Method for synthesizing alkyl carbamate from ammonia gas and dialkyl carbonate

Abstract

The invention discloses a method for synthesizing carbamic acid alkyl ester by ammonia gas and dialkyl carbonate, which comprises the following steps of: reacting ammonia gas and dialkyl carbonate for 1-24 hours at 20-90 DEG C by using a zinc-based acid-base bifunctional catalyst and corresponding small molecular alcohol as a solvent to obtain the product carbamic acid alkyl ester. The method has the main characteristics that the reaction conditions are mild (20-100 DEG C), the product selectivity is up to 100%, and the product yield gt is high; one of the raw materials NH3 is cheap and easy to obtain, unreacted raw materials can be recycled, the catalyst is easy to recover and good in reusability, and the product purity is high. Compared with the prior art, the catalyst is simple in preparation process, high in catalytic activity, low in reaction temperature, economical, green and environment-friendly.

Description

Technical Field

[0001] The invention provides a method for preparing carbamate by reacting ammonia and dialkyl carbonate, belonging to the technical field of chemical synthesis. Background Art

[0002] Small molecule alkyl carbamates, including methyl carbamate (MC), ethyl carbamate (EC), butyl carbamate (BC), etc., are important fine chemicals and are widely used in medicine, pesticides, and organic synthesis intermediates. For example, in addition to the individual characteristics of methyl carbamate, ethyl carbamate can also be used as an intermediate for medicine, pesticides, and spices, used in the production of sleeping pills, sedatives, as an antidote for strychnine and resorcinol, a bactericide, a solvent for injections, and a colorant for the printing and dyeing industry, and can also be used for biochemical research. In addition, ethyl carbamate itself can be used as a drug with anticancer properties and is used to treat multiple myeloma and chronic leukemia. The large-scale synthesis of carbamates mainly uses the phosgene method, but the raw material phosgene in this process is highly toxic, and the by-product hydrogen chloride seriously corrodes the production equipment. In recent years, in order to meet the requirements of green chemistry and sustainable development, various scientific research institutions and chemical companies have been actively seeking green alternatives. The non-phosgene routes that are currently studied more are mainly concentrated on the reduction carbonylation of nitrobenzene compounds, the oxidative carbonylation of amine compounds, the direct synthesis of CO2 with alcohols and amines, urea alcoholysis and the aminolysis of organic carbonates, etc. However, in the first two processes, toxic CO is used as a carbonylating agent, the catalytic system is mainly based on precious metals, and the reaction conditions are harsh, and the catalyst is easily deactivated; using CO2, amines and alcohols as raw materials to directly synthesize N-substituted carbamates is the most ideal process, but in view of the chemical inertness of CO2, the process reaction conditions are harsh, the target product yield is low, and a dehydrating agent needs to be quantitatively used to improve the product yield, which is currently not suitable for industrial production. The synthesis of small molecule carbamates is mainly urea alcoholysis (US 3574711, US3013064), which is simple in process and high in yield, and is a more potential synthesis method, but the disadvantage is that the by-product ammonia should be removed in time during the reaction process at high temperature and high pressure. The dialkyl carbonate aminolysis method (W00156977) synthesizes carbamates. This method is carried out under relatively mild conditions, has a clear process route, and produces few by-products. It is currently a hot topic in the research of non-phosgene synthesis of carbamates. Patent (CN112481319A) reports the reaction of ammonia water and dialkyl carbonate to synthesize carbamates. In this process, ammonia water and enzyme catalyst (not easy to preserve) are used, and the excess ammonia water is neutralized with glacial acetic acid. The product is separated by organic solvent extraction. The separation process is complicated and difficult, and the product purity is not high. The presence of water will cause the dialkyl carbonate to hydrolyze, and the carbamate yield is about 80%, and the product selectivity is not high. Here, we use ammonia and dialkyl carbonate to directly synthesize carbamates, which has rarely been reported in the literature before. At present, dialkyl carbonates, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc., as environmentally friendly carbonates, are widely used as solvents or in the field of polycarbonate. Especially with the rapid development of lithium-ion batteries, their market demand as the main component of battery electrolyte has increased sharply.As an important base for the production and use of dimethyl carbonate in the world, China's market size and output have shown significant growth. However, at present, the prices of coal and chemical raw materials are high, and the production capacity of dialkyl carbonate is oversupplied, which has led to a significant drop in its price. The direct synthesis of high-value-added carbamates from ammonia and dialkyl carbonate, while producing a molecule of alcohol as a by-product, has high atomic economy and certain economic advantages, and meets the requirements of current green chemistry. In addition, the direct synthesis of carbamates from ammonia and dialkyl carbonate has mild reaction conditions, clear process routes, and few by-products. Summary of the invention

[0003] The present invention aims to solve the technical problems of harsh synthesis reaction conditions, more by-products, difficult separation and purification, and easy deactivation of catalysts in the existing synthesis process of carbamate compounds, and provides a method for preparing alkyl carbamate by reacting ammonia and dialkyl carbonate.

[0004] 1. Preparation of zinc-based acid-base bifunctional catalyst for synthesis of alkyl carbamate A method for preparing a catalyst for carbamate synthesis comprises the following steps: firstly dissolving an azole organic ligand in deionized water, then adding a zinc-based precursor thereto and stirring at room temperature for 8 to 10 hours to generate a white precipitate, filtering and washing the precipitate, and drying the precipitate at 80°C to obtain a zinc-based acid-base bifunctional catalyst.

[0005] The molar ratio of the zinc-based precursor to the nitrogen azole organic ligand is 1: (1-3).

[0006] The zinc-based precursor is at least one of Zn(OH)2, Zn2(OH)2CO3, ZnCl2, Zn(OAC)2, and Zn(NO3)2, and the azole organic ligand is one of triazole, aminotriazole, nitrotriazole, diaminotriazole, tetrazole, and aminotetrazole.

[0007] Structural characterization of the catalyst: In the infrared spectrum of the catalyst (attached Figure 1 , 2, 3), at 3200-3400cm -1 It is the stretching vibration of the NH bond of the -NH2 group in the azole organic ligand, at 480cm -1 It is the stretching vibration of Zn-N bond, indicating that the nitrogen azole organic ligand reacts with the zinc-based precursor to form a Zn-N bond, proving that the catalyst was successfully synthesized.

[0008] 2. Synthesis of Alkyl Carbamate The zinc-based acid-base bifunctional catalyst is used to catalyze the reaction of NH3 and dialkyl carbonate in the presence of a corresponding small molecule alcohol solvent to prepare alkyl carbamate, wherein the molar ratio of dialkyl carbonate to ammonia is 1:3~1:15, the reaction temperature is 20~100 ºC, the reaction time is 1~24h, and the amount of the catalyst is 2wt%~15wt% of the mass of the dialkyl carbonate.

[0009] The small molecule alcohol solvent is one of methanol, ethanol, propanol, isopropanol, butanol and benzyl alcohol.

[0010] The dialkyl carbonate is one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate and dibenzyl carbonate; the solid-liquid ratio of the dialkyl carbonate to the reaction solvent is 1g: (2-5)mL.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a zinc-based acid-base bifunctional catalyst in the process of preparing alkyl carbamate. The catalyst is prepared by simple acid-base neutralization. The catalyst has both acid-base bifunctionality, has the advantages of high activity, good stability, etc., is economical, green, and environmentally friendly. NH3 and dialkyl carbonate are used as raw materials, the reaction conditions are mild, the product yield is high, easy to separate, and the product purity is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Infrared spectrum of catalyst [Zn(OAC)(TZ)].

[0013] Figure 2 Infrared spectrum of catalyst [Zn(OAC)(ATZ)].

[0014] Figure 3 Infrared spectrum of catalyst [Zn(OAC)(5-AT)]. DETAILED DESCRIPTION

[0015] The present invention is further explained below with reference to specific embodiments.

[0016] Example 1 Preparation of catalyst zinc triazole acetate [Zn(OAC)(TZ)]: weigh 0.69 g triazole and add it into a 250 ml beaker, add 80 ml deionized water, and then stir to dissolve at room temperature, add 2.19 g Zn(OAC)∙2H2O and stir at room temperature for 4 hours to produce a white precipitate, which is filtered, washed and dried at 80°C to obtain the [Zn(OAC)(TZ)] catalyst.

[0017] Example 2 Preparation of the catalyst aminotriazole zinc acetate [Zn(OAC)(ATZ)]: weigh 0.84 g of aminotriazole and add it into a 250 ml beaker, add 80 ml of deionized water, and then stir to dissolve at room temperature, add 2.19 g of Zn(OAC)∙2H2O and stir at room temperature for 4 hours to produce a white precipitate, which is filtered, washed and dried at 80°C to obtain the [Zn(OAC)(ATZ)] catalyst.

[0018] Example 3 Preparation of catalyst 5-aminotetrazolyl acetate zinc salt [Zn(OAC)(5-AT)]: weigh 0.85g 5-aminotetrazolyl acetate into a 250ml beaker, add 80ml deionized water, and then stir to dissolve at room temperature, add 2.19g Zn(OAC)∙2H2O and stir at room temperature for 4h to produce a white precipitate, which is filtered, washed and dried at 80°C to obtain the [Zn(OAC)(5-AT)] catalyst.

[0019] Example 4 In a 100mL autoclave, 0.9 g of dimethyl carbonate, 0.1 g of the catalyst [Zn(OAC)(TZ)] prepared in Example 1, 3 mL of methanol, and 1 MPa of NH3 were added. The reaction was completed after 6 hours at a temperature of 25°C and a stirring speed of 500 rpm. The autoclave was opened and the catalyst [Zn(OAC)(TZ)] was filtered and recovered, which could be directly reused. The filtrate was colorless and clear, and the filtrate was taken for gas chromatography analysis. The chromatographic analysis results showed that the conversion rate of dimethyl carbonate was >99%, the yield of methyl carbamate was 99%, and the selectivity was greater than 99%.

[0020] Example 5 In a 100 mL autoclave, 1.18 g of diethyl carbonate, 0.1 g of the catalyst [Zn(OAC)(ATZ)] prepared in Example 2, 3 mL of ethanol, and 0.5 L to 4 L of NH3 were added. The reaction was carried out at a temperature of 60-100 °C and a stirring speed of 500 rpm for 4-20 h. The autoclave was opened and the catalyst [Zn(OAC)TZ] was recovered by filtration and can be directly reused. The filtrate was colorless and clear. The filtrate was analyzed by gas chromatography. The results are shown in Table 1.

[0021] Table 1 Evaluation of catalyst activity under different reaction conditions Activity evaluation results (1, 2, 3) show that the conversion rate of DEC increases with the extension of reaction time, and the maximum conversion rate of DEC is 97%, and the selectivity of ethyl carbamate is 99%. Activity evaluation results (4, 5) show that the conversion rate of DEC increases with the increase of catalyst dosage, and the selectivity of ethyl carbamate remains unchanged at 99%. Activity evaluation results (6, 7) show that the conversion rate of DEC increases with the increase of ammonia ratio, and the maximum conversion rate of DEC is 95%, and the selectivity of ethyl carbamate is 99%. Activity evaluation results (8, 9) show that the conversion rate of DEC is low at 60 degrees. When the reaction temperature is increased to 100 degrees, the conversion rate of DEC increases significantly, but the selectivity of ethyl carbamate decreases due to the decomposition of DEC at high temperature. Activity evaluation results (2, 10) show that the catalytic performance of the catalyst used in multiple cycles is still maintained at a high level, with a DEC conversion rate of more than 80% and a selectivity of ethyl carbamate of more than 95%.

[0022] Example 6 In a 100mL autoclave, 1.74g of dibutyl carbonate, 0.1g of the catalyst [Zn(OAC)(5-AT)] prepared in Example 3, 3mL of butanol, 1MPa of NH3 were charged, and the reaction was terminated after 24h at a temperature of 90°C and a stirring speed of 500 rpm. The autoclave was opened, and the catalyst [Zn(OAC)(5-AT)] was filtered and recovered, which could be directly reused. The filtrate was colorless and clear, and the filtrate was taken for gas chromatography analysis. The chromatographic analysis results showed that the conversion rate of dibutyl carbonate was >90%, the yield of butyl carbamate was 89%, and the selectivity was greater than 99%.

Claims

1. A method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate, characterized in that: The method uses a zinc-based acid-base bifunctional catalyst and a corresponding small molecule alcohol as a solvent. Ammonia and dialkyl carbonate react at 20-90°C for 1-24 hours to obtain the product alkyl carbamate.

2. A method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate as claimed in claim 1, characterized in that: The zinc-based acid-base bifunctional catalyst is prepared by the following method: firstly, the azole organic ligand is dissolved in deionized water, and then the zinc-based precursor is added thereto and stirred at room temperature for 8 to 10 hours to produce a white precipitate, which is filtered and washed, and then dried at 80°C to obtain the zinc-based acid-base bifunctional catalyst.

3. A method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate as claimed in claim 2, characterized in that: The zinc-based precursor is at least one of Zn(OH)2, Zn2(OH)2CO3, ZnCl2, Zn(OAC)2 and Zn(NO3)2, and the azole organic ligand is one of triazole, aminotriazole, nitrotriazole, diaminotriazole, tetrazole and aminotetrazole; the molar ratio of the zinc-based precursor to the azole organic ligand is 1:(1~3).

4. A method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate as claimed in claim 1, characterized in that: The small molecule alcohol is one of methanol, ethanol, propanol, isopropanol, butanol and benzyl alcohol.

5. A method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate as claimed in claim 1, characterized in that: The dialkyl carbonate is one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate and dibenzyl carbonate.

6. A method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate as claimed in claim 1, characterized in that: The solid-liquid ratio of the dialkyl carbonate to the reaction solvent is 1 g: (2-5) mL.

7. A method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate as claimed in claim 1, characterized in that: The molar ratio of ammonia to dialkyl carbonate is (3-15):

1.

8. A method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate as claimed in claim 1, characterized in that: The amount of the zinc-based acid-base bifunctional catalyst used is 2% to 15% of the mass of the dialkyl carbonate.

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