JPS6121467B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an aromatic carbamate, and more specifically, the present invention relates to a method for producing an aromatic carbamate, and more specifically, an aromatic nitro compound is reacted with a lower aliphatic alcohol and carbon monoxide in the presence of a catalyst to produce an aromatic carbamate. This invention relates to improvements in the method for producing acid esters. For example, aromatic isocyanates such as tolylene diisocyanate are useful as raw materials for polyurethane, and are usually produced by reacting aromatic amines obtained by hydrogen reduction of aromatic nitro compounds with phosgene. ing. However, this method is complicated,
Also, use phosgene, which is a fractional gas,
Furthermore, it has drawbacks such as the generation of hydrogen chloride during the phosgenation reaction and the problem of equipment corrosion. Therefore, in recent years, several new methods for producing isocyanates that do not use phosgene have been proposed, such as reacting aromatic nitro compounds with lower aliphatic alcohols such as ethanol and carbon monoxide in the presence of a catalyst. A method is known in which an aromatic isocyanate is obtained by producing an aromatic carbamate ester and then thermally decomposing the ester. In this method, the technical point is the catalyst for producing the aromatic carbamate ester, and various catalysts have been proposed to obtain high conversion and selectivity. Among these catalysts, the palladium-vanadium-tertiary amine catalyst has extremely high reaction activity and is industrially superior, so the applicant previously filed a patent application for this catalyst (patent application). However, when this catalyst is used, there is a problem that aromatic amines, in which part of the nitro group of the aromatic nitro compound becomes an amino group, are easily produced as a by-product during the reaction. If the amount of aromatic amine by-produced can be suppressed, the selectivity can be further improved, which is industrially more preferable. In view of the above-mentioned circumstances, the present inventor has developed various methods to suppress the by-product of aromatic amines when producing aromatic carbamate esters using catalysts containing palladium-valadium-tertiary amines. As a result of investigation, the inventors have found that when the reaction is carried out while maintaining the water concentration in the reaction pot below a certain level, the amount of aromatic amine by-product is significantly reduced, and the present invention has been completed. That is, the gist of the present invention is to provide a method for producing an aromatic carbamate ester by reacting a nitro compound with a lower aliphatic alcohol and carbon oxide in the presence of a catalyst. using a catalyst containing
Moreover, the method for producing aromatic carbamate esters is characterized in that the reaction is carried out while maintaining the water concentration in the reaction system at 0 to 700 ppm. The present invention will be explained in detail below. The aromatic nitro compound used in the present invention may be either a mononitro compound or a polynitro compound, such as nitrobenzene, o-,
m- and p-nitrotoluene, o-nitro-p-
xylene, o-, m- and p-chloronitrobenzene, 1-bromo-4-nitrobenzene, o-,
m- and p-nitrophenicarbamate, o-,
m- and p-nitroanisole, m-nitrobenzaldehyde, p-nitrobenzoyl chloride,
Mononitrobenzenes such as ethyl p-nitrobenzoate, m-nitrobenzenesulfonyl chloride, 3-nitrophthalic anhydride, m- and p-
dinitrobenzene, 2,4-dinitrotoluene,
2,6-dinitrotoluene, dinitromesitylene, 1-chloro-2,4-dinitrobenzene, 1
- dinitrobenzenes such as fluoro-2,4-dinitrobenzene, trinitrobenzenes such as 2,4,6-trinitrotoluene, mono- or polynitro-substituted fused ring compounds such as 1-nitronaphthalene, 1,5-dinitronaphthalene, 4,4'-dinitrobiphenyl, 2,4-dinitrobiphenyl,
Nitrobiphenyls such as 3,3'-dimethyl-4,4'-dinitrobiphenyl, bis(nitrophenyl)alkanes such as bis(4-nitrophenyl)methane and 4,4'-dinitrobibenzyl, bis(4-
bis(nitrophenyl) ethers such as bis(2,4-dinitrophenyl) ether, bis(nitrophenyl) thioethers such as bis(4-nitrophenyl) thioether, bis(4-nitrophenyl) sulfone, etc. Nitrophenyl) sulfones, bis(4
- bis(nitrophenoxy) alkanes such as ethane, heteroaromatic nitro compounds such as 5-nitropyrimidine, or α,
Examples include α'-dinitro-p-xylene and α,α'-dinitro-m-xylene. The initial concentration of these aromatic nitro compounds in the reaction solution is usually selected within the range of 1 to 70% by weight, preferably 5 to 30% by weight. Further, examples of the lower aliphatic alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol, and ethanol is preferred from an industrial standpoint. It is necessary to use at least one molecule of these alcohols for each nitro group of the aromatic nitro compound used as a raw material, and usually they are used in large excess relative to the aromatic nitro compound as they also serve as reaction solvents. used in In the present invention, the above-mentioned aromatic nitro compound and lower aliphatic alcohol are reacted with carbon monoxide, but in this case, it is essential to use a catalyst containing palladium-vanadium-tertiary amine. It is something. Examples of palladium as a catalyst component of the present invention include metal palladium, halogenated palladium,
palladium cyanide, palladium thiocyanide,
Examples include palladium isocyanide, palladium oxide, palladium sulfate, palladium nitrate, and palladium acetate. Usually, these palladium catalysts are supported on a carrier such as activated carbon, graphite, silica, alumina, diatomaceous earth, or bentonite. In this case, the supported amount is usually 0.05 to 20% by weight, preferably 0.2 to 5% by weight of palladium metal based on the carrier. Furthermore, in the present invention, a catalyst is used in which at least a portion of palladium is made into a metal state by previously treating a carrier on which palladium is supported with a reducing agent such as hydrogen, hydrazine, formaldehyde, methanol, or carbon oxide. It is preferable to do so. The amount of palladium used is usually 0.0001 to 1% by weight, preferably 0.001 to 1% by weight of the metal based on the reaction solution.
It is 0.1% by weight. Next, vanadium is usually used as a compound, specifically, chlorides such as vanadium trichloride and vanadium tetrachloride, salts of chlorides such as vanadium()potassium chloride, vanadium oxydichloride, vanadium oxytrichloride, etc. oxychloride, vanadium oxide (), vanadium oxide (), vanadium oxide
oxides such as (), vanadic acids such as pyrovanadic acid and metavanadate, vanadates such as sodium orthovanadate, ammonium metavanadate, potassium metavanadate, vanadium sulfate
Vanadium salts of acids such as ()ammonium, vanadium oxalate ()potassium, vanadium oxysulfate
(), vanadyl salts of acids such as vanadium oxyoxalate, acetylacetone salts such as vanadium ()oxyacetylacetonate, and vanadium trichloride and vanadium tetrachloride are particularly preferred. It is necessary to use at least 1 gram atom of these vanadium compounds in terms of vanadium per 1 gram atom of palladium, but there is no particular restriction on the upper limit of the amount used. However, if the amount exceeds 1000 gram atoms per 1 gram atom of palladium, little increase in the effect is expected and it is economically disadvantageous, and it is usually within the range of 10 to 100 gram atoms per 1 gram atom of palladium. used in Furthermore, examples of tertiary amines include aliphatic tertiary amines such as trimethylamine, triethylamine, tripropylamine, and tributylamine;
Fatty aromatic tertiary amines such as N,N-dimethylaniline, N,N-diethylaniline, N,N-dipropylaniline, N,N-dimethylcyclohexylamine, N,N-diethylcyclohexylamine, N,N -Aliphatic tertiary amines such as dipropylcyclohexylamine, 1,4-diazabicyclo(2,2,2)-octane, 1,8-diazabicyclo(5,4,0)-undecene-7,1,5
Heterocyclic tertiary amines such as -diazabicyclo(4,3,0)-nonene-5, aromatic tertiary amines such as triphenylamine, heteroaromatic tertiary amines such as pyridine, quinoline, isoquinoline, etc. can be mentioned. In particular, heteroaromatic tertiary amines are effective for improving the yield of urethane, and specifically, pyridine, 2-chloropyridine, 2-chloropyridine,
-Brompyridine, 2-fluoropyridine, 3-
Chlorpyridine, 2,6-dichloropyridine, 4
-Phenylpyridine, α-pyricone, γ-picoline, 2-methyl-5-ethylpyridine, 2,6-
Lutidine, γ-collidine, 2-vinylpyridine,
2-chloro-4-methylpyridine, 4-phenylthiopyridine, 2-methoxypyridine, 2,6-
Pyridine derivatives such as dicyanopyridine, 4-dimethylaminopyridine, phenyl picolinate, γ-methyl picolinate, α-picolinaldehyde, α-picolinamide, 2,2′-dipyridyl;
Quinoline or 2-chloroquinoline, 5,6,
Quinoline derivatives such as 7,8-tetrahydroquinoline; acridine, phenanthridine, 5,6-benzoquinoline, 6,7-benzoquinoline, 7,8
-Benzoquinoline such as benzoquinoline; Isoquinoline; Pyrrole derivatives such as 1-methylpyrrole and 1-phenylpyrrole; Imidazole derivatives such as 1-methylimidazole; 1-methylindole and 1-phenylindole derivatives; 1-methylcarbazole Carbazole derivatives such as pyrazine, 2,6-dimethylpyrazine, pyridazine, pyrimidine, etc.; quinoxaline, 2,3-
Dimethylquinosaline, quinazoline, phthalazine,
Examples include benzodiane such as cinnoline and phenazine; indolenine; indolizine; naphthyridine; pteridine. It is also possible to use it in the form of a polymer such as polyvinylpyridine. The amount of the tertiary amine used may be 1 mol or more per 1 gram atom of vanadium in the vanadium compound, but it is usually selected within the range of 1 to 50 mol, preferably 1 to 20 mol. . In the present invention, the water concentration in the reaction system is set to 0 to
It is an essential requirement that the concentration be maintained at 700ppm. Normally, when the reaction of the present invention is carried out according to a known method using the above-mentioned reaction materials and catalyst, the water concentration in the reaction system is about 2000 to 2000.
It will be around 2500ppm. In other words, water is not actively added, but lower aliphatic alcohols for industrial or reagent use usually contain at least 2,500 to 50% water.
This is because the content is approximately 3000 ppm, and the tertiary amine of the catalyst component also contains some water. Therefore, in the present invention, the water concentration in the reaction system can be adjusted by sufficiently removing the water in each component supplied into the reaction system in advance. If the water concentration in the reaction system is higher than 1000 ppm, it is not preferable because the amount of aromatic amine produced as a by-product in the reaction cannot be sufficiently suppressed. In the present invention, the water concentration in the reaction system is usually adjusted by dehydrating the lower aliphatic alcohol that has the highest water content, and reducing the water content from 0 to 0.
It is preferable to use it after setting it to 700ppm. It is also more effective to remove some of the water contained in the tertiary amine. Usually, the dehydration treatment can be carried out by, for example, dehydration using an adsorbent such as molecular sieve, dehydration using magnesium alkoxide, or the like. Although the reaction is carried out using the reaction raw materials treated in this manner, in the present invention, care must be taken to ensure that a large amount of water is not supplied to all other components that are supplied into the reaction system. In the reaction of the present invention, lower aliphatic alcohol, which is a reaction component, is usually used in large excess and also serves as a solvent, but an inert solvent may also be used separately. For example, these solvents include benzene,
Aromatic hydrocarbons such as toluene and xylene, nitriles such as acetonitrile and benzonitrile, sulfones such as sulfolane, 1,1,2-trichlor-
Halogenated aliphatic hydrocarbons such as 1,2,2-trifluoroethane, halogenated aromatic hydrocarbons such as chlorobenzene, dichlorobenzene, trichlorobenzene, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane Ether, etc.
Alternatively, ketones, esters, etc. can be used. When using these solvents, it is necessary to thoroughly dehydrate the water contained therein in advance. To carry out the present invention, normally, an aromatic nitro compound, a dehydrated lower aliphatic alcohol, and a catalyst are charged into a reactor, and an inert solvent is further charged as necessary, and then 1 to 500 kg of carbon monoxide is charged. /
cm ² , preferably 10 to 200 Kg/cm ² , and stirred at 100 to 240°C, preferably
The reaction is carried out at a temperature of 140 to 200°C for about 10 minutes to 6 hours. Further, after the reaction is completed, first, solid substances such as the palladium catalyst are removed, and then the mother liquor is crystallized to precipitate and recover the aromatic carbamate ester. On the other hand, after the product is collected, the mother liquor contains vanadium and a tertiary amine catalyst, so it can be used again in the reaction after being subjected to treatments such as concentration adjustment. As described above, according to the present invention, a highly active catalyst made of palladium-vanadium-tertiary amine is used, and the amount of aromatic amine by-produced can be significantly suppressed, making it an industrially excellent product. It's a method. In the present invention, we focused on the trace amount of water contained in lower aliphatic alcohols, and adjusted the water concentration in the reaction system to below a specific value. It is surprising that the amount of by-products can be significantly reduced. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example: Special grade dinitrotoluene for reagents was placed in a 200ml autoclave equipped with a vertical stirring device and a CO supply port.
6.4g, 1.4g of activated carbon carrying 2wt% palladium metal for reagent, 0.8g of vanadyl trichloride for reagent, and 1.1g of pyridine for reagent (content 350ppm).
Then, reagent grade ethanol (water content 3000ppm)
Ethanol 55 dehydrated to the water content shown in Table 1
After adding G, the inside of the system was replaced with N ₂ gas in a closed system, and the temperature was raised to 140℃ and 14Kg/cm ² while stirring, and then CO gas was injected until it reached 80Kg/cm ² G. The mixture was reacted at 160°C for 3 hours. After the reaction, the solid matter was filtered, and the mother liquor was analyzed using liquid high performance chromatography to determine the yield of diethyltolylene-2,4-dicarbamate, the target product, and 2-amino-4 carbamate, the by-product. The production rates of toluene and 4-amino-2 carbamate toluene were measured and the results shown in Table 1 were obtained. 【table】

Claims (1)

[Claims] 1. In a method for producing an aromatic carbamate ester by reacting it with a lower aliphatic alcohol and carbon monoxide in the presence of an aromatic nitro compound medium, a catalyst containing palladium-vanadium-tertiary amine is used. A method for producing an aromatic carbamate ester, which is further characterized in that the reaction is carried out while maintaining the water concentration in the reaction system at 0 to 700 ppm.