A process for the preparation of 3,5-dibromo-o-aminobenzaldehyde

Abstract

This invention discloses a method for preparing 3,5-dibromo-o-aminobenzaldehyde, belonging to the field of pharmaceutical intermediate synthesis technology. The method includes a reduction step, a bromination step, and a purification step. In the reduction step, o-nitrobenzaldehyde is used as raw material, and is obtained by iron powder reduction, toluene extraction, and dilute sulfuric acid back-extraction to obtain an aqueous solution of o-aminobenzaldehyde sulfate. In the bromination step, a hydrogen peroxide and hydrobromic acid system is used for the bromination reaction to obtain a crude product and a centrifuged acid mother liquor. The centrifuged acid mother liquor is decolorized, concentrated, and the dilute sulfuric acid is recovered and reused in the reduction step. In the purification step, the crude product is dissolved in acetone, crystallized, and dried to obtain a refined product. The acetone mother liquor is decolorized and subjected to multi-stage distillation to recover acetone for recycling. This invention achieves the recycling of dilute sulfuric acid and acetone, significantly reducing waste emissions, lowering production costs, and improving product yield and purity. It has the advantages of being green, environmentally friendly, economical, and efficient, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of pharmaceutical intermediate synthesis technology, specifically relating to a method for preparing 3,5-dibromo-o-aminobenzaldehyde. Background Technology

[0002] 3,5-Dibromo-o-aminobenzaldehyde is a key intermediate in the synthesis of the expectorant ambroxol hydrochloride. Its traditional synthetic method typically uses o-nitrobenzaldehyde as a raw material, which is reduced with iron powder to obtain o-aminobenzaldehyde, followed by a bromination reaction to introduce two bromine atoms. There are many existing production processes for 3,5-dibromo-o-aminobenzaldehyde. For example, Chinese Patent Publication No. CN118851924A discloses a process for preparing 3,5-dibromo-o-aminobenzaldehyde, which includes the following steps: an organic solution of o-nitrobenzaldehyde is stirred and reacted under controlled temperature and pressure in the presence of a metal catalyst and hydrogen gas; after the reaction is completed, the pressure is reduced, the filtrate is steam distilled, the distilled components are condensed, and the organic phase is extracted with an organic solvent. After the organic solvent is removed by distillation, o-aminobenzaldehyde is obtained; o-aminobenzaldehyde is dissolved in an organic solvent, hydrogen peroxide is added and mixed evenly, potassium bromide hydrobromic acid solution is added dropwise, and the mixture is heated to carry out a bromination reaction; after the reaction is completed, the pH value of the reaction solution is adjusted, the filtrate is filtered, the organic layer is retained after separation, and the organic solvent is removed by distillation to obtain a crude product; the crude product is added to an organic solvent and heated to dissolve the crude product, filtered and frozen, and crystals are precipitated to obtain the target product. During the reduction reaction, adding a small amount of iron powder during stirring improves the yield and reduces byproducts. For example, Chinese Patent Publication No. CN113444004B discloses a process for producing 3,5-dibromo-o-aminobenzaldehyde. Iron powder and hydrochloric acid are mixed, followed by the addition of an extractant and o-nitrodibromobenzyl. After the reaction is complete, the pH is adjusted to 7-9, and the mixture is filtered to obtain an o-aminodibromobenzyl extract reaction solution. Sulfuric acid is added to the aforementioned reaction solution, and after stirring, the mixture is separated to obtain an o-aminodibromobenzyl sulfuric acid reaction solution. Hydrobromic acid is added to the aforementioned sulfuric acid reaction solution, and bromine source and / or oxidant are added dropwise, controlling the monobromine content to ≤0.2%. Chloroform is added to obtain a 3,5-dibromo-o-aminodibromobenzyl organic solution. Dimethylamine aqueous solution and sodium bicarbonate are added to the aforementioned organic solution. After the reaction is complete, the mixture is separated to obtain a 3,5-dibromo-o-aminobenzaldehyde chloroform reaction solution. The aforementioned chloroform reaction solution is concentrated, purified, and decolorized to obtain 3,5-dibromo-o-aminobenzaldehyde. The method described in this application can be used for the industrial synthesis of 3,5-dibromo-o-aminobenzaldehyde and can also utilize the nitro waste generated during the production of o-nitrobenzaldehyde.

[0003] However, existing processes have the following problems: the reduction process generates a large amount of phenol-containing wastewater, resulting in high treatment costs; the bromination reaction uses bromine or bromides, leading to poor atom economy and the generation of bromine-containing waste acid; the refining process consumes a large amount of solvent with low recovery rates; and the overall process generates a large amount of waste gas, wastewater, and solid waste, placing significant environmental pressure on the industry. Therefore, developing an efficient, environmentally friendly, and resource-recycling method for preparing 3,5-dibromo-o-aminobenzaldehyde has significant industrial application value. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing 3,5-dibromo-o-aminobenzaldehyde. This method optimizes the reduction, bromination, and purification processes, realizes the recycling of the mother liquor acid and the multi-stage recovery of acetone solvent, significantly reduces the discharge of waste, lowers production costs, and improves product yield and purity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing 3,5-dibromo-o-aminobenzaldehyde, comprising the following steps: (1) Reduction process: o-nitrobenzaldehyde is reduced by iron powder to generate o-aminobenzaldehyde. The reaction solution is filtered to separate the iron residue. The filtrate is extracted with toluene. The extract is back-extracted with dilute sulfuric acid to obtain an aqueous solution of o-aminobenzaldehyde sulfate. (2) Bromination process: The aqueous solution of o-aminobenzaldehyde sulfate obtained in step (1) is mixed with hydrobromic acid, and hydrogen peroxide is added dropwise to carry out the bromination reaction. The reaction solution is separated by centrifugation to obtain crude 3,5-dibromo-o-aminobenzaldehyde and centrifuged acid mother liquor. The centrifuged acid mother liquor is recovered. (3) Refining process: Crude 3,5-dibromo-o-aminobenzaldehyde is dissolved in acetone, crystallized, washed and dried to obtain refined product; In step (2), the centrifuged acid mother liquor is decolorized and vacuum concentrated to recover dilute sulfuric acid, which is then returned to step (1) for back-extraction.

[0006] Preferably, the reduction process in step (1) specifically involves: adding water, iron powder, and o-nitrobenzaldehyde to a reduction reactor, adding hydrochloric acid with a concentration of 25-30%, heating to 70-75°C and maintaining the temperature for 2.5-3.5 hours, separating the filtrate containing o-aminobenzaldehyde by secondary pressure filtration after the reaction, thoroughly soaking and washing the iron slag with hot water at 80-90°C, combining the washing liquid with the filtrate and pressing it into an extraction reactor to fully mix with the toluene pre-stored in the extraction reactor, lowering the temperature in the extraction reactor to 15-20°C, letting it stand for 25-30 minutes, turning on the automatic separator to separate the heavy phase aqueous layer into a water receiving tank with an oil-separation function, while the mixture of the light phase toluene and o-aminobenzaldehyde remains in the extraction reactor, and then transferring it to the extraction reactor. Sulfuric acid with a concentration of 14-16% is pumped into the reaction vessel. The extraction vessel is stirred and frozen to ensure thorough mixing so that o-aminobenzaldehyde and dilute sulfuric acid form a salt. After standing for 25-30 minutes, the automatic separator is turned on. The o-aminobenzaldehyde sulfate solution is automatically separated into layers and transferred to the receiving tank. The solution is then pumped into a transfer tank for freezing and storage as the main raw material for the bromination reaction. The toluene in the upper layer remaining in the extraction vessel is washed with fresh water and stirred. After standing, the layers are separated again. The lower water layer is discharged into a high COD wastewater storage tank after passing through an oil separator receiving tank. The upper toluene layer remains in the extraction vessel for use in the next batch of extraction. The mass ratio of water, iron powder, o-nitrobenzaldehyde, hydrochloric acid, toluene, and sulfuric acid is 9-11:2-4:1-3:0.2-0.4:5:5.

[0007] Preferably, the bromination reaction in step (2) is specifically as follows: an aqueous solution of o-aminobenzaldehyde sulfate is mixed with hydrobromic acid of 45-48% concentration, the temperature is lowered to 8-10℃, hydrogen peroxide of 25-28% concentration is slowly added dropwise, the dropwise rate is controlled by temperature interlock, the reaction temperature is maintained at 20-25℃, and after the conversion rate of o-aminobenzaldehyde reaches more than 99%, the temperature is lowered to 12-15℃, and the bromination reaction is completed. The mass ratio of the aqueous solution of o-aminobenzaldehyde sulfate, hydrobromic acid and hydrogen peroxide is 3-5:2-4:1.

[0008] Preferably, the method for recovering centrifuged acid mother liquor in step (2) is as follows: after collecting the centrifuged mother liquor, add concentrated sulfuric acid to adjust the concentration, add activated carbon to decolorize at room temperature for 2-3 hours, filter to remove activated carbon, concentrate the filtrate under vacuum degree ≤-0.09MPa, remove the fraction below 60℃, and when the sulfuric acid concentration in the reactor reaches 13-16% and the hydrogen bromide concentration reaches 4-6%, cool to below 30℃ to obtain recovered dilute sulfuric acid.

[0009] Preferably, the crude product dissolution and crystallization in step (3) specifically involves: adding acetone with a concentration of 93-96% to a dissolution vessel, adding crude 3,5-dibromo-o-aminobenzaldehyde, heating to 55-58°C and refluxing for 2-2.5 hours, then pressing it into a crystallization vessel with nitrogen gas, freezing the crystallization vessel to 4-6°C, centrifuging and discharging the material, condensing the waste nitrogen and a small amount of acetone volatilized from the crystallization vessel through its own condenser and then discharging it into the tail gas treatment facility, washing the crystallized 3,5-dibromo-o-aminobenzaldehyde with 90-92% acetone, and drying it, and drying the centrifuged filter cake to obtain refined 3,5-dibromo-o-aminobenzaldehyde, combining the centrifugation mother liquor and washing liquid for collection and recovery, and the mass ratio of crude 3,5-dibromo-o-aminobenzaldehyde to acetone is 3-7:14-16.

[0010] Preferably, the method for recovering the centrifugal mother liquor and washing liquid is as follows: the collected acetone centrifugal mother liquor and washing liquid are added to activated carbon, decolorized at 45-55℃ for 1-2 hours, filtered by pressure, and the filtrate enters the acetone recovery kettle. The acetone is recovered by distillation at atmospheric pressure to 50-60℃. The temperature of the first-stage condenser outlet is controlled to be ≤40℃ and the temperature of the second-stage condenser outlet is controlled to be ≤25℃. The recovered acetone is recycled. After accumulating six batches of continuous distillation in the distillation kettle, the remaining liquid in the kettle is cooled to 25-30℃, centrifuged and dried. The filter cake is washed with acetone and then dried. The finished filter cake is sent for drying to obtain 3,5-dibromo-o-aminobenzaldehyde. The centrifuged liquid is subjected to a second distillation. The acetone recovered by the second distillation is low-boiling acetone. The low-boiling acetone is used for centrifugal washing in the acetone centrifugal mother liquor recovery process after a third distillation.

[0011] Preferably, the drying step in step (3) is as follows: the wet refined 3,5-dibromo-o-aminobenzaldehyde obtained after centrifugation is added to a double cone rotary vacuum dryer, the hot water temperature is controlled at 45-50℃, the vacuum degree is ≤-0.09MPa, the drying is carried out for 2-3 hours, and the material is discharged at 30-35℃ to obtain refined 3,5-dibromo-o-aminobenzaldehyde.

[0012] Preferably, the acetone volatilized during the drying process in step (3) is condensed into liquid and enters a vacuum buffer tank for low-concentration acetone recovery and reuse.

[0013] Compared with the prior art, the present invention has the following advantages: In the reduction process of this invention, the iron slag is treated as general solid waste after being washed with hot water to recover the product, thus reducing the amount of hazardous waste generated; the dilute sulfuric acid back-extraction solution is obtained from the bromination process to recover acid, realizing the recycling of acid and reducing the consumption of sulfuric acid and hydrogen bromide. The bromination process of this invention uses a hydrogen peroxide / hydrobromic acid system to replace bromine, avoiding the risks of using and storing bromine. The reaction has good selectivity and few by-products. The centrifuged mother liquor is decolorized and concentrated to recover dilute sulfuric acid and hydrogen bromide, which are then returned to the reduction process for reuse, realizing the recycling of bromine resources and significantly reducing raw material costs. In the refining process of this invention, the acetone mother liquor is decolorized and recovered through multi-stage distillation to obtain acetone of different purities for reuse, with a total acetone recovery rate of over 95%; the acetone in the drying exhaust gas is recovered through condensation and water absorption, reducing VOC emissions. The method of this invention operates in a closed system throughout the entire process, reducing the volatilization of organic solvents. The exhaust gas is purified by a treatment system, resulting in a significant reduction in waste emissions and meeting the requirements of green chemistry. By optimizing the reaction conditions of each step and the solvent recovery system, the total product yield can reach over 85%, with a purity ≥99.5%, making it suitable for large-scale industrial production. Detailed Implementation

[0014] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and 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. Example

[0015] A method for preparing 3,5-dibromo-o-aminobenzaldehyde includes the following steps: (1) Reduction process: In the reduction reactor, add 500 kg of water, start stirring, add 200 kg of iron powder and 150 kg of o-nitrobenzaldehyde, and add 20 kg of 30% hydrochloric acid dropwise from the high-level tank. Heat to 75°C and keep the temperature for 3 hours. After the o-nitrobenzaldehyde is completely converted, filter the reaction material through a stainless steel filter press. Wash the filter cake with 150 kg of 90°C hot water. Combine the washing liquid with the filtrate. Collect the iron slag as general solid waste. Transfer the combined filtrate to the extraction reactor, add 250 kg of toluene, stir and cool to 20°C, and let stand for 30 minutes to separate the layers. Send the aqueous phase to high COD wastewater treatment. Add 250 kg of dilute sulfuric acid to the extraction reactor, stir to form salt, let stand to separate the layers. Transfer the lower layer of o-aminobenzaldehyde sulfate aqueous solution to a transfer tank for frozen storage for bromine substitution. Wash the upper layer of toluene with water and recycle it.

[0016] (2) Bromination process: Add the above-mentioned aqueous solution of o-aminobenzaldehyde sulfate to the bromination reactor, add 200 kg of 48% hydrobromic acid, cool to 10°C, and begin adding 150 kg of 27% hydrogen peroxide dropwise. Control the dropping rate through temperature interlocking, maintain the reaction temperature at 25°C, and complete the dropping in about 4 hours. If the conversion rate of o-aminobenzaldehyde is >99%, cool to 15°C. Place the bromination solution into a fully sealed centrifuge for centrifugation. Wash the filter cake with fresh water until neutral to obtain crude 3,5-dibromo-o-aminobenzaldehyde. Collect the washing wastewater and neutralize it. Collect the centrifugation mother liquor (dilute sulfuric acid) into an acid-adjusting reactor, add 98% concentrated sulfuric acid, add 4 kg of activated carbon, decolorize at room temperature for 2 hours, and remove carbon by pressure filtration. The filtrate enters a concentration vessel and is concentrated under vacuum at a vacuum degree of -0.095 MPa to remove the fraction below 60°C. When the sulfuric acid concentration in the vessel reaches 15% and the hydrogen bromide concentration reaches 5%, it is cooled to below 30°C to obtain recovered dilute sulfuric acid for use in the reduction process.

[0017] (3) Refining process: Add 675 kg of 95% acetone to the dissolving kettle, add the above wet crude product, heat to 56°C and reflux for 2 hours to dissolve, pressurize with nitrogen into the crystallization kettle, cool to 5°C and crystallize for 2 hours, and centrifuge to separate. Wash the filter cake with 90% acetone, spin dry to obtain wet refined product, and send to dry; combine the centrifugal mother liquor and washing liquid for collection. Add 4 kg of activated carbon to the combined acetone mother liquor, decolorize at 50°C for 1 hour, filter by pressure and enter the acetone recovery kettle. Recover acetone by atmospheric pressure heating distillation, control the first-stage condenser outlet ≤40°C and the second-stage condenser outlet ≤25°C, recover acetone, and recycle. After six batches of continuous distillation in the distillation kettle, cool the remaining liquid in the kettle to 30°C, centrifuge to separate the solid (the crude product is returned to refining), and the liquid enters the low-boiling acetone recovery kettle for secondary distillation to recover low-boiling acetone. After three distillations, it is used for centrifugal washing. The distillation residue is disposed of as hazardous waste. The wet concentrate was added to a double-cone rotary vacuum dryer, with the hot water temperature controlled at 50℃ and the vacuum degree at -0.09MPa. Drying was carried out for 2 hours, followed by cooling to 30℃ before discharge, yielding 260 kg of 3,5-dibromo-o-aminobenzaldehyde concentrate. Acetone volatilized during the drying process was recovered by condensation, and the absorbent liquid from the water jet pump was periodically discharged into a high-COD wastewater storage tank.

[0018] Testing showed that the 3,5-dibromo-o-aminobenzaldehyde obtained in this example had a purity of 99.72%, a total yield of 86.3%, an acetone recovery rate of 96%, a dilute sulfuric acid recovery and reuse rate of over 90%, and a wastewater discharge reduction of over 70%. Example 2

[0019] A method for preparing 3,5-dibromo-o-aminobenzaldehyde includes the following steps: (1) Reduction process: In the reduction reactor, add 500 kg of water, start stirring, add 150 kg of iron powder and 100 kg of o-nitrobenzaldehyde, and add 15 kg of 30% hydrochloric acid dropwise from the high-level tank. Heat to 75°C and keep the temperature for 3 hours. After the o-nitrobenzaldehyde is completely converted, filter the reaction material through a stainless steel filter press. Wash the filter cake with 150 kg of 90°C hot water. Combine the washing liquid with the filtrate. Collect the iron slag as general solid waste. Transfer the combined filtrate to the extraction reactor, add 250 kg of toluene, stir and cool to 20°C, and let stand for 30 minutes to separate the layers. Send the aqueous phase to high COD wastewater treatment. Add 250 kg of dilute sulfuric acid to the extraction reactor, stir to form salt, let stand to separate the layers. Transfer the lower layer of o-aminobenzaldehyde sulfate aqueous solution to a transfer tank for frozen storage for bromine substitution. Wash the upper layer of toluene with water and recycle it.

[0020] (2) Bromination process: Add the above-mentioned o-aminobenzaldehyde sulfate aqueous solution to the bromination reactor, add 300 kg of 48% hydrobromic acid, cool to 10°C, and start adding 100 kg of 27% hydrogen peroxide dropwise. Control the dropping rate through temperature interlocking, maintain the reaction temperature at 25°C, and complete the dropping in about 4 hours. If the conversion rate of o-aminobenzaldehyde is >99%, cool to 15°C. Place the bromination solution into a fully sealed centrifuge for centrifugation. Wash the filter cake with fresh water until neutral to obtain crude 3,5-dibromo-o-aminobenzaldehyde. Collect the washing wastewater and neutralize it. Collect the centrifugation mother liquor (dilute sulfuric acid) into an acid-adjusting reactor, add 98% concentrated sulfuric acid, add 4 kg of activated carbon, decolorize at room temperature for 2 hours, and filter to remove carbon. The filtrate enters a concentration vessel and is concentrated under vacuum at a vacuum degree of -0.095 MPa to remove the fraction below 60°C. When the sulfuric acid concentration in the vessel reaches 15% and the hydrogen bromide concentration reaches 5%, it is cooled to below 30°C to obtain recovered dilute sulfuric acid for use in the reduction process.

[0021] (3) Refining process: Add 600 kg of 95% acetone to the dissolving kettle, add the above wet crude product, heat to 56°C and reflux for 2 hours to dissolve, pressurize with nitrogen into the crystallization kettle, cool to 5°C and crystallize for 2 hours, then centrifuge. Wash the filter cake with 100 kg of 90% acetone, spin dry to obtain wet refined product, and send to dry; combine the centrifugal mother liquor and washing liquid for collection. Add 4 kg of activated carbon to the combined acetone mother liquor, decolorize at 50°C for 1 hour, filter by pressure and enter the acetone recovery kettle. Recover acetone by atmospheric pressure heating distillation, control the first-stage condenser outlet ≤40°C and the second-stage condenser outlet ≤25°C, recover acetone, and recycle. After six batches of continuous distillation in the distillation kettle, cool the remaining liquid in the kettle to 30°C, centrifuge to separate the solid, and enter the low-boiling acetone recovery kettle for secondary distillation to recover low-boiling acetone. After three distillations, it is used for centrifugal washing, and the distillation residue is disposed of as hazardous waste. The wet concentrate was added to a double-cone rotary vacuum dryer, with the hot water temperature controlled at 50℃ and the vacuum degree at -0.09MPa. Drying was carried out for 2 hours, followed by cooling to 30℃ before discharge, yielding 172 kg of 3,5-dibromo-o-aminobenzaldehyde concentrate. Acetone volatilized during the drying process was recovered by condensation, and the absorbent liquid from the water jet pump was periodically discharged into a high-COD wastewater storage tank.

[0022] Testing showed that the 3,5-dibromo-o-aminobenzaldehyde obtained in this example had a purity of 99.70%, a total yield of 86.1%, an acetone recovery rate of 95%, a dilute sulfuric acid recovery and reuse rate of over 90%, and a wastewater discharge reduction of over 70%.

[0023] A method for preparing 3,5-dibromo-o-aminobenzaldehyde includes the following steps: (1) Reduction process: In the reduction reactor, add 550 kg of water, start stirring, add 200 kg of iron powder and 150 kg of o-nitrobenzaldehyde, and add 20 kg of 30% hydrochloric acid dropwise from the high-level tank. Heat to 75°C and keep the reaction at that temperature for 3 hours. After the o-nitrobenzaldehyde is completely converted, filter the reaction material through a stainless steel filter press. Wash the filter cake with 150 kg of 90°C hot water. Combine the washing liquid with the filtrate. Collect the iron slag as general solid waste. Transfer the combined filtrate to the extraction reactor, add 250 kg of toluene, stir and cool to 20°C, and let stand for 30 minutes to separate the layers. Send the aqueous phase to high COD wastewater treatment. Add 250 kg of dilute sulfuric acid to the extraction reactor, stir to form salt, let stand to separate the layers. Transfer the lower layer of o-aminobenzaldehyde sulfate aqueous solution to a transfer tank for frozen storage for bromine substitution. Wash the upper layer of toluene with water and then recycle it.

[0024] (2) Bromination process: Add the above-mentioned o-aminobenzaldehyde sulfate aqueous solution to the bromination reactor, add 200 kg of 48% hydrobromic acid, cool to 10°C, and start adding 100 kg of 27% hydrogen peroxide dropwise. Control the dropwise addition rate through temperature interlocking, maintain the reaction temperature at 25°C, and complete the addition in about 4 hours. If the conversion rate of o-aminobenzaldehyde is >99%, cool to 15°C. Place the bromination solution into a fully sealed centrifuge for centrifugation. Wash the filter cake with fresh water until neutral to obtain crude 3,5-dibromo-o-aminobenzaldehyde. Collect the washing wastewater and neutralize it. Collect the centrifugation mother liquor (dilute sulfuric acid) into an acid-adjusting reactor, add 98% concentrated sulfuric acid, add 4 kg of activated carbon, decolorize at room temperature for 2 hours, and filter to remove carbon. The filtrate enters a concentration vessel and is concentrated under vacuum at a vacuum degree of -0.095 MPa to remove the fraction below 60°C. When the sulfuric acid concentration in the vessel reaches 15% and the hydrogen bromide concentration reaches 5%, it is cooled to below 30°C to obtain recovered dilute sulfuric acid for use in the reduction process.

[0025] (3) Refining process: Add 650 kg of 95% acetone to the dissolving kettle, add the above wet crude product, heat to 56°C and reflux for 2 hours to dissolve, pressurize with nitrogen into the crystallization kettle, cool to 5°C and crystallize for 2 hours, centrifuge to separate, wash the filter cake with 100 kg of 90% acetone, spin dry to obtain wet refined product, and send to dryer; combine the centrifugation mother liquor and washing liquid for collection. Add 4 kg of activated carbon to the combined acetone mother liquor, decolorize at 50°C for 1 hour, filter by pressure and enter the acetone recovery kettle. Acetone was recovered by atmospheric pressure heating distillation, with the temperature controlled at ≤40℃ at the primary condenser outlet and ≤25℃ at the secondary condenser outlet. The recovered acetone was recycled. After six batches of continuous distillation in the distillation vessel, the remaining liquid was cooled to 30℃, and the solids were separated by centrifugation. The liquid was then fed into a low-boiling acetone recovery vessel for secondary distillation to recover low-boiling acetone. After a third distillation, the liquid was used for centrifugal washing. The distillation residue was treated as hazardous waste. The wet concentrate was added to a double-cone rotary vacuum dryer, with the hot water temperature controlled at 50℃ and the vacuum at -0.09MPa, and dried for 2 hours. After cooling to 30℃, the product was discharged, yielding 257 kg of 3,5-dibromo-o-aminobenzaldehyde concentrate. Acetone volatilized during the drying process was recovered by condensation, and the absorbent liquid from the water jet pump was periodically discharged into a high-COD wastewater storage tank.

[0026] Testing showed that the 3,5-dibromo-o-aminobenzaldehyde obtained in this example had a purity of 99.68%, a total yield of 86.5%, an acetone recovery rate of 95%, a dilute sulfuric acid recovery and reuse rate of over 90%, and a wastewater discharge reduction of over 70%.

[0027] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing 3,5-dibromo-o-aminobenzaldehyde, characterized in that, Includes the following steps: (1) Reduction process: o-nitrobenzaldehyde is reduced by iron powder to generate o-aminobenzaldehyde. The reaction solution is filtered to separate the iron residue. The filtrate is extracted with toluene. The extract is back-extracted with dilute sulfuric acid to obtain an aqueous solution of o-aminobenzaldehyde sulfate. (2) Bromination process: The aqueous solution of o-aminobenzaldehyde sulfate obtained in step (1) is mixed with hydrobromic acid, and hydrogen peroxide is added dropwise to carry out the bromination reaction. The reaction solution is separated by centrifugation to obtain crude 3,5-dibromo-o-aminobenzaldehyde and centrifuged acid mother liquor. The centrifuged acid mother liquor is recovered. (3) Refining process: The crude 3,5-dibromo-o-aminobenzaldehyde obtained in step (2) is dissolved in acetone, crystallized, centrifuged and dried to obtain refined 3,5-dibromo-o-aminobenzaldehyde. The acetone centrifugation mother liquor and washing liquid are pumped into the decolorization kettle for recovery. In step (2), the centrifuged acid mother liquor is decolorized and vacuum concentrated to recover dilute sulfuric acid, which is then returned to step (1) for back-extraction.

2. The method for preparing 3,5-dibromo-o-aminobenzaldehyde according to claim 1, characterized in that, The reduction process in step (1) is as follows: water, iron powder, and o-nitrobenzaldehyde are added to the reduction reactor, and hydrochloric acid with a concentration of 25-30% is added dropwise. The mixture is heated to 70-75℃ and kept at that temperature for 2.5-3.5 hours. After the reaction is completed, the reaction material is separated by secondary pressure filtration to obtain the filtrate containing o-aminobenzaldehyde. The iron slag is thoroughly soaked and washed with hot water at 80-90℃. The washing liquid and the filtrate are combined and pressed into the extraction reactor and thoroughly mixed with the toluene pre-stored in the extraction reactor. The temperature in the extraction reactor is lowered to 15-20℃ and allowed to stand for 25-30 minutes. The automatic separator is then turned on to separate the heavy phase aqueous layer into a water receiving tank with an oil-water separation function. The mixture of light phase toluene and o-aminobenzaldehyde remains in the extraction reactor and is transferred to the extraction reactor. Sulfuric acid with a concentration of 14-16% should be pumped into the extraction vessel. The extraction vessel should be stirred and frozen to fully mix the o-aminobenzaldehyde and dilute sulfuric acid to form a salt. After standing for 25-30 minutes, the automatic separator should be turned on. The o-aminobenzaldehyde sulfate solution with dilute sulfuric acid will automatically separate into layers and be transferred to the material receiving tank. The solution will be pumped into a transfer tank and stored for freezing as the main raw material for the bromination reaction. The toluene in the upper layer remaining in the extraction vessel should be washed with fresh water and stirred. After standing, the layers should be separated again. The lower water layer should be discharged into a high COD wastewater storage tank after passing through an oil separator receiving tank. The upper toluene layer should remain in the extraction vessel for the next batch of extraction. The mass ratio of water, iron powder, o-nitrobenzaldehyde, hydrochloric acid, toluene, and sulfuric acid is 9-11:2-4:1-3:0.2-0.4:5:

5.

3. The method for preparing 3,5-dibromo-o-aminobenzaldehyde according to claim 1, characterized in that, The bromination reaction in step (2) is specifically as follows: an aqueous solution of o-aminobenzaldehyde sulfate is mixed with hydrobromic acid at a concentration of 45-48%, the temperature is lowered to 8-10℃, and hydrogen peroxide at a concentration of 25-28% is slowly added dropwise. The dropwise addition rate is controlled by temperature interlocking, and the reaction temperature is maintained at 20-25℃. After the conversion rate of o-aminobenzaldehyde reaches more than 99%, the temperature is lowered to 12-15℃, and the bromination reaction is completed. The mass ratio of the aqueous solution of o-aminobenzaldehyde sulfate, hydrobromic acid, and hydrogen peroxide is 3-5:2-4:

1.

4. The method for preparing 3,5-dibromo-o-aminobenzaldehyde according to claim 1, characterized in that, The specific method for recovering centrifuged acid mother liquor in step (2) is as follows: after collecting the centrifuged mother liquor, add concentrated sulfuric acid to adjust the concentration, add activated carbon to decolorize at room temperature for 2-3 hours, filter to remove activated carbon, concentrate the filtrate under vacuum degree ≤-0.09MPa, remove the fraction below 60℃, and when the sulfuric acid concentration in the reactor reaches 13-16% and the hydrogen bromide concentration reaches 4-6%, cool to below 30℃ to obtain recovered dilute sulfuric acid.

5. The method for preparing 3,5-dibromo-o-aminobenzaldehyde according to claim 1, characterized in that, The crude product dissolution and crystallization in step (3) specifically involves: adding acetone with a concentration of 93-96% to the dissolution vessel, adding crude 3,5-dibromo-o-aminobenzaldehyde, heating to 55-58℃ and refluxing for 2-2.5 hours, then pressing it into the crystallization vessel with nitrogen gas, freezing the crystallization vessel to 4-6℃, centrifuging and discharging the material, condensing the waste nitrogen and a small amount of acetone volatilized from the crystallization vessel through the condenser on its own and discharging it into the tail gas treatment facility, washing the crystallized 3,5-dibromo-o-aminobenzaldehyde with 90-92% acetone and spin-drying it, and drying the centrifuged filter cake to obtain refined 3,5-dibromo-o-aminobenzaldehyde, combining the centrifugation mother liquor and washing liquid for collection and recovery, and the mass ratio of crude 3,5-dibromo-o-aminobenzaldehyde to acetone is 3-7:14-16.

6. The method for preparing 3,5-dibromo-o-aminobenzaldehyde according to claim 5, characterized in that, The method for recovering the centrifugal mother liquor and washing liquid is as follows: The collected acetone centrifugal mother liquor and washing liquid are added to activated carbon and decolorized at 45-55℃ for 1-2 hours. After pressure filtration, the filtrate enters the acetone recovery kettle, and is heated to 50-60℃ under normal pressure for distillation to recover acetone. The temperature of the first-stage condenser outlet is controlled to be ≤40℃, and the temperature of the second-stage condenser outlet is controlled to be ≤25℃. The recovered acetone is recycled. After accumulating six batches of continuous distillation in the distillation kettle, the remaining liquid in the kettle is cooled to 25-30℃, centrifuged and dried. The filter cake is washed with acetone and then dried again. The finished filter cake is sent for drying to obtain 3,5-dibromo-o-aminobenzaldehyde. The centrifuged liquid is subjected to a second distillation. The acetone recovered from the second distillation is low-boiling acetone. The low-boiling acetone is then distilled three times and used for centrifugal washing in the acetone centrifugal mother liquor recovery process.

7. The method for preparing 3,5-dibromo-o-aminobenzaldehyde according to claim 1, characterized in that, The drying step in step (3) is as follows: the wet refined 3,5-dibromo-o-aminobenzaldehyde obtained after centrifugation is added to a double cone rotary vacuum dryer, the hot water temperature is controlled at 45-50℃, the vacuum degree is ≤-0.09MPa, and the drying is carried out for 2-3 hours. The product is then cooled to 30-35℃ and discharged to obtain refined 3,5-dibromo-o-aminobenzaldehyde.

8. The method for preparing 3,5-dibromo-o-aminobenzaldehyde according to claim 1, characterized in that, In step (3), the acetone volatilized during the drying process condenses into liquid and enters a vacuum buffer tank for low-concentration acetone recovery and reuse.