JPH0124784B2 - - 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 particularly, the present invention provides at least one compound selected from the group consisting of a mixture of a noble metal or a compound thereof and a heteroaromatic nitrogen compound, a complex of a noble metal coordinated with the nitrogen compound, and a mixture of the complex and the nitrogen compound. The present invention relates to a method for directly producing a corresponding aromatic isocyanate by reacting an aromatic nitro compound and carbon monoxide under high temperature and pressure by adding chlorine in the presence of a catalyst containing one type of catalyst. 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 one step, without using hydrogen or chlorine in the intermediate, and without 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 a main component according to the following formula to form an aromatic isocyanate Ar(NO ₂ ) _o +3nCO→Ar(NCO ) _o + _2nCO2
...() Methods for directly synthesizing compounds are well known, and many various catalyst systems using noble metal compounds as main catalysts have been proposed, but none have been put into practical use yet. In order to carry out this reaction, a large amount of expensive main catalyst is required, and in addition, the use of complex metal promoters and promoters makes it difficult to recover the catalyst, and furthermore, the yield of isocyanate is low. It is caused by As a method for directly synthesizing aromatic isocyanates using reaction formula (), for example, U.S. Patent No.
No. 3,576,835 discloses a method using a catalyst consisting of a mixture of a noble metal compound and a heteroaromatic nitrogen compound and a complex thereof, but even if a large amount of the catalyst is used, the yield of isocyanate is low and it is not practical. US Pat. No. 3,884,952 discloses a method in which an aromatic nitro compound is vaporized and the vapor is reacted with carbon monoxide in the gas phase in the presence of an active palladium catalyst and a halogen-donating gas. However, even with this method, the isocyanate yield is extremely low, and useful dinitro compounds that are difficult to evaporate cannot be used as raw materials. In JP-A-49-108001, the reaction is carried out in the presence of a catalyst consisting of a reduction metal and iodine or bromine, but only isocyanate is detected. In addition, as a method using halogen derivatives,
A method of adding hydrogen halide is known in JP-A No. 48-99144, but even if 2.5 mol% of palladium catalyst is used with respect to raw material 2,4-dinitroluene (hereinafter abbreviated as DNT), 2,4- The yield of tolylene diisocyanate (hereinafter abbreviated as TDI) is 38
%, and corrosion of the reactor due to hydrogen halides becomes a problem. In Japanese Patent Publication No. 45-35774, an acid halide (phosgene) is added to vanadium oxide as a co-catalyst.
A yield of TDI of 11.9% was obtained by using this method in combination, but this method is also not practical. On the other hand, in U.S. Pat. No. 3,481,968, a halogenated aromatic isocyanate is produced by reacting an aromatic nitro compound with a halogenated oxide, such as phosgene and carbon monoxide in the presence of a metal catalyst, albeit in a low yield. , provides a method for synthesis. As described above, isocytyl chloride is an isocyanate which uses iodine, bromine, or halogen derivatives such as hydrogen halides and acid halides as cocatalysts, reaction promoters, or reaction reagents in the reductive carbonylation reaction of aromatic nitro compounds with carbon monoxide. Although methods for producing Nate are known, methods using chlorine as a cocatalyst or promoter are not known. The above-mentioned known methods have the disadvantage that, due to low catalyst activity and selectivity, a large amount of an expensive precious metal main catalyst must be used relative to the starting nitro compound, and the yield of the target product is also low. be. In addition, the main catalyst decomposes during the reaction and adheres to the wall of the reactor (plate-out), further reducing the catalyst activity and making recovery of the catalyst difficult. Furthermore, adding various known co-catalysts to increase the activity of the catalyst will make recovery of the catalyst even more complicated, which is not economical. Corrosion of the reactor is also a problem. In order to solve these drawbacks, the present inventors have conducted intensive research on the catalytic function of halogens, especially chlorine, and have surprisingly found that chlorine can act as a co-catalyst in the direct isocyanate synthesis reaction. It has also been found that it exhibits far more effective effects than halogen derivatives. Further, by studying the usage pattern, it was determined that the above-mentioned drawbacks could be solved, and the present invention was completed. The main purpose of the present invention is to develop a practical method for directly producing the corresponding isocyanates industrially by reacting aromatic nitro compounds with carbon monoxide using a novel catalyst with excellent activity and selectivity at low concentrations. The purpose is to provide a method. Another object of the present invention is to make the catalyst extremely simple, and in the simplest case, the metal component in the catalyst is only the noble metal of the main catalyst, and by making the co-catalyst a volatile substance, it can be recycled as a catalyst.・Providing products that are easy to collect and use. Yet another object is to provide a catalyst that is extremely corrosive and to provide a process that allows the use of conventional materials for the reactor. That is, the present invention provides a mixture of a noble metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, and platinum and a heteroaromatic nitrogen compound, a complex of the noble metal coordinated with the nitrogen compound, and at least one selected from the group consisting of a mixture of a complex and the nitrogen compound;
This is a method for directly producing isocyanates by reacting aromatic nitro compounds with carbon monoxide at high temperature and high pressure in the presence of a seed catalyst and a chlorine promoter. Furthermore, the present invention can be carried out by using one or more of the conventionally known Lewis acids, metal compounds, organic and inorganic compounds, co-catalysts, promoters, additives, etc. in the above-mentioned catalyst system. can. The aromatic nitro compound used as a raw material in the present invention is an aromatic mono- or polynitro compound, 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-isocyanato-4-nitrotoluene, 2-nitro-4-isocyanatotoluene, 2- Isocyanate-6
-nitrotoluene, nitronaphthalene, 5-nitronaphthylisocyanate, nitroanthracene, (4-isocyanatophenyl)-(4'-nitrophenyl)methane, m-dinitrobenzene,
2,4-dinitrotoluene, 2,6-dinitrotoluene, a,a'-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, 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. The noble metals or compounds thereof used as the main catalyst include elemental substances of ruthenium, rhodium, palladium, osmium, iridium, and platinum, or halides, nitrates, isocyanides, carbonates, carboxylates, oxides, and chelates of these noble metals. and organic complexes containing ligands such as carbonyl, alkyl, olefin, and π-allyl. Preferably, for example, palladium asbestos, palladium-carbon, palladium chloride, palladium bromide, palladium iodide, sodium chloride palladate, tetraammine palladium chloride, dichlorodiammine palladium, rhodium chloride, rhodium bromide, rhodium iodide, sodium chloride rhodate, Ammonium chloride rhodate, bis-ethylene palladium chloride, bis-
Examples include π-allyl palladium chloride. The main catalyst can be supported on, for example, silica, alumina, silica-alumina, zeolite, carbon, celite, bentonite, diatomaceous earth, activated clay, calcium carbonate, barium sulfate, asbestos, etc., or mixed with it, as mentioned above. can be used. This allows the function of the catalyst to be adjusted and ease of handling and recovery. 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, 2-methyl-4-ethylpyridine, 2-chloro-4-methylpyridine, 2,6
-dicyanopyridine, 5,6,7,8-tetrahydroquinoline, 5,6,7,8-tetrahydroisoquinoline, quinoline, isoquiniline, acridine, benzoquinoline, benzoisoquinoline, phenanthridine, pyridazine, pyrimidine, pyrazine, cinnoline, Examples include quinazoline, quinoxaline, phthalazine, naphthalizine, 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 (), tris(isoquinoline) trichlororhodium (), and the like. 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 the direct production method of isocyanates is most closely related to the activity, selectivity and recovery of the catalyst. Therefore, increasing the activity and selectivity of the main catalyst containing precious metals,
Furthermore, the development of co-catalysts that facilitate the recovery and reuse of expensive precious metal catalysts is of utmost importance, and in this regard, the present invention has developed a new catalyst system that improves the above-mentioned drawbacks. Chlorine used as a cocatalyst in the present invention has a remarkable effect of accelerating the reaction, and the amount of the noble metal main catalyst to be used can be greatly reduced by simply adding a catalytic amount. Since the economic efficiency of the direct isocyanate production method is greatly influenced by the concentration of the catalyst used, this effect will significantly contribute to reducing production costs. Further, chlorine is highly desirable in that, when used in an appropriate amount, it can exhibit the effect of increasing catalytic activity without significantly reducing reaction selectivity, unlike the general characteristics of other co-catalysts. Under the conditions of use of the present invention, chlorine is surprisingly not found to act as a chlorinating agent for organic substances in the system during the reaction. Furthermore, it is demonstrated by examples that the cocatalytic effect of chlorine has the above-mentioned desirable features that are clearly different from the reaction promoting effect accompanied by a drastic decrease in the selectivity of hydrogen chloride, which occurs if aromatic nuclei are chlorinated, for example. . Furthermore, isocyanate can be obtained in high yield even when no separate metal promoter is used in the catalyst system of the present invention. In such a case, since the reaction solution does not contain a different metal, there is an advantage that the palladium main catalyst can be easily separated and recovered. Of course, the present invention can be used in combination with other known promoters, promoters, additives, etc. In this case as well, the use of chlorine has the effect of suppressing the decomposition of the main catalyst and facilitating its reuse. . The reaction between aromatic nitro compounds and carbon monoxide uses a noble metal or its compound (main catalyst) and a heteroaromatic nitrogen compound (ligand) as essential catalyst components.
and chlorine (cocatalyst). The amount of noble metal used as the main catalyst is 0.001 to 10 mol%, preferably 0.01 to 2 mol%, based on the nitro compound.
The range is mol%. The amount of the ligand of the heteroaromatic nitrogen compound is generally 1 to 500 times the mole of the main catalyst, preferably 2 to 100 times the mole of the main catalyst. The appropriate amount of chlorine as a promoter varies depending on the reaction conditions, but it is usually used in an amount of 0.01 to 500 times the mole of the main catalyst, preferably 0.1 to 50 times the mole of the main catalyst. Chlorine is used in a gaseous, liquid or solution form. The method of use of the catalyst component is not specified, and it can be used by bringing it into contact with the reaction raw material in a liquid phase 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 dichloromethane, perchlorethylene, tetrachloroethane, chlorobenzene, dichlorobenzene, halogenated hydrocarbons such as chloronaphthalene, nitriles, ethers, ketones, etc. are used. It will be done. 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 are no particular restrictions on the method of mixing solvents, and aromatic nitro compounds,
They can be mixed with the main catalyst and co-catalyst in quite any order and proportions. The amount of carbon monoxide consumed as a reaction raw material is stoichiometrically 3 moles per mole of nitro group according to formula (), and at the same time 2 moles of carbon dioxide are by-produced. 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 molar amount relative to the amount of nitro groups in the reactor,
The amount is usually 5 to 100 times the amount, preferably 7 to 20 times the amount. 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. The reaction mixture after a predetermined period of time is cooled, separated into gas and liquid, and then subjected to overdistillation, extraction, etc., and separated into product isocyanates, solvent, catalyst, and by-products. The separated and recovered catalyst and solvent are exhausted or, if necessary, subjected to appropriate treatment and used again in the reaction. Also, if small amounts of raw materials or nitroisocyanate intermediates remain in the reaction mixture, these can also be separated and recycled to the reactor at the same time. The product isocyanates are subjected to conventional purification operations depending on the intended use. Thus, for example, the use of a highly active catalyst system in the process of the invention makes it possible to economically prepare the corresponding isocyanates from aromatic nitro compounds in high yields. EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.
Note that the yield (or selectivity) from the nitro compound to the target isocyanate can be easily increased by increasing the catalyst. The present invention will be explained below with reference to Examples. Example 1 Autoclave (SUS-316, 500ml)
Prepared 195 g of O-dichlorobenzene in which 15.0 g of DNT, 0.492 g of dichlorobis(quinoline) palladium, 7.46 g of quinoline and 0.30 g of chlorine gas were dissolved.
After replacing with carbon monoxide twice, the pressure was increased to 160 Kg/cm ² . The temperature was raised to 220°C with stirring, and after reacting at the same temperature for 3 hours and 10 minutes, it was cooled to room temperature, the pressure was released, and the reaction solution was subjected to gas chromatography (15% silicon DC550/
Gaschrome Q, 150℃, biphenyl internal standard)
It was analyzed in The product liquid does not contain raw material DNT, and contains 11.83g of TDI,
A trace amount of 2-nitro-4-isocyanatotoluene (hereinafter abbreviated as 2N4IT) and 0.087g of 4-nitro-2
-Isocyanate toluene (hereinafter abbreviated as 4N2IT)
It contained. The yield relative to DNT is
82.5%, and its precursor 4N2IT was 0.6%.
Also the obtained target for NO ₂ group in DNT
If the NCO yield is the proportion of NCO groups in TDI and both precursors, this is 82.8%. After the reaction, no plate-out of metallic palladium was observed from the palladium main catalyst, and palladium was recovered in the form of the charged complex. Furthermore, no corrosion of the materials was observed in the reactors such as autoclaves and stirring blades in which the Examples described in this specification and the experiments pertaining to the present invention were repeatedly conducted. Examples 2 to 7 The reaction was carried out in the same manner as in Example 1, except that the amounts of the main catalyst and chlorine co-catalyst used and the reaction time were as shown in Table 1, and 46 mol% of quinoline was used based on PNT. The results are shown in Table 1. Comparative Example 1 In order to demonstrate the effect of chlorine promoter, a reaction was carried out under the same reaction conditions as in Examples 5 to 7, except that chlorine was not used and 14.8 g of DNT was used instead of 15.0 g. The results are also listed in Table 1. The effect of the chlorine co-catalyst according to the present invention was compared with Examples 2 to 4 or 5 to 7 in which the amount of chlorine added was varied at a constant amount of palladium and quinoline, and the latter with Comparative Example 1 in which no chlorine was added. It becomes clear from the comparison. That is, by using chlorine, DNT
The conversion rate increased, reaching 100% in a shorter time, and the desired TDI yield increased by about 40% or more. This reaction promoting effect functions without significantly reducing reaction selectivity. It can be seen that in both series of examples with different main catalyst concentrations, as the amount of chlorine used increases, the reaction promotion effect becomes more pronounced and the TDI yield generally increases.

[Table] Examples 8 to 11 The amount of main catalyst used was 0.2% by weight of Pd/DNT,
The same procedure as in Example 2 was carried out except that the reaction was carried out for 5 hours using the amount of chlorine shown in Table 2. The results are shown in Table 2. Comparative Example 2 A reaction was carried out under the same conditions as in Examples 8 to 11, except that chlorine was not used and 14.8 g of DNT was used instead of 15.0 g. Comparative Examples 3, 4 and 5 The reaction was carried out in the same manner as in Example 9 except that bromine, iodine and phosgene dimer were added in molar ratios of 15, 15 and 8 to the main catalyst, respectively, in place of chlorine. The results are also listed in Table 2. Comparative Example 6 Same as Example 8 except that hydrogen chloride was added as quinoline hydrochloride in place of chlorine at a molar ratio of 29 to the main catalyst, quinoline was used in a predetermined amount in total, and the reaction was carried out for 3.5 hours. I went in the same way. The results are also listed in Table 2.

[Table] From the consideration of Examples 8 to 11 and Comparative Example 2, the same promoter effect of chlorine as mentioned above is recognized. It is generally known that in this type of sequential reaction, as the TDI yield increases, the selectivity for all isocyanates tends to decrease significantly, but in Examples 9 to 11, the TDI yield was approximately three times that of Comparative Example 2. Despite this improvement, the selectivity of all isocyanates remains almost unchanged. Therefore, it is easily seen that chlorine in the catalyst of the present invention has the effect of increasing the reaction rate and significantly increasing the yield of diisocyanate TDI while suppressing a decrease in reaction selectivity. It is clear from the correspondence between Comparative Examples 3 or 4 and Example 9 that when halogens such as bromine or iodine are added, the activity and selectivity of the catalyst are rather significantly reduced, but chlorine exhibits the completely opposite desired effect. . Also, from the comparison between Example 9 and Comparative Example 5, chlorine as a cocatalyst gives higher DNT conversion, TDI yield, and total isocyanate selectivity than phosgene (which is easily generated by thermal decomposition of dimer), and therefore It is clear that the reaction promotion effect and selectivity improvement effect are both uniquely excellent. It can be seen from Table 2 that hydrogen chloride greatly speeds up the reaction but severely reduces the selectivity, whereas chlorine can increase the TDI yield without reducing the selectivity. Example 12 Using 20.3 g of nitrobenzene instead of DNT,
The reaction was carried out in the same manner as in Example 9 except that the reaction was carried out for 3 hours. The yield of phenyl isocyanate is
It was 86.3%. Example 13 Example 6 except that 0.100 g of palladium chloride was used instead of dichlorobis(quinoline)palladium.
The reaction was carried out in the same manner. Product yield is TDI74.0
%, 2N4IT 1.0% and 4N2IT 5.2%. Example 14 A reaction was carried out in the same manner as in Example 6 except that 0.118 g of rhodium trichloride was used as the main catalyst and the reaction was carried out for 5 hours. Yield is TDI40.0%, 2N4IT8.8% and 4N2IT27.0
It was %. Example 15 The reaction was carried out in the same manner as in Example 10, except that 0.095 g of dichlorobis(pyridine)palladium was used as the main catalyst and 3.0 g of pyridine was used instead of quinoline.
DNT conversion rate was 97.4%, yield was TDI 28.2%,
2N4IT was 13.3% and 4N2IT was 28.6%. Comparative Example 7 As a comparison with Example 15, when chlorine is not used, the DNT conversion rate is 63.5% and the yield is TDI 4.6%.
2N4IT was 20.0% and 4N2IT was 29.8%. Example 16 When 0.049 g of vanadium oxytrichloride and 0.087 g of phosphorus oxytrichloride were used together as another promoter in Example 10, the yield was 61.2% TDI and 4.0 2N4IT.
% and 4N2IT12.3% were obtained. Example 17 When 0.183 g of t-butyl chloride was used as another reaction accelerator in Example 10, yields of 68.7% of TDI, 0.7% of 2N4IT, and 5.2% of 4N2IT were obtained.

Claims (1)

[Claims] 1 A mixture of an aromatic nitro compound and carbon monoxide, a noble metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, and platinum, and a heteroaromatic nitrogen compound; Using chlorine as a co-catalyst in a method for producing isocyanates in which the reaction is carried out at high temperature and pressure in the presence of a catalyst containing at least one selected from the group consisting of a complex of the noble metal and a mixture of the complex and the nitrogen compound. A method for producing aromatic isocyanates, characterized by: