Preparation method of beta-acetylnaphthalene

Abstract

The invention discloses a preparation method of beta-acetylnaphthalene, and belongs to the technical field of organic synthesis. The preparation method comprises the following steps: dissolving naphthalene, aluminum chloride and nitrobenzene, heating to 40-50 DEG C, dropwise adding acetyl chloride at controlled temperature, and reacting for 0.5-2 hours; adding into an ice-water mixture for hydrolysis reaction, separating liquid, removing an organic solvent from an organic phase, adding ethanol to dissolve a solid at 15-25 DEG C, cooling to 0-5 DEG C for recrystallization, adding ethanol to a filter cake for dissolving, externally steaming until 20-30% of ethanol is left, stopping heating and stirring, cooling to 15-25 DEG C in a gradient manner according to a rate of 3-5 DEG C / min, and filtering to obtain the product. Continuously carrying out gradient cooling to-10 to 0 DEG C at the rate of 1 to 2 DEG C / min, carrying out secondary recrystallization, and drying a filter cake to obtain the beta-acetylnaphthalene. According to the method, nitrobenzene is selected as a solvent and a complexing agent, the beta-site selectivity of Friedel-Crafts acylation reaction is greater than or equal to 88% by controlling reaction conditions, alpha and beta-site acetyl naphthalene is separated in a recrystallization manner, ethanol is used as a crystallizing agent, the steps are simple and safe, the product quality is high, and industrial popularization is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing beta-acetylnaphthalene. Background Art

[0002] β-acetylnaphthalene, as a dye, fragrance and pharmaceutical intermediate, can be used for the synthesis of flavors, cosmetics, dyes and medicines. Among them, 2-vinylnaphthalene synthesized from β-acetylnaphthalene, because it contains active vinyl, is widely used in the preparation of pharmaceutical intermediates, dye intermediates, and optical element coating raw materials. Moreover, the addition of 2-vinylnaphthalene in the polymer synthesis process can give high molecular polymers high heat resistance, low dielectric constant, low dielectric loss, high refractive index, flame retardancy and low hygroscopicity and other characteristics, and is a widely used chemical raw material. At present, the mainstream method for producing 2-vinylnaphthalene is to use β-acetylnaphthalene as a raw material, in an alcohol aqueous solution, reduce the carbonyl group to a hydroxyl intermediate through a reducing agent such as sodium borohydride, and then catalytically dehydrate and purify to obtain vinylnaphthalene. Therefore, the market demand for β-acetylnaphthalene is extremely large, especially high-purity β-acetylnaphthalene.

[0003] The mainstream method for producing β-acetylnaphthalene is to use naphthalene as raw material, and react it with acetyl chloride in the presence of aluminum chloride to undergo Friedel-Crafts acylation to simultaneously produce α-acetylnaphthalene and β-acetylnaphthalene, which are then separated using the difference in melting points to obtain high-purity β-acetylnaphthalene. Similar technologies and improvements: Kon and Weller et al. reported a process for synthesizing 2-methyl-6-acetylnaphthalene using acetyl chloride and 2-methylnaphthalene as raw materials and nitrobenzene as solvent (J.CHEM.SOC, 792-793, 1939); Patent CN100334058C proposed a Friedel-Crafts acylation reaction using 2-alkylnaphthalene and acetyl chloride as raw materials, alkyl halides or aromatic halides as solvents, nitrobenzene or nitroethane as complexing agents, and Lewis acid as catalyst, and then hydrolyzed with an alcohol aqueous solution, separated, and distilled under reduced pressure to obtain 2-methyl-6-acetylnaphthalene; Patent CN101270040B proposed a Friedel-Crafts acylation reaction using β-naphthyl ether and acetyl chloride as raw materials, Lewis acid as catalyst, alkyl halides as solvents, and nitroalkanes as complexing agents, and then hydrolyzed with an alcohol aqueous solution, separated, and distilled under reduced pressure to obtain 6-methoxy-2-acetylnaphthalene.

[0004] The above technologies are all aimed at improving the β-acylation technology of naphthalene compounds. If the production cost of β-acetylnaphthalene is to be further reduced and the product yield is to be increased, the selectivity of the Friedel-Crafts acylation reaction needs to be further improved, the degree of product separation needs to be improved, and the separation consumption needs to be reduced. Since α-acetylnaphthalene and β-acetylnaphthalene have high and similar boiling points and low flash points, vacuum distillation also requires high temperature, which consumes more energy and has potential safety hazards. In this regard, the present invention provides a method for preparing β-acetylnaphthalene. Summary of the invention

[0005] Aiming at the problems of low selectivity, low yield and high separation technology cost in the prior art method for synthesizing β-acetylnaphthalene, the present invention provides a method for preparing β-acetylnaphthalene, which has high yield of β-acetylnaphthalene and adopts recrystallization to replace traditional high-temperature distillation to separate α and β acetylnaphthalene, has simple and safe steps and low cost.

[0006] The present invention is achieved through the following technical solutions: A method for preparing β-acetylnaphthalene comprises the following steps: (1) Mix and dissolve naphthalene, aluminum chloride and nitrobenzene, raise the temperature to 40-50°C, add acetyl chloride dropwise under temperature control, and react for 0.5-2h after the addition is complete; (2) Step (2) The reaction solution is added to an ice-water mixture for hydrolysis reaction, and after the reaction is completed, the liquids are separated and the organic solvent is removed from the organic phase; (3) The solid from which the organic solvent is removed in step (2) is dissolved in ethanol at 15-25°C, cooled to 0-5°C at a rate of 1-2°C / min for recrystallization, filtered, and the filter cake is dissolved in ethanol. The ethanol is evaporated while stirring and the temperature is increased. After 20-30% of the ethanol remains, the heating and stirring are stopped, the temperature is gradually decreased to 15-25°C at a rate of 3-5°C / min, and the temperature is further gradually decreased to -10-0°C at a rate of 1-2°C / min for secondary recrystallization. The filter cake is filtered, and the filter cake is dried to obtain β-acetylnaphthalene.

[0007] Furthermore, in step (1), the molar ratio of naphthalene, aluminum chloride, nitrobenzene and acetyl chloride is 1:1.2-1.3:3-5:1.1-1.2.

[0008] Furthermore, step (1) is completed within 0.5 to 1 h of adding acetyl chloride.

[0009] Furthermore, the temperature during the hydrolysis reaction in step (2) is controlled to be ≤40°C.

[0010] Furthermore, in step (2), the ice-water mixture is prepared by mixing dilute hydrochloric acid having a mass fraction of 10-15% and ice cubes in a mass ratio of 1:1-2, and the amount of the ice-water mixture is 1-10 times the mass of the reaction solution.

[0011] Furthermore, in step (2), the organic solvent nitrobenzene is evaporated out under negative pressure.

[0012] Furthermore, the external steam negative pressure is -90~-80KPa.

[0013] Furthermore, in step (1), the mass ratio of ethanol to solid is 1:1. Beneficial Effects

[0014] The preparation method of β-acetylnaphthalene provided by the present invention selects nitrobenzene as a solvent and a complexing agent, and controls the reaction conditions so that the β-position selectivity of the Friedel-Crafts acylation reaction is ≥88%. In addition, the present invention uses a recrystallization method to replace the traditional high-temperature distillation to separate α- and β-acetylnaphthalene, thereby avoiding the influence of high temperature on product quality and improving production safety. Anhydrous ethanol is used as a crystallizing agent, and β-acetylnaphthalene with a purity greater than 99% can be obtained by two recrystallizations. The steps are simple and safe, and are conducive to industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a liquid chromatogram after the Friedel-Crafts acylation reaction in Example 1; Figure 2 This is the liquid chromatogram of the product after secondary recrystallization in Example 1; Figure 3 This is the liquid phase chromatogram of the product after the second recrystallization of Comparative Example 4; DETAILED DESCRIPTION

[0016] The present invention is further explained below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application. Example 1

[0017] (1) Add 128g of naphthalene, 160g of aluminum chloride and 370g of nitrobenzene to the reaction kettle in sequence, start stirring, raise the temperature to 31±1°C, and after the solid is completely dissolved, add 86g of acetyl chloride dropwise at a rate of 2.87g / min. The addition should be completed within 30 minutes. During the addition process, the temperature in the kettle should be controlled at 41±1°C, and the reaction should be continued at this temperature for 1h; (2) Add 2200 g of ice-water mixture (the ice-water mixture is prepared by mixing 10% by mass hydrochloric acid and ice cubes in a mass ratio of 1:2) into the hydrolysis kettle, start stirring, slowly add 726 g of the reaction solution from step (1) into the kettle for hydrolysis, and control the temperature in the kettle to be ≤40°C during the hydrolysis process. After the addition is completed, let the mixture stand for separation, collect 542.3 g of the lower organic phase, continue to wash the separated phase with an equal mass of pure water twice, and then evaporate the nitrobenzene from the organic phase under a vacuum pressure of -90 KPa. The liquid chromatogram of the remaining solid is as follows: Figure 1 As shown; (3) The remaining 170.1 g of solid was cooled to 20°C, an equal amount of anhydrous ethanol was added to dissolve it, and then the temperature was gradually reduced to 0°C at a rate of 1°C / min for a first recrystallization. After suction filtration, 128.5 g of wet cake was added to an equal amount of anhydrous ethanol to dissolve it, and ethanol was distilled at normal pressure until 30% ethanol remained in the kettle. The temperature was gradually reduced to 20°C at a rate of 3°C / min, and then the temperature was gradually reduced to -10°C at a rate of 1°C / min for a second recrystallization. After suction filtration, the wet cake was dried at 80°C to obtain 109.4 g of β-acetylnaphthalene. The liquid chromatogram of the product after the second recrystallization is shown as follows: Figure 2 As shown; According to liquid phase detection, the product purity was 99.58%, the β-position selectivity was 90.22%, and the recrystallization yield was 71.03%. Example 2

[0018] (1) Add 128g of naphthalene, 173g of aluminum chloride and 615g of nitrobenzene to the reaction kettle in sequence, start stirring, raise the temperature to 39±1°C, and after the solid is completely dissolved, add 94g of acetyl chloride dropwise at a rate of 1.57g / min. The addition is completed within 60min. During the addition process, the temperature in the kettle is controlled at 49±1°C, and the reaction is continued at this temperature for 1h; (2) Add 3030 g of ice-water mixture (the ice-water mixture is prepared by mixing 10% hydrochloric acid and ice cubes in a mass ratio of 1:2) into the kettle, start stirring, slowly add the above 1010 g of insulation liquid into the kettle for hydrolysis, and control the temperature in the kettle to be ≤50°C during the hydrolysis process. After the addition is completed, let the mixture stand for separation, collect 787.6 g of the lower organic phase, continue to wash the separated liquid with an equal mass of pure water twice, and then evaporate the nitrobenzene from the organic phase under a vacuum pressure of -80 KPa; (3) The remaining 170 g of solid was cooled to 20°C, an equal amount of anhydrous ethanol was added to dissolve it, and then the temperature was gradually reduced to 5°C at a rate of 2°C / min for recrystallization. After suction filtration, 129.4 g of wet cake was added to an equal amount of anhydrous ethanol to dissolve it, and ethanol was distilled at normal pressure until 20% ethanol remained in the kettle. The temperature was gradually reduced to 20°C at a rate of 5°C / min, and then the temperature was gradually reduced to 0°C at a rate of 2°C / min for a second recrystallization. After suction filtration, the wet cake was dried at 100°C to obtain 112.8 g of β-acetylnaphthalene; According to liquid phase detection, the product purity was 99.23%, the β-selectivity was 89.54%, and the recrystallization yield was 73.53%.

[0019] Comparative Example 1 Compared with Example 1, the amount of aluminum chloride used in Comparative Example 1 is 1.1 times the molar amount of naphthalene, and other conditions are the same as those in Example 1; The results show that when the amount of aluminum chloride is reduced to 1.1 times the molar amount of naphthalene, naphthalene cannot react completely and there will be 7.35% residue.

[0020] Comparative Example 2 Compared with Example 1, in Comparative Example 2, when acetyl chloride was added dropwise and the insulation temperature was 70±1°C, after insulation for 1 hour, a light yellow insoluble viscous substance was found on the inner wall of the reaction vessel, and detection showed that the contents of α-acetylnaphthalene and β-acetylnaphthalene were reduced, proving that other side reactions occurred at 70°C, resulting in reduced product conversion.

[0021] Comparative Example 3 Compared with Example 1, when the acetyl chloride addition and insulation temperature in Comparative Example 3 was 10±1°C, and other conditions were the same as those in Example 1, the product was tested by liquid phase, and the β-selectivity of the product was 83.89%, which was significantly reduced, indicating that the reduction of the addition and insulation temperature would reduce the β-selectivity in this reaction system.

[0022] Comparative Example 4 Step (1) and step (2) are the same as in Example 1; (3) 170 g of solid was cooled to 20°C, an equal amount of anhydrous ethanol was added to dissolve it, and then the temperature was gradually reduced to 0°C at a rate of 1°C / min for a first recrystallization. After suction filtration, an equal amount of anhydrous ethanol was added to the wet cake to dissolve it, and ethanol was evaporated at normal pressure until 30% of ethanol remained in the kettle. The temperature was gradually reduced to 5°C at a rate of 3°C / min, and then the temperature was gradually reduced to -10°C at a rate of 1°C / min for a second recrystallization. After suction filtration, the wet cake was dried at 80°C to obtain β-acetylnaphthalene. The liquid chromatogram of the product after the second recrystallization is as follows: Figure 3 As shown, the results of liquid phase detection showed that the product purity was 95.32%, the β-selectivity was 90.13%, and the recrystallization yield was 74.06%. The results showed that too fast a gradient cooling rate would cause β-acetylnaphthalene to wrap more α-acetylnaphthalene, resulting in a decrease in product purity.

[0023] From the comparison between the examples and the comparative examples, it can be seen that the present invention can significantly improve the selectivity of the β position of the Friedel-Crafts acylation reaction by controlling the conditions; the ethanol low temperature gradient crystallization method used in the present invention can replace high temperature distillation to purify β-acetylnaphthalene.

[0024] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing β-acetylnaphthalene, characterized in that: The following steps are involved: (1) Mix and dissolve naphthalene, aluminum chloride and nitrobenzene, raise the temperature to 40-50°C, add acetyl chloride dropwise under temperature control, and react for 0.5-2h after the addition is complete; (2) Step (2) The reaction solution is added to an ice-water mixture for hydrolysis reaction, and after the reaction is completed, the liquids are separated and the organic solvent is removed from the organic phase; (3) The solid from which the organic solvent is removed in step (2) is dissolved in ethanol at 15-25°C, cooled to 0-5°C at a rate of 1-2°C / min for recrystallization, filtered, and the filter cake is dissolved in ethanol. The ethanol is evaporated while stirring and the temperature is increased. After 20-30% of the ethanol remains, the heating and stirring are stopped, the temperature is gradually decreased to 15-25°C at a rate of 3-5°C / min, and the temperature is further gradually decreased to -10-0°C at a rate of 1-2°C / min for secondary recrystallization. The filter cake is filtered, and the filter cake is dried to obtain β-acetylnaphthalene.

2. The method for preparing β-acetylnaphthalene according to claim 1, wherein In step (1), the molar ratio of naphthalene, aluminum chloride, nitrobenzene and acetyl chloride is 1:1.2-1.3:3-5:1.1-1.

2.

3. The method for preparing β-acetylnaphthalene according to claim 1, characterized in that: Step (1) is completed by adding acetyl chloride over 0.5-1h.

4. The method for preparing β-acetylnaphthalene according to claim 1, characterized in that: During the hydrolysis reaction in step (2), the temperature is controlled to be ≤40°C.

5. The method for preparing β-acetylnaphthalene according to claim 1, characterized in that: In step (2), the ice-water mixture is prepared by mixing dilute hydrochloric acid having a mass fraction of 10-15% and ice cubes in a mass ratio of 1:1-2, and the amount of the ice-water mixture is 1-10 times the mass of the reaction solution.

6. The method for preparing β-acetylnaphthalene according to claim 1, characterized in that: In step (2), the organic solvent nitrobenzene is evaporated out under negative pressure.

7. The method for preparing β-acetylnaphthalene according to claim 6, characterized in that: The external steam negative pressure is -90~-80KPa.

8. The method for preparing β-acetylnaphthalene according to claim 1, characterized in that: The mass ratio of ethanol to solid in step (1) is 1:1.

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