Novel synthesis method of 2, 6-naphthalic acid
By employing a two-step reaction system using a nickel catalyst and a manganese-cobalt-bromine catalyst, the high cost and low yield problems of 2,6-naphthalenedicarboxylic acid synthesis in existing technologies have been solved, achieving efficient and low-cost preparation of 2,6-naphthalenedicarboxylic acid.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG UNIV OF TECH
- Filing Date
- 2026-02-09
- Publication Date
- 2026-05-15
AI Technical Summary
Existing methods for synthesizing 2,6-naphthalenedicarboxylic acid suffer from problems such as expensive raw materials, costly catalysts, long reaction steps, low overall yield, and excessive waste.
Using a nickel catalyst and a manganese-cobalt-bromine catalyst system, 2,6-naphthalenedicarboxylic acid is efficiently prepared through a two-step reaction. The first step involves a Grignard reaction/coupling reaction, and the second step involves catalytic oxidation. Air is used as the oxidant, which simplifies the reaction steps and reduces costs.
The synthesis of 2,6-naphthalenedicarboxylic acid with high selectivity, high yield and low cost was achieved, with an overall yield of up to 85% and few by-products, making it suitable for industrial production.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of organic synthesis technology, and specifically to a novel method for synthesizing 2,6-naphthalenedicarboxylic acid. Background Technology
[0002] 2,6-Naphthalenedicarboxylic acid (2,6-Naphthalenedicarboxylic acid) is an important intermediate in the manufacture of high-strength, dyeable polyester fibers and Class F insulation materials. It is also a key monomer in high-performance polyethylene naphthalate (PEN), pyrolytic boron nitride (PBN), liquid crystal polymers (LCP), and polyurethane resins. Furthermore, it is a crucial intermediate in the synthesis of dyes and fluorescent whitening agents. PEN materials, in particular, possess excellent physical and mechanical properties, gas barrier properties, chemical stability, and resistance to heat, ultraviolet radiation, and staining. Due to its linear polymer characteristics, it is a material with good rigidity, high strength, and good thermal processing properties.
[0003] Currently, the main methods for synthesizing 2,6-naphthalenedicarboxylic acid are: (1) According to Japanese patent JP2011168501A, 2,6-naphthalenedicarboxylic acid is obtained by five steps of reaction, namely addition, cyclization, dehydrogenation, isomerization and oxidation, using 1,3-butadiene and o-xylene as raw materials, with a total yield of 51%. The raw materials are cheap, but the multi-step reaction requires expensive catalysts, the reaction steps are long, the operation is complicated, there is a lot of waste, and the total yield is low. The specific reaction route and conditions are as follows:
[0004] (2) Chinese patent CN117945881B reports a method using 2,6-dibromonaphthalene and ethanol as raw materials. High-pressure carbon monoxide gas is introduced, and under high-temperature conditions and with the action of a palladium composite catalyst, a dicarbonylation esterification reaction is carried out to generate the intermediate diethyl 2,6-naphthalenedicarboxylate. This intermediate is then hydrolyzed to obtain 2,6-naphthalenedicarboxylic acid, with a yield of 60%. This method has fewer reaction steps, but the raw materials and catalyst are expensive, the yield is low, and a significant amount of waste is generated. The specific reaction route and conditions are as follows:
[0005] Therefore, it is of great significance to study a new synthetic method for 2,6-naphthalenedicarboxylic acid and overcome the above-mentioned process deficiencies. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the present invention aims to provide a novel synthetic method for 2,6-naphthalenedicarboxylic acid. This method, through the design of a novel reaction pathway and an optimized catalytic system, achieves the efficient preparation of high-purity 2,6-naphthalenedicarboxylic acid from readily available raw materials via a two-step highly selective reaction, significantly improving the overall yield and substantially reducing production costs.
[0007] This invention provides a novel method for the synthesis of 2,6-naphthalenedicarboxylic acid. The specific reaction equation is as follows:
[0008] The process is a stepwise synthesis of 2,6-naphthalenedicarboxylic acid, comprising the following steps: Step a: In a solvent under a nitrogen atmosphere, 2-bromo-6-methoxynaphthalene is used as a starting material. A Grignard reaction / coupling reaction is carried out in the presence of a nickel catalyst, ligands, and a methylating agent to yield 2,6-dimethylnaphthalene. This step innovatively utilizes a nickel catalytic system to achieve the continuous conversion of bromine atoms and methoxy groups, highly selectively converting both functional groups to methyl groups. This allows for the one-step, efficient preparation of the key intermediate 2,6-dimethylnaphthalene, with high reaction selectivity, few byproducts, and simplified post-processing.
[0009] Step b involves subjecting the obtained 2,6-dimethylnaphthalene to liquid-phase catalytic oxidation in a closed reactor using oxygen-containing gas within a system containing a manganese-cobalt-bromine catalyst and acetic acid solvent. This catalyst system exhibits high activity and selectivity, efficiently oxidizing the two methyl groups to carboxyl groups using air as a cheap oxygen source to generate the target product, 2,6-naphthalenedicarboxylic acid. Furthermore, the product is easily separated and purified.
[0010] Further, in step a, the nickel catalyst is one of nickel chloride, nickel dichloride (bis(tricyclohexylphosphine) chloride), nickel bromide, nickel acetylacetonate, nickel bis(1,5-cyclooctadiene) chloride, nickel acetate, and nickel iodide, and the molar ratio of 2-bromo-6-methoxynaphthalene to the nickel catalyst is 1:(0.01~0.1). Preferably, it is 1:(0.04~0.07).
[0011] Further, in step a, the ligand is one of tricyclohexylphosphine, tri-tert-butylphosphine, 1,1'-bis(diphenylphosphine)ferrocene, 1,2-bis(dicyclohexylphosphine)ethane, triphenylphosphine, 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-ylene, and 1,3-bis(2,4,6-trimethylphenyl)imidazolium-2-ylene. When the nickel catalyst is nickel dichloride (bis(tricyclohexylphosphine)), the ligand is not required. The molar ratio of 2-bromo-6-methoxynaphthalene to the ligand is 1:(0.06~0.15), preferably 1:(0.09~0.12). The addition of the ligand can drive the activation of the C-O bond, and the large steric hindrance can significantly improve the reaction selectivity.
[0012] Further, in step a, the methylating agent is one of methylmagnesium bromide and dimethylzinc, and the molar ratio of 2-bromo-6-methoxynaphthalene to the methylating agent is 1:(2.0~3.0). Preferably, it is 1:(2.3~2.7).
[0013] Further, in step a, the solvent is one of toluene, xylene, n-hexane, tetrahydrofuran, N,N-dimethylformamide and diethyl ether, preferably toluene; the mass ratio of 2-bromo-6-methoxynaphthalene to the solvent is 1:(15~35), preferably 1:(20~30).
[0014] Further, in step a, the reaction temperature is 30~120℃, preferably 60~90℃. The reaction time is 3~5h.
[0015] Further, in step b, the manganese-cobalt-bromine catalyst is a mixture of manganese acetate, cobalt acetate, and bromide, with a molar ratio of 1:(0.1~1):(0.1~1) between the catalyst components. The bromide is one of sodium bromide, potassium bromide, and ammonium bromide. The catalyst dosage is such that the molar ratio of 2,6-dimethylnaphthalene to the manganese-cobalt-bromine catalyst mixture is 1:(0.1~1), preferably 1:(0.3~0.7).
[0016] Furthermore, in step b, the oxygen-containing gas is air or oxygen.
[0017] Further, in step b, the pressure of the oxidation reaction is 2.0~5.0 MPa, preferably 3~4 MPa.
[0018] Furthermore, in step b, the reaction temperature during the initial initiation stage is 150~200℃, preferably 160~190℃.
[0019] Furthermore, in step b, the reaction temperature in the later reaction stage is 180~250℃, preferably 200~230℃.
[0020] Further, in step b, the mass ratio of 2,6-dimethylnaphthalene to the solvent acetic acid is 1:(50~130), preferably 1:(80~100), and the reaction time in step b is (3~6) h.
[0021] This invention uses 2-bromo-6-methoxynaphthalene and Grignard reagent methyl magnesium bromide as raw materials. Under the action of a nickel catalyst and ligands, the bromo and methoxy functional groups undergo a Grignard reaction / coupling reaction sequentially, efficiently yielding the intermediate 2,6-dimethylnaphthalene in a one-step reaction. Then, under the action of a manganese-cobalt-bromine catalyst and with air as the oxygen source, a catalytic oxidation reaction is carried out to generate the target product 2,6-naphthalenedicarboxylic acid, with a maximum overall yield of up to 85%. This process features high overall yield, inexpensive catalyst, fewer reaction steps, simple operation, high reaction selectivity, easy purification, low energy consumption, and minimal waste. Therefore, overall, the production cost is low, making it suitable for industrial production.
[0022] Compared with the prior art, the present invention has the following advantages: (1) Innovative route design and significantly simplified steps: Starting from 2-bromo-6-methoxynaphthalene, the target product is obtained through two-step reaction. Compared with the traditional multi-step route (such as the five-step method), the process flow is significantly shortened, and the equipment investment and operating costs are reduced. One of the steps uses 2-bromo-6-methoxynaphthalene as raw material and directly produces 2,6-dimethylnaphthalene through a one-pot Fagwick / coupling reaction. This enables 2-bromo-6-methoxynaphthalene to undergo two different C-bond formation reactions (coupling followed by substitution) in the same reaction system to efficiently construct symmetrical 2,6-dimethylnaphthalene.
[0023] (2) The catalyst system is highly efficient and low cost: the first step uses a non-precious metal nickel catalyst to replace the expensive palladium catalyst; the second step uses a manganese-cobalt-bromine low-cost metal composite catalyst with air as the oxidant, and the catalyst cost is significantly lower than that of the existing precious metal catalyst system.
[0024] (3) High overall yield and purity: By optimizing the reaction conditions and catalyst ratio of each step, the yield of intermediates and final products both exceed 90%, the overall yield can reach more than 85%, and the product purity is as high as 99%, which is far superior to existing reports.
[0025] (4) The raw materials are readily available and the atom economy is good: the starting material 2-bromo-6-methoxynaphthalene is relatively widely available, the synthetic route has high atom utilization and few by-products.
[0026] (5) Environmentally friendly and suitable for industrialization: The amount of waste generated is small, the post-treatment is simple, the reaction conditions are mild and controllable, and it is easy to achieve large-scale production. Detailed Implementation
[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are only for explaining the invention and are not limited to the following implementation examples. Example 1
[0028] This invention provides a method for synthesizing 2,6-naphthalenedicarboxylic acid, comprising the following steps: Step a: 23.7 g (0.1 mol) of 2-bromo-6-methoxynaphthalene and 3.45 g (0.005 mol) of nickel dichloride (bis(tricyclohexylphosphine)) were added to a Shrek tube. After purging with nitrogen, 50 mL of anhydrous toluene was added, and the mixture was stirred until the solids were completely dissolved. 28.6 g (0.24 mol) of methyl magnesium bromide was slowly added in a low-temperature ice-water bath, and then the mixture was transferred to an 80°C oil bath for reaction. The reaction was monitored by TLC. After 2 hours, the reaction was stopped and cooled to room temperature. The reaction solution was quenched with 15 ml of 27 wt% ammonium chloride aqueous solution to quench the residual methyl magnesium bromide. The solution was filtered, and the filtrate was extracted with ethyl acetate (20 ml × 3). The organic phase was then distilled to remove the solvent, and the residue was separated by column chromatography with petroleum ether as the eluent. Finally, 14.25 g (0.091 mol) of 2,6-dimethylnaphthalene was obtained, with a separation yield of 91.3% and a purity of 99.6%.
[0029] Step b, preparation of the manganese-cobalt-bromine catalyst system: Add 2.23 g (0.089 mol) cobalt acetate tetrahydrate and 3.21 g (0.013 mol) manganese acetate tetrahydrate to a flask, add 70 ml anhydrous acetic acid and 5 ml deionized water, and stir in a 70°C oil bath for 30 min. Once the solids are completely dissolved and the solution turns light red, remove the flask from the oil bath and cool. After complete cooling, add 0.533 g (0.004 mol) potassium bromide to the flask and stir at room temperature for 15-20 min. Set aside for later use.
[0030] 14 g (0.1 mol) of 2,6-dimethylnaphthalene and pre-activated catalyst solution were added to a reaction vessel. The mixture was purged with nitrogen three times, then air was introduced to a pressure of 3.5 MPa. The temperature was raised to 180 °C and maintained for 30 min to initiate the reaction. The temperature was then raised to 210 °C and the reaction was continued for 4.5 h. The reaction was terminated when the pressure no longer decreased. The solid was filtered and washed with 8 wt% oxalic acid aqueous solution (20 ml × 3), followed by washing with methanol (20 ml × 3) to obtain 18.12 g (0.084 mol) of crude 2,6-naphthalenedicarboxylic acid. Recrystallization was then performed using 80 ml of DMSO-water (1:1.5) to obtain the pure product, with a yield of 93.5% and a purity of 99.1%. Example 2
[0031] In step a, the nickel catalyst was replaced with nickel acetylacetone and tricyclohexylphosphine was added as the ligand. The rest was the same as in Example 1. Finally, 13.9 g (0.089 mol) of 2,6-dimethylnaphthalene was obtained with a separation yield of 89.1% and a purity of 99.5%.
[0032] In step b, the bromide was replaced with sodium bromide, and the rest was the same as in Example 1. Finally, 17.95 g (0.083 mol) of 2,6-naphthalenedicarboxylic acid was obtained, with a separation yield of 92.7% and a purity of 99.3%. Example 3
[0033] In step a, the nickel catalyst was replaced with nickel bromide, and the rest was the same as in Example 2. Finally, 13.57 g (0.087 mol) of 2,6-dimethylnaphthalene was obtained, with a separation yield of 86.9% and a purity of 99.5%.
[0034] In step b, the amount of potassium bromide added was changed to 0.429 g (0.003 mol), and the rest was the same as in Example 1. Finally, 17.8 g (0.082 mol) of 2,6-naphthalenedicarboxylic acid was obtained, with a separation yield of 91.8% and a purity of 99.1%. Example 4
[0035] In step a, the molar ratio of 2-bromo-6-methoxynaphthalene to the methylating agent was changed to 1:2.0, and the rest was the same as in Example 1. Finally, 13.77 g (0.088 mol) of 2,6-dimethylnaphthalene was obtained, with a separation yield of 88.1% and a purity of 99.7%.
[0036] In step b, the amount of cobalt acetate was changed to 3.11 g (0.013 mol), and the amount of manganese acetate was changed to 3.06 g (0.012 mol). The rest was the same as in Example 1. Finally, 16.97 g (0.078 mol) of 2,6-naphthalenedicarboxylic acid was obtained, with a yield of 87.5% and a purity of 99.3%. Example 5
[0037] In step a, the molar ratio of 2-bromo-6-methoxynaphthalene to nickel dichloride (tricyclohexylphosphine) was changed to 1:0.07, and the rest was the same as in Example 1. Finally, 14.07 g (0.09 mol) of 2,6-dimethylnaphthalene was obtained, with a separation yield of 90.1% and a purity of 99.7%. Example 6
[0038] In step b, the reaction temperature was changed to 220℃, and the rest was the same as in Example 1. Finally, 17.59g (0.081mol) of 2,6-naphthalenedicarboxylic acid was obtained, with a separation yield of 90.7% and a purity of 99.7%. Example 7
[0039] In step b, air was replaced with oxygen, and the rest was the same as in Example 1. Finally, 18.09 g (0.083 mol) of 2,6-naphthalenedicarboxylic acid was obtained, with a separation yield of 93.4% and a purity of 99.3%. Example 8
[0040] In step a, the solvent was replaced with anhydrous diethyl ether, and the rest was the same as in Example 1. Finally, 13.15 g (0.084 mol) of 2,6-dimethylnaphthalene was obtained, with a separation yield of 84.2% and a purity of 99.4%. Example 9
[0041] In step a, the reaction temperature was adjusted to 60°C, and the rest was the same as in Example 1. Finally, 13.48 g (0.086 mol) of 2,6-dimethylnaphthalene was obtained, with a separation yield of 86.2% and a purity of 99.5%.
[0042] In step b, the main reaction temperature was adjusted to 200℃, and the rest was the same as in Example 1. Finally, 17.81g (0.082mol) of 2,6-naphthalenedicarboxylic acid was obtained, with a separation yield of 91.9% and a purity of 99.2%. Example 10
[0043] In step a, the ligand was replaced with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-yl group, the catalyst was nickel acetylacetonate, and the rest was the same as in Example 2. Finally, 13.87 g (0.088 mol) of 2,6-dimethylnaphthalene was obtained, with a separation yield of 88.8% and a purity of 99.5%.
[0044] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent modifications or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A novel method for synthesizing 2,6-naphthalenedicarboxylic acid, characterized in that, Includes the following steps: Step a: Under a nitrogen atmosphere and in a solvent, 2-bromo-6-methoxynaphthalene is used as a raw material, and a Grignard reaction / coupling reaction is carried out in the presence of a nickel catalyst, a ligand, and a methylating agent to obtain 2,6-dimethylnaphthalene. Step b involves using 2,6-dimethylnaphthalene as a raw material and conducting a liquid-phase catalytic oxidation reaction of 2,6-dimethylnaphthalene with oxygen-containing gas in a closed reactor within a system containing a manganese-cobalt-bromine catalyst and acetic acid solvent.
2. The novel synthetic method for 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that, In step a, the nickel catalyst is one of bis(tricyclohexylphosphine) dichloride, bis(1,5-cyclooctadiene) nickel, nickel chloride, nickel bromide, nickel iodide, nickel acetylacetone, and nickel acetate. The molar ratio of 2-bromo-6-methoxynaphthalene to the nickel catalyst is 1:(0.01~0.1).
3. The novel synthetic method for 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that, In step a, the ligand is one of tricyclohexylphosphine, tri-tert-butylphosphine, 1,1'-bis(diphenylphosphine)ferrocene, 1,2-bis(dicyclohexylphosphine)ethane, triphenylphosphine, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylene, and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylene; when the nickel catalyst is nickel dichloride, the ligand is not required; the molar ratio of 2-bromo-6-methoxynaphthalene to the ligand is 1:(0.06~0.15).
4. The novel synthetic method for 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that, In step a, the methylating agent is one of methyl magnesium bromide and dimethyl zinc; the molar ratio of 2-bromo-6-methoxynaphthalene to the methylating agent is 1:(2.0~3.0).
5. The novel synthetic method for 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that, In step a, the solvent is one of toluene, xylene, n-hexane, tetrahydrofuran, N,N-dimethylformamide, and diethyl ether; the mass ratio of 2-bromo-6-methoxynaphthalene to the solvent is 1:(15~35).
6. The novel method for synthesizing 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that... In step a, the reaction temperature is 30~120℃; the reaction time is 3~5h.
7. The novel synthetic method for 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that, In step b, the manganese-cobalt-bromine catalyst is a mixture of manganese acetate, cobalt acetate and bromide, and the molar ratio between the components of the manganese-cobalt-bromine catalyst is 1:(0.1~1):(0.1~1), wherein the bromide is one of sodium bromide, potassium bromide and ammonium bromide; the catalyst dosage is: the molar ratio of 2,6-dimethylnaphthalene to manganese-cobalt-bromine catalyst is 1:(0.1~1).
8. The novel synthetic method for 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that, In step b, the oxygen-containing gas is air or oxygen; the pressure of the oxidation reaction is 2~5 MPa.
9. The novel method for synthesizing 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that, In step b, the reaction temperature is controlled in stages: the reaction temperature in the initial initiation stage is 150~200℃; the reaction temperature in the later reaction stage is 180~250℃, and the reaction time is 3~6h.
10. The novel method for synthesizing 2,6-naphthalenedicarboxylic acid as described in claim 1, characterized in that, In step b, the mass ratio of 2,6-dimethylnaphthalene to the solvent acetic acid is 1:(50~130).