JPS5811942B2 - Aromatic urethane purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention deals with the production of an aromatic urethane obtained by reacting an aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide using a catalyst system containing a platinum group metal or its compound, in an acidic aqueous solution. This invention relates to a method for purifying aromatic urethane, which is characterized by treating aromatic urethane, and its purpose is to thermally decompose the aromatic urethane produced by the above reaction to produce a corresponding aromatic isocyanate. The objective is to obtain an aromatic urethane with good thermal stability.

Conventionally, isocyanates have been produced from amine compounds and phosgene, but in recent years, new production methods have been developed due to the lack of raw material resources, soaring prices, and the strong toxicity of intermediate raw materials for producing isocyanates. It's here.

One of these methods is to produce an aromatic urethane from alcohol, carbon monoxide and an aromatic nitro compound, and then thermally decompose the aromatic urethane to produce the corresponding aromatic isocyanate.

When producing aromatic urethanes from alcohol, carbon monoxide, and aromatic nitro compounds, most of the conventionally known methods employ a catalyst system in which a platinum group metal compound is used as a main catalyst and a compound containing a Lewis acid is used as a promoter. I am using it.

For example, a method using a Group Ⅰ metal carbonyl group-containing derivative and a salt of a metal existing in two or more valence states as a catalyst (Japanese Patent Publication No. 43-23939), a method using palladium and a Lewis acid as a catalyst (US Pat. No. 3,531) ,512
) A method using rhodium chloride and ferric chloride as catalysts (
Special Publication No. 45-24137) is known.

In these methods, even if a large amount of catalyst is used and the reaction is carried out for a long time, the yield of the target product is low, or in order to obtain a high yield, the initial pressure of carbon monoxide is 190 to 350 kg/cm2 and the temperature is 19
whether strict reaction conditions of 0 to 200°C are required;
Alternatively, in addition to disadvantages such as severe corrosion of the reactor due to the use of Lewis acids such as ferric chloride, aromatic isocyanates are produced by thermally decomposing the aromatic urethane obtained by these methods. It was found that it had poor thermal stability and was unsatisfactory in terms of quality as a raw material.

In addition, the present inventors first reacted an aromatic nitro compound, a hydrous acid group compound, and carbon monoxide using a catalyst system as described below, thereby producing an aromatic urethane in good yield under relatively mild reaction conditions. He discovered that it could be manufactured and applied for a patent.

However, the aromatic urethane obtained by such a method is also unstable under heat, and when trying to obtain isocyanate by thermally decomposing it, tar substances other than the target isocyanate are likely to be produced, so that the target isocyanate cannot be obtained. It was found that the yield was low.

Therefore, the present inventors conducted intensive studies on the method for purifying the aromatic urethane obtained in this way, and as a result, discovered a method for obtaining high-quality aromatic urethane suitable for producing isocyanates through simple operations, and the method of the present invention I was able to complete it.

That is, the method of the present invention is an aromatic nitro compound obtained by reacting an aromatic nitro compound, a hydrous acid group compound, and carbon monoxide using a catalyst system consisting of a platinum group metal or its compound, a Lewis acid, and a nitrogen-containing heteroaromatic compound. This method of purifying aromatic urethane is characterized by treating urethane with an acidic aqueous solution to remove impurities.

In the reaction for synthesizing aromatic urethane from an aromatic nitro compound, a hydrous acid group compound, and carbon monoxide, the following raw materials and catalyst systems can be used.

The aromatic nitro compound used as the main raw material may be either a mononitro compound or a polynitro compound.

For example, these include nitrobenzenes, dinitrobenzenes, dinitrotoluenes, nitrobenzenes, nitroanthracenes, nitrobiphenyls, bis-trophenyl) alkanes, bis-trophenyl) ethers,
Examples include heteroaromatic compounds such as bis-trophenyl) thioethers, bis-trophenyl) sulfones, nitrodiphenoxyalkanes, nitrophenothiazines, and 5-nitropyrimidine.

Further, the hydrous acid group compounds include monohydric alcohols or polyhydric alcohols, monohydric phenols, and polyhydric phenols containing primary, secondary, or tertiary hydroxyl groups.

Typical compounds include ethanol and phenol.

The platinum group metals and their compounds used as the main catalyst are palladium, rhodium, and ruthenium, and are used alone or in the form of a compound or a mixture of one or more of them.

Forms of compounds include halides, cyanides, thiocyanides, isocyanides, oxides, sulfates, nitrates, carbonyl compounds, addition compounds or complexes with tertiary amines such as triethylamine, pyridine, isoquinoline, and triphenylphosphine. A complex with an organic phosphorus compound is used.

These may be used in the reaction as they are, or may be supported on a carrier.

Furthermore, these carriers may be supplied to the reactor separately from the catalyst.

A Lewis acid is used as a promoter, and the Lewis acid referred to here is, for example, Jack Hine's Phyaical
Organic Chomistry, 1962. (M
e Grow HillBook, CO,, New Y
Brønsted acids are also included.

For example, tin, titanium, germanium, aluminum,
Examples include halides, sulfates, acetates, phosphates, and nitrates of iron, copper, nickel, zinc, cobalt, manganese, etc.

More specifically, ferric chloride, ferrous chloride, tin chloride,
Examples include stannous chloride, aluminum chloride, cupric chloride, cuprous chloride, and copper acetate.

Particularly preferred Lewis acids are ferrous chloride and ferric chloride.

The nitrogen-containing heteroaromatic compound used together with the Lewis acid as a cocatalyst may be in an unsubstituted form, or may have a suitable substituent inert to this reaction, such as a halogen atom, an alkyl group, an aryl group, an alkenyl group, a cyan group, It may have a substituent such as an aldehyde group, an alkoxy group, a phenoxy group, a thioalkoxy group, a thiophenoxy group, a carbalkoxy group, a carbamyl group, a carboallyloxy group, or a thiocarbamyl group.

Also, single salts of nitrogen-containing heteroaromatic compounds, such as nitrates,
Hydrohalides, sulfates, acetates, etc. can also be used.

Furthermore, quaternary salts of nitrogen-containing heteroaromatic compounds and oxides of nitrogen-containing heteroaromatic compounds can also be used.

These nitrogen-containing heteroaromatic compounds may be added to the reactor separately from the feedstock and other catalyst components, or they may be treated with some of the other components of the catalyst system beforehand to form appropriate complexes, adducts, etc. It can also be used in place of other compounds.

These complexes can be prepared according to conventional methods for preparing complexes.

For example, a complex can be easily formed by stirring the components of the complex to be prepared in a suitable solvent such as benzene, monochlorobenzene, dichlorobenzene, ethanol, etc. or in an excess of a nitrogen-containing heteroaromatic compound.

It is desirable to remove as much water as possible from the solvent and complex components used.

Furthermore, if the complex is prepared in a carbon monoxide atmosphere, a more active complex may be obtained.

If necessary, the solvent or excess nitrogen-containing compound is distilled off.

All of these nitrogen-containing heteroaromatic compounds suppress material corrosion caused by Lewis acids.

The amount of the nitrogen-containing heteroaromatic compound added for this purpose is preferably an amount equivalent to 0.5 molar ratio to 5 molar ratio relative to the anion of the Lewis acid, particularly an approximately equimolar equivalent amount. It is appropriate to use

In this urethanization reaction, most of the catalyst system used is separated and recovered from the reaction liquid as a reaction wave solid.

Although the form of the recovered catalyst is not clear, it can be recycled as it is or after being purified by an appropriate method such as a solvent washing method.

Further, after recovering the catalyst, the filtrate is cooled, and the reaction mother liquor obtained by separating the precipitated crude urethane can be recycled to the reaction system again after adding the recovered catalyst or a new catalyst.

This urethanization reaction can be carried out without the presence of a solvent.

The reaction is preferably carried out using an organic compound containing a hydroxyl group in at least an equimolar ratio to the nitro group of the nitro compound and carbon monoxide.

The amount of platinum group metal used for the nitro compound can vary widely depending on the type and other reaction conditions;
1 to 1 in weight ratio as a single metal to the nitro compound
x10-5, preferably in the range of 5 x 10-2 to 1 x 10-4.

The Lewis acid used as a promoter is used in a weight ratio of 2 to 2 x 10-3, preferably 1 to 5 x 10-2, based on the nitro group.

Although there are no particular restrictions on the method of supply, it is desirable to add the nitro compound and Lewis acid after dissolving or partially dissolving them in a hydrous acid group compound or a suitable solvent.

The order of addition is also not limited, but can be varied within the constraints of the equipment used.

For example, in a suitable pressure reactor such as an autoclave,
A hydrous acid group compound, a catalyst, an amine, and an organic nitro compound are charged, carbon monoxide is introduced under pressure, and the mixture is heated and stirred until the desired reaction is completed.

Carbon monoxide can also be supplied intermittently or continuously by exhausting carbon dioxide gas generated as the reaction progresses.

The reaction may be carried out in a batch, semi-continuous or continuous manner, and excess carbon monoxide after the reaction can be recycled.

The reaction temperature is generally maintained in the range of 80° to 230°C, with a range of 140° to 200°C being particularly preferred.

The reaction proceeds faster at higher temperatures, but usually 150-1
A temperature of 60°C is sufficient.

When the concentration of nitro compounds is high and there is a risk of decomposition during the reaction, the first stage reaction may be carried out at two temperatures, for example at
After carrying out the reaction at a temperature around 0°C, the second stage reaction may be carried out at a temperature around 190°C, but usually such a method is not necessary.

The appropriate reaction time varies depending on the nature of the nitro compound used, the reaction temperature, the reaction pressure, the type and amount of the catalyst, the reaction apparatus, etc., but is generally carried out in the range of 5 minutes to 6 hours.

After the reaction is complete, the reaction mixture is cooled and evacuated, and the reaction products are processed by conventional methods including filtration, distillation or other suitable separation methods to remove unreacted materials, by-products, solvents,
Separates urethane from catalysts, etc.

By treating the urethane thus obtained with an acidic aqueous solution to remove trace amounts of impurities, the aromatic urethane has good thermal stability and can be used as a raw material for obtaining aromatic isocyanates by thermal decomposition. can be obtained.

Here, the acidic aqueous solution refers to water-soluble inorganic and organic acids, such as mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic carboxylic acids such as formic acid, oxalic acid, and acetic acid.

The treatment with the acidic aqueous solution is carried out by bringing the aromatic urethane or its solution into contact with the acidic aqueous solution.

For example, the crude aromatic urethane separated from the reaction solution may be stirred in an acidic aqueous solution, or the crude aromatic urethane may be mixed with chloroform, dichloroethane, carbon tetrachloride, benzene, etc.
An effective method is to mix and stir a solution dissolved in a suitable solvent such as toluene or o-dichlorobenzene and an acidic aqueous solution.

The concentration of the acidic aqueous solution is preferably 50% or less, particularly 5 to 10%.

Although it can be used at a concentration of 50% or more, if the concentration is too high, there is a risk that the aromatic urethane will decompose.

For the same reason, the processing temperature is as low as possible, preferably 1
A temperature of 00°C or lower is suitable.

The amount of the acidic aqueous solution used varies depending on the quality of the crude aromatic urethane to be treated, the type and concentration of the acid used, the treatment temperature, etc., but is generally 0.5 to 100 times the weight of the aromatic urethane. Preferably 1 to 50 times is used.

A specific example of the effect of the amount of acidic aqueous solution used is Example 1.
It will be described in

After the treatment, the product is washed with water to remove traces of attached or mixed acid residue, and then the aromatic urethane is dried or the aromatic urethane solution is concentrated and the solvent is removed to obtain a pure aromatic urethane.

There is almost no substantial loss of aromatic urethane during the purification process in acidic aqueous solution.

The aromatic urethane purified in this way has excellent thermal stability and is less subject to thermal deterioration due to heating, and the degree of thermal deterioration is the same as that of pure aromatic urethane.

On the other hand, when acid treatment is not performed, thermal deterioration is severe.For example, when the raw material is melted and stored under heating in a raw material storage tank as a raw material for obtaining aromatic isocyanate by thermal decomposition, it deteriorates and the purity decreases. .

Furthermore, when such aromatic urethane is thermally decomposed, the yield of aromatic isocyanate obtained is low.

Various methods have been proposed for the thermal decomposition of aromatic urethanes.

For example, a method of thermal decomposition in the gas phase at a high temperature of 400 to 600°C (Japanese Patent Publication No. 44-17773, Japanese Patent Publication No. 11774-1983)
5, etc.), a method of thermal decomposition in a liquid phase using a solvent at a relatively low temperature of 250°C or less (US Pat. No. 2,409,712, JP-A-50-30832, JP-A-52-19624).
Generally, the liquid phase method has a better thermal decomposition yield.

When the aromatic urethane purified by the method of the present invention is thermally decomposed using the method described in JP-A-52-19624, the yield of isocyanate compounds is 90% or more in all cases, but 70% in the unpurified product. The amount of tar during thermal decomposition is large.

The invention is explained in more detail by the following examples without being restricted thereto.

In these creations, all reactions were performed using stainless steel (SUS3).
2) was used.

In addition, material corrosion was calculated from the weight loss and surface area of the stirring blade (SUS32).

The conversion rate, yield, and purity shown in the examples were calculated from the results of gas chromatography glass analysis and liquid chromatography glass analysis.

Note that the purity was determined using the following formula.

(Diurethane content in sample (g))/(Sample weight used for analysis (g)) x 100 (%) Note) - Based on liquid chromatography analysis using chlornitrobenzene as an internal standard.

Example 1 36.4 g of 2,4-dinitrotoluene, 3.12 g of 1.5% palladium-carbon, 8.4 g of ferric chloride, and 12.6 g of pyridine were placed in an autoclave with an internal volume of 11, and the system was purged with nitrogen. After replacing with gas, carbon oxide was filled to an initial pressure of 70 kg/cm2G.

When the internal solution was heated to 160℃ while stirring and allowed to react at the same temperature for 150 minutes, no pressure drop was observed.
The reaction has finished.

After the autoclave was cooled to 60°C, it was evacuated and the reaction solution was discharged.

The insoluble matter in the reaction solution was filtered at 60°C, and the recovered catalyst 20.2
I got g.

The filtrate was cooled to room temperature, and the precipitated crystals were filtered to 30 m
After washing with cold ethanol in Step 1, drying yielded 34.6 g of product.
I got it.

The analysis result of the product is diethyltoluene-2,4-cyca-
Purity is 99 as bamate (hereinafter abbreviated as diurethane)
．． It was 0%.

Crude diurethane (A) thus obtained: 10.0
g was added to 20 ml of 5% aqueous hydrochloric acid solution, stirred well at 50°C, filtered twice, and then mixed with the same amount of water.
After washing twice and drying, 9.9 g of purified diurethane (B) (purity of 99% or more) was obtained.

In addition, 10.0 g of crude diurethane (A) was added to 10 m of benzene.
1, add 25ml of 5% hydrochloric acid aqueous solution and
After stirring at ℃ and separating the liquid four times, the benzene layer was washed three times with the same amount of water, and concentrated to dryness to obtain 9.9 g of purified diurethane (C) (purity of 99% or more). Ta.

Further, a diurethane synthesized separately by reacting 2,4-diisocyanatetoluene and ethanol was recrystallized three times with ethanol to obtain a pure standard diurethane (D) (purity of 99% or more).

1 g each of the crude diurethane (A), purified diurethane (B), (C), and standard diurethane (D) obtained by the above method was placed in a test tube, and heated at 200°C under a nitrogen atmosphere for 1 g.
After heating for ~5 hours, it was cooled and dissolved in ethanol to measure purity.

Table 1 shows the relationship between heating time and diurethane purity.

In the liquid chromatograph of diurethane after heating, in addition to the peak of diurethane, the main component, peaks of high molecular weight compounds were observed.

This is thought to be because a part of the diurethane was thermally degraded and changed into a polymer having urea bonds, allophanate bonds, carbodiimide bonds, etc.

Example 2 36.4 g of 2,4-dinitrotoluene, 0.05 g of palladium chloride, 8.4 g of ferric chloride, 12.6 g of pyridine
The reaction was carried out in the same manner as in Example 1 using 300 ml of ethanol and 34.2 g of phase diurethane was obtained.

99% purity.

10.0 g of the crude diurethane thus obtained was
Dissolved in 10 ml of dichlorobenzene, stirred with 40 ml each of 3% sulfuric acid aqueous solution at 50°C, separated three times, washed three times with the same amount of water, and concentrated and dried the o-dichlorobenzene layer to obtain refined diurethane. 9.9g was obtained.

The purity after heating this at 200° C. for 5 hours was 88%.

When crude diurethane without sulfuric acid treatment was similarly heated, the purity decreased to 35%.

Example 3 When the diurethane after the reaction was purified in the same manner as in Example 2 using a 5% nitric acid aqueous solution instead of treating it with a 3% sulfuric acid aqueous solution, a diurethane with good thermal stability similar to that of Example 2 was obtained. .

Example 4 A crude dinitrotoluene mixture (2,4-dinitrotoluene 76
%, 2,6-dinitrotoluene 19% 2.3- and 3
, 4-dinitrotoluene 4%) 365 g, ethanol 1
0100O, ferrous chloride-pyridine complex (ferrous chloride 1
27.3 g (adjusted from 2 moles of pyridine and 2 moles of pyridine) and 0.26 g of palladium chloride were placed in an autoclave with an internal volume of 51 cm, carbon monoxide was pressurized at room temperature to 90 kg/cm2G, the temperature was raised while stirring, and the temperature was kept at 170°C for 5 hours. Ta.

After the reaction, the solid catalyst is filtered from the reaction solution, the filtrate is concentrated to remove excess ethanol, and the crude diurethane mixture 831
I got g.

The analysis result was 91.2% as a total purity of 2,4- and 2,6-mono-diurethane.

This crude diurethane mixture was prepared in the manner described in Example 1 for 20
When heated at 0° C. for 5 hours, the purity after heating decreased to 30%.

Dissolve 100 g of crude diurethane in 300 ml of dichloroethane, shake at 60°C with 500 ml of 5% aqueous hydrochloric acid solution, perform liquid separation three times, wash with 500 ml of water, and concentrate and dry the dichloroethane layer to obtain 93 g of purified diurethane mixture. I got it.

Purity is (as 2,4 unit and 2,6 unit total) 98
%Met.

When this purified diurethane was heated at 200° C. for 5 hours, the purity after heating was 88%.

Example 5 In Example 4, 100 g of the crude diurethane mixture was replaced with 500 ml of 10% acetic acid aqueous solution instead of using 5% hydrochloric acid aqueous solution.
The same treatment was performed using

The purified diurethane obtained weighed 92 g and had a purity of 98%.

When this purified diurethane was heated at 200° C. for 5 hours, the purity after heating was 86%.

Example 6 According to the method described in Japanese Patent Publication No. 45-24137, 100 g of nitrobenzene, 50 g of methanol, 350 g of toluene, 1 g of rhodium trichloride and 5 ferric chloride
Put 15 g of carbon monoxide into an autoclave with an internal volume of 11, pressurize it with carbon monoxide at an initial pressure of 80 kg/cm2G, and add 15 g while stirring.
The temperature was raised to 0°C and the reaction was continued for 13 hours.

After the reaction, the reaction solution was filtered to remove trace amounts of insoluble matter, and then distilled under reduced pressure to remove toluene and excess methanol, yielding 120 g of purified methyl-N-phenyl urethane.

The purity of the crude urethane was 70%.

When the crude urethane was heat-treated at 150°C for 2 hours, the purity decreased to 30%.

100 g of crude urethane was dissolved in 200 ml of chloroform, mixed three times with 300 ml of 5% aqueous hydrochloric acid solution, washed with water, the chloroform layer was concentrated, and the chloroform was distilled off to obtain 72 g of purified urethane (purity 97%).

After heating this refined urethane at 150° for 2 hours, the purity was 90%.

Claims (1)

[Claims] 1. An aromatic urethane obtained by reacting an aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide using a catalyst system in which a platinum group metal or its compound as a main catalyst and a compound containing a Lewis acid as a cocatalyst. A method for purifying aromatic urethane, characterized by treatment with an aqueous solution.