Acylation reaction catalyst as well as preparation method and application thereof

Abstract

The invention provides an acylation reaction catalyst as well as a preparation method and application thereof. The preparation method of the acylation reaction catalyst comprises the following steps: (1) adding cation exchange resin into a 0.1 mol / L-10mol / L hydrochloric acid solution, carrying out ultrasonic treatment for 1-60 minutes, filtering, washing with water until the filtrate is neutral, and filtering; and (2) adding the cation exchange resin obtained in the step (1) into a chromatographic column, adding 0.01 mol / L-5 mol / L of Lewis acid solution for leaching, filtering, washing with water, and drying to obtain the acylation reaction catalyst. The acylation reaction catalyst can efficiently realize acylation catalytic reaction of a naphthalene-containing compound, and is good in catalytic effect and simple in post-treatment.

Description

Technical Field

[0001] The present invention belongs to the field of fine chemicals, and particularly relates to an acylation reaction resin catalyst, a preparation method thereof and an application thereof. Background Art

[0002] Aromatic ketone compounds are important chemical intermediates and are widely used in the fields of medicine, dyes, pesticides, etc. For example, 2-acyl-6-methoxynaphthalene is used for synthesizing the anti-inflammatory analgesic drug - naproxen; o-hydroxybenzophenone compounds, as highly efficient and broad-spectrum ultraviolet absorbers, are widely used in industries such as plastics, resins, coatings, synthetic rubbers and cosmetics. The Friedel-Crafts reaction is an important method for synthesizing aromatic ketone compounds.

[0003] The Friedel-Crafts reaction is one of the most important organic chemical reactions. It refers to the reaction of introducing an alkyl group or an acyl group onto an aromatic ring compound under the catalysis of a protonic acid or a Lewis acid. Among them, the introduction of an alkyl group is called an alkylation reaction, and the introduction of an acyl group is called an acylation reaction. Friedel and Crafts discovered and confirmed that aluminum chloride is an effective catalyst for the acylation reaction of aromatic compounds. Although this reaction was discovered earlier, the current research in this field is still very active, especially in the research and development of new catalysts.

[0004] Currently, the most widely used acylation catalysts are Lewis acids, such as AlCl 3 , FeCl 3 etc. However, this type of catalyst will form a complex with the product during the reaction, increasing the amount of catalyst used, and it is difficult to separate the catalyst from the product and it cannot be regenerated. A large amount of acidic wastewater will be generated during the post-treatment process, polluting the environment. The supported catalyst formed by loading a Lewis acid on a solid acid is another research direction, which overcomes the disadvantages of difficult product separation and serious environmental pollution of traditional catalysts. Some researchers have loaded aluminum chloride on carriers such as clay, molecular sieve, mesoporous silica gel, etc., and studied the activity and selectivity for the Friedel-Crafts reaction. The research results show that the activity and selectivity of the supported catalyst are better than those of the unsupported catalyst. Mitsui Corporation synthesized highly selective anthraquinone using different modified molecular sieves. In addition, some researchers have also synthesized anthraquinone using zeolite molecular sieves under gas-solid multiphase catalytic conditions, but the gas-solid multiphase catalytic method cannot accurately control the material ratio, and the reaction device is not conducive to industrial production. In addition, ion exchange resins, solid superacids, solid heteropolyacids, ionic liquids, etc. have been reported in the literature for catalyzing the Friedel-Crafts acylation reaction, but they have disadvantages such as poor stability, high price, difficult preparation, and poor catalytic effect.

[0005] Based on the above-mentioned current situation and deficiencies, it is very necessary to develop a class of environmentally friendly, highly catalytically efficient, and easily prepared acylation catalysts. Summary of the Invention

[0006] In order to solve the technical problems such as the complex catalytic system, difficult product separation, and poor catalytic effect in traditional acylation reactions, the object of the present invention is to provide an acylation reaction catalyst, its preparation method and application. This acylation reaction catalyst can efficiently realize the acylation catalytic reaction of naphthalene-containing compounds, has good catalytic effect, and simple post-treatment.

[0007] In order to achieve the above object, the present invention provides a preparation method of an acylation reaction catalyst, which comprises the following steps:

[0008] (1) Add cation exchange resin to 0.1 mol / L - 10 mol / L hydrochloric acid solution, filter after ultrasonic treatment for 1 - 60 min, wash with water until the filtrate is neutral, and then filter;

[0009] (2) Add the cation exchange resin obtained in step (1) to a chromatography column, add a 0.01 mol / L - 5 mol / L Lewis acid solution for elution, filter, wash with water, and dry to obtain the acylation reaction catalyst.

[0010] According to a specific embodiment of the present invention, preferably, the cation exchange resin includes hydrogen-type strongly acidic styrene-based cation exchange resin and / or sodium-type strongly acidic styrene-based cation exchange resin.

[0011] According to a specific embodiment of the present invention, preferably, the cation exchange resin includes one or a combination of two or more of 732 cation resin, 734 cation resin, D001 cation resin, Amberlite-113, Amberlyst-15, Amberlyst-35, Amberlyst-16, Amberlyst-36, Amberlyst-45, and Amberlyst-46.

[0012] According to a specific embodiment of the present invention, preferably, the Lewis acid includes Al 3+ , Fe 3+ , Zn 2+ , Cu 2+ , Ni 2+ in the form of one or a combination of two or more of its hydrochlorides, hydrobromides, and nitrates.

[0013] According to a specific embodiment of the present invention, preferably, in step (1), the concentration of the hydrochloric acid solution is 1 mol / L - 6 mol / L.

[0014] According to a specific embodiment of the present invention, preferably, in step (1), the solid-liquid mass ratio of the cation exchange resin to the hydrochloric acid solution is 1:1 - 1:10, more preferably 1:2 - 1:5.

[0015] According to a specific embodiment of the present invention, preferably, in step (1), the ultrasonic time is 10 - 30 min.

[0016] According to a specific embodiment of the present invention, preferably, in step (1), the ultrasonic frequency is 60 KHz - 150 KHz, and the ultrasonic temperature is 30 - 60 °C.

[0017] According to a specific embodiment of the present invention, preferably, in step (2), the Lewis acid solution is a metal salt solution of one or a combination of two or more of the hydrochlorides, hydrobromides, and nitrates of Al 3+ 、Fe 3+ 、Zn 2+ 、Cu 2+ 、Ni 2+ .

[0018] According to a specific embodiment of the present invention, preferably, the concentration of the Lewis acid solution is 0.02 - 2 mol / L.

[0019] According to a specific embodiment of the present invention, preferably, in step (2), the volume ratio of the Lewis acid solution to the cation exchange resin is 50:1 - 2:1, more preferably 20:1 - 5:1.

[0020] According to a specific embodiment of the present invention, preferably, in step (2), during elution, the flow rate of the Lewis acid solution is 5 mL / min - 50 mL / min, more preferably 10 mL / min - 20 mL / min.

[0021] The present invention also provides an acylation reaction catalyst prepared by the above preparation method.

[0022] The present invention also provides the application of the above acylation reaction catalyst in catalyzing aryl acylation.

[0023] According to a specific embodiment of the present invention, preferably, the reaction of the aryl acylation is as follows:

[0024]

[0025] Among them, A is the raw material naphthalene, B or C is the acylation reagent, and D is the acylated naphthalene product; R 1 is selected from H, C 1 -C 5 alkyl, C 1 -C 4 alkoxy, halogen, hydroxyl, R 1The number of substitutions is 0-7; R 2 is selected from C 1 -C 5 alkyl, phenyl, phenylmethylene; X is Cl or Br.

[0026] According to a specific embodiment of the present invention, preferably, the aryl acylation reaction comprises the following steps:

[0027] Adding the raw material naphthalene, the acylation reagent, and the acylation reaction catalyst into a solvent, and stirring and reacting at 60-100 °C for 1-24 hours to obtain an acylated naphthalene product, and the acylation reaction catalyst is recovered by filtration.

[0028] According to a specific embodiment of the present invention, preferably, the molar ratio of the raw material naphthalene to the acylation reagent is 1:1-1:4, and the mass ratio of the acylation reaction catalyst to the raw material naphthalene is 1:20-1:4.

[0029] According to a specific embodiment of the present invention, preferably, the solvent is one or a combination of two or more of nitrobenzene, chlorobenzene, and dichlorobenzene, and the mass ratio of the solvent to the raw material naphthalene is 2:1-10:1.

[0030] The present invention has the following beneficial effects:

[0031] (1) The acylation reaction catalyst of the present invention can efficiently realize the acylation catalytic reaction of naphthalene-containing compounds by loading and modifying metal ions on a cation resin, has good catalytic effect, and the post-treatment of the reaction system is simple, avoiding the problems of difficult product adsorption and separation caused by using AlCl 3 catalyst in the prior art;

[0032] (2) The preparation method of the acylation reaction catalyst of the present invention is simple and economical and can be widely applied. Specific Embodiments

[0033] In order to have a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0034] Unless otherwise specified, the reagents, methods, instruments, and equipment used in the present invention are conventional reagents, methods, instruments, and equipment in the art.

[0035] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available and of analytical purity grade.

[0036] Preparation Example 1

[0037] This preparation example provides an acylation reaction resin catalyst, which is prepared by the following steps:

[0038] 100 g of Amberlyst-15 resin was added to 200 mL of 1 mol / L hydrochloric acid solution. After ultrasonic treatment (frequency 100 Hz, temperature 45 °C) for 30 min, it was filtered, washed with deionized water until the filtrate was neutral, and the obtained resin was added to a chromatography column. 2000 mL of 0.2 mol / L AlCl 3 solution was eluted at a flow rate of 20 mL / min, and then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain the resin catalyst Cat-1.

[0039] Preparation Example 2

[0040] This preparation example provides an acylation reaction resin catalyst, which is prepared by the following steps:

[0041] 100 g of 734 cation resin was added to 150 mL of 6 mol / L hydrochloric acid solution. After ultrasonic treatment (frequency 120 Hz, temperature 60 °C) for 10 min, it was filtered, washed with deionized water until the filtrate was neutral, and the obtained resin was added to a chromatography column. 800 mL of 1 mol / L ZnCl 2 solution was eluted at a flow rate of 10 mL / min, and then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain the resin catalyst Cat-2.

[0042] Preparation Example 3

[0043] This preparation example provides an acylation reaction resin catalyst, which is prepared by the following steps:

[0044] 100 g of D001 cation resin was added to 500 mL of 3 mol / L hydrochloric acid solution. After ultrasonic treatment (frequency 130 Hz, temperature 55 °C) for 40 min, it was filtered, washed with deionized water until the filtrate was neutral, and the obtained resin was added to a chromatography column. 1600 mL of 2 mol / L ZnCl 2 solution was eluted at a flow rate of 15 mL / min, and then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain the resin catalyst Cat-3.

[0045] Preparation Example 4

[0046] This preparation example provides an acylation reaction resin catalyst, which is prepared by the following steps:

[0047] 100 g of Amberlyst-45 cation resin was added to 1000 mL of 5 mol / L hydrochloric acid solution. After ultrasonic treatment (frequency 80 Hz, temperature 50 °C) for 30 min, it was filtered, washed with deionized water until the filtrate was neutral, and the obtained resin was added to a chromatography column. 1000 mL of 1.5 mol / L AlCl3 The solution was eluted at a flow rate of 20 mL / min, and then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain the resin catalyst Cat-4.

[0048] Preparation Example 5

[0049] This preparation example provides an acylation reaction resin catalyst, which is prepared by the following steps:

[0050] 100 g of Amberlite-113 cation resin was added to 700 mL of 0.2 mol / L hydrochloric acid solution, ultrasonicated (frequency 100 Hz, temperature 35 °C) for 60 min and then filtered, washed with deionized water until the filtrate was neutral, and the obtained resin was added to a chromatography column, 1400 mL of 2.5 mol / L NiBr 2 The solution was eluted at a flow rate of 10 mL / min, and then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain the resin catalyst Cat-5.

[0051] Preparation Example 6

[0052] This preparation example provides an acylation reaction resin catalyst, which is prepared by the following steps:

[0053] 100 g of Amberlyst-36 cation resin was added to 800 mL of 4 mol / L hydrochloric acid solution, ultrasonicated (frequency 150 Hz, temperature 60 °C) for 25 min and then filtered, washed with deionized water until the filtrate was neutral, and the obtained resin was added to a chromatography column, 1800 mL of 2.5 mol / L Cu(NO 3 ) 2 The solution was eluted at a flow rate of 16 mL / min, and then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain the resin catalyst Cat-6.

[0054] Example 1

[0055] 2-Methylnaphthalene, propionyl chloride, nitrobenzene and the resin catalyst Cat-1 were added to a reactor, where the feed amount of 2-methylnaphthalene was 100 g, the molar ratio of 2-methylnaphthalene to propionyl chloride was 1:2, the mass ratio of Cat-1 to 2-methylnaphthalene was 1:10, and the mass ratio of nitrobenzene to 2-methylnaphthalene was 5:1. The reaction was carried out at 80 °C for 12 hours. After filtration, concentration, separation and purification, the yield of the propionylation product was 75%.

[0056] Example 2

[0057] 2-Methoxynaphthalene, acetic anhydride, nitrobenzene, and resin catalyst Cat-3 were added to a reactor. The feed amount of 2-methoxynaphthalene was 100 g. The molar ratio of 2-methoxynaphthalene to acetic anhydride was 1:4. The mass ratio of Cat-3 to 2-methoxynaphthalene was 1:4. The mass ratio of nitrobenzene to 2-methoxynaphthalene was 10:1. The reaction was carried out at 75 °C for 24 hours. After filtration, concentration, and separation and purification, the yield of the acetylation product was 81%.

[0058] Example 3

[0059] 1-Bromo-4-ethylnaphthalene, benzoyl chloride, dichlorobenzene, and resin catalyst Cat-6 were added to a reactor. The feed amount of 1-bromo-4-ethylnaphthalene was 100 g. The molar ratio of 1-bromo-4-ethylnaphthalene to benzoyl chloride was 1:2.5. The mass ratio of Cat-6 to 1-bromo-4-ethylnaphthalene was 1:8. The mass ratio of dichlorobenzene to 1-bromo-4-ethylnaphthalene was 5:1. The reaction was carried out at 100 °C for 20 hours. After filtration, concentration, and separation and purification, the yield of the benzoylation product was 69%.

[0060] Example 4

[0061] 1-Ethylnaphthalene, acetyl chloride, chlorobenzene, and resin catalyst Cat-1 were added to a reactor. The feed amount of 1-ethylnaphthalene was 100 g. The molar ratio of 1-ethylnaphthalene to acetyl chloride was 1:1. The mass ratio of Cat-1 to 1-ethylnaphthalene was 1:20. The mass ratio of chlorobenzene to 1-ethylnaphthalene was 2:1. The reaction was carried out at 85 °C for 22 hours. After filtration, concentration, and separation and purification, the yield of the acetylation product was 71%.

[0062] Example 5

[0063] 2-Isopropylnaphthalene, isobutyric anhydride, nitrobenzene, and resin catalyst Cat-1 were added to a reactor. The feed amount of 2-isopropylnaphthalene was 100 g. The molar ratio of 2-isopropylnaphthalene to isobutyric anhydride was 1:2. The mass ratio of Cat-1 to 2-isopropylnaphthalene was 1:10. The mass ratio of nitrobenzene to 2-isopropylnaphthalene was 3:1. The reaction was carried out at 85 °C for 18 hours. After filtration, concentration, and separation and purification, the yield of the acylation product was 82%.

[0064] Comparative Example 1

[0065] 100 g of Amberlyst-15 resin was added to 200 mL of 1 mol / L hydrochloric acid solution. After soaking for 30 min, it was filtered, washed with deionized water until the filtrate was neutral. The obtained resin was added to a chromatography column, and 2000 mL of 0.2 mol / L AlCl 3 solution was eluted at a flow rate of 20 mL / min, and then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain resin catalyst Cat-c1.

[0066] 2-Methylnaphthalene, propionyl chloride, nitrobenzene and resin catalyst Cat-c1 were added to a reactor. The feed amount of 2-methylnaphthalene was 100 g, the molar ratio of 2-methylnaphthalene to propionyl chloride was 1:2, the mass ratio of Cat-c1 to 2-methylnaphthalene was 1:10, and the mass ratio of nitrobenzene to 2-methylnaphthalene was 5:1. The reaction was carried out at 80 °C for 12 hours. After filtration, concentration, separation and purification, the yield of the propionylation product was 43%.

[0067] Comparative Example 2

[0068] 100 g of Amberlyst-15 resin was added to 200 mL of 1 mol / L hydrochloric acid solution. After ultrasonic treatment (frequency 100 Hz, temperature 45 °C) for 30 min, it was filtered, washed with deionized water until the filtrate was neutral. The obtained resin was added to 2000 mL of 0.2 mol / L AlCl 3 solution, soaked for 2 hours and then filtered. Then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain resin catalyst Cat-c2.

[0069] 2-Methylnaphthalene, propionyl chloride, nitrobenzene and resin catalyst Cat-c2 were added to a reactor. The feed amount of 2-methylnaphthalene was 100 g, the molar ratio of 2-methylnaphthalene to propionyl chloride was 1:2, the mass ratio of Cat-c2 to 2-methylnaphthalene was 1:10, and the mass ratio of nitrobenzene to 2-methylnaphthalene was 5:1. The reaction was carried out at 80 °C for 12 hours. After filtration, concentration, separation and purification, the yield of the propionylation product was 38%.

[0070] Comparative Example 3

[0071] 100 g of D001 cation resin was added to 500 mL of 3 mol / L hydrochloric acid solution. After ultrasonic treatment (frequency 40 Hz, temperature 25 °C) for 40 min, it was filtered, washed with deionized water until the filtrate was neutral. The obtained resin was added to a chromatography column, and 1600 mL of 2 mol / L ZnCl 2 solution was eluted at a flow rate of 15 mL / min. Then the resin was washed with deionized water until there were no metal ions in the filtrate, and dried to obtain resin catalyst Cat-c3.

[0072] 2-Methoxynaphthalene, acetic anhydride, nitrobenzene and resin catalyst Cat-c3 were added to a reactor. The feed amount of 2-methoxynaphthalene was 100 g, the molar ratio of 2-methoxynaphthalene to acetic anhydride was 1:4, the mass ratio of Cat-c3 to 2-methoxynaphthalene was 1:4, and the mass ratio of nitrobenzene to 2-methoxynaphthalene was 10:1. The reaction was carried out at 75 °C for 24 hours. After filtration, concentration, separation and purification, the yield of the acetylation product was 48%.

[0073] Comparative Example 4

[0074] 2-isopropylnaphthalene (100 g), isobutyric anhydride, nitrobenzene and Amberlyst-15 resin were added into a reactor, wherein the molar ratio of 2-isopropylnaphthalene to isobutyric anhydride was 1:2, the mass ratio of Amberlyst-15 to 2-isopropylnaphthalene was 1:10, and the mass ratio of nitrobenzene to 2-isopropylnaphthalene was 3:1. The reaction was carried out at 85° C. for 18 hours. After filtering, concentrating, separating and purifying, the yield of the acylated product was 12%.

[0075] Comparative Example 5

[0076] Prepare AlCl at low temperature 3 A nitrobenzene solution of isobutyric anhydride and a nitrobenzene solution of 2-isopropylnaphthalene (100 g), wherein the molar ratio of 2-isopropylnaphthalene to isobutyric anhydride is 1:2, the mass ratio of aluminum chloride to 2-isopropylnaphthalene is 1:10, and the mass ratio of nitrobenzene to 2-isopropylnaphthalene is 3:1, are reacted at 85° C. for 18 hours, and the reaction is quenched, filtered, concentrated, separated and purified. The yield of the acylated product is 62%. After the reaction is quenched, floccules are generated, which affects the separation effect and adsorbs the product, resulting in a reduced yield.

[0077] It can be seen from the results of the above examples and comparative examples that the present invention can effectively catalyze the acylation reaction of naphthalene compounds, greatly improve the conditions of the acylation reaction, simplify the operation process, and has obvious technical advantages.

[0078] Although the present invention has been described in detail above by means of general description, specific implementation methods and tests, it is obvious to those skilled in the art that some modifications or improvements may be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A preparation method of an acylation reaction catalyst, which comprises the following steps: (1) Add cation exchange resin into a 0.1 mol / L - 10 mol / L hydrochloric acid solution, ultrasonic for 1 - 60 min and then filter, wash with water until the filtrate is neutral, and filter; (2) Add the cation exchange resin obtained from step (1) into a chromatography column, add a 0.01 mol / L - 5 mol / L Lewis acid solution for elution, filter, wash with water and dry to obtain the acylation reaction catalyst.

2. The preparation method according to claim 1, wherein, the cation exchange resin comprises a hydrogen-type strongly acidic styrene-based cation exchange resin and / or a sodium-type strongly acidic styrene-based cation exchange resin.

3. The preparation method according to claim 2, wherein, the cation exchange resin comprises one or a combination of two or more of 732 cation resin, 734 cation resin, D001 cation resin, Amberlite-113, Amberlyst-15, Amberlyst-35, Amberlyst-16, Amberlyst-36, Amberlyst-45, Amberlyst-46.

4. The preparation method according to claim 1, wherein, The Lewis acid includes Al 3+ , Fe 3+ 、Zn 2+ , Cu 2+ 、Ni 2+ One or a combination of two or more of the hydrochloride, hydrobromide and nitrate.

5. The preparation method according to claim 1, wherein, In step (1), the concentration of the hydrochloric acid solution is 1 mol / L - 6 mol / L.

6. The preparation method according to claim 1, wherein, In step (1), the solid-liquid mass ratio of the cation exchange resin to the hydrochloric acid solution is 1:1 - 1:10, preferably 1:2 - 1:

5.

7. The preparation method according to claim 1, wherein, In step (1), the ultrasonic time is 10 - 30 min; Preferably, the ultrasonic frequency is 60 KHz - 150 KHz, and the ultrasonic temperature is 30 - 60 °C.

8. The preparation method according to claim 1, wherein, In step (2), the Lewis acid solution is a metal salt solution which is one or a combination of two or more of the hydrochlorides, hydrobromides, and nitrates of Al 3+ , Fe 3+ , Zn 2+ , Cu 2+ , Ni 2+ .

9. The preparation method according to claim 1, wherein, the concentration of the Lewis acid solution is 0.02 - 2 mol / L.

10. The preparation method according to claim 1, wherein, In step (2), the volume ratio of the Lewis acid solution to the cation exchange resin is 50:1 - 2:1, preferably 20:1 - 5:

1.

11. The preparation method according to claim 1, wherein, In step (2), during elution, the flow rate of the Lewis acid solution is 5 mL / min - 50 mL / min, preferably 10 mL / min - 20 mL / min.

12. An acylation reaction catalyst prepared by the preparation method according to any one of claims 1 - 11.

13. Application of the acylation reaction catalyst according to claim 12 in catalyzing aryl acylation.

14. The application according to claim 13, wherein, the reaction of the aryl acylation is as follows: wherein, A is the raw material naphthalene, B or C is the acylation reagent, and D is the acylated naphthalene product; R 1 selected from H, C 1 -C 5 alkyl, C 1 -C 4 alkoxy, halogen, hydroxyl, R 1 is substituted in an amount of 0 - 7; R 2 is selected from C 1 -C 5 alkyl, phenyl, phenylmethylidene; X is Cl or Br.

15. The application according to claim 14, wherein, the reaction of the aryl acylation comprises the following steps: Add the raw material naphthalene, the acylating agent, and the acylating reaction catalyst into a solvent, and stir and react at 60 - 100 °C for 1 - 24 hours to obtain an acylated naphthalene product. The acylating reaction catalyst is recovered by filtration.

16. According to the application described in claim 15, wherein, the molar ratio of the raw material naphthalene to the acylating agent is 1:1 - 1:4, and the mass ratio of the acylating reaction catalyst to the raw material naphthalene is 1:20 - 1:4; Preferably, the solvent is one or a combination of two or more of nitrobenzene, chlorobenzene, and dichlorobenzene, and the mass ratio of the solvent to the raw material naphthalene is 2:1 - 10:1.

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