JPS6160825B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for directly synthesizing a corresponding isocyanate compound from an aromatic nitro compound and carbon monoxide. More specifically, the invention provides
High-temperature, high-pressure reaction of an aromatic nitro compound with carbon monoxide in the presence of a catalyst system consisting of (A) a platinum group metal compound, (B) a heteroaromatic cyclic nitrogen compound and/or a complex thereof, and (C) molybdic acid. The invention relates to a method for producing the corresponding isocyanate. 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 a nitro group with carbon monoxide and converting it into an isocyanate group in one step without using hydrogen or chlorine as an intermediate and without 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. There is a known method for directly synthesizing aromatic isocyanates by reacting an aromatic nitro compound and carbon monoxide 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. )n+3nCO
→Ar(NCO)n+2nCO ₂ ...(1) Various catalyst systems using noble metal compounds as main catalysts have been proposed, but have not yet been put into practical use.
For example, Japanese Patent Publication No. 45-22722 (Using at least one of palladium and rhodium halides and oxides and at least one of panadium, molybdenum, tungsten, niobium, chromium, and tantalum oxides as a catalyst system) method), U.S. Patent No.
No. 3576835 (method using the addition of a heterocyclic compound or its complex), Japanese Patent Publication No. 47-38436 (method using a composition of two or more noble metals), Japanese Patent Publication No. 1537-1987
(method of adding a small amount of water) etc. are known.
However, with these methods, the yield of the desired isocyanate is low due to low catalytic activity, and the main catalyst consisting of platinum group metal decomposes significantly and adheres to the reactor wall, making it difficult to recover the expensive platinum group metal catalyst. Become. The present inventors searched for various co-catalysts to improve the above-mentioned drawbacks, and as a result found that molybdic acid exhibited superior effects to molybdenum oxide, leading to the completion of the present invention. The main object of the present invention is to develop a method of using molybdic acid as a co-catalyst to increase the activity of a main catalyst made of platinum group metal, to suppress decomposition of the main catalyst, to extend the catalyst life, and to facilitate catalyst recovery. This is what we provide. That is, the method according to the invention comprises the steps of: (A) a platinum group metal compound; (B) a heteroaromatic cyclic nitrogen compound and/or a complex thereof; and (C) an aromatic nitro compound in the presence of a catalyst system comprising molybdic acid. The goal is to directly synthesize the corresponding isocyanate by reacting it with carbon monoxide at high temperature and high pressure. The aromatic nitro compound used as a raw material in the present invention is an aromatic mono- or polynitro compound having 32 or less carbon atoms, and may contain an isocyanate group or 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-nitrophenethole, nitrobenzaldehyde, nitrobenzoyl chloride, methylnitrobenzoate, nitrobenzenesulfonyl chloride, nitrobenzonitrile, 2-isocyanate-4-nitrotoluene, 2-nitro-4-isocyanatetoluene,
2-Isocyanate-6-nitrotoluene, nitronaphthalene, 5-nitronaphthylisocyanate, nitroanthracene, (4-isocyanatophenyl)-(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-nitrophenyl)thioether, bis (P-nitrophenyl)sulfone, trinitrobenzene, etc. Among these, nitrobenzene, 2,4
- and 2,6-dinitrotoluene, 1,2-dichloro-4-nitrobenzene, 1,5-dinitronaphthalene, bis(P-nitrophenyl)methane, and the like are preferably used for practical purposes. The essential catalyst for the carbonylation reaction of a nitro group according to the present invention is composed of (A) a platinum group metal compound, (B) a heteroaromatic cyclic nitrogen compound, and (C) a cocatalyst that is molybdic acid. (A) Platinum group 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 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, and sodium chloride rhodate. , 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 cyclic 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, and 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, 2-methyl-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, phthalazine, naphthyridine, phenazine, etc. Can be mentioned. Representative 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). ) diiotopalladium (), bis(α-picoline) dichloropalladium (), bis(quinoline) dichloropalladium (), bis(isoquinoline) dichloropalladium, (pyridine) (carbonyl) dichloropalladium (), (2,6- dimethylpyridine) (carbonyl) dichloropalladium (), tris(pyridine) trichlororhodium (), tris(pyridine) tribromorodium (), tris(γ-picoline) trichlororhodium (), tris(isoquinoline) trichlororhodium (), etc. There is. 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. 3,576,835), but as is clear from the comparative example below, the catalytic activity is too low. The yield of the desired isocyanate is extremely low. Additionally, during the reaction, the platinum group metal catalyst undergoes decomposition and is reduced to a metallic form, which adheres firmly to the walls of the reactor and forms a so-called mirror surface, making it extremely difficult to recover the expensive catalyst. . For example, if molybdenum trioxide is used as a co-catalyst in the main catalyst made of the platinum group metal,
22722), the isocyanate yield is slightly improved, but it is still too low for practical use, and recovery of the catalyst is also difficult because the reductive decomposition of the main catalyst to the metal state is not suppressed. Adding a small amount of water to the reaction system
1573), the reaction rate increases and the yield apparently increases, but this effect is insufficient and the selectivity decreases, and there is a tendency to accelerate the decomposition of the main catalyst. The economic efficiency of the direct production method of isocyanate is most closely related to the yield of isocyanate, that is, the activity of the catalyst and the recoverability of the catalyst, and the fundamental reason why the direct method has not yet reached industrialization is the above fact. This is largely due to. Therefore, it is most important to develop a co-catalyst that can form a highly active catalyst from a platinum group metal main catalyst with low activity and facilitate the recovery of the expensive main catalyst, and the present invention addresses these drawbacks. It constitutes an improvement. The cocatalyst used in the present invention is molybdic acid. When the molybdenum compound used as a co-catalyst is used in an acid form such as molybdic acid rather than molybdenum trioxide, it exhibits extremely superior properties in terms of the above two effects, that is, high activation and stabilization of the main catalyst. Although the mechanism of action of molybdic acid is not clear, molybdic acid may also exist in a polymolybdic acid structure in the reaction solution. Since heteroaromatic nitrogen compounds coexist, depending on the amount present, they generally participate in the reaction as mono and polymolybdates of nitrogen bases such as mono, di, tri, hexer, octa, and todecarmolybdates. Sometimes I do. The reaction between the aromatic nitro compound and carbon monoxide is carried out in the presence of (A) a platinum group metal compound, (B) a heteroaromatic cyclic nitrogen compound and/or a complex thereof, and (C) molybdic acid. The amount of the catalyst used in this case is such that the amount of the main catalyst as platinum group metal is usually 0.001 to 10% by weight, preferably 0.1 to 5% by weight, based on the aromatic nitro compound. The molybdic acid cocatalyst is used in an amount corresponding to the atomic ratio of molybdenum to platinum group metal, usually from 0.01 to 100, preferably from 0.2 to 10. In addition, the amount of the heteroaromatic cyclic nitrogen compound used is usually 1 to 1 to the platinum group metal compound.
The molar ratio is preferably 2 to 100, although it varies depending on the reaction conditions. The method of adding the catalyst is not specified, and the catalyst can be mixed with the reaction raw materials in any order and method and reacted. Further, the main catalyst and co-catalyst can be supported on various known carriers. 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 usually, for example, heptane, cyclohexane, benzene, toluene, xylene, and various petroleum distillates. Various aliphatic, cycloaliphatic and aromatic hydrocarbons, such as halogenated hydrocarbons such as dichloromethane, perchloroethylene, titrachloroethane, 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 differs 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 molar amount relative to the amount of nitro groups in the reactor, usually 5 to 100 times the molar amount, preferably 7 to 20 times the molar amount. 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 dissolved in a solvent and each component of the catalyst are mixed prior to the reaction, or charged into separate reactors (batch type) or continuously fed (continuous type). 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 the retention time has elapsed, 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 separated into product isocyanate, solvent, remaining catalyst and by-products. The recovered catalyst and solvent are used again in the reaction as they are or after being subjected to appropriate treatment if necessary. Also,
If a small amount of raw materials or nitroisocyanate intermediates when polynitro compounds are used as raw materials remain unreacted in the reaction mixture, these are simultaneously separated and recycled to the reactor. The product isocyanate is subjected to conventional purification operations depending on the intended use. Thus, according to the process of the present invention, the corresponding isocyanates can be economically produced in high yields from aromatic nitro compounds by using highly active catalyst systems. 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, pressurized reaction between an aromatic nitro compound and mono-liquefied carbon in an autoclave, all reactions are carried out in an autoclave in order to avoid contamination of the autoclave due to the metal components of the catalyst sticking to the vessel walls as described above. It is carried out in a glass container inserted tightly against the inner wall, and results with good reproducibility are obtained. However, in the reaction using the catalyst of the present invention, no adhesion of the metal to the container wall was observed, and similar results were obtained even when the reaction was carried out without using a glass container. Example 1 After thoroughly drying the inside of a glass container inserted in an autoclave (100ml SUS316), 4.00g of 2,4-dinitrotoluene (abbreviated as DNT),
Dichlorobis(pyridine)palladium as catalyst
560 mg and 300 mg of molybdic acid, and O- as a solvent.
52.0 g of dichlorobenzene was charged. The inside of the autoclave was replaced twice with 20 kg/cm ² of carbon monoxide, and then carbon monoxide was pressurized to 170 kg/cm ² . contents
The temperature was raised to 190°C in about 30 minutes while stirring at 300 rpm, and the internal pressure reached 230 Kg/cm ² . After reacting at the same temperature for 3 hours, the internal pressure dropped to 210 Kg/cm ² . The autoclave was cooled to room temperature and depressurized, the contents were taken out, the insoluble matter was added to the liquid as an internal standard, and biphenyl was added and quantitatively analyzed using gas chromatography (15% silicon DC550/Gaschrome Q).
The reaction solution was 2,4 toluene diisocyanate (hereinafter referred to as
(abbreviated as TDI) 0.833g, 2-nitro 4-isocyanate toluene (hereinafter abbreviated as 2N4I)
0.752 g, 1.326 g of 2-isocyanate 4-nitrotoluene (hereinafter abbreviated as 2I4N), and unreacted
It contained 0.511g of DNT. From this analysis value, DNT conversion rate is 87.2%, TDI yield is
23.1%, 2N4I yield of 19.2%, and 2I4N yield of 33.9% were obtained. The main catalyst palladium compound and co-catalyst were recovered from a separate cake, and most of the charged palladium catalyst was recovered from the residue from which the product was separated by vacuum distillation of the reaction solution by chloroform extraction. Example 2 The reaction was carried out in the same manner as in Example 1, except that 3.00 g of DNT, 50.2 mg of palladium chloride, 51.1 mg of molybdic acid, 0.60 g of pyridine, and 39.0 g of O-dichlorobenzene were charged and reacted at 220°C and 1000 rpm for 5 hours. .
DNT conversion rate 99.3%, TDI yield 56.1%, 2N4I yield
The yield of 2I4N was 5.0%. More than 90% of the main catalyst palladium was recovered. Example 3 24.7 mg of dichlorobis(quinoline) palladium, 10.2 mg of molybdic acid, and 0.98 g of quinoline as a catalyst
The reaction was carried out in the same manner as in Example 2 except that .
In this reaction, using a very small amount of palladium (0.2% by weight relative to DNT) as the main catalyst,
Conversion rate 98.9%, TDI yield 33.4%, 2N4I yield 8.0%,
The 2I4N yield was 24.9%. Example 4 2 hours and 20 minutes in the same manner as in Example 3, except that 4.06 g of nitrobenzene, 124 mg of dichlorobis(quinoline) palladium, 123 mg of molybdic acid, and 33.2 g of chlorobenzene were used instead of O-dichlorobenzene. The reaction was carried out. Analysis was conducted in the same manner as in Example 1 using O-dichlorobenzene instead of biphenyl as an internal standard substance. The nitrobenzene conversion rate was 100%, and the phenyl isocyanate yield was 85.5%. Comparative Examples 1 to 2 In order to clarify the effect of the catalyst according to the present invention, the case where equimolar molybdenum oxide was used instead of molybdic acid (Comparative Example 1) and the case where no promoter was used (Comparative Example 2) were investigated. The experiment was carried out under exactly the same conditions as in Example 1. The results obtained are shown below in comparison with Examples.

[Table] Compared to Comparative Examples 1 and 2, Example 1 had a higher DNT conversion rate,
Both TDI yields are extremely high. In this reaction, as can be seen from Comparative Examples 1 and 2, it is generally recognized that as the yield of TDI increases, the overall selectivity of the three products tends to decrease. However, although the TDI yield of Example 1 is doubled compared to Comparative Example 1, the overall selectivity is rather higher. Therefore, it can be seen that molybdic acid is an excellent cocatalyst having higher activity and selectivity than molybdenum trioxide. Further, when comparing the state of the catalyst after the reaction, in the comparative example, the palladium catalyst was considerably decomposed and a large amount of metallic palladium adhered to the vessel wall, but in Example 1, this was not observed.

Claims (1)

[Claims] 1. Using molybdic acid as a cocatalyst in the isocyanate production process in which an aromatic nitro compound and carbon monoxide are reacted in the presence of a catalyst consisting of a platinum group metal compound, a heteroaromatic cyclic nitrogen compound, and/or a complex thereof. A method for producing aromatic isocyanate characterized by: