Green synthesis process of aminomethylbenzoic acid

Abstract

The invention belongs to the technical field of chemical synthesis, and particularly relates to a green synthesis process of aminomethylbenzoic acid. The process comprises the following steps: adding ammonium bicarbonate and metal nitrate into an aqueous solution to form a metal-containing ammonium bicarbonate precursor; the method comprises the following steps: by taking p-chloromethyl benzoic acid as a raw material, ammonifying to obtain an aminomethylbenzoic acid crude product and a byproduct 4, 4 '-(aza-diyl-bis (methylene)) dibenzoic acid; the method comprises the following steps: adding a byproduct 4, 4 '-(azadiyl bis (methylene)) dibenzoic acid into catalytic hydrogenation to prepare an aminomethylbenzoic acid crude product; and finally purifying the aminomethylbenzoic acid crude product to obtain an aminomethylbenzoic acid refined product. According to the process, on one hand, ammonium bicarbonate is introduced into a system as a catalyst and is combined with metal nitrate, the reaction condition is mild, the dosage of ammonia water can be reduced, and generation of byproducts can be inhibited; on the other hand, by-products are continuously reduced as raw materials, so that the by-products are utilized to the maximum extent, and resource waste is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and particularly relates to a green synthesis process of aminomethylbenzoic acid. Background Art

[0002] Aminomethylbenzoic acid, chemical name: 4-aminomethylbenzoic acid, also known as antifibrinolytic aromatic acid, is a commonly used procoagulant in clinical practice and is also the main raw material for the preparation of the hemostatic drug tranexamic acid. It has high market demand.

[0003] At present, the preparation methods of tranexamic acid mainly include: (1) cyanide method: using para-cyanobenzoic acid as raw material, the reaction of this method involves high-risk reaction reduction amination, and requires the use of highly toxic sodium cyanide, and also involves hydrogen reduction reaction with production risks. It also has high requirements on the equipment, factory buildings, and the quality of operators, and has great production safety risks; (2) chloromethylbenzoic acid substitution method: invention patent 202411648835.8 uses chloromethylbenzoic acid reaction and replaces traditional ammonium carbonate catalyst with calcium hydroxide, but the whole reaction process requires the use of cold solvents and strictly controls the steps, which has high requirements on equipment and operators; using chloromethylbenzoic acid as raw material and urotropine as catalyst, the production of by-products is reduced by controlling the temperature, but the amount of ammonia water used is large, the wastewater generated is polluted, and the cost of treating the three wastes is high. (3) 4-[(2-carboxybenzamido)methyl]benzoic acid acidification method: 4-[(2-carboxybenzamido)methyl]benzoic acid is used as raw material and hydrolyzed under acidic conditions. The raw material structure is complex and expensive. (4) Acetamide method. Invention patent 202110588759.6 uses acetamide as a new nitrogen source for the synthesis of aminobenzoic acid to replace ammonia water. However, this method also uses metal hydride as the alkaline raw material, which is used in large quantities and is not suitable for industrial production. Therefore, exploring a green, environmentally friendly, inexpensive and easily available synthesis process for aminobenzoic acid to achieve higher economic benefits is an urgent problem to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in response to the above-mentioned defects, the present invention provides a green synthesis process of aminomethylbenzoic acid. On the one hand, ammonium bicarbonate is introduced into the system as a catalyst and combined with a metal nitrate. The reaction conditions are mild, the amount of ammonia water used can be reduced, and the generation of by-products can be suppressed. On the other hand, the by-products are further reduced as raw materials, so that the by-products are maximized and resource waste is avoided.

[0005] The present invention solves the technical problem by adopting the following technical solution: a green synthesis process of aminomethylbenzoic acid, comprising the following steps:

[0006] Step S1, catalyst precursor preparation: adding ammonium bicarbonate and metal nitrate into an aqueous solution to form a metal-containing ammonium bicarbonate precursor;

[0007] Step S2, preparation of aminomethylbenzoic acid: adding water to a reaction kettle, introducing liquid ammonia, controlling the temperature with jacket cooling water, adding the ammonium bicarbonate precursor and unreacted ammonium bicarbonate in step S1, adding dropwise a methanol solution of p-chloromethylbenzoic acid, and reacting under normal pressure under reflux; after completion of the reaction, post-processing is performed to obtain a crude aminomethylbenzoic acid product and a by-product 4,4'-(azadiylbis(methylene))dibenzoic acid;

[0008] Step S3, hydrogenation of by-products: adding the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid obtained in step S2 into a hydrogenation reactor, adding an organic solvent, replacing the reactor with hydrogen, adding a palladium-carbon catalyst, and continuously introducing hydrogen. After the reaction is completed, filtering with diatomaceous earth and post-processing to obtain a crude product of aminomethylbenzoic acid;

[0009] Step S4, purification of crude aminobenzoic acid: the crude aminobenzoic acid obtained in step S2 and the crude aminobenzoic acid obtained in step S3 are combined, water, ammonia water and activated carbon are added thereto, the mixture is heated to dissolve, the activated carbon is removed by filtration, the solution is concentrated to remove ammonia gas, crystallized, centrifuged, soaked in ethanol and refluxed, centrifuged and dried to obtain aminobenzoic acid.

[0010] The reaction equation is as follows:

[0011]

[0012] Through the above technical solution, metal nitrate and ammonium bicarbonate are used to form a metal ammonium bicarbonate precursor, which delays the release of ammonium ions, avoids the direct addition of catalysts causing excessive reaction rate, and reduces the generation of by-products; liquid ammonia is used as a nitrogen source, which is less toxic than organic amines. Except for aminobenzoic acid and the main by-products, the rest are water-soluble ammonium salts, which reduces the generation of toxic substances; in addition, the by-products are converted into aminobenzoic acid through a hydrogenation reaction, improving the atomic economy to as high as more than 95%, achieving the "zero waste" goal, and realizing the high-value utilization of by-products. Hydrogen is used as a clean reducing agent, and the product is pure, avoiding the pollution of traditional reducing agents.

[0013] Furthermore, the metal nitrate is one of cobalt nitrate and copper nitrate. Using the above technical solution, cobalt nitrate or copper nitrate is used with ammonium bicarbonate to form a metal ammonium bicarbonate precursor, which decomposes to form a metal oxide catalyst. The reaction conditions are mild and the use of highly toxic metal salts is avoided, thereby reducing the risk of heavy metal pollution.

[0014] Furthermore, in step S1, the molar ratio of ammonium bicarbonate to metal nitrate is 1:(0.1-0.3). By optimizing the metal loading, while ensuring catalytic activity, metal residue is reduced. In subsequent reactions, the catalyst may promote the formation of C-N bonds, increase the reaction rate, and achieve both controllable loading and efficient catalysis.

[0015] Furthermore, the molar ratio of p-chloromethylbenzoic acid in step S2 to ammonium bicarbonate in step S1 is 1:(0.1-0.3), and the molar ratio of p-chloromethylbenzoic acid to liquid ammonia is 1:(5-10).

[0016] Furthermore, in step S2, the concentration of the p-chloromethylbenzoic acid methanol solution is 0.5-1 mol / L. Controlling the concentration of the methanol solution can reduce solvent consumption on the one hand, and avoid excessive concentration caused by too little solvent, which can increase the number of byproducts caused by the intense reaction on the other hand.

[0017] Furthermore, the post-treatment in step S2 includes standing for stratification, concentrating the ammoniated solution to neutrality, reusing the concentrated ammonia water to a liquid ammonia storage tank, and recovering the distilled methanol for reuse; adjusting the pH of the concentrate to 1-3 with hydrochloric acid, and separating the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid by filtration; neutralizing the mother liquor after filtration to neutrality with sodium hydroxide, concentrating to remove water, crystallizing, and filtration to obtain crude aminomethylbenzoic acid.

[0018] By adopting the above scheme, ammonia and methanol are recovered in the post-treatment, realizing a closed-loop cycle and reducing resource waste; the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid is efficiently separated by pH adjustment to avoid impurity accumulation and provide raw materials for subsequent hydrogenation conversion.

[0019] Furthermore, the organic solvent in step S3 is methanol, ethanol, ethyl acetate, or methanol-water solution or ethyl acetate-water solution. Low-toxic solvents such as methanol / ethanol are easily recyclable, and the ether extraction and pH adjustment steps in the post-processing optimize product separation and reduce solvent residue.

[0020] Furthermore, the amount of palladium-carbon catalyst used in step S3 is 1-5% of the mass of the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid. The palladium-carbon catalyst used in a low amount (1-5%) can be recovered and reused by filtering through diatomaceous earth.

[0021] Furthermore, the post-treatment operation in step S3 is to concentrate the filtered mother liquor, add ether to dissolve it, adjust the pH value to 1-3 with hydrochloric acid, and after separation, dropwise add NaOH solution to the aqueous layer until the pH is ≥10 to deprotonate the ammonium salt and precipitate the crude aminomethylbenzoic acid.

[0022] Furthermore, in step S4, the pH of the solution is adjusted to ≥9 by using ammonia water.

[0023] The beneficial effects of the present invention are:

[0024] 1. By adopting the above scheme, in the green synthesis process of aminomethylbenzoic acid, on the one hand, ammonium bicarbonate is introduced into the system as a catalyst and combined with a metal nitrate, and the reaction conditions are mild, which can reduce the amount of ammonia water used and inhibit the generation of by-products; on the other hand, the by-products are further reduced as raw materials to maximize the utilization of the by-products, the conversion of by-products reduces the cost of raw materials, the recycling of solvents reduces production costs, avoids waste of resources, and reduces the discharge of three wastes.

[0025] 2. This process uses long tooth reflux and jacket cooling water to achieve low temperature control, reduce energy consumption, and mild reaction conditions.

[0026] 3. This process achieves high-efficiency, low-toxicity, and low-emission green synthesis through catalytic system optimization, by-product resource utilization, solvent closed-loop circulation, and green purification technology. It complies with the principles of green chemistry and performs particularly well in terms of atomic economy, energy efficiency, and pollution prevention, and has significant industrial application value. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] The green synthesis process of aminomethylbenzoic acid, the reaction equation is as follows:

[0029]

[0030] Example 1

[0031] The green synthesis process of aminomethylbenzoic acid includes the following steps:

[0032] Step S1, catalyst precursor preparation: 2.3 g of ammonium bicarbonate and 0.54 g of cobalt nitrate are added to an aqueous solution to form a metal-containing ammonium bicarbonate precursor;

[0033] Step S2, preparation of aminomethylbenzoic acid: add water to the reactor, slowly introduce 0.8L of liquid ammonia, control the temperature with jacket cooling water, add the ammonium bicarbonate precursor and unreacted ammonium bicarbonate in step S1, dropwise add a mixed solution of 50g of p-chloromethylbenzoic acid in 300mL of methanol, and reflux under normal pressure; after the reaction is completed, stand and separate, and concentrate the ammoniated liquid to neutrality. The concentrated ammonia water is applied to the liquid ammonia storage tank, and the distilled methanol is recovered and reused; the pH value of the concentrated solution is adjusted to 1-3 with hydrochloric acid, and the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid is separated by pressure filtration to obtain 8g; the mother liquor after pressure filtration is neutralized to neutrality with sodium hydroxide, concentrated to remove water, crystallized, and pressure filtered to obtain the crude product of aminomethylbenzoic acid;

[0034] Step S3, hydrogenation of by-products: 8 g of the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid obtained in step S2 was added to a hydrogenation reactor, methanol was added, and the reactor was replaced with hydrogen. Then, 0.1 g of palladium-carbon catalyst was added and hydrogen was continuously introduced. After the reaction was completed, the mother liquor was filtered through diatomaceous earth, concentrated, and dissolved in ether. The pH value was adjusted to 1-3 with hydrochloric acid. After separation, NaOH solution was added dropwise to the aqueous layer until the pH was ≥10 to deprotonate the ammonium salt and precipitate crude aminomethylbenzoic acid;

[0035] Step S4, purification of crude aminobenzoic acid: The crude aminobenzoic acid obtained in step S2 and the crude aminobenzoic acid obtained in step S3 are combined, water, aqueous ammonia and activated carbon are added thereto, the pH of the solution is adjusted to ≥ 9 with aqueous ammonia, the temperature is raised to dissolve the crude aminobenzoic acid, the activated carbon is removed by filtration, the solution is concentrated to remove ammonia gas, crystallized, centrifuged, soaked in ethanol and refluxed, centrifuged and dried to obtain 42.0 g of aminobenzoic acid with a purity greater than 99.5%.

[0036] Example 2

[0037] The green synthesis process of aminomethylbenzoic acid includes the following steps:

[0038] Step S1, catalyst precursor preparation: 2.3 g of ammonium bicarbonate and 1.65 g of copper nitrate are added to an aqueous solution to form a metal-containing ammonium bicarbonate precursor;

[0039] Step S2, preparation of aminomethylbenzoic acid: add water to the reactor, slowly introduce 0.4L liquid ammonia, control the temperature with jacket cooling water, add the ammonium bicarbonate precursor and unreacted ammonium bicarbonate in step S1, dropwise add a mixed solution of 50g p-chloromethylbenzoic acid dissolved in 580mL methanol, and reflux under normal pressure; after the reaction is completed, stand and separate, and concentrate the ammoniated liquid to neutrality. The concentrated ammonia water is applied to the liquid ammonia storage tank, and the distilled methanol is recovered and reused; the pH value of the concentrated solution is adjusted to 1-3 with hydrochloric acid, and the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid 13.4g is obtained by filtration separation; the mother liquor after filtration is neutralized to neutrality with sodium hydroxide, concentrated to remove water, crystallized, and filtration is performed to obtain the crude product of aminomethylbenzoic acid;

[0040] Step S3, hydrogenation of by-products: 13.4 g of the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid obtained in step S2 was added to a hydrogenation reactor, and after adding a methanol aqueous solution and replacing the reactor with hydrogen, 0.27 g of palladium-carbon catalyst was added, and hydrogen was continuously introduced. After the reaction was completed, the mother liquor was filtered through diatomaceous earth, concentrated, and dissolved in ether. The pH value was adjusted to 1-3 with hydrochloric acid. After separation, NaOH solution was added dropwise to the aqueous layer until the pH was ≥10 to deprotonate the ammonium salt and precipitate the crude aminomethylbenzoic acid;

[0041] Step S4, purification of crude aminobenzoic acid: The crude aminobenzoic acid obtained in step S2 and the crude aminobenzoic acid obtained in step S3 are combined, water, aqueous ammonia and activated carbon are added thereto, the pH of the solution is adjusted to ≥ 9 with aqueous ammonia, the temperature is raised to dissolve the crude aminobenzoic acid, the activated carbon is removed by filtration, the solution is concentrated to remove ammonia gas, crystallized, centrifuged, soaked in ethanol and refluxed, centrifuged and dried to obtain 39.8 g of aminobenzoic acid with a purity greater than 99.5%.

[0042] Example 3

[0043] The green synthesis process of aminomethylbenzoic acid includes the following steps:

[0044] Step S1, catalyst precursor preparation: 4.6 g of ammonium bicarbonate and 2.1 g of cobalt nitrate are added to an aqueous solution to form a metal-containing ammonium bicarbonate precursor;

[0045] Step S2, preparation of aminomethylbenzoic acid: add water to the reactor, slowly introduce 0.5L of liquid ammonia, control the temperature with jacket cooling water, add the ammonium bicarbonate precursor and unreacted ammonium bicarbonate in step S1, dropwise add a mixed solution of 50g of p-chloromethylbenzoic acid dissolved in 450mL of methanol, and reflux under normal pressure; after the reaction is completed, stand and separate, and concentrate the ammoniated liquid to neutrality. The concentrated ammonia water is applied to the liquid ammonia storage tank, and the distilled methanol is recovered and reused; the pH value of the concentrated solution is adjusted to 1-3 with hydrochloric acid, and the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid is separated by pressure filtration to obtain 6.7g of the by-product; the mother liquor after pressure filtration is neutralized to neutrality with sodium hydroxide, concentrated to remove water, crystallized, and pressure filtered to obtain the crude product of aminomethylbenzoic acid;

[0046] Step S3, hydrogenation of by-products: 6.7 g of the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid obtained in step S2 was added to a hydrogenation reactor, and an ethyl acetate aqueous solution was added. After the reactor was replaced with hydrogen, 0.3 g of palladium-carbon catalyst was added and hydrogen was continuously introduced. After the reaction was completed, the mother liquor was filtered through diatomaceous earth, concentrated, and dissolved in ether. The pH value was adjusted to 1-3 with hydrochloric acid. After separation, a NaOH solution was added dropwise to the aqueous layer until the pH was ≥10 to deprotonate the ammonium salt and precipitate a crude aminomethylbenzoic acid product.

[0047] Step S4, purification of crude aminobenzoic acid: The crude aminobenzoic acid obtained in step S2 and the crude aminobenzoic acid obtained in step S3 are combined, water, aqueous ammonia and activated carbon are added thereto, the pH of the solution is adjusted to ≥ 9 with aqueous ammonia, the temperature is raised to dissolve the crude aminobenzoic acid, the activated carbon is removed by filtration, the solution is concentrated to remove ammonia gas, crystallized, centrifuged, soaked in ethanol and refluxed, centrifuged and dried to obtain 41.5 g of aminobenzoic acid with a purity greater than 99.5%.

[0048] Example 4

[0049] The green synthesis process of aminomethylbenzoic acid includes the following steps:

[0050] Step S1, catalyst precursor preparation: 6.9 g of ammonium bicarbonate and 3.2 g of cobalt nitrate are added to an aqueous solution to form a metal-containing ammonium bicarbonate precursor;

[0051] Step S2, preparation of aminomethylbenzoic acid: add water to the reactor, slowly introduce 0.6L of liquid ammonia, control the temperature with jacket cooling water, add the ammonium bicarbonate precursor and unreacted ammonium bicarbonate in step S1, dropwise add a mixed solution of 50g of p-chloromethylbenzoic acid dissolved in 450mL of methanol, and reflux under normal pressure; after the reaction is completed, stand and separate, and concentrate the ammoniated liquid to neutrality. The concentrated ammonia water is applied to the liquid ammonia storage tank, and the distilled methanol is recovered and reused; the pH value of the concentrated solution is adjusted to 1-3 with hydrochloric acid, and the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid is separated by pressure filtration to obtain 7.4g; the mother liquor after pressure filtration is neutralized to neutrality with sodium hydroxide, concentrated to remove water, crystallized, and pressure filtered to obtain crude aminomethylbenzoic acid;

[0052] Step S3, hydrogenation of by-products: 7.4 g of the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid obtained in step S2 was added to a hydrogenation reactor, ethyl acetate was added, and the reactor was replaced with hydrogen. 0.25 g of palladium-carbon catalyst was added and hydrogen was continuously introduced. After the reaction was completed, the mother liquor was filtered through diatomaceous earth, concentrated, and dissolved in ether. The pH value was adjusted to 1-3 with hydrochloric acid. After separation, NaOH solution was added dropwise to the aqueous layer until the pH was ≥10 to deprotonate the ammonium salt and precipitate crude aminomethylbenzoic acid;

[0053] Step S4, purification of crude aminobenzoic acid: The crude aminobenzoic acid obtained in step S2 and the crude aminobenzoic acid obtained in step S3 are combined, water, aqueous ammonia and activated carbon are added thereto, the pH of the solution is adjusted to ≥ 9 with aqueous ammonia, the temperature is raised to dissolve the crude aminobenzoic acid, the activated carbon is removed by filtration, the solution is concentrated to remove ammonia gas, crystallized, centrifuged, soaked in ethanol and refluxed, centrifuged and dried to obtain 42.3 g of aminobenzoic acid with a purity greater than 99.5%.

[0054] The above examples show that when the concentration of p-chloromethylbenzoic acid is low, the reaction activity is low and more by-products are produced; however, by recycling the by-products through catalytic hydrogenation, the final yield of aminomethylbenzoic acid is greater than 90%.

[0055] Example 5

[0056] The difference between this embodiment and embodiment 4 is that, in the green synthesis process of aminobenzoic acid, no cobalt nitrate is added to 6.9 g of ammonium bicarbonate, and other reaction conditions are the same. After the reaction, step S2 obtains 30 g of by-product, and the by-product is hydrogenated and the crude aminobenzoic acid is purified to obtain 33.2 g of refined aminobenzoic acid.

[0057] The present invention provides a green synthesis process for obtaining aminomethylbenzoic acid. On the one hand, ammonium bicarbonate is introduced into the system as a catalyst and combined with a metal nitrate, and the reaction conditions are mild, the amount of ammonia water used can be reduced, and the generation of by-products can be suppressed. On the other hand, the by-products are further reduced as raw materials, and the by-products are maximized. The conversion of the by-products reduces the raw material cost, the solvent is recycled to reduce the production cost, resource waste is avoided, and the discharge of three wastes is reduced.

[0058] With the above-mentioned ideal embodiment of the present invention as inspiration, and through the above description, relevant personnel can make various changes and modifications without departing from the scope of the technical concept of this invention patent. The technical scope of this invention patent is not limited to the content of the specification, but must be determined according to the scope of the claims.

Claims

1. The green synthesis process of aminomethylbenzoic acid includes the following steps: Step S1, catalyst precursor preparation: adding ammonium bicarbonate and metal nitrate into an aqueous solution to form a metal-containing ammonium bicarbonate precursor; Step S2, preparation of aminomethylbenzoic acid: adding water to a reaction kettle, introducing liquid ammonia, controlling the temperature with jacket cooling water, adding the ammonium bicarbonate precursor and unreacted ammonium bicarbonate in step S1, adding dropwise a methanol solution of p-chloromethylbenzoic acid, and reacting under normal pressure under reflux; after completion of the reaction, post-processing is performed to obtain a crude aminomethylbenzoic acid product and a by-product 4,4'-(azadiylbis(methylene))dibenzoic acid; Step S3, hydrogenation of by-products: adding the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid obtained in step S2 into a hydrogenation reactor, adding an organic solvent, replacing the reactor with hydrogen, adding a palladium-carbon catalyst, and continuously introducing hydrogen. After the reaction is completed, filtering with diatomaceous earth and post-processing to obtain a crude product of aminomethylbenzoic acid; Step S4, purification of crude aminobenzoic acid: the crude aminobenzoic acid obtained in step S2 and the crude aminobenzoic acid obtained in step S3 are combined, water, ammonia water and activated carbon are added thereto, the mixture is heated to dissolve, the activated carbon is removed by filtration, the solution is concentrated to remove ammonia gas, crystallized, centrifuged, soaked in ethanol and refluxed, centrifuged and dried to obtain aminobenzoic acid.

2. The green synthesis process of aminomethylbenzoic acid according to claim 1, wherein: The metal nitrate is one of cobalt nitrate and copper nitrate.

3. The green synthesis process of aminomethylbenzoic acid according to claim 1, wherein: In step S1, the molar ratio of ammonium bicarbonate to metal nitrate is 1:(0.1-0.3).

4. The green synthesis process of aminomethylbenzoic acid according to claim 1, wherein: The molar ratio of p-chloromethylbenzoic acid in step S2 to ammonium bicarbonate in step S1 is 1:(0.1-0.3), and the molar ratio of p-chloromethylbenzoic acid to liquid ammonia is 1:(5-10).

5. The green synthesis process of aminomethylbenzoic acid according to claim 1, wherein: In step S2, the concentration of the p-chloromethylbenzoic acid methanol solution is 0.5-1 mol / L.

6. The green synthesis process of aminomethylbenzoic acid according to claim 1, wherein: The post-treatment in step S2 includes standing for stratification and concentrating the ammoniated solution to neutrality. The concentrated ammonia water is recycled to a liquid ammonia storage tank, and the distilled methanol is recovered and recycled. The pH of the concentrated solution is adjusted to 1-3 with hydrochloric acid, and the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid is separated by filtration. The mother liquor after filtration is neutralized to neutrality with sodium hydroxide, concentrated to remove water, crystallized, and filtered to obtain crude aminomethylbenzoic acid.

7. The green synthesis process of aminomethylbenzoic acid according to claim 1, wherein: The organic solvent in step S3 is methanol, ethanol, ethyl acetate or a methanol aqueous solution or an ethyl acetate aqueous solution.

8. The green synthesis process of aminomethylbenzoic acid according to claim 1, wherein: The amount of palladium-carbon catalyst used in step S3 is 1-5% of the mass of the by-product 4,4'-(azadiylbis(methylene))dibenzoic acid.

9. The green synthesis process of aminomethylbenzoic acid according to claim 1, wherein: The post-treatment operation in step S3 is to concentrate the filtered mother liquor, add ether to dissolve it, adjust the pH value to 1-3 with hydrochloric acid, and after separation, dropwise add NaOH solution to the aqueous layer until the pH is ≥10 to deprotonate the ammonium salt and precipitate the crude aminomethylbenzoic acid.

10. The green synthesis process of aminomethylbenzoic acid according to claim 1, characterized in that: In step S4, the pH value of the solution is adjusted to ≥9 by using ammonia water.

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