JPH068270B2 - Method for producing aromatic polycarbamate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing polymethylene polyphenyl polycarbamate (hereinafter abbreviated as polycarbamate) using N-phenylcarbamate and a methyleneating agent as raw materials.

More specifically, in a method for producing a polycarbamate by allowing a methyleneating agent such as formaldehyde to act on N-phenylcarbamate in the presence of an aqueous acid solution of a catalyst,
After the condensation reaction, the binuclear compound in the condensation reaction product is precipitated and separated using an aromatic solvent, and the remaining condensation product in the mother liquor is directly condensed again using the aqueous acid solution and the methyleneating agent. And a method for producing a polycarbamate.

Polycarbamate is a substance useful as an intermediate raw material for medicines, agricultural chemicals, and chemical products, and particularly polymethylene polyphenyl polyisocyanate (hereinafter,
It is useful as an intermediate for the production of polyisocyanate since it is converted into polyisocyanate.

Polyisocyanate, and above all, a binuclear methylenediphenyldiisocyanate (MDI), is a useful substance as a raw material for producing polyurethane elastomers and coating materials, and the amount used in this application is highly volatile and highly toxic. It surpasses the existing tolylene diisocyanate (TDI), and is in mass production on an industrial scale.

(Prior Art) Conventionally, aromatic isocyanates have generally been industrially produced by reducing an aromatic nitro compound with hydrogen to obtain an aromatic amine, and reacting this with phosgene to form an isocyanate. However, this method has complicated steps and
There are problems such as using toxic phosgene and producing a large amount of hydrogen chloride as a by-product. Therefore, methods for producing aromatic isocyanates without using phosgene have been actively studied for 20 years.

Methods that do not use phosgene are roughly classified into the direct method and the carbamate-mediated method.

The first direct method is a method in which carbon monoxide is allowed to act on an aromatic nitro compound in an inert solvent in the presence of a palladium-based catalyst to directly produce an aromatic isocyanate compound, but the reaction conditions are severe. However, there are drawbacks that the productivity of the catalyst is low and side reactions are likely to occur simultaneously. Further, fatally, this method is difficult to apply to the production of polyisocyanates having a polynuclear structure such as MDI.

The second via carbamate method is to react carbon monoxide with an aromatic nitro compound and an alcohol in the presence of a platinum group metal catalyst or a selenium catalyst to obtain an intermediate aromatic carbamate, and then heat the carbamate. It is a method of decomposing to obtain an aromatic isocyanate.

The method for producing a polycarbamate of the present invention is carried out in the production of the above-mentioned polyisocyanate by the second method via a carbamate. In this method, as shown in the following reaction formula, N-phenylcarbamate (I) is crosslinked by condensation with a methyleneating agent such as formaldehyde in the presence of an acid catalyst to form polycarbamate (II). .

(In the formula, m is 0 or an integer of 1 to 6, and R is a carbon number of 1 to 6.
Means a lower alkyl group of. ) The resulting polycarbamate, when pyrolyzed, has the formula (III)
Is converted to the corresponding polyisocyanate represented by

(In the formula, m and R have the same meanings as above.) In this method, since an excellent method for synthesizing N-phenylcarbamate as a raw material from a nitro compound or an amino compound has been developed in recent years, polycarbamate and polyisocyanate are obtained. Has been attracting attention as an advantageous production method of.

Among the polyisocyanates of the above general formula (III), 4,4'-methylenediphenyl diisocyanate (hereinafter abbreviated as 4,4'-MDI) generally called pure MDI has the highest reactivity, and is therefore a high-value product. Is. Therefore, with respect to the polycarbamate of the general formula (II) which is a raw material for producing polyisocyanate, 4,4'-methylenediphenyldicarbamate (hereinafter, referred to as 4,4'-M
(Abbreviated as DU) is the most desirable product. However, in the above condensation reaction, even if the reaction conditions are adjusted so as to obtain 4,4'-MDU, M other than 4,4'-form is obtained.
DU isomers, namely 2,2'-MDU and 2,
Generation of 4'-MDU, trinuclear or more [m ≧ in general formula (II)]
The formation of the polycarbamate of 1] is inevitable. Usually, about 5 to 20% of the total amount of produced MDU is 2,4'-isomer, the 2,2'-isomer is generally in a trace amount, and the rest is 4,4'-MDU. The polynuclear polycarbamate having 3 or more nuclei is usually produced in an amount of about 5 to 20% by weight based on the whole.

However, since polycarbamate has a very high boiling point,
It is very difficult to separate the condensation product into each compound by distillation to separate the desired 4,4'-MDU.
Therefore, the purification of the condensation product by distillation is limited to the recovery of unreacted N-phenylcarbamate in the past.
The remaining polycarbamate condensation product mixture was directly supplied to the heat separation step without being separated into the respective constituent components. Therefore, the thermal decomposition reaction products are various polyisocyanates corresponding to various polycarbamates produced in the condensation reaction, that is, 2,4'- and 2,2'-MDI in addition to the desired 4,4'-MDI. , And a polynuclear polyisocyanate having 3 or more nuclei, which was purified by means such as distillation and crystallization.

When polyisocyanates are exposed to a high temperature for a long time, they are likely to undergo a side reaction and deteriorate. Therefore, in the case of purification of a pyrolysis reaction product by distillation, most of the 4,4 The ′ -MDI is taken out to obtain a pure MDI product, and the remaining distillation residue containing 4,4′-MDI and polyisocyanate having three or more nuclides is polymerized MDI (or crude) without further distillation separation. MDI) is used, and high-value pure MDI is mainly used as a raw material for various polyurethane products, and polymeric MDI is mainly used as a raw material for rigid urethane foam.

In this purification method, the pure MDI taken out contains its isomers, namely 2,4'- and 2,2'-MDI.
Coexist. Since these MDI isomers have a low boiling point and can be removed from pure MDI by rectification, they have low reactivity and currently have no potential use. Therefore, they are mixed with polymeric MDI and digested. It is the current situation.

Therefore, in order to improve the product distribution, Pure MDI
It is desirable in the production of polyisocyanates to increase the yield of (4,4'-MDI) and reduce the amount of 2,4'- and 2,2'-MDI produced, and the same applies to the polycarbamate used as the raw material. It is desirable to increase the yield of 4,4'-MDU and suppress the formation of 2,4'- and 2,2'-MDU.

Further, in the above-mentioned conventional method, separation of unreacted N-phenylcarbamate in the treatment of the polycarbamate condensation product, separation of pure MDI of the thermal decomposition reaction product,
Furthermore 2,4'- and 2,2 'from Pure MDI
-Distillation is used both for the separation of the isomers. But,
By distillation, it is difficult to separate isomers with a small difference in boiling point, and when a thermally unstable compound such as polycarbamate or polyisocyanate is distilled, the yield of the target product decreases and the quality deteriorates. It is desirable to have as few opportunities for distillation as possible, since

On the other hand, as a method of purifying a polycarbamate condensation product that does not rely on distillation, the present inventors have proposed a method of performing a precipitation treatment of a condensation reaction purified product using an aromatic solvent. In this method, the condensation reaction product is treated with an aromatic solvent,
4'-MDU is preferentially precipitated and taken out as high-purity crystals, and this is pyrolyzed to obtain high-value pure MDI, while the mother liquor remaining after the crystal separation in the precipitation step is unreacted N by distillation. -After removing the phenylcarbamate, it is thermally decomposed separately to obtain a polymeric MDI (which may be separated from the pure MDI by utilizing the above precipitation treatment). But even with this method,
Distillation was used to remove N-phenylcarbamate, and 2,4'- and 2,2'-of the binuclear MDUs produced were used.
Most of the 2'-MDU remains in the mother liquor, and the corresponding MDI isomer produced after thermal decomposition is polymeric MDI.
Remaining in the desired pure MDI and 4,4 '
-Improved MDU yield and isomers 2,4'- and 2,
It does not lead to a reduction in the amount of 2'-MDI and MDU produced.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to provide a method for producing an aromatic polycarbamate that can be carried out without utilizing purification by distillation or product separation.

Another object of the present invention is to reduce the amount of unreacted N-phenylcarbamate, increase the yield of the desired 4,4'-MDU, and obtain the isomers 2,4'- and 2,2'-MDU. It is an object of the present invention to provide a method for producing an aromatic polycarbamate, which hardly produces a product and has excellent raw material conversion and raw material conversion.

(Means for Solving the Problems) According to the present inventor, the above-mentioned object is to achieve N in the presence of an aqueous acid solution.
In a method for producing a polycarbamate by condensing a phenylcarbamate with a methyleneating agent, the condensation reaction product is treated with an aromatic solvent so that 4,4'-methylenediphenyldicarbamate in the produced polycarbamate is preferentially treated. And a polycarbamate and unreacted N-phenylcarbamate remaining in the mother liquor after separating the precipitate are subjected to a condensation reaction with a methyleneating agent again in the presence of an aqueous acid solution. Achieved by

(Operation) Hereinafter, the present invention will be described in detail.

The starting material for the method for producing a polycarbamate of the present invention is N-phenylcarbamate represented by the general formula (I). In the general formula (I), R is particularly preferably methyl or ethyl because the subsequent thermal decomposition reaction is easy.

Formaldehyde or a substance that generates formaldehyde is used as the methyleneating agent. The substance that generates formaldehyde is a substance that generates formaldehyde by decomposition under the above condensation reaction conditions,
Specific examples include trioxane, paraformaldehyde, methylal and other formales. Aqueous formaldehyde solution (formalin) is usually used as the methyleneating agent, mainly for economic reasons.

As the acid catalyst, sulfuric acid, hydrochloric acid, phosphoric acid, polysulfuric acid, polyphosphoric acid, boric acid, hydrobromic acid, inorganic acids such as perchloric acid,
Lewis acids such as boron trifluoride and organic acids such as methanesulfonic acid can be used, but strong inorganic acids, especially sulfuric acid, are preferred.

Hereinafter, for simplification of the description, formaldehyde is representatively used as a methyleneating agent, and sulfuric acid is representatively represented as an acid catalyst.

The feed ratio of formaldehyde to N-phenylcarbamate is preferably in the range of 0.2 to 0.6 in terms of molar ratio. If it is lower than this supply ratio, the conversion rate of the raw material is low, and if it is higher than this, the production rate of high-boiling substances (that is, polynuclear bodies of three or more nuclides) increases.

The acid concentration of the aqueous sulfuric acid solution used is preferably 20 to 80% by weight, more preferably 40 to 60% by weight. If the concentration of sulfuric acid supplied is less than 20% by weight or more than 80% by weight, the yield of the desired condensation product tends to be low.

The supply ratio of the aqueous sulfuric acid solution and N-phenylcarbamate is
The molar ratio of sulfuric acid to N-phenylcarbamate is preferably 2 or more. Below this supply ratio, the reaction promoting effect on the condensation reaction is reduced. The condensation reaction is usually carried out in the absence of an organic solvent, but it can be carried out in the presence of various organic solvents as long as it does not react with formaldehyde under the reaction conditions. However, when the organic solvent is not an aromatic solvent used in the precipitation treatment, a treatment such as distillation is taken after the reaction so as not to interfere with the precipitation treatment.

The reaction temperature is preferably 60 to 120 ° C., more preferably 80.
~ 100 ° C. If the reaction temperature is too low, the condensation reaction rate will decrease, while if it is too high, the amount of polynuclear bodies produced will increase.

The reaction time varies depending on the reaction conditions, but is 0.1 to 10 hours, preferably 0.5 to 5 hours. This is because if the reaction time is too short, the reaction cannot be completed, and if it is too long, side reactions occur remarkably.

The condensation reaction can be carried out in any of a batch system, a continuous system and a semi-continuous system, and the addition order of the reaction components is not particularly limited, but generally, a methyleneating agent is added to a mixture of N-phenylcarbamate and an acid catalyst. Preference is given to carrying out the reaction.

The reaction mixture produced by the condensation is subjected to a precipitation treatment using an aromatic solvent according to the present invention. This precipitation treatment is carried out by dissolving the condensation product in an aromatic solvent and then concentrating the obtained organic solvent, if desired, as described below.
It means an operation of precipitating a part of the melted product by cooling and separating it.

First, in a reaction mixture containing a sulfuric acid aqueous solution of a catalyst and a polycarbamate produced, 1 to 10 with respect to the polycarbamate produced.
About twice the amount (weight ratio) of aromatic solvent is added. In some cases, a part or all of this aromatic solvent may be present in the condensation reaction system in advance, and the reaction may be carried out in the coexistence of this solvent. If the addition amount of the organic solvent is less than the same weight, it is difficult to dissolve the entire amount of the polycarbamate product, while if it exceeds 10 times, the cost required for the processing equipment such as the recovery of the aromatic solvent is high. , Not economical.
However, this solvent ratio can be appropriately changed in consideration of the solubility of the solvent used in the polycarbamate product, the amount of precipitate, the purity, the processing temperature, and the like.

The aromatic solvent is not particularly limited as long as the precipitation treatment of the present invention is possible, but a solvent having a normal pressure boiling point of 80 to 250 ° C. is preferable because the solvent can be easily distilled and recovered. Examples of particularly preferable aromatic solvents that can be used are one or more solvents selected from benzene, toluene and xylene. In addition, butylbenzene, tetralin, cyclohexynebenzene, and the like, as well as halogen-substituted products of the above hydrocarbon solvents can be used.

These aromatic solvents can easily dissolve condensation reaction products containing various polycarbamates, and can preferentially precipitate 4,4'-MDU from the solution by cooling, and by using them, the purity of 4,4'-MDU can be increased. High 4,4'-MDU can be easily obtained. Moreover, it is a hydrophobic solvent and can be easily separated from the sulfuric acid aqueous solution which is the catalyst.

The mixture is preferably heated appropriately during or after the addition of the aromatic solvent so as to promote complete dissolution of the polycarbamate product and at the same time facilitate the precipitation operation.
After dissolution, the organic layer containing the polycarbamate product is phase separated from the aqueous sulfuric acid catalyst. The aqueous sulfuric acid solution can be reused in the condensation reaction step as it is or after treatment such as concentration.

When the separated organic solution is cooled, polycarbamate,
In particular, 4,4'-MDU preferentially precipitates and unreacted N-
The phenyl carbamate remains in solution. As for the cooling temperature, as long as the solvent does not solidify, the colder the temperature, the more the amount of precipitated polycarbamate becomes, which is preferable. Prior to cooling, a part of the aromatic solvent may be evaporated and concentrated, if necessary.

The precipitated polycarbamate crystals are separated from the mother liquor of the aromatic hydrocarbon solvent by a conventional solid-liquid separation means. By repeating the above precipitation treatment (that is, by the recrystallization treatment from the aromatic hydrocarbon solvent), the polycarbamate separated in this way is subjected to 4,4′-MD.
It is also possible to increase the purity of U. The polyisocyanate obtained by thermally decomposing this precipitate contains 4,4'-MDI in a high concentration and has a quality that can be used as it is as a pure MDI product.

On the other hand, the mother liquor remaining after the crystal separation contained a polycarbamate product that did not precipitate, unreacted N-phenylcarbamate, and a small amount of other by-products,
As a result of preferential precipitation of 4,4'-MDU, polycarbamate remaining in the mother liquor contains polynuclear bodies and 2,2'-
And 2,4'-MDU are present in a higher relative proportion compared to the condensation reaction product.

From this mother liquor, the aromatic solvent is first recovered by distillation, which can be reused in the operation of dissolving the condensation product.

On the other hand, the residue after removing the solvent from the mother liquor consists of the unprecipitated polycarbamate product and unreacted N-phenylcarbamate. In the method of the present invention, the residue is subjected to the condensation reaction again. Repeating this condensation reaction is based on the next knowledge of the present inventors.

That is, when N-phenylcarbamate and a methyleneating agent were allowed to act on a mixture of dinuclear MDU isomers in the presence of an acid catalyst, 4,4′-MDU was stable under the condensation reaction conditions and the condensation reaction It was found that the conversion reaction to 2,4'- and 2,2'-MDU was reduced by half in the second condensation reaction as compared with the first condensation reaction. Therefore, by the second condensation reaction, 4,4'-MDU which produces pure MDI is left, and 4,4'-MDU is converted to 1 from unreacted N-phenylcarbamate.
It can be produced with a higher selectivity than the first time, and the product distribution of polycarbamate can be improved. Moreover, according to this method, the step of removing the unreacted N-phenylcarbamate by distillation is unnecessary, so that the deterioration of the product due to distillation is avoided and the product quality is further improved.

This second condensation reaction can be carried out under the same conditions as the above-mentioned first condensation reaction, but the amounts of formaldehyde and acid catalyst added are such that residual N-phenylcarbamate and 2,4'- and 2,2 'are added. -Adjust appropriately according to the amount of MDU. If the residual amount of unreacted N-phenylcarbamate is small relative to the amount of polycarbamate, it may be replenished appropriately.

Due to this condensation reaction, 2,4'- and 2,2'-MD
In addition to the condensation of U and N-phenylcarbamate with formaldehyde to form a trinuclear polycarbamate, unreacted N-phenylcarbamate is condensed with formaldehyde to give 4,4′-MDU as in the first condensation reaction. The main dinuclear and polynuclear bodies are produced, and
Since the selectivity to 4'-MDU is higher than that of the first time, the amount of unreacted N-phenylcarbamate and 2,4'- and 2,2 as a whole are higher than those in the conventional method in which the condensation reaction is performed only once. ′ -MDU production is reduced, which is preferable 4,4 ′
Increased production of MDU and polynuclear polycarbamates. The products of the second condensation reaction are mainly 4,4′-MD.
Pyrolysis of U and polynuclear polycarbamates gives polyisocyanate products with good quality as Polymec MDI.

Alternatively, this condensation reaction product is again subjected to a precipitation treatment with an aromatic hydrocarbon solvent as described above to precipitate a 4,4'-MDU-rich component, and heat treatment is performed together with the precipitation product of the first precipitation treatment. It may be decomposed into a pure MDI product, and a polymec MDI product may be obtained by thermal decomposition from the polycarbamate product remaining in this precipitation treatment. This is advantageous because the yield of high-value pure MDI becomes very high.

Next, the present invention will be illustrated by examples. In the examples,% is% by weight unless otherwise specified. The analysis in the examples was performed by high performance liquid chromatography and gel permeation chromatography.

Example 1 (A) Condensation Reaction I 200 g of ethyl N-phenylcarbamate (EPC) and 1186.9 g of 50% sulfuric acid were placed in a 2 volume round bottom flask equipped with a thermometer, a stirrer, a reflux condenser and a dropping funnel.
Heated with stirring. At the temperature of 50 ° C., 49.08 g of 37% aqueous formaldehyde solution was added dropwise, and after completion of the addition, the mixed solution was heated to 90 ° C. with stirring, and the condensation reaction was carried out at 90 ° C. for 2 hours.

After completion of the reaction, while maintaining the temperature at 90 ° C, hot toluene 600c
The condensation product was thermally extracted at m ³ . The sulfuric acid layer separated from the organic layer was washed with 150 cm ³ of hot toluene, and this toluene layer was combined with the toluene solution obtained by the above extraction, washed with hot water, and then analyzed by high performance liquid chromatography.

As a result of the analysis, the obtained toluene solution was 4,4'-MD.
U110.1g, 2,4'-MDU13.6g, and unreacted E
It contained 21.2 g of PC.

(B) Precipitation treatment The hot toluene solution containing the polycarbamate condensation product obtained in (A) above was cooled to room temperature, and the precipitated crystals were separated by filtration to obtain 111.5 g of crystals. As a result of analysis, it was 4,4'-MDU 95.4%, 2,4'-M.
It contained 0.5% DU and no EPC.

When toluene was distilled off from the mother liquor after crystal separation, 88.3 g of an oily substance remained. This residue contains 4,4'-MD
U23.5%, 2,4'-MDU14.6% and EPC22.7%
And the rest are considered to be polynuclear bodies of 3 or more nuclear bodies and reaction intermediates.

From this result, 4,4'-MDU was preferentially precipitated by dissolution and precipitation of the condensation product in the toluene solution, and unreacted EPC and MDU isomers other than 4,4'-form and polynuclear It can be seen that the body is concentrated.

(C) Condensation reaction II Residual oily substance obtained from the mother liquor after the precipitation treatment in (B) above 8
The condensation reaction was performed using 5 g. This condensation reaction is 37
% Formaldehyde aqueous solution 4.46 g and 55% sulfuric acid 178.5
was carried out in the same manner as in the condensation reaction I described above at 90 ° C. for 2 hours. After completion of the reaction, extraction and washing treatment with toluene were carried out similarly to the condensation reaction I to obtain 283.1 g of a toluene solution. This solution contained 3,4 g of 4,4'-MDU,
It contained 12.9 g of 2,4'-MDU and 3.1 g of unreacted EPC.

Judging from the composition of the charged oily substance, 16.1 g of EP
This means that C was consumed by the condensation reaction, and 12.4 g and 0.54 g of 4,4'-MDU and 2,4'-MDU were produced, respectively.

The obtained toluene solution was cooled to give 12.6 g of crystals.
Got As a result of analysis, this crystal was 4,4'-MDU95.5.
%, 2,4'-MDU 0.7% and EPC 0.4%. The oily substance obtained by distilling toluene from the mother liquor after crystal separation contains 4,4'-MDU 28.1%, 2,
It contained 17.9% of 4'-MDU and 6.0% of EPC.

(Effects of the Invention) According to the present invention, as illustrated in Examples, by utilizing the precipitation treatment with an aromatic solvent, it is possible to obtain 4, out of various polycarbamates contained in the condensation reaction product.
4'-MDU can be preferentially taken out as crystals. When pyrolyzed, 4,4'-M with high purity
It is possible to obtain high-quality pure MDI without the need for purification / separation operation by distillation which may generate DI and deteriorate the quality of the product after pyrolysis.

Further, the polycarbamate product remaining in the mother liquor after removing the crystals is subjected to the condensation reaction again, whereby the remaining 4,4′-MDU is stably maintained and unreacted N-
The condensation of phenylcarbamate produces 4,4'-MDU with a higher selectivity than the first condensation reaction. Therefore, it is possible to improve the conversion rate of the condensation reaction and the yield of 4,4′-MDU which produces high-value pure MDI,
At the same time, the production amount of 2,4'- and 2,2'-MDU is reduced and these are polynuclearized, so that 4,4'-MDU is produced.
By thermal decomposition of the residual polycarbonate after decomposition, a high quality polymeric MDI can be obtained.

As described above, the method of the present invention achieves a high quality product distribution, does not require a recovery facility for distilling unreacted raw materials, and does not cause deterioration of polycarbamate due to this distillation. The quality is improved.

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Claims (1)

[Claims] 1. A method for producing polymethylene polyphenyl polycarbamate by condensing N-phenylcarbamate with a methyleneating agent in the presence of an aqueous acid solution, wherein the condensation reaction product is treated with an aromatic solvent to produce the product. 4,4'-methylenediphenyldicarbamate in polycarbamate is preferentially precipitated, and the polymethylenepolyphenylpolycarbamate and unreacted N-phenylcarbamate remaining in the mother liquor after separating the precipitate in the presence of an aqueous acid solution. Characterized in that the condensation reaction with the methyleneating agent is carried out again.
Process for producing polymethylene polyphenyl polycarbamate.