An isophorone diamine composition and isophorone diisocyanate composition

Abstract

The present application relates to a kind of isophorone diamine composition and isophorone diisocyanate composition.The content of hydroxyl nitrile compound in the isophorone diamine composition is 0.0001-0.0500wt%, preferably 0.0001-0.0300wt%, more preferably 0.0005-0.0300wt%.The isophorone diisocyanate composition prepared using the isophorone diamine composition has moderate reactivity with polyols, and the reaction solution has lower color and turbidity, and less residual monomer.

Description

TECHNICAL FIELD

[0001] The present application provides an isophorone diamine composition and an isophorone diisocyanate composition. BACKGROUND

[0002] Isophorone diamine (IPDA for short) is mainly used as a curing agent for epoxy resin, and is mainly used in epoxy formulations requiring low color, low odor, high flexural strength and excellent chemical resistance, and is suitable for floor coatings, paving fillers and mixtures. Another use is as a raw material for isophorone diisocyanate (IPDI for short).

[0003] IPDI is a colorless or light yellow liquid at room temperature, is an aliphatic isocyanate, is also a cycloaliphatic isocyanate, has lower reactivity than aromatic isocyanates, has lower vapor pressure, and has relatively less toxicity than isocyanates. Due to the absence of benzene rings in its structure, it has excellent weather resistance and can be used to prepare high-end polyurethane materials with light stability, weather resistance and excellent mechanical properties, such as elastomers, waterborne polyurethane dispersions, UV resins, etc. IPDI can also self-polymerize to form polyisocyanates with multiple functional groups, and the coatings prepared therefrom dry very quickly and have excellent applications in automotive refinish paints. In the above applications, the requirements for the various components and impurity contents in the IPDI monomer are relatively strict.

[0004] With the gradual deepening of environmental protection concepts, more and more attention is being paid to the VOC volatilization problem during the use of isocyanate monomers in the market. In order to reduce the volatilization of solvents during use, CN94108263.6 adopts a method of reacting isocyanate monomers with polyols to form prepolymers. Since the molecular weight of the prepolymers is relatively large, the VOC volatilization during use is relatively small, and therefore this scheme is increasingly popular in the market.

[0005] As for IPDI, due to the difference in activity between the two NCOs, the reaction is carried out by the NCO with higher activity in the early stage, and by the NCO with lower activity in the later stage. However, the viscosity of the system gradually increases in the later stage, and the dispersion of IPDI and polyol is poor, so the required reaction time is relatively long. On the other hand, the local molecular and energy aggregation caused by the increase in viscosity can lead to excessive polymerization, resulting in turbidity of the reaction solution.

[0006] To solve this problem, DD151466A1 provides a solution to carry out the reaction in a solvent, but this subsequent operation exists desolventizing, and also causes a part of the solvent to remain in the prepolymer, which will emit VOC in the subsequent use process. CN94108263.6 adopts a solution of controlling 2% IPDI monomer residue to reduce the viscosity of the reaction system, thereby promoting the reaction of NCO and polyol, but the residual IPDI also has certain VOC volatilization, so from the environmental protection point of view, it is not the best solution. In addition, increasing the temperature is also a way to reduce the viscosity, but long-term high-temperature residence will cause the color number of IPDI monomer and prepolymer to increase, thereby affecting the performance of its high-end application, and the same problem will also exist through high-temperature separation and other means.

[0007] Therefore, it is of great significance to develop an IPDI monomer with moderate activity, less residual monomer after reaction with polyol, and lower turbidity and color number of the prepolymer. SUMMARY

[0008] In view of the above problems existing in the prior art, the present application aims to provide an isophorone diamine composition and an isophorone diisocyanate composition. The isophorone diisocyanate composition has moderate reactivity with alcohol, less residual monomer after reaction with polyol, and lower turbidity and color number of the prepolymer.

[0009] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0010] An isophorone diamine (IPDA) composition, characterized in that the content of hydroxyl nitrile compound in the isophorone diamine composition is 0.0001-0.0500wt%, preferably 0.0001-0.0300wt%, and more preferably 0.0005-0.0300wt%.

[0011] The above-mentioned isophorone diamine composition is subjected to phosgenation reaction with phosgene raw material to obtain the isophorone diisocyanate composition.

[0012] The hydroxyl nitrile compound in the isophorone diamine composition is 3-nitrile-3, 5, 5-trimethylcyclohexanol, and the structural formula is:

[0013]

[0014] The preparation method of the isophorone diamine composition of the present application does not have specific requirements, and the isophorone diamine composition of this composition can be obtained by any achievable way in the prior art.

[0015] In some embodiments of the present application, the isophorone composition is prepared by adding a hydroxycarbonitrile compound to IPDA, or by mixing a high-concentration hydroxycarbonitrile IPDA composition with conventional IPDA.

[0016] According to the preparation process of the isophorone diisocyanate full industry chain provided in the patent CN109761855A, the conventional preparation method of isophorone diamine is obtained by aminating and hydrogenating isophorone nitrile, wherein the amination process is to ammoniate the carbonyl group in isophorone nitrile to obtain an amine group, and the hydrogenation process is to hydrogenate the nitrile group in isophorone nitrile to obtain an amine group. In the conventional preparation process, it is difficult to obtain an IPDA composition containing a hydroxycarbonitrile compound.

[0017] Therefore, the present application adopts a direct hydrogenation method for isophorone nitrile to prepare a hydroxycarbonitrile compound, and the specific synthesis method is as follows:

[0018] a) In the presence of a hydrogenation catalyst, hydrogen and isophorone nitrile are mixed and reacted in a 1-5wt% KOH ethanol solution to obtain a reaction product containing 3-nitrile-3, 5, 5-trimethylcyclohexanol (hydroxycarbonitrile compound);

[0019] b) The reaction product obtained in step a) is separated and purified to obtain the hydroxycarbonitrile compound required by the present application.

[0020] The reaction temperature of the hydrogenation reaction of step a) is 50-200℃, and is further preferably 50-150℃, such as 60℃, 70℃, 80℃, 100℃, 120℃, 140℃; the pressure is 0.3-2MPa, and is further preferably 0.5-1.5MPa, such as 0.6MPa, 0.8MPa, 1.0MPa, 1.2MPa, 1.4MPa; the selected catalyst is Raney copper and / or Raney nickel.

[0021] In step a), the mass ratio of the hydrogenation catalyst to the reaction raw material isophorone nitrile is 1:100-1000, and is further preferably 1:200-750, such as 1:500, 1:250.

[0022] In step b), the separation and purification process of the reaction product is carried out by rectification, and the rectification process is carried out by a rectification column with 10-20 trays to obtain a hydroxycarbonitrile compound with a purity of >99%. By adding a certain amount of hydroxycarbonitrile compound to conventional IPDA, an IPDA composition with a hydroxycarbonitrile compound content of 0.0001-0.0500wt%, preferably 0.0001-0.0300wt%, and more preferably 0.0005-0.0300wt% can be obtained.

[0023] There can be other methods for controlling the content of the hydroxyl nitrile compound in the IPDA composition, which are not listed one by one in the present application. The above-mentioned methods can be used in combination or individually, and the present application does not limit the way of obtaining the IPDA composition.

[0024] The content of the hydroxyl nitrile compound in the isophorone diamine composition described in the present application can be analyzed by gas chromatography. The present application does not have specific requirements, and in some specific examples, the method used is as follows: after the sample is dissolved with a solvent (preferably dichloromethane), it is analyzed by gas chromatography, detected by a hydrogen ion flame detector (FID), and quantitatively calculated by area normalization method.

[0025] The present application also provides a preparation method of isophorone diisocyanate composition (IPDI), which comprises subjecting the isophorone diamine composition described above to phosgenation reaction with a phosgene raw material to obtain the isophorone diisocyanate composition.

[0026] The phosgenation reaction can be any one of gas phase phosgenation reaction, cold and hot phosgenation reaction, and salt phosgenation reaction. The phosgenation reaction is carried out by reacting isophorone diamine with one or more of phosgene, diphosgene, triphosgene, fluorophosgene or bromophosgene.

[0027] The phosgenation reaction described above can be carried out in gas phase, and the specific method is described in Chinese patent CN105214568A, which is incorporated by reference into the present application. Specifically, 1) the amine is vaporized to form an amine gas stream containing amine droplets; 2) the amine droplets contained in the amine gas stream are removed to obtain an amine gas stream substantially free of amine droplets; 3) the amine gas stream substantially free of amine droplets is subjected to gas phase phosgenation reaction with phosgene to obtain isocyanate; at the same time, a heater is used to remove the amine droplets contained in the amine gas stream. The specific structure of the heater can be found in patent document CN105214568A.

[0028] The reaction temperature of the above-mentioned gas phase phosgenation is 200-550℃, preferably 250-400℃, such as 300℃, 320℃; the reaction pressure is 0.01-1MPa, preferably 0.03-0.3MPa, such as 0.08MPa, 0.2MPa. In some specific ways, the mixed gas after the reaction of phosgene and isophorone diamine (abbreviated as IPDA) needs to be absorbed and cooled by a liquid inert medium or / and a mixture of inert medium and isocyanate. The inert gas is preferably nitrogen or argon or steam of toluene, xylene, chlorobenzene, o-dichlorobenzene; the liquid inert medium is selected from all inert liquids suitable for preparing isocyanate, and the inert liquid is preferably chlorobenzene, dichlorobenzene, o-dichlorobenzene, toluene, chlorotoluene, xylene and / or a mixture thereof.

[0029] The above-mentioned phosgenation reaction can be carried out in liquid phase, and the specific method is described in Chinese patent CN103319372B, which is incorporated herein by reference. Specifically, a') cold reaction, temperature is 0-130°C, preferably 40-70°C; pressure is 0.1-1 MPa; toluene, chlorobenzene, benzene, dichlorobenzene, cyclohexane, xylene or a mixture thereof is used as solvent, especially preferably chlorobenzene, dichlorobenzene is used as solvent; with super stoichiometric phosgene, reaction residence time is 2-120 min, preferably 5-45 min; b') is a hot reaction, temperature is 60-190°C, preferably 110-165°C; pressure is 0.1-1 MPa; toluene, chlorobenzene, benzene, dichlorobenzene, cyclohexane, xylene or a mixture thereof is used as solvent, especially preferably chlorobenzene, dichlorobenzene is used as solvent, with super stoichiometric phosgene, reaction residence time is 0.5-5 h, preferably 1-4 h. The above-mentioned phosgenation reaction can be carried out in hydrogen chloride and / or carbon dioxide salt phosgenation reaction, and the specific method is described in Chinese patents CN105218422B and CN107337615A, which are incorporated herein by reference. Specifically, 1') hydrogen chloride or / and carbon dioxide is reacted with amine in an inert solvent, the molar equivalent ratio of the hydrogen chloride to the amino group of the amine is 1-2.5:1, preferably 1.2-2:1, the molar equivalent ratio of the carbon dioxide to the amino group of the amine is 0.5-5:1, preferably 0.6-3:1, the mass ratio of the solvent to the amine is 25-5:1, preferably 20-5:1; the temperature of the salt formation reaction is 0-50°C, preferably 5-30°C, the pressure is 0.1-1 MPa, preferably 0.2-0.5 MPa; the reaction residence time is 1-15 min, preferably 5-10 min; the reaction pressure is 0.1-1 MPa, preferably 0.2-0.5 MPa. The reaction solution of the hydrochloride or carbonate obtained after the salt formation reaction of a) is subjected to 2') phosgenation reaction, the temperature is 100-170°C, preferably 110-165°C; the pressure is 0.1-1 MPa, preferably 0.2-0.5 MPa; with super stoichiometric phosgene, reaction residence time is 1-5 h, preferably 1.5-4 h. The inert solvent is toluene, chlorobenzene, benzene, dichlorobenzene, cyclohexane, xylene or a mixture thereof, more preferably chlorobenzene, dichlorobenzene.

[0030] In some specific embodiments, in the reaction process of the above-mentioned gas phase phosgenation, liquid phase phosgenation and salt phosgenation method, the phosgene is excessive in the phosgenation reaction, and the excessive phosgene after the phosgenation reaction is preferably removed at about 50-180°C, absolute pressure 0.05-0.1 MPa.

[0031] The IPDA composition containing the hydroxyl nitrile compound provided by the application has moderate reactivity with polyols after phosgenation reaction. If the reaction is slow, the production efficiency is affected; if the reaction is fast, the reaction may be intensified or even out of control, which in turn causes the viscosity of the alcohol-modified product to be too large, even turbidity, and even a high color number of the reaction solution.

[0032] The hydroxyl nitrile compound of the application will undergo the following reaction in the phosgenation process:

[0033]

[0034] The hydroxyl group in the hydroxyl nitrile compound first reacts with phosgene to form an acyl chloride in the phosgenation process, and then decomposes to form a chloronitrile compound upon further heating.

[0035] It is further speculated that at the initial stage of the reaction of IPDI with polyols, the nitrile compound in the chloronitrile compound contained in the IPDI composition is prone to hydrolysis to form a carboxylic acid structure in the presence of a catalyst and polyols, thereby further promoting the reaction of polyols with IPDI, improving the reaction efficiency of the IPDI composition with polyols, and avoiding excessive monomer residues caused by low efficiency in the reaction process; when the reaction of the IPDI composition with polyols proceeds to a certain extent, the reaction temperature becomes higher and higher, and the reaction rate becomes faster and faster, the chlorine in the chloronitrile compound decomposes, which reduces the catalytic activity of the catalyst, thereby inhibiting the reaction of IPDI with polyols.

[0036] When the content of the chloronitrile compound in the IPDI composition is too high, the content of the carboxylic acid obtained by hydrolysis of the nitrile at the initial stage is too large, which may cause the reaction to intensify or even be out of control, thereby causing the viscosity of the alcohol-modified product to be too large, even turbidity, and even a high color number of the reaction solution.

[0037] Therefore, the application limits the content of the hydroxyl nitrile compound in the IPDA composition used to prepare the IPDI composition to 0.0001-0.0500wt%, preferably 0.0001-0.0300wt%, and more preferably 0.0005-0.0300wt%.

[0038] Compared with the prior art, the isophorone diamine composition provided by the application has the following advantages:

[0039] 1. The IPDI composition obtained by phosgenation of the IPDA composition provided by the application has moderate reactivity with polyols;

[0040] 2. The prepolymers obtained by the reaction of the IPDI composition with polyols have a lower color number and less residual monomers. DETAILED DESCRIPTION

[0041] The technical solutions of the present application are further illustrated by specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application. The polypropylene glycol used in the embodiments is produced by Wanhua Chemical Group Co., Ltd. and has a specification of PPG-2000.

[0042] The quantitative analysis of the hydroxyl nitrile compound in the isophorone diamine composition is carried out on a gas chromatograph, and the gas chromatograph analysis conditions are as follows:

[0043] Chromatographic column: Agilent HP-5 (specification: 30 m*0.32 mm*0.25 mm); injection port temperature: 280℃; split ratio: 30:1; column flow rate: 1.5 ml / min; column temperature: 100℃, after 0.5 min, increased to 260℃ at 15℃ / min, and maintained for 8 min; detector temperature: 280℃; H2 flow rate: 35 ml / min.

[0044] Example 1: Preparation of IPDA compositions with different contents of hydroxyl nitrile compounds

[0045] (1) Synthesis of isophorone nitrile (IPN)

[0046] By the method provided in patent CN109761855A, isophorone is sent to a preheater at a speed of 200 kg / h to be preheated to a reaction temperature of 120℃, and then HCN and the basic catalyst sodium methoxide are sent into the reactor disclosed in Example 1 of CN103301799B and operated under the conditions at a molar ratio of 2:1:0.003 to react, and the reaction pressure is 1 MPa, and after 25 min of reaction, isophorone nitrile (3-cyano-3,5,5-trimethylcyclohexanone, abbreviated as IPN) is obtained;

[0047] (2) Hydroxyl nitrile compound

[0048] The isophorone nitrile (IPN) obtained above is reacted with hydrogen in the presence of a catalyst, as follows: in the presence of a hydrogenation catalyst, Raney copper, the space velocity of the catalyst is 1.5 g of 3-cyano-3,5,5-trimethylcyclohexanone / (ml of catalyst·hour), and the hydrogen and IPN are mixed and reacted in a 3% KOH-ethanol solution, and the reaction is carried out at a temperature of 120℃ and an absolute pressure of 1 MPa to obtain a reaction product containing 3-cyano-3,5,5-trimethylcyclohexanol (hydroxyl nitrile compound);

[0049] The reaction product containing 3-cyano-3,5,5-trimethylcyclohexanol (hydroxyl nitrile compound) is purified by the method provided in Chinese patent CN107304168A to obtain a hydroxyl nitrile compound with a purity of more than 99%.

[0050] (3) Preparation of conventional IPDA composition

[0051] The isophoronenitrile obtained in step (1), ammonia and hydrogen were reacted in the presence of a catalyst, specifically as follows: a) the isophoronenitrile obtained in step (1) was reacted with ammonia in a tubular reactor, the reaction was carried out at a temperature of 60℃ and an absolute pressure of 15 MPa, the molar ratio of ammonia to isophoronenitrile was 50:1, to obtain 3-cyano-3,5,5-trimethylcyclohexylimine;

[0052] b) hydrogen, NH3 and the 3-cyano-3,5,5-trimethylcyclohexylimine obtained in step a) were mixed and reacted in the presence of a hydrogenation catalyst, Raney cobalt, the space velocity of the catalyst was 1.5 grams of 3-cyano-3,5,5-trimethylcyclohexanone / (milliliter of catalyst·hour), the reaction was carried out at a temperature of 80℃ and an absolute pressure of 18 MPa, to obtain a product containing 3-aminomethyl-3,5,5-trimethylcyclohexylamine (abbreviated as IPDA) and 3-cyano-3,5,5-trimethylcyclohexylamine;

[0053] In step b), the mass ratio of the KOH-ethanol solution to the added isophoronenitrile was 1:600, the molar ratio of NH3 to isophoronenitrile was 50:1, and the molar ratio of hydrogen to isophoronenitrile was 80:1;

[0054] c) hydrogen, NH3 and the product containing 3-aminomethyl-3,5,5-trimethylcyclohexylamine and 3-cyano-3,5,5-trimethylcyclohexylamine obtained in step b) were mixed and reacted in the presence of a hydrogenation catalyst, Raney cobalt, the space velocity of the catalyst was 1.8 grams of 3-cyano-3,5,5-trimethylcyclohexanone / (milliliter of catalyst·hour), the reaction was carried out at a temperature of 120℃ and an absolute pressure of 18 MPa, to convert 3-cyano-3,5,5-trimethylcyclohexylamine into 3-aminomethyl-3,5,5-trimethylcyclohexylamine. In step c), the mass ratio of the acetic acid-ethanol solution to the IPN obtained in step 1) was 1:500, the molar ratio of hydrogen to the IPN obtained in step 1) was 30:1, and the molar ratio of ammonia to the IPN obtained in step (1) was 50:1.

[0055] The isophoronediamine was purified by the method provided in Chinese patent CN107304168A to obtain a conventional IPDA composition. The content of the hydroxyl nitrile compound therein was 0.00005wt%.

[0056] (4) Preparation of IPDA composition with different contents of hydroxyl nitrile compound

[0057] The hydroxyl nitrile compound obtained in step (2) was mixed into the conventional IPDA prepared in step (3) to obtain IPDA compositions with hydroxyl nitrile compound contents of 0.0003 wt%, 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.02 wt%, 0.04 wt%, and 0.1 wt%, respectively.

[0058] Preparation of IPDI compositions with different contents of chlorinated nitrile compounds

[0059] The conventional IPDA composition obtained in example (1) (with a hydroxyl nitrile compound content of 0.00005 wt%) and IPDA compositions with hydroxyl nitrile compound contents of 0.0003 wt%, 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.02 wt%, 0.04 wt%, and 0.1 wt%, respectively, were reacted with phosgene to obtain corresponding IPDI composition samples, which were named as sample 1, sample 2, sample 3, sample 4, sample 5, sample 6, sample 7, and sample 8, respectively.

[0060] The specific method is as follows: the obtained IPDA is gasified and heated to 355°C using the heater mentioned in example 1 of Chinese patent CN105214568A, and is continuously added into a reactor with gaseous phosgene heated to 355°C via respective feeding pipes under the protection of nitrogen, the reaction pressure is 0.05 MPa, and the temperature is 360°C; wherein, the feeding amount of IPDA is 800 Kg / h, and the feeding amount of phosgene is 3000 Kg / h; the mixed gas after reaction is rapidly cooled to 100°C using o-dichlorobenzene solution through a gas jet absorption device to obtain a product IPDI phosgenation solution; the excess phosgene is removed at 180°C and an absolute pressure of 0.1 MPa to obtain IPDI crude product without phosgene; then the crude product is subjected to rectification through a rectification column to obtain IPDI composition product at a 0.5 KPa, 150-160°C distillation range.

[0061] Evaluation of IPDI composition reaction with polyols

[0062] a) The catalyst dilauric dibutyl tin (T12) was diluted with toluene to a concentration of 1% for use;

[0063] b) 67.5 g of PPG-2000 with a water content of 300 ppm was added to a 500 ml reaction kettle, the reaction kettle was placed in an 82°C oil bath, and the stirring was started for preheating, and the stirring speed was 180 r / min;

[0064] c) After the temperature in the reaction kettle reached 80°C, 0.3 g of the catalyst T12 prepared in step a) and 7.6 g of the IPDI composition were added into the reaction kettle, respectively, and the reaction was carried out;

[0065] d) During the reaction, samples were taken every 5 minutes to monitor the NCO content. When the NCO content no longer decreased, the reaction was determined to have stopped, heating was stopped, and the reaction time was recorded;

[0066] e) After the temperature of the reactor decreased to room temperature, samples were taken and analyzed by GPC to obtain the area normalization of the reaction liquid, to obtain the residual monomer content, and to measure the color value by the method of GB / T605-2006.

[0067] The IPDI compositions of samples 2, 3, 4, 5, 6, and 7 were respectively tested in the examples to obtain reaction liquids of different batches.

[0068] Comparative Example 1

[0069] The same method as in Example 3 was used, but the IPDI compositions used were samples 1 and 8, respectively, to obtain reaction liquids of different batches.

[0070]

[0071] The results in the above table show that the reactivity of the isophorone diisocyanate compositions of the six batches tested in Example 3 with the polyols was moderate, and the color and turbidity of the obtained reaction liquids were low, and the residual monomer content was less than 0.01%, which had obvious advantages compared with the comparative examples.

[0072] The above examples illustrate the detailed methods of the present application, but the present application is not limited to the above detailed methods, i.e., it does not mean that the present application must rely on the above detailed methods to be implemented. Those skilled in the art should understand that any improvement on the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present application.

Claims

1. An isophorone diamine composition, characterized in that, The isophorone diamine composition contains 0.0001-0.0500 wt% of a hydroxynitrile compound; the hydroxynitrile compound is 3-acrylonitrile-3,5,5-trimethylcyclohexanol.

2. The composition according to claim 1, characterized in that, The content of hydroxynitrile compound in the isophorone diamine composition is 0.0001-0.0300 wt%.

3. The composition according to claim 1, characterized in that, The content of hydroxynitrile compound in the isophorone diamine composition is 0.0005-0.0300 wt%.

4. The composition according to claim 1, characterized in that, The method for preparing the hydroxynitrile compound includes the following steps: a) In the presence of a hydrogenation catalyst, hydrogen and isophorone nitrile are mixed and reacted in a 1-5 wt% KOH ethanol solution to obtain 3-cyano-3,5,5-trimethylcyclohexanol. b) Separate and purify the reaction product obtained in step a).

5. The composition according to claim 4, characterized in that, The hydrogenation reaction in step a) is carried out at a temperature of 50-200℃ and a pressure of 0.3-2MPa. The catalyst used is Raney copper and / or Raney nickel.

6. The composition according to claim 5, characterized in that, The hydrogenation reaction in step a) is carried out at a temperature of 50-150°C and a pressure of 0.5-1.5 MPa.

7. The composition according to claim 4, characterized in that, In step a), the mass ratio of the hydrogenation catalyst to the reaction feedstock isophorone nitrile is 1:100-1000.

8. The composition according to claim 4, characterized in that, In step a), the mass ratio of the hydrogenation catalyst to the reactant isophorone nitrile is 1:200-750.

9. An isophorone diisocyanate composition, characterized in that, Using the isophorone diamine composition according to any one of claims 1-8 as raw material, a phosgenation reaction is carried out.

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