JPS6160826B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for directly synthesizing the corresponding isocyanate from an aromatic nitro compound and carbon monoxide. More specifically, the present invention comprises a mixture of a platinum metal compound and a heteroaromatic nitrogen compound, a complex of a platinum metal compound and a heteroaromatic nitrogen compound, and a mixture of the complex and a heteroaromatic nitrogen compound. In the presence of a catalyst system consisting of at least one main catalyst selected from the group and a co-catalyst of a composite metal oxide of zinc and molybdenum, an aromatic nitro compound and carbon monoxide are reacted under high temperature and pressure. The present invention relates to a method for producing isocyanate. Isocyanates are practically extremely useful substances mainly as raw materials for polyurethane, and among them, tolylene diisocyanate is produced on the largest scale. The current industrial method for producing isocyanates is to reduce a nitro compound to an amine, and then react the amine with phosgene, which is separately synthesized from carbon monoxide and chlorine, to obtain an isocyanate. However, it would be desirable if aromatic isocyanates could be produced by directly reacting nitro groups with carbon monoxide and converting them into isocyanate groups in the process without using hydrogen or chlorine or handling highly toxic phosgene. This direct isocyanation method is economically advantageous because isocyanate can be produced from a nitro compound in a one-step reaction without producing hydrochloric acid as a by-product. An aromatic nitro compound and carbon monoxide are reacted at high temperature and pressure in the presence of a suitable catalyst containing a platinum group metal compound as a main component according to the following formula to form an aromatic Ar(NO ₂ )n+3nCO
→Ar(NCO)n+2nCO ₂ ...(1) Methods for directly synthesizing aromatic isocyanates are well known, and many various catalyst systems using platinum group metal compounds as main catalysts have been proposed, but none have been put into practical use yet. . As a catalyst system for the direct synthesis of aromatic isocyanates according to reaction formula (1), for example,
22722 (method using oxides of palladium, molybdenum, tungsten, niobium, chromium and tantalum), US Patent No. 3576835 (method using addition of heterocyclic compound or complex thereof), Tokko Sho
47-38436 (a method using a composition of two or more heavy metals), Japanese Patent Publication No. 48-43108 (a method in which iron oxide particles are added to molybdenum or chromium oxide), etc. are known. However, in these methods, even if a large amount of catalyst is used, the yield of isocyanate is extremely low, and the platinum metal compound as the main catalyst is significantly decomposed. JP-A-47-13525 (method using iron or manganese molybdate and East German patent no.
No. 123807 (a method using a composite oxide of iron and palladium) describes a high yield. However, in these cases as well, the main catalyst decomposes during the reaction and palladium is precipitated and deposited on the reactor wall, making it difficult to recover the expensive catalyst and making it impractical. The present inventors have proposed a method using a composite oxide of nickel and molybdenum (Japanese Unexamined Patent Publication No. 79251/1983) or a composite oxide of copper and molybdenum (Japanese Patent Application No. 67629/1989) to improve the above-mentioned drawbacks. As a result of further research, it was discovered that a composite oxide of zinc and molybdenum has excellent catalyst activation and stabilizing effects. That is, although zinc oxide itself exhibits a negative effect as a co-catalyst, the composite oxide of zinc and molybdenum surprisingly exhibits a much better co-catalyst effect than molybdenum oxide itself. It has been found that a very highly active carbonylation catalyst is formed in the presence of , and the recovery of the catalyst is facilitated. Based on this discovery, the present inventors succeeded in solving the above-mentioned drawbacks of the direct isocyanate synthesis method, and completed a method for easily producing aromatic isocyanates using a practical method. The main object of the present invention is to provide a method for producing the corresponding isocyanates from aromatic nitro compounds in high yields using a new highly active and practical catalyst system. Another object of the present invention is to use zinc as a co-catalyst to increase the catalytic activity of the platinum group metal compound as the main catalyst, and at the same time, suppress metal precipitation of the platinum group metal to extend the catalyst life and facilitate catalyst recovery. The object of the present invention is to provide a method for using a composite oxide of molybdenum and molybdenum, and also to provide a method for preparing the same. The method according to the invention comprises a mixture of a platinum metal compound and a heteroaromatic nitrogen compound, a complex of a platinum metal compound and a heteroaromatic nitrogen compound, a mixture of said complex and a heteroaromatic nitrogen compound. The aromatic nitro compound is reacted with carbon monoxide under high temperature and pressure in the presence of a catalyst system consisting of at least one selected main catalyst and a co-catalyst of a composite metal oxide of zinc and molybdenum to produce the corresponding isocyanate. It consists in direct synthesis. The aromatic nitro compound used as a raw material in the present invention is an aromatic mono- and polynitro compound having 32 or less carbon atoms, and may contain an isocyanate group and a substituent that does not react with the isocyanate group. Representative examples include, for example, nitrobenzene, O-, m- and P-nitrotoluene, O-nitro-P-xylene, nitromesitylene 1-chloro-2-nitrobenzene, 1,2-dichloro-4-nitrobenzene, 1-bromo- 4-nitrobenzene, 1-fluoro-4-nitrobenzene, 1-trifluoromethyl-4-nitrobenzene, O-, m- and P-
Nitrophenyl isocyanate, O- and P-nitroanisole, O- and P-nitrophenetol, nitrobenzaldehyde, nitrobenzoyl chloride, methylnitrobenzoate, nitrobenzenesulfonyl chloride, nitrobenzonitrile, 2-isocyanate-4-nitrotoluene ,
2-nitro-4-isocyanate toluene, 2-
Isocyanate-6-nitrotoluene, nitronaphthalene, 5-nitronaphthyl isocyanate,
Nitroanthracene, (4-isocyanatephenyl)-(4'-nitrophenyl)methane, m-dinitrobenzene, 2,4-dinitrotoluene, 2,
6-dinitrotoluene, α,α′-dinitro-P
-xylene, dinitromesitylene, 1-chloro-
2,4-dinitrobenzene, 2,4-dinitroanisole, 1,5-dinitronaphthalene, 4,
4'-dinitrobiphenyl, 3,3'-dimethyl-
4,4'-dinitrobiphenyl, bis(P-nitrophenyl)methane, bis(P-nitrophenyl)
Examples include ether, bis(P-nitrophenyl)thioether, bis(P-nitrophenyl)sulfone, trinitrobenzene, and the like. Among these, nitrobenzene, 2,4-
and 2,6-dinitrotoluene, 1,2-dichloro-4-nitrobenzene, 1,5-dinitronaphthalene, bis(P-nitrophenyl)methane, etc. are preferably used for practical purposes. Platinum group metal compounds used as main catalysts include halides of ruthenium, rhodium, palladium, osmium, iridium, or platinum;
nitrates, isocyanides, carbonates, carboxylates,
Examples include inorganic compounds such as oxides and chelates, and organic complexes containing ligands such as carbonyl, alkyl, olefin, and π-allyl groups. Preferred are compounds containing halogen, such as palladium chloride, palladium bromide, palladium iodide, sodium chloropalladate, tetraammine palladium chloride, dichlorodiammine palladium, rhodium chloride, rhodium bromide, rhodium iodide, rhodium chloride acid. Examples include sodium, ammonium rhodate chloride, bis-ethylene palladium chloride, bis-π-allyl palladium chloride, and the like. In the case of a platinum group metal compound that does not contain a halogen, it is desirable to separately add a halogen-containing compound such as a hydrogen halide, a halogenated hydrocarbon, or an acid halide. The heteroaromatic nitrogen compound that acts as a ligand to the platinum group metal of the main catalyst is a compound consisting of an aromatic ring containing a nitrogen atom, such as pyrrole, N-methylpyrrole, pyrazole, imidazole, triazole, Pyridine, α-, β or γ-picoline, 4-phenylpyridine, 4-vinylpyridine, 2-fluoropyridine, 2-chloropyridine, 3-chloro-pyridine, 2-bromopyridine, 3-hydroxypyridine, 2- Methoxypyridine, α-picolinaldehyde, α-picolinate methyl ester, α-picolinamide, 2,
6-dimethylpyridine, 2methyl-4-ethylpyridine, 2-chloro-4-methylpyridine, 2,
6-dicyanopyridine, 5,6,7,8-tetrahydroquinoline, 5,6,7,8-tetrahydroisoquinoline, quinoline, isoquinoline, acridine, benzoquinoline, benzisoquinoline, phenanthridine, pyridazine, pyrimidine, pyrazine, cinnoline , quinazoline, quinoxaline,
Examples include phthalazine, naphthyridine, and phenazine. Typical examples of complexes of platinum group metal halides with heteroaromatic nitrogen compounds include palladium and rhodium, such as bis(pyridine) dichloropalladium (), bis(pyridine) dibromopalladium (), and bis(pyridine). Diiodopalladium (), bis(α-picoline) dichloropalladium (), bis(quinoline) dichloropalladium (), bis(isoquinoline) dichloropalladium, (pyridine) (carbonyl) dichloropalladium (), (2,6-dimethyl pyridine)(carbonyl)dichloropalladium(), tris(pyridine)trichlorodium(), tris(pyridine)tribromorodium(), tris(γ-picoline)trichlororhodium(), tris(isoquinoline)trichlororhodium(), etc. be. Although the production of isocyanate by carbonylation of aromatic nitro compounds proceeds even in the presence of the above-mentioned main catalyst alone (US Pat. No. 5,376,835),
As is clear from the comparative examples described below, the catalyst activity is too low and the yield of isocyanate is extremely low. Using molybdenum trioxide (Japanese Patent Publication No. 45-22722) or a mixture of molybdenum trioxide and zinc oxide as a co-catalyst for the above main catalyst improves the yield, but it is far from practical, and the main catalyst is reductively decomposed into a metallic state. It is difficult to recover the catalyst because it is not suppressed. The activity and recovery of the catalyst are most closely related to the economic efficiency of the direct isocyanate production method, and the reason why the direct method has not yet been commercialized is due to the above-mentioned fact. Therefore, it is important to develop co-catalysts that can form highly active catalysts from low-activity platinum group metal catalysts and facilitate the recovery of expensive main catalysts, and the present invention improves the aforementioned drawbacks in this regard. . The promoter used in the present invention is a composite metal oxide consisting of zinc and molybdenum. It is not just a mixture of zinc oxide and molybdenum trioxide and is generally prepared as follows. That is, the composite metal oxide consists of zinc and molybdenum metal powders, oxides,
It can be obtained by mixing zinc and molybdenum metals or compounds selected from acids, inorganic salts, and organic salts in a conventional manner, and optionally pulverizing and firing. Inorganic salts include nitrates, halogenates, sulfates, ammonium salts, hydroxides, sulfides, carbonates, phosphates, etc., and organic salts include organic acids such as formic acid, acetic acid, oxalic acid, and naphthenic acid. Salts, alkoxides and phenoxides, chelate compounds, etc. are used. Both zinc and molybdenum raw materials as mentioned above have an atomic ratio of zinc to molybdenum of 0.01 to 100, preferably 0.1 to 10.
Usually in proportions of 100 to 300 before or after mixing in suspension or solution with a medium such as water
Dry and pre-fired at 300-1000℃, then
Preferably at 400-700℃, in air or oxygen.
Baked for ~100 hours, preferably 3-20 hours.
The composite metal oxides composed of zinc and molybdenum thus obtained are ZnMoO ₄ , Zn ₃ Mo ₂ O ₉ ,
It contains substances such as Zn ₃ MoO ₆ , ZnMo ₂ O ₇ , ZnMo ₃ O ₁₀ and ZnMo ₃ O ₈ . The composite oxide of zinc and molybdenum synthesized as described above is used as the co-catalyst, but it can also be used by being supported on a carrier by a conventional method. Examples of carriers include silica, alumina, silica alumina, zeolite, carbon, celite,
A wide variety of commonly used carriers can be used, such as bentonite, diatomaceous earth, activated clay, calcium carbonate, barium sulfate, asbestos, and the like. Supporting a cocatalyst can adjust the activity of the catalyst and facilitate the handling and recovery of the catalyst, and the reaction can be easily carried out as a fixed bed, fluidized bed or moving bed catalyst mode. The reaction between aromatic nitro compounds and carbon monoxide takes place in the presence of a catalyst system consisting of a main catalyst and a co-catalyst. The amount of catalyst used in this case is that the main catalyst is the platinum group metal in an amount corresponding to usually 0.001 to 10% by weight, preferably 0.1 to 5% by weight of the nitro compound, and the co-catalyst is the total metal of zinc and molybdenum. The amount used is usually from 0.01 to 100 atomic ratios, preferably from 0.2 to 10 atomic ratios to the platinum group metal. In addition, the amount of heteroaromatic nitrogen compound used is
The molar ratio to the platinum group metal is usually 1 to 500, although it varies depending on the reaction conditions, preferably 2 to 500.
100 molar ratio. The method of adding the catalyst is not specified, and the catalyst can be mixed with the reaction raw materials in any order and reacted. Since the co-catalyst is insoluble, it can be easily separated and recovered, and it can also be used as a fixed bed catalyst by filling a reactor in advance and using a conventional method. Synthesis of 2,4-tolylene diisocyanate [hereinafter abbreviated as TDI] from 2,4-dinitrotoluene [hereinafter abbreviated as DNT] in the presence of dichlorobis(pyridine)palladium and molybdenum trioxide by the above-mentioned known method. If the reaction is carried out for a long time, the DNT conversion rate will not reach 100% and the TDI
In addition to the low yield, the palladium compound used as a catalyst is reduced by carbon monoxide to produce metallic palladium, which adheres firmly to the reactor wall and forms a so-called mirror surface, resulting in catalyst loss. The drawback was that it was difficult to recover the active and expensive palladium catalyst. On the other hand, even if the promoter of the present invention is used in a small amount, this phenomenon caused by undesirable reduction of the palladium catalyst can be prevented.
Not only can the main catalyst be used effectively and TDI can be obtained in high yield, but the main catalyst and co-catalyst can be easily recovered. All catalyst components contained in the reaction solution can be separated from the product by conventional chemical engineering operations such as filtration, centrifugation, distillation, extraction, etc., and can be used again as a catalyst in the reaction. Although the method of the present invention can be carried out without using a solvent, it is preferable to dilute the aromatic nitro compound with a solvent before reacting. The solvent used is any liquid that is inert to the raw materials and products, and is not particularly limited, but typically includes heptane, isooctane, cyclohexane, benzene, toluene, xylene, and various petroleum distillates. aliphatic, cycloaliphatic and aromatic hydrocarbons, such as
For example, halogenated hydrocarbons such as dichloromethane, perchloroethylene, tetrachloroethane, chlorobenzene, dichlorobenzene, and chloronaphthalene are used. The amount of the solvent to be used is not particularly limited and is completely arbitrary, and the appropriate amount varies depending on the type of reaction. However, the amount used usually ranges from 3 to 50% by weight of the aromatic nitro compound in the solvent. There is no particular restriction on the method of mixing the solvent, and the solvent can be mixed with the aromatic nitro compound, the main catalyst, and the co-catalyst in any order and proportion. The amount of carbon monoxide consumed as a reaction raw material is stoichiometrically 3 per mole of nitro group according to formula (1).
mol, and 2 mol of carbon dioxide is produced as a by-product at the same time. The amount of carbon monoxide actually used in the reactor varies depending on the concentration of the aromatic nitro compound, the amount of catalyst used, the type of reactor, reaction temperature, reaction pressure, etc., but the appropriate amount is the minimum amount. The limit is 3 times the mole amount relative to the amount of nitro groups in the reactor, usually 3 to 100 times the mole, preferably 5 to 20 times the mole. In addition, the reaction can be carried out batchwise while containing carbon dioxide as a by-product, but carbon monoxide is supplied at the same time as carbon dioxide, which increases as the reaction progresses, is removed from the reactor. It is preferable to carry out the reaction while keeping the molar ratio of carbon dioxide in the reactor small. Reaction temperature is 100-250℃, preferably 150-230℃
range is used. Reaction pressure is 10-1000Kg/cm ² , usually 50-500
A range of Kg/cm ² is used. The reaction time is usually in the range of 0.5 to 10 hours, and the practical optimum time is determined within this range depending on the selection of the above conditions. To elaborate on embodiments of the invention, the reaction can be carried out batchwise, semi-continuously or continuously. Usually, a solution of an aromatic nitro compound in a solvent and each component of the catalyst are mixed before the reaction or are separately charged (batch type) or fed (continuous type) into a reactor. Incidentally, the co-catalyst can also be filled in the reactor in advance to form a fixed bed. The reactor is pressurized with carbon monoxide to reaction pressure and maintained at reaction temperature. In the continuous type, the carbon dioxide mixture gas in the reactor is continuously discharged and carbon monoxide is injected under pressure. After a predetermined period of time, the reaction mixture is cooled to room temperature and subjected to gas-liquid separation, and then an insoluble catalyst consisting of a portion of the main catalyst and a co-catalyst is separated and recovered through a solid-liquid separation operation. The resulting reaction mixture was
It is subjected to distillation, extraction, etc., and is divided into product isocyanate, solvent, remaining main catalyst, and by-products. The recovered catalyst and solvent are exhausted or, if necessary, subjected to appropriate treatment and used again in the reaction. Furthermore, if a small amount of raw materials or nitroisocyanate intermediates when a polynitro compound is used as a raw material remain in an unreacted state in the reaction mixture, these are also separated and recycled to the reactor at the same time. The product isocyanate is subjected to conventional purification operations depending on the intended use. Thus, according to the method of the present invention, the corresponding isocyanates can be economically produced in high yields from aromatic nitro compounds by using highly active catalyst systems. EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.
When carrying out the high-temperature and pressurized reaction between aromatic nitro compounds and carbon monoxide in an autoclave, the reaction is carried out on the inner wall of the autoclave in order to avoid contamination of the autoclave due to adhesion of the metal components of the catalyst to the vessel wall as described above. It is carried out in a glass container inserted in close contact, and results with good reproducibility are obtained. However, as a result, no adhesion of the metal to the container wall was observed in the reaction using the catalyst of the present invention, and similar results were obtained even when the reaction was carried out without using a glass container. Next, a method for producing the co-catalyst used in the Examples will be described below. (1) Cocatalyst (A) 17.7g of ammonium paramolybdate and 200ml of water
29.7 g of zinc nitrate was added to the aqueous solution.
After adding 100 ml, it was evaporated to dryness on a steam bath.
The lumps were crushed, precalcined at 300°C for 2 hours under air circulation, further crushed, calcined at 550°C for 8 hours, and rapidly cooled to produce 22.0 g of grayish white fine powder as cocatalyst A.
was gotten. According to the analysis, Zn and Mo are almost 1:
It has a composition of ZnMoO ₄ of 1. (2) Co-catalyst (B) Co-catalyst B with a composition of ZnO・MoO ₃ (1:4) was prepared in the same manner as in (1) except that 7.44 g of zinc nitrate was used.
15.8g of was obtained. (3) Cocatalyst (C) Add 20 ml of an aqueous solution of 1.77 g of ammonium paramolybdate to a slurry of 9.2 g of Cyroid AL-1 (high purity silica fine powder manufactured by Tomito Davison) and 30 ml of water, and add zinc nitrate while stirring. 2.97g of 10
ml aqueous solution was added. The product was evaporated to dryness, pulverized, and calcined in the same manner as in (1) to obtain 10.1 g of supported cocatalyst C.
The loading rates of Zn and Mo are 6.28wt% and 9.31wt, respectively.
It was %. (4) Cocatalyst (D) 10.8 g of cocatalyst D was prepared in the same manner as in (3) except that Celite 505 (diatomaceous earth manufactured by Johns-Manville) was used as the carrier instead of Thyroid AL-1.
Obtained. The loading rate of Zn and Mo is 5.87wt each.
% and 8.70wt%. (5) Cocatalyst (E) 3.53 g of ammonium paramolybdate was dissolved in 50 ml of water, and 1.6 g of oxalic acid was added. On the other hand, 2.87 g of zinc chloride (95% product) was dissolved in 30 ml of water, and 6.6 g of aqueous ammonia was added. After mixing both, ZnO・MoO ₃ (1:
4.3g of co-catalyst E of 1) was obtained. (6) Cocatalyst (F) Add molybdic acid to 50ml aqueous solution of 5.95g zinc nitrate.
After adding 3.60 g, 4.1 g of ZnO・MnO ₃ (1:1) promoter F was obtained by processing in the same manner as in (1).
Obtained. (7) Cocatalyst (G) 1.44 g of molybdenum trioxide, 0.81 g of zinc oxide, and 9.2 g of Thyroid AL-1 were thoroughly ground and mixed, calcined at 400°C for 3 hours, finely ground, and further
Cocatalyst G was 10.4 by calcining at ℃ for 5 hours.
g was obtained. The loading rates of Zn and Mo are respectively
They were 6.04wt% and 8.86wt%. (8) Cocatalyst (H) A 50 ml aqueous solution of 2.42 g of sodium molybdate was added to a 50 ml aqueous solution of 2.19 g of zinc acetate, and after heating with stirring for 1 hour, the precipitate was separated, and the white solid was further washed with water several times. . After drying this, it was crushed and calcined in the same manner as in (1) to obtain 3.5 g of cocatalyst H containing ZnMoO ₄ as the main component. Example 1 8.00 g of DNT, 1.120 g of dichlorobis(pyridine) palladium as a catalyst, 0.752 g of promoter A, and 104.0 g of O-dichlorobenzene as a solvent were charged into a glass container inserted into an autoclave (200 ml, SUS316). . The autoclave was purged twice with 20 kg/cm ² of carbon monoxide and then pressurized to 170 kg/cm ² . for 30 minutes while stirring the contents at 1000 rpm.
When the temperature was raised to 200°C, the internal pressure reached 260 Kg/cm ² , and when the temperature was maintained for 5 hours, the internal pressure decreased to 233 Kg/cm ² . The autoclave was cooled, depressurized, and the contents separated. According to gas chromatography, the liquid
TDI5.618g, 2-nitro-4-isocyanatetoluene (hereinafter abbreviated as 2N4I) 0.023g, 2-
Isocyanate-4-nitrotoluene (hereinafter
(abbreviated as 2I4N) and 0.055 g of DNT. From this analysis value, DNT conversion rate is 99.3%, TDI yield
73.7%, 2N4I yield of 0.3%, and 2I4N yield of 2.3% were obtained. The main catalyst palladium compound and co-catalyst were recovered from a separate cake, and the main catalyst was also recovered from the residue from which the product was separated by distillation with chloroform. Example 2 DNT6.00g, dichlorobis(quinoline)palladium 0.246g, cocatalyst A0.127g, quinoline 1.96g
Prepare 78.0g of O-dichlorobenzene and 210℃
When reacting in the same manner as in Example 1 except that heating was performed,
DNT conversion rate 100%, TDI yield 76.1%, 2N4I yield 0.2
%, a 2I4N yield of 1.5% was obtained. No deposition of palladium on the vessel wall due to reductive decomposition of the catalyst was observed, and the catalyst was recovered from the reaction solution. Example 3 Palladium chloride 0.100g, pyridine as catalyst
Example 2 except that 1.20 g and 0.149 g of cocatalyst B were used.
The reaction was carried out in the same manner. DNT conversion rate 99.0%, TDI
A yield of 68.0%, a 2N4I yield of 3.5%, and a 2N4I yield of 6.8% were obtained. Examples 4 to 9 Instead of promoter B, promoters C, D, E, F,
The reaction was carried out in the same manner as in Example 3, except that G and H were used in amounts equivalent to equimole with palladium chloride (amounts listed in Table 1). The results are shown in Table 1 together with the results of Example 3.

[Table] Examples 10 to 12 3.00g of DNT in a 100ml autoclave, No. 2 below.
0.282 mmol of platinum metal catalyst, 0.141 mmol of heteroaromatic nitrogen compound, cocatalyst listed in the table
0.032 g of A and 39.0 g of O-dichlorobenzene were charged and reacted at 220° C. in the same manner as in Example 2. The results are shown in Table 2.

[Table] Example 13 The reaction was carried out in the same manner as in Example 2 except that 4.06 g of nitrobenzene was used instead of DNT. As a result, a nitrobenzene conversion of 100% and a phenyl isocyanate yield of 85.0% were obtained. Comparative Examples 1 to 4 In order to clearly demonstrate the effect of the catalyst of the present invention, there were cases in which a mixture of zinc oxide and molybdenum trioxide was used instead of promoter A (Comparative Example 1), and cases in which only zinc oxide was used ( Comparative Example 2), a case where only molybdenum trioxide was used (Comparative Example 3), and a case where no promoter was used at all (Comparative Example 4) were conducted as comparative examples. Zinc oxide and molybdenum trioxide are high purity reagents.
Example 1 using fine powder dried at 200°C for 2 hours
The reaction was carried out in exactly the same manner as in Example 1, except that the same amount as that contained in co-catalyst A was used. The results obtained are shown in Table 3 together with the results of Example 1.

[Table] Zinc oxide does not exhibit a cocatalyst effect by itself (comparison of Comparative Examples 2 and 4), and even shows a negative effect when added to a known method (Comparative Example 3) (Comparative Example 1). . However, in the case of the present invention (Example 1), the yield of the target product TDI is much higher than in the comparative example, and the reductive decomposition of the main catalyst is suppressed, and the remarkable effect of the co-catalyst of the composite metal oxide is recognized. . Comparative Example 5 A reaction was carried out in the same manner as in Example 3, except that instead of promoter B, palladium chloride and equimolar amounts of zinc oxide and molybdenum trioxide were used. The results are shown in the bottom row of Table 1 in comparison with Examples 4 to 9. As is clear from this, the TDI yield is extremely low compared to the cocatalyst according to the present invention.

Claims (1)

[Scope of Claims] 1. An aromatic nitro compound and carbon monoxide, a mixture of a platinum group metal compound and a heteroaromatic nitrogen compound, a complex of a platinum group metal compound and a heteroaromatic nitrogen compound, a complex of the above complex and a heteroaromatic nitrogen compound, at least one selected from the group consisting of: a mixture of aromatic cyclic nitrogen compounds;
A method for producing an aromatic isocyanate, which comprises using a composite metal oxide containing zinc and molybdenum as a co-catalyst in the method for producing an isocyanate by reacting in the presence of a seed catalyst. 2. A composite metal oxide containing zinc and molybdenum is prepared by mixing zinc and molybdenum compounds selected from oxides of zinc and molybdenum, inorganic salts, and organic salts and firing the mixture at a temperature of 300 to 1000°C. A method for producing an aromatic isocyanate according to claim 1.