A method for the efficient synthesis of aromatic nitro compounds

Abstract

This invention discloses a highly efficient method for synthesizing aromatic nitro compounds, belonging to the field of organic chemistry. Using aromatic hydrocarbons or substituted aromatic hydrocarbons and concentrated nitric acid as raw materials, the aromatic nitro compounds described in this invention are obtained in one step in the presence of an acid catalyst in hexafluoroisopropanol. This method requires no heating and can be carried out smoothly in air and at room temperature. It has advantages such as simple operation, high yield, high product quality, wide substrate applicability, and ease of large-scale production. A series of aromatic nitro compounds can be obtained using this method.

Description

Technical Field

[0001] This invention belongs to the field of organic chemistry technology and relates to a method for synthesizing aromatic nitro compounds, specifically a method for acid-catalyzed synthesis of aromatic nitro compounds. Background Technology

[0002] Nitroaromatics are important organic intermediates due to their excellent properties in approved pesticides, explosives, and dyes, and their wide application in chemical synthesis. For example, nitrobenzene, nitrobenzene, and nitrochlorobenzene are dye intermediates, and some nitro compounds are elemental explosives (such as TNT). The reduction of aromatic nitro compounds can yield various primary aromatic amines. Traditionally, as an important part of the electrophilic aromatic substitution developed in the 19th century, electrophilic nitration of aromatics has been widely used as a very effective method for preparing aryl nitrates. However, traditional nitration reaction conditions are strict, using concentrated nitric acid or even fuming nitric acid as the nitrating agent, concentrated sulfuric acid as the catalyst, and heating under mixed acid conditions to achieve the reaction. This poses significant safety risks in actual production. The reaction equation is as follows:

[0003]

[0004] In 2019, a method for the efficient synthesis of various nitroaromatic hydrocarbons was reported in the literature. This method uses N-nitro-o-phenylthioimide as the nitrating agent and hexafluoroisopropanol or acetonitrile as the solvent. The reaction requires heating to 55-85℃. The reaction equation is as follows:

[0005]

[0006] However, the nitrating agent in this method needs to be synthesized, which requires fuming nitric acid, and the reaction needs to be carried out at high temperatures, making it neither economical nor efficient.

[0007] Concentrated nitric acid is relatively stable, readily available, and inexpensive, making it commercially viable and widely used in electrophilic substitution reactions. However, the mixed acid method has been difficult to apply to the nitration of electron-deficient aromatic compounds, and most of these reactions require heating, posing significant safety risks. Heating and the resulting acidic gases cause substantial environmental pollution, and the yield is low. Furthermore, some common functional groups, such as hydroxyl, aldehyde, carbon-carbon double, and carbon-carbon triple bonds, are easily oxidized by concentrated sulfuric acid. Once deactivated and oxidized, the properties of the product change, limiting the application of the mixed acid method in current nitration synthesis. Therefore, the synthesis of aromatic nitro compounds, especially electron-deficient aromatic nitro compounds, using traditional methods presents significant limitations.

[0008] Therefore, it is very important to develop synthetic methods that conform to the development direction of green chemistry, use readily available and stable nitrating reagents, and prepare aromatic nitro compounds with high selectivity. Summary of the Invention

[0009] In view of this, this application provides a simple method for the one-step synthesis of aromatic nitro compounds under ambient temperature and pressure catalytic conditions using concentrated nitric acid as the nitrating agent. This method avoids the drawbacks of traditional preparation methods, such as harsh reaction conditions, numerous side reactions, high-temperature requirements, and severe environmental pollution. This method allows for the quantitative catalytic synthesis of aromatic nitro compounds.

[0010] The purpose of this invention is to provide a method for synthesizing aromatic nitro compounds, the synthetic route of which is shown in the following formula:

[0011]

[0012] The method for synthesizing aromatic nitro compounds described above includes the following steps: using aromatic compound 1 and nitric acid as raw materials, reacting them in an organic solvent in the presence of an acid catalyst to obtain aromatic nitro compound 2.

[0013] Furthermore, in the above technical solution, the aromatic compound 1 is selected from benzene or substituted phenyl groups, and the substituents in the substituted phenyl groups are selected from one or more of C1-C4 alkyl, carboxyl, halogen, and aldehyde groups.

[0014] Furthermore, in the above technical solution, the organic solvent is one of hexafluoroisopropanol, trifluoroethanol, n-hexane, chloroalkanes, and trifluoromethanesulfonic acid.

[0015] Furthermore, in the above technical solution, the nitric acid is concentrated nitric acid or fuming nitric acid.

[0016] Furthermore, in the above technical solution, the molar ratio of compound 1, nitric acid and acid catalyst is 1:1.0-1.2:0.1-2.0.

[0017] Furthermore, in the above technical solution, the reaction does not require heating and is carried out at room temperature and pressure.

[0018] Furthermore, in the above technical solution, the reaction does not require inert gas protection and is carried out in air.

[0019] Beneficial effects of the invention

[0020] (1) The present invention is simple to operate. Only the substrate aromatic compound, nitrating agent and a small amount of catalyst need to be added to the solvent. No other reagents or complex reaction processes are required during the synthesis process. The process is simple.

[0021] (2) The nitrating reagent required in the reaction process of this invention is readily available and can be purchased directly; the reaction cost is low.

[0022] (3) The present invention generates little waste during the reaction process, which will not cause environmental pollution and will not harm the health of workers. It has the potential for large-scale synthesis. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific implementation examples. These implementation examples are carried out under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following implementation examples.

[0024] Example 1

[0025]

[0026] Taking the synthesis of mononitrobenzene from benzene as an example, the reaction conditions were optimized as follows:

[0027]

[0028] After screening, the optimal conditions for synthesizing mononitrobenzene were selected as follows: using 0.5 equivalents of trifluoromethanesulfonic acid (HOTf) as a catalyst, with a molar ratio of benzene to nitrating agent of 1:1.2, and reacting at room temperature for 30 min in hexafluoroisopropanol (HFIP) solvent.

[0029] The typical operating procedure is as follows: In a reaction flask, hexafluoroisopropanol (1 mL), benzene (1 mmol, 88.76 μL), 68% nitric acid (1.2 mmol, 78.85 μL), and trifluoromethanesulfonic acid (0.5 mmol, 43.93 μL) are added sequentially. The mixture is stirred at room temperature for 30 min. 15 mL of saturated sodium bicarbonate solution is added to the system, and the mixture is extracted three times with 30 mL of dichloromethane. The organic phases are combined, dried over anhydrous sodium sulfate, and evaporated to dryness to obtain mononitrobenzene with a yield >99%. 1 H NMR (400MHz, CDCl3) δ8.23–8.20(m,2H),7.70–7.68(m,1H),7.57-7.52(m,2H). 13C NMR (101 MHz, CDCl3) δ 148.24(s), 134.57(s), 129.31(s), 123.48(s). NMR data analysis: Chemical shift δ 8.23–8.20, multiplet, attributed to hydrogens 2 and 6 on the benzene ring; chemical shift δ 7.76–7.59, multiplet, attributed to hydrogen 4 on the benzene ring; chemical shift δ 7.54, multiplet, attributed to hydrogens 3 and 5 on the benzene ring; chemical shift δ 148.24, attributed to carbon 1 on the benzene ring; chemical shift δ 134.57, attributed to carbon 4 on the benzene ring; chemical shift δ 129.31, attributed to carbons 3 and 5 on the benzene ring; chemical shift δ 123.48, attributed to carbons 2 and 6 on the benzene ring. Based on the above NMR results, the target compound can be identified as mononitrobenzene.

[0030] Example 2

[0031]

[0032] In a reaction flask, hexafluoroisopropanol (HFIP) (1 mL), fluorobenzene (1 mmol, 94.22 μL), 68% nitric acid (1.2 mmol, 78.85 μL), and hexafluoroisopropanol (0.5 mmol, 43.93 μL) were added sequentially. The mixture was stirred at room temperature for 30 min. Then, 15 mL of saturated sodium bicarbonate solution was added to the system, followed by extraction three times with 30 mL of dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and evaporated to dryness to obtain a mixture of ortho and para-fluoronitrobenzene. The target products, p-fluoronitrobenzene and o-fluoronitrobenzene, were then separated and purified by column chromatography. The yield of p-fluoronitrobenzene was 79%. 1 H NMR (400MHz, CDCl3) δ8.34–8.22(m,2H),7.28–7.18(m,2H). 19 F NMR (377MHz, CDCl3) δ -102.07. 13 C NMR (101MHz, CDCl3) δ 166.18 (d, J = 256.0Hz), 144.32, 126.21 (d, J = 9.9Hz), 116.30 (d, J = 23.0Hz). o-Fluoronitrobenzene, yield 20%. 1 H NMR (400MHz, CDCl3) δ8.09–8.04(m,1H),7.70-7.64(m,1H),7.34–7.26(m,2H). 19 F NMR (377MHz, CDCl3) δ -117.68. 13C NMR (101MHz, CDCl3) δ 155.48 (d, J = 262.8Hz), 137.47, 135.58 (d, J = 8.6Hz), 126.03 (d, J = 2.8Hz), 124.54 (d, J = 4.3Hz), 118.35 (d, J = 20.3Hz).

[0033] Example 3

[0034] Using the same reaction conditions as in Example 2, but changing only the reaction substrate 1, a series of products 1c-g and 1c'-1f' were obtained. The specific results are as follows:

[0035]

[0036] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for efficiently synthesizing aromatic nitro compounds, characterized in that, Includes the following steps: ； Aromatic compound 1 and nitric acid are reacted in an organic solvent in the presence of an acid catalyst to obtain aromatic nitro compound 2. Aromatic compound 1 is selected from benzene or substituted phenyl groups, where the substituents in the substituted phenyl groups are selected from one or more of C1-C4 alkyl, carboxyl, halogen, and aldehyde groups. The organic solvent is hexafluoroisopropanol. The acid catalyst is trifluoromethanesulfonic acid. The nitric acid is concentrated nitric acid. The molar ratio of aromatic compound 1, nitric acid, and acid catalyst is 1:1.0-1.2:0.

5. The reaction can be carried out at room temperature and pressure without heating.

Images