A method for preparing aminobenzoic acid as a raw material of EDB or EHA

Abstract

The invention relates to the field of EDB or EHA raw material preparation, and in particular to a method for preparing aminobenzoic acid, which is a raw material of EDB or EHA. The invention relates to a method for preparing aminobenzoic acid, which is a raw material of EDB or EHA, and the specific method is as follows: nitrotoluene is dissolved in a low eutectic solvent, and in the presence of elemental sulfur, sodium sulfide and alkali, an oxidation-reduction reaction occurs at room temperature, the methyl group on the benzene ring is oxidized to a carboxyl group, and the nitro group is reduced to an amino group, and aminobenzoic acid is finally obtained; the low eutectic solvent is preferably a mixture of choline chloride, ethylene glycol and antimony trichloride.

Description

Technical Field

[0001] The invention relates to the field of EDB or EHA raw material preparation, and in particular to a method for preparing aminobenzoic acid which is an EDB or EHA raw material. Background Art

[0002] Aminobenzoic acid is an important fine chemical intermediate. For example, it is an important raw material for the preparation of EHA (isooctyl p-dimethylaminobenzoate) or EDB (ethyl p-dimethylaminobenzoate). Isooctyl p-dimethylaminobenzoate is a good UV absorber in the UVB region, and its maximum UV absorption peak is 311 nm (ethanol solution). As an effective anti-ultraviolet ingredient, it is widely used in sunscreen cosmetics abroad in large quantities. The U.S. FDA lists sunscreen containing this product ingredient as the first recommended cosmetic. The synthetic route for producing EHA using aminobenzoic acid as raw material is as follows:

[0003] .

[0004] Ethyl p-dimethylaminobenzoate (EDB) is a highly efficient amine accelerator, generally used together with free radical photoinitiators, mainly used for UV curing of varnish coating systems on paper, wood, metal and plastic surfaces, and can also be used for UV radiation polymerization of single or multiple monomers. Therefore, it is an excellent sensitizer, and when used in combination with thiophenones and acetophenones, it can not only promote photoinitiation, but also effectively eliminate the interference of oxygen on photoinitiated polymerization. The synthetic route for producing EDB using aminobenzoic acid as raw material is as follows:

[0005] .

[0006] In summary, aminobenzoic acid is a very important class of fine chemicals. The existing synthesis method of aminobenzoic acid series products is basically to use nitrotoluene as raw material, first carry out oxidation reaction to obtain nitrobenzoic acid, and then reduce the nitro group to amino group to obtain aminobenzoic acid products. The first step of oxidation reaction is mainly to use dilute nitric acid as oxidant in industry to generate nitrobenzoic acid under high temperature (about 180℃) and high pressure (2MPa). This process will produce a large amount of low-concentration dilute nitric acid and a large amount of nitrogen oxide (NOx) waste gas, and the pressure of three waste treatment is very high. Or use metal oxidants such as potassium permanganate and sodium dichromate for oxidation. Although the temperature is milder than the dilute nitric acid method, there is a large amount of heavy metal-containing wastewater, which seriously affects the environment. The second step is also a reaction that mainly reduces the nitro group to amino group. In the past, the industry mainly used iron powder reduction. Although this technology has low cost and stable product quality, it produces a large amount of iron mud and is difficult to treat three wastes. In recent years, catalytic hydrogenation technology has gradually replaced the iron powder reduction process, which has the advantages of less three wastes, high atomic economy and good quality. The catalysts used in the current industrial catalytic hydrogenation technology are generally divided into Raney nickel catalysts and palladium carbon catalysts. Although Raney nickel catalysts are cheaper than palladium carbon, they are very prone to spontaneous combustion during the production process, causing safety accidents. Palladium carbon catalysts are very expensive because they contain precious metal palladium, which has always restricted the large-scale industrial production of aminobenzoic acid series products.

[0007] In addition, the existing Chinese patent CN97106992.1, a method for synthesizing p-bromobenzaldehyde, reports that p-nitrotoluene is used as a raw material, sodium polysulfide is used as a catalyst in an ethanol solution, and a phase transfer catalyst is added to produce p-aminobenzoic acid by intramolecular disproportionation reaction. However, alcohol solvents are easy to volatilize during use, causing organic waste gas (VOC) emissions. At the same time, distillation is required during the recovery and purification process, which consumes more energy and produces distillation residues and wastewater. Summary of the invention

[0008] In view of the above problems, the present invention has developed a one-step method to directly use nitrotoluene as a raw material and simultaneously undergo an oxidation-reduction reaction to obtain aminobenzoic acid. The specific scheme is as follows:

[0009] A method for preparing aminobenzoic acid as a raw material of EDB or EHA, wherein the specific method is as follows: nitrotoluene represented by formula (I) is dissolved in a low eutectic solvent, and an oxidation-reduction reaction occurs at room temperature in the presence of elemental sulfur, sodium sulfide and alkali, wherein the methyl group on the benzene ring is oxidized to a carboxyl group and the nitro group is reduced to an amino group, thereby finally obtaining aminobenzoic acid represented by formula (II);

[0010]

[0011] The nitro group in formula (I) may be at the ortho, meta or para position to the methyl group, and the amino group in formula (II) may be at the ortho, meta or para position to the carboxyl group.

[0012] The deep eutectic solvent is a mixture of choline chloride, ethylene glycol and antimony trichloride.

[0013] The mass ratio of choline chloride, ethylene glycol and antimony trichloride in the deep eutectic solvent is: 1:2-2.5:0.05-0.1.

[0014] The preparation method of the deep eutectic solvent is as follows: choline chloride, ethylene glycol and antimony trichloride are stirred and mixed in proportion, and then heated to 70-90° C., and after the solid choline chloride and antimony trichloride are completely dissolved, the mixture is cooled to room temperature for use.

[0015] The alkali is an inorganic alkali such as sodium hydroxide or potassium hydroxide.

[0016] The molar ratio of elemental sulfur to sodium sulfide is 1:0.5-2.5.

[0017] The molar ratio of the nitrotoluene to the alkali is 1:0.8-1.5.

[0018] The total amount ratio of the nitrotoluene, elemental sulfur and sodium sulfide is 1:1.0-3.0.

[0019] The mass ratio of the nitrotoluene to the deep eutectic solvent is 1:5-20.

[0020] The room temperature is 25° C.-35° C.; the time of the redox reaction is 2-10 hours.

[0021] The present invention develops a new process for synthesizing aminobenzoic acid in one step using nitrotoluene as a raw material, which has the following advantages:

[0022] (1) In this system, the trivalent antimony of antimony trichloride is oxidized to a high-valent pentavalent antimony ion in the presence of elemental sulfur. The electron-deficient pentavalent antimony ion reacts with the raw material nitrotoluene, the methyl group is oxidized to a carboxyl group, and the pentavalent antimony ion is reduced to a trivalent antimony ion. At the same time, the trivalent antimony ion reacts with the intermediate nitrobenzoic acid to obtain aminobenzoic acid and pentavalent antimony ions, and the pentavalent antimony ions are reduced to trivalent antimony ions in the presence of divalent sulfur anions. In the whole process, it is the antimony ion that actually reacts with the raw material nitrotoluene. Antimony ions can effectively reduce the activation energy of the reaction during the reaction, so the reaction temperature is relatively low, and a good yield can be obtained at room temperature. The reaction principle is as follows:

[0023] .

[0024] (2) Compared with the prior art, the present invention has the advantages of simple steps, mild reaction, high yield, less waste, etc. The existing industrial production technology of aminobenzoic acid requires firstly oxidation reaction to obtain nitrobenzoic acid, separation, and then reduction reaction to obtain nitrobenzoic acid.

[0025] (3) In the system of the present invention, the low eutectic solvent has a strong polarity and the solubility of the related substances is large, so a phase transfer catalyst is not required.

[0026] (4) Choline chloride in the deep eutectic solvent of the present invention can not only form a ternary deep eutectic solvent with ethylene glycol and antimony trichloride, but also act as a phase transfer catalyst in the system to improve the reaction yield.

[0027] (5) The ternary low eutectic solvent involved in the present invention is a highly polar solvent due to the presence of a large number of hydrogen bonds. Therefore, it has better solubility for sodium sulfide and elemental sulfur than other common solvents, which is not only beneficial to improving the reaction yield, but also reducing the loss of sodium sulfide and elemental sulfur during the solvent circulation process, which not only reduces production costs but also reduces environmental pollution.

[0028] (6) Using common solvents such as ethanol as the reaction medium, inorganic substances such as elemental sulfur, sodium sulfide and alkali have very low solubility in common solvents. Therefore, after the product is filtered, there are more inorganic salts in the product, which needs to be further purified, resulting in more wastewater. The low eutectic solvent involved in the present invention has good solubility for inorganic substances in the reaction system. It can be recycled and reused in the low eutectic solvent, not only does the precipitated product not need to be purified, but also greatly saves the consumption of raw materials.

[0029] (7) The low eutectic solvent is a kind of ionic liquid, so the vapor pressure is very low, that is, the boiling point is very high. In the system of the present invention, the addition of the ternary low eutectic solvent greatly promotes the activity of the reaction, and the reaction can be carried out at room temperature. Compared with the use of traditional methanol and ethanol solvents, VOC emissions and solvent consumption are avoided during the reaction process, and the production cost and energy consumption are greatly reduced. DETAILED DESCRIPTION

[0030] Example 1

[0031] Preparation of low eutectic solvent: Mix 100 g of choline chloride, 200 g of ethylene glycol and 5 g of antimony trichloride and heat to 90°C. After the solid choline chloride and antimony trichloride are completely dissolved, cool to room temperature for use.

[0032] Put 68.6 g of p-nitrotoluene, 16 g of elemental sulfur, 39 g of sodium sulfide, 20 g of sodium hydroxide and 686 g of a low eutectic solvent into a three-necked flask, stir evenly at room temperature (25°C), react for 8 hours, filter, recover the filtrate, wash the filter cake with a small amount of cold water, and dry to obtain 68.1 g of p-aminobenzoic acid with HPLC purity of 99.1% and molar yield of 98.5% (relative to p-nitrotoluene).

[0033] Example 2

[0034] Preparation of low eutectic solvent: Mix 100 g of choline chloride, 250 g of ethylene glycol and 10 g of antimony trichloride and heat to 70°C. After the solid choline chloride and antimony trichloride are completely dissolved, cool to room temperature for use.

[0035] Put 68.6 g of p-nitrotoluene, 16 g of elemental sulfur, 19.5 g of sodium sulfide, 30 g of sodium hydroxide and 343 g of a low eutectic solvent into a three-necked flask, stir evenly at room temperature, react for 10 hours, then filter, recover the filtrate and wash the filter cake with a small amount of cold water and dry to obtain 67.5 g of p-aminobenzoic acid with HPLC purity of 99.5% and molar yield of 98.0% (relative to p-nitrotoluene).

[0036] Example 3

[0037] The preparation of the deep eutectic solvent is as in Example 1.

[0038] Put 68.6 g of o-nitrotoluene, 4.5 g of elemental sulfur, 28.1 g of sodium sulfide, 30 g of sodium hydroxide and 1372 g of a low eutectic solvent into a three-necked flask, stir evenly at room temperature, react for 6 hours, then filter, recover the filtrate and wash the filter cake with a small amount of cold water and dry to obtain 67.8 g of o-aminobenzoic acid with HPLC purity of 99.6% and molar yield of 98.4% (relative to o-nitrotoluene).

[0039] Example 4

[0040] The preparation of the deep eutectic solvent is as in Example 1.

[0041] Put 68.6 g of o-nitrotoluene, 4.5 g of elemental sulfur, 28.1 g of sodium sulfide, 30 g of sodium hydroxide and 1372 g of a low eutectic solvent into a three-necked flask, stir evenly at room temperature, react for 10 hours, then filter, recover the filtrate and wash the filter cake with a small amount of cold water and dry to obtain 67.6 g of o-aminobenzoic acid with HPLC purity of 99.3% and molar yield of 97.9% (relative to o-nitrotoluene).

[0042] Example 5

[0043] The preparation of the deep eutectic solvent is as in Example 2.

[0044] 68.6 g of o-nitrotoluene, 16 g of elemental sulfur, 39 g of sodium sulfide, 28 g of potassium hydroxide and 686 g of a low eutectic solvent were put into a three-necked flask, stirred evenly at room temperature, reacted for 2 hours while stirring, filtered after the reaction was completed, the filtrate was recovered and reused, the filter cake was washed with a small amount of cold water, and dried to obtain 68.2 g of o-aminobenzoic acid with HPLC purity of 99.1% and molar yield of 98.5% (relative to o-nitrotoluene).

[0045] The above embodiments are only used to explain the inventive concept of the present invention, rather than to limit the protection of the rights of the present invention. Any non-substantial changes to the present invention using this concept shall fall within the protection scope of the present invention.

Claims

1. A method for preparing aminobenzoic acid as a raw material of EDB or EHA, characterized in that: The specific method is as follows: nitrotoluene shown in formula (I) is dissolved in a low eutectic solvent, and in the presence of elemental sulfur, sodium sulfide and alkali, a redox reaction occurs at room temperature, the methyl group on the benzene ring is oxidized to a carboxyl group, and the nitro group is reduced to an amino group, and finally aminobenzoic acid shown in formula (II) is obtained; ， (I) (II) The nitro group in formula (I) is at the ortho, meta or para position to the methyl group, and the amino group in formula (II) is at the ortho, meta or para position to the carboxyl group; The mass ratio of choline chloride, ethylene glycol and antimony trichloride in the deep eutectic solvent is: 1:2-2.5:0.05-0.1; the room temperature is 25°C-35°C; The preparation method of the deep eutectic solvent is as follows: choline chloride, ethylene glycol and antimony trichloride are stirred and mixed in proportion, and then heated to 70-90° C., and after the solid choline chloride and antimony trichloride are completely dissolved, the mixture is cooled to room temperature for use.

2. The method for preparing aminobenzoic acid as a raw material of EDB or EHA as claimed in claim 1, characterized in that: The alkali is sodium hydroxide or potassium hydroxide.

3. The method for preparing aminobenzoic acid as a raw material of EDB or EHA as claimed in claim 1, characterized in that: The molar ratio of elemental sulfur to sodium sulfide is 1:0.5-2.

5.

4. The method for preparing aminobenzoic acid as a raw material of EDB or EHA as claimed in claim 1, characterized in that: The molar ratio of the nitrotoluene to the alkali is 1:0.8-1.

5.

5. The method for preparing aminobenzoic acid as a raw material of EDB or EHA as claimed in claim 1, characterized in that: The total amount ratio of the nitrotoluene, elemental sulfur and sodium sulfide is 1:1.0-3.

0.

6. The method for preparing aminobenzoic acid as a raw material of EDB or EHA as claimed in claim 1, characterized in that: The mass ratio of the nitrotoluene to the deep eutectic solvent is 1:5-20.

7. The method for preparing aminobenzoic acid as a raw material of EDB or EHA as claimed in claim 1, characterized in that: The oxidation-reduction reaction time is 2-10 hours.

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