Preparation method of 1, 4-dimethylnaphthalene
By introducing β-cyclodextrin as a promoter, highly selective chloromethylation and reduction reactions of 1,4-dimethylnaphthalene were achieved, solving the problems of poor selectivity and low yield in existing technologies, and obtaining high-purity products suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-04
- Publication Date
- 2026-04-14
AI Technical Summary
Existing methods for synthesizing 1,4-dimethylnaphthalene suffer from poor regioselectivity, difficulty in isomer separation, harsh reaction conditions, use of high-risk reagents, and low overall yield, which limit their industrial application.
Using 1-methylnaphthalene as raw material, a two-step reaction of chloromethylation and reduction was carried out, with β-cyclodextrin as a selective promoter, to achieve highly selective chloromethylation at the 4-position. The high-purity product was obtained by mild reduction and distillation purification.
It improves regional selectivity by more than 90%, product purity by more than 97%, and total yield by 78%-86%. The reaction conditions are mild and safe, making it suitable for industrial production.
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Figure CN121850824A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of organic chemical synthesis technology, and in particular to a method for preparing 1,4-dimethylnaphthalene. Background Technology
[0002] 1,4-Dimethylnaphthalene is an important fine chemical intermediate with wide applications in plant growth regulators, fluorescent whitening agents, and high-performance materials. Existing synthetic routes, such as direct methylation, cyclization, and Grignard reagent methods, generally suffer from poor regioselectivity, difficulty in isomer separation, harsh reaction conditions, use of expensive or high-risk reagents, and low overall yield, which limits its industrial application.
[0003] The chloromethylation-reduction route is a potential pathway for the synthesis of 1,4-dimethylnaphthalene, but its effectiveness is highly dependent on the regioselectivity of the chloromethylation step. 1-Methylnaphthalene has multiple reactive sites on its naphthalene ring (e.g., positions 2, 4, 5, 6, and 7). Efficiently and selectively introducing a chloromethyl group at the 4-position is crucial for improving the overall economics and feasibility of the process. Traditional chloromethylation methods typically exhibit low selectivity, generating numerous positional isomers, which greatly complicates subsequent separation and purification, resulting in low product purity and high production costs.
[0004] Therefore, developing a preparation method that can achieve 4-chloromethylation with high selectivity, thereby simplifying the process and improving product purity and yield, has significant industrial value. Summary of the Invention
[0005] This invention addresses the shortcomings of existing technologies by providing a method for preparing high-purity 1,4-dimethylnaphthalene from 1-methylnaphthalene via a two-step reaction of chloromethylation and reduction. The core of this method lies in achieving highly selective chloromethylation at the 4-position through a flexible combination of reagents and processes, followed by gentle reduction and distillation purification to obtain a product with a purity ≥97%.
[0006] The technical solution of this invention is implemented as follows: This invention provides a method for preparing 1,4-dimethylnaphthalene, comprising the following steps: S1. Using 1-methylnaphthalene as a raw material, a chloromethylating agent, β-cyclodextrin and a catalyst are added to react and 1-chloromethyl-4-methylnaphthalene is obtained. S2. The 1-chloromethyl-4-methylnaphthalene obtained in step S1 is reacted to obtain 1,4-dimethylnaphthalene.
[0007] Based on the above technical solution, preferably, in step S1, the amount of β-cyclodextrin added is 5%-20% of the mass of 1-methylnaphthalene. In the chloromethylation reaction system, β-cyclodextrin includes the naphthalene ring of 1-methylnaphthalene, utilizing the stereoconfined effect of its hydrophobic cavity to directionally guide the chloromethylating agent to attack the 4-position of the naphthalene ring, significantly improving regioselectivity. Simultaneously, this inclusion effect reduces side reactions of the reaction intermediates, making the reaction cleaner and facilitating subsequent separation and distillation. If the addition amount is less than 5%, the inclusion effect is insufficient, and the selectivity improvement effect is limited; if it is higher than 20%, it may cause difficulties in mixing and separation, which is detrimental to the smooth progress of the reaction and subsequent purification.
[0008] More preferably, in step S1, the amount of β-cyclodextrin added is 10% of the mass of 1-methylnaphthalene.
[0009] More preferably, in step S1, the catalyst is selected from one or more acidic mixtures composed of aluminum trichloride, zinc chloride, ferric chloride, tin tetrachloride, boron trifluoride, titanium tetrachloride, antimony pentachloride, sulfuric acid, phosphoric acid, and acetic acid. The amount of the catalyst relative to 1-methylnaphthalene is 0.1-0.3 equivalents.
[0010] Based on the above technical solution, preferably, in step S1, the chloromethylation reagent is a formaldehyde source and a chlorinating agent. The molar ratio of the formaldehyde source and the chlorinating agent is 1:(1.0-2.0).
[0011] More preferably, the formaldehyde source is selected from one or more of paraformaldehyde, formaldehyde solution, gaseous formaldehyde, and methyl acetal; the chlorinating agent is selected from one or more of hydrogen chloride gas, hydrochloric acid, acetyl chloride, thionyl chloride, and sulfonyl chloride.
[0012] More preferably, in step S1, the molar ratio of 1-methylnaphthalene to formaldehyde source is 1:(1.0-3.0); the reaction temperature is 40-75℃; and the reaction time is 4-12 hours.
[0013] More preferably, in the method where the chloromethylating agent is a formaldehyde source and the chlorinating agent is the above, a phase transfer catalyst may also be added, selected from one or more of triethylbenzylammonium chloride, tetrabutylammonium hydrogen sulfate, tetrabutylammonium bromide, hexadecyltrimethylammonium bromide, trioctylmethylammonium chloride, tetrabutylphosphonium bromide, and triphenylmethylphosphonium chloride. The molar ratio of the phase transfer catalyst to 1-methylnaphthalene is approximately 1:25.
[0014] Based on the above technical solutions, preferably, in step S1, the chloromethylation reagent is a chloromethyl ether reagent.
[0015] More preferably, the chloromethyl ether reagent is selected from one or more of chloromethyl methyl ether, dichloromethyl ether, and chloromethyl ethyl ether.
[0016] More preferably, in step S1, the reaction solvent is selected from one or more of acetic acid, dichloroethane, dichloromethane, chloroform, carbon tetrachloride, n-hexane, n-heptane, n-pentane, cyclohexane, and petroleum ether.
[0017] More preferably, in step S1, the molar ratio of 1-methylnaphthalene to chloromethyl ether reagent is 1:(1.0-3.0); the reaction temperature is -10-30℃; and the reaction time is 4-12 hours.
[0018] Based on the above technical solutions, preferably, in step S2, the reaction is a reduction reaction, and the reduction reaction is selected from any of the following methods: reaction with hydrogen in the presence of a hydrogenation catalyst or reaction with an active metal element.
[0019] More preferably, the hydrogenation catalyst is selected from palladium / carbon, Raney nickel, platinum, and ruthenium; the amount of hydrogenation catalyst used is 5%-10% of the mass of 1-chloromethyl-4-methylnaphthalene, and the reaction time is 5-6 hours; the reaction is carried out in a solvent, which includes one or more of ethyl acetate, methanol, and tetrahydrofuran; the reaction is carried out under a hydrogen pressure of 0.1-5 MPa.
[0020] More preferably, the active metal element is selected from zinc powder, iron powder, aluminum powder, and tin powder; the reaction temperature is 20-100℃, and the reaction time is 4-5 hours; the reaction is carried out in a solvent, which includes one or more of methanol, tetrahydrofuran, 1,4-dioxane, and ethyl acetate; optionally, a protic acid is added, which includes one of formic acid, hydrochloric acid, phosphoric acid, and sulfuric acid; the amount of the active metal element relative to 1-chloromethyl-4-methylnaphthalene is 1.0-4.0 equivalents.
[0021] Based on the above technical solutions, preferably, after the reaction is completed, distillation purification is carried out. The distillation is vacuum distillation, with an operating pressure of -0.09 MPa to -0.1 MPa, and the fraction with a boiling range of 80~140℃ is collected.
[0022] The preparation method of 1,4-dimethylnaphthalene provided by this invention has the following advantages over the prior art: (1) High selectivity and easy purification: By introducing β-cyclodextrin as a selectivity promoter, the chloromethylation reaction is specifically directed to the 4-position of the naphthalene ring using its host-guest inclusion effect, with a regioselectivity of more than 90%. This significantly reduces isomer byproducts from the source, making subsequent separation and purification easier, and the final product purity can reach more than 97%.
[0023] (2) High yield and good economy: Due to the good reaction selectivity and few side reactions, the total yield of the method of the present invention (based on 1-methylnaphthalene) can reach 78%-86%, which is much higher than the 25%-35% of the traditional method. The raw material utilization rate is high and the economic benefits are significant.
[0024] (3) Mild conditions, safe and environmentally friendly: The chloromethylation reaction is carried out under mild conditions, and the reduction step is preferably carried out by catalytic hydrogenation, which avoids the use of high temperature, strong corrosion and high-risk reagents. The generation of waste is small, the operation is safe, and it conforms to the principles of green chemistry.
[0025] (4) Flexible process and easy to industrialize: It provides two main chloromethylation routes, namely the chloromethyl ether method and the formaldehyde-hydrochloric acid method, and can be flexibly combined with different reduction processes. It is highly adaptable, and the raw materials are readily available. The steps are simple and very suitable for large-scale production. Attached Figure Description
[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a roadmap for the preparation method of 1,4-dimethylnaphthalene according to the present invention; Figure 2 The HPLC chromatogram of 1-chloromethyl-1-methylnaphthalene synthesized in Example 2 of this invention is shown below. Figure 3 The 1,4-dimethylnaphthalene synthesized in Example 2 of this invention 1 H NMR spectrum; Figure 4 This is the GC spectrum of 1,4-dimethylnaphthalene synthesized in Example 2 of the present invention. Detailed Implementation
[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0029] Table 1: Material Source Description Table
[0030] Example 1: S1. In a dry reaction flask, add 7.11 g (50 mmol) of 1-methylnaphthalene, 0.71 g (0.63 mmol) of β-cyclodextrin, 50 mL of dichloroethane, and 0.64 g (2 mmol) of tetrabutylammonium bromide. Stir the mixture at 75°C for 1 hour to ensure sufficient pre-dispersion and inclusion of β-cyclodextrin and 1-methylnaphthalene. Then add 2.25 g (75 mmol) of paraformaldehyde, 10 mL of 12 M concentrated hydrochloric acid, and 0.68 g (5 mmol) of anhydrous zinc chloride. Stir the reaction at 40°C for 6 hours. After the reaction is complete, separate the organic layer, wash with water, dry with anhydrous sodium sulfate, and concentrate under reduced pressure to obtain crude 1-chloromethyl-4-methylnaphthalene. HPLC analysis showed a regioselectivity of greater than 90% at the 4-position and a yield of 93%.
[0031] S2. Add the above crude product, 9.81 g, 150 mmol of zinc powder, and 50 mL of methanol to a reaction flask. While stirring, add approximately 1 mL of acetic acid dropwise to maintain a slightly acidic environment. Heat to reflux at 65°C for 5 hours. After the reaction is complete, filter and concentrate the filtrate under reduced pressure. Dissolve the residue in ethyl acetate, wash with water, dry, and concentrate to obtain crude 1,4-dimethylnaphthalene. Distill the crude product under reduced pressure, collecting the fraction at 120-125°C / 1.33 kPa to obtain a colorless, transparent liquid, 1,4-dimethylnaphthalene, with a purity ≥98% and a yield of 92%.
[0032] Example 2: S1. In a dry reaction flask, add 7.11 g (50 mmol) of 1-methylnaphthalene, 0.71 g (0.63 mmol) of β-cyclodextrin, and 50 mL of dichloromethane. While cooling in an ice-water bath, add 1.00 g (7.5 mmol) of anhydrous aluminum trichloride in portions. After the addition is complete, slowly add 7.10 g (75 mmol) of chloromethyl ethyl ether dropwise while maintaining a low temperature of 0°C. Then, raise the temperature to room temperature (25-30°C) and stir the reaction for 8 hours. Pour the reaction solution into ice water, separate the layers, and wash the organic phase successively with saturated sodium bicarbonate solution and water. Dry under anhydrous sodium sulfate and concentrate under reduced pressure to obtain crude 1-chloromethyl-4-methylnaphthalene. HPLC analysis showed a regioselectivity of greater than 86% at the 4-position and a yield of 87%.
[0033] S2. Dissolve the above crude product in 50 mL of ethyl acetate, add approximately 0.38 g of 5% Pd / C catalyst (5% based on the crude product weight), and transfer to an autoclave. After purging with hydrogen three times, purge with hydrogen to 2 MPa and stir at 40 °C for 6 hours. After the reaction is complete, filter to remove the catalyst, and concentrate the filtrate under reduced pressure to obtain crude 1,4-dimethylnaphthalene. Distill the crude product under reduced pressure, collecting the fraction at 120-125 °C / 1.33 kPa to obtain a colorless, transparent liquid 1,4-dimethylnaphthalene with a purity ≥97% and a yield of 92%.
[0034] Example 3: S1. In a dry reaction flask, add 80 mmol (11.38 g) of 1-methylnaphthalene, 0.57 g (0.50 mmol) of β-cyclodextrin, and 100 mL of dichloroethane. Cool to -10°C, add 3.20 g (24 mmol) of anhydrous aluminum trichloride in portions, maintain the temperature at 0°C, and slowly add 22.69 g (240 mmol) of chloromethyl ethyl ether dropwise. Then raise the temperature to room temperature (25-30°C) and stir for 4 hours. Quench the reaction solution in ice water containing dilute hydrochloric acid, separate the dichloroethane layer, wash with water, dry, and concentrate to obtain the intermediate 1-chloromethyl-4-methylnaphthalene. HPLC analysis showed a regioselectivity of greater than 85% at the 4-position and a yield of 93%.
[0035] S2. Add the above intermediate, 20.92 g, 320 mmol zinc powder, 120 mL ethyl acetate, and 20 mL glacial acetic acid to a reaction flask, and heat to reflux at 80°C for 4 hours. Cool, filter, and wash the filter cake with ethyl acetate. Combine the filtrates, wash with saturated sodium bicarbonate solution until neutral, wash with water, dry, and concentrate. Distill the crude product under reduced pressure to obtain 1,4-dimethylnaphthalene with a purity ≥98% and a yield of 91%.
[0036] Example 4: S1. In a reaction flask equipped with a gas inlet tube and a tail gas absorption device, add 28.44 g of 1-methylnaphthalene (200 mmol), 5.69 g of β-cyclodextrin (5.01 mmol), 2.73 g of anhydrous zinc chloride (20 mmol), and 150 mL of glacial acetic acid. While stirring, simultaneously introduce gaseous formaldehyde and dry hydrogen chloride gas, controlling the gas introduction rate to 1.0-1.5 L / min; control the respective introduction rates to ensure a total introduction volume of 200 mmol for each; control the temperature at 10-15℃ and react for 6 hours. Stop the gas introduction, pour the reaction mixture into crushed ice, and extract with dichloromethane. Combine the organic phases, wash successively with saturated sodium bicarbonate solution and water, dry with anhydrous sodium sulfate, and concentrate to obtain crude 1-chloromethyl-4-methylnaphthalene, a light brown solid. HPLC analysis showed a regioselectivity of greater than 88% at the 4-position and a yield of 92%. (The tail gas is introduced into a two-stage alkaline absorption bottle (10% NaOH solution) to neutralize the unreacted hydrogen chloride gas.)
[0037] S2. Dissolve the crude product in 200 mL of ethanol and add approximately 2.60 g of 10% Pd / C catalyst. Hydrogenate at 0.8 MPa hydrogen pressure and 50 °C for 5 hours. After the reaction, remove the catalyst by hot filtration. After cooling the filtrate, add 1 mL of triethylamine and stir for 0.5 hours. Filter to remove the generated salt, and evaporate the solvent from the filtrate under reduced pressure. Distill the residue under reduced pressure to obtain the target product, 1,4-dimethylnaphthalene, with a purity ≥97% and a yield of 90%.
[0038] Example 5: The amount of β-cyclodextrin added was 5% of the mass of 1-methylnaphthalene. S1. In a dry reaction flask, add 7.11 g (50 mmol) of 1-methylnaphthalene, 0.21 g (0.19 mmol) of β-cyclodextrin, 50 mL of dichloroethane, and 0.64 g (2 mmol) of tetrabutylammonium bromide. Stir the mixture at 40°C for 1 hour to allow the β-cyclodextrin and 1-methylnaphthalene to be fully pre-dispersed and encapsulated. Then add 2.25 g (75 mmol) of paraformaldehyde, 10 mL of 12 M concentrated hydrochloric acid, and 0.68 g (5 mmol) of anhydrous zinc chloride. Stir the reaction at 40°C for 6 hours. After the reaction is complete, separate the organic layer, wash with water, dry with anhydrous sodium sulfate, and concentrate under reduced pressure to obtain crude 1-chloromethyl-4-methylnaphthalene. HPLC analysis showed a 4-position regioselectivity of 91% and a yield of 84%.
[0039] S2. Add the above crude product, 9.81 g, 150 mmol of zinc powder, and 50 mL of methanol to a reaction flask. While stirring, add approximately 1 mL of acetic acid dropwise to maintain a slightly acidic environment. Heat to reflux at 65°C for 5 hours. After the reaction is complete, filter and concentrate the filtrate under reduced pressure. Dissolve the residue in ethyl acetate, wash with water, dry, and concentrate to obtain crude 1,4-dimethylnaphthalene. Distill the crude product under reduced pressure, collecting the fraction at 120-125°C / 1.33 kPa to obtain a colorless, transparent liquid, 1,4-dimethylnaphthalene, with a purity of 98% and a yield of 93%.
[0040] Example 6: The amount of β-cyclodextrin added was 20% of the mass of 1-methylnaphthalene. S1. In a dry reaction flask, add 7.11 g (50 mmol) of 1-methylnaphthalene, 1.44 g (1.25 mmol) of β-cyclodextrin, 50 mL of dichloroethane, and 0.64 g (2 mmol) of tetrabutylammonium bromide. Stir the mixture at 40°C for 1 hour to allow the β-cyclodextrin and 1-methylnaphthalene to be fully pre-dispersed and encapsulated. Then add 2.25 g (75 mmol) of paraformaldehyde, 10 mL of 12 M concentrated hydrochloric acid, and 0.68 g (5 mmol) of anhydrous zinc chloride. Stir the reaction at 40°C for 6 hours. After the reaction is complete, separate the organic layer, wash with water, dry with anhydrous sodium sulfate, and concentrate under reduced pressure to obtain crude 1-chloromethyl-4-methylnaphthalene. HPLC analysis showed a 4-position regioselectivity of 92% and a yield of 85%.
[0041] S2. Add the above crude product, 9.81 g, 150 mmol of zinc powder, and 50 mL of methanol to a reaction flask. While stirring, add approximately 1 mL of acetic acid dropwise to maintain a slightly acidic environment. Heat to reflux at 65°C for 5 hours. After the reaction is complete, filter and concentrate the filtrate under reduced pressure. Dissolve the residue in ethyl acetate, wash with water, dry, and concentrate to obtain crude 1,4-dimethylnaphthalene. Distill the crude product under reduced pressure, collecting the fraction at 120-125°C / 1.33 kPa to obtain a colorless, transparent liquid, 1,4-dimethylnaphthalene, with a purity of 97% and a yield of 94%.
[0042] Comparative Example 1: The amount of β-cyclodextrin added was 3% of the mass of 1-methylnaphthalene. S1. In a dry reaction flask, add 7.11 g (50 mmol) of 1-methylnaphthalene, 0.21 g (0.19 mmol) of β-cyclodextrin, 50 mL of dichloroethane, and 0.64 g (2 mmol) of tetrabutylammonium bromide. Stir the mixture at 40°C for 1 hour to ensure sufficient pre-dispersion and inclusion of β-cyclodextrin and 1-methylnaphthalene. Then add 2.25 g (75 mmol) of paraformaldehyde, 10 mL of 12 M concentrated hydrochloric acid, and 0.68 g (5 mmol) of anhydrous zinc chloride. Stir the reaction at 40°C for 6 hours. After the reaction is complete, separate the organic layer, wash with water, dry with anhydrous sodium sulfate, and concentrate under reduced pressure to obtain crude 1-chloromethyl-4-methylnaphthalene. HPLC analysis showed a 4-position regioselectivity of 80% and a yield of 83%.
[0043] S2. Add the above crude product, 9.81 g, 150 mmol of zinc powder, and 50 mL of methanol to a reaction flask. While stirring, add approximately 1 mL of acetic acid dropwise to maintain a slightly acidic environment. Heat to reflux at 65°C for 5 hours. After the reaction is complete, filter and concentrate the filtrate under reduced pressure. Dissolve the residue in ethyl acetate, wash with water, dry, and concentrate to obtain crude 1,4-dimethylnaphthalene. Distill the crude product under reduced pressure, collecting the fraction at 120-125°C / 1.33 kPa to obtain a colorless, transparent liquid, 1,4-dimethylnaphthalene, with a purity of 88% and a yield of 82%.
[0044] Comparative Example 2: The amount of β-cyclodextrin added was 25% of the mass of 1-methylnaphthalene. S1. In a dry reaction flask, add 7.11 g (50 mmol) of 1-methylnaphthalene, 1.78 g (1.57 mmol) of β-cyclodextrin, 50 mL of dichloroethane, and 0.64 g (2 mmol) of tetrabutylammonium bromide. Stir the mixture at 40 °C for 1 hour to allow the β-cyclodextrin and 1-methylnaphthalene to be fully pre-dispersed and encapsulated. Then add 2.25 g (75 mmol) of paraformaldehyde, 10 mL of 12 M concentrated hydrochloric acid, and 0.68 g (5 mmol) of anhydrous zinc chloride. Stir the reaction at 40 °C for 6 hours. After the reaction is complete, separate the organic layer, wash with water, dry with anhydrous sodium sulfate, and concentrate under reduced pressure to obtain crude 1-chloromethyl-4-methylnaphthalene. HPLC analysis showed a 4-position regioselectivity of 82% and a yield of 85%.
[0045] S2. Add the above crude product, 9.81 g, 150 mmol of zinc powder, and 50 mL of methanol to a reaction flask. While stirring, add approximately 1 mL of acetic acid dropwise to maintain a slightly acidic environment. Heat to reflux at 65°C for 5 hours. After the reaction is complete, filter and concentrate the filtrate under reduced pressure. Dissolve the residue in ethyl acetate, wash with water, dry, and concentrate to obtain crude 1,4-dimethylnaphthalene. Distill the crude product under reduced pressure, collecting the fraction at 120-125°C / 1.33 kPa to obtain a colorless, transparent liquid, 1,4-dimethylnaphthalene, with a purity of 87% and a yield of 84%.
[0046] As can be seen from the comparison between Example 1 and Comparative Examples 1 and 2, Comparative Examples 1 and 2 represent examples where the amount of β-cyclodextrin added was too large and too small, respectively. When the amount was too small, its function as a phase transfer catalyst and molecular recognition template was not fully utilized. The main reason was the insufficient catalytic sites, which prevented the effective encapsulation of most 1-methylnaphthalene molecules. At the same time, the inability to form a sufficiently concentrated "bridge" at the interface between the aqueous and organic phases led to a decrease in the contact efficiency between the reactants and the electrophilic reagents, and the reaction was diffusion-controlled. When the amount was too large, the excess β-cyclodextrin molecules were prone to self-aggregation in water, forming supramolecular aggregates or precipitates, which significantly increased the viscosity of the system and severely hindered the diffusion and mass transfer of the reactants. In addition, excess β-cyclodextrin may not only encapsulate the reactants but also intermediates and even products, thereby changing the reaction equilibrium, inhibiting the main reaction or inducing side reactions. The large amount of residual β-cyclodextrin may also enter the subsequent reduction steps, and its hydroxyl functional groups may affect the active surface of zinc powder or interact with the slightly acidic environment, thereby reducing the reduction efficiency.
[0047] Comparative Example 3: Unlike Example 1, Comparative Example 3 did not add β-cyclodextrin, and the remaining steps were the same as in Example 1. In step S1, HPLC analysis showed a 4-position regioselectivity of 65% and a yield of 80%. The colorless and transparent liquid 1,4-dimethylnaphthalene obtained in step S2 had a purity of only 85% and a yield of 68%.
[0048] A comparison of Comparative Example 3 and Example 1 shows that the absence of β-cyclodextrin significantly reduces regioselectivity. The chloromethyl cation indiscriminately attacks multiple active sites on the 1-methylnaphthalene ring, generating a complex mixture of isomers. This drastically reduces the selectivity of the 4-position product and results in the reduction step using a mixture of isomers at various chloromethylation positions, leading to a mixture of various dimethylnaphthalene isomers after reduction. These isomers have very similar boiling points, making separation by distillation extremely difficult and preventing the acquisition of high-purity 1,4-dimethylnaphthalene. Simultaneously, the lack of the "molecular bridge" effect of β-cyclodextrin reduces mass transfer efficiency between the two phases, slows the reaction rate, and leads to incomplete conversion, ultimately affecting the yield. Furthermore, the disappearance of the local concentration effect further restricts the main reaction. These results conversely confirm the core role of β-cyclodextrin in this invention: achieving regioselectivity control through selective inclusion and pre-organization, and synergistically enhancing reaction efficiency through phase transfer catalysis and the local concentration effect.
[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing 1,4-dimethylnaphthalene, characterized in that, Includes the following steps: S1. Using 1-methylnaphthalene as a raw material, a chloromethylating agent, β-cyclodextrin and a catalyst are added to react and 1-chloromethyl-4-methylnaphthalene is obtained. S2. The 1-chloromethyl-4-methylnaphthalene obtained in step S1 is subjected to a reduction reaction to obtain 1,4-dimethylnaphthalene.
2. The preparation method according to claim 1, characterized in that, In step S1, the amount of β-cyclodextrin added is 5%-20% of the mass of 1-methylnaphthalene.
3. The preparation method according to claim 1, characterized in that, In step S1, the catalyst is selected from one or more of the following acidic mixtures: aluminum trichloride, zinc chloride, ferric chloride, tin tetrachloride, boron trifluoride, titanium tetrachloride, antimony pentachloride, sulfuric acid, phosphoric acid, and acetic acid.
4. The preparation method according to claim 1, characterized in that, In step S1, the chloromethylation reagent is a formaldehyde source and a chlorinating agent.
5. The preparation method according to claim 4, characterized in that, The formaldehyde source is selected from one or more of paraformaldehyde, formaldehyde solution, gaseous formaldehyde, and methyl acetal; the chlorinating agent is selected from one or more of hydrogen chloride gas, hydrochloric acid, acetyl chloride, thionyl chloride, and sulfonyl chloride.
6. The preparation method according to claim 4, characterized in that, In step S1, the molar ratio of 1-methylnaphthalene to formaldehyde source is 1:(1.0-3.0); the reaction temperature is 40-75℃; and the reaction time is 4-12 hours.
7. The preparation method according to claim 1, characterized in that, In step S1, the chloromethylating agent is a chloromethyl ether reagent.
8. The preparation method according to claim 7, characterized in that, The chloromethyl ether reagents are selected from one or more of chloromethyl methyl ether, dichloromethyl ether, and chloromethyl ethyl ether.
9. The preparation method according to claim 7, characterized in that, In step S1, the molar ratio of 1-methylnaphthalene to chloromethyl ether reagent is 1:(1.0-3.0); the reaction temperature is -10-30℃; and the reaction time is 4-12 hours.
10. The preparation method according to claim 1, characterized in that, In step S2, the reduction reaction is selected from any of the following: reaction with hydrogen in the presence of a hydrogenation catalyst or reaction with an active metal element.