JPS61191661A - Production of aromatic isocyanate - Google Patents

Abstract

PURPOSE:The reaction between an aromatic nitro compound and carbon monoxide is carried out in the presence of a major catalyst and a cocatalyst of vanadium compound to enable easy and high-yield production of the titled compound which is used a feedstock for polyurethane or agricultural chemicals. CONSTITUTION:When an aromatic isocyanate is produced by reaction between an aromatic nitro compound and carbon monoxide in the presence of a catalyst selected from a mixture of Pd or its mixture with a nitrogen-containing heterocy clic compound, Pd complex containing the said heterocyclic compound as a ligand and a mixture thereof with the said nitrogen-containing heterocyclic compound at elevated temperature and pressure, the reaction is carried out in the presence of an active hydrogen-bearing compound such as HCN, using a cocatalyst which is composed of a phosphorus compound such as PF3, a vanadium compound such as VCl3 and tertiary amine such as triethylamine. The objective compound is obtained by distillation of the reaction mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing aromatic isocyanates useful as raw materials for polyurethanes, agricultural chemicals, and the like.

More specifically, the present invention relates to a method for directly producing the corresponding isocyanate from an aromatic nitro compound and carbon monoxide.

[Conventional technology]

The current industrial method for producing aromatic 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 the isocyanate.

However, 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 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 under high temperature and pressure in the presence of a suitable catalyst containing a noble metal compound as a main component according to formula (1) to form Ar (NO2) n + 3nCO-”Ar (NG
O) n + 2nCO2.-(1) Methods for directly synthesizing aromatic isocyanates are known, and many various catalyst systems using noble metal compounds as main catalysts have been proposed.

That is, many methods have been proposed in which a noble metal, a compound of a noble metal, or a complex compound thereof is used as a main catalyst and various co-catalysts are used.

For example, as a method using a vanadium compound as a promoter, a method using vanadium oxide is
22722, Special Publication No. 45-35774 and Special Publication No. 48
-42632, a method using vanadium chloride is described in Japanese Patent Publication No. 4B-43110.

Further, a method is described in Japanese Patent Publication No. 35774/1974 in which a vanadium oxide and a phosphorus acid halide are used as co-catalysts.

However, in both cases, although a large amount of the main catalyst is used, the reaction rate is slow, and the conversion rate and yield of aromatic isocyanate are low.

On the other hand, using a catalyst selected from the group consisting of palladium halogen (l), its pyridine or quinoline complex, and a mixture of palladium halide and vanadium oxide as the main catalyst, the reaction is carried out in the presence of a hydroxy-substituted hydrocarbon. The method for producing aromatic isocyanates was published in 1977.
B-43113. However, as shown in the examples, the yield is low and a large amount of catalyst is required, which seems to be insufficient for industrial implementation.

[Problem that the invention seeks to solve]

As mentioned above, in the process of producing aromatic isocyanates from aromatic nitro compounds and carbon monoxide, methods have been proposed in which palladium or its compounds are used as the main catalyst and various co-catalyst systems are used to improve the reaction. However, in the known methods, the activity and selectivity of the catalyst are low, so 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.

In addition, the main catalyst decomposes during the reaction and deposits on the reactor wall (
plate out), the catalytic activity further decreases, and
There is a drawback that catalyst recovery is also difficult.

The present invention has been made in view of the above, and the object of the present invention is to use a new catalyst system, use a very small amount of precious metal catalyst in combination with additives,
The object of the present invention is to provide a method for producing aromatic isocyanates in high yield and in a simplified process.

[Means for solving problems]

In order to achieve the above object, the present inventors made extensive studies and finally arrived at the present invention.

That is, the present invention combines an aromatic nitro compound and carbon monoxide with a mixture of palladium or its compound and a nitrogen-containing heterocyclic compound, a complex of palladium coordinated with the nitrogen-containing heterocyclic compound, and the complex. In the method for producing aromatic isocyanates, the reaction is carried out at high temperature and high pressure in the presence of one or more catalysts selected from the group consisting of mixtures with nitrogen-containing heterocyclic compounds. aromatic isocyanate, characterized in that it is carried out using a cocatalyst system consisting of a halogenated phosphorous compound, a vanadium compound, and a tertiary amine in the presence of a phosphorus compound, and the aromatic isocyanate is separated from the resulting reactant by distillation. This is a method for producing group 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-lm- and p-nitrotoluene, o-nitro-p-xylene, nitromesitylene.

1-chloro-2-nitrobenzene, 1,2-dichloro-4-nitrobenzene, 1-7'romo-4-nitrobenzene, 1-fluoro-4-nitrobenzene, 1-trifluoromethyl -4-nitrobenzene, O-, m- and p
-Nitrophenyl isocyanate, o- and p-nitroanisole, 〇- and p-nitrophenetol, nitrobenzaldehyde, nitrobenzoyl chloride, methylnitrobenzoate, dil-lovenzenesulfonyl chloride, nitrobenzonitrile, 2- Isocyanato-4-
Nitrotoluene, 2-nitro-4-isocyanatotoluene, 2-isocyanato-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, l-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, and the like.

Among these, nitrobenzene, 2.4- and 2.
6-dinitrotoluene, 1,2-dichloro-4-nitrobenzene, 1,5-dinitrotoluene, bis(p-nitrophenyl)methane, etc. are preferably used for practical purposes.

The active hydrogen compound used in the method of the present invention is a compound that reacts with isocyanate and is stable at room temperature and easily dissociates at high temperature to react as isocyanate, that is, blocked isocyaner.
nate), and in the method of the present invention, the dissociation onset temperature (weight loss by differential thermal analysis is 5
%) represents a compound with active hydrogen that produces blocked German cyanate at a temperature of 200°C or less. The active hydrogen compounds used in the present invention include the following.

That is, cyano compounds such as hydrogen cyanide and ethyl cyanoacetate, malonic acid esters, and acetoacetyl compounds such as acetylacetone and ethyl acetoacetate.

Hydroxylamine or oxime derivatives such as hydroxylamine and acetone oxime, N-substituted aromatic amines such as N-methylaniline and diphenylamine, aliphatic and aromatic mercaptans, aromatic hydroxyl such as phenols and 6-hydroxytetralin. Examples include lactams such as α-pyrrolidone and caprolactam, 5-pyrazolone compounds such as 1-phenol-3-methyl-5-pyrazolone, imidazoles and triazoles. In addition, the phenols used in the present invention include:
Phenol, chlorophenol, cresol, ethylphenol or alkylphenols such as linear or branched propyl-, butyl-, nonylphenol, catechol, resorcinol, pyrogallol, fluoro-glucinol, 4,4'-dihydroxydiphenylmethane, 2,
Examples include 2-isopyrrobylidene diphenol, α- and β-naphthol, anthranol, and phenanthrol. These phenols may be substituted with substituents that are inert to this reaction, such as monovalent substituents such as halogen atoms, alkyl groups, or carboxylic acid ester groups, or may be substituted with alkylene groups, oxy groups, carbonyl groups, etc. There is no problem even if it is crosslinked with a divalent substituent.

When these active hydrogen compounds are used in small amounts, they are effective in promoting the reaction and improving the yield significantly compared to when they are not used at all. Usually 0.0% for the nitro group of the aromatic nitro compound.
0.05 molar ratio or more, preferably 0.1 molar ratio or more. Using a large amount in excess of the aromatic nitro compound is not only not economically advisable, but also tends to lower the yield. Usually 1 for the nitro group of aromatic nitro compounds
It is used in a molar ratio of 0 or less, preferably 5 or less.

On the other hand, ordinary alcohols react with isocyanates to produce urethane, but the dissociation initiation temperature of the produced urethane is as high as 250° C. or higher, and therefore is not included in the active hydrogen compounds of the method of the present invention.

Noble metal compounds used as main catalysts include inorganic compounds such as palladium and palladium halides, nitrates, isocyanides, carbonates, carboxylates, oxides, and chelates, and carbonyl, alkyl, olefin, and π-allyl groups. Examples include organic complexes containing ligands. Preferred are compounds containing halogen, such as palladium chloride, palladium bromide, palladium iodide, sodium chloropalladate, tetraammine palladium chloride, dichlorodiammine palladium, bis(ethylene) palladium chloride, bis(π-allyl) palladium chloride. etc. 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.

Examples of the nitrogen-containing heterocyclic compound that acts as a ligand to the noble metal of the main catalyst include pyrrole, N-methylpyrrole, pyrazole, imidazole, triazole, pyridine, α-9β- or γ-picoline, and 4-phenylpyridine. , 4-vinylpyridine, 2-fluoropyridine, 2
-Chloropyridine, 3-chloropyridine, 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-dicyazpyridine, 5.
6. 7. 8-tetrahydroquinoline, 5,6,7.
Examples include 8-tetrahydroisoquinoline, quinoline, isoquinoline, acridine, benzoquinoline, benzisoquinoline, phenanthridine, pyridazine, pyrimidine, pyrazine, cinnoline, quinazoline, quinoxaline, phthalazine, naphthyridine, phenazine, and the like.

Typical examples of complexes of noble metal halides with nitrogen-containing heterocyclic compounds include dichlorobis(pyridine)palladium, dibromobis(pyridine)palladium, short bis(pyridine)palladium, dichlorobis(α-picoline)palladium, and dichlorobis(quinoline). ) palladium, dichlorobis(isoquinoline)palladium, dichlorocarbonyl(pyridine)palladium, dichlorocarbonyl(2,6-dimethylpyridine)palladium, and the like.

The process of the present invention is characterized by the use of a co-catalyst system consisting of a combination of a special compound consisting of a halogenated phosphorus compound, a vanadium compound and a tertiary amine in addition to the main catalyst palladium or its compound.

In order to carry out the method of the present invention effectively, the use of each catalyst component is essential, but the addition of halogenated phosphorus compounds is particularly effective, increasing the activity of the catalyst system and promoting the reaction. , suppressing the formation of by-products and increasing the selectivity of the target product.

Examples of the halogenated phosphorus compounds used in the method of the present invention include phosphorus trifufluoride, phosphorus trichloride, phosphorus tribromide, phosphorus triiodide, phosphorus pentafluoride, phosphorus pentachloride, phosphorus pentabromide, and phosphorus tetrabromide. Halogenated phosphorus compounds such as niline chloride and niline tetraiodide; alkyl- or aryl-substituted halogenated phosphorus compounds such as dimethylbromophosphine, diphenylchlorophosphine, and ethylphosphorus tetrachloride;
Phosphoryl fluoride, phosphoryl chloride, phosphoryl bromide,
- Phosphorus oxyhalides such as phosphoryl difluoride chloride, phosphoryl difluoride, pyrophosphoryl chloride, and phosphorus oxyhalide; Quaternary phosphonium halides such as tetraethylphosphonium chloride; Phosphonyl halides such as ethylphosphonate dichloride ; Examples include alkyl phosphate halogenides such as methyl phosphate dichloride.

These halogenated phosphorus compounds are used in amounts of 0.05 to 20 grams of phosphorus, preferably 0.1 to 10 grams of phosphorus, per 1 gram atom of palladium. Further, it is desirable to use the compound at a concentration of 1X10-3 mol or more per mole of the raw material nitro compound, and a concentration of 1X10-4 or more per 1 kg of the total reaction solution in the reaction solution.

Any vanadium compound can be used as the vanadium compound. Further, the valence of vanadium in the vanadium compound used is not particularly limited.

Vanadium compounds that can be used in the method of the present invention include, for example, chlorides such as vanadium trichloride and vanadium tetrachloride; chloride salts such as potassium vanadium chloride (TV);
Chlorinated oxides such as vanadium dichloride oxide, vanadium trichloride oxide, vanadium oxide (■), vanadium oxide (■)
, oxides such as vanadium (V) oxide, pyrovanadic acid,
Vanadate such as metavanadate, vanadate salts such as sodium orthovanadate, ammonium metavanadate, potassium metavanadate, vanadium sulfate (I[[)
Ammonium, vanadium salts of acids such as potassium vanadium (III) oxalate, vanadyl salts of acids such as vanadium oxysulfate (■), vanadium oxyoxalate, vanadium (I
V) Acetylacetone salts such as oxyacetylacetonate, hexacarbonyl vanadium, etc.

These vanadium compounds are used in an amount of 0.05 to 20 gram atoms, preferably 0.1 to 10 gram atoms, in terms of vanadium per gram atom of vanadium. 0
．． If less than 0.5 gram atoms are used, the activity is low, and if more than 20 gram atoms are used, the selectivity decreases. Also, for 1 mole of raw material nitro compound, lX10-' to lX10-
It is preferable to use 1 mol, preferably in the range of 1XIO-3 to 5XIO-2 mol.

Tertiary amines include aliphatic □, aliaromatic, alicyclic,
Aromatic tertiary amines and nitrogen-containing heterocyclic compounds are used. If these may be in unsubstituted form, suitable substituents inert to this reaction may be used, such as halogen atoms, alkyl groups, aryl groups, alkenyl groups, cyan groups,
It may have a substituent such as an aldehyde group, an alkoxy group, a phenoxy group, an alkylthio group, a phenylthio group, a carbamyl group, a carbalkoxy group, or a thiocarbamyl group. These include, for example, aliphatic tertiary amines such as trimethylamine, triethylamine, tripropylamine, and tributylamine, N,N-dimethylaniline, N
, N-diethylaniline, N,N-diisopropylaniline and other fatty aromatic amines, N,N-dimethylcyclohexylamine, N,N-diethylcyclohexylamine, N,N-diisopropylcyclohexylamine,
1-4-diazabicyclo (alicyclic tertiary amines such as 2,2,23 octane, aromatic tertiary amines such as triphenylamine, nitrogen-containing heterocyclic compounds such as pyridine, quinoline, isoquinoline) Among them, nitrogen-containing heterocyclic compounds are particularly effective in improving the yield and reaction rate of urethane.Further examples of effective nitrogen-containing heterocyclic compounds other than the above include 1-methylpyrrole, 1-phenylpyrrole, l-methylindole, 1
-Methylindole, 1-phenylindole, indolenine, 2-isobenzazole, indolizine, 1-methylcarbazole, 2-chloropyridine, 2-bromopyridine, 2-fluoropyridine, 4-phenylpyridine, 2-23- and 4-methylpyridine, 2-methyl-
5-ethylpyridine, 2,6-dimethylpyridine, 2
．． 4.6-drimethylpyridine, 2-vinylpyridine,
? -Styrylpyridine, 3-chloropyridine, 2.6-
dichloropyridine, 2-chloro-4-methylpyridine,
4-phenylthiopyridine, 2-methoxypyridine, 4
-dimethylaminopyridine, α-picolinate phenyl ester, T-picolinate methyl ester, 2,6-dichloropyridine, α-picolinaldehyde, α-picolinamide, 5°6.7. &-tetrahydroquinoline, 2,
2-dipyridyl, 2-chloroquinoline, acridine, phenanthridine, benzoquinoline, benzisoquinoline, naphthyridine, pyrazine, 4,6-dimethylvirazine, 2,6-dimethylpyrazine, pyridazine, pyrimidine, quinoxaline, 2,3-dimethyl Examples include quinoxaline, quinazoline, phthalazine, phenazine, cinnoline, and pteridine. They can also be used as polymers such as polyvinylpyridine. The third of these
If the class amine can be added to the reactor separately from the raw materials and other catalyst components, a portion of it can be previously treated with a portion of the other components of the catalyst system to convert it into a suitable compound such as a complex or adduct. It can also be used as

- For example, palladium chloride and pyridine can be added separately to a reactor and reacted, but if a palladium chloride-pyridine complex is made in advance,
The complex, other raw materials, catalyst components, and tertiary amine can be additionally added and reacted.

The amount of tertiary amine used is at least 0.05 molar ratio, preferably at least 0.1 molar ratio, based on the nitro group of the nitro compound used as a raw material. If the molar ratio is less than 0.05, the reaction becomes extremely slow and the selectivity decreases.

Furthermore, the present invention can be carried out by using one or more of the conventionally known co-catalyst additives consisting of various Lewis acids, metal compounds, organic and inorganic compounds, etc., in combination with the above-mentioned catalyst system.

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. Any solvent can be used as long as it is a liquid that is inert to the raw materials and products, and there are no particular restrictions on the solvent. Usually, for example, heptane, cyclohexane,
Aliphatic, cycloaliphatic and aromatic hydrocarbons such as benzene, toluene, xylene, various petroleum fractions, halogenated hydrocarbons such as dichloromethane, perchloroethylene, tetrachloroethane, chlorobenzene, dichlorobenzene, chloronaphthalene. etc. are used.

The amount of the solvent used is not particularly limited (it is arbitrary, and the appropriate amount varies depending on the reaction type. However, the amount used is usually 3 to 50% as the concentration of the aromatic nitro compound in the solvent).
% by weight. 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 moles per mole of nitro group according to the formula (11), and at the same time 2 moles of carbon dioxide are by-produced. The appropriate amount of carbon monoxide to be charged 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 minimum amount is based on the amount of nitro groups in the reactor. The amount is usually 5 to 100 times the mole, preferably 7 to 20 times the mole.Also, the reaction can be carried out batchwise while still containing carbon dioxide as a by-product, but the reaction It is preferable to remove carbon dioxide, which increases as the reaction progresses, from the reactor while simultaneously recycling and replenishing carbon monoxide to maintain a small molar ratio of carbon dioxide to carbon oxide in the reactor.

The reaction temperature is 100-250°C, preferably 150-23°C.
A range of 0°C is used.

The reaction pressure is 10 to 1000 kg/c112, usually 50
A range of ~500 kg/cm2 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 in a solvent and each component of the catalyst are mixed or separately fed into the reactor prior to the reaction. 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 oxide is injected under pressure.

After a predetermined period of time, the reaction mixture is cooled or its raw gas is separated. The resulting reaction mixture is subjected to distillation and separated into product isocyanate, solvent, catalyst and by-products. The recovered catalyst and solvent can be used again in the reaction as they are or after being 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 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 produced economically in high yields from aromatic nitro compounds by using highly active catalyst systems.

〔Example〕

The present invention will be specifically explained using Examples or Comparative Examples.

In the following Examples and Comparative Examples, an electromagnetic stirring autoclave made of stainless steel (SOS-316L) was used for all reactions.

In addition, the conversion rate and yield in the examples are 15% silicon DC5.
Calculated from the results of gas chromatography analysis using biphenyl internal standard at 150° C.

In the examples, dinitrotoluene is abbreviated as DNT, diisocyanate is abbreviated as TDI, nitrotolyl isocyanate is abbreviated as NIT, and when it is necessary to indicate the position of a substituent,
For example, 2,4-dinitrotoluene is prefixed with a number indicating the position, such as 2,4-DNT.

Example-1 2.4-ON↑ in an autoclave with an internal volume of 500 ml
30 g, phenol 3.1 g, dichlorobis(pyridine) palladium 0.378 g, phosphoryl chloride 0.34
A solution consisting of 6 g of vanadium trichloride oxide, 0.096 g of vanadium trichloride oxide, and 9.8 g of quinoline and 172 g of o-dichlorobenzene was charged.

The inside of the autoclave was replaced with nitrogen, and -160% with carbon oxide.
The pressure was increased to kg/cm2G. 210℃ while stirring
The temperature was raised to 1, and the reaction was continued at the same temperature for 300 minutes. On the way, the pressure was 2
26 carbon monoxide for every drop to 40 kg/am2G
Pressure was supplied to 0 kg/cm2G.

After the reaction was completed, the autoclave was depressurized while being maintained at the reaction temperature without being cooled, and 0-dichlorobenzene, phenol, and some quinoline accompanying the exhaust gas were condensed and collected through a condenser. After evacuation to normal pressure, a portion of the reaction solution in the autoclave was taken and analyzed. As a result, the reaction solution contained 2.
It was found that 22.1g of 4-TDI was contained.

This corresponds to a yield of 77 mol% based on the charged 2.4-DNT.

Gradually depressurize the autoclave, collect the fraction consisting of a mixture of quinoline and 2,4-TDI distilled out under reduced pressure, and distill the fraction using a conventional rectification column,
2.4-TDI (120~117'c/15~
9 tm Hg) was obtained.

Comparative Example-1 and Examples-2 to 7 In order to demonstrate the effect of the active hydrogen compound in the method of the present invention, Comparative Example-1 is a case in which phenol is not used, and Examples-2 to 7 are cases in which the amount of phenol used is changed. As 4,
Instead of phenol, Fufu p-phenylphenol, ε
- Cases in which caprolactam or acetone oxime was used are shown in Table 1 as Examples 5 to 7.

Other usage amounts and methods are the same as in Example-1.

Comparative example-1 in which no active hydrogen compound is used
As a result of the increased reaction rate compared to the above, the nitro group conversion rate improved, and the yield of 2.4-TDr and the total yield of 2.4-TDI+NIT also increased, indicating that the selectivity was improved.

Comparative Examples 2 to 3 Comparative Examples to demonstrate the effect of co-catalyst in the method of the present invention
In Comparative Example 2, phosphoryl chloride was not used, and in Comparative Example 3, 2.4-DNT and carbon monoxide were reacted in the same manner as in Example 1, except that vanadium trichloride oxide was not used. The table is again shown together with the results of Example-1.
Shown in 2.

The absence of any of the cocatalyst components in the process of the present invention resulted in decreased nitro group conversion and total isocyanate yield.

Examples 8 to 12 Table 3 shows the results of reactions conducted in the same manner as in Example 2, except that some of the raw materials or catalysts used in Example 1 were changed to the types or amounts shown in Table 3.

Example-13 Crude DNT obtained by nitration of toluene 31.3
g<724 g of 2.4-DN, 76 g of 2.6-DN as well as a small amount of nitrotoluene and 2.3-13.4- and 2.
(including 5-DNT isomer) phenol 34.0 g, dichlorobis(quinoline) palladium 0.492 g, phosphoryl chloride 0.173 g, vanadium trichloride oxide 0.0
96g, quinoline 4.9g, o-dichlorohenzene 14
The reaction was carried out in the same manner as in Example-1, except that 5 g was used and the reaction was carried out at a reaction temperature of 190° C. for 3.5 hours.

As a result of analyzing the reaction solution in the autoclave after evacuation, no unreacted DNT or intermediate NIT was observed, and a total of 24.4 g of 2.4- and 2.6-TDr was contained. This corresponds to a yield of 85% based on the charged 2.4- and 2.6-D NT. The reaction solution in the autoclave was distilled in the same manner as in Example 1, and 2,4- and 2.6-
-23.8 g of TDI was obtained.

〔Effect of the invention〕

According to the method of the present invention, aromatic isocyanates can be produced in high yield from aromatic nitro compounds and carbon monoxide through simple steps under mild conditions.

Claims (1)

[Scope of Claims] 1) An aromatic nitro compound and carbon monoxide, a mixture of palladium or its compound and a nitrogen-containing heterocyclic compound, a complex of palladium coordinated with the nitrogen-containing heterocyclic compound, and In a method for producing an aromatic isocyanate, the reaction is activated at high temperature and pressure in the presence of one or more catalysts selected from the group consisting of a mixture of the complex and the nitrogen-containing heterocyclic compound. It is characterized in that it is carried out in the presence of a hydrogen compound using a promoter system consisting of a halogenated phosphorus compound, a vanadium compound, and a tertiary amine, and aromatic isocyanates are separated from the resulting reaction product by distillation. A method for producing an aromatic isocyanate.