 100% sulfuric acid. If the dosages of the reactants are represented as molar ratio, the molar ratio between m-phenylene diamine and sulfuric acid or fuming sulfuric acid (based on 100% sulfuric acid) is in the range of 1:1-1:5, more preferably in the range of 1:1.3-1:3.3, and particularly more preferably in the range of 1:1.7-1:2.6. The main advantages of the invention include: (1) the environmental pollution problem in the prior art caused by using a large amount of sulfuric acid and the high cost problem can be avoided effectively by the synthesis process of the invention which prepares 2,4-diaminobenzene sulfonic acid by sulfonating m-phenylene diamine with sulfuric acid or fuming sulfuric acid in a given solvent, for this process can reduce significantly the amount of the sulfuric acid or the fuming sulfuric acid to be used, while the solvent used in the reaction can be recycled over and over; (2) the equipments and the processes for industrial production are simplified greatly due to the short reaction route and the simple procedure, which is considerably desirable from both ecological and economic point of view; (3) high yield and high production efficiency, as well as good product quality, for example, high product purity, can be achieved by the synthesis process for the invention. The invention will be further explained with reference to specific examples. It is to be understood that these examples are only used to clarify the invention without any intention to limit the scope of the invention. In the following examples, if no specific conditions are denoted for any given testing process, in general, either conventional conditions or conditions advised by manufacturers should be followed. Unless otherwise noted, all parts and percentages are based on weight. Example 1 300 g o-dichlorobenzene, 100 mL 98% sulfuric acid (184 g) (corresponding to 180 g 100% sulfuric acid or 1.84 mol 100% sulfuric acid) and 100 g 100% m-phenylene diamine (corresponding to 0.926 mol) were added into a reactor equipped with a condenser having an oil-water separator, and the temperature was raised to 175 °C. After 4 hours of reaction at 175-180 °C, the resultant mixture was cooled, and 400 mL water was added. The organic phase and the water phase were separated, wherein the organic phase could be used as the solvent for next batch of reaction, and the water phase was purified and decolorized to give 168.8 g 2,4-diaminobenzene sulfonic acid. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 95% (based on m-phenylene diamine). Example 2 30 g phosphoric acid, 155 g 98% sulfuric acid (corresponding to 150 g 100% sulfuric acid) and 100 g 100% m-phenylene diamine were added into a reactor, and the temperature was raised to 195°C. After 6 hours of reaction at 195-200 °C, the resultant mixture was cooled, and 400 mL water was added. The water phase was purified and decolorized to give 168.0 g 2,4-diaminobenzene sulfonic acid. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 95% (based on m-phenylene diamine). Example 3 The reaction was carried out in the same procedure as that of Example 2, except that 50 g phosphoric acid and 30 g polyphosphoric acid, i.e. H6P40i3, were used. 167 g 2,4-diaminobenzene sulfonic acid was obtained. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 94% (based on m-phenylene diamine). Example 4 200 g o-dichlorobenzene, 50 g phosphoric acid, 245 g 98% sulfuric acid (corresponding to 240 g 100% sulfuric acid) and 100 g 100% m-phenylene diamine were added into a reactor equipped with a condenser having an oil-water separator, and the temperature was raised to 175°C. After 4 hours of reaction at 175~180°C, the resultant mixture was cooled, and 400 mL water was added. The organic phase and the water phase were separated, wherein the organic phase could be used as the solvent for next batch of reaction, and the water phase was purified and decolorized to give 170 g 2,4-diaminobenzene sulfonic acid. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 95.7% (based on m-phenylene diamine). Example 5 700 g nitrobenzene, 260 g 100% sulfuric acid and 100 g 100% m-phenylene diamine were added into a reactor equipped with a condenser having an oil-water separator, and the temperature was raised to 210°C. After 4 hours of reaction at 210~215°C, the resultant mixture was cooled, and 400 mL water was added. The organic phase and the water phase were separated, wherein the organic phase could be used as the solvent for next batch of reaction, and the water phase was purified and decolorized to give 159.9 g 2,4-diaminobenzene sulfonic acid. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 90% (based on m-phenylene diamine). Example 6 500 g 1,3,5-trichlorobenzene, 120 g 1% fuming sulfuric acid (corresponding to 120 g 100% sulfuric acid) and 100 g 100% m-phenylene diamine were added into a reactor equipped with a condenser having an oil-water separator, and the temperature was raised to 170 °C. After 5 hours of reaction at 170-175 °C, the resultant mixture was cooled, and 400 mL water was added. The organic phase and the water phase were separated, wherein the organic phase could be used as the solvent for next batch of reaction, and the water phase was purified and decolorized to give 163.4 g 2,4-diaminobenzene sulfonic acid. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 92% (based on m-phenylene diamine). Example 7 150 g 1,3,5-trimethylbenzene, 194 g 85% sulfuric acid (corresponding to 165 g 100% sulfuric acid) and 100 g 100% m-phenylene diamine were added into a reactor equipped with a condenser having an oil-water separator, and the temperature was raised to 160 °C. After 6 hours of reaction at 160-165 °C, the resultant mixture was cooled, and 400 mL water was added. The organic phase and the water phase were separated, wherein the organic phase could be used as the solvent for next batch of reaction, and the water phase was purified and decolorized to give 158.1 g 2,4-diaminobenzene sulfonic acid. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 89% (based on m-phenylene diamine). Example 8 100 g undecane, 100 g nonane, 211 g 90% sulfuric acid (corresponding to 190 g 100% sulfuric acid) and 100 g 100% m-phenylene diamine were added into a reactor equipped with a condenser having an oil-water separator, and the temperature was raised to 150 °C. After 6 hours of reaction at 150-155 °C, the resultant mixture was cooled, and 400 mL water was added. The organic phase and the water phase were separated, wherein the organic phase could be used as the solvent for next batch of reaction, and the water phase was purified and decolorized to give 161.7 g 2,4-diaminobenzene sulfonic acid. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 91% (based on m-phenylene diamine). Example 9 2,4-diaminobenzene sulfonic acid as obtained in Example 1 was reacted with about 100 mL 30% sodium hydroxide at 35 °C. The product was purified to give 178.6 g sodium 2,4-diaminobenzene sulfonate. As white crystal, the resultant product had its chromatographic content determined to be 99% (determined by HPLC), and its chemical content determined to be 98% (determined by diazotization titration). The yield of the product was 90% (based on m-phenylene diamine). All references mentioned in the invention are incorporated herein by reference, as if each of them set forth independently. Moreover, it is to be understood that variations or modifications of the invention may be made by those skilled in the art after reading the foregoing teachings, and these equivalents will fall in the scope defined by the appended claims of the application. Claims 1. A process for preparing 2,4-diaminobenzene sulfonic acid, which comprises reacting m-phenylene diamine with sulfuric acid or fuming sulfuric acid in a solvent at a temperature in the range of 140—-250 °C to obtain 2,4-diaminobenzene sulfonic acid, wherein the solvent is one or more solvents selected from inorganic solvents selected from phosphoric acid, polyphosphoric acid and a combination thereof, and organic solvents having a boiling point of above 140 °C under normal pressure. 2. A process for preparing 2,4-diaminobenzene sulfonate, which comprises obtaining 2,4-diaminobenzene sulfonic acid in accordance with claim 1, then conducting a salification reaction to obtain 2,4-diaminobenzene sulfonate as desired. 3. The process of claim 1 or 2, wherein the organic solvent is an organic solvent having a boiling point in the range of 140-300 °C under normal pressure. 4. The process of claim 1 or 2, wherein the organic solvent is one or more solvents selected from the group consisting of aromatics or alkylaromatics or arylalkanes containing 8~20 carbon atoms, aromatics or alkylaromatics or arylalkanes containing 6~20 carbon atoms and substituted by halogen and/or nitro-group, acetophenone, saturated alkanes containing 9~30 carbon atoms, saturated alkanes containing 2~30 carbon atoms and substituted by halogen, cyclohexanone, cyclobutyl sulfone, butanedinitrile and adipic dinitrile. 5. The process of claim 4, wherein the organic solvent is one or more solvents selected from the group consisting of xylene, trimethyl benzene, isopropyl benzene, isobutyl benzene, tert-butyl benzene, isopropyl biphenyl, naphthalene, methyl naphthalene, tetralin, diphenyl methane, di-p-tolyl methane, dimethylchlorobenzene, trimethylchlorobenzene, dichlorobenzene, trichlorobenzene, bromobenzene, chlorotoluene, dichlorotoluene, bromotoluene, dimethylbromobenzene, nitrobenzene, nitrotoluene, nitroethylbenzene, nitroxylene, trimethylnitrobenzene, nitrochlorobenzene, acetophenone, nonane, undecane, paraffin, chloroparaffin, high-temperature kerosene, heat-conducting oil, tetrabromoethane, trichloropropane, tetrabromobutane, cyclohexanone, cyclobutyl sulfone, butanedinitrile and adipic dinitrile. 6. The process of claim 1 or 2, wherein the weight ratio between the inorganic solvent and m-phenylene diamine is in the range of 0.1:1-5:1, and the weight ratio between the organic solvent and m-phenylene diamine is in the range of 0.1:1-30:1. 7. The process of claim 6, wherein the weight ratio between the inorganic solvent and m-phenylene diamine is in the range of 0.2:1-1:1, and the weight ratio between the organic solvent and m-phenylene diamine is in the range of 1:1-10:1. 8. The process of claim 1 or 2, wherein the weight ratio between m-phenylene diamine and sulfuric acid or fuming sulfuric acid is in the range of 1:0.9-1: 4.5 based on 100% sulfuric acid. 9. The process of claim 1 or 2, wherein the fuming sulfuric acid is selected from those with S03 concentration greater than 0% but not greater than 70%. 10. The process of claim 1 or 2, wherein the sulfuric acid is selected from those sulfuric acids with concentration in the range of 0.1-100% or those fuming sulfuric acids with any concentration that is diluted with water to form 0.1-100% sulfuric acid. 11. The process of claim 1 or 2, wherein m-phenylene diamine and sulfuric acid or fuming sulfuric acid react at a temperature in the range of 160~210°C, and the organic solvent has a boiling point of above 160°C under normal pressure. A process for synthesizing 2, 4-diamino benzene sulfonic acid, which comprises the following step: reacting m-phenylenediamine and sulfuric acid or oleum in a solvent at the temperature of 140-250°C to obtain 2,4-diamino benzene sulfonic acid, said solvent being one or more solvents selected from inorganic solvent phosphoric acid or polyphosphoric acid and organic solvent having a boiling point above 140°C under the normal pressure. A preparation process of 2.4-diamino benzene sulfonate, which comprises the following steps: obtaining 2, 4-diamino benzene sulfonic acid by the above-men- tioned process, then conducting the salt forming reaction to obtain 2,4-diamino benzene sulfonate. The present invention can effectively resolve the environmental problem caused by large amount of sulfuric acid and high cost problem, together with high yield and quality.

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