Preparation method of isooctyl nitrate

Abstract

The invention belongs to the technical field of organic synthesis, and particularly relates to a preparation method of isooctyl nitrate. According to the method, cyclohexane is used as a solvent, urea is used as a stabilizer, composite aerogel is used as a catalyst, and isooctyl nitrate is generated from isooctyl alcohol under the nitration effect of concentrated nitric acid. According to the method, use of sulfuric acid can be avoided, the prepared isooctyl nitrate is high in yield and purity, the whole preparation process is safe and environmentally friendly, and safe and efficient preparation of the isooctyl nitrate can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a preparation method of isooctyl nitrate. Background Art

[0002] Isooctyl nitrate is a colorless, transparent liquid with strong volatility and a pungent odor. It has a wide range of applications. Not only can it be used as a gasoline additive to effectively improve the combustion performance of diesel and reduce ignition energy, it can also be used in the pharmaceutical field. Due to its special effect in dilating blood vessels, it is used in the preparation of drugs for the prevention and treatment of heart disease.

[0003] In the prior art, the synthesis of isooctyl nitrate generally uses the mixed acid method (e.g., CN1017146A). This involves adding isooctyl alcohol to mixed acid within a certain temperature range to react, followed by separation of the reaction product. However, this method suffers from difficult-to-control reaction processes, concentrated heat release, high risk, and the susceptibility to side reactions and overreactions. Furthermore, it requires the use of excessive amounts of sulfuric acid, generating a large amount of waste acid. In recent years, the use of microchannel reactors for the continuous synthesis of isooctyl nitrate has become a relatively safe and effective method (e.g., CN110683953A). This method can reduce the amount of raw acid used, significantly reducing wastewater generation and lowering risks. However, the use of sulfuric acid remains a significant issue. Therefore, it is particularly important to provide a method for safely and efficiently preparing isooctyl nitrate that avoids the use of sulfuric acid. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for preparing isooctyl nitrate. The method can avoid the use of sulfuric acid, and the prepared isooctyl nitrate has high yield and purity. The entire preparation process is safe and environmentally friendly, and can achieve safe and efficient preparation of isooctyl nitrate.

[0005] Specifically, the present invention provides a method for preparing isooctyl nitrate, using cyclohexane as a solvent, urea as a stabilizer, and a composite aerogel as a catalyst, so that isooctyl alcohol is nitrated by concentrated nitric acid to generate a nitration product; The nitration product is allowed to stand for stratification, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate.

[0006] The preparation method of the composite aerogel catalyst comprises the following steps: S1: Mix ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid, and hydrolyze in a water bath at 60-70°C for 5-6 hours. Then, add p-toluenesulfonic acid and carboxymethyl cellulose, and stir thoroughly to form a mixed solution. S2: adding ammonia water dropwise to the mixed solution, stirring rapidly to carry out gelation reaction, filtering and washing, and then drying with supercritical carbon dioxide to obtain aerogel; S3: Immersing the aerogel in a cerium nitrate solution, allowing it to stand, drying, and calcining to obtain a composite aerogel catalyst.

[0007] Furthermore, the addition ratio of cyclohexane, urea, composite aerogel, isooctyl alcohol, and concentrated nitric acid is 30-50 mL: 0.05-0.1 mol: 2-5 g: 1 mol: 1-1.2 mol; and the mass fraction of concentrated nitric acid is 65-80%.

[0008] Furthermore, in the process of nitrating isooctyl alcohol to generate isooctyl nitrate under the nitration action of concentrated nitric acid, the reaction temperature is 20-25° C. and the reaction time is 3-5 hours.

[0009] Furthermore, the molar ratio of ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid is 1:5-10:6-8:0.02-0.04.

[0010] Furthermore, the molar ratio of ethyl orthosilicate, p-toluenesulfonic acid, and carboxymethyl cellulose is 1:0.2 to 0.3:0.1.

[0011] Furthermore, the concentration of the ammonia water is 0.6-0.8 mol / L, and the volume ratio of the ammonia water to the mixed solution is 1-2:10.

[0012] Furthermore, after adding ammonia water dropwise, the mixture was rapidly stirred for 5 to 10 minutes to perform a gelation reaction.

[0013] Furthermore, when supercritical carbon dioxide drying is performed, the pressure is 10-20 MPa, the temperature is 40-50°C, the pressure holding time is 5-6 hours, and the pressure release rate is 4-5 MPa / h.

[0014] Furthermore, in step S3, the concentration of the cerium nitrate solution is 0.5 mol / L; the standing time is 6-8 hours, the drying temperature is 70-80° C., the roasting temperature is 450-500° C., and the roasting time is 2-3 hours.

[0015] The beneficial effects achieved by one or more technical solutions of the present invention are as follows: 1. In the preparation method of isooctyl nitrate provided by the present invention, the composite aerogel catalyst adopts a gel method in conjunction with an impregnation process. The resulting aerogel material contains a porous structure, which is not only conducive to the diffusion of the reactant isooctyl alcohol, but also provides a large specific surface area. The sulfonic acid group and cerium are fully loaded into the structural system, thereby forming abundant catalytic active sites, effectively improving the yield of isooctyl nitrate. Based on this composite aerogel catalyst, isooctyl nitrate can be efficiently prepared, with a yield of isooctyl nitrate exceeding 98.91% and a purity exceeding 99.5%.

[0016] 2. The large number of porous structures of the composite aerogel also has a strong structural guiding effect, inhibiting the agglomeration and shedding of active components in the reaction and enhancing the stability of the catalyst. At the same time, the use of carboxymethyl cellulose in the preparation of the composite aerogel can not only promote the dispersion of sulfonic acid groups within the system, but also form a three-dimensional network of interlaced fibers inside the aerogel, which can further effectively improve the stability of the catalyst structure, extend the service life of the catalyst, and thus reduce the cost of industrial production of isooctyl nitrate. After the composite aerogel catalyst prepared by the present invention was operated for 216 hours, the yield of isooctyl nitrate decreased very little and was able to be maintained at more than 97%. Even after 480 hours of recycling, the yield was still able to maintain more than 90%. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0018] Example 1 This embodiment provides a method for preparing isooctyl nitrate, which comprises the following steps: (1) Preparation of composite aerogel catalyst: S1: Mix ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid (the molar ratio of ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid is 1:5:6:0.02), hydrolyze in a water bath at 60°C for 6 h, then add p-toluenesulfonic acid and carboxymethyl cellulose (the molar ratio of ethyl orthosilicate, p-toluenesulfonic acid, and carboxymethyl cellulose is 1:0.2:0.1), and stir thoroughly to form a mixed solution; S2: Add 0.8 mol / L ammonia water dropwise to the mixed solution in a volume ratio of 1:10, stir rapidly for 5 minutes to carry out gelation reaction, filter and wash, and then dry with supercritical carbon dioxide (pressure 10 MPa, temperature 50°C, pressure holding time 5 hours, pressure release rate 4 MPa / h) to obtain aerogel; S3: The aerogel was immersed in a cerium nitrate solution with a concentration of 0.5 mol / L, allowed to stand for 6 h, dried at 70° C., and then calcined at 500° C. for 2 h to obtain a composite aerogel catalyst.

[0019] (2) Preparation of 2-ethylhexyl nitrate: To 30 mL of cyclohexane, add 0.05 mol of urea, 2 g of composite aerogel, 1 mol of isooctyl alcohol, and 1 mol of concentrated nitric acid (the mass fraction of concentrated nitric acid is 65%), and carry out nitration reaction at 25°C for 5 h. The nitration product is allowed to stand for stratification, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate.

[0020] Example 2 This embodiment provides a method for preparing isooctyl nitrate, which comprises the following steps: (1) Preparation of composite aerogel catalyst: S1: Mix ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid (the molar ratio of ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid is 1:10:8:0.04), hydrolyze in a water bath at 70°C for 6 h, then add p-toluenesulfonic acid and carboxymethyl cellulose (the molar ratio of ethyl orthosilicate, p-toluenesulfonic acid, and carboxymethyl cellulose is 1:0.3:0.1), and stir thoroughly to form a mixed solution; S2: 0.8 mol / L ammonia water was added dropwise to the mixed solution, with the volume ratio of ammonia water to the mixed solution being 1:10. The solution was rapidly stirred for 10 min to undergo gelation reaction. After filtration and washing, the solution was dried with supercritical carbon dioxide (pressure of 20 MPa, temperature of 40°C, holding time of 5 h, and pressure release rate of 4 MPa / h) to obtain aerogel. S3: The aerogel was immersed in a cerium nitrate solution with a concentration of 0.5 mol / L, allowed to stand for 6 h, dried at 70° C., and then calcined at 450° C. for 3 h to obtain a composite aerogel catalyst.

[0021] (2) Preparation of 2-ethylhexyl nitrate: To 30 mL of cyclohexane, add 0.06 mol of urea, 3 g of composite aerogel, 1 mol of isooctyl alcohol, and 1.1 mol of concentrated nitric acid (the mass fraction of concentrated nitric acid is 65%), and carry out nitration reaction at 25°C for 5 h. The nitration product is allowed to stand for stratification, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate.

[0022] Example 3 This embodiment provides a method for preparing isooctyl nitrate, which comprises the following steps: (1) Preparation of composite aerogel catalyst: S1: Mix ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid (the molar ratio of ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid is 1:8:7:0.04), hydrolyze in a water bath at 70°C for 5 h, then add p-toluenesulfonic acid and carboxymethyl cellulose (the molar ratio of ethyl orthosilicate, p-toluenesulfonic acid, and carboxymethyl cellulose is 1:0.2:0.1), and stir thoroughly to form a mixed solution; S2: Add 0.6 mol / L ammonia water to the mixed solution in a volume ratio of 1:5, stir rapidly for 10 min to carry out gelation reaction, filter and wash, and then dry with supercritical carbon dioxide (pressure 20 MPa, temperature 50°C, pressure holding time 6 h, pressure release rate 5 MPa / h) to obtain aerogel; S3: The aerogel was immersed in a cerium nitrate solution with a concentration of 0.5 mol / L, allowed to stand for 8 h, dried at 80° C., and then calcined at 450° C. for 3 h to obtain a composite aerogel catalyst.

[0023] (2) Preparation of 2-ethylhexyl nitrate: To 50 mL of cyclohexane, add 0.1 mol of urea, 5 g of composite aerogel, 1 mol of isooctyl alcohol, and 1.2 mol of concentrated nitric acid (the mass fraction of concentrated nitric acid is 65%), and carry out nitration reaction at 25°C for 5 h. The nitration product is allowed to stand for stratification, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate.

[0024] Example 4 This embodiment provides a method for preparing isooctyl nitrate, which comprises the following steps: (1) Preparation of composite aerogel catalyst: S1: Mix ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid (the molar ratio of ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid is 1:6:7:0.04), hydrolyze in a water bath at 70°C for 5 h, then add p-toluenesulfonic acid and carboxymethyl cellulose (the molar ratio of ethyl orthosilicate, p-toluenesulfonic acid, and carboxymethyl cellulose is 1:0.2:0.1), and stir thoroughly to form a mixed solution; S2: 0.6 mol / L ammonia water was added dropwise to the mixed solution in a volume ratio of 1:5, and the mixture was rapidly stirred for 10 min to undergo gelation reaction. After filtration and washing, the mixture was dried with supercritical carbon dioxide (pressure of 15 MPa, temperature of 40°C, holding time of 6 h, and pressure release rate of 5 MPa / h) to obtain aerogel. S3: The aerogel was immersed in a cerium nitrate solution with a concentration of 0.5 mol / L, allowed to stand for 8 h, dried at 80° C., and then calcined at 500° C. for 2 h to obtain a composite aerogel catalyst.

[0025] (2) Preparation of 2-ethylhexyl nitrate: To 50 mL of cyclohexane, add 0.05 mol of urea, 3 g of composite aerogel, 1 mol of isooctyl alcohol, and 1 mol of concentrated nitric acid (the mass fraction of concentrated nitric acid is 80%), and carry out nitration reaction at 25°C for 3 h. The nitration product is allowed to stand for stratification, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate.

[0026] Comparative Example 1 The comparative example provides a method for preparing isooctyl nitrate, which comprises the following steps: To 50 mL of cyclohexane, add 0.1 mol of urea, 5 g of p-toluenesulfonic acid, 1 mol of isooctyl alcohol, and 1.2 mol of concentrated nitric acid (the mass fraction of concentrated nitric acid is 65%). Perform the nitration reaction at 25°C for 5 hours. The nitration product is allowed to stand for stratification, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate.

[0027] Comparative Example 2 This comparative example provides a method for preparing isooctyl nitrate, which comprises the following steps: (1) Preparation of composite aerogel catalyst: S1: Mix ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid (the molar ratio of ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid is 1:8:7:0.04), hydrolyze in a water bath at 70°C for 5 h, then add p-toluenesulfonic acid (the molar ratio of ethyl orthosilicate to p-toluenesulfonic acid is 1:0.2), and stir thoroughly to form a mixed solution; S2: Add 0.6 mol / L ammonia water to the mixed solution with a volume ratio of ammonia water to the mixed solution of 1:5, and stir rapidly for 10 minutes to carry out gelation reaction. After filtering and washing, supercritical carbon dioxide drying (pressure of 20 MPa, temperature of 50°C, pressure holding time of 6 hours, pressure release rate of 5 MPa / h) is carried out to obtain a composite aerogel catalyst.

[0028] (2) Preparation of 2-ethylhexyl nitrate: To 50 mL of cyclohexane, add 0.1 mol of urea, 5 g of composite aerogel, 1 mol of isooctyl alcohol, and 1.2 mol of concentrated nitric acid (the mass fraction of concentrated nitric acid is 65%), and carry out nitration reaction at 25°C for 5 h. The nitration product is allowed to stand for stratification, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate.

[0029] Comparative Example 3 This comparative example provides a method for preparing isooctyl nitrate, which comprises the following steps: (1) Preparation of composite aerogel catalyst: S1: Mix ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid (the molar ratio of ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid is 1:8:7:0.04), hydrolyze in a water bath at 70°C for 5 h, then add p-toluenesulfonic acid and carboxymethyl cellulose (the molar ratio of ethyl orthosilicate, p-toluenesulfonic acid, and carboxymethyl cellulose is 1:0.2:0.1), and stir thoroughly to form a mixed solution; S2: Add 0.6 mol / L ammonia water to the mixed solution with a volume ratio of ammonia water to the mixed solution of 1:5, and stir rapidly for 10 minutes to carry out gelation reaction. After filtering and washing, supercritical carbon dioxide drying (pressure of 20 MPa, temperature of 50°C, pressure holding time of 6 hours, pressure release rate of 5 MPa / h) is carried out to obtain a composite aerogel catalyst.

[0030] (2) Preparation of 2-ethylhexyl nitrate: To 50 mL of cyclohexane, add 0.1 mol of urea, 5 g of composite aerogel, 1 mol of isooctyl alcohol, and 1.2 mol of concentrated nitric acid (the mass fraction of concentrated nitric acid is 65%), and carry out nitration reaction at 25°C for 5 h. The nitration product is allowed to stand for stratification, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate.

[0031] Comparative Example 4 This comparative example provides a method for preparing isooctyl nitrate, which comprises the following steps: S1: Mix concentrated nitric acid and concentrated sulfuric acid in a molar ratio of 1:1 (the mass fraction of concentrated nitric acid is 80% and the mass fraction of concentrated sulfuric acid is 98%) to obtain a mixed acid solution; S2: Add urea and isooctyl alcohol (the molar ratio of concentrated nitric acid, urea, and isooctyl alcohol is 1:0.1:1) to the mixed acid solution. The reaction temperature is 20°C and stirred for 1 hour. Then, the nitration product is allowed to stand and separate into layers. The organic phase is separated and washed with water, washed with alkali, and then washed with water again until neutral. Then, it is distilled and dried to obtain isooctyl nitrate.

[0032] Performance testing: Table 1 shows the yield (%) and purity (%) of isooctyl nitrate finally obtained in Examples 1 to 4 and Comparative Examples 1 to 4.

[0033] Table 1

[0034] As can be seen from Table 1, using the preparation method provided by the present invention, the yield of isooctyl nitrate is above 98.91% and the purity is above 99.5%. Compared with the traditional mixed acid method in Comparative Example 4, the yield and purity are significantly improved, indicating that the preparation method provided by the present invention can efficiently prepare isooctyl nitrate.

[0035] Table 2 shows the changes in the yield (%) of isooctyl nitrate after the composite aerogel catalysts prepared in Examples 1 to 4 and Comparative Examples 2 and 3 have been run for a period of time.

[0036] Table 2

[0037] It can be seen that after the catalysts in Examples 1 to 4 were run for 216 h, the yield of isooctyl nitrate decreased very little and was maintained at more than 97%. Even after 480 h of recycling, the yield was still maintained at more than 90%, demonstrating that the composite aerogel catalyst prepared by the present invention has good stability while maintaining excellent catalytic activity and can be repeatedly used in the industrial production of isooctyl nitrate, thereby effectively reducing production costs.

Claims

1. A method for preparing isooctyl nitrate, characterized in that: Using cyclohexane as solvent, urea as stabilizer, and composite aerogel as catalyst, isooctyl alcohol is nitrated by concentrated nitric acid to generate nitration products. The nitration product is allowed to stand for decomposition, and the organic phase is separated, washed with water, washed with alkali, and then washed with water again until neutral, and then distilled and dried to obtain isooctyl nitrate; The preparation method of the composite aerogel catalyst comprises the following steps: S1: Mix ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid, and hydrolyze in a water bath at 60-70°C for 5-6 hours. Then, add p-toluenesulfonic acid and carboxymethyl cellulose, and stir thoroughly to form a mixed solution. S2: adding ammonia water dropwise to the mixed solution, stirring rapidly to carry out gelation reaction, filtering and washing, and then drying with supercritical carbon dioxide to obtain aerogel; S3: Immersing the aerogel in a cerium nitrate solution, allowing it to stand, drying, and calcining to obtain a composite aerogel catalyst; The addition ratio of cyclohexane, urea, composite aerogel, isooctyl alcohol, and concentrated nitric acid is 30-50 mL: 0.05-0.1 mol: 2-5 g: 1 mol: 1-1.2 mol; the mass fraction of concentrated nitric acid is 65-80%; The molar ratio of ethyl orthosilicate, anhydrous ethanol, deionized water, and hydrochloric acid is 1:5~10:6~8:0.02~0.04; The molar ratio of ethyl orthosilicate, p-toluenesulfonic acid and carboxymethyl cellulose is 1:0.2~0.3:0.

1.

2. The preparation method of isooctyl nitrate as claimed in claim 1, wherein: In the process of nitration of isooctyl alcohol to generate isooctyl nitrate under the nitration action of concentrated nitric acid, the reaction temperature is 20~25℃ and the time is 3~5h.

3. The preparation method of isooctyl nitrate as claimed in claim 1, wherein: The concentration of ammonia water is 0.6~0.8mol / L, and the volume ratio of ammonia water to the mixed solution is 1~2:

10.

4. The preparation method of isooctyl nitrate as claimed in claim 1, wherein: After adding ammonia water, stir rapidly for 5 to 10 minutes to carry out gelation reaction.

5. The preparation method of isooctyl nitrate as claimed in claim 1, wherein: When supercritical carbon dioxide drying is performed, the pressure is 10~20MPa, the temperature is 40~50℃, the pressure holding time is 5~6h, and the pressure release rate is 4~5MPa / h.

6. The preparation method of isooctyl nitrate as claimed in claim 1, wherein: In step S3, the concentration of the cerium nitrate solution is 0.5 mol / L; the standing time is 6-8 hours, the drying temperature is 70-80° C., the roasting temperature is 450-500° C., and the roasting time is 2-3 hours.

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