A new method for synthesizing isocyanates

Abstract

The present invention relates to a catalytic synthesis of isocyanate technology, and discloses a new method for synthesizing isocyanate, which makes the isocyanate production process safe and low in production cost. In order to achieve the above object, the technical scheme adopted by the present invention is: N-chloroamide thermal decomposition method is used to synthesize isocyanate, that is, in a suitable medium, under the action of a suitable catalyst, heating reaction for a suitable time, so that N-chloroamide is thermally decomposed to generate isocyanate and hydrogen chloride, so that the isocyanate production process is safe and low in production cost. The reaction process of synthesizing isocyanate by catalytic thermal decomposition method is as follows:

Description

Technical Field

[0001] The invention belongs to the field of chemical synthesis, and in particular relates to a method for synthesizing isocyanate. Background Art

[0002] Isocyanates are important and versatile chemical intermediates for manufacturing a variety of products such as flexible and rigid polyurethane materials, thermal insulation foams, agrochemicals and pharmaceuticals. It is a bulk chemical, with China's polyurethane industry producing about 15 million tons / year and consuming 12.5 million tons in 2022.

[0003] Nowadays, the main varieties of isocyanates are TDI, MDI, HDI, etc. In industry, alkylamine or aromatic amine is reacted with phosgene at low temperature to generate carbamoyl chloride, which is then thermally decomposed at high temperature to obtain the corresponding isocyanate, while releasing a large amount of hydrogen chloride gas. This production method has low raw material cost, easy separation and purification of the product, and relatively simple process. It is suitable for large-scale industrial production. However, the fatal disadvantage of this method is that it uses extremely dangerous phosgene, so it has high requirements for equipment and operation management.

[0004] Therefore, the non-phosgene method for producing isocyanates has become the goal of technical pursuit. The easy leakage of highly toxic phosgene is the main reason for its industrial danger. There are many research reports on the use of diphosgene or triphosgene instead of phosgene to synthesize isocyanates (CN111747868B; CN1687022; CN103553969). Diphosgene is a liquid at room temperature, while the triphosgene method is a solid at room temperature, which is basically non-toxic, easy to store and transport, and easy to use. However, compared with the phosgene method, the cost is much higher and is not suitable for the production of large-tonnage isocyanates.

[0005] In recent years, the use of green dimethyl carbonate (DMC) as a raw material to synthesize isocyanates has attracted much attention. DMC is used as a carbonyl source to react with amines to form N-substituted carbamates, which are then catalytically decomposed into the corresponding isocyanates (US20090918848; US5773643; Green Chem, 2016, 18: 6681–6686;). Common catalysts include base catalysts and Lewis acid catalysts. The process conditions are mild, the reaction is relatively mild, and it can be carried out without pressure. The by-product is CH3OH, and the process is suitable for the green concept. However, the cost of DMC itself is not as low as predicted in the early days, and DMC is a carbonylating agent as well as a good alkylating agent. The boiling points of the corresponding alkylated products are close to those of the target products, making them difficult to separate, which has an adverse effect on the subsequent thermal cracking reaction. The effects of these factors make it difficult for the DMC method to replace the current industrial phosgene method.

[0006] US Patent No. 4223145 (September 16, 1980) and Chinese Patent No. CN113861077 (December 31, 2021) both proposed the use of acidified urea thermal decomposition to prepare isocyanates. For example, the process of thermal decomposition of cyclohexanediurea hydrochloride to prepare cyclohexanediisocyanate is shown in Formula 1.

[0007]

[0008] The acidified urea thermal decomposition method does not require the use of extremely dangerous phosgene and is safe to operate, but it consumes stoichiometric amounts of organic amines, which results in a large amount of organic amine salt emissions, causing a significant increase in costs.

[0009] Among all non-phosgene methods, the Curtius rearrangement is considered to be the cleanest and most productive method for synthesizing isocyanates, with relatively cheap reagents and inert byproducts. However, this method cannot be produced on a large scale due to safety concerns about the preparation of the intermediate acyl azide.

[0010] US Patent No. 5319133 (June 7, 1994) proposed a method for rearranging N-chloroamide and liquid alkali in oil-water phases at 0-60°C under the catalysis of quaternary ammonium salt to generate isocyanate. See Formula 2. This method has low cost and safe operation, but still discharges a large amount of salt-containing wastewater.

[0011] Summary of the invention

[0012] The purpose of the present invention is to provide a new catalytic synthesis technology of isocyanate, so that the isocyanate production process is safe and the production cost is low.

[0013] To achieve the above purpose, the technical scheme adopted by the present invention is: synthesizing isocyanate by thermal decomposition of N-chloroamide. In a non-protonic solvent medium, under the action of alkaline organic catalyst, heating reaction for a suitable time, adding inert protective medium to the reaction system, thermally decomposing N-chloroamide to generate isocyanate and hydrogen chloride, and separating the isocyanate product; the reaction process of synthesizing isocyanate by catalytic thermal decomposition is as shown in Formula 3:

[0014]

[0015] The isocyanate produced by the pyrolysis reaction is separated by an appropriate method to obtain the isocyanate product. The by-product hydrogen chloride gas is taken out with an inert protective medium.

[0016] Furthermore, the general formula of N-chloroamide is R(CONHCl)n, where R can be an aromatic ring, such as a benzene ring; an aliphatic ring, such as a cyclohexyl group; or an aliphatic chain, such as an aliphatic chain of 4 to 12 carbon atoms. In the general formula, n=1 to 3.

[0017] Furthermore, N-chloroamide: aprotic solvent = 1: 1 to 4 (by weight); basic organic matter: N-chloroamide = 2 to 10: 100 (by weight).

[0018] Furthermore, the boiling point of the aprotic solvent should be higher than 145°C, so as to facilitate the reflux reaction at a temperature above 150°C at normal pressure. Aprotic solvents include: aromatic hydrocarbons, such as trimethylbenzene, tetramethylbenzene, methylethylbenzene, etc.; amides, such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, etc.; halogenated hydrocarbons, such as o-dichlorobenzene, trichlorobenzene, etc.; and ethers, such as diethylene glycol dibutyl ether, diphenyl ether, etc.

[0019] Furthermore, the alkaline organic matter can be a tertiary amine compound, such as triethylamine, tributylamine, 4-dimethylaminopyridine (DMAP) (CAS No. 1122-58-3), diazabicyclo (DBU) (CAS No. 6674-22-2), 1,57-triazidobicyclo (4.4.0) dec-5-ene (TBD) (CAS No. 5807-14-7) or a mixture of one or more thereof; it can also be a tertiary phosphine compound, such as triethylphosphine, tributylphosphine, tricyclohexylphosphine, etc.

[0020] Furthermore, the heating reaction is to carry out the N-chloroamide pyrolysis reaction at 150-200°C. The specific pyrolysis temperature depends on the activity of the N-chloroamide. The N-chloroamide connected with the aromatic ring has higher activity, and the suitable pyrolysis temperature is 150-175°C. Other N-chloroamides with lower activity are preferably pyrolyzed at 170-200°C.

[0021] Furthermore, the heating pyrolysis time is 1.0 to 2.0 hours.

[0022] Further, the method for separating the isocyanate product can be a freezing crystallization method or a distillation method.

[0023] Furthermore, the inert protective medium is an inert gas or an inert liquid with a low boiling point; the inert gas refers to a gas that does not chemically react with hydrogen chloride and isocyanate at the pyrolysis reaction temperature, and can be a room temperature gas such as nitrogen, carbon dioxide, etc.; it can also be an inert liquid with a low boiling point, such as dichloromethane, chloroform, dichloroethane, ether, cyclopentane, etc.

[0024] After the generated hydrogen chloride gas is taken out of the reaction system, the mixed gas is preferably refrigerated to separate the low-boiling-point inert liquid from the hydrogen chloride gas. The condensed inert liquid is recycled.

[0025] When an inert liquid with a low boiling point is used as a protective medium, the appropriate temperature for freezing the mixed gas is 50°C lower than the boiling point of the inert liquid, which ensures that the inert liquid is fully recovered on the one hand, and that relatively pure hydrogen chloride gas is obtained on the other hand, which is convenient for other uses. When an inert gas is used as a protective medium, the reaction gas cooling temperature is room temperature. The technical method of the present invention has the following beneficial effects:

[0026] (1) Using N-chloroamide as a raw material reduces the cost of producing isocyanate because N-chloroamide is derived from amide chlorination, and amide is generally much cheaper than amine.

[0027] (2) The present invention adopts a method of high temperature thermal dehydrochlorination under catalysis without consuming chemically measured liquid alkali, which significantly reduces the production cost of isocyanate.

[0028] (3) The method of the present invention adopts a method of dehydrochlorination by high temperature pyrolysis under catalysis, instead of using a liquid alkali elimination method as in U.S. Pat. No. 5,319,133, thereby avoiding the generation of waste brine and making the production process clean and environmentally friendly.

[0029] (4) The method of the present invention uses high-temperature pyrolysis to dehydrochlorinate, and through the tail gas separation method, relatively pure HCl gas is obtained, which can be utilized as a resource, thereby achieving the purpose of emission reduction and efficiency improvement. DETAILED DESCRIPTION

[0030] The present invention is further described below with reference to examples, but is not limited thereto.

[0031] Example 1: Preparation of 2-isocyanate decane

[0032]

[0033] 223.0 g of N-chloro-2-methyldecanoic acid amide (98.5% by weight), 223.0 g of trichlorobenzene and 4.46 g of DMAP were heated to 180°C and N2 was introduced into the reaction system. The tail gas was cooled at 30°C and the condensate was refluxed into the reaction system. The tail gas was HCl and N2.

[0034] After 1.6 hours of reaction, the heating was stopped, the reaction liquid was cooled, and the reaction solution was subjected to high vacuum distillation, and the 90-95°C / 3-6 mmHg fraction was collected. 151.4 g of 2-isocyanate decane was obtained. The content of the 2-isocyanate decane was 97.4% by gas chromatography analysis, and the yield was 80.4%.

[0035] Example 2: Preparation of p-phenylene diisocyanate

[0036]

[0037] 234.0 g N-chloroterephthalamide (99.5% by weight), 468.0 g N,N-dimethylformamide, 9.36 g triethylamine were added. The temperature was raised to 150°C, and CO2 was introduced into the reaction system. The tail gas was cooled at 30°C, and the condensate was refluxed into the reaction system. The tail gas was HCl and CO2.

[0038] After 1.4 hours of reaction, stop heating. Distill off about 300g of solvent under reduced pressure, and place the residual liquid in a refrigerator for crystallization (about -20°C) for 12 hours. Filter and dry under vacuum at 60°C. Obtain 140.8g of p-phenylene diisocyanate. Melting point: 92-94°C, liquid chromatography analysis content 99.1%. Yield 87.2%.

[0039] Example 3: Preparation of 1,3,5-m-phenylene triisocyanate

[0040]

[0041] 158.5 g (0.5 mol) of N-chloroisophthalamide (98.0% by weight), 634 g of trimethylbenzene (mixed trimethylbenzene), and 9.5 g of tributylphosphine were heated to 160°C, and dichloromethane was introduced into the reaction solution using a feed pump. The tail gas was cooled at -30°C, and the condensate was collected, and the tail gas was HCl.

[0042] After 1.2 hours of reaction, stop heating. Distill off about 450g of solvent under reduced pressure, and place the residual liquid in a refrigerator for crystallization (about -20°C) for 12 hours. Filter and dry under vacuum at 60°C. Obtain 86.5g of 1,3,5-m-phenylene triisocyanate. Melting point: 77-79°C, liquid chromatography analysis content 98.3%. Yield 84.6%.

[0043] Example 4: Preparation of 1,4-butanediisocyanate

[0044]

[0045] 216.2.0 g (1.0 mol) of N-chloroadipamide (99.0% by weight), 648.6 g of diphenyl ether, and 17.3 g of DBU were added. The temperature was raised to 200°C, and chloroform was introduced into the reaction solution using a feed pump. The tail gas was cooled at -30°C, and the condensate was collected. The tail gas was HCl.

[0046] After 1.0 hour of reaction, the heating was stopped and the mixture was cooled. The fraction at 82-89°C / 3-6 mmHg was collected by high vacuum distillation. 114.8 g of 1,4-butylene diisocyanate was obtained. The content of the product according to gas chromatography was 99.2%. The yield was 81.3%.

[0047] Example 5: Preparation of phenyl isocyanate

[0048]

[0049] 157.9 g (1.0 mol) of N-chlorobenzamide (98.5% by weight), 160 g of diethylene glycol dibutyl ether, and 3.2 g of TBD were added. The temperature was raised to 180°C, and cyclopentane was introduced into the reaction solution using a feed pump. The tail gas was cooled at -30°C, and the condensate was collected. The tail gas was HCl.

[0050] After 1.0 hour of reaction, stop heating. Cool, distill the reaction solution under high vacuum, and collect the 45-48°C / 3-6 mmHg fraction. Obtain 108.4 g of phenyl isocyanate. Gas chromatography analysis shows a content of 99.2%. Yield 90.4%. Example 6: Preparation of 3-isocyanate heptane

[0051]

[0052] 180.4 g (1.0 mol) of N-chloroisooctanoic acid amide (weight content 98.5%), 180.4 g of N,N-dimethylacetamide, and 9.2 g of tributylamine were added. The temperature was raised to 170°C, and N2 gas was introduced into the reaction solution. The reaction was refluxed with water at room temperature, and the tail gas was HCl and N2.

[0053] After 2.0 hours of reaction, the heating was stopped, the reaction liquid was cooled, and high vacuum distillation was performed to collect the 61-66°C / 3-6 mmHg fraction. 118.5 g of 3-isocyanate heptane was obtained. The content of the 3-isocyanate heptane was 98.9% by gas chromatography analysis. The yield was 83.0%.

[0054] Example 7: Preparation of 1,7-diisocyanate heptane

[0055]

[0056] 260.4 g (1.0 mol) of N-chlorononane diamide (weight content 98.0%), 390.6 g of diethylene glycol dimethyl ether, and 13.0 g of triethylphosphine were added. The temperature was raised to 160°C, and N2 gas was introduced into the reaction solution. The reaction was refluxed with water at room temperature, and the tail gas was HCl and N2.

[0057] After 2.0 hours of reaction, the heating was stopped, the reaction liquid was cooled, and the reaction liquid was subjected to high vacuum distillation, and the 114-120°C / 3-6 mmHg fraction was collected. 147.6 g of 1,7-diisocyanate heptane was obtained. The content of the 1,7-diisocyanate heptane was 97.8% by gas chromatography analysis, and the yield was 79.2%.

[0058] Example 8: Preparation of n-undecyl isocyanate

[0059]

[0060] 237.4 (1.0 mol) of N-chlorolauric acid amide (weight content 98.5%), 237.4 g of methylethylbenzene, and 14.25 g of tricyclohexylphosphine were added. The temperature was raised to 180°C, and N2 gas was introduced under the reaction solution. The reaction was refluxed with room temperature water, and the tail gas was HCl and N2.

[0061] After 1.6 hours of reaction, the heating was stopped, the reaction liquid was cooled, and high vacuum distillation was performed to collect the 98-103°C / 3-6 mmHg fraction. 161.5 g of n-undecyl isocyanate was obtained. The content of the product according to gas chromatography was 98.2%, and the yield was 80.2%.

[0062] Comparative Example 1

[0063] Reference to U.S. Pat. No. 5,319,133 Example 5-E2-Preparation of Isocyanate Decane

[0064] 223.0 g (1.0 mol) of N-chloro-2-methyldecanoic acid amide (98.5% by weight) was dissolved in 1000 ml of dichloromethane and cooled to 2° C. in an ice bath. 8.5 g of tetrabutylammonium hydroxide (2.5 mol% based on N-chloroamide) was added, followed by a solution of 400 ml of ice water and 40.5 g of sodium hydroxide. The mixture was stirred at low temperature for 25 minutes, the organic layer was collected, and 25 g of magnesium sulfate was added to dry it.

[0065] The solvent was evaporated, and the crude product was subjected to high vacuum distillation, and the 90-95°C / 3-6 mmHg fraction was collected to obtain 131.2 g of 2-isocyanate decane with a purity of 97.6% according to gas chromatography analysis, and a yield of 69.9%.

[0066] Comparing Example 1 with Control Example 1, it can be seen that the method of the present invention does not use a stoichiometric amount of liquid caustic so that there is no discharge of a large amount of saline wastewater, and the production cost is therefore lower.

[0067] Comparative Example 2. Alkaline aqueous solution reaction (Hofmann reaction conditions)

[0068] 223.0 g (1.0 mol) of N-chloro-2-methyldecanoic acid amide (98.5% by weight) was suspended in 800 ml of water and cooled to 5° C. in an ice bath. Then, a solution formed by 400 ml of ice water and 42 g of sodium hydroxide was added within 1 hour. The temperature was then raised to 85° C. and reacted for 1 hour. The reaction system turned into a brown turbid liquid. The mixture was extracted 3 times with 400 ml of dichloromethane.

[0069] After the extract was desolventized, the crude product was distilled under high vacuum, but no 90-95°C / 3-6mmHg fraction was collected, and the yield was zero.

[0070] Comparison of Example 1 and Control Example 2 shows that no isocyanate product is obtained under the Hofmann reaction conditions, which illustrates the effectiveness of the method of the present invention (i.e., aprotic solvent, organic base catalysis, high temperature pyrolysis).

Claims

1. A method for synthesizing isocyanate, characterized in that: In an aprotic solvent, add N-chloroamide raw material, heat to react at 150-200°C under the action of alkaline organic catalyst, add inert protective medium to the reaction system, thermally decompose N-chloroamide to generate isocyanate and hydrogen chloride, and separate the isocyanate product; The reaction process of synthesizing isocyanate by catalytic thermal decomposition is as follows: ； R is an aromatic ring, an aliphatic ring, or a 4-12 carbon aliphatic chain; The boiling point of the aprotic solvent is higher than 145°C; the alkaline organic catalyst is one of a tertiary amine compound or a tertiary phosphine compound; the inert protective medium is an inert gas or an inert liquid with a low boiling point; The tertiary amine compound is specifically a mixture of one or more of triethylamine, tributylamine, 4-dimethylaminopyridine, diazabicyclo, 1 5 7-triazidebicyclo (4.4.0) dec-5-ene; the tertiary phosphine compound is a mixture of one or more of triethylphosphine, tributylphosphine and tricyclohexylphosphine.

2. The method for synthesizing isocyanate according to claim 1, characterized in that: The weight ratio of N-chloroamide: aprotic solvent is 1:1~4.

3. The method for synthesizing isocyanate according to claim 1, characterized in that: The weight ratio of alkaline organic catalyst to N-chloroamide is 2-10:

100.

4. The method for synthesizing isocyanate according to claim 1, characterized in that: The heating reaction time is 1.0~2.0 hours.

5. The method for synthesizing isocyanate according to claim 1, characterized in that: The inert gas is nitrogen or carbon dioxide; the low boiling point inert liquid is dichloromethane, chloroform, dichloroethane, ether or cyclopentane.

6. The method for synthesizing isocyanate according to claim 1, characterized in that: Isolation of the isocyanate product is accomplished by cryo-crystallization or distillation.

7. The method for synthesizing isocyanate according to claim 1, characterized in that: The reaction gas is cooled and recovered during the reaction process; when an inert liquid with a low boiling point is used as the protective medium, the reaction gas cooling temperature is 50°C lower than the boiling point of the inert liquid; when an inert gas is used as the protective medium, the reaction gas cooling temperature is the room temperature.

8. The method for synthesizing isocyanate according to claim 1, characterized in that: The aprotic solvent having a boiling point higher than 145° C. is one of aromatic hydrocarbons, amides, halogenated hydrocarbons and ethers.

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