Preparation method of 2-alkyl-6-acyl naphthalene

Abstract

The invention discloses a preparation method of 2-alkyl-6-acyl naphthalene, and belongs to the technical field of organic synthesis. The preparation method comprises the following steps: dropwise adding a catalysis-base solution into an acylation solution; reacting after charging is completed; and pouring the mixed solution obtained by the reaction into ice water, adjusting the pH value to be neutral, extracting, carrying out reduced pressure distillation, and recrystallizing to obtain the 2-alkyl-6-acyl naphthalene. According to the invention, the Lewis acid catalyst and the substrate are complexed and activated in advance, and the carbon atom at the No.6 site of the substrate 2-alkylnaphthalene is activated, so that the electronegativity is increased, the electrophilic attack of an acylation intermediate (acyl cations or acyl halide-Lewis acid complex) is facilitated, and the selectivity of the 2, 6-isomer is improved. Meanwhile, due to the activation effect of Lewis acid on the substrate, the reaction energy barrier is reduced, and conversion of the substrate is more facilitated. The method disclosed by the invention is simple to operate, high in selectivity of para-arone products and high in substrate conversion rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing 2-alkyl-6-acylnaphthalene. Background Art

[0002] 2-alkyl-6-acylnaphthalene is an important class of chemical intermediates. Especially 2-methyl-6-acylnaphthalene can be oxidized to prepare 2,6-naphthalenedicarboxylic acid (2,6-NDA), and 2,6-NDA is a key monomer for synthesizing various high-performance polynaphthalate, polyurethane, and liquid crystal polyester resin (LCP). Reacting it with ethylene glycol gives polyethylene naphthalate (PEN). All aspects of the physical and chemical properties of PEN are superior to those of polyethylene terephthalate (PET) commonly used at present. PEN has a wide range of applications in the fields of fibers, films, and electronics.

[0003] Some studies have been carried out on the synthesis route of 2-alkyl-6-acylnaphthalene. Patent CN1817843A discloses a method for preparing 2-alkyl-6-acylnaphthalene, using a halogenated hydrocarbon as a solvent and a nitro compound as a complexing agent. The acylation reaction temperature is relatively low, which improves the product selectivity, but increases the reaction complexity. Patent CN107879909A discloses a method for synthesizing acylnaphthalene using a microchannel reactor, but the reaction has high requirements for corrosion resistance, and the microchannel reactor is expensive, greatly increasing the production cost and making it difficult to industrialize. Patent CN1146213228A discloses a method for synthesizing acylnaphthalene using a modified H β zeolite molecular sieve, which is environmentally friendly and has a small wastewater discharge, but the selectivity for synthesizing 2-alkyl-6-acylnaphthalene is relatively low. Patent 115554914A discloses a device for continuously acylating to prepare propionylnaphthalene, with small reactor backmixing, relatively high reaction conversion rate and selectivity, but the process is relatively cumbersome. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing 2-alkyl-6-acylnaphthalene. After mixing the catalyst and the substrate, they are added to the acylating reagent solution to prepare 2-alkyl-6-acylnaphthalene. This method is applicable to a variety of 2-alkylnaphthalene substrates, further improving the substrate conversion rate and the selectivity of 2,6-acylnaphthalene.

[0005] The present invention provides a method for preparing 2-alkyl-6-acylnaphthalene, comprising the following steps: dropping the catalyst-substrate solution into the acylating solution; carrying out the reaction after the feeding is completed; pouring the obtained reaction mixture into ice water, adjusting the pH to neutral, extracting, distilling under reduced pressure, and recrystallizing to obtain the 2-alkyl-6-acylnaphthalene; dissolving the catalyst and 2-alkylnaphthalene in a solvent to obtain the catalyst-substrate solution; dissolving the acylating reagent in a solvent to obtain the acylating solution.

[0006] The chemical structural formula of the 2-alkyl-6-acylnaphthalene is as follows: Wherein, R is C 1 ~C 4 alkyl, and R 1 is ethyl or propyl.

[0007] The chemical structural formula of the 2-alkylnaphthalene is as follows: Wherein, R is C 1 ~C 4 alkyl, preferably C 1 and C 2 .

[0008] The catalyst is a Lewis acid catalyst, selected from aluminum chloride, iron chloride, zinc chloride or gallium chloride; and / or, the acylating reagent is an acyl halide or an acid anhydride; and / or, the solvent is a nitro compound.

[0009] The acyl halide includes one or more of acetyl chloride, acetyl bromide, propionyl chloride and propionyl bromide;

[0010] The acid anhydride includes one or several of acetic anhydride and propionic anhydride;

[0011] The nitro compound includes one or more of nitromethane, nitroethane and nitrobenzene;

[0012] Preferably, the mass ratio of the solvent to 2-alkylnaphthalene is (3~10):1.

[0013] Furthermore, the molar ratio of the catalyst to 2-alkylnaphthalene is (1~1.2):1.

[0014] Furthermore, the mass ratio of the acylating reagent to the solvent is 1:(6.5~7.7).

[0015] Preferably, the dropping rate is 60 mL / h and the temperature is 0 °C.

[0016] Preferably, the reaction temperature is 20 °C and the time is 2 h.

[0017] Preferably, the solvent for recrystallization is an alcohol-aqueous solution.

[0018] More preferably, the mass concentration of the alcohol-aqueous solution is 95%, and the alcohol includes one or two of methanol, ethanol or isopropanol.

[0019] The recrystallization is carried out at 55 °C.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] In the present invention, through the pre-complexation activation of the Lewis acid catalyst and the substrate, the carbon atom at the 6-position of the substrate 2-alkylnaphthalene is activated, increasing its electronegativity, which is beneficial to the electrophilic attack of the acylation intermediate (acyl cation or acyl halide-Lewis acid complex), thereby improving the selectivity of the 2,6-isomer. Meanwhile, the activation of the substrate by the Lewis acid reduces the reaction energy barrier, making it more conducive to the conversion of the substrate. The method adopted in the present invention is simple to operate, with high selectivity for the para-aryl ketone product and high substrate conversion rate. Brief Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 It is a schematic flow chart of the preparation method of 2-alkyl-6-acylnaphthalene provided by the present invention;

[0024] Figure 2 It is a schematic diagram of the mechanism of acetylation of 2-methylnaphthalene catalyzed by AlCl 3 Detailed Embodiments

[0025] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0026] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0027] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0028] ​Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the description of the present invention, which will be obvious to those skilled in the art. Other embodiments obtained from the description of the present invention will be obvious to those skilled in the art. The description and examples of the present invention are merely exemplary.

[0029] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0030] An embodiment of the present invention provides a method for preparing 2-alkyl-6-acylnaphthalene, comprising the following steps:

[0031] (1) Dissolve the catalyst in the solvent nitro compound and add the substrate 2-alkylnaphthalene to obtain a catalytic-bottom solution.

[0032] (2) In a three-necked flask, dissolve the acylating reagent in the solvent nitro compound to obtain an acylating solution, and drop the catalytic-bottom solution obtained in step (1) into the three-necked flask (at 60 mL / h, 0 °C).

[0033] (3) After the feeding is completed, react (at 20 °C, 2 h), pour the obtained reaction mixture into ice water, and adjust the pH to neutral.

[0034] (4) Extract the mixture, separate the aqueous phase, and obtain the crude product of 2-alkyl-6-acylnaphthalene after vacuum distillation of the organic phase.

[0035] (5) Recrystallize the crude product of 2-alkyl-6-acylnaphthalene with an alcohol-aqueous solution to obtain the product of 2-alkyl-6-acylnaphthalene.

[0036] Figure 1 It is a process schematic diagram of the method for preparing 2-alkyl-6-acylnaphthalene provided by the present invention. By mixing the catalyst and the substrate and then adding them to the acylating reagent, the present invention effectively improves the conversion rate of the substrate and the selectivity of 2-alkyl-6-acylnaphthalene.

[0037] The raw materials and reagents required in the embodiments of the present invention are all obtained by purchasing commercially.

[0038] Example 1

[0039] In this example, 2-methylnaphthalene, acetyl chloride, and aluminum chloride are used as raw materials, and the specific synthesis steps are as follows:

[0040] (1) 6.67 g (0.05 mol) of aluminum chloride and 40 g of nitrobenzene were placed in a single-necked flask. After being fully stirred and dissolved, 7.1 g (0.05 mol) of 2-methylnaphthalene was added to obtain a catalytic-bottom liquid. 3.93 g (0.05 mol) of acetyl chloride and 30 g of nitrobenzene were placed in a three-necked flask to obtain an acylation liquid, which was placed in a low-temperature bath. The catalytic-bottom liquid was slowly added to this three-necked flask through a feed pump, controlling the dropping rate at 60 mL / min, and the temperature of the low-temperature bath was kept constant at 0 °C. After the addition of the catalytic-bottom liquid was completed, the reaction was carried out at 20 °C for 2 h. The reaction product was poured into ice water containing crushed ice, stirred for 0.5 h, then 4.5 g of sodium bicarbonate was added to adjust the pH to neutral, and it was poured into a separatory funnel for phase separation. The organic layer was taken, and the fraction at 160 °C / 2 mmHg was collected by vacuum distillation to obtain 6.0 g of crude 2-methyl-6-acetylnaphthalene. The obtained crude product was analyzed by gas chromatography, and the yield of 2-methyl-6-acetylnaphthalene was 65.2%;

[0041] (2) 6.0 g of the crude product and 25 g of 95 wt% methanol-aqueous solution were placed in a 150 mL single-necked flask. After being fully dissolved at 55 °C for 1 h, the temperature was programmed to decrease (decrease at a rate of 20 °C / h to 30 °C, and then at a rate of 10 °C / h to 5 °C and kept for 1 h), filtered by suction and dried to obtain 2.9 g of 2-methyl-6-acetylnaphthalene with a purity of 99.1%.

[0042] In this example, the substrate conversion rate was 84.3%.

[0043] Figure 2 For AlCl 3 Schematic diagram of the mechanism of acetylation of 2-methylnaphthalene catalyzed by

[0044] Example 2

[0045] In this example, 2-methylnaphthalene, propionyl chloride, and aluminum chloride were used as raw materials, and the specific synthesis steps were as follows:

[0046] (1) Put 6.67 g of aluminum chloride (0.05 mol) and 40 g of nitrobenzene into a single-necked flask. After fully stirring and dissolving, add 7.1 g (0.05 mol) of 2-methylnaphthalene to obtain a catalytic-bottom liquid. Put 4.63 g (0.05 mol) of propionyl chloride and 30 g of nitrobenzene into a three-necked flask to obtain an acylation liquid. Place it in a low-temperature bath. Slowly add the catalytic-bottom liquid to this three-necked flask through a feed pump, control the dropping rate at 60 mL / min, and keep the temperature of the low-temperature bath constant at 0 °C. After the catalytic-bottom liquid is added dropwise, react for 2 h at 20 °C. Pour the reaction product into ice water containing crushed ice, stir for 0.5 h, then add 4.5 g of sodium bicarbonate to adjust the pH to neutral, pour it into a separatory funnel for phase separation, take the organic layer, and collect the fraction at 160 °C / 2 mmHg through vacuum distillation to obtain 6.6 g of crude 2-methyl-6-propionylnaphthalene. Perform gas chromatography analysis on the obtained crude product, and the yield of 2-methyl-6-propionylnaphthalene is 66.7%;

[0047] (2) Put 6.6 g of the crude product and 25 g of 95 wt% methanol-aqueous solution into a 150 mL single-necked flask. After fully dissolving at 55 °C for 1 h, program the temperature to decrease (decrease at a rate of 20 °C / h to 30 °C, and then at a rate of 10 °C / h to 5 °C, keep for 1 h), filter by suction and dry to obtain 3.2 g of 2-methyl-6-propionylnaphthalene with a purity of 98.9%.

[0048] In this example, the substrate conversion rate is 83.9%.

[0049] Example 3

[0050] In this example, 2-methylnaphthalene, acetyl chloride, and iron chloride are used as raw materials. The specific synthesis steps are as follows:

[0051] (1) Put 8.1 g (0.05 mol) of iron chloride and 40 g of nitrobenzene into a single-necked flask. After fully stirring and dissolving, add 7.1 g (0.05 mol) of 2-methylnaphthalene to obtain a catalytic-bottom liquid. Put 3.93 g (0.05 mol) of acetyl chloride and 30 g of nitrobenzene into a three-necked flask to obtain an acylation liquid. Place it in a low-temperature bath. Slowly add the catalytic-bottom liquid to this three-necked flask through a feed pump, control the dropping rate at 60 mL / min, and keep the temperature of the low-temperature bath constant at 0 °C. After the catalytic-bottom liquid is added dropwise, react for 2 h at 20 °C. Pour the reaction product into ice water containing crushed ice, stir for 0.5 h, then add 4.5 g of sodium bicarbonate to adjust the pH to neutral, pour it into a separatory funnel for phase separation, take the organic layer, and collect the fraction at 160 °C / 2 mmHg through vacuum distillation to obtain 5.8 g of crude 2-methyl-6-acetylnaphthalene. Perform gas chromatography analysis on the obtained crude product, and the yield of 2-methyl-6-acetylnaphthalene is 62.8%;

[0052] (2) Dissolve 5.8 g of the crude product and 25 g of 95 wt% methanol - aqueous solution in a 150 mL single - necked flask. After fully dissolving at 55 °C for 1 h, cool the temperature programmatically (cool at a rate of 20 °C / h to 30 °C, then cool at a rate of 10 °C / h to 5 °C, and maintain for 1 h), filter by suction and dry to obtain 2.8 g of 2 - methyl - 6 - acetylnaphthalene with a purity of 98.3%.

[0053] In this example, the substrate conversion rate is 79.2%.

[0054] Example 4

[0055] In this example, 2 - methylnaphthalene, propionyl chloride, and iron chloride are used as raw materials. The specific synthesis steps are as follows:

[0056] (1) Put 8.1 g (0.05 mol) of iron chloride and 40 g of nitrobenzene into a single - necked flask. After fully stirring and dissolving, add 7.1 g (0.05 mol) of 2 - methylnaphthalene to obtain a catalytic - substrate solution; put 4.63 g (0.05 mol) of propionyl chloride and 30 g of nitrobenzene into a three - necked flask to obtain an acylation solution. Place it in a low - temperature bath. Slowly add the catalytic - substrate solution to this three - necked flask through a feed pump, control the dropping rate at 60 mL / min, and keep the temperature of the low - temperature bath constant at 0 °C. After the catalytic - substrate solution is added dropwise, react at 20 °C for 2 h. Pour the reaction product into ice - water containing crushed ice, stir for 0.5 h, then add 4.5 g of sodium bicarbonate to adjust the pH to neutral, pour it into a separatory funnel for phase separation, take the organic layer, and collect the fraction at 160 °C / 2 mmHg by vacuum distillation to obtain 6.3 g of crude 2 - methyl - 6 - propionylnaphthalene. Perform gas chromatography analysis on the obtained crude product. The yield of 2 - methyl - 6 - propionylnaphthalene is 63.9%;

[0057] (2) Dissolve 6.3 g of the crude product and 25 g of 95 wt% methanol - aqueous solution in a 150 mL single - necked flask. After fully dissolving at 55 °C for 1 h, cool the temperature programmatically (cool at a rate of 20 °C / h to 30 °C, then cool at a rate of 10 °C / h to 5 °C, and maintain for 1 h), filter by suction and dry to obtain 3.4 g of 2 - methyl - 6 - propionylnaphthalene with a purity of 99.1%.

[0058] In this example, the substrate conversion rate is 77.8%.

[0059] Example 5

[0060] In this example, 2 - methylnaphthalene, acetyl chloride, and aluminum chloride are used as raw materials. The specific synthesis steps are as follows:

[0061] (1) Put 8 g (0.06 mol) of aluminum chloride and 50 g of nitrobenzene into a single-necked flask. After stirring and dissolving thoroughly, add 7.1 g (0.05 mol) of 2-methylnaphthalene to obtain the catalyst-bottom liquid. Put 4.3 g (0.055 mol) of acetyl chloride and 30 g of nitrobenzene into a three-necked flask to obtain the acylation liquid. Place it in a low-temperature bath. Slowly add the catalyst-bottom liquid to this three-necked flask through a feed pump, control the dropping rate at 60 mL / min, and keep the temperature of the low-temperature bath constant at 0 °C. After the catalyst-bottom liquid is added dropwise, react for 2 h at 20 °C. Pour the reaction product into ice water containing crushed ice, stir for 0.5 h, then add 5.0 g of sodium bicarbonate to adjust the pH to neutral, pour it into a separatory funnel for phase separation, take the organic layer, and collect the fraction at 160 °C / 2 mmHg through vacuum distillation to obtain 6.4 g of crude 2-methyl-6-acetylnaphthalene. Perform gas chromatography analysis on the obtained crude product, and the yield of 2-methyl-6-acetylnaphthalene is 69.2%;

[0062] (2) Put 6.4 g of the crude product and 25 g of 95 wt% methanol-aqueous solution into a 150 mL single-necked flask. After fully dissolving at 55 °C for 1 h, program the temperature reduction (reduce the temperature to 30 °C at a rate of 20 °C / h, and then reduce the temperature to 5 °C at a rate of 10 °C / h and keep it for 1 h), filter by suction and dry to obtain 3.2 g of 2-methyl-6-acetylnaphthalene with a purity of 98.9%.

[0063] In this example, the substrate conversion rate is 90.2%.

[0064] Example 6

[0065] This example uses 2-methylnaphthalene, acetyl chloride, and iron chloride as raw materials. The specific synthesis steps are as follows:

[0066] (1) Put 9.72 g (0.06 mol) of iron chloride and 50 g of nitrobenzene into a single-necked flask. After stirring and dissolving thoroughly, add 7.1 g (0.05 mol) of 2-methylnaphthalene to obtain the catalyst-bottom liquid. Put 4.3 g of acetyl chloride and 30 g of nitrobenzene into a three-necked flask to obtain the acylation liquid. Place it in a low-temperature bath. Slowly add the catalyst-bottom liquid to this three-necked flask through a feed pump, control the dropping rate at 60 mL / min, and keep the temperature of the low-temperature bath constant at 0 °C. After the catalyst-bottom liquid is added dropwise, react for 2 h at 0 °C. Pour the reaction product into ice water containing crushed ice, stir for 0.5 h, then add 5.0 g of sodium bicarbonate to adjust the pH to neutral, pour it into a separatory funnel for phase separation, take the organic layer, and collect the fraction at 160 °C / 2 mmHg through vacuum distillation to obtain 6.2 g of crude 2-methyl-6-acetylnaphthalene. Perform gas chromatography analysis on the obtained crude product, and the yield of 2-methyl-6-acetylnaphthalene is 67.2%;

[0067] (2) Dissolve 6.2 g of the crude product and 25 g of 95 wt% methanol - aqueous solution in a 150 mL single - necked flask. After fully dissolving at 55 °C for 1 h, cool the temperature programmatically (cool at a rate of 20 °C / h to 30 °C, then cool at a rate of 10 °C / h to 5 °C and maintain for 1 h), filter by suction, and dry to obtain 3.2 g of 2 - methyl - 6 - acetylnaphthalene with a purity of 99.0%.

[0068] In this example, the substrate conversion rate is 86.7%.

[0069] Example 7

[0070] In this example, 2 - ethylnaphthalene, acetyl chloride, and aluminum chloride are used as raw materials. The specific synthesis steps are as follows:

[0071] (1) Put 8 g (0.06 mol) of aluminum chloride and 50 g of nitrobenzene into a single - necked flask. After fully stirring and dissolving, add 7.6 g (0.49 mol) of 2 - ethylnaphthalene to obtain the catalytic - substrate solution; put 4.3 g of acetyl chloride and 30 g of nitrobenzene into a three - necked flask to obtain the acylation solution, and place it in a low - temperature bath. Slowly add the catalytic - substrate solution to this three - necked flask through a feed pump, control the dropping rate at 60 mL / min, and keep the temperature of the low - temperature bath constant at 0 °C. After the catalytic - substrate solution is completely dropped, react at 20 °C for 2 h. Pour the reaction product into ice - water containing crushed ice, stir for 0.5 h, then add 5.0 g of sodium bicarbonate to adjust the pH to neutral, pour it into a separatory funnel for phase separation, take the organic layer, and collect the fraction at 164 °C / 2 mmHg by vacuum distillation to obtain 6.9 g of crude 2 - ethyl - 6 - acetylnaphthalene. Perform gas chromatography analysis on the obtained crude product, and the yield of 2 - ethyl - 6 - acetylnaphthalene is 70.9%.

[0072] (2) Dissolve 6.9 g of the crude product and 25 g of 95 wt% methanol - aqueous solution in a 150 mL single - necked flask. After fully dissolving at 55 °C for 1 h, cool the temperature programmatically (cool at a rate of 20 °C / h to 30 °C, then cool at a rate of 10 °C / h to 5 °C and maintain for 1 h, filter by suction, and dry to obtain 3.5 g of 2 - ethyl - 6 - acetylnaphthalene with a purity of 98.9%.

[0073] In this example, the substrate conversion rate is 90.9%.

[0074] Example 8

[0075] In this example, 2 - ethylnaphthalene, acetyl chloride, and ferric chloride are used as raw materials. The specific synthesis steps are as follows:

[0076] (1) 9.7 g (0.06 mol) of ferric chloride and 50 g of nitrobenzene were placed in a single-necked flask. After stirring and dissolving thoroughly, 7.6 g (0.49 mol) of 2-ethylnaphthalene was added to obtain a catalyst-bottom liquid. 4.3 g (0.055 mol) of acetyl chloride and 30 g of nitrobenzene were placed in a three-necked flask to obtain an acylation liquid, which was placed in a low-temperature bath. The catalyst-bottom liquid was slowly added to this three-necked flask through a feed pump, controlling the dropping rate at 60 mL / min, and the temperature of the low-temperature bath was kept constant at 0 °C. After the addition of the catalyst-bottom liquid was completed, the reaction was carried out at 20 °C for 2 h. The reaction product was poured into ice water containing crushed ice, stirred for 0.5 h, then 4.5 g of sodium bicarbonate was added to adjust the pH to neutral, and it was poured into a separating funnel for phase separation. The organic layer was taken, and the fraction at 160 °C / 2 mmHg was collected by vacuum distillation to obtain 7.0 g of crude 2-ethyl-6-acetylnaphthalene. The obtained crude product was analyzed by gas chromatography, and the yield of 2-ethyl-6-acetylnaphthalene was 69.1%.

[0077] (2) 7.0 g of the crude product and 25 g of 95 wt% methanol-aqueous solution were placed in a 150 mL single-necked flask. After dissolving thoroughly at 55 °C for 1 h, the temperature was decreased stepwise (the temperature was decreased to 30 °C at a rate of 20 °C / h, and then to 5 °C at a rate of 10 °C / h and kept for 1 h), filtered by suction and dried to obtain 3.5 g of 2-ethyl-6-acetylnaphthalene with a purity of 99.1%.

[0078] In this example, the substrate conversion rate was 87.3%.

[0079] Comparative Example 1

[0080] In this comparative example, 2-methylnaphthalene, acetyl chloride, and aluminum chloride (Elbs method) were used as raw materials. The specific synthesis steps were as follows:

[0081] (1) 8 g (0.06 mol) of aluminum chloride and 50 g of nitrobenzene were placed in a single-necked flask and stirred and dissolved thoroughly to obtain a catalyst liquid. 4.3 g (0.055 mol) of acetyl chloride, 7.1 g (0.05 mol) of 2-methylnaphthalene, and 30 g of nitrobenzene were placed in a three-necked flask. The three-necked flask was placed in a low-temperature bath. After stirring and dissolving thoroughly, the obtained catalyst liquid was slowly added to this three-necked flask through a feed pump, controlling the dropping rate at 60 mL / min, and the temperature of the low-temperature bath was kept constant at 0 °C. After the addition of the catalyst liquid was completed, the reaction was carried out at 20 °C for 2 h. The reaction product was poured into ice water containing crushed ice, stirred for 0.5 h, then 5.0 g of sodium bicarbonate was added to adjust the pH to neutral, and it was poured into a separating funnel for phase separation. The organic layer was taken, and the fraction at 160 °C / 2 mmHg was collected by vacuum distillation to obtain 5.7 g of crude 2-methyl-6-acetylnaphthalene. The obtained crude product was analyzed by gas chromatography, and the yield of 2-methyl-6-acetylnaphthalene was 62.4%.

[0082] (2) Dissolve 5.7 g of the crude product and 25 g of 95 wt% methanol-aqueous solution in a 150 mL single-necked flask. After fully dissolving at 55 °C for 1 h, cool the temperature programmatically (cool at a rate of 20 °C / h to 30 °C, then cool at a rate of 10 °C / h to 5 °C and hold for 1 h), filter by suction, and dry to obtain 2.6 g of 2-methyl-6-acetylnaphthalene with a purity of 99.4%.

[0083] In this comparative example, the substrate conversion rate is 83.4%.

[0084] Comparative Example 2

[0085] This comparative example uses 2-methylnaphthalene, acetyl chloride, and aluminum chloride (Perrir method) as raw materials. The specific synthesis steps are as follows:

[0086] (1) Put 7.1 g (0.05 mol) of 2-methylnaphthalene and 30 g of nitrobenzene into a single-necked flask, stir and dissolve fully to obtain a substrate solution. Put 8 g (0.06 mol) of aluminum chloride, 4.3 g (0.055 mol) of acetyl chloride, and 50 g of nitrobenzene into a three-necked flask. Place the three-necked flask in a low-temperature bath, and slowly add the substrate solution to this three-necked flask through a feed pump, controlling the dropping rate at 60 mL / min. The temperature of the low-temperature bath is kept constant at 0 °C. After the substrate solution is added dropwise, react at 20 °C for 2 h. Pour the reaction product into ice water containing crushed ice, stir for 0.5 h, then add 5.0 g of sodium bicarbonate to adjust the pH to neutral, pour it into a separatory funnel for phase separation, take the organic layer, and collect the fraction at 160 °C / 2 mmHg by vacuum distillation to obtain 4.7 g of crude 2-methyl-6-acetylnaphthalene. Perform gas chromatography analysis on the obtained crude product, and the yield of 2-methyl-6-acetylnaphthalene is 51.7%.

[0087] (2) Put 4.7 g of the crude product and 25 g of 95 wt% methanol-aqueous solution in a 150 mL single-necked flask. After fully dissolving at 55 °C for 1 h, cool the temperature programmatically (cool at a rate of 20 °C / h to 30 °C, then cool at a rate of 10 °C / h to 5 °C and hold for 1 h), filter by suction, and dry to obtain 2.2 g of 2-methyl-6-acetylnaphthalene with a purity of 99.3%.

[0088] In this comparative example, the substrate conversion rate is 85.2%.

[0089] Comparative Example 3

[0090] This comparative example uses 2-methylnaphthalene, acetyl chloride, and aluminum chloride (Bouveault method) as raw materials.

[0091] (1) 4.3 g (0.055 mol) of acetyl chloride and 30 g of nitrobenzene were placed in a single-necked flask and stirred well to dissolve, obtaining an acylation reagent solution. 8 g (0.06 mol) of aluminum chloride, 7.1 g (0.05 mol) of 2-methylnaphthalene, and 50 g of nitrobenzene were placed in a three-necked flask. The three-necked flask was placed in a low-temperature bath, and the acylation reagent solution was slowly added to this three-necked flask through a feeding pump, controlling the dropping rate at 60 mL / min, and the temperature of the low-temperature bath was kept constant at 0 °C. After the acylation reagent solution was added dropwise, the reaction was carried out at 20 °C for 2 h. The reaction product was poured into ice water containing crushed ice, stirred for 0.5 h, then 5.0 g of sodium bicarbonate was added to adjust the pH to neutral, poured into a separating funnel for phase separation, and the organic layer was taken. The fraction at 160 °C / 2 mmHg was collected by vacuum distillation to obtain 4.6 g of crude 2-methyl-6-acetylnaphthalene. The obtained crude product was analyzed by gas chromatography, and the yield of 2-methyl-6-acetylnaphthalene was 49.5%.

[0092] (2) 4.6 g of the crude product and 25 g of 95 wt% methanol-aqueous solution were placed in a 150 mL single-necked flask, and were fully dissolved at 55 °C for 1 h, then the temperature was decreased stepwise (decreased to 30 °C at a rate of 20 °C / h, and then decreased to 5 °C at a rate of 10 °C / h and kept for 1 h), filtered by suction and dried to obtain 2 g of 2-methyl-6-acetylnaphthalene with a purity of 99.4%.

[0093] In this comparative example, the substrate conversion rate was 78.1%.

[0094] Comparative Example 4

[0095] This comparative example used 2-methylnaphthalene, acetyl chloride, and aluminum chloride (Brown method) as raw materials, and the specific synthesis steps were as follows:

[0096] (1) 8 g (0.06 mol) of aluminum chloride, 4.3 g (0.055 mol) of acetyl chloride, and 50 g of nitrobenzene were placed in a single-necked flask and stirred well to dissolve, obtaining a catalyst-acylation reagent mixture. 7.1 g (0.05 mol) of 2-methylnaphthalene and 30 g of nitrobenzene were placed in a three-necked flask. The three-necked flask was placed in a low-temperature bath, and the catalyst-acylation reagent mixture was slowly added to this three-necked flask through a feeding pump, controlling the dropping rate at 60 mL / min, and the temperature of the low-temperature bath was kept constant at 0 °C. After the catalyst-acylation reagent mixture was added dropwise, the reaction was carried out at 20 °C for 2 h. The reaction product was poured into ice water containing crushed ice, stirred for 0.5 h, then 5.0 g of sodium bicarbonate was added to adjust the pH to neutral, poured into a separating funnel for phase separation, and the organic layer was taken. The fraction at 160 °C / 2 mmHg was collected by vacuum distillation to obtain 5.4 g of crude 2-alkyl-6-acylnaphthalene. The crude product was analyzed by gas chromatography, and the yield of 2-methyl-6-acetylnaphthalene was 58.2%;

[0097] (2) 5.4 g of the crude product and 25 g of 95 wt% methanol-aqueous solution were placed in a 150 mL single-necked flask. After being fully dissolved at 55 °C for 1 h, the temperature was decreased stepwise (decreased to 30 °C at a rate of 20 °C / h, and then decreased to 5 °C at a rate of 10 °C / h and maintained for 1 h). After suction filtration and drying, 2.7 g of 2-methyl-6-acetylnaphthalene with a purity of 98.4% was obtained.

[0098] In this comparative example, the substrate conversion rate was 81.6%.

[0099] Comparative Example 5

[0100] In this comparative example, 2-methylnaphthalene, acetyl chloride, and aluminum chloride (Claus method) were used as raw materials. The specific synthesis steps were as follows:

[0101] (1) 7.1 g (0.05 mol) of 2-methylnaphthalene, 4.3 g (0.055 mol) of acetyl chloride, and 30 g of nitrobenzene were placed in a single-necked flask and stirred thoroughly to dissolve, obtaining an acylation reagent-substrate mixed solution. 8 g (0.06 mol) of aluminum chloride and 50 g of nitrobenzene were placed in a three-necked flask. The three-necked flask was placed in a low-temperature bath. The acylation reagent-substrate mixed solution was slowly added to this three-necked flask through a feed pump, controlling the dropping rate at 60 mL / min, and the temperature of the low-temperature bath was kept constant at 0 °C. After the acylation reagent-substrate mixed solution was completely added dropwise, the reaction was carried out at 20 °C for 2 h. The reaction product was poured into ice water containing crushed ice, stirred for 0.5 h, then 5.0 g of sodium bicarbonate was added to adjust the pH to neutral, and it was poured into a separating funnel for phase separation. The organic layer was taken, and the fraction at 160 °C / 2 mmHg was collected by vacuum distillation to obtain 3.8 g of crude 2-methyl-6-acetylnaphthalene. The crude product was analyzed by gas chromatography, and the yield of 2-methyl-6-acetylnaphthalene was 41.8%;

[0102] (2) 3.8 g of the crude product and 25 g of 95 wt% methanol-aqueous solution were placed in a 150 mL single-necked flask. After being fully dissolved at 55 °C for 1 h, the temperature was decreased stepwise (decreased to 30 °C at a rate of 20 °C / h, and then decreased to 5 °C at a rate of 10 °C / h and maintained for 1 h). After suction filtration and drying, 1.4 g of 2-methyl-6-acetylnaphthalene with a purity of 99.3% was obtained.

[0103] In this comparative example, the substrate conversion rate was 76.9%.

[0104] Table 1 summarizes the experimental results of the yields, conversion rates, and selectivities of Examples 1-8 and Comparative Examples 1-5.

[0105] Table 1

[0106] Example 1 Example 2 Example 3 Example 4 Yield (%) 65.2 66.7 62.8 63.9 Conversion rate (%) 84.3 83.9 79.2 77.8 Selectivity (%) 77.3 79.5 79.3 82.1 Example 5 Example 6 Example 7 Example 8 Yield (%) 69.2 67.2 70.9 69.1 Conversion rate (%) 90.2 86.7 90.9 87.3 Selectivity (%) 76.7 77.5 78.0 79.1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Yield (%) 62.4 51.7 49.5 58.2 Conversion rate (%) 83.4 85.2 78.1 81.6 Selectivity (%) 74.8 60.7 63.4 71.3 Comparative Example 5 Yield (%) 41.8 Conversion rate (%) 76.9 Selectivity (%) 54.4

[0107] Among them, the yield = conversion rate × selectivity

[0108] Example 1 and Example 2 are under aluminum chloride catalyst, and Example 3 and Example 4 are under ferric chloride catalyst. These four groups are all equimolar reactions (2-methylnaphthalene: acylating agent: catalyst = 1: 1: 1). The catalytic effect of ferric chloride is equivalent to or even better than aluminum chloride in terms of selectivity, but it will significantly reduce the conversion rate; and Example 2 and Example 4 are compared with Example 1 and Example 3 because the acylating agent used is propionyl chloride, which has greater steric hindrance itself, and is more conducive to attacking the 6-position, which is the least hindered place on the naphthalene ring, in the process of attacking the substrate 2-methylnaphthalene, so the selectivity will be a little higher. In Examples 5-8, the catalyst and acylating agent are slightly excessive (catalyst: acylating agent: 2-methylnaphthalene = 1.2: 1.1: 1) and the acylating agent is acetyl chloride. Because the Friedel-Crafts acylation reaction is a stoichiometric reaction, an excess of catalyst will increase the conversion rate, but may reduce the selectivity. In Example 5, aluminum chloride is added, and in Example 6, ferric chloride is added, which is compared with Example 1 and Example 3. For Example 7 and Example 8, the substrate is 2-ethylnaphthalene, which is more active and has a stronger electronic effect than the methyl group. In this case, if the product is 2-alkyl-1-acetylnaphthalene, the activity of 2-methylnaphthalene will be higher because position 1 will be more hindered (2-ethylnaphthalene). However, for the target product of the present invention, 2-alkyl-6-acetylnaphthalene, the electronic effect of 2-ethylnaphthalene is more dominant, resulting in improved conversion and selectivity in Example 7 and Example 8 compared to Examples 5 and 6.

[0109] Comparative Examples 1-6 are all based on slightly excessive reaction conditions: aluminum chloride: acetyl chloride: 2-methylnaphthalene = 1.2: 1.1: 1. Compared with Example 5, the yield, conversion rate and selectivity of Comparative Examples 1-5 are all lower than those of Example 5; the higher conversion rate of Comparative Example 2 is due to the fact that the substrate 2-methylnaphthalene is added last. In the acylation reactions of other substrates in the past, this method has a relatively higher conversion rate, but its yield is too low compared with the preparation method provided by the present invention.

[0110] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing 2-alkyl-6-acylnaphthalene, characterized in that: The following steps are involved: The catalyst-base liquid is added dropwise to the acylation liquid; after the addition is completed, the reaction is carried out; the mixture obtained by the reaction is poured into ice water, the pH is adjusted to neutral, an organic phase is obtained by extraction, and the organic phase is distilled under reduced pressure and recrystallized to obtain the 2-alkyl-6-acylnaphthalene; The preparation steps of the catalyst-base liquid are: dissolving the catalyst and 2-alkylnaphthalene in a solvent to obtain the catalyst-base liquid; the preparation steps of the acylation liquid are: dissolving the acylation agent in a solvent to obtain the acylation liquid.

2. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 1, characterized in that: The catalyst is a Lewis acid catalyst; the acylating agent is an acyl halide or anhydride; and the solvents are all nitro compounds.

3. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 1, characterized in that: The mass ratio of the solvent to 2-alkylnaphthalene in the catalyst-base liquid is (3-10):

1.

4. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 1, characterized in that: The molar ratio of the catalyst to 2-alkylnaphthalene is (1-1.2):

1.

5. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 1, characterized in that: The mass ratio of the acylating agent to the solvent in the acylating solution is 1:(6.5-7.7).

6. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 1, characterized in that: The dropping rate was 60 mL / h and the temperature was 0°C.

7. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 1, characterized in that: The reaction temperature is 20°C and the reaction time is 2h.

8. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 1, characterized in that: The solvent for the recrystallization is an alcohol-water solution.

9. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 8, characterized in that: The mass concentration of the alcohol-water solution is 95%.

10. The method for preparing 2-alkyl-6-acylnaphthalene according to claim 8, characterized in that: The recrystallization was carried out at 55°C.

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