JPS6342614B2 - - 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. and at least one cyclopentadienyl halide or oxyhalide of a Group A transition metal of the periodic table as a cocatalyst, and a heteroaromatic nitrogen compound is applied to the noble metal compound and/or the complex.
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 using a molar ratio of 10 to 500 times. 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 isocyanate can be produced from a nitro compound in a one-step reaction without producing hydrochloric acid as a by-product. An aromatic nitro compound and carbon monoxide are reacted at high temperature and under pressure in the presence of a suitable catalyst containing a noble metal compound as the main component according to the following formula to form aromatic A _r (NO ₂ ) n + 3 n CO → Ar (NCO) n + 2 n CO ₂
...(1) Methods for directly synthesizing aromatic 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 all of them require a large amount of main catalyst to carry out this reaction, and furthermore, the yield of isocyanate is low. As a catalyst system containing a salt of Group A metal for synthesizing aromatic isocyanates according to reaction formula (1), 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 48-43110
A method is known in which a mixture of palladium halide and pyridine or isoquinoline, or a complex thereof, is used as a main catalyst, and a halide of a non-noble metal containing a Group A metal is used as a co-catalyst. As a catalyst, palladium is 4.9% by weight of the raw material dinitrotoluene (8.3% for the nitro group).
Even if mol%) is used, the isocyanate yield is 23%.
It is described that other than this is a by-product. 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. In order to improve the above-mentioned drawbacks of catalysts, the present inventors conducted extensive research on the catalytic functions and reaction conditions of various Group A metal compounds, and found that cyclopentadienyl halide or -We have discovered that oxyhalide compounds exhibit an extremely excellent cocatalytic effect on the reductive carbonylation reaction (formula (1)) of aromatic nitro compounds with carbon monoxide. Furthermore, by studying the usage of the direct synthesis method of isocyanates, the above-mentioned drawbacks were solved and the present invention was completed. 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 excellent activity and selectivity. 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 chloride palladate, tetraamine palladium chloride, dichlorodiammine palladium, rhodium chloride, rhodium bromide, rhodium iodide, rhodium chloride. sodium chloride, ammonium rhodate chloride,
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, benzisoquinoline, phenanthridine, pyridazine, pyrimidine, pyrazine, cinnoline , quinazoline, quinoxaline,
Examples include phthalazine, naphthyridine, and phenazine. 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, the development of a co-catalyst that enhances the activity and selectivity of the main catalyst containing precious metals and facilitates the recovery and reuse of expensive precious metal catalysts is of utmost importance, 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 is a cyclopentadienyl halide or oxyhalide compound of a Group A transition metal of the periodic table. These are generally
CpMX ₃ , Cp ₂ MX , Cp ₂ MX ₂ , Cp ₂ MX ₃ ,
CpMOX ₂ (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,
CpVBr ₁ , Cp ₂ VI, CP ₂ VCl ₂ , Cp ₂ VBr ₂ ,
_Cp2NbCl , _Cp2NbBr3 , _{Cp2TaBr3 , CpVOCl2 ,}
CpVOBr ₂ etc. are used, preferably (cyclopentadienyl) vanadium trichloride, di(cyclopentadienyl) vanadium dichloride, di(cyclopentadienyl) vanadium dibromide, (cyclopentadienyl) vanadium oxydichloride. used. Report by Nefedov et al. [Dokl, Akad.Nank
SSSR, Vol. 246, p. 118 (1979)], the pressurized reaction between nitrobenzene and carbon monoxide was carried out using a catalyst consisting of palladium chloride (1.74 mol% relative to nitrobenzene) and pyridine (4 times the mol relative to palladium chloride). It has been found that when di(cyclopentadienyl)vanadium dichloride is added to the atomic ratio V/Pd=1, phenyl isocyanate is not produced, but 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, this catalyst system does not react with the intermediate phenylnitrene coordinated to the palladium pyridine complex with carbon monoxide, but instead abstracts hydrogen from the cyclopentadienyl ring. This is thought to be because it gives aniline. On the other hand, the present inventors found that the palladium nitrene complex, which is considered to be a reaction intermediate in the production of isocyanate from aromatic nitro compounds, decomposes in the above catalyst system due to insufficient pyridine ligand concentration. I guessed that I wouldn't get it. Furthermore, in order to cause this nitrene complex to react catalytically with carbon monoxide, a nitrogen aromatic cyclic compound in large excess relative to palladium must coexist 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. Surprisingly, based on this main catalyst composition, aromatic nitro compounds and carbon monoxide can be pressurized by coexisting a cyclopentadienyl halide or oxyhalide of a group A transition metal with a low concentration of a noble metal compound. As a result of studying the reaction, it was possible to obtain isocyanates in much higher yields than with conventionally known catalyst systems without producing amines.
Since the co-catalyst according to the present invention has an extremely remarkable reaction promoting effect, the amount of the noble metal main catalyst used can be reduced to about 1/10 of the conventionally known amount. In the present invention, by using only a small amount of the noble metal main catalyst, the selective reductive carbonylation reaction of the nitro group can proceed, providing isocyanates in high yield, and the main catalyst can be easily recovered. As described above, the present catalyst, which is composed of a noble metal compound, a heteroaromatic cyclic compound, and a cyclopentadienyl halide or oxyhalide of a Group A transition metal, is the best isocyanate with high activity at a lower concentration than conventionally known catalysts. It is clear that it is a direct synthesis catalyst. The cocatalyst according to the invention can also be used together with conventionally known cocatalysts, such as metal halides and metal oxides, and various 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 ratio, preferably
A range of 20 to 200 fold molar ratios is used. The suitability of vanadium compounds as co-catalysts varies depending on the amount of main catalyst used, but they are usually suitable for noble metal compounds.
A molar ratio of 0.01 to 50 times, preferably 0.1 to 5 times, is used. The method of adding the catalyst is not specified, 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, 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. Furthermore, if a small amount of raw materials or nitroisocyanate intermediates when a polynitro compound is used as a raw material remain in an unreacted state in the reaction mixture, these are also separated and recycled to the reactor at the same time. The product 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 2,4 in autoclave (500ml, SUS316)
-Dinitrotoluene (hereinafter abbreviated as DNT) 14.8g,
Dichlorobis(quinoline)palladium (main catalyst)
0.242g, di(cyclopentadienyl)vanadium dichloride (cocatalyst) 0.070g, quinoline 4.77
After preparing gas and 192 g of 0-dichlorobenzene (solvent), gas was replaced with carbon monoxide at 20 Kg/cm ² twice.
The pressure was increased to 160Kg/cm ² . When the temperature is raised to 220℃ in about 1 hour while stirring (1000rpm), the internal pressure becomes 258℃.
Kg/ ^cm2 was reached. After reacting at the same temperature for 4 to 5 hours, it was cooled to room temperature and the pressure was released, and the reaction product liquid was analyzed by gas chromatography (15% silicon DC550/Gaschrome Q, biphenyl internal standard). This solution contains raw material DNT, intermediate 2-nitro-4-isocyanate toluene (hereinafter abbreviated as 2N4IT) and 4-
Nitro-2-isocyanate toluene (hereinafter
10.5g of 2,4-tolylene diisocyanate (hereinafter abbreviated as TDI) without any 4N2IT (abbreviated as 4N2IT)
It contained. Further, even after the reaction, the catalyst was hardly separated out and remained dissolved in the reaction solution. Examples 2-3 In order to demonstrate the effect of the amount of co-catalyst added, Example 1
The reaction was carried out in the same manner as in Example 1, except that the amount of vanadium cocatalyst used and the reaction time were changed to the predetermined values shown. The results are summarized in Table 1 together with Example 1. Comparative Example 1 In order to demonstrate the remarkable effect of the co-catalyst according to the present invention, the same procedure as in Example 1 was carried out except that no co-catalyst was used and the reaction time was changed to 5 hours. The results are also listed in Table 1.

[Table] As is clear from the comparison between Example 3 and Comparative Example 1,
By simply adding cocatalyst CP ₂ VCl ₂ by 0.25 times the mole of the main catalyst, the conversion rate of DNT and NO ₂ groups increases, reaching the target value.
TDI yield is increasing. It can be seen from the reaction time that when the amount of this co-catalyst used is increased (Examples 1 to 2), the reaction is significantly accelerated, and the TDI yield is
Pd/DNT reaches 74% at 0.4% by weight. Such excellent results could not be obtained without the use of the promoter according to the invention, demonstrating the remarkable effectiveness of the invention. Further, no plate-out phenomenon of palladium on the reactor wall due to decomposition of the main catalyst was observed, and results with good reproducibility were obtained through experiments using the method according to the present invention despite the small amount of catalyst. Examples 4 to 7 Reactions were carried out in the same manner as in Example 1, except that the amount of the main catalyst was 0.121 g, which was half the amount of Example 1, and the amount of co-catalyst used and the reaction time were changed to the predetermined values indicated. The results obtained are shown in Table 2. Comparative Example 2 In order to compare with Examples 4 to 7, the same procedure as Examples 4 to 7 was carried out except that no cocatalyst was used and the reaction time was 5 hours. The results are also listed in Table 2.

[Table] Examples 4 to 7 are the results of examining the effect of the co-catalyst by making the concentration of the main catalyst more diluted than in Examples 1 to 3 as indicated. The same conclusion as Table 1 is obtained from Example 4.
7 and Comparative Example 2.
In Example 7, the TDI yield was 67.8%, and such a high yield has not been obtained with known catalyst systems with the same amount of noble metal compound used. Examples 8-9 Autoclave (200ml, SUS-316)
The same procedure as in Example 1 was carried out except that 6.00 g of DNT, 0.0377 g of dichlorobis(pyridine) palladium, 1.20 g of pyridine, 78 g of O-dichlorobenzene and the cocatalyst were used as indicated and the reaction was carried out for 5 hours. The results are shown in Table 3. Comparative Example 3 The reaction was carried out in the same manner as in Examples 8 and 9 except that no promoter was used. The results are also shown in Table 3.

[Table] Also in Examples 8 to 9, in which dichlorobis(pyridine)palladium was used as the main catalyst at 0.2% by weight of Pd/DNT, Tables 1 and 2 were compared with Comparative Example 3.
It is clear that there is a promoter effect similar to that of Example 10 The reaction was carried out in the same manner as in Example 8 except that 0.0755 g of palladium main catalyst and 0.0260 g of (cyclopentadienyl)vanadium oxydichloride were used as co-catalyst. As a result, the DNT conversion rate was 94.5% and the yield was TDI was 137.2%, 2N4I was 16.9%, and 4N2I was 16.9%. Comparative Example 4 The reaction was carried out in the same manner as in Example 10 without using a promoter, and the DNT conversion rate was 72.8% and the yield was TDI 15.5.
%, 2N4I 17.8%, and 4N2I 26.5%. Example 11 Palladium chloride 0.0200g as a noble metal compound,
1.96 g of quinoline instead of pyridine, di(cyclopentadienyl)niobium dichloride as cocatalyst
When the reaction was carried out in the same manner as in Example 8 except that 0.0261 g was used, the DNT conversion rate was 99.2%, the yield was TDI 30.9%,
2N4I 12.1% and 4N2I 34.2% were obtained. Example 12 The same procedure as in Example 6 was carried out, except that 20.28 g of nitrobenzene was used instead of DNT, and 166 g of chlorobenzene was added instead of O-dichlorobenzene, and carbon monoxide was introduced under pressure at 140 kg/cm ² and reacted for 3 hours. I went. A nitrobenzene conversion rate of 99.1% and a phenyl isocyanate yield of 83.8% were obtained.

Claims (1)

[Claims] 1 A mixture of an aromatic nitro compound and carbon monoxide, a noble metal compound and a heteroaromatic nitrogen compound,
In the method for producing isocyanates, 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 and a mixture of the nitrogen compound, coordinated with the nitrogen compound. At least one cyclopentadienyl halide or oxyhalide of a Group VA transition metal in the table is used as a cocatalyst, and a heteroaromatic nitrogen compound is reacted with a 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.