JPH02138166A - Production of aromatic urethane - Google Patents

Abstract

PURPOSE:To enable efficient recovery and reuse of the catalyst to avoid the quality deterioration of the product, in the production of an aromatic urethane by the carbonylation reaction, by separating the catalyst from the product in the coexistence of an aliphatic hydrocarbon solvent. CONSTITUTION:In the production of an aromatic urethane by reaction of an aromatic nitro compound, a hydroxyl organic compound such as alcohol, phenol and carbon monoxide in the presence of a catalyst system comprising a platinum metal, as a major catalyst, a Lewis acid, as a cocatalyst and a nitrogen- containing aromatic compound, as a ligand, the separation of the catalyst from the aromatic urethane product is conducted in the coexistence of an aliphatic hydrocarbon solvent such as straight-chained or branched alkane and cycloalkane, for example, n-heptane, isohexane or cyclohexane. Thus, the recovery and reuse of the catalyst is facilitated and the deterioration of the product can be avoided.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing an aromatic urethane compound, and in particular, a non-phosgene method for producing polymethylene polyphenyl polyisocyanate (hereinafter abbreviated as PMPPI), which is a raw material for polyurethane. The present invention relates to a method for producing an aromatic urethane compound that is a starting material in the production process.

Specifically, in the production of aromatic urethane, which involves reacting an aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide in the presence of a platinum group metal/Lewis acid/nitrogen-containing heteroaromatic compound catalyst system, This invention relates to an improved method that allows easy recovery and reuse of products and prevents deterioration of product quality.

(Prior technology) PMP is used in large quantities as a raw material for polyurethane
PI has conventionally been produced industrially by the phosgene method in which phosgene is reacted with an aromatic amine obtained by reducing an aromatic nitro compound. However, this method has problems such as the use of toxic phosgene, the need for expensive chlorine for phosgene synthesis, and the production of large amounts of hydrogen chloride as a by-product.

Therefore, P? by the non-phosgene method that does not use phosgene?
Methods for synthesizing 1PPI have been actively studied.

One of the non-phosgene methods involves using an aromatic nitro compound as a starting material and passing through three steps: carbonylation, condensation, and thermal decomposition. For details, see aromatic nitro compounds,
Carbonylation (to synthesize aromatic urethane by reacting carbon monoxide and a hydrous acid group organic compound in the presence of a catalyst),
Next, this urethane is crosslinked by a condensation reaction with a methylenating agent such as formaldehyde to synthesize a polyurethane compound (condensation), and the hydrous acid group organic compound (alcohol or phenol) is eliminated from this polyurethane compound (thermal decomposition). P? This is the method to obtain IPPI.

Taking the synthesis of MDI (methylene diphenyl diisocyanate), which is a representative example of PMPPI, as an example, the above reaction route is shown in the following reaction formula.

Carbonylation: Condensation: Thermal decomposition: MDU = methylene diphenyl cycarbamate The present invention relates to a method for producing urethane compounds such as RPC by a reaction corresponding to the carbonylation step of the above reaction route.

A method for producing an aromatic urethane by performing the above carbonylation step in the presence of a catalyst system consisting of a platinum group metal (main catalyst), a Lewis acid (cocatalyst), and a nitrogen-containing heteroaromatic compound (ligand). It is publicly known. This urethane synthesis method has the advantage that the catalyst can be recovered, the yield is high, and corrosion of the reaction equipment is suppressed.

After this reaction, the catalyst and aromatic urethane are recovered from the resulting reaction mixture, the catalyst is reused in the carbonylation reaction, and the aromatic urethane is thermally decomposed through the condensation step in the next step.
Converted to old. Therefore, industrially, it is important to recover the catalyst in a reusable state and to recover the aromatic urethane product with high purity and high yield so that it can be used in the next step. With these points in mind, the following methods have been proposed in the past.

Japanese Patent Publication No. 56-3861 states that after the completion of the reaction, the catalyst insoluble in the reaction solution was separated and recovered by filtration while hot, and then the filtrate was cooled to recover the precipitated aromatic urethane product. A method is disclosed in which the mother liquor is used together with the recovered catalyst in the next urethane synthesis.

JP-A-53-137929 describes a method for purifying the aromatic urethane obtained by the above method by treating it with an acidic aqueous solution. This improves the thermal stability of the urethane product and suppresses the by-product of tar substances other than the target isocyanate in the next thermal decomposition step.

Furthermore, a method is also known in which, after the reaction is completed, the insoluble catalyst is recovered by hot filtration or the like, and the filtrate is concentrated or distilled to recover the aromatic urethane.

(Problems to be Solved by the Invention) In the above-mentioned urethane synthesis method, it has been usual to use a large excess of the hydrated acid group organic compound as a reactant, which also serves as a solvent. This hydrous acid group organic compound has a high ability to dissolve catalysts, especially Lewis acids. Therefore, even if the insoluble catalyst is separated from the reaction solution by filtration after the reaction is completed, a considerable amount of the catalyst still remains in the filtrate and is mixed into the filtrate. In some cases, less than half of the Lewis acid is recovered by filtration, with most of the Lewis acid remaining in the filtrate. Therefore, when aromatic urethane is recovered from this filtrate by distillation, the aromatic urethane product is thermally degraded by the Lewis acid in the catalyst remaining in the filtrate, resulting in a decrease in the yield and deterioration of the quality of the urethane product.

especially? Aromatic urethane (RPC) is a raw material for IDI synthesis.
), it is difficult to apply the crystallization method as disclosed in Japanese Patent Publication No. 56-3861, so a distillation method must be used.

FIG. 1 shows the residual rate of EPC when various amounts of Lewis acid pecI* were added to RPC, which is a urethane product, and the mixture was heated at 110° C. for 1 hour. From this, it can be seen that the larger the amount of Lewis acid coexisting in urethane, the lower the residual rate.In other words, in the coexistence of Lewis acid, the thermal stability of urethane decreases and it undergoes thermal deterioration, but the larger the amount of Lewis acid coexisting, the lower the residual rate. It can be seen that thermal deterioration becomes severe.

Therefore, when recovering a urethane product by distillation as described above, as the distillation progresses, the amount of urethane in the thin distillate decreases, and the relative amount of catalyst that does not distill out to urethane increases, so what happens at the end of distillation? Thermal deterioration of urethane becomes significant and its yield decreases.

Furthermore, since the amount of catalyst remaining in the filtrate is large, the amount of catalyst recovered as solid content by filtration is also low, and it becomes necessary to add a new catalyst for reuse.

Even when the urethane product is recovered from the filtrate by cooling and crystallization, a large amount of catalyst remains in the filtrate as described above, and this precipitates out together with the urethane product, resulting in poor quality of the recovered urethane product. worsen. In addition, the catalyst and urethane product remain in a coexisting state in the mother liquor after crystallization separation.
If this mother liquor is used in the next reaction, thermal deterioration of the urethane product is unavoidable.

The purpose of the present invention is to improve the efficiency of separating the aromatic urethane product from the catalyst in the above-mentioned method for producing aromatic urethane by carbonylation reaction, thereby improving the reuse rate of the catalyst and improving the efficiency of the catalyst as a raw material for the next step. The objective is to improve the quality and yield of aromatic urethane.

(Means for Solving the Problems) As a result of repeated studies on means for efficiently separating catalysts, especially Lewis acids that degrade products, from aromatic urethane products, the present inventors discovered that aliphatic hydrocarbon solvents It has been found that when separation is performed by adding , the Lewis acid becomes insolubilized and the catalyst can be efficiently separated from the urethane product that remains in the dissolved state.

Thereby, almost the entire amount of the catalyst can be recovered as an insoluble content and reused. At the same time, the recovery rate of the catalyst is improved, and since only a small amount of Lewis acid exists in the separated aromatic urethane, there is no decrease in yield due to thermal denaturation even when the urethane is recovered by distillation, resulting in high purity and high recovery. It also becomes possible to recover the product at a high rate.

Although an aliphatic hydrocarbon solvent can be added during separation of the catalyst and urethane product, it is also possible to add this solvent before the reaction and carry out the carbonylation reaction in the presence of this solvent. It was also found that similar results were obtained.

The gist of the present invention is to use an aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide as main catalysts, and a platinum group metal,
In a method for producing aromatic urethanes by reaction in the presence of a catalyst system consisting of a Lewis acid as a cocatalyst and a nitrogen-containing heteroaromatic compound as a ligand, the separation of the aromatic urethane product and the catalyst is performed using an aliphatic This is a method for producing aromatic urethane, which is characterized in that it is carried out in the coexistence of a hydrocarbon solvent.

This aliphatic hydrocarbon solvent can be added either before or after the reaction.

(Function) As described above, the present invention is characterized in that the catalyst and urethane product are separated using an aliphatic hydrocarbon solvent in the production of aromatic urethane through the carbonylation reaction. The reactants, reaction conditions, etc. may be the same as those in the conventional method, but will be briefly explained below.

The aromatic nitro compound used as the main raw material may be either a mononitro compound or a polynitro compound, and has a III group other than a nitro group that is inactive under the reaction conditions (e.g., alkyl, alkenyl, alkoxy, halogen, carboxyl, cyano, isocyanate, etc.). These include nitrobenzenes, dinitrobenzenes, dinitrotoluenes, nitronaphthalenes, nitroanthracenes, nitrobiphenyls,
Examples include bis-trophenyl) alkanes, bis-trophenyl) ethers, nitrodiphenoxyalkanes, and heteroaromatic compounds such as 5-nitropyridine.

The hydrous acid group organic compound is an alcohol or a phenol, and may be either a monovalent or polyvalent compound. In the case of alcohol, the hydrocarbon residue from which the Off group is removed is a straight-chain or branched alkyl, cycloalkyl, alkylene, cycloalkylene or aralkyl. The hydrous acid group organic compound can contain substituents containing oxygen, nitrogen or halogen atoms, such as carbonyl, carboxylic acid ester groups, amines, amides or halogens.

As the platinum group metal serving as the main catalyst, one or more of palladium, rhodium, platinum, ruthenium, and osmium or a compound thereof can be used. Examples of the compound include halides, oxides, sulfates, nitrates, acetyl acetates, carbonyl compounds, and complexes with organic phosphorus compounds such as triphenylphosphine. Further, the main catalyst may be used in the reaction as it is, or after being kept in a suitable container.

As the Lewis acid which is a co-catalyst, under the reaction conditions, groups IIIA to Vm of the periodic table and IB to which perform a redox reaction are used.
Compounds obtained from elements of the VB subgroup are suitable. For example, halides such as tin, titanium, zirconium, vanadium, niobium, germanium, aluminum, iron, nickel, molybdenum, tungsten, manganese, cobalt, oquine halides, sulfates, phosphates, nitrates, oxides, acetylacetate and /or oxyacetylacetate.

The nitrogen-containing heteroaromatic compound as a ligand can be used in an unsubstituted form or with a substituent that is inert under the reaction conditions, such as halogen, alkyl, aryl, alkenyl, cyano, aldehyde, alkoxy, phenoxy, carbalkoxy, 11'ffA such as carbamyl, carboallyloxy
It may also contain a group.

Acid addition salts, quaternary salts, or oxides of nitrogen-containing heteroaromatic compounds can also be used.

These nitrogen-containing heteroaromatic compounds form a complex with a Lewis acid, so among the components of the catalyst system, the Lewis acid and the nitrogen-containing heteroaromatic compound can be used in the form of a complex by reacting them in advance. .

The carbonylation reaction is preferably carried out using carbon monoxide at a molar ratio of at least three times the nitro groups of the aromatic nitro compound as the main raw material.

It is necessary to use the hydrous acid group organic compound in an amount equal to or more than the nitro group. However, if it is used in large excess, the amount of dissolved catalyst increases, and the amount of aliphatic hydrocarbon solvent required to separate the catalyst as an insoluble component in the present invention increases. Therefore, it is preferable to use the hydrous acid group organic compound in a molar ratio of 1:I to 10:1 to the nitro group.

There are no particular restrictions on the charging method or order of addition of the reactants and catalyst, and they can be changed within the limitations of the equipment used. The reaction may be carried out batchwise, semi-continuously or continuously.

Although the reaction can be carried out in the absence of a solvent, it is preferable to carry out the reaction with the addition of an organic solvent, especially when the amount of the hydrous acid group organic compound is small. In this case, aromatic hydrocarbons, halogenated hydrocarbons, nitriles, ethers, esters, ketone solvents, etc. can be used as the reaction solvent, but as will be explained in detail later, the present invention enables separation of the catalyst. It is preferable to use the aliphatic hydrocarbon solvent used in the reaction solvent as the reaction solvent. If a reaction solvent other than these is used, it is desirable to remove the reaction solvent by distillation or the like before adding the aliphatic hydrocarbon solvent so as not to interfere with the separation of the catalyst according to the present invention.

The reaction temperature is within the range of 100 to 250°C, especially 140 to 1
The temperature is preferably within the range of 90°C. The reaction pressure is in the range of 10 to 1000 kg/cal-G, more preferably 30 to 300 kg/cal-G, as a partial pressure of carbon monoxide. The reaction time varies depending on various factors such as the type of reactant used, reaction temperature, reaction pressure, type and amount of catalyst, and reaction apparatus, but 0.5 to 10 hours is sufficient for -II.

After the reaction is complete, the reaction mixture is cooled to room temperature or depressurized without cooling. In the reaction mixture thus obtained, a portion of the catalyst is present as an insoluble component, but as described above, a considerable portion of the catalyst is present in a dissolved state. Therefore, the catalyst cannot be completely separated by simply filtering the reaction mixture, and the catalyst remaining in the urethane product causes deterioration of the product.

Therefore, in order to improve the yield and quality of the urethane product and to increase the recovery of the catalyst, it is necessary to separate the catalyst from the urethane product as completely as possible, and according to the present invention: By separating the catalyst in the coexistence of an aliphatic hydrocarbon solvent, almost the entire amount of the catalyst can be recovered as a solid content.

Aliphatic hydrocarbon solvents are particularly suitable for this purpose because they are capable of dissolving the urethane product without melting the catalyst and are inert to the reaction.

Aliphatic hydrocarbon solvents that can be used in the present invention include linear or branched alkanes as well as cycloalkanes. Specific examples include n-pentane, n-hexane, n-
Hebutane, n-octane, n-nonane, n-decane, n-
Undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, isopentane, isohexane, 3-methylpentane, 2,2-dimethylbutane, 2
．． 3-dimethylbutane, 2.3-dimethylpenkune, 2
-Ethylhexane, cyclopenkune, cyclohexane,
Cyclohebutane, cyclooctane, cyclononane, methylcyclopenkune, methylcyclohexane, 1,1-dimethylcyclohexane, 12-dimethylcyclohexane,
Examples include 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane. Isomers of these compounds or mixtures of two or more solvents can also be used.

In the method of the present invention, the timing of adding the aliphatic hydrocarbon solvent is not particularly limited.

For example, as described above, this solvent can be added as a reaction solvent to the reaction system before the reaction, and the reaction can be carried out in the presence of this solvent. In this case, the amount of the aliphatic hydrocarbon solvent added is the amount necessary to substantially completely insolubilize the catalyst, particularly the Lewis acid, which can be dissolved in the unreacted hydrous acid group organic compound after the reaction. For this purpose, the above-mentioned solvent is used in an amount of 1:1 or more by volume with respect to the amount of the hydrous acid group organic compound charged into the reactor.

When the reaction is carried out in the presence of an aliphatic hydrocarbon catalyst as described above, after the reaction is completed, the reaction mixture is cooled to room temperature and depressurized. The presence of this solvent renders the catalyst insolubilized, so that when the reaction mixture is filtered, the catalyst, particularly the Lewis acid, can be recovered almost completely as a solid content. The recovered catalyst can be purified as is or by an appropriate method such as solvent washing.
After adjusting the composition, it can be recycled.

The aliphatic hydrocarbon solvent can also be added to the reaction mixture immediately after the reaction. That is, even when this solvent is added to the depressurized reaction mixture after cooling or without cooling, the catalyst can be made substantially insolubilized in the same manner as described above. In this case, the amount of the solvent added may be the same as above because unreacted hydrous acid group organic compounds remain in the reaction mixture, and the catalyst can be recovered and recycled in the same manner as above.

Alternatively, the reaction mixture may be filtered after the reaction, the undissolved catalyst removed from the reaction mixture by filtration, and the solvent may be added to the reaction solution containing the resulting urethane product and residual catalyst. By adding this solvent, the catalyst, particularly the Lewis acid, dissolved in the reaction solution becomes insolubilized, and the urethane product remains in a dissolved state. After that, il! Almost all of the remaining catalyst can be recovered as solid content by filtration. The catalyst thus recovered, together with the catalyst recovered by the first filtration, is recycled if necessary after being purified as described above. The amount of solvent used in this case may also be the same as above.

After first filtering the reaction mixture to remove the undissolved catalyst as described above, the reaction mixture may be concentrated under normal pressure or reduced pressure before adding the aliphatic hydrocarbon solvent to the resulting reaction mixture. good. As a result, low-boiling components such as unreacted hydrous acid group organic compounds and nitrogen-containing heteroaromatic compounds are removed from the reaction solution.

In this case, since the amount of the hydrous acid group organic compound that solubilizes the catalyst is small, the amount of aliphatic hydrocarbon solvent added necessary for insolubilizing the catalyst may be smaller than the above.

In this case, the amount of the solvent added is generally 5:1 or more, preferably 10:1 or more by weight to the aromatic urethane product in the concentrated reaction solution. After addition of the solvent, the insolubilized catalyst is separated by filtration and recycled in the same manner as above.

The above catalyst separation operations can also be appropriately combined. For example, when the reaction is carried out in the presence of an aliphatic hydrocarbon solvent, if the catalyst is not sufficiently insolubilized, this type of solvent can be added after the reaction to separate the catalyst. Alternatively, it is also possible to add a small amount of solvent after the reaction, filter the catalyst, concentrate the resulting reaction solution, and further add a solvent to completely separate the catalyst. In this way, when adding an aliphatic hydrocarbon solvent two or more times, the solvents used may be the same or different.

In addition to filtration, the catalyst can be separated by any solid-liquid separation means such as centrifugation and decantation.

When the catalyst is separated in the presence of an aliphatic hydrogenated solvent as described above, a reaction solution containing almost no catalyst can be obtained. The aromatic urethane product is recovered from this reaction solution by an appropriate method such as distillation or crystallization. Since there is no catalyst, even if urethane is recovered by distillation, there will be no reduction in product yield or quality deterioration due to thermal denaturation or the like. Thereby, a substantially pure aromatic urethane product can be obtained in high yield without any particular purification. At the same time, since almost the entire amount of catalyst can be recovered, it is possible to recycle the catalyst with little or no additional catalyst.

Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, an electromagnetic stirring autoclave was used. The conversion rate and yield were calculated from the results of measurements by liquid chromatography.

This example illustrates a reaction in the coexistence of an aliphatic hydrocarbon solvent, n-hexane.

Contents: Nitrobenzene (NB) in a 160m autoclave.
) 1.2311g, pyridine 0.3955g, anhydrous ferric chloride 0.4055g, 5% palladium-carbon 0.1
064g, 5 parts of dehydrated ethanol and 10 parts of n-hexane
After charging II112 and replacing a sufficient amount of the air inside with carbon monoxide, carbon monoxide was charged until the initial pressure became 80 kg/c+d-(H.The contents were heated to 160°C while stirring at 500 rpm I11. After the reaction was completed, the reaction mixture was cooled to room temperature, evacuated, and replaced with nitrogen gas.

After adding 100 mq of n-hexane to the obtained reaction mixture, it was filtered to recover the catalyst as an insoluble matter.

The amount of recovered catalyst was 0.1214 g.

The obtained filtrate was almost colorless and transparent. The filtrate was analyzed and the desired product, ethyl phenyl carbamate (E
The production amount of PC) was determined, and the NB conversion rate and RPC yield were calculated. In addition, the total amount of Fe in the filtrate was measured by spectrophotometry, and the ratio to Fe1l in the charged FeCl5 (
The Fe residual rate in the filtrate was determined.

In the experiment, reactions and post-treatments were carried out in the same manner as in Example 1, using various aliphatic hydrocarbons as solvents in place of n-hexane.

Kitamoto L [LjL=ni] Reaction and post-treatment were carried out in the same manner as in Example 1, using various organic solvents other than aliphatic hydrocarbons in place of n-hexane.

The above results are summarized in Table 1.

(The following is a blank space) Table 1 ffi The present invention is an example in which an aliphatic hydrocarbon solvent is added after the reaction to separate the catalyst.

Nitrobenzene (
NB) 36.93g, pyridine 11.87g, anhydrous ferric chloride 12.17g, 5% palladium-carbon 3.19g
300g of dehydrated ethanol were charged and reacted in the same manner as in Example 1. After the reaction was completed, evacuation and nitrogen substitution were performed in the same manner.

After adding too much ethanol to the resulting reaction mixture, it was filtered, and a portion of the catalyst was treated as an ethanol-insoluble component.
1.30g was collected. Analysis of the ili liquid revealed that the NB conversion rate was 100% and the RPC yield was 95.4%.

The obtained filtrate was concentrated under reduced pressure using a rotary evaporator to remove ethanol and pyridine, and then 10,100 O of n-hexane was added to the concentrated solution, and the insoluble matter and the filtrate were separated by filtration. With this filtrate, an additional 11.90 g
of catalyst was recovered. The filtrate was almost colorless and transparent, and analysis revealed that 95% of the produced EPC was dissolved. In addition, the total amount of Fe in the filtrate was measured by spectrophotometry, and the
The ratio (residual rate) to the amount of Fe in e(:13) was found to be 1%.

The reaction was carried out in the same manner as in Example 9 for Ohode U2, and a portion of the catalyst was separated by adding ethanol and filtering in the same manner. As a result of analyzing the filtrate, the NB conversion rate was 100% and the RPC yield was 9.
It was 5.0%. This was carried out under reduced pressure in the same manner as in Example 9.
+, and after removing ethanol and pyridine, concentrate 1
．． 20 g each was sampled, 100 g each of various aliphatic hydrocarbon solvents other than n-hexane were added and filtered, and the insoluble matter and the filtrate were separated. The amount of RPC and total Fe in the filtrate were analyzed, and the recovery rate of RPC and the residual rate of Fe were calculated.

Reaction and ethanol treatment were carried out in the same manner as in Example 9 to obtain a filtrate. As a result of analyzing this filtrate, the NB conversion rate was 100.
%, and the EPC yield was 93.0%. This was concentrated under reduced pressure in the same manner as in Example 9 to remove ethanol and pyridine, and then sampled in the same manner as in Examples 10 to 16 and treated with a solvent other than aliphatic hydrocarbon. R in the filtrate
The amount of PC and the total amount of Fe were analyzed, and the recovery rate of RPC, Pe
The remaining rate was calculated.

The above results are summarized in Table 2.

Table 2 From Tables 1 and 2, it is clear that according to the present invention, almost all of the catalyst, especially the Lewis acid, can be recovered as insoluble matter, whereas conventional methods or solvents other than aliphatic hydrocarbons can be recovered. In the comparative example using Lewis acid 12-6
It can be seen that 5% remains in the filtrate.

(Effects of the invention) By separating the catalyst in the presence of an aliphatic hydrocarbon solvent, the method of the present invention substantially completely insolubilizes the catalyst components, especially the Lewis acid, which was difficult to insolubilize using conventional methods. Almost all of the Lewis acid can be recovered as insoluble matter. As a result, it is possible to prevent contamination and deterioration of the aromatic urethane product by Lewis acids, improve the quality and yield of the aromatic urethane as the main raw material for the next process, and improve the recovery rate of the catalyst. The catalyst can be reused with minimal replenishment of new catalyst. In addition, the hydrocarbon solvent used in the present invention to separate the catalyst can be recovered by distillation from the urethane product-containing filtrate and used repeatedly, making the method simple yet economically effective. be.

[Brief explanation of the drawing]

FIG. 1 is a graph showing a decrease in thermal stability of aromatic urethane (RPC) due to the coexistence of Lewis acid (FeCIz).

Claims (1)

[Claims] An aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide are reacted in the presence of a catalyst system consisting of a platinum group metal as a main catalyst, a Lewis acid as a promoter, and a nitrogen-containing heteroaromatic compound as a ligand. A method for producing an aromatic urethane, the method comprising: separating a catalyst and an aromatic urethane product in the coexistence of an aliphatic hydrocarbon solvent.