Method for synthesizing 1, 5-naphthalene dicarbamate under catalysis of cerium oxide
By using cerium oxide catalyst instead of homogeneous zinc salt, the atmospheric pressure and low temperature reaction of 1,5-naphthyldiamine and dimethyl carbonate was achieved, solving the problems of easy catalyst deactivation and complex high temperature and high pressure operation in the prior art. This resulted in a highly efficient and environmentally friendly synthesis of methyl 1,5-naphthyldicarbamate, which is suitable for industrial applications.
Patent Information
- Application Number
- CN202511908063.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-17
- Publication Date
- 2026-03-17
AI Technical Summary
In the existing technology, the methoxycarbonylation reaction of 1,5-naphthyldiamine with dimethyl carbonate uses a homogeneous zinc salt catalyst, which is prone to deactivation and requires complex separation steps after the reaction, resulting in high production costs and the product being easily contaminated by the catalyst. In addition, the traditional high temperature and high pressure synthesis route has high equipment costs and complex operation.
Cerium oxide was used as the sole active catalyst to replace the traditional homogeneous zinc salt in the reaction of 1,5-naphthyldiamine with dimethyl carbonate. The reaction was carried out under atmospheric or pressurized conditions. The efficient synthesis of methyl 1,5-naphthyldicarbamate was achieved through the synergistic effect of the Lewis acid sites and oxygen vacancies of cerium oxide. The catalyst was then separated by simple filtration.
It reduces production costs, is environmentally friendly, allows the catalyst to be recycled multiple times, maintains high conversion and selectivity, simplifies the operation process, and is suitable for industrial production.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of organic chemical technology, specifically relating to a method for preparing methyl 1,5-naphthalenedicarbamate using cerium oxide catalysis. Background Technology
[0002] 1,5-Naphthalenedicarbamate (NDC) is a key intermediate in the synthesis of 1,5-naphthalenediisocyanate (NDI), which is an important raw material for the preparation of high-end polyurethane materials. NDI-based polyurethane elastomers have increased market demand due to their advantages such as strong tear strength, resilience, functionality, and heat resistance. With the continuous deepening of related research and the continuous optimization of production processes, the NDI market size is expected to expand further, and the industry has great potential for future development (Synthetic Rubber Industry, 1996, 19(3): 185-187). Therefore, the development process of NDI has a very broad prospect and is of great significance to the development of my country's polyurethane industry. Traditionally, the production of NDI mainly relies on the phosgene method, but the phosgene method has many drawbacks, such as the use of highly toxic phosgene raw materials, harsh operating environment, harsh reaction conditions, serious pollution, long process flow, complex technology, and difficulty in removing residual chlorine in the product. Therefore, the development of non-phosgene method for synthesizing NDI has become a research hotspot, and the synthesis of NDC is a key step in this route.
[0003] Mitsubishi Corporation of Japan synthesizes 1,5-dinitronaphthalene and CO under high temperature and pressure, using Rh, I2, and nitrogen-containing heterocyclic compounds as catalysts, or iodides of metallic Rh and aromatic nitrogen-containing heterocyclic compounds. This synthetic route requires high temperature and pressure, is complex to operate, and has high equipment costs; large-scale industrial production has not yet been reported.
[0004] Dimethyl carbonate (DMC), as a green methylation and carbonylation reagent, has advantages such as low toxicity and biodegradability, and has received widespread attention in recent years as a substitute for phosgene. Therefore, DMC is widely used in synthetic processes such as carbonylation, methylation, and methoxycarbonylation. At present, the methoxycarbonylation reaction of 1,5-naphthyldiamine with dimethyl carbonate mostly uses homogeneous catalysts, such as zinc acetate, zinc stearate, and zinc cyclohexanebutyrate (Chinese Journal of Catalysis, 2006, 27(7): 573-578.), which utilizes the Lewis acid dual-coordination activation characteristics of zinc ions to achieve the stepwise methoxycarbonylation reaction of 1,5-naphthyldiamine. Although this process has high conversion rate and selectivity, it is prone to deactivation and requires complex steps such as distillation and recrystallization after the reaction to separate the product, which cannot be directly recycled, resulting in increased production costs and the product is easily contaminated by catalyst residues. Summary of the Invention
[0005] The purpose of this invention is to address the limitations of current technologies by providing a method for synthesizing methyl 1,5-naphthyldicarbamate using cerium oxide as the catalytic catalyst. This method uses cerium oxide as the sole active catalyst, replacing traditional homogeneous zinc salts, to catalyze the reaction of 1,5-naphthyldiamine with dimethyl carbonate. Under normal or pressurized conditions, the target products methyl 1,5-naphthyldicarbamate and methyl 5-amino-naphthyl-1-carbamate (NMC) are obtained in high yield. This invention reduces costs and is environmentally friendly, generating no toxic gases, chlorine-containing waste, or catalyst waste liquid. The operation process is simple, and the catalyst can be recycled multiple times.
[0006] This invention is achieved through the following technical solution: A method for synthesizing methyl 1,5-naphthalenedicarbamate using cerium oxide catalysis, the method comprising the following steps: 1,5-naphthyldiamine, dimethyl carbonate and catalyst were added to a reactor and stirred under a nitrogen atmosphere, at 150-180°C and normal pressure for 5-10 hours to obtain methyl 1,5-naphthyldicarbamate. The catalyst is cerium oxide, and the amount added is 40% to 80% of the mass of 1,5-naphthyldiamine; the molar ratio of dimethyl carbonate to 1,5-naphthyldiamine is 30 to 68:1.
[0007] The process also includes the following steps: After the reaction is complete, the mixture is filtered to obtain a filter cake and a filtrate; the product in the filter cake is then dissolved with N,N-dimethylformamide (DMF), and the mixture is filtered to obtain the catalyst and the product; the filtrate after the two filtrations is evaporated to dryness to obtain the product.
[0008] The method for preparing cerium oxide includes the following steps: (1) Dry cerium acetate with a purity ≥ 99.0% in a vacuum drying oven at 40~100℃ for 2~6h to obtain dried cerium acetate; (2) Next, heat the dried cerium acetate to 400~800℃ and keep it at that temperature for 1~4 hours, then let it cool naturally to room temperature; (3) Grind the product to a particle size ≤10μm.
[0009] The heating rate in step (2) is 2~5℃ / min.
[0010] The essential features of this invention are: This invention uses cerium oxide as a catalyst for a heterogeneous reaction. Due to the strong steric hindrance of the naphthalene ring in 1,5-naphthyldiamine, the amino group has lower reactivity than aliphatic amines, and the activation of the CO bond in DMC requires "acid-base bifunctionality + oxygen vacancy synergy." This invention utilizes cerium oxide's "Lewis acid site anchoring of the amino group + oxygen vacancy + basic site activation of DMC + Ce" properties. 3+ / Ce 4+The synergistic effect of the "redox cyclic stabilizing intermediate" is adapted to the steric hindrance characteristics of 1,5-naphthyldiamine; through precise control of "60℃ vacuum drying → heating to 600℃ at 5℃ / min and holding for 2h → grinding to particle size ≤10μm", the oxygen vacancy density and acid-base site ratio of the catalyst are guaranteed.
[0011] The cerium oxide of the present invention is prepared by calcination oxidation of cerium acetate, which avoids the presence of trace impurities in commercially available cerium oxide, thus reducing catalytic efficiency; it also avoids the residual nitrogen oxide impurities or the generation of acidic gases during the heating and decomposition of cerium nitrate hexahydrate, thus reducing catalytic active sites.
[0012] The present invention has the following beneficial effects: (1) This invention uses dimethyl carbonate instead of phosgene, and the only reaction byproduct is methanol. The reaction is carried out at normal pressure and low temperature, which reduces cost and loss and is environmentally friendly. No toxic gases, chlorine-containing waste or catalyst waste liquid are generated, and the operation process is simple. (2) The prepared cerium oxide catalyst is a heterogeneous catalyst, which can be separated from the reaction system by simple filtration and can be recycled multiple times. After being reused 5 times, the NDA conversion rate is still above 95% and the total yield of carbamate is ≥85%. In contrast, the existing homogeneous zinc salt catalyst cannot be recovered and the catalyst is lost in a single reaction. In comparison, the present invention has better prospects for industrialization. Detailed Implementation
[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.
[0014] Example 1 Cerium acetate with a purity ≥99.0% was dried in a vacuum drying oven at 60℃ for 2 hours to remove surface adsorbed water. The corundum crucible was soaked in 5% dilute hydrochloric acid for 20 minutes, rinsed with deionized water, and then dried at 120℃. Next, 5g of dried cerium acetate was accurately weighed, placed into the crucible, and evenly spread. After recording the mass, the crucible was placed in the center of the muffle furnace. The temperature was then increased to 600℃ at a rate of 5℃ / min and held for 2 hours. The temperature was observed periodically during the heating process, and a 1-2mm gap was left in the furnace door for gas venting during the holding period. After the holding period, the power was turned off, and the furnace door was slightly opened for natural cooling to below 300℃, then further cooled to below 100℃ before the crucible was transferred to a desiccator for room temperature cooling. The product was subsequently ground to a particle size ≤10μm.
[0015] Weigh 1 g (6.3 mmol) of 1,5-naphthyldiamine, 30 ml (0.36 mol) of dimethyl carbonate, and 0.4 g of catalyst into a high-pressure reactor. After purging twice with nitrogen, react at 170 °C under nitrogen atmosphere and atmospheric pressure for 7 h. After the reaction, filter to obtain a filter cake and filtrate. Dissolve the product in the filter cake with N,N-dimethylformamide, and filter to obtain the catalyst and product. Evaporate the filtrate after two filtrations to dryness to obtain the products methyl 1,5-naphthyldicarbamate and methyl 5-amino-naphthyl-1-carbamate.
[0016] Liquid chromatography analysis showed that the NDA conversion rate was 99%, the NMC yield was 70%, and the NDC yield was 19%. The total yield of carbamates was 89%.
[0017] Example 2 The other steps were the same as in Example 1, except that 0.5 g of CeO2 was added as catalyst. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 71%, and an NDC yield of 19%. The total yield of carbamates was 90%.
[0018] Example 3 The other steps were the same as in Example 1, except that 0.6 g of CeO2 was added as catalyst. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 71%, and an NDC yield of 20%. The total yield of carbamates was 91%.
[0019] Example 4 The other steps were the same as in Example 1, except that 0.7 g of CeO2 was added as catalyst. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 72%, and an NDC yield of 21%. The total yield of carbamates was 93%.
[0020] Example 5 The other steps were the same as in Example 1, except that 0.8 g of CeO2 was added as catalyst. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 72%, and an NDC yield of 21%. The total yield of carbamates was 93%.
[0021] Example 6 The other steps were the same as in Example 4, except that the reaction temperature was 150°C. The reaction results showed an NDA conversion rate of 98%, an NMC yield of 74%, and an NDC yield of 15%. The total yield of carbamates was 89%.
[0022] Example 7 The other steps were the same as in Example 4, except that the reaction temperature was 160°C. The reaction results showed an NDA conversion rate of 98%, an NMC yield of 73%, and an NDC yield of 18%. The total yield of carbamates was 91%.
[0023] Example 8 The other steps were the same as in Example 4, except that the reaction temperature was 180°C. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 68%, and an NDC yield of 21%. The total yield of carbamates was 89%.
[0024] Example 9 The other steps were the same as in Example 4, except that the reaction time was 5 hours. The reaction results showed an NDA conversion rate of 95%, an NMC yield of 68%, and an NDC yield of 15%. The total yield of carbamates was 83%.
[0025] Example 10 The other steps were the same as in Example 4, except that the reaction time was 6 hours. The reaction results showed an NDA conversion rate of 97%, an NMC yield of 69%, and an NDC yield of 17%. The total yield of carbamates was 86%.
[0026] Example 11 The other steps were the same as in Example 4, except that the reaction time was 8 hours. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 69%, and an NDC yield of 21%. The total yield of carbamates was 90%.
[0027] Example 12 The other steps were the same as in Example 4, except that the reaction time was 9 hours. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 67%, and an NDC yield of 21%. The total yield of carbamates was 88%.
[0028] Example 13 The other steps were the same as in Example 4, except that the reaction time was 10 hours. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 67%, and an NDC yield of 21%. The total yield of carbamates was 88%.
[0029] Example 14 The other steps were the same as in Example 4, except that the amount of dimethyl carbonate used was 0.25 mol. The reaction results showed an NDA conversion rate of 98%, an NMC yield of 68%, and an NDC yield of 20%. The total yield of carbamates was 88%.
[0030] Example 15 The other steps were the same as in Example 4, except that the amount of dimethyl carbonate used was 0.21 mol. The reaction results showed an NDA conversion rate of 98%, an NMC yield of 68%, and an NDC yield of 18%. The total yield of carbamates was 86%.
[0031] Example 16 The other steps were the same as in Example 4, except that the amount of dimethyl carbonate used was 0.41 mol. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 74%, and an NDC yield of 14%. The total yield of carbamates was 88%.
[0032] Example 17 The other steps were the same as in Example 4, except that the amount of dimethyl carbonate used was 0.47 mol. The reaction results showed an NDA conversion rate of 99%, an NMC yield of 75%, and an NDC yield of 12%. The total yield of carbamates was 87%.
[0033] Example 18 Cerium nitrate hexahydrate with a purity ≥99.0% was loaded into a crucible and spread evenly. After recording the mass, the crucible was placed in the center of the muffle furnace. A heating program was then set to increase the temperature to 600℃ at a rate of 5℃ / min and hold for 2 hours. The temperature was observed periodically during the heating process. During the holding period, a 1-2 mm gap was left in the furnace door for gas venting. After the holding period, the power was turned off, and the furnace door was slightly opened for natural cooling to below 300℃, then further cooled to below 100℃. The crucible was then moved to a desiccator for room temperature cooling. The product was subsequently ground to a particle size ≤10 μm. Other steps were the same as in Example 4. The reaction results showed an NDA conversion rate of 98%, an NMC yield of 71%, and an NDC yield of 18%. The total yield of carbamates was 89%.
[0034] A comparison between this embodiment and Example 4 shows that the performance of cerium oxide obtained by calcining cerium nitrate hexahydrate is not as good as that of cerium oxide obtained by calcining cerium acetate. This is because when cerium nitrate hexahydrate is heated and decomposed, in addition to generating CeO2, nitrogen oxide impurities or acidic gases may remain, affecting the number and purity of active sites on the CeO2 surface. Furthermore, cerium acetate has no water of crystallization after drying, making it easier to form uniform CeO2 crystals with a high specific surface area during the calcination process. In contrast, the water of crystallization in cerium nitrate hexahydrate may cause particle agglomeration during calcination, reducing the number of catalytic active sites.
[0035] Example 19 The other steps were the same as in Example 18, except that the catalyst dosage was 0.4 g. The reaction results showed an NDA conversion rate of 96%, an NMC yield of 68%, and an NDC yield of 15%. The total carbamate yield was 83%.
[0036] Example 20 The other steps were the same as in Example 18, except that the catalyst dosage was 0.8 g. The reaction results showed an NDA conversion rate of 98%, an NMC yield of 70%, and an NDC yield of 18%. The total carbamate yield was 88%.
[0037] Example 21 Commercially available cerium oxide was dried in a vacuum drying oven at 60°C for 2 hours to remove surface adsorbed water. Other steps were the same as in Example 4. The reaction results showed an NDA conversion rate of 95%, an NMC yield of 68%, and a total carbamate yield of 68%.
[0038] A comparison between this embodiment and Example 4 shows that the performance of commercially available cerium oxide is not as good as that of cerium oxide obtained by calcining cerium acetate. This is because commercially available cerium oxide may contain trace impurities (such as other metal ions, surface contaminants, etc.), which can occupy active sites and reduce catalytic efficiency. Furthermore, commercially available products may have issues such as uneven particle size, particle agglomeration, or mismatched crystal forms, resulting in insufficient exposure of active sites.
[0039] Example 22 The catalyst (filter residue) after the reaction in Example 4 was recovered and dried under vacuum at 60°C for 2 hours to remove adsorbed products and solvent, yielding the recovered catalyst. The recovered catalyst was reused 5 times under the reaction conditions of Example 4, and the results of each reaction were recorded. First recycling: NDA conversion rate 99%, NMC yield 71%, NDC yield 20%, total yield 91%; Third recycling: NDA conversion rate 98%, NMC yield 69%, NDC yield 20%, total yield 89%; 5th recycling: NDA conversion rate 97%, NMC yield 68%, NDC yield 19%, total yield 87%; The results show that the cerium oxide catalyst of the present invention maintains high catalytic activity after five cycles, meeting the requirements of continuous industrial production.
[0040] As can be seen from the above examples, the method for preparing methyl 1,5-naphthalenedicarbamate according to the present invention has mild reaction conditions, simple operation process, and the prepared cerium oxide has good activity and is easy to separate from the reaction system, thus having good prospects for industrialization.
[0041] The above description is only a part of the specific examples of the present invention, but the scope of protection of the present invention is not limited thereto, nor does the order of the various embodiments cause any limitation to the present invention. Any modifications, improvements or equivalent substitutions made by those skilled in the art within the scope of the technology reported in the present invention should be covered within the scope of protection of the present invention.
[0042] Matters not covered in this invention are common knowledge.
Claims
1. A process for the catalytic synthesis of 1,5-naphthalene dicarbamic acid methyl ester with cerium oxide, characterized in that, The method comprises the following steps: 1,5-naphthalene diamine, dimethyl carbonate and catalyst are added into a reactor, and the reaction is stirred under the conditions of nitrogen atmosphere, 150-180 DEG C, normal pressure and 5-10 h to obtain 1,5-naphthalene diamino methyl carbonate; The catalyst is cerium oxide, and the addition amount is 40-80% of the mass of 1,5-naphthalene diamine; the molar ratio of dimethyl carbonate to 1,5-naphthalene diamine is 30-68:
1.
2. The process for the catalytic synthesis of methyl 1,5-naphthalene dicarbamate with cerium oxide according to claim 1, characterized in that, The method further comprises the following steps: after the reaction is completed, filtration is performed to obtain a filter cake and a filtrate; the product in the filter cake is dissolved with N,N-dimethylformamide (DMF), and filtration is performed to obtain a catalyst and a product; the filtrate after the two filtrations is evaporated to dryness, and the product is obtained.
3. The process for the catalytic synthesis of methyl 1,5-naphthalene dicarbamate with cerium oxide according to claim 1, characterized in that, The preparation method of the cerium oxide comprises the following steps: (1) cerium acetate with a purity of greater than or equal to 99.0% is dried in a vacuum drying box at 40-100 DEG C for 2-6 h to obtain dried cerium acetate; (2) then, the dried cerium acetate is heated to 400-800 DEG C and kept for 1-4 h, and then naturally cooled to room temperature; (3) the product is ground, and finally the cerium oxide is obtained.
4. The process for the catalytic synthesis of methyl 1,5-naphthalene dicarbamate with cerium oxide according to claim 3, characterized in that, The heating rate in step (2) is 2-5 DEG C / min.
5. The process for the catalytic synthesis of methyl 1,5-naphthalene dicarbamate with cerium oxide according to claim 3, characterized in that, The grinding is performed to a particle size of less than or equal to 10 μm.