JPS6342615B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for directly synthesizing corresponding isocyanates from aromatic nitro compounds and carbon monoxide. More specifically, the present invention provides at least one main catalyst selected from the group consisting of a mixture of a noble metal compound and a heteroaromatic nitrogen compound, and a mixture of the nitrogen compound and a complex of a noble metal coordinated with the nitrogen compound. A heteroaromatic nitrogen compound is combined with a noble metal compound and or The present invention relates to a method for directly producing a corresponding aromatic isocyanate by reacting an aromatic nitro compound and carbon monoxide at high temperature and pressure using a molar ratio of 10 to 500 times that of the complex. 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 isocyanates. 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 isocyanates 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 noble metal compound as the main component according to the following formula to form an aromatic Ar(NO ₂ )n+3nCO→Ar(NCO)n+2nCO ₂
...Methods for directly synthesizing group (1) isocyanates are known, and many various catalyst systems using noble metal compounds as main catalysts have been proposed, but they have not yet been put into practical use. This is because a large amount of main catalyst is required to carry out this reaction, and the yield of isocyanate is low. Catalyst systems containing salts of group A metals for synthesizing aromatic isocyanates according to reaction formula (1) include, for example, U.S. Pat. Methods using these halides and the like are known, but even if a large amount of catalyst is used, the yield of isocyanates is extremely low. Also, special public service in 1977-
No. 43110 discloses a method in which a mixture of palladium halide and pyridine or isoquinoline, or a complex thereof, is used as the main catalyst, and a halide of a non-noble metal containing a Group A metal is used as a co-catalyst. It is stated that even if palladium is used as a cocatalyst at 4.9% by weight (8.3% by mole based on the nitro group) of the raw material dinitrotoluene, the isocyanate yield is as low as 23%, and the rest becomes by-products. There is. In other words, these catalyst systems have low activity and selectivity, and the main catalyst, which is made of expensive precious metals, decomposes during the reaction and plate-out adheres to the reactor wall, losing catalytic activity and causing the catalyst to deteriorate. Recovery will also be difficult. The inventors have identified these drawbacks,
As a method to improve the particularly low activity, the use of a heteroaromatic cyclic nitrogen compound as a cocatalyst of at least one cyclopentadienyl halide and -oxyhalide compound of a Group A metal and a noble metal compound and/or The activity of the catalyst system containing this cocatalyst, which we previously applied for using a method using a 10 to 500 times molar ratio to the complex, is much higher than conventional methods, and it is possible to obtain isocyanates in high yields using a small amount of noble metal. Although this has become possible, further improvement in reaction selectivity was desired in order to implement it industrially. Therefore, the present inventors conducted research focusing on the selectivity of the catalyst, and found that the selectivity was significantly improved by coexisting an appropriate amount of phosphorus oxytrichloride.
The present invention was completed after repeated studies on the usage conditions. The main object of the present invention is to provide a method for industrially producing the corresponding isocyanates from aromatic nitro compounds using a novel catalyst system with the highest level of activity and selectivity. That is, the present invention provides at least one main catalyst selected from the group consisting of a mixture of a noble metal compound and a heteroaromatic nitrogen compound, and a mixture of a noble metal complex coordinated with the nitrogen compound and the nitrogen compound; A heteroaromatic nitrogen compound is mixed with a noble metal compound and/or a complex thereof in the presence of a cocatalyst consisting of at least one cyclopentadienyl halide and -oxyhalide compound of a Group A transition metal of the periodic table and phosphorus oxytrichloride. used at a molar ratio of 10 to 500 times,
This is a method for directly producing isocyanate by reacting an aromatic nitro compound with carbon monoxide at high temperature and pressure. The aromatic nitro compounds used as raw materials in the present invention are aromatic mono- and polynitro compounds, and may contain an isocyanate group and a substituent that does not react with the isocyanate group. Representative examples include 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-isocyanatetoluene, 2-isocyanate- 6
-Nitrotoluene, nitronaphthalene, 5-nitronaphthylisocyanate, 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)ether, bis(P-
Examples include nitrophenyl)thioether, bis(P-nitrophenyl)sulfone, and trinitrobenzene. 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. The noble metal compounds used as the main catalyst include inorganic compounds such as halides, nitrates, isocyanides, carbonates, carboxylates, oxides, and chelates of ruthenium, rhodium, palladium, osmium, iridium, or platinum;
Examples include organic complexes containing ligands such as alkyl, offrein, 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, and sodium chloride rhodate. , ammonium chloride rhodate,
Bis-ethylene palladium chloride, bis-π-
Examples include allyl palladium chloride. In the case of a noble metal compound that does not contain a halogen, it is desirable to separately add a halogen-containing compound such as a hydrogen halide, phosgene, a halogenated hydrocarbon, or an acid halide. The heteroaromatic nitrogen compound that acts as a ligand to the noble 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 -Picolinic acid 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, benzoisoquinoline, phenanthridine, pyridazine, pyrimidine, pyrazine, cinnoline, quinazoline , quinoxaline, phthalazine, naphthyridine, phenazine and the like. Typical examples of complexes of noble metal halides with heteroaromatic nitrogen compounds include palladium and rhodium, such as bis(pyridine).
Dichloropalladium (), bis(pyridine) dibromopalladium (), bis(pyridine) diiodopalladium (), bis(α-picoline) dichloropalladium (), bis(quinoline) dichloropalladium (), bis(isoquinoline) dichloropalladium , (pyridine) (carbonyl) dichloropalladium (), (2,6-dimethylpyridine) (carbonyl) dichloropalladium (),
Tris (pyridine), trichlororhodium (),
tris(pyridine) tribromorodium (),
Examples include tris(γ-picoline) trichlororhodium () and tris(isoquinoline) trichlororhodium (). The production of isocyanates by carbonylation of aromatic nitro compounds proceeds even in the presence of the above-mentioned main catalyst alone (US Pat. No. 3,576,835).
As is clear from the comparative examples described below, the catalyst activity is too low and the yield of the target isocyanates is extremely low. The economic efficiency of direct production of isocyanates is most closely related to catalyst activity, selectivity and recovery.
Therefore, it is most important to develop a co-catalyst that increases the activity and selectivity of the main catalyst containing precious metals and facilitates the recovery and reuse of expensive precious metal catalysts, and the present invention improves the above-mentioned drawbacks in this regard. A new catalyst system has been developed. The co-catalyst used in the present invention consists of a cyclopentadienyl halide or -oxyhalide compound of a Group A transition metal of the periodic table and phosphorus oxytrichloride. The former are generally CpMX ₃ , Cp ₂ MX, Cp ₂ MX,
Cp ₂ MX ₂ , Cp ₂ MX ₃ , CpMOX ₂ (where Cp is a cyclopentadienyl group, M is vanadium, niobium or tantalum, and X is chlorine, bromine or iodine). Specifically, for example, CpVCl ₃ , CpVBr ₃ ,
Cp ₂ VCl, Cp ₂ VBr, Cp ₂ VI, Cp ₂ VCl ₂ ,
Cp ₂ VBr ₂ , Cp ₂ NbCl, Cp ₂ NbBr ₃ , Cp ₂ TaBr ₃ ,
CpVOCl ₂ , CpVOBr ₂ and the like are used, preferably (cyclopentadienyl)vanadium trichloride, di(cyclopentadienyl)vanadium dichloride, di(cyclopentadienyl)vanadium dibromide, (cyclopentadienyl)vanadium Oxydichloride is used. Report by Nefedov et al. [Dokl, Akad.Nank
SSSR, Vol. 246, p. 118 (1979)], the pressurized reaction of nitrobenzene and carbon monoxide was carried out using a catalyst consisting of palladium chloride and pyridine (four times the mole of palladium chloride) to react with di(cyclopentadienyl). The atomic ratio of vanadium dichloride is V/Pd=
It has been found that when added at step 1, no phenyl isocyanate is formed and aniline is obtained in a yield of 65%. That is, they claim that the catalyst system of palladium chloride and this vanadium compound is a catalyst for synthesizing aniline from aromatic mononitro compounds. In the above literature, the reaction is carried out using a catalyst consisting of 0.4 or 9 times the molar amount of pyridine relative to palladium chloride, and it is said that aniline is selectively produced by adding the vanadium compound. Although there is no experimental basis for this interpretation, in this catalyst system, the intermediate nitrene coordinated to the palladium pyridine complex does not react with carbon monoxide, and hydrogen is extracted from the cyclopentadienyl ring to form the aniline. It was thought that this was because it gave In contrast, the present inventors discovered that the palladium nitrene complex, which is considered to be a reaction intermediate for isocyanate production from aromatic nitro compounds, decomposes in the above catalyst system due to insufficient pyridine ligand concentration, resulting in isocyanate formation. I guessed that I wouldn't be able to get it. Furthermore, in order to catalytically react the nitrene complex with carbon monoxide, a large excess of nitrogen aromatic cyclic compound relative to palladium must be present as a ligand to effectively stabilize the nitrene complex as a catalytically active species. I thought it was necessary. Based on the expectation that if this could be done, a highly active isocyanate direct synthesis catalyst system could be constructed, the nitrogen aromatic cyclic compound was added at least 10 times the mole of the noble metal compound and/or the complex, for example, from 67 to 67 in the example. Repeated studies were conducted using 135 times the molar amount. Based on this main catalyst composition, it is surprisingly possible to produce aromatic aromas by a catalyst system consisting of a low concentration of a noble metal compound, a heteroaromatic nitrogen compound and a cyclopentadienyl halide or oxyhalide of a Group A transition metal. From the pressurized reaction of a group nitro compound and carbon monoxide, isocyanates can be obtained in a much higher yield than with conventionally known catalyst systems without producing amines. The cocatalyst consisting of cyclopentadienyl halide or -oxyhalide of the Group A transition metal has an extremely remarkable effect of promoting the reaction, so it is possible to reduce the amount of the noble metal main catalyst used to about 1/10 of the conventionally known amount. did it. Furthermore, in the present invention, phosphorus oxytrichloride is added as a cocatalyst to increase the selectivity of this catalyst system. As is clear from the examples, this effect can increase the selectivity from aromatic nitro compounds to isocyanate by about 10% compared to the above catalyst system, thereby further increasing the yield of isocyanate. It became possible. That is, based on the main catalyst system in which the nitrogen aromatic cyclic compound has a molar ratio of 10 to 500 times that of the noble metal compound and/or the complex, the compound of the Group A transition metal, which has a particularly remarkable catalyst activation effect, is used. In particular, by using phosphorus oxytrichloride, which greatly increases reaction selectivity, as a cocatalyst, the reaction can be carried out with the concentration of the main catalyst nitrogen compound reduced to an extremely low concentration (approximately 1/10) compared to conventional catalyst systems. It has also become possible to directly synthesize isocyanates with extremely high yields. Since the economic efficiency of the direct isocyanate production method is controlled by the concentration of expensive noble metal catalyst used, the above effect is extremely significant in reducing isocyanate production costs. Furthermore, the cocatalyst according to the present invention can be used together with various conventionally known additives. The catalyst component is supported on a known carrier such as silica, alumina, silica alumina, zeolite, carbon, celite, bentonite, diatomaceous earth, activated clay, calcium carbonate, barium sulfate, asbestos, or Can be used in combination. This adjusts the performance of the catalyst,
Handling and recovery can be facilitated. 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 the noble metal compound used as the main catalyst is in the range of 0.001 to 10 mol%, preferably 0.01 to 1.7 mol%, based on the nitro group in the raw material, and the heteroaromatic nitrogen compound is usually 10 to 500 times molar, preferably 20
to 200 times the molar range is used. The amount of vanadium compound used as a co-catalyst depends on the amount of main catalyst used.
The appropriate amount varies, but usually for noble metal compounds.
A molar ratio of 0.01 to 50 times, preferably 0.1 to 5 times, is used. In addition, phosphorus oxytrichloride is
Usually 0.1 to 100 times the mole of the noble metal compound,
Preferably, a 1 to 10-fold molar range is used. The method of adding the catalyst is not limited, and the catalyst can be mixed with the reaction raw materials by any method. 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 it is usually a solvent such as heptane, cyclohexane, benzene, toluene, xylene, or various petroleum distillates. aliphatic,
Alicyclic and aromatic hydrocarbons such as halogenated hydrocarbons such as dichloromethane, perchloroethylene, tetrachloroethane, chlorobenzene, dichlorobenzene, chloronaphthalene, etc. 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 5 to 100 times the mole, preferably 7 to 20 times the mole. In addition, the reaction can be carried out batchwise while containing the by-product carbon dioxide, but while the carbon dioxide that increases as the reaction progresses is removed from the reactor, at the same time carbon monoxide is recycled and replenished, monoxide It is preferable to carry out the reaction while keeping the molar ratio of carbon dioxide to carbon 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 dissolved in a solvent and each component of the catalyst are mixed before the reaction or are fed separately into the reactor. 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 has elapsed, the reaction mixture is cooled and subjected to gas-liquid separation, and then a portion of the main catalyst and co-catalyst are separated and recovered through a solid-liquid separation operation. The obtained reaction mixture is subjected to distillation, extraction, etc., and is separated into product isocyanates, solvent, and the remaining catalyst and by-products. The recovered catalyst and solvent are used again in the reaction after being exhausted or subjected to appropriate treatment if necessary. If a small amount of raw materials or nitroisocyanate intermediates when a polynitro compound is used as raw materials remain in the reaction mixture, these are simultaneously separated and recycled to the reactor. The product isocyanates are 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 a highly active catalyst system. EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto. Example 1 In an autoclave (SUS-316, 500ml),
4-dinitrotoluene (hereinafter abbreviated as DNT) 14.8
g, dichlorobis(quinoline)palladium 0.121
g, 0.070 g of di(cyclopentadienyl)vanadium dichloride, 0.086 g of phosphorus oxytrichloride, 4.86 g of quinoline and 192 g of 0-dichlorobenzene, and after replacing with carbon monoxide twice at 20 Kg/cm ² , the mixture was heated to 160 g.
The pressure was increased to Kg/cm ² . When the temperature is raised to 220℃ in about 1 hour while stirring (1000rpm), the internal pressure becomes 255Kg/cm ²
reached. After reacting at the same temperature for 5 hours, it was cooled to room temperature, the pressure was released, and the reaction solution was subjected to gas chromatography (15
% silicon DC550/gas chrome Q, biphenyl internal standard). This solution does not contain the raw material DNT, but contains 2,4-tolylene diisocyanate (hereinafter abbreviated as TDI) 6.471
g, 1.700 g of 2-nitro-4-isocyanate toluene (hereinafter abbreviated as 2N4IT) and 4-nitro-2-
Isocyanate toluene (hereinafter abbreviated as 4N2IT)
It contained 3.884g of. Even after the reaction, the catalyst was hardly separated out and remained dissolved in the reaction solution. Examples 2 and 3 Conversion rate of nitro group (hereinafter abbreviated as NO ₂ ) contained in DNT and useful generated isocyanate (TDI
In order to determine the relationship between the yield of its precursors 2N4IT and 4N2IT) and the isocyanate group contained therein (hereinafter abbreviated as NCO) yield*), the reaction was carried out in the same manner as in Example 1, except that the reaction time was changed. Ivy. The results of Examples 1, 2, and 3 are shown in Table 1 and FIG. 1. * (TDI for nitro group in DNT, 2N4IT,
(yield of all isocyanate groups contained in 4N2IT) Comparative Examples 1 to 5 In order to demonstrate the synergistic effect of the vanadium compound and phosphorus oxytrichloride as promoters, phosphorus oxytrichloride was not used in Comparative Examples 1 to 3. In Comparative Example 4, the reaction was carried out in the same manner as in Example 1, without using a vanadium compound, and in Comparative Example 5, using a catalyst system without using either co-catalyst. Table 1 shows the results.
is also shown in Figure 1.

[Table] From the comparison of Comparative Examples 4 and 5 in Table 1, it was found that the cocatalyst phosphorus oxytrichloride has the effect of simultaneously increasing the conversion rate and selectivity.The effect of improving the conversion rate is relatively small, but the selectivity The improvement effect is remarkable and noteworthy. On the other hand, from the comparison between Comparative Examples 1 and 5, it is understood that the vanadium co-catalyst has a particularly large activation effect on the catalyst. The method of using both cocatalysts according to the present invention at the same time shows the activity and selectivity of the catalyst system by comparing Examples 1 to 3 with Comparative Examples 1 to 3 or Comparative Example 4, respectively, in Table 1 and FIG. The effects of this can be understood. That is, from the NO ₂ conversion rate or TDI yield in Table 1,
It can be seen that the catalytic activity of the present invention is slightly lower than when only Cp ₂ VCl ₂ is used as a cocatalyst, but much higher than when only POCl ₃ is used. The feature of the catalyst of the present invention is particularly its selectivity, and as is clear from comparing the total isocyanate yield, NCO yield, and TDI yield in Figure 1 at the same nitro group conversion rate, both cocatalysts coexist simultaneously. When used, it is more effective than when used alone.
At a conversion rate of NO ₂ groups of 70% or more, each yield is approximately 10
% or more. That is, the catalyst system of the present invention exhibits a remarkable improvement in yield (particularly selectivity) due to the synergistic action of both co-catalysts. In a reaction like this example using a small amount of Pd as the main catalyst at 0.2% by weight based on DNT, the total isocyanate yield was 80%.
The excellent cocatalyst effect of the present invention is evident from the fact that an unprecedented high yield of 70% or a TDI yield of nearly 70% was obtained. Examples 4 to 8 Reactions were conducted in the same manner as in Example 1, except that the amounts of the vanadium compound and phosphorus oxytrichloride used as cocatalysts were set to predetermined values. The results are shown in Table 2.

[Table] Example 9 Autoclave (SUS-316, 200ml)
DNT6.00g, dichlorobis(pyridine)palladium 0.0755g, cyclopentadienylvanadium oxydichloride 0.0460g, oxytrichloride phosphorus
0.0693 g, pyridine 1.20 g, and 0-dichlorobenzene 78 g were charged, and the reaction was carried out in the same manner as in Example 1. DNT conversion rate is 93.0%, yield is TDI 36.8%,
A total of 83.5% was obtained with 2N4IT 15.5% and 4N2IT 31.2%. Comparative Example 6 A reaction was carried out in the same manner as in Example 9 without using phosphorus oxytrichloride. DNT conversion rate is 94.5%, yield is
Total at TDI37.2%, 2N4IT16.9% and 4N2IT16.9%
It was 71.0%. Example 10 As a catalyst, palladium chloride 0.0200g, di(cyclopentadienyl)niobium dichloride 0.0261g
The reaction was carried out in the same manner as in Example 9, except that 0.0347 g of phosphorus oxytrichloride and 1.96 g of quinoline were used.
DNT conversion rate is 99.0%, yield is TDI 36.0%,
A total of 85.0% was obtained with 2N4IT 13.8% and 4N2IT 35.2%. Comparative Example 7 The reaction of Example 10 was carried out in the same manner as in Example 10 using a catalyst system that did not contain phosphorus oxytrichloride. The DNT conversion rate was 99.2%, the yield was 30.9% for TDI, 12.1% for 2N4IT, and 34.2% for 4N2IT, for a total of 77.2%.

[Brief explanation of the drawing]

Figure 1 shows a cocatalyst according to the present invention (Cp ₂ VCl ₂ +
When using a catalyst system (A) containing POCl ₃ ), a catalyst system (B) containing only (Cp ₂ VCl ₂ ) as co-catalyst and a catalyst system (C) containing only (POCl ₃ ) as co-catalyst, Total isocyanate yield, NCO yield and
The relationship between TDI yield and NO ₂ conversion rate is shown. In the figure, 1, 1', 1" are the total isocyanate, NCO, and TDI yields of the A catalyst system, and 2, 2', 2" are the yields of B
The respective yields of total isocyanate, NCO, and TDI of the catalyst system; 3, 3', and 3'' represent the respective yields of total isocyanate, NCO, and TDI of the C catalyst system.

Claims (1)

[Claims] 1 A mixture of an aromatic nitro compound and carbon monoxide, a noble metal compound and a heteroaromatic nitrogen compound,
A method for producing isocyanates in which the reaction is carried out at high temperature and pressure in the presence of at least one catalyst selected from the group consisting of a complex of a noble metal coordinated with the nitrogen compound and a mixture of the nitrogen compound. table of laws
At least one of cyclopentadienyl halide and -oxyhalide compounds of group VA transition metals and phosphorus oxytrichloride are used as promoters, and a heteroaromatic nitrogen compound is added to the noble metal compound and/or the complex. A method for producing aromatic isocyanates, characterized in that aromatic isocyanates are used at a molar ratio of 1 to 500 times.