A process for the synthesis of alkyl carbamates from ammonia and dialkyl carbonate

Abstract

The application discloses a method for synthesizing alkyl carbamate from ammonia and dialkyl carbonate. The method adopts a zinc-based acid-base bifunctional catalyst, and a corresponding small-molecule alcohol as a solvent. Ammonia and dialkyl carbonate are reacted at 20-90 DEG C for 1-24 h, and the product alkyl carbamate is obtained. The main features are that the reaction condition is mild (20-100 DEG C), the product selectivity is 100%, the product yield is high (>99%), one of the raw materials NH3 is cheap and easy to obtain, the unreacted raw material can be recycled, the catalyst is easy to recover and has good reusability, and the product has high purity. Compared with the prior art, the catalyst preparation process is simple, the catalytic activity is high, the reaction temperature is low, the method is economical and green, and the environment is friendly.

Description

TECHNICAL FIELD

[0001] The present application provides a method for preparing carbamates by reacting ammonia and dialkyl carbonate, belonging to the technical field of chemical synthesis. BACKGROUND

[0002] Small molecule alkyl carbamates including methyl carbamate (MC), ethyl carbamate (EC), butyl carbamate (BC), etc. are an important fine chemical, widely used in medicine, pesticides and organic synthesis intermediates, etc. For example, in addition to the individual characteristics of methyl carbamate, ethyl carbamate can also be used as an intermediate for medicine, pesticide, perfume, used for the production of hypnotics, sedatives, used as an antidote for strychnine, resorcinol, fungicides, injection solubilizers and printing and dyeing industry colorants, and can also be used for biochemical research. In addition, ethyl carbamate itself can be used as a medicine, has anticancer performance, and is used for the treatment of multiple myeloma and chronic leukemia, etc. The large-scale synthesis of carbamate mainly uses phosgene method, but the raw material phosgene 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, scientific research institutions and chemical enterprises are actively seeking green alternative methods. At present, the non-phosgene route mainly focuses on the reductive carbonylation of nitrobenzene compounds, the oxidative carbonylation of amine compounds, the direct synthesis of CO2 and alcohol, amine, urea alcoholysis and amineysis of organic carbonate, etc. However, in the first two processes, toxic CO is used as the carbonylation agent, the catalyst system mainly uses noble metal, and the reaction conditions are harsh, and the catalyst is easy to deactivate; the direct synthesis of N-substituted carbamate from CO2, amine and alcohol is the most ideal process, but due to the chemical inertness of CO2, the process has harsh reaction conditions, low yield of target product, and needs to use dehydrating agent quantitatively to improve the yield of product, which is not suitable for industrial production at present. The main method for synthesizing small molecule carbamate is urea alcoholysis (US 3574711, US3013064), which has the advantages of simple process and high yield, and is a potential synthesis method, but the disadvantages are high temperature and high pressure, and the by-product ammonia needs to be removed in time during the reaction process. The amineysis of dialkyl carbonate (W00156977) is a hot spot for the synthesis of carbamate by non-phosgene method at present, which is carried out under mild conditions and has clear process route and less by-products. Patent (CN112481319A) reports the synthesis of carbamate from ammonia and dialkyl carbonate, which uses ammonia and enzyme catalyst (not easy to store) in the process, and the excess ammonia is neutralized with glacial acetic acid, the product is separated by organic solvent extraction, the separation process is complex and difficult, and the purity of the product is not high. The presence of water will cause the hydrolysis of dialkyl carbonate, and the yield of carbamate is about 80%, and the selectivity of the product is not high. Here, we use ammonia and dialkyl carbonate to directly synthesize carbamate, which has rarely been reported before. At present, dialkyl carbonate, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), etc. as an environmentally friendly carbonate, is widely used as a solvent or in the field of polycarbonate, especially with the rapid development of lithium ion batteries, the market demand for it as a main component of battery electrolyte has increased rapidly.China is an important base for global production and use of dimethyl carbonate, and its 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 excessive, which has led to a significant decrease in the price of dialkyl carbonate. Direct synthesis of carbamate from ammonia and dialkyl carbonate has certain economic advantages, meets the requirements of current green chemistry, and has high atom economy, because one molecule of alcohol is produced as a byproduct. In addition, direct synthesis of carbamate from ammonia and dialkyl carbonate has mild reaction conditions, a clear process route, and fewer byproducts. SUMMARY

[0003] The present application solves the technical problems of harsh synthesis reaction conditions, more byproducts, difficult separation and purification, and easy deactivation of the catalyst in the synthesis process of existing carbamate compounds, and provides a method for preparing alkyl carbamate by reacting ammonia and dialkyl carbonate.

[0004] I. Preparation of zinc-based acid-base bifunctional catalyst for synthesis of alkyl carbamate

[0005] A preparation method of a catalyst for carbamate synthesis, first dissolving an azole organic ligand in deionized water, then adding a zinc-based precursor thereto and stirring at room temperature for 8-10 h to produce a white precipitate, filtering and washing, and drying at 80 ºC to obtain a zinc-based acid-base bifunctional catalyst.

[0006] The molar ratio of the zinc-based precursor to the azole organic ligand is 1: (1-3).

[0007] 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, diamino triazole, tetrazole and aminotetrazole.

[0008] Structure characterization of the catalyst: in the infrared spectrum of the catalyst (attached Figure 1 , 2, 3), the stretching vibration of the -NH2 group N-H bond in the azole organic ligand is at 3200-3400 cm -1 , the stretching vibration of the Zn-N bond is at 480 cm -1 , which indicates that the azole organic ligand reacts with the zinc-based precursor to form a Zn-N bond, proving that the catalyst is successfully synthesized.

[0009] II. Synthesis of alkyl carbamate

[0010] The zinc-based acid-base bifunctional catalyst is used to catalyze the reaction of NH3 and carbonic acid dialkyl ester in the presence of a corresponding small molecule alcohol solvent to prepare alkyl carbamate, wherein the molar ratio of carbonic acid dialkyl ester to ammonia is 1:3-1:15, the reaction temperature is 20-100 °C, the reaction time is 1-24 h, and the amount of the catalyst is 2wt%-15wt% of the mass of the carbonic acid dialkyl ester.

[0011] The small molecule alcohol solvent is one of methanol, ethanol, propanol, isopropanol, butanol and benzyl alcohol.

[0012] The carbonic acid dialkyl ester is one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate and dibenzyl carbonate; and the solid-liquid ratio of the carbonic acid dialkyl ester to the reaction solvent is 1g:(2-5)mL.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] In the preparation of alkyl carbamate, the zinc-based acid-base bifunctional catalyst is used, the catalyst is prepared by simple acid-base neutralization, the catalyst has the functions of acid and base, has the advantages of high activity, good stability, is economical and green, and is environment-friendly; NH3 and carbonic acid dialkyl ester are used as raw materials, the reaction conditions are mild, the product yield is high, the product is easy to separate, and the product purity is high. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The infrared spectrum of the catalyst [Zn(OAC)(TZ)].

[0016] Figure 2 The infrared spectrum of the catalyst [Zn(OAC)(ATZ)].

[0017] Figure 3 The infrared spectrum of the catalyst [Zn(OAC)(5-AT)]. DETAILED DESCRIPTION

[0018] The present application will be further explained and described below in combination with specific embodiments.

[0019] Example 1

[0020] Preparation of the catalyst triazole zinc acetate [Zn(OAC)(TZ)]: 0.69g of triazole was taken into a 250ml beaker, 80ml of deionized water was added, then it was stirred and dissolved at room temperature, 2.19g of Zn(OAC)·2H2O was added and stirred at room temperature for 4h, a white precipitate was generated, filtered, washed and dried at 80°C to obtain the [Zn(OAC)(TZ)] catalyst.

[0021] Example 2

[0022] Preparation of catalyst zinc amino triazole acetate salt [Zn(OAC)(ATZ)]: 0.84 g of amino triazole was weighed into a 250 ml beaker, 80 ml of deionized water was added, and then stirred and dissolved at room temperature. After adding 2.19 g of Zn(OAC) 2H2O, it was stirred at room temperature for 4 h, a white precipitate was produced, filtered, washed, and dried at 80°C to obtain the [Zn(OAC)(ATZ)] catalyst.

[0023] Example 3

[0024] Preparation of catalyst zinc 5-amino tetrazole acetate salt [Zn(OAC)(5-AT)]: 0.85 g of 5-amino tetrazole was weighed into a 250 ml beaker, 80 ml of deionized water was added, and then stirred and dissolved at room temperature. After adding 2.19 g of Zn(OAC) 2H2O, it was stirred at room temperature for 4 h, a white precipitate was produced, filtered, washed, and dried at 80°C to obtain the [Zn(OAC)(5-AT)] catalyst.

[0025] Example 4

[0026] In a 100 ml high-pressure reactor, 0.9 g of dimethyl carbonate, the catalyst [Zn(OAC)(TZ)] prepared in Example 1 0.1 g, and 3 ml of methanol were added, and the pressure of NH3 was charged to 1 MPa. After the reaction was completed at a temperature of 25°C and a stirring speed of 500 rpm for 6 h, the reactor was opened, the catalyst [Zn(OAC)(TZ)] was recovered by filtration, and could be directly reused. The filtrate was colorless and clear, and gas chromatography analysis was performed on the filtrate. The results of the chromatographic analysis were that the conversion rate of dimethyl carbonate was >99%, the yield of methyl carbamate was 99%, and the selectivity was >99%.

[0027] Example 5

[0028] In a 100 ml high-pressure reactor, 1.18 g of diethyl carbonate, the catalyst [Zn(OAC)(ATZ)] prepared in Example 2 0.1 g, and 3 ml of ethanol were added, and the pressure of NH3 was charged to 0.5-4 L. After the reaction was completed at a temperature of 60-100°C and a stirring speed of 500 rpm for 4-20 h, the reactor was opened, the catalyst [Zn(OAC)(TZ)] was recovered by filtration, and could be directly reused. The filtrate was colorless and clear, and gas chromatography analysis was performed on the filtrate. The results are shown in Table 1.

[0029] Table 1 Activity evaluation of catalysts under different reaction conditions

[0030]

[0031] The activity evaluation results (1, 2, 3) show that the conversion of DEC increases with the extension of the reaction time, and the conversion of DEC is up to 97%, and the selectivity of ethyl carbamate is 99%. The activity evaluation results (4, 5) show that the conversion of DEC increases with the increase of the amount of catalyst, and the selectivity of ethyl carbamate is 99%. The activity evaluation results (6, 7) show that the conversion of DEC increases with the increase of the proportion of ammonia, and the conversion of DEC is up to 95%, and the selectivity of ethyl carbamate is 99%. The activity evaluation results (8, 9) show that the conversion of DEC is low at 60 degrees, and the conversion of DEC increases obviously when the reaction temperature is increased to 100 degrees, but the selectivity of ethyl carbamate decreases due to the decomposition of DEC at high temperature. The activity evaluation results (2, 10) show that the catalytic performance of the catalyst used for multiple cycles still maintains at a high level, and the conversion of DEC is above 80% and the selectivity of ethyl carbamate is above 95%.

[0032] Example 6

[0033] In a 100 mL high-pressure reaction kettle, 1.74 g of dibutyl carbonate, the catalyst [Zn(OAC)(5-AT)] prepared in Example 3 0.1 g, butanol 3 mL, and NH3 pressure 1 MPa were added, and the reaction was carried out at a temperature of 90°C and a stirring speed of 500 rpm for 24 h, then the reaction kettle was opened, the catalyst [Zn(OAC)(5-AT)] was recovered by filtration and could be directly reused; the filtrate was colorless and clear, and the filtrate was analyzed by gas chromatography. The chromatographic analysis results are that the conversion of dibutyl carbonate is >90%, the yield of butyl carbamate is 89%, and the selectivity is greater than 99%.

Claims

1. A process for the synthesis of alkyl carbamates from ammonia and a dialkyl carbonate, characterized in that, The method adopts a zinc-based acid-base bifunctional catalyst, takes a corresponding small molecule alcohol as a solvent, and reacts ammonia gas and a dialkyl carbonate at 20-90ºC for 1-24h to obtain the product alkyl carbamate; The zinc-based acid-base bifunctional catalyst is prepared by the following method: first, dissolving an organic azole ligand in deionized water, then adding a zinc-based precursor to the solution, stirring at room temperature for 8-10h to produce a white precipitate, filtering and washing, and drying at 80ºC to obtain the zinc-based acid-base bifunctional catalyst; wherein 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 organic azole ligand is one of triazole, aminotriazole, nitrotriazole, diamino triazole, tetrazole, and aminotetrazole; the molar ratio of the zinc-based precursor to the organic azole ligand is 1:(1-3).

2. The process for the synthesis of alkyl carbamates from ammonia and dialkyl carbonate according to claim 1, characterized in that, The small molecule alcohol is one of methanol, ethanol, propanol, isopropanol, butanol, and benzyl alcohol.

3. The process for the synthesis of alkyl carbamates from ammonia and dialkyl carbonate according to claim 1, characterized in that, The dialkyl carbonate is one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, and dibenzyl carbonate.

4. The process for the synthesis of alkyl carbamates from ammonia and dialkyl carbonate according to claim 1, characterized in that, The solid-liquid ratio of the dialkyl carbonate to the reaction solvent is 1g:(2-5)mL.

5. The process for the synthesis of alkyl carbamates from ammonia and dialkyl carbonate according to claim 1, characterized in that, The molar ratio of the ammonia gas to the dialkyl carbonate is (3-15):

1.

6. The process for the synthesis of alkyl carbamates from ammonia and dialkyl carbonate according to claim 1, characterized in that, The amount of the zinc-based acid-base bifunctional catalyst is 2%-15% of the mass of the dialkyl carbonate.

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