A preparation method of N-alkyl-4-nitrophthalimide

Abstract

The invention discloses a method for preparing N-alkyl-4-nitrophthalimide, which mainly comprises a specific equivalent nitric acid and an organic catalyst, so that after the nitration reaction is completed, a nitric acid aqueous solution is evaporated and the organic catalyst is recovered by double-step reduced pressure distillation, and the nitric acid aqueous solution is re-formulated to a specific concentration and then reused for the next batch of reactions, and high-purity N-alkyl-4-nitrophthalimide is obtained. The preparation method of the invention has no waste acid, avoids the treatment of a large amount of concentrated sulfuric acid waste acid in industry, and has the characteristics of environmental protection.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for preparing N-alkyl-4-nitrophthalimide. Background Art

[0002] N-Alkyl-4-nitrophthalimide is an important chemical raw material, which is widely used in the fields of medicine, optoelectronic materials, dyes, etc. In the field of new materials, this monomer is mainly used in the field of organic synthesis, especially for the preparation of bisphenol A diether dianhydride and biphenyl ether dianhydride. This type of dianhydride monomer can be used to synthesize high-performance special engineering plastics such as polyetherimide (PEI), polyimide (PI) and liquid crystal polymer (LCP), and is a key monomer for the synthesis of special engineering plastics.

[0003] The traditional synthesis method of N-alkyl-4-nitrophthalimide is to use N-alkyl-4-nitrophthalimide and fuming nitric acid as raw materials, and to carry out nitration reaction under the system of sulfuric acid to prepare (CN113549001A). The preparation method has high product yield but low selectivity, and isomer N-alkyl-3-nitrophthalimide is generated, and the use of a large amount of sulfuric acid and excessive nitric acid causes environmental pollution, and waste acid treatment also causes great cost. With the progress of social development, industrial development pays more and more attention to environmental impact, therefore, the synthesis method is not conducive to the industrial production of N-alkyl-4-nitrophthalimide.

[0004] Patent CN111153802A provides a new method for nitrification of N-alkylphthalimide. This patent uses ionic liquid instead of concentrated sulfuric acid as a catalyst for the nitration reaction. This process does not generate waste acid, is relatively green, reduces the negative impact of the nitration reaction on the environment, and has high application potential. However, this solution has the disadvantages of expensive catalysts, the need for specific post-treatment methods for the catalyst, low product yield and low atomic utilization, which is currently not conducive to industrial production. Summary of the invention

[0005] The object of the present invention is to overcome the above technical defects and provide a method for preparing N-alkyl-4-nitrophthalimide, which has simple post-treatment and does not generate a large amount of waste acid.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing N-alkyl-4-nitrophthalimide comprises the following steps:

[0008] Step A: Add N-alkyl-phthalimide, organic catalyst and nitric acid into a batch or continuous reactor, and the nitration reaction temperature is 20°C-70°C for 10 minutes-7 hours, wherein the equivalent of nitric acid is 1.00-1.50, and the reaction equation is:

[0009]

[0010] Step B: After the nitration reaction is completed, the unreacted nitric acid and water are first evaporated at a pressure of 0.01-10Kpa and a temperature of 60-75°C, and then the temperature is raised to 100-180°C to evaporate the organic catalyst;

[0011] Step C: discharging the product in a molten state, cooling and crushing it to obtain N-alkyl-4-nitrophthalimide;

[0012] Wherein, the organic catalyst is selected from at least one of an organic acid or an organic anhydride; the organic acid is selected from at least one of trichloroacetic acid, salicylic acid, propionic acid, trifluoromethanesulfonic acid, n-butyric acid, p-fluorobenzoic acid, proline, methacrylic acid, p-toluenesulfonic acid, 2,3,4,5-tetrafluorobenzoic acid, trimethylacetic acid, isobupropionic acid, and isobutyric acid; the organic anhydride is selected from at least one of isobutyric anhydride, trifluoromethanesulfonic anhydride, trichloroacetic anhydride, methacrylic anhydride, n-butyric anhydride, p-toluenesulfonic anhydride, trimethylacetic anhydride, and propionic anhydride; when the organic acid catalyst is selected from an organic acid, the equivalent is 2-5, and when the organic acid catalyst is selected from an organic anhydride, the equivalent is 0.8-1; the mass concentration of nitric acid is 50-99%.

[0013] The N-alkyl-phthalimide is selected from one of the following structures: Wherein, n = 0-3; Wherein, n = 0-2;

[0014] Wherein, R1=Me, Et, Pr, Bu, Ph;

[0015] Preferably, the organic catalyst is selected from one of trichloroacetic acid, trichloroacetic anhydride, trifluoromethanesulfonic anhydride, isobutyric anhydride, 2,3,4,5-tetrafluorobenzoic acid and trifluoromethanesulfonic acid.

[0016] Preferably, the N-alkyl-phthalimide is selected from one of the following structures: Where n = 0-3, Among them, n=0-2.

[0017] When the organic catalyst of the present invention is selected, a nitric acid equivalent of 1.0 can also complete the nitration reaction, and appropriately increasing the amount of nitric acid can improve the reaction efficiency. Therefore, when the nitric acid equivalent is 1.00-1.50, the nitric acid solution evaporated in the first process of reduced pressure distillation is used to re-formulate a 50-99% nitric acid solution with concentrated nitric acid, and then put into the next batch of nitration reaction again, the environmental protection treatment cost is low, and the product will not turn yellow due to residual nitric acid.

[0018] The present invention has the following beneficial effects:

[0019] First, the present invention uses a specific organic catalyst, which has the advantages of high catalytic efficiency, mild reaction and few by-products. In addition, compared with the sulfuric acid catalyst commonly used in the prior art, the organic catalyst can be recycled, is more environmentally friendly, and greatly reduces the cost of waste acid treatment.

[0020] Secondly, the present invention performs reduced pressure distillation at a relatively low temperature of 60-75° C. after the reaction is completed to remove the dilute nitric acid for later use, thereby preventing the nitric acid from causing the product to turn yellow or even black during the distillation process.

[0021] Third, the equivalent of the organic catalyst is investigated, and the equivalent of the organic catalyst is reduced without reducing the product conversion rate and purity, so that the catalyst can be evaporated smoothly.

[0022] In summary, the preparation method of the present invention can obtain a product with a purity greater than 99.9% and a yield greater than 99.5%. DETAILED DESCRIPTION

[0023] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0024] Preparation process of N-alkyl-phthalimide of Example 1-18: Step A: Add N-alkyl-phthalimide, organic catalyst (trichloroacetic anhydride, 0.9 equivalent), and nitric acid (mass concentration of 60%, 1.00 equivalent) into a reaction kettle, and react at a nitration reaction temperature of 30° C.-40° C. for 1-1.5 hours;

[0025] Step B: After the nitration reaction is completed, the unreacted nitric acid and water are first evaporated at a pressure of 0.01-10Kpa and a temperature of 60-75°C, and then the temperature is raised to 150-175°C to evaporate the organic catalyst;

[0026] Step C: The product is discharged in a molten state, cooled and crushed to obtain N-alkyl-4-nitrophthalimide.

[0027] Table 1: Results of Examples 1-18

[0028]

[0029] Preparation process of N-methyl-phthalimide of other embodiments and comparative examples: Step A: N-methyl-phthalimide, an organic catalyst (type and equivalent are shown in the table below), and nitric acid (mass concentration is 60%, equivalent is shown in the table below) are added to a reactor, and the nitration reaction temperature is 20°C-70°C for 0.5-7 hours (specific reaction time is shown in the table below); Step B: After the nitration reaction is completed, the unreacted nitric acid and water are first evaporated at a pressure of 0.01-10Kpa and a temperature of 60-75°C, and then the organic catalyst is evaporated at 100-180°C (specific temperature is shown in the table below); Step C: The product is discharged in a molten state, cooled and crushed to obtain N-alkyl-4-nitrophthalimide.

[0030] Table 2: Process parameters and results of other embodiments and comparative examples

[0031]

[0032] Table 2 continued:

[0033]

[0034] Table 2 continued:

[0035]

[0036] It can be seen from Examples 19-36 that the preferred catalyst has higher purity and yield.

[0037] Regarding other organic acid catalysts in the art:

[0038] When oxalic acid is selected as a catalyst, due to the high boiling point of oxalic acid, the high temperature during evaporation causes the product to turn black.

[0039] When 3-nitrobenzenesulfonic acid is used as the catalyst, the temperature for evaporating the catalyst is high and the product is taken out at the same time, resulting in low product yield and purity.

[0040] When 2,4,6-trinitrobenzoic acid is used as a catalyst, polynitro compounds have explosive properties and high safety risks, and are not suitable for industrial production.

[0041] When trifluoroacetic acid is used as a catalyst, due to its low boiling point, it cannot be separated from water and excess nitric acid, the catalyst recycling effect is poor, and the reaction efficiency and product purity are greatly reduced.

[0042] When citric acid is selected as a catalyst, the solubility of citric acid in the product is low, the system is a heterogeneous reaction, and the reaction effect is poor.

[0043] When acetic anhydride is selected as the catalyst, the acetic anhydride absorbs water to promote the reaction during the reaction, and the acetic anhydride reacts to form acetic acid. However, the solubility of acetic acid in the raw materials and products is low, the reaction system is heterogeneous, and the reaction efficiency is low.

[0044] When 1-ethyl-3-methylimidazolium tetrafluoroborate is selected as the catalyst, the boiling point of the ionic liquid is too high to be removed by vacuum distillation, and the recovery method should be a distillation method after liquid separation, which is complicated to operate.

Claims

1. A method for preparing N-alkyl-4-nitrophthalimide, characterized in that: The method comprises the following steps: Step A: adding N-alkyl-phthalimide, an organic catalyst and nitric acid into an intermittent or continuous reactor, and the nitration reaction temperature is 20° C.-70° C. for 10 minutes-7 hours, wherein the equivalent of nitric acid is 1.00-1.50, and the reaction equation is: Step B: After the nitration reaction is completed, the unreacted nitric acid and water are first evaporated at a pressure of 0.01-10Kpa and a temperature of 60-75°C, and then the temperature is raised to 100-180°C to evaporate the organic catalyst; Step C: The product is discharged in a molten state, cooled and crushed to obtain N-alkyl-4-nitrophthalimide; wherein the organic catalyst is selected from at least one of an organic acid or an organic anhydride; the organic acid is selected from at least one of trichloroacetic acid, salicylic acid, propionic acid, trifluoromethanesulfonic acid, n-butyric acid, p-fluorobenzoic acid, proline, methacrylic acid, p-toluenesulfonic acid, 2,3,4,5-tetrafluorobenzoic acid, trimethylacetic acid, isobutylpropionic acid, and isobutyric acid; the organic anhydride is selected from at least one of isobutyric anhydride, trifluoromethanesulfonic anhydride, trichloroacetic anhydride, methacrylic anhydride, n-butyric anhydride, p-toluenesulfonic anhydride, trimethylacetic anhydride, and propionic anhydride; when the organic acid catalyst is selected from an organic acid, the equivalent is 2-5, and when the organic acid catalyst is selected from an organic anhydride, the equivalent is 0.8-1; and the mass concentration of nitric acid is 50-99%.

2. The method for preparing N-alkyl-4-nitrophthalimide according to claim 1, characterized in that: The N-alkyl-phthalimide is selected from one of the following structures: Wherein, n = 0-3; Wherein, n = 0-2; Wherein, R1=Me, Et, Pr, Bu, Ph; 3. The method for preparing N-alkyl-4-nitrophthalimide according to claim 1, characterized in that: The organic catalyst is selected from trichloroacetic acid, trichloroacetic anhydride, trifluoromethanesulfonic anhydride, isobutyric anhydride, 2,3,4,5-tetrafluorobenzoic acid, and trifluoromethanesulfonic acid.

4. The method for preparing N-alkyl-4-nitrophthalimide according to claim 2, characterized in that: The N-alkyl-phthalimide is selected from one of the following structures: Where n = 0-3, Among them, n=0-2.

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