A method for synthesizing 1,6-hexamethylene dimethylcarbamate with bismuth metal salt as catalyst

Abstract

This invention discloses a method for synthesizing methyl 1,6-hexamethylenedicarbamate using a bismuth-based metal salt as a catalyst. The method includes the following steps: adding 1,6-hexanediamine, dimethyl carbonate, and a catalyst to a reactor, and stirring the reaction at 60–100°C and atmospheric pressure for 6–9 hours to obtain methyl 1,6-hexamethylenedicarbamate; the catalyst is a bismuth acetate metal salt or a supported bismuth acetate. The catalyst preparation process of this invention is simple, can be recycled multiple times, reduces cost and loss, and improves product yield.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical technology, specifically relating to a method for preparing methyl 1,6-hexamethylenedicarbamate using bismuth-based metal salts as catalysts. Background Technology

[0002] 1,6-Hexamethylene dicarboxylate (HDC) is an intermediate in the production of 1,6-hexamethylene diisocyanate. 1,6-Hexamethylene diisocyanate is a widely used aliphatic isocyanate in the polyurethane industry, possessing outstanding chemical stability and excellent oil resistance, abrasion resistance, anti-chalking, gloss retention, and color retention. It is widely used in plastics, coatings, textiles, and rubber industries. Industrially, 1,6-hexamethylene diisocyanate is mainly prepared using the phosgene process. However, this method uses highly toxic phosgene as a raw material, causing severe environmental pollution and high production costs. Therefore, there is an urgent need to develop green and environmentally friendly non-phosgene production processes. Among these, the pyrolysis method of carbamates has attracted widespread attention from researchers. This method uses dimethyl carbonate instead of highly toxic phosgene and mainly includes the synthesis and pyrolysis of the intermediate HDC. The above reaction process is under mild conditions, and the raw materials have low toxicity, meeting the requirements of green chemical development.

[0003] Dimethyl carbonate (DMC), as an environmentally friendly chemical raw material, is widely used in synthetic processes such as carbonylation, methylation, and methoxycarbonylation due to its pollution-free and highly reactive characteristics. In recent years, breakthroughs have been achieved in the catalytic synthesis of HDC via the methoxycarbonylation of DMC and 1,6-hexanediamine. This method offers mild conditions, is easy to control, and the byproduct methanol can be recycled as a raw material to produce DMC. Currently, the methoxycarbonylation reaction of DMC and 1,6-hexanediamine mostly employs homogeneous catalysts, such as Mn(OAc)₂, NaOCH₃, NaOAC, Zn(OAC)₂, and Bi(NO₃)₃. Although these catalysts offer high conversion rates and selectivity in the process, they all suffer from drawbacks such as easy deactivation, difficulty in separation and recovery, and inability to be recycled.

[0004] For example, Wang Yue et al. (CN101565389A) used heterogeneous catalysis of various metal oxides to synthesize HDC. The metal oxides used were obtained by direct calcination of metal precursors or by sol-gel or precipitation of metal precursors. This method requires the addition of excess dimethyl carbonate, and the conversion rate of raw materials and the selectivity of products are low. Xiao Fukui et al. (CN105126804A) used an impregnation method to prepare an X / SiO2 heterogeneous catalyst, where X is one of the metal salts NaOCH3, Bi(NO3)2, NaOAc, Pb(OAc)2, Zn(OAc)2, Sc(OTf)3, NaCF3SO3, Na2C2O4, C6H5ONa, NaNO3, or C7H5NaO2. However, the reaction time is as long as 36 hours, the efficiency is low, and the product yield is generally low. In summary, heterogeneous catalysts can solve the problem of separation and recovery, but the reaction efficiency is low. Therefore, it is very important to develop a method for synthesizing HDC with low cost and loss, easy catalyst recovery and recycling, and high reaction efficiency. Summary of the Invention

[0005] The purpose of this invention is to address the problems of high cost and waste, complex operation, non-recyclable catalysts, and low product yield in current methods for synthesizing methyl 1,6-hexamethylenedicarbamate (MCD). This invention provides a method for synthesizing MCD using bismuth-based metal salts as catalysts. This method uses bismuth acetate or supported bismuth acetate as catalysts. Supported bismuth acetate is impregnated with any one of silica gel, activated carbon, or molecular sieves as a support. The catalyst preparation process is simple and can be recycled multiple times. Compared with previous catalysts, this invention eliminates the need for excess dimethyl carbonate, reducing cost and waste and improving product yield.

[0006] The technical solution adopted in this invention is:

[0007] A method for synthesizing methyl 1,6-hexamethylenedicarbamate using bismuth-based metal salts as catalysts, the method comprising the following steps:

[0008] 1,6-hexamethylenediamine, dimethyl carbonate and catalyst were added to a reactor and stirred at 60-100°C and atmospheric pressure for 6-9 hours to obtain methyl 1,6-hexamethylenedicarbamate.

[0009] The catalyst is either a metal salt bismuth acetate or a supported bismuth acetate, and the amount added is 5% to 20% of the mass of 1,6-hexanediamine; the molar ratio of dimethyl carbonate to 1,6-hexanediamine is 2 to 6:1.

[0010] The process also includes the following steps: after the reaction is complete, a solvent is added to dissolve the reaction mixture, the solid catalyst is removed by centrifugation and filtration, and the filtrate is diluted and then analyzed by gas chromatography.

[0011] The solvent is methanol or ethanol.

[0012] The preparation method of the aforementioned bismuth acetate metal salt catalyst includes the following steps:

[0013] (1) Weigh Bi2O3, acetic acid, and acetic anhydride into a reactor and reflux at 140-160℃ for 1-3 hours; wherein, add 1-10g of Bi2O3 and 1-5mL of acetic anhydride to every 30mL of acetic acid;

[0014] (2) Filter the filtrate obtained in the previous step, and evaporate it at 60-70℃ to obtain crystals;

[0015] (3) Dissolve the crystals obtained in step (2) in acetic acid at 70-100℃, and then cool to room temperature to obtain crystals; wherein, 0.5-2.0g of crystals are added to every 15mL of acetic acid;

[0016] (4) The solid obtained from the filtration step (3) is dried under vacuum at 50°C for 8-12 hours to obtain the metal salt bismuth acetate.

[0017] The preparation method of the supported bismuth acetate catalyst includes the following steps:

[0018] (1) Dissolve bismuth acetate in acetic acid and stir continuously at 70-100℃ until completely dissolved; add 0.2-1.0g of bismuth acetate and 1-3g of carrier to every 15mL of acetic acid;

[0019] (2) Add the carrier to the salt solution of step (1) and stir for 12-36 hours;

[0020] (3) Filter to remove the liquid from step (2), and dry the solid under vacuum at 50°C for 8-12 hours to obtain supported bismuth acetate.

[0021] Preferably, the carrier includes silica gel, activated carbon or molecular sieve, and the metal salt loading is 10 to 40 wt%.

[0022] The essential features of this invention are:

[0023] This invention uses bismuth acetate as the active component of a catalyst, utilizing Bi... 3+ It coordinates with the carbonyl oxygen in dimethyl carbonate, enhancing the positive charge of the carbonyl carbon, thereby promoting the nucleophilic attack of the nitrogen anion in 1,6-hexanediamine on the carbonyl carbon of dimethyl carbonate; and unlike other acetates, bismuth acetate is insoluble in the reaction solution and also insoluble in methyl ethanol. Like supported bismuth acetate, it is heterogeneous and can be directly separated by centrifugation.

[0024] The present invention has the following beneficial effects:

[0025] (1) This invention uses dimethyl carbonate instead of toxic phosgene, which is environmentally friendly. The reaction is carried out at normal pressure and low temperature, which is mild and has little safety risk.

[0026] (2) This invention is the first to use bismuth-based metal salts as active components. The preparation process is simple, the catalytic performance is good, and the conversion rate can reach up to 100%.

[0027] (3) The bismuth-based catalyst prepared by the present invention is a heterogeneous catalyst that can be recycled and reused multiple times. At the same time, the reaction process does not require excess dimethyl carbonate, thus reducing cost and loss. Detailed Implementation

[0028] 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.

[0029] Example 1

[0030] Take 4g Bi2O3, 30ml acetic acid, and 3ml acetic anhydride into a 100ml three-necked flask, reflux at 150℃ for 2h, filter after dissolution to obtain filtrate, evaporate the filtrate at 60℃ to obtain crystals, then take 1g of solid and redissolve it in 15ml acetic acid at 70℃ and cool to room temperature to crystallize, finally dry under vacuum at 50℃ for 10h to obtain the metal salt bismuth acetate catalyst.

[0031] 5.81 g (0.05 mol) of 1,6-hexanediamine, 17 mL (0.2 mol) of dimethyl carbonate, and 0.872 g of the bismuth acetate catalyst obtained above were weighed and placed in a three-necked flask equipped with a condenser and stirrer. The mixture was reacted at 80 °C for 8 h. Then, 50 mL of ethanol was added to fully dissolve the reaction mixture. The solid catalyst was separated by centrifugation, and the filtrate was diluted and analyzed by gas chromatography. The reaction results showed that the conversion rate of 1,6-hexanediamine was 100%, and the yield of HDC was 78%.

[0032] Example 2

[0033] 0.5 g of bismuth acetate was dissolved in 15 ml of acetic acid and stirred in a water bath at 70 °C. After dissolution, 2 g of HY molecular sieve was added and stirred continuously for 12 h. Then, the mixture was centrifuged and the solid was dried in a vacuum at 50 °C for 10 h to obtain 20 wt% Bi(C2H3O2)3 / HY catalyst.

[0034] 0.05 mol of 1,6-hexanediamine, 0.2 mol of dimethyl carbonate, and 0.872 g of 20 wt% Bi(C₂H₃O₂)₃ / HY were weighed and placed in a three-necked flask equipped with a condenser and stirrer. The mixture was reacted at 80 °C for 8 h. Then, 50 mL of ethanol was added to fully dissolve the reaction mixture. The solid catalyst was separated by centrifugation, and the filtrate was diluted and analyzed by gas chromatography. The reaction results showed that the conversion rate of 1,6-hexanediamine was 100%, and the yield of HDC was 71%.

[0035] Example 3

[0036] The other steps are the same as in Example 2, except that 0.872 g of 20 wt% Bi(C2H3O2)3 / MCM-41 catalyst was added. The reaction results showed that the conversion rate of 1,6-hexanediamine was 99% and the yield of HDC product was 66%.

[0037] Example 4

[0038] The other steps are the same as in Example 2, except that 0.872 g of 20 wt% Bi(C2H3O2)3 / TS catalyst was added. The reaction result showed that the conversion rate of 1,6-hexanediamine was 100% and the yield of HDC product was 62%.

[0039] Example 5

[0040] The other steps are the same as in Example 2, except that 0.872 g of 20 wt% Bi(C2H3O2)3 / ZSM-5 catalyst is added. The reaction conditions are the same as in Example 1. The reaction results show that the conversion rate of 1,6-hexanediamine is 99% and the yield of HDC product is 67%.

[0041] Example 6

[0042] The other steps are the same as in Example 2, except that 0.872 g of 20 wt% Bi(C2H3O2)3 / SiO2 catalyst was added. The reaction results showed that the conversion rate of 1,6-hexanediamine was 99% and the yield of HDC product was 65%.

[0043] Example 7

[0044] The other steps are the same as in Example 2, except that 0.872 g of 20 wt% Bi(C2H3O2)3 / AC catalyst was added. The reaction result showed that the conversion rate of 1,6-hexanediamine was 100% and the yield of HDC product was 69%.

[0045] Example 8

[0046] The other steps are the same as in Example 2, except that 0.291 g of 20 wt% Bi(C2H3O2)3 / HY catalyst is added. The reaction conditions are the same as in Example 1, and the reaction results show that the conversion rate of 1,6-hexanediamine is 99% and the yield of HDC product is 57%.

[0047] Example 9

[0048] The other steps are the same as in Example 2, except that 0.581 g of 20 wt% Bi(C2H3O2)3 / HY catalyst is added. The reaction conditions are the same as in Example 1, and the reaction results show that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 67%.

[0049] Example 10

[0050] The other steps are the same as in Example 2, except that 1.162 g of 20 wt% Bi(C2H3O2)3 / HY catalyst is added. The reaction conditions are the same as in Example 1. The reaction results show that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 69%.

[0051] Example 11

[0052] The other steps are the same as in Example 2, except that 0.872 g of 10 wt% Bi(C2H3O2)3 / HY catalyst is added. The reaction conditions are the same as in Example 1, and the reaction results show that the conversion rate of 1,6-hexanediamine is 98% and the yield of HDC product is 61%.

[0053] Example 12

[0054] The other steps are the same as in Example 2, except that 0.872 g of 30 wt% Bi(C2H3O2)3 / HY catalyst is added. The reaction conditions are the same as in Example 1. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100%, and the yield of HDC is 68%.

[0055] Example 13

[0056] The other steps are the same as in Example 2, except that 0.872 g of 40 wt% Bi(C2H3O2)3 / HY catalyst is added. The reaction conditions are the same as in Example 1. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 66%.

[0057] Example 14

[0058] The other steps are the same as in Example 2, except that the reaction time is 6 hours. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 62%.

[0059] Example 15

[0060] The other steps are the same as in Example 2, except that the reaction time is 7 hours. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 67%.

[0061] Example 16

[0062] The other steps are the same as in Example 2, except that the reaction time is 9 hours. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 64%.

[0063] Example 17

[0064] The other steps are the same as in Example 2, except that the reaction temperature is 60°C. The reaction results show that the conversion rate of 1,6-hexanediamine is 94% and the yield of HDC product is 58%.

[0065] Example 18

[0066] The other steps are the same as in Example 2, except that the reaction temperature is 70°C. The reaction results show that the conversion rate of 1,6-hexanediamine is 96% and the yield of HDC product is 62%.

[0067] Example 19

[0068] The other steps are the same as in Example 2, except that the reaction temperature is 90°C. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 67%.

[0069] Example 20

[0070] The other steps are the same as in Example 2, except that the reaction temperature is 100°C. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 56%.

[0071] Example 21

[0072] The other steps are the same as in Example 2, except that 0.1 mol of dimethyl carbonate is added. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 61%.

[0073] Example 22

[0074] The other steps are the same as in Example 2, except that 0.15 mol of dimethyl carbonate is added. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 64%.

[0075] Example 23

[0076] The other steps are the same as in Example 2, except that 0.25 mol of dimethyl carbonate is added. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 69%.

[0077] Example 24

[0078] The other steps are the same as in Example 2, except that 0.3 mol of dimethyl carbonate is added. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 59%.

[0079] Example 25

[0080] The other steps are the same as in Example 1, except that the catalyst added is bismuth acetate, a metal salt that has been recycled and reused for the second time. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 75%.

[0081] Example 26

[0082] The other steps are the same as in Example 1, except that the catalyst added is bismuth acetate, a metal salt that has been recycled and reused for the third time. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 74%.

[0083] Example 27

[0084] The other steps are the same as in Example 1, except that the catalyst added is bismuth acetate, a metal salt that has been recycled and reused for the fourth time. The reaction result shows that the conversion rate of 1,6-hexanediamine is 100% and the yield of HDC product is 71%.

[0085] As can be seen from the above examples, the method for preparing methyl 1,6-hexamethylenedicarbamate according to the present invention has mild reaction conditions, simple operation process, and the prepared bismuth-based metal salt has good activity and is easy to separate from the reaction system, thus having good prospects for industrialization.

[0086] 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.

[0087] Matters not covered in this invention are common knowledge.

Claims

1. A method for synthesizing methyl 1,6-hexamethylenedicarbamate catalyzed by a bismuth-based metal salt, characterized in that the method comprises the following steps: 1,6-hexamethylenediamine, dimethyl carbonate and catalyst were added to a reactor and stirred at 60-100°C and atmospheric pressure for 6-9 hours to obtain methyl 1,6-hexamethylenedicarbamate. in, The catalyst is either a metal salt bismuth acetate or a supported bismuth acetate, and the amount added is 5% to 20% of the mass of 1,6-hexanediamine; the molar ratio of dimethyl carbonate to 1,6-hexanediamine is 2 to 4:

1. The preparation method of the aforementioned bismuth acetate metal salt catalyst includes the following steps: (1) Weigh Bi2O3, acetic acid, and acetic anhydride into a reactor and reflux at 140-160℃ for 1-3 hours; wherein, add 1-10g of Bi2O3 and 1-5mL of acetic anhydride to every 30mL of acetic acid; (2) Filter the filtrate obtained in the previous step, and evaporate it at 60-70℃ to obtain crystals; (3) Dissolve the crystals obtained in step (2) in acetic acid at 70-100℃, and then cool to room temperature to obtain crystals; wherein, 0.5-2.0g of crystals are added to every 15mL of acetic acid; (4) The solid obtained from the filtration step (3) is dried under vacuum at 50°C for 8-12 hours to obtain the metal salt bismuth acetate.

2. The method for synthesizing methyl 1,6-hexamethylenedicarbamate catalyzed by a bismuth-based metal salt as described in claim 1, characterized in that, In supported bismuth acetate, the bismuth acetate loading is 10–40 wt%.

3. The method for synthesizing methyl 1,6-hexamethylenedicarbamate by bismuth-based metal salt catalysis as described in claim 1, characterized in that it further comprises the following steps: after the reaction is completed, a solvent is added to dissolve the reaction mixture, and the solid catalyst is removed by centrifugation and filtration; The solvent is methanol or ethanol.

4. The method for synthesizing methyl 1,6-hexamethylenedicarbamate by catalysis using bismuth-based metal salts as described in claim 1, characterized in that the preparation method of the supported bismuth acetate catalyst includes the following steps: (1) Dissolve bismuth acetate in acetic acid and stir continuously at 70-100℃ until completely dissolved; add 0.2-1.0g of bismuth acetate and 1-3g of carrier to every 15mL of acetic acid; (2) Add the carrier to the salt solution of step (1) and stir for 12-36 hours; (3) Filter to remove the liquid from step (2), and dry the solid under vacuum at 50°C for 8-12 hours to obtain supported bismuth acetate.

5. The method for synthesizing methyl 1,6-hexamethylenedicarbamate by catalysis of bismuth-based metal salts as described in claim 4, characterized in that the support is selected from silica gel, activated carbon, or molecular sieves.