Process for the preparation of o-nitrobenzaldehyde

Abstract

This invention relates to the field of fine chemical organic synthesis technology and discloses a process for preparing o-nitrobenzaldehyde. This process uses o-nitrotoluene as a raw material, hydrogen peroxide as a green oxidant, and a composite catalytic system of metal salt and phase transfer catalyst to carry out a selective oxidation reaction under weakly alkaline conditions. After post-treatment separation, the reaction solution is recrystallized in an ethanol-water mixed solvent and vacuum dried to obtain the finished product. This invention optimizes reaction parameters and the catalytic system, effectively suppressing excessive oxidation side reactions. The reaction conditions are mild, controllable at ambient pressure, and there is no heavy metal pollution; the solvent can be recycled. This process solves the problems of high pollution, low yield, and poor purity of traditional processes. It is simple to operate, low in cost, and suitable for the large-scale industrial production of o-nitrobenzaldehyde.

Description

Technical Field

[0001] This invention relates to the field of fine chemical organic synthesis technology, specifically to a preparation process for o-nitrobenzaldehyde. Background Technology

[0002] o-Nitrobenzaldehyde is an important fine chemical intermediate widely used in pharmaceuticals, pesticides, dyes, organic synthesis and other fields. It is a core raw material for the synthesis of cardiovascular drugs such as nifedipine and nimodipine, and is also used in the preparation of photosensitive materials, fragrances and rubber additives.

[0003] Currently, the mainstream industrial preparation method for o-nitrobenzaldehyde is the o-nitrotoluene oxidation method. However, this technology has significant drawbacks: First, it uses strong oxidants such as sodium dichromate, potassium permanganate, and sodium hypochlorite, which have poor oxidation selectivity and easily generate byproducts such as o-nitrobenzic acid. The product yield is only 70% to 80%, and there are serious heavy metal salt residues, resulting in extremely high waste treatment costs. Second, some processes use high-temperature and high-pressure reaction conditions, which require high-end equipment, consume a lot of energy, and pose safety hazards. Third, the post-processing is complex, requiring multiple extractions and distillations, making it difficult to achieve pharmaceutical-grade purity and meet the demands of the high-end market.

[0004] Therefore, developing a green, environmentally friendly, mild, high-yield, high-purity o-nitrobenzaldehyde preparation process suitable for industrial production has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a preparation process for o-nitrobenzaldehyde, which solves the problems of high oxidant pollution, low product yield and purity, and high difficulty in industrialization in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a preparation process for o-nitrobenzaldehyde, comprising the following steps:

[0007] S1 Ingredients and Reaction: Add o-nitrotoluene, organic solvent, and composite catalyst to the reactor, stir and mix evenly, adjust the pH of the system to weakly alkaline, raise the temperature to the reaction temperature, add hydrogen peroxide solution dropwise at a uniform rate, and keep the reaction at the temperature.

[0008] S2 post-processing separation: After the reaction is completed, cool to room temperature, let stand and separate the liquid, collect the organic phase; add 70-75g of sodium metabisulfite dissolved in 200mL of deionized water, react at 25-40℃ for 1-4 hours to form salt, separate the layers, take the aqueous layer, adjust the pH to 10-11 with 20% sodium hydroxide solution, precipitate the crude product, filter, and obtain the crude product.

[0009] S3 purification and refining: The crude product is added to a recrystallization solvent, heated to dissolve, and then a decolorizing agent is added for heat preservation and decolorization. The product is then hot filtered, the filtrate is cooled to crystallize, centrifuged, and vacuum dried to obtain o-nitrobenzaldehyde.

[0010] Further, in step S1, the composite catalyst is composed of a metal salt catalyst and a phase transfer catalyst in a mass ratio of 1:2 to 4; the metal salt catalyst is any one of cobalt acetylacetonate, manganese acetylacetonate, and copper chloride; the phase transfer catalyst is any one of tetrabutylammonium bromide, benzyltriethylammonium chloride, and polyethylene glycol-400.

[0011] Further, in step S1, the mass fractions of each material are: 100 parts of o-nitrotoluene, 150-300 parts of organic solvent, 2-5 parts of composite catalyst, and 120-180 parts of 30% hydrogen peroxide solution.

[0012] Further, in step S1, the organic solvent is either 1,2-dichloroethane or ethyl acetate; the pH of the system is adjusted to 8.0-9.0 using a 5% sodium carbonate aqueous solution; the reaction temperature is 60-85℃; the hydrogen peroxide is added dropwise for 2-4 hours; and the reaction is maintained at this temperature for 3-6 hours.

[0013] Furthermore, in step S2, the vacuum degree of the reduced pressure distillation is -0.085 to -0.098 MPa, and the distillation temperature is 70 to 90°C.

[0014] Furthermore, in step S3, the recrystallization solvent is a mixture of anhydrous ethanol and water in a volume ratio of 3:1; the recrystallization dissolution temperature is 65~75℃, the cooling crystallization temperature is 0~5℃, and the crystallization time is 2~4h.

[0015] Furthermore, in step S3, the vacuum drying temperature is 40~50℃, and the vacuum degree is ≥-0.095MPa.

[0016] Furthermore, in step S3, the drying time is 6~10 hours.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] This invention employs a composite catalytic system combining a metal salt and a phase transfer catalyst to synergistically catalyze the selective oxidation of hydrogen peroxide under a weakly alkaline environment, avoiding excessive oxidation of raw materials to generate impurities such as o-nitrobenzoic acid. The process is green and environmentally friendly, using hydrogen peroxide as a clean oxidant, with water as the reaction byproduct. It eliminates the need for traditional heavy metal oxidants, resulting in no heavy metal ion residues or high-salt waste acid, thus reducing emissions. The organic solvent can be efficiently recovered and recycled, meeting green chemical production requirements and reducing environmental governance costs. The reaction conditions are mild, suitable for industrial production, requiring no high-temperature or high-pressure equipment, resulting in low equipment investment and energy consumption, thus reducing production and operating costs. This invention also boasts high purification efficiency and excellent product quality. The purification method, employing vacuum distillation combined with mixed solvent recrystallization, removes trace organic impurities and catalyst residues, yielding a product with high purity and low impurity content, meeting the standard application requirements of the pharmaceutical and fine chemical industries. Detailed Implementation

[0019] 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.

[0020] Example 1

[0021] A preparation process for o-nitrobenzaldehyde, the specific steps of which are as follows:

[0022] S1 reaction: Weigh 100g of o-nitrotoluene, 150g of 1,2-dichloroethane, and 2g of composite catalyst (cobalt acetylacetonate + tetrabutylammonium bromide, mass ratio 1:2) and add them to the reactor, stirring until homogeneous; adjust the pH of the system to 8.0 using a 5% sodium carbonate aqueous solution, raise the temperature to 60℃, and add 120g of 30% hydrogen peroxide solution dropwise at a uniform rate over 2 hours. After the addition is complete, keep the reaction at this temperature for 3 hours.

[0023] S2 post-processing separation: After the reaction is completed, the temperature is cooled to room temperature, and the liquid is separated by standing. The organic phase is collected. Then, 70g of sodium metabisulfite dissolved in 200mL of deionized water is added to it. The salt formation reaction is carried out at 25℃ for 1 hour. The layers are separated, the aqueous layer is taken, and the pH is adjusted to 10 with 20% sodium hydroxide solution. The crude product is precipitated, filtered, and the organic solvent is recovered to obtain crude o-nitrobenzaldehyde.

[0024] S3 Purification and Refining: Add the crude product to a recrystallization solvent of anhydrous ethanol and water in a volume ratio of 3:1, heat to 65℃ until completely dissolved, and add the crude product mass... The activated carbon was decolorized by heat preservation and hot filtration; the filtrate was cooled to 0℃, allowed to stand for crystallization for 2 hours, separated by centrifugation, and then vacuum dried for 6 hours at 40℃ and a vacuum degree of ~0.095MPa to obtain the finished product.

[0025] High performance liquid chromatography analysis showed that the raw material conversion rate was 98.5%, the product yield was 82.0%, and the product purity was 99.80%.

[0026] Example 2

[0027] A preparation process for o-nitrobenzaldehyde, the specific steps of which are as follows:

[0028] S1 reaction: Weigh 100g of o-nitrotoluene, 225g of 1,2-dichloroethane, and 3.5g of composite catalyst (manganese acetylacetone + benzyltriethylammonium chloride, mass ratio 1:3) and add them to the reactor, stirring until homogeneous; adjust the pH of the system to 8.5 using a 5% sodium carbonate aqueous solution, raise the temperature to 72℃, and add 150g of 30% hydrogen peroxide solution dropwise at a uniform rate over 3 hours. After the addition is complete, maintain the temperature for 4.5 hours.

[0029] S2 post-processing separation: After the reaction is completed, the temperature is cooled to room temperature, and the liquid is separated by standing. The organic phase is collected. Then, 75g of sodium metabisulfite dissolved in 200mL of deionized water is added to it. The salt formation reaction is carried out at 40℃ for 4 hours. The layers are separated, the aqueous layer is taken, and the pH is adjusted to 11 with 20% sodium hydroxide solution. The crude product is precipitated, filtered, and the crude o-nitrobenzaldehyde is obtained.

[0030] S3 Purification and Refining: Add the crude product to a recrystallization solvent of anhydrous ethanol and water in a volume ratio of 3:1, heat to 70℃ until completely dissolved, and add the crude product mass... The activated carbon was kept warm and decolorized, and then hot filtered. The filtrate was cooled to 2.5℃, allowed to stand for crystallization for 3 hours, centrifuged, and then vacuum dried at 45℃ and a vacuum degree of ~0.096MPa for 8 hours to obtain the finished product.

[0031] High performance liquid chromatography analysis showed that the raw material conversion rate was 99.1%, the product yield was 83.2%, and the product purity was 99.86%.

[0032] Example 3

[0033] A preparation process for o-nitrobenzaldehyde, the specific steps of which are as follows:

[0034] S1 Ingredient Preparation and Reaction: Weigh 100g of o-nitrotoluene, 300g of ethyl acetate, and 5g of composite catalyst (copper chloride + polyethylene glycol 400, mass ratio 1:4) and add them to the reaction vessel, stirring until homogeneous; adjust the pH of the system to 9.0 using a 5% sodium carbonate aqueous solution, raise the temperature to 85℃, and add 180g of 30% hydrogen peroxide solution dropwise at a uniform rate over 4 hours. After the addition is complete, keep the reaction at this temperature for 6 hours.

[0035] S2 post-processing separation: After the reaction is completed, the temperature is cooled to room temperature, and the liquid is separated by standing. The organic phase is collected. Then, 72g of sodium metabisulfite dissolved in 200mL of deionized water is added to it. The salt formation reaction is carried out at 30℃ for 2 hours. The layers are separated, the aqueous layer is taken, and the pH is adjusted to 11 with 20% sodium hydroxide solution. The crude product is precipitated, filtered, and the crude o-nitrobenzaldehyde is obtained.

[0036] S3 Purification and Refining: Add the crude product to a recrystallization solvent of anhydrous ethanol and water in a volume ratio of 3:1, heat to 75°C until completely dissolved, and add the crude product mass... The activated carbon was heat-insulated for decolorization and hot filtration; the filtrate was cooled to 5°C, allowed to stand for crystallization for 4 hours, centrifuged, and then vacuum-dried at 50°C and a vacuum degree of ~0.098MPa for 10 hours to obtain the finished product.

[0037] High performance liquid chromatography analysis showed that the raw material conversion rate was 98.9%, the product yield was 82.7%, and the product purity was 99.83%.

[0038] Comparative Example 1

[0039] The difference between this comparative example and Example 3 is that no composite catalyst is added in step S1, while the other raw material ratios, process parameters, and post-treatment methods are completely the same.

[0040] Testing revealed that the raw material conversion rate was 61.8%, the product yield was 40.5%, and the product purity was 92.3%. The oxidation reaction was incomplete, producing a large amount of o-nitrobenzoic acid as a byproduct, which has no industrial value.

[0041] Comparative Example 2

[0042] The difference between this comparative example and Example 3 is that in step S1, equimolar potassium permanganate is used instead of hydrogen peroxide as the oxidant, the pH of the system is not adjusted, and the other process parameters are completely the same.

[0043] Tests showed that the raw material conversion rate was 84.7%, the product yield was 75.2%, and the product purity was 94.1%; however, a large amount of wastewater containing manganese heavy metals was generated.

[0044] Comparative Example 3

[0045] The difference between this comparative example and Example 3 is that the pH of the system was adjusted to 6.0 (acidic environment) in step S1, while the other raw material ratios and process parameters were completely the same.

[0046] Testing revealed that the raw material conversion rate was 72.3%, the product yield was 58.6%, the oxidation selectivity decreased significantly, the by-product content increased significantly, and the product purity was only 93.5%.

[0047] In the various embodiments and comparative examples of this invention, the purity of the product and the conversion rate of the raw materials were detected by high performance liquid chromatography (HPLC).

[0048] The formula for calculating "product yield" in this invention is as follows: Y = (m0 / m1) × 100%, where, Product yield; m1 represents the actual mass of the refined o-nitrobenzaldehyde product; m2 represents the theoretical yield of o-nitrobenzaldehyde calculated based on the mass of o-nitrobenzaldehyde fed into the plant.

[0049] 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 a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0050] 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 preparation process for o-nitrobenzaldehyde, characterized in that, Includes the following steps: S1 Ingredients and Reaction: Add o-nitrotoluene, organic solvent, and composite catalyst to the reactor, stir and mix evenly, adjust the pH of the system to weakly alkaline, raise the temperature to the reaction temperature, add hydrogen peroxide solution dropwise at a uniform rate, and keep the reaction at the temperature. S2 post-processing separation: After the reaction is completed, cool to room temperature, let stand and separate the liquid, collect the organic phase; add 70-75g of sodium metabisulfite dissolved in 200mL of deionized water, react at 25-40℃ for 1-4 hours to form salt, separate the layers, take the aqueous layer, adjust the pH to 10-11 with 20% sodium hydroxide solution, precipitate the crude product, filter, and obtain the crude product. S3 purification and refining: The crude product is added to a recrystallization solvent, heated to dissolve, and then a decolorizing agent is added for heat preservation and decolorization. The product is then hot filtered, the filtrate is cooled to crystallize, centrifuged, and vacuum dried to obtain o-nitrobenzaldehyde.

2. The preparation process of o-nitrobenzaldehyde according to claim 1, characterized in that, In step S1, the composite catalyst is prepared by compounding a metal salt catalyst and a phase transfer catalyst in a mass ratio of 1:2 to 4; the metal salt catalyst is any one of cobalt acetylacetonate, manganese acetylacetonate, and copper chloride; the phase transfer catalyst is any one of tetrabutylammonium bromide, benzyltriethylammonium chloride, and polyethylene glycol-400.

3. The preparation process of o-nitrobenzaldehyde according to claim 1, characterized in that, In step S1, the mass fractions of each material are: 100 parts of o-nitrotoluene, 150-300 parts of organic solvent, 2-5 parts of composite catalyst, and 120-180 parts of 30% hydrogen peroxide solution.

4. The preparation process of o-nitrobenzaldehyde according to claim 1, characterized in that, In step S1, the organic solvent is either 1,2-dichloroethane or ethyl acetate; the pH of the system is adjusted to 8.0-9.0 using a 5% sodium carbonate aqueous solution; the reaction temperature is 60-85℃; the hydrogen peroxide is added dropwise for 2-4 hours; and the reaction is maintained at this temperature for 3-6 hours.

5. The preparation process of o-nitrobenzaldehyde according to claim 1, characterized in that, In step S2, the vacuum degree of the reduced pressure distillation is -0.085 to -0.098 MPa, and the distillation temperature is 70 to 90°C.

6. The preparation process of o-nitrobenzaldehyde according to claim 1, characterized in that, In step S3, the recrystallization solvent is a mixture of anhydrous ethanol and water in a volume ratio of 3:1; the recrystallization dissolution temperature is 65~75℃, the cooling crystallization temperature is 0~5℃, and the crystallization time is 2~4h.

7. The preparation process of o-nitrobenzaldehyde according to claim 1, characterized in that, In step S3, the vacuum drying temperature is 40~50℃ and the vacuum degree is ≥-0.095MPa.

8. The preparation process of o-nitrobenzaldehyde according to claim 1, characterized in that, In step S3, the drying time is 6-10 hours.