JPS6318939B2 - - 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. In the presence of one main catalyst and a co-catalyst of a vanadium chelate compound consisting of 1,3 diketone,
This invention relates to a method for directly producing the corresponding aromatic isocyanates by reacting aromatic nitro compounds and carbon monoxide at high temperature and pressure. 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 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 a main component according to the following formula to form an aromatic A _r (NO ₂ ) _o +3 _o CO →A _r (NCO) _o +2 _o CO ₂ ...The method of directly synthesizing group (1) isocyanates is well known, and many various catalyst systems using noble metal compounds as the main catalyst have been proposed, but none have been put into practical use yet. do not have. This is because a large amount of main catalyst is required to carry out this reaction, and the yield of isocyanate is low. As a method for directly synthesizing aromatic isocyanates according to reaction formula (1), for example, a method using a catalyst system consisting of noble metals or their oxides or salts and non-noble metals such as vanadium or their halides is disclosed in US Pat. No. 3,523,966. , US Pat. No. 3,576,835, a method using a heteroaromatic nitrogen compound or a noble metal complex thereof is known, but the yield of isocyanates is extremely low even if a large amount of catalyst is used. Also, in Japanese Patent Publication No. 48-43110, a mixture of palladium halide and pyridine or isoquinoline,
Alternatively, in a method using a complex thereof as the main catalyst and a vanadium halide as a promoter, the diisocyanate yield is as low as 23% even if palladium is used as the main catalyst at a proportion of 4.9% by weight of the raw material dinitrotoluene. has become a by-product. Japanese Patent Publication 1973-
In the method according to No. 52044 using acetylacetonate of chromium and molybdenum as a cocatalyst, the diisocyanate yield is low even if palladium is used as the main catalyst at a proportion of 3.0% by weight of dinitrotoluene.
It is 32.4%. That is, since these catalyst systems have low activity and selectivity, a large amount of an expensive noble metal main catalyst must be used relative to the starting nitro compound, and furthermore, the yield of the target product is low. Further, the main catalyst decomposes during the reaction and adheres to the wall of the reactor (plates out), further reducing the catalytic activity and making recovery of the catalyst difficult. As a result of searching for a wide range of non-noble metal compounds to solve these drawbacks, the present inventors found that 1,3
We have discovered that a vanadium chelate compound consisting of a diketone exhibits extremely effective action as a cocatalyst. By further studying the usage pattern, we have completed the present invention which solves the above-mentioned drawbacks. The main purpose of the present invention is to provide a method for industrially directly producing the corresponding isocyanates through the reaction of aromatic nitro compounds and carbon monoxide using a novel catalyst system with excellent activity and selectivity. be. That is, 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.
This is a method for directly producing isocyanates by subjecting an aromatic nitro compound to a high-temperature, pressurized reaction with carbon monoxide in the presence of a vanadium chelate compound co-catalyst consisting of a seed catalyst and 1,3-diketone. In addition, a monohydric alcohol or phenol, carbon monoxide, and an aromatic nitro compound are heated and reacted in the presence of a catalyst consisting of a halide of a platinum group noble metal and an acetylacetonate of several metals such as vanadium to produce an aromatic aroma. A method for producing group urethanes (Japanese Patent Publication No. 54-38092) is known, but a highly active catalyst system using a vanadium chelate compound consisting of 1,3-diketone as a promoter by the method shown in the present invention is not known. This is the first time for a direct synthesis reaction of isocyanates. Furthermore, it is well known that transition metal chelate compounds such as acetylacetonate act as isocyanate trimerization catalysts to form isocyanurate rings. It can be seen that the compound acts extremely effectively as a cocatalyst for the reductive carbonylation of aromatic nitro compounds to isocyanates without catalytically trimerizing the produced isocyanates. 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, 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, 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, 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 groups. 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, Examples include ammonium rhodate chloride, bis-ethylene palladium chloride, and bis-π-allyl palladium chloride. In the case of a noble metal compound that does not contain halogen, it is desirable to separately add a halogen-containing compound such as hydrogen halide, phosgene, halogenated hydrocarbon, or 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 group 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 (), 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 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 promoter used in the present invention has the general formula
1, represented by RCOCHR″COR′ (where R, R′ and R″ are aliphatic, alicyclic or aromatic monovalent organic groups, and R″ may be a hydrogen or halogen atom);
It is a vanadium chelate compound containing at least one chelate bond consisting of 3-diketone. Specifically, for example, tris(2,4-pentanediono)vanadium V(acac) ₃ , tris(1,
1-dichloro-2,4-pentanediono)vanadium, tris(1,1,1-trifluoro-2,
4-pentanediono)vanadium, tris(ethylacetoacetate)vanadium, tris(1-
Phenyl-1,3-butanediono)vanadium V
(bzac) ₃ , tris(3-chloro-2,4-pentanediono)vanadium, bis(2,4-pentanediono)oxovanadium VO(acac) ₂ , bis(3H,3H-hexafluoro-2,4- pentanediono)oxovanadiumVO( _F6- acac) ₂ , bis(1-cyclohexyl-1,3-butanediono)oxovanadium, bis(1-phenyl-
1,3-butanediono)oxovanadium VO
(bzac) ₂ , bis(1-p-chlorophenyl-1,
3-butanediono)oxovanadium, bis(1,1,1-trifluoro-4(2-thiophene)-2,4-butanediono)oxovanadium,
Bis(1,3-diphenyl-1,3-propanediono)oxovanadium VO(dbzm) ₂ , bis(1
-phenyl-3(2-furyl)-1,3-propanediono)oxovanadium, bis(1-phenyl-3(2-thiophene)-1,3-propanediono)oxovanadium, bis(1(2-furyl) )−
3(2-thiophene)-1,3-propanediono)
Oxovanadium, bis(3-chloro-2,4-
pentanediono) oxovanadium VO (acac−
C) ₂ , bis(3-bromo-2,4-pentanediono)oxovanadium VO(acac-Br) ₂ , bis(3-methyl-2,4-pentanediono)oxovanadium, (2,4-pentanediono) ) dichlorooxovanadium VOC ₂ (acac), bis(2,
4-pentanediono)chlorooxovanadium
A wide variety of chelating compounds are used, such as VOC (acac) ₂ . This co-catalyst has an extremely remarkable reaction-promoting effect, so by adding only a small amount, the amount of noble metal main catalyst used can be reduced to less than 1/10 of the amount conventionally used, and the selectivity can also be improved. did it. Since the economic efficiency of the isocyanate direct production method is controlled by the concentration of expensive noble metal catalyst used, the above effect is extremely significant in reducing the isocyanate production cost. Further, the co-catalyst according to the present invention can be used together with various conventionally known co-catalysts and 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 or its compound to be 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 1 to 500 times the mole, preferably 2 to 100 times the mole. The appropriate amount of the vanadium chelate compound as a promoter varies depending on the amount of the main catalyst used, but it is usually 0.01 to 50 times the mole of the noble metal compound, preferably
A range of 0.1 to 5 moles 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, 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 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 resulting reaction mixture is subjected to distillation, extraction, etc., and is separated into product isocyanates, solvent, 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.
Incidentally, the yield (or selectivity) of the desired isocyanate from the nitro compound can be easily increased by increasing the amount of catalyst. Example 1 In an autoclave (SUS-316, 200ml),
4-dinitrotoluene (hereinafter abbreviated as DNT)
6.00g, dichlorobis(quinoline)palladium
49.2 mg, 39.4 mg of tris(2,4-pentanediono)vanadium V (acac) ₃ as a cocatalyst (equimolar to the palladium compound), 1.98 g of quinoline and 78 g of O-dichlorobenzene, and 20 kg/g of tris(2,4-pentanediono) vanadium V (acac) 3 as a cocatalyst.
cm ² , and after displacement twice, the pressure was increased to 160 Kg/cm ² . The temperature was raised to 220° C. in about 30 minutes while stirring (1000 rpm), and the internal pressure reached 247 Kg/cm ² . After reacting at the same temperature for 5 hours, the reaction solution was cooled to room temperature and depressurized, and the reaction solution was analyzed by gas chromatography (15% silicon DC550/Gaschrome Q, biphenyl internal standard). This solution does not contain the raw material DNT, but contains 2,4-tolylene diisocyanate (hereinafter abbreviated as TDI).
3.123g, 2-nitro-4-isocyanatotoluene (hereinafter abbreviated as 2N4IT) 0.280g and 4-nitro-2
-Isocyanate toluene (hereinafter abbreviated as 4N2IT)
Containing 0.720g, the yields are 54.4% and 4.8%, respectively.
It was 12.3%. Almost all of the catalyst remained dissolved in the reaction solution even after the reaction. Examples 2 to 10 The reaction was carried out in the same manner as in Example 1, except that the vanadium chelate compound listed in Table 1 was used as a cocatalyst in an amount equal to the palladium compound. The results are shown in Table 1.

[Table] Comparative Example 1 In order to clearly demonstrate the effect of the co-catalyst, a 500ml autoclave was used without using a vanadium chelate compound.
The same reaction as in Example 1 was carried out except that DNT, catalyst component, and solvent were charged in 2.5 times the amount of Example 1. The results are also listed in Table 1. Examples 1 to 10 and Comparative Example 1 are the results of reactions conducted with the amount of catalyst palladium used relative to DNT reduced to 0.2% by weight (0.34 mol%), which is less than 1/10 of the conventional amount normally used. As is clear from comparing these, when a very small amount of vanadium chelate compound is used as a cocatalyst (equimolar to the palladium main catalyst), the reaction rate is increased and the DNT conversion rate and especially the TDI yield are greatly improved. Furthermore, it is generally known that in this type of sequential reaction, as the TDI yield increases, the total isocyanate yield or selectivity tends to decrease significantly.
It can be seen that the total isocyanate yield is high even though it has more than doubled, and the selectivity has been substantially improved. Therefore, it can be seen that the catalyst according to the present invention is an extremely highly active catalyst that has the effect of increasing the reaction rate and significantly increasing the conversion rate to diisocyanate while suppressing a decrease in reaction selectivity. Increasing the amount of palladium catalyst in the catalyst system of this example increases the reaction rate and selectivity to isocyanate, making it easy to obtain a yield of 80% or more. Example 11 Except that 20.0 mg of equimolar palladium chloride was used instead of dichlorobis(quinoline)palladium.
The reaction was carried out in exactly the same manner as in Example 7. DNT conversion rate is 100%, yield is TDI 47.5%, 2N4IT 9.2%.
4N2IT19.3% was obtained. Examples 12-13 Except that 75.5 mg of dichlorobis(pyridine)palladium was used instead of dichlorobis(quinoline)palladium, 1.12g of pyridine was used instead of quinoline, and the vanadium chelate compound listed in Table 2 was used as a cocatalyst in an equimolar amount with the palladium compound. The reaction was carried out in the same manner as in Example 1. The results are shown in Table 2.

[Table] Comparative Example 2 A reaction was carried out in exactly the same manner as in Example 12, except that 1.20 g of pyridine was used without using a vanadium chelate compound as a promoter. The results are also listed in Table 2. The effect of the cocatalyst according to the present invention is clear from Table 2, and it can be seen that the vanadium chelate compound exhibits the same excellent effects on activity and selectivity in the catalyst system made of pyridine. Example 14 8.12g of 2 times the mole of nitrobenzene instead of DNT
and chlorobenzene instead of O-dichlorobenzene
The reaction was carried out in the same manner as in Example 7, except that 66.4 g was used and the reaction was carried out for 3 hours. Nitrobenzene conversion rate is 100%, phenyl isocyanate yield is 85.5%
It was hot.

Claims (1)

[Claims] 1 Aromatic nitro compound and carbon monoxide from the group consisting of a mixture of a noble metal or its compound 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. An aromatic isocyanate characterized in that a vanadium chelate compound consisting of a 1,3 diketone is used as a cocatalyst in a method for producing isocyanates in which the reaction is carried out at high temperature and pressure in the presence of at least one selected catalyst. Method for producing natos.