Synthesis method of 2-chloronicotinic acid

Abstract

The invention discloses a synthesis method of 2-chloronicotinic acid, and relates to the field of organic synthesis.The method comprises the steps that under the action of a first oxidation system potassium persulfate, TEMPO and a sodium hypochlorite solution, 2-chloro-3-pyridinecarboxaldehyde is prepared through oxidation of 2-chloro-3-pyridinecarboxaldehyde; and oxidizing the 2-chloro-3-pyridylaldehyde under the action of hydrogen peroxide and alkali in a second oxidation system to prepare the 2-chloronicotinic acid. According to the method, two-step oxidation is only carried out on the site 3 of a chloropyridine ring, chlorination is not needed, waste liquid containing phosphorus and chlorine is prevented from being generated, and the bottleneck that chlorine atoms are prone to hydrolysis and falling off in a traditional strong acid and strong alkali system is broken through. The method has the advantages of simple process steps, easily available raw materials, mild and controllable conditions, high selectivity and stable yield, avoids the generation of highly toxic substances or waste liquid, is green and environment-friendly, and is suitable for large-scale production.

Description

A method for synthesizing 2-chloronicotinic acid Technical Field

[0001] This invention relates to the field of organic synthesis technology, specifically to a method for synthesizing 2-chloronicotinic acid. Background Art

[0002] 2-Chloronicotinic acid, also known as 2-chloronicotinic acid, belongs to the pyridine nitrogen heterocyclic class of compounds and possesses unique physiological activities. In many pesticide and pharmaceutical studies, the structure of 2-chloronicotinic acid and its derivatives serves as a building block for the synthesis of antiviral and anti-inflammatory drugs, as well as pesticides, fungicides, insecticides, and herbicides. Therefore, 2-chloronicotinic acid can be considered a very important intermediate in pharmaceuticals, pesticides, and food additives. In the pesticide field, 2-chloronicotinic acid has been used as a raw material to prepare a highly efficient selective post-emergence herbicide for corn fields—nicosulfuron (Yunongle). In the pharmaceutical field, the German company Boehringer Ingelheim has developed a non-nucleoside HIV reverse transcriptase inhibitor—nevirapine—using 2-chloronicotinic acid as a raw material. Compared with other anti-AIDS drugs, nevirapine has advantages such as strong antiviral activity, long half-life, high bioavailability, strong resistance to drug resistance, fewer adverse reactions, and low cost. Therefore, it is widely used in clinical practice. In addition, other companies have successively developed anti-inflammatory and analgesic drugs (such as niflufenicol and pranoprofen) and antidepressants. Furthermore, 2-chloronicotinic acid itself is not directly used as a food additive, but rather participates as a key intermediate in the synthesis of nicotinic acid, nicotinamide, and nicotinic acid esters. These two substances play a crucial role in the field of food additives. In conclusion, 2-chloronicotinic acid has potential research value and broad application prospects.

[0003] Currently, the synthesis of 2-chloronicotinic acid mainly relies on the pyridine ring construction method and the pyridine derivative method. Among them, the pyridine derivative method for synthesizing 2-chloronicotinic acid mainly includes: (1) using nicotinic acid as the starting material, 2-chloronicotinic acid is prepared through nitration, reduction, diazotization / Sandmeier reaction and chlorination. This method has lengthy steps and poor chlorination selectivity; (2) using 2-chloro-3-methylpyridine as the starting material, 2-chloronicotinic acid is prepared by oxidizing the methyl group to the carboxyl group with the strong oxidant potassium permanganate. This method has scarce raw materials and low yield, and potassium permanganate is expensive, making it unsuitable for industrial production; (3) using 2-chloro-3-trifluoromethylpyridine as the starting material, 2-chloronicotinic acid is synthesized through hydrolysis and oxidation. However, this method requires high temperature and high pressure for hydrolysis, resulting in many side reactions and high cost; (4) using 3-cyanopyridine as the starting material, 2-chloronicotinic acid is prepared through oxidation, chlorination and hydrolysis. The reaction requires the addition of a large amount of POCl3, which will generate a large amount of phosphorus-containing wastewater, causing serious pollution, and the chlorination selectivity is difficult to control; (5) 2-chloronicotinic acid is synthesized by hydroxy chlorination and carboxylation reaction using 2-hydroxypyridine as raw material. This method uses highly toxic substances such as POCl3 and generates a large number of chlorinated byproducts.

[0004] Therefore, it is of great significance to study a simple, efficient, green and environmentally friendly method for synthesizing 2-chloronicotinic acid. Summary of the Invention

[0005] In view of this, the present invention provides a method for synthesizing 2-chloronicotinic acid. This method uses 2-chloro-3-pyridinemethanol as the starting material and involves a two-step oxidation reaction only at the 3-position of the chloropyridine ring, eliminating the need for chlorination and avoiding the generation of phosphorus- and chlorine-containing waste liquids. It also overcomes the bottleneck of easy hydrolysis and detachment of chlorine atoms in traditional strong acid and strong base systems. The present invention features simple process steps, readily available raw materials, mild and controllable conditions, high selectivity, stable yield, and is environmentally friendly, possessing excellent prospects for industrial development.

[0006] To better solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for synthesizing 2-chloronicotinic acid includes the following steps:

[0008] (1) 2-Chloro-3-pyridinemethanol was oxidized to the intermediate 2-chloro-3-pyridinemethane under the action of potassium persulfate, TEMPO and sodium hypochlorite solution in the first oxidation system;

[0009] (2) 2-chloronicotinic acid was prepared by oxidizing 2-chloro-3-pyridine carboxaldehyde under the action of hydrogen peroxide and alkali in the second oxidation system.

[0010] Furthermore, in step (1), the solvent used to oxidize 2-chloro-3-pyridinemethanol to obtain the intermediate 2-chloro-3-pyridinemethane is dichloromethane.

[0011] Furthermore, in step (1), during the process of adding sodium hypochlorite solution, the temperature of the reaction solution is kept at 0°C, and after the addition is completed, the mixture is stirred at 5°C for 5-10 minutes.

[0012] Further, in step (1), the molar ratio of 2-chloro-3-pyridinemethanol to sodium hypochlorite is 1:1.0-4.5; preferably, the molar ratio of 2-chloro-3-pyridinemethanol to sodium hypochlorite is 1:1.5-2.5, and more preferably, the molar ratio of 2-chloro-3-pyridinemethanol to sodium hypochlorite is 1:2.

[0013] Further, in step (1), the molar ratio of 2-chloro-3-pyridinemethanol to potassium persulfate is 1:0.01-1.0; preferably, the molar ratio of 2-chloro-3-pyridinemethanol to potassium persulfate is 1:0.1-0.5, and more preferably, the molar ratio of 2-chloro-3-pyridinemethanol to potassium persulfate is 1:0.2.

[0014] Preferably, in step (1), the molar ratio of 2-chloro-3-pyridinemethanol to TEMPO is 1:0.01-0.2; more preferably, the molar ratio of 2-chloro-3-pyridinemethanol to TEMPO is 1:0.02-0.1; and even more preferably, the molar ratio of 2-chloro-3-pyridinemethanol to TEMPO is 1:0.05.

[0015] Furthermore, in step (1), the reaction temperature for oxidizing 2-chloro-3-pyridinemethanol to obtain the intermediate 2-chloro-3-pyridinemethane is 40°C, and the reaction time is 2-12 h; preferably, the reaction time is 6-10 h, and more preferably, the reaction time is 8 h.

[0016] Furthermore, in step (2), the solvent used to oxidize 2-chloro-3-pyridine carboxaldehyde to obtain 2-chloronicotinic acid is selected from at least one of acetonitrile, dichloromethane, dichloroethane, tetrahydrofuran, acetone, chloroform, methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, and diethyl ether.

[0017] Furthermore, in step (2), the alkali is selected from at least one of sodium carbonate, cesium carbonate, potassium carbonate, sodium methoxide, potassium tert-butoxide, sodium hydroxide, and potassium hydroxide. The alkali provides an alkaline environment for the reaction system, promoting the deprotonation of hydrogen peroxide to generate the more nucleophilic hydrogen peroxide anion HOO. - .

[0018] Further, in step (2), the molar ratio of 2-chloro-3-pyridine carboxaldehyde to hydrogen peroxide is 1:0.5~1.8; preferably, the molar ratio of 2-chloro-3-pyridine carboxaldehyde to hydrogen peroxide is 1:1-1.4, and more preferably, the molar ratio of 2-chloro-3-pyridine carboxaldehyde to hydrogen peroxide is 1:1.2.

[0019] Furthermore, in step (2), the molar ratio of 2-chloro-3-pyridine carboxaldehyde to the base is 1:0.1-1.3; preferably, the molar ratio of 2-chloro-3-pyridine carboxaldehyde to the base is 1:0.5-1, and even more preferably, the molar ratio of 2-chloro-3-pyridine carboxaldehyde to the base is 1:0.8.

[0020] Furthermore, in step (2), the hydrogen peroxide is added at a temperature of 0°C.

[0021] Furthermore, in step (2), the reaction temperature for oxidizing 2-chloro-3-pyridine carboxaldehyde to obtain 2-chloronicotinic acid is 25-80℃, and the reaction time is 3-12h; preferably, the reaction time is 5-10h, and more preferably, the reaction time is 8h.

[0022] Compared with the prior art, the present invention has at least the following advantages:

[0023] 1. This invention uses inexpensive and readily available 2-chloro-3-pyridinemethanol as the starting material and employs a two-step oxidation process. By optimizing reaction conditions such as the amount of oxidant, catalyst, type and amount of alkali, temperature, and time, high-purity and high-yield 2-chloronicotinic acid is obtained. This avoids the generation of chlorine-containing waste liquid and highly toxic substances, making it environmentally friendly. At the same time, it effectively solves problems such as the stability of chlorine atoms in the synthesis of 2-chloronicotinic acid, such as chlorination side reactions and chlorine hydrolysis, and achieves highly selective conversion of primary alcohols to carboxylic acids, which has promising industrial application prospects.

[0024] 2. This invention employs a two-step oxidation system. In the first step, the oxidation of alcohol to aldehyde, a TEMPO / sodium hypochlorite / potassium persulfate system is used. This system efficiently and selectively oxidizes primary alcohols to aldehydes, while making further oxidation to acids extremely difficult, ensuring the purity of the intermediate product. In the second oxidation step, a hydrogen peroxide / alkali system is used, avoiding the hydrolysis or substitution side reactions of chlorine atoms that may occur under strong oxidizing agents or strong acid conditions. This protects the structural integrity of the product, thereby improving the purity and yield of the target product. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 is a gas chromatogram of 2-chloronicotinic acid prepared in Example 1. Detailed Implementation

[0027] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0028] This invention provides a method for synthesizing 2-chloronicotinic acid. The method uses 2-chloro-3-pyridinemethanol as the starting material, and sequentially prepares the intermediate 2-chloro-3-pyridinecarboxaldehyde through two-stage oxidation reactions, followed by further oxidation to obtain 2-chloronicotinic acid, thereby achieving highly selective preparation of the target product. The specific process is as follows:

[0029] S1. Under the action of potassium persulfate, TEMPO and sodium hypochlorite solution in the first oxidation system, 2-chloro-3-pyridinemethanol is oxidized to obtain intermediate 2-chloro-3-pyridinemethane.

[0030] S2. In the second oxidation system, 2-chloro-3-pyridinecarboxaldehyde is oxidized to produce 2-chloronicotinic acid under the action of hydrogen peroxide and alkali.

[0031] In this invention, there are no special restrictions on the source of the 2-chloro-3-pyridinemethanol, potassium persulfate, TEMPO, and sodium hypochlorite solution; they can be commercially available products.

[0032] In this invention, the concentration of the sodium hypochlorite solution is not particularly limited, and sodium hypochlorite solution of commonly used specifications in the art can be selected; the sodium hypochlorite solution is preferably added to the reaction system dropwise to facilitate control of exothermic reaction and improve selectivity.

[0033] In step S1:

[0034] This invention, through the rational selection of oxidation system and oxidation conditions, ensures that 2-chloro-3-pyridinemethanol is oxidized only to aldehydes, without being over-oxidized to acids, while not destroying the pyridine ring and chlorine atoms.

[0035] In some embodiments of the present invention, dichloromethane is used as the solvent when 2-chloro-3-pyridinemethanol is oxidized to the intermediate 2-chloro-3-pyridinecarboxaldehyde. The formation of a two-phase system between dichloromethane and water-soluble NaClO facilitates the dissolution of the aldehyde product in the organic phase and further prevents excessive oxidation by the oxidant in the aqueous phase.

[0036] In some embodiments of the present invention, the temperature of the reaction solution is maintained at 0°C during the dropwise addition of sodium hypochlorite solution, and the mixture is stirred at 5°C for 5-10 minutes after the addition is completed. Because oxidation reactions are typically exothermic, low-temperature dropwise addition can prevent side reactions caused by excessively high local temperatures.

[0037] In some embodiments of the present invention, the molar ratio of 2-chloro-3-pyridinemethanol to sodium hypochlorite is 1:1.0-4.5; specifically, the molar ratio of 2-chloro-3-pyridinemethanol to sodium hypochlorite can be 1:1.1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, or 1:4.5. Preferably, the molar ratio of 2-chloro-3-pyridinemethanol to sodium hypochlorite is 1:1.5-2.5, and more preferably, the molar ratio of 2-chloro-3-pyridinemethanol to sodium hypochlorite is 1:2.

[0038] In some embodiments of the present invention, the molar ratio of 2-chloro-3-pyridinemethanol to potassium persulfate is 1:0.01-1.0; specifically, the molar ratio of 2-chloro-3-pyridinemethanol to potassium persulfate can be 1:0.01, 1:0.05, 1:0.1, 1:0.2, 1:0.5, or 1:1. Preferably, the molar ratio of 2-chloro-3-pyridinemethanol to potassium persulfate is 1:0.1-0.5, and more preferably, the molar ratio of 2-chloro-3-pyridinemethanol to potassium persulfate is 1:0.2.

[0039] In some embodiments of the present invention, the molar ratio of 2-chloro-3-pyridinemethanol to TEMPO is 1:0.01-0.2; specifically, the molar ratio of 2-chloro-3-pyridinemethanol to TEMPO can be 1:0.01, 1:0.02, 1:0.05, 1:0.1, or 1:0.2. Preferably, the molar ratio of 2-chloro-3-pyridinemethanol to TEMPO is 1:0.02-0.1, and more preferably, the molar ratio of 2-chloro-3-pyridinemethanol to TEMPO is 1:0.05.

[0040] In some embodiments of the present invention, the reaction temperature for oxidizing 2-chloro-3-pyridinemethanol to obtain the intermediate 2-chloro-3-pyridinemethane is 40°C, and the reaction time is 2-12 h; specifically, the reaction time is preferably 2 h, 4 h, 6 h, 8 h, 10 h, and 12 h; preferably, the reaction time is 6-10 h, and more preferably, the reaction time is 8 h.

[0041] In this invention, after the reaction in step S1 is completed, post-processing is performed to obtain the intermediate 2-chloro-3-pyridinecarboxaldehyde. The post-processing method is not particularly limited and can be any conventional means in the art. Preferably, it includes: cooling to room temperature after the reaction, washing, drying, and concentration.

[0042] In step S2:

[0043] In some embodiments of the present invention, the solvent used to oxidize 2-chloro-3-pyridinecarboxaldehyde to obtain 2-chloronicotinic acid is selected from at least one of acetonitrile, dichloromethane, dichloroethane, tetrahydrofuran, acetone, chloroform, methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, and diethyl ether.

[0044] In some embodiments of the present invention, the base is selected from at least one of sodium carbonate, cesium carbonate, potassium carbonate, sodium methoxide, potassium tert-butoxide, sodium hydroxide, and potassium hydroxide. The base provides an alkaline environment to the reaction system, promoting the deprotonation of hydrogen peroxide to generate the more nucleophilic hydrogen peroxide anion HOO. - This facilitates the oxidative conversion of aldehydes into carboxylic acids.

[0045] In some embodiments of the present invention, the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to hydrogen peroxide is 1:0.5-1.8; specifically, the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to hydrogen peroxide is selected from 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.5, and 1:1.8. Preferably, the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to hydrogen peroxide is 1:1-1.4, and more preferably, the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to hydrogen peroxide is 1:1.2.

[0046] In some embodiments of the present invention, the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to the base is 1:0.1-1.3; specifically, the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to the base is selected from 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1, 1:1.2, and 1:1.3. Preferably, the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to the base is 1:0.5-1, and more preferably, the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to the base is 1:0.8.

[0047] In some embodiments of the present invention, the hydrogen peroxide is added at a temperature of 0°C.

[0048] In this invention, the concentration of hydrogen peroxide is not particularly limited, and conventional hydrogen peroxide solutions in the art can be used; preferably, it is added to the reaction system dropwise to facilitate control of exothermic reactions and improve reaction controllability.

[0049] In some embodiments of the present invention, the reaction temperature for oxidizing 2-chloro-3-pyridinecarboxaldehyde to obtain 2-chloronicotinic acid is 25-80°C, and the reaction time is 3-12 hours; specifically, the reaction temperature can be selected from 25°C, 40°C, 50°C, 60°C, 70°C, and 80°C; the reaction time can be selected from 3 hours, 5 hours, 8 hours, 10 hours, and 12 hours. Preferably, the reaction time is 5-10 hours, and more preferably, the reaction time is 8 hours.

[0050] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0051] In the following examples, the yield (%) = (actual product yield / theoretical product yield) × 100%.

[0052] Example

[0053] A method for synthesizing 2-chloronicotinic acid includes the following steps:

[0054] (1) Measure 2.0 g of 2-chloro-3-pyridinemethanol and place it in a reaction flask. Add dichloromethane as a solvent to the reaction flask, and then add 0.753 g of potassium persulfate and 0.1088 g of TEMPO. Lower the temperature of the reaction flask to 0°C and slowly add 27.654 g of 7.5 wt% sodium hypochlorite solution while stirring (the addition is completed within 30 min). After the addition is completed, gradually raise the temperature of the reaction system to 40°C and keep it at that temperature for 8 h. After the reaction is complete as detected by TLC, lower the reaction system to room temperature, add purified water to wash, stir and let it stand to separate the layers. Repeat this process 3 times, combine the organic layers and remove the solvent under reduced pressure to concentrate the compound 2-chloro-3-pyridinemethanol with a yield of 92%. 1H NMR (400 MHz, CDCl3) δ (ppm) 10.45 (s, 1H), 8.61 (dd, J = 4.7, 2.1 Hz, 1H), 8.24 (dd, J = 7.7, 2.1 Hz, 1H), 7.42 (dd, J = 7.6, 4.8 Hz, 1H).

[0055] (2) Weigh 1.0 g of 2-chloro-3-pyridinecarboxaldehyde and 0.599 g of anhydrous sodium carbonate from step (1) and dissolve them in acetonitrile. Cool the reaction system to 0°C and add 0.961 g of 30wt% hydrogen peroxide solution dropwise. After the addition is complete, heat the reaction system to 70°C and stir for 8 hours. Detect the reaction by TLC thin layer. After the raw materials have reacted completely, cool the reaction system to room temperature, concentrate under reduced pressure, add an appropriate amount of purified water for precipitation, filter, wash the filter cake with ice water and dry it under vacuum to obtain the target product 2-chloronicotinic acid with a yield of 98%. 1 H NMR (400 MHz, DMSO-d6) δ (ppm) 10.45 (s, 1H), 8.56 (dd, J =4.8, 2.0 Hz, 1H), 8.23 ​​(dd, J = 7.7, 1.9 Hz, 1H), 7.55 (dd, J = 7.6, 4.8 Hz, 1H). 13C NMR (101 MHz, DMSO-d6) δ (ppm) 168.2, 148.1, 146.6, 137.9, 136.3,122.7.

[0056] The gas chromatogram of 2-chloronicotinic acid is shown in Figure 1. As can be seen from Figure 1, the purity of 2-chloronicotinic acid is 98%.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for synthesizing 2-chloronicotinic acid, characterized in that, Includes the following steps: (1) 2-chloro-3-pyridinemethanol was oxidized to obtain intermediate 2-chloro-3-pyridinemaldehyde under the action of potassium persulfate, TEMPO and sodium hypochlorite solution in the first oxidation system; (2) 2-chloro-3-pyridinemaldehyde was oxidized to obtain 2-chloronicotinic acid under the action of hydrogen peroxide and alkali in the second oxidation system.

2. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (1), the solvent used to oxidize 2-chloro-3-pyridinemethanol to obtain the intermediate 2-chloro-3-pyridinemethane is dichloromethane.

3. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (1), during the addition of sodium hypochlorite solution, the temperature of the reaction solution is kept at 0°C, and after the addition is completed, the solution is stirred at 5°C for 5-10 minutes.

4. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (1), the molar ratio of 2-chloro-3-pyridinemethanol to sodium hypochlorite is 1:1.0-4.5; the molar ratio of 2-chloro-3-pyridinemethanol to potassium persulfate is 1:0.01-1.0; and the molar ratio of 2-chloro-3-pyridinemethanol to TEMPO is 1:0.01-0.

2.

5. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (1), the reaction temperature for oxidizing 2-chloro-3-pyridinemethanol to obtain the intermediate 2-chloro-3-pyridinemethane is 40℃ and the reaction time is 2-12h.

6. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (2), the solvent used to oxidize 2-chloro-3-pyridine carboxaldehyde to obtain 2-chloronicotinic acid is selected from at least one of acetonitrile, dichloromethane, dichloroethane, tetrahydrofuran, acetone, chloroform, methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, and diethyl ether.

7. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (2), the alkali is selected from at least one of sodium carbonate, cesium carbonate, potassium carbonate, sodium methoxide, potassium tert-butoxide, sodium hydroxide, and potassium hydroxide.

8. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (2), the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to hydrogen peroxide is 1:0.5~1.8; the molar ratio of 2-chloro-3-pyridinecarboxaldehyde to alkali is 1:0.1~1.

3.

9. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (2), the hydrogen peroxide is added at a temperature of 0°C.

10. The method for synthesizing 2-chloronicotinic acid according to claim 1, characterized in that, In step (2), the reaction temperature for oxidizing 2-chloro-3-pyridine carboxaldehyde to obtain 2-chloronicotinic acid is 25-80℃ and the reaction time is 3-12h.

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