Preparation method of 4-bromophenylhydrazine hydrochloride
By controlling the addition rate and temperature of sodium nitrite aqueous solution and optimizing the diazotization and reduction reaction conditions, the problems of long preparation cycle and low yield of 4-bromophenylhydrazine hydrochloride in the existing technology were solved, and efficient and high-purity preparation was achieved.
Patent Information
- Application Number
- CN202410729826.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-06-06
- Publication Date
- 2025-12-16
AI Technical Summary
Existing methods for preparing 4-bromophenylhydrazine hydrochloride have long reaction cycles, low product yields, and low production efficiency.
The diazotization and reduction reaction conditions were optimized by controlling the addition rate and temperature of sodium nitrite aqueous solution. This included adding sodium nitrite at 0–5°C, controlling the temperature between 0 and 5°C, and carrying out the reduction reaction at 80–85°C. Zinc powder or iron powder was added to improve the purity.
It shortens the diazotization and reduction reaction time, improves the yield and purity of 4-bromophenylhydrazine hydrochloride, and enhances production efficiency.
Abstract
Description
Technical Field
[0001] This invention relates to the field of organic synthesis technology, specifically to a method for preparing 4-bromophenylhydrazine hydrochloride. Background Technology
[0002] 4-Bromophenylhydrazine hydrochloride is an organic compound soluble in water, as well as in alcohols and ethers. It can be used as a reducing agent in organic synthesis, exhibiting high selectivity for reducing nitro compounds to amine groups. It is also used in the synthesis of dyes, pigments, and pesticides such as glyphosate.
[0003] Existing methods for preparing 4-bromophenylhydrazine hydrochloride involve reacting 4-bromophenylhydrazine with hydrochloric acid, typically by dissolving 4-bromophenylhydrazine in hydrochloric acid and then crystallizing it. However, these methods are time-consuming, have low product yields, and are inefficient. Therefore, there is an urgent need for a more efficient and pure method for preparing 4-bromophenylhydrazine hydrochloride. Summary of the Invention
[0004] (a) Technical problems to be solved
[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing 4-bromophenylhydrazine hydrochloride, solving at least one of the technical problems mentioned in the background art.
[0006] (II) Technical Solution
[0007] The technical solution adopted in this invention is:
[0008] A method for preparing 4-bromophenylhydrazine hydrochloride includes the following steps:
[0009] Step S1 Diazotization: 4-Bromoaniline and concentrated hydrochloric acid are mixed, and sodium nitrite aqueous solution is added under stirring. After the reaction, a reaction solution is obtained.
[0010] Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is completed, crystals precipitate and are filtered.
[0011] Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained.
[0012] During step S1, the diazotization process, the rate of adding sodium nitrite aqueous solution is controlled at 70-85 mL / min during stirring.
[0013] Preferably, in step S1 diazotization, sodium nitrite aqueous solution is added when the temperature is controlled at 0-5°C after mixing 4-bromoaniline and concentrated hydrochloric acid.
[0014] In step S1 diazotization, starting from the addition of sodium nitrite aqueous solution, the temperature is controlled to rise to 15 degrees, then lowered to 5 degrees under controlled temperature, and maintained at 0-5 degrees.
[0015] The temperature is controlled to rise at a rate of 1 degree Celsius per minute and to fall at a rate of 2 degrees Celsius per minute.
[0016] Preferably, in step S1 diazotization, the molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:2.3 to 3:1 to 1.2.
[0017] Preferably, in step S2, ammonium sulfite and concentrated hydrochloric acid are added at a molar ratio of 1:2 to 3.5:2.5 to 3 with 4-bromoaniline.
[0018] Preferably, the weight-to-volume ratio of the product obtained after filtration in step S2 in step S3 salt formation to concentrated hydrochloric acid is 2-3:4-5.
[0019] Preferably, in step S2, after adding concentrated hydrochloric acid and ammonium sulfite, the reaction is carried out at a controlled temperature of 80-85°C.
[0020] Preferably, zinc powder or iron powder is added and stirred after the reaction in step S2 reduction is completed.
[0021] Preferably, in step S2, zinc powder or iron powder is added in a weight ratio of 1:0.1 to 0.5 with 4-bromoaniline.
[0022] (III) Beneficial Effects
[0023] This invention provides a method for preparing 4-bromophenylhydrazine hydrochloride, which has the following advantages compared with the prior art:
[0024] 1. The present invention provides a method for preparing 4-bromophenylhydrazine hydrochloride. By controlling the addition rate of sodium nitrite, the rate of adding the sodium nitrite aqueous solution is controlled at 70-85 mL / min. This avoids excess nitrite in the reaction due to the rapid addition rate of sodium nitrite, which could lead to the decomposition of the diazonium salt. At the same time, it can reasonably shorten the reaction time of diazotization.
[0025] 2. The present invention provides a method for preparing 4-bromophenylhydrazine hydrochloride, wherein sodium nitrite is added at 0-5°C, the temperature is increased by one degree per minute until it reaches 15°C, then the temperature is decreased by two degrees per minute, and the reaction is maintained at approximately 5°C. Diazotization is an exothermic reaction, and diazonium salts are thermally unstable. Therefore, by reasonably controlling the temperature increase and decrease, and finally maintaining the reaction at 0-5°C, the reaction process can be effectively accelerated, the reaction time of diazotization can be shortened, and side reactions can be effectively avoided. Specific implementation methods
[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0027] To better understand the above technical solution, the following will provide a detailed explanation of the technical solution in conjunction with specific implementation methods:
[0028] This invention provides a method for preparing 4-bromophenylhydrazine hydrochloride, comprising the following steps:
[0029] Step S1 Diazotization: 4-Bromoaniline and concentrated hydrochloric acid are mixed, and sodium nitrite aqueous solution is added under stirring. After the reaction, a reaction solution is obtained.
[0030] Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is completed, crystals precipitate and are filtered.
[0031] Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained.
[0032] During step S1, the diazotization process, the rate of adding sodium nitrite aqueous solution is controlled at 70-85 mL / min during stirring.
[0033] If sodium nitrite is added too quickly, excess nitrite will occur during the reaction, leading to the decomposition of the diazonium salt. This results in a tar-like substance appearing on the liquid surface, accompanied by yellow fumes, which are nitrogen oxides, nitrogen gas, and irritating hydrochloric acid gas. The decomposition of the diazonium salt inevitably affects the product yield and prevents the attainment of satisfactory product purity. Conversely, slow addition of sodium nitrite results in a prolonged diazotization reaction time and low efficiency.
[0034] In one embodiment, during the diazotization step S1, sodium nitrite aqueous solution is added after 4-bromoaniline and concentrated hydrochloric acid are mixed and the temperature is controlled at 0-5°C.
[0035] In step S1 diazotization, starting from the addition of sodium nitrite aqueous solution, the temperature is controlled to rise to 15 degrees, then lowered to 5 degrees under controlled temperature, and maintained at 0-5 degrees.
[0036] The temperature is controlled to rise at a rate of 1 degree Celsius per minute and to fall at a rate of 2 degrees Celsius per minute.
[0037] During the diazotization reaction, sodium nitrite is added at a controlled temperature of 0–5°C. The temperature is then increased, followed by a decrease, raising the temperature by one degree per minute until it reaches 15°C. The temperature is then decreased by two degrees per minute, maintaining this temperature for approximately 5 minutes. Diazotization is an exothermic reaction, and diazonium salts are thermally unstable; therefore, it must be carried out under cooling conditions. The reaction temperature is generally set between 0 and 5°C. If the temperature is increased, the decomposition of the diazonium salt in water becomes more pronounced; if the temperature is too low, the reaction is too slow. These methods effectively accelerate the diazotization process while minimizing side reactions.
[0038] Specifically, in step S1 diazotization, the molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:2.3 to 3:1 to 1.2.
[0039] In step S2, ammonium sulfite and concentrated hydrochloric acid are added at a molar ratio of 1:2 to 3.5:2.5 to 3 with 4-bromoaniline. By reasonably controlling the proportion of raw materials, such as controlling the amount of concentrated hydrochloric acid, the decomposition reaction of the diazonium salt can be effectively inhibited.
[0040] Furthermore, in step S3, the weight-to-volume ratio of the product obtained after filtration in step S2 to concentrated hydrochloric acid is 2-3:4-5. Specifically, the concentrated hydrochloric acid used in steps S1 to S3 can be 37% concentrated hydrochloric acid.
[0041] Furthermore, in step S2, concentrated hydrochloric acid and ammonium sulfite are added, and the reaction is carried out at a controlled temperature of 80-85°C.
[0042] Furthermore, after the reduction reaction in step S2 is completed, zinc powder or iron powder is added and stirred. Specifically, zinc powder or iron powder is added at a weight ratio of 1:0.1 to 0.5 with 4-bromoaniline. After the diazo liquid reduction reaction, a small amount of zinc powder or iron powder is added to reduce any trace amounts of benzene nitro compounds that may be present in the reactants, thereby eliminating impurities in the phenylhydrazine product and improving the product's purity.
[0043] The following detailed explanation is provided with reference to specific embodiments:
[0044] Example 1
[0045] Step S1 Diazotization: 4-Bromoaniline and concentrated hydrochloric acid are mixed, and then sodium nitrite aqueous solution is added under stirring. The reaction yields a reaction solution. During stirring, the rate of addition of sodium nitrite aqueous solution is controlled at 80 mL / min. After mixing 4-bromoaniline and concentrated hydrochloric acid, the temperature is controlled at 0–5°C before adding sodium nitrite aqueous solution. From the start of adding sodium nitrite aqueous solution, the temperature is controlled to rise to 15°C, then controlled to drop to 5°C, and maintained at 0–5°C. The rate of temperature increase is controlled at 1°C per minute, and the rate of temperature decrease is controlled at 2°C per minute. The molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:2.5:1.1.
[0046] Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is complete, crystals precipitate and are filtered. Ammonium sulfite and concentrated hydrochloric acid are added at a molar ratio of 1:3.2:2.8 with 4-bromoaniline. The reaction is carried out at a controlled temperature of 80-85℃. After the reaction is complete, zinc powder is added at a weight ratio of 1:0.3 with 4-bromoaniline.
[0047] Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained. The weight-to-volume ratio of the product obtained after filtration in step S2 to concentrated hydrochloric acid is 2.5:4.5.
[0048] The final yield of 4-bromophenylhydrazine hydrochloride was 68%, and the purity was 99.3%. The reaction time for step S1, diazotization, was 40 min, and the reaction time for step S2, reduction, was 65 min.
[0049] Example 2
[0050] Step S1 Diazotization: 4-Bromoaniline and concentrated hydrochloric acid are mixed, and then sodium nitrite aqueous solution is added under stirring. The reaction yields a reaction solution. During stirring, the rate of addition of sodium nitrite aqueous solution is controlled at 70 mL / min. After mixing 4-bromoaniline and concentrated hydrochloric acid, the temperature is controlled at 0–5°C before adding sodium nitrite aqueous solution. From the start of adding sodium nitrite aqueous solution, the temperature is controlled to rise to 15°C, then controlled to drop to 5°C, and maintained at 0–5°C. The rate of temperature increase is controlled at 1°C per minute, and the rate of temperature decrease is controlled at 2°C per minute. The molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:2.3:1.
[0051] Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is complete, crystals precipitate and are filtered. Ammonium sulfite and concentrated hydrochloric acid are added at a molar ratio of 1:2:2.5 with 4-bromoaniline. The reaction is carried out at a controlled temperature of 80-85℃. After the reaction is complete, zinc powder is added at a weight ratio of 1:0.1 with 4-bromoaniline.
[0052] Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained. The weight-to-volume ratio of the product obtained after filtration in step S2 to concentrated hydrochloric acid is 2-3:4-5.
[0053] The final yield of 4-bromophenylhydrazine hydrochloride was 67%, and the purity was 99.2%. The reaction time for step S1, diazotization, was 40 min, and the reaction time for step S2, reduction, was 65 min.
[0054] Example 3
[0055] Step S1 Diazotization: 4-Bromoaniline and concentrated hydrochloric acid are mixed, and then sodium nitrite aqueous solution is added under stirring. The reaction yields a reaction solution. During stirring, the rate of addition of sodium nitrite aqueous solution is controlled at 85 mL / min. After mixing 4-bromoaniline and concentrated hydrochloric acid, the temperature is controlled at 0–5°C before adding sodium nitrite aqueous solution. From the start of adding sodium nitrite aqueous solution, the temperature is controlled to rise to 15°C, then controlled to drop to 5°C, and maintained at 0–5°C. The rate of temperature increase is controlled at 1°C per minute, and the rate of temperature decrease is controlled at 2°C per minute. The molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:3:1.2.
[0056] Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is complete, crystals precipitate and are filtered. Ammonium sulfite and concentrated hydrochloric acid are added in a molar ratio of 1:3.5:3 with 4-bromoaniline. The reaction is carried out at a controlled temperature of 80-85℃. After the reaction is complete, iron powder is added in a weight ratio of 1:0.5 with 4-bromoaniline.
[0057] Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained. The weight-to-volume ratio of the product obtained after filtration in step S2 to concentrated hydrochloric acid is 3:5.
[0058] The final yield of 4-bromophenylhydrazine hydrochloride was 67%, with a purity of 99.2%. The diazotization reaction time in step S1 was 45 min, and the reduction reaction time in step S2 was 70 min.
[0059] Example 4
[0060] Step S1 Diazotization: 4-Bromoaniline and concentrated hydrochloric acid are mixed, and then sodium nitrite aqueous solution is added under stirring. After the reaction, a reaction solution is obtained. During stirring, the rate of adding sodium nitrite aqueous solution is controlled at 80 mL / min. After mixing 4-bromoaniline and concentrated hydrochloric acid, the temperature is controlled at 0–5 °C, and then sodium nitrite aqueous solution is added. The molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:2.5:1.1.
[0061] Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is complete, crystals precipitate and are filtered. Ammonium sulfite and concentrated hydrochloric acid are added at a molar ratio of 1:3.2:2.8 with 4-bromoaniline. The reaction is carried out at a controlled temperature of 80-85℃. After the reaction is complete, zinc powder is added at a weight ratio of 1:0.3 with 4-bromoaniline.
[0062] Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained. The weight-to-volume ratio of the product obtained after filtration in step S2 to concentrated hydrochloric acid is 2.5:4.5.
[0063] The final yield of 4-bromophenylhydrazine hydrochloride was 56%, and the purity was 97.5%. The reaction time for step S1, diazotization, was 60 min, and the reaction time for step S2, reduction, was 70 min.
[0064] Example 5
[0065] Step S1 Diazotization: 4-Bromoaniline and concentrated hydrochloric acid are mixed, and then an aqueous solution of sodium nitrite is added under stirring. The reaction yields a reaction solution. After mixing 4-bromoaniline and concentrated hydrochloric acid, the temperature is controlled at 0–5°C, and then the aqueous solution of sodium nitrite is added. From the start of adding the aqueous solution of sodium nitrite, the temperature is controlled to rise to 15°C, then controlled to drop to 5°C, and maintained at 0–5°C. The rate of temperature increase is controlled at 1°C per minute, and the rate of temperature decrease is controlled at 2°C per minute. The molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:2.5:1.1.
[0066] Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is complete, crystals precipitate and are filtered. Ammonium sulfite and concentrated hydrochloric acid are added at a molar ratio of 1:3.2:2.8 with 4-bromoaniline. The reaction is carried out at a controlled temperature of 80-85℃. After the reaction is complete, zinc powder is added at a weight ratio of 1:0.3 with 4-bromoaniline.
[0067] Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained. The weight-to-volume ratio of the product obtained after filtration in step S2 to concentrated hydrochloric acid is 2.5:4.5.
[0068] The final yield of 4-bromophenylhydrazine hydrochloride was 53.8%, and the purity was 97.2%. The reaction time for step S1, diazotization, was 75 min, and the reaction time for step S2, reduction, was 75 min.
[0069] Example 6
[0070] Step S1 Diazotization: 4-Bromoaniline and concentrated hydrochloric acid are mixed, and then sodium nitrite aqueous solution is added under stirring. The reaction yields a reaction solution. During stirring, the rate of addition of sodium nitrite aqueous solution is controlled at 80 mL / min. After mixing 4-bromoaniline and concentrated hydrochloric acid, the temperature is controlled at 0–5°C before adding sodium nitrite aqueous solution. From the start of adding sodium nitrite aqueous solution, the temperature is controlled to rise to 15°C, then controlled to drop to 5°C, and maintained at 0–5°C. The rate of temperature increase is controlled at 1°C per minute, and the rate of temperature decrease is controlled at 2°C per minute. The molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:2.5:1.1.
[0071] Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is complete, crystals precipitate and are filtered. Ammonium sulfite and concentrated hydrochloric acid are added at a molar ratio of 1:3.2:2.8 with 4-bromoaniline. The reaction is carried out at a controlled temperature of 80-85℃.
[0072] Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained. The weight-to-volume ratio of the product obtained after filtration in step S2 to concentrated hydrochloric acid is 2.5:4.5.
[0073] The final yield of 4-bromophenylhydrazine hydrochloride was 67%, and the purity was 90.2%. The reaction time for step S1, diazotization, was 40 min, and the reaction time for step S2, reduction, was 60 min.
[0074] The embodiments 1-3 of the present invention effectively reduce the diazotization reaction time and the subsequent reduction reaction time by controlling the diazotization temperature and the addition rate of sodium nitrite aqueous solution.
[0075] In contrast, Example 4 only controlled the diazotization temperature and did not control the addition rate of sodium nitrite aqueous solution, resulting in a significantly increased diazotization reaction time compared to Examples 1-3.
[0076] In contrast, Example 4 only controlled the addition rate of sodium nitrite aqueous solution without controlling the nitridation temperature, resulting in a significantly increased diazotization reaction time compared to Examples 1-3.
[0077] However, in Example 6, no zinc powder or iron powder was added after the reduction in step S2, and the purity of the final product was significantly lower than that of Examples 1-3.
[0078] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0079] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for preparing 4-bromophenylhydrazine hydrochloride, characterized in that, Includes the following steps: step S1 diazotization: 4-bromoaniline and concentrated hydrochloric acid are mixed and then sodium nitrite aqueous solution is added under stirring. The reaction solution is obtained after the reaction. Step S2 Reduction: Concentrated hydrochloric acid and ammonium sulfite are added to the reaction solution obtained in step S1. After the reaction is completed, crystals precipitate and are filtered. Step S3 Salt formation: The product obtained after filtration in step S2 is dissolved in concentrated hydrochloric acid and stirred at 80-85°C until crystals precipitate. After filtration and drying, 4-bromophenylhydrazine hydrochloride is obtained. During step S1, the diazotization process, the rate of adding sodium nitrite aqueous solution is controlled at 70-85 mL / min during stirring.
2. The method for preparing 4-bromophenylhydrazine hydrochloride according to claim 1, characterized in that: In step S1 diazotization, after mixing 4-bromoaniline and concentrated hydrochloric acid, and controlling the temperature at 0-5°C, an aqueous solution of sodium nitrite is added.
3. The method for preparing 4-bromophenylhydrazine hydrochloride according to claim 1, characterized in that: In step S1 diazotization, starting from the addition of sodium nitrite aqueous solution, the temperature is controlled to rise to 15 degrees, then lowered to 5 degrees under controlled temperature, and maintained at 0-5 degrees. The temperature is controlled to rise at a rate of 1 degree Celsius per minute and to fall at a rate of 2 degrees Celsius per minute.
4. The method for preparing 4-bromophenylhydrazine hydrochloride according to claim 1, characterized in that: In step S1, during diazotization, the molar ratio of 4-bromoaniline, concentrated hydrochloric acid, and sodium nitrite is 1:2.3 to 3:1 to 1.
2.
5. The method for preparing 4-bromophenylhydrazine hydrochloride according to claim 1, characterized in that: In step S2, ammonium sulfite and concentrated hydrochloric acid are added at a molar ratio of 1:2 to 3.5:2.5 to 3 with 4-bromoaniline.
6. The method for preparing 4-bromophenylhydrazine hydrochloride according to claim 1, characterized in that: In step S3, the product obtained after filtration in step S2 has a weight-to-volume ratio of 2-3:4-5 with concentrated hydrochloric acid.
7. The method for preparing 4-bromophenylhydrazine hydrochloride according to claim 1, characterized in that: In step S2, concentrated hydrochloric acid and ammonium sulfite are added for reduction, and the reaction is carried out at a controlled temperature of 80-85°C.
8. The method for preparing 4-bromophenylhydrazine hydrochloride according to claim 1, characterized in that: After the reaction in step S2 is completed, zinc powder or iron powder is added and stirred.
9. The method for preparing 4-bromophenylhydrazine hydrochloride according to claim 8, characterized in that: In step S2, zinc powder or iron powder is added at a weight ratio of 1:0.1 to 0.5 with 4-bromoaniline.