JPH02108658A - Production of aromatic polycarbamate - Google Patents

Abstract

PURPOSE:To obtain the subject compound having low content of intermediate product in high yield by treating a reaction mixture of phenyl carbamate and a methylation agent with an aromatic solvent, precipitating MDU crystal from separated organic phase by crystallization and treating the residual solution with an inorganic acid. CONSTITUTION:The objective compound can be produced by reacting phenyl carbamate with a methylation agent in the presence of an acid catalyst, treating the obtained reaction mixture with an aromatic solvent to form an aqueous phase containing the acid catalyst and the methylation agent and an organic phase containing the reaction product, etc., crystallizing 4,4'-MDU (methylenediphenyl dicarbonate) from the organic phase separated from the aqueous phase, treating the organic solution left after the separation of the crystal with an aqueous solution of an inorganic acid (preferably sulfuric acid) to convert the N-benzyl compound of formula I (R is 1-6C alkyl) and the bisanilino compound of formula II to a polycarbonate and recovering the polycarbonate separately from the above crystal in the form of pure substance or a solution.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a polymethylene polyphenyl polycarbamate made from phenyl carbamate and a methylenating agent.
(hereinafter abbreviated as polycarbamate).

More specifically, in the method of producing polycarbamate through a condensation reaction in which phenyl carbamate is reacted with a methylenating agent such as formaldehyde in the presence of an acid catalyst, polycarbamate is extracted from the reaction mixture by extraction with an aromatic organic solvent and crystallization. An improved method for producing polycarbamate in which the amount of reaction intermediates produced is reduced by obtaining the main product methylene diphenyl dicarbamate as crystals and then adding an acid catalyst to the mother liquor organic solution for reaction. .

(Prior art) Polycarbamate is a substance useful as an intermediate raw material for pharmaceuticals, agricultural chemicals, and chemical products, and in particular, polymethylene polyphenyl polyisocyanate (hereinafter referred to as
Since it is converted into polyisocyanate (simply abbreviated as polyisocyanate), it is useful as an intermediate for polyisocyanate production.

Polyisocyanates, especially dinuclear methylene diphenyl diisocyanate (hereinafter abbreviated as MDI), are useful substances as raw materials for the production of polyurethane elastomers and coating materials, and the amount used in this application is highly volatile and highly toxic. It has now surpassed the problematic tolylene diisocyanate (TDI), and is being mass-produced on an industrial scale.

Conventionally, aromatic isocyanates have generally been industrially produced by reducing an aromatic nitro compound with hydrogen to obtain an aromatic amine, which is then treated with phosgene to form an isocyanate. However, this method is complicated, and
Problems include the use of toxic phosgene and the production of large amounts of hydrogen chloride. Therefore, methods for producing aromatic isocyanes (11) that do not use phosgene have been actively researched for the past 20 years.

Methods that do not use phosgene are broadly divided into ∎direct method and ∎carbamate-mediated method.

The first direct method involves reacting aromatic nitro compounds with carbon monoxide in the presence of a palladium-based catalyst in an inert solvent to directly produce aromatic isocyanate compounds, but the reaction conditions are harsh. However, there are drawbacks such as low catalyst productivity and the tendency for side reactions to occur together. Furthermore, fatally, it is difficult to apply this method to the production of polyisocyanate having a polynuclear structure such as MDI.

In the 20th carbamate method, an aromatic nitro compound and an alcohol are reacted with carbon monoxide in the presence of a platinum group metal catalyst or a selenium catalyst to obtain an intermediate aromatic carbamate, and then this carbamate is heated. This is a method to obtain aromatic isocyanate by decomposition.

The polycarbamate production method of the present invention is carried out in the production of the above-mentioned polyisocyanate by this second carbamate-mediated method. In this method, as shown in the reaction formula below, phenyl carbamate (+) is crosslinked by condensation with a methylenating agent such as formaldehyde in the presence of an acid catalyst to produce polycarbamate (I[), This condensation reaction is described, for example, in U.S. Pat.
It is disclosed in the issue.

(In the formula, m is O or an integer of 1 to 6, R is a carbon number of 1 to 6
means a lower alkyl group>.

When the obtained polycarbamate is pyrolyzed, it has the formula (m)
is converted to the corresponding polyisocyanate shown as

(In the formula, m has the same meaning as above).

This method has attracted attention as an advantageous method for producing polycarbamates and polyisocyanates because an excellent method for synthesizing phenyl carbamate as a raw material from a nitro compound or an amino compound has been developed in recent years.

Among the polyisocyanates of the general formula (+11), 4,4°-methylene diphenyl diisocyanate (hereinafter abbreviated as 4.4′-MDI), which is generally called pure MDI, has the highest reactivity and is therefore of high value. However, in the above condensation reaction, the precursor 4,4
°-methylene diphenyl dicarbamate (hereinafter referred to as 4.
Even if the reaction conditions are adjusted to obtain the highest yield of 4.4'=MDU), the dinuclear body M other than 4.4'
DU isomers, i.e. 22'-MDU and 2.4'
-MDU, the production of various polycarbamate products such as trinuclear or more [general formula (formerly m≧1) polynuclear polycarbamate], and also the production of reaction intermediates are unavoidable.

Since polycarbamate has a very high boiling point, the condensation product is separated into its components by distillation to obtain the desired 4.4'
- It was very difficult to separate the MDU. Therefore, conventionally, the condensation reaction product is thermally decomposed as it is without separating it into each product, and 4,4''-MDI is separated from the obtained polyisocyanate product, usually by distillation, to produce a pure MDI product. It was common to recover all of the 4,4'-MDI, other MDI isomers, and 3
Contains more polyisocyanate than the core. Pure MD
I is mainly used as a raw material for manufacturing various polyurethane products, and polymeric MDI is mainly used as a raw material for manufacturing rigid urethane foam. However, this method has the disadvantage that the polyisocyanate is easily subject to thermal deterioration during distillation (product quality is reduced).

The present inventors have discovered that 4,4'-MDU can be efficiently separated by crystallization treatment using an aromatic organic solvent, and have filed a patent application to first propose a method for producing polyisocyanate based on this treatment. (Sho 63-29085).

In this method, separated 4,4'-MDU crystals and
When the polycarbamate remaining in the mother liquor is pyrolyzed separately, the former pyrolysis yields a pure MDI product, and the latter pyrolysis yields polymeric MDI, making it unnecessary to separate the polyisocyanate obtained by pyrolysis by distillation. Therefore, product deterioration can be avoided.

However, a problem with this method is that it is difficult to separate intermediates produced in the condensation reaction, so they may be subjected to thermal decomposition while remaining in the mother liquor.

Intermediates produced in the condensation reaction include an N-benzyl compound (TV) and a bisanilino compound (V) shown in the following formula.

(R: lower alkyl group having 1 to 6 carbon atoms) These reaction intermediates do not undergo conversion into isocyanate by thermal decomposition, so they become impurities in the polyisocyanate product.
The lime produced by thermal decomposition of the mother liquor deteriorates the quality of limerick MDI.

These reaction intermediates also cause various side reactions with the polyisocyanate produced by thermal decomposition of the polycarbamate, causing a decrease in the yield and quality of the desired polyisocyanate.

However, since the condensation reaction of compound (1) to (It) proceeds at least partially through the above-mentioned intermediate, it is necessary to complete the reaction in order to obtain a polycarbamate product that does not contain this intermediate. It is necessary to carry out the condensation reaction under extremely harsh reaction conditions so that the reaction proceeds to the next stage, which is difficult to carry out industrially.

Even in the conventional method of distilling the polyisocyanate product to produce a product without separating the condensation product, these intermediates cause the same problems as above. Several treatment methods have been proposed to date.

(2) JP-A No. 54-59264 discloses a method of converting benzyl compounds into polycarbamates using a protic acid or a Lewis acid having a strength of at least 75% sulfuric acid or higher. However, with this method, it is not easy to separate and recover the strong acid used.

■JP-A-56-7749 discloses a method in which only the bisanilino compound is heated in the presence of an acid catalyst to convert it into polycarbamate, but the reaction rate is slow and the bisanilino compound cannot be completely removed. . Furthermore, in order to apply the methods of ■ and ■ for this purpose, a separate operation is required to separate only one of the intermediates, and other intermediates require separate treatment. , operation becomes complicated.

■ JP-A-56-12357 describes a method in which phenyl carbamate and formaldehyde are reacted with an acid catalyst in the coexistence of a benzyl compound and a bisanilino compound, but a substantial amount of the intermediate remains after the reaction. , its effect is insufficient.

■Unexamined Japanese Patent Publication No. 59-106453 discloses that a strong rubonic acid such as trifluoroacetic acid is applied to the organic phase separated from the inorganic acid after the reaction under non-aqueous conditions, and intermediates and polynuclear bodies are converted into dinuclear M
Although a method for converting to DU is disclosed, it requires a dehydration step to perform the acid treatment under non-aqueous conditions. Furthermore, trifluoroacetic acid is highly volatile and highly hygroscopic, making it difficult to handle.

(Problems to be Solved by the Invention) As described above, at present, there is no satisfactory method that can industrially produce polycarbamates that ultimately do not contain condensation reaction intermediates.

Therefore, the object of the present invention is to provide a method for producing polycarbamate from phenyl carbamate and a methylenating agent in the presence of an aqueous acid solution, which allows obtaining a polycarbamate product containing no intermediates by a simple process. It is to provide.

Another object of the present invention is to improve the method for producing polycarbamate by crystallizing and separating the condensation reaction product described above using an aromatic organic solvent so that a product containing no intermediate can be obtained. be.

(Means for Solving the Problems) The present inventors separated MDtJ crystals using the previously proposed method of extracting a condensation reaction mixture with an aromatic organic solvent and crystallizing MDU from the separated organic layer. By treating the remaining organic solution with an inorganic acid aqueous solution, the condensation reaction intermediate is reduced and the yield of polycarbamate is increased. discovered that it could be reused.
The present invention has been completed.

That is, the gist of the present invention is a method for producing a polycarbamate by reacting a phenyl carbamate with a methylenating agent in the presence of an acid catalyst, comprising: (A) treating the resulting reaction mixture with an aromatic solvent; (B) to separate into an aqueous layer containing an acid catalyst and an organic layer containing a reaction product.
MDU crystals were obtained from this organic layer by crystallization, (C)
The solution obtained after crystal separation is free of 9! This is a method for producing polycarbamate, which is characterized in that after treatment with an acid aqueous solution, the product is isolated or recovered in solution form from this solution separately from the above-mentioned crystals.

In a preferred embodiment, after the treatment in step (C), the used acid aqueous solution is recovered and reused in this treatment.

(effect) The present invention will be explained in detail below.

The starting material for the polycarbamate production method of the present invention is phenyl carbamate represented by the above general formula ([). In the general formula (1), R is a lower alkyl group having 1 to 6 carbon atoms, and a methyl group or an ethyl group is particularly preferable because it facilitates the subsequent thermal decomposition reaction.

As the methylenating agent, formaldehyde or a substance that generates formaldehyde is used. A substance that generates formaldehyde is a substance that generates formaldehyde by decomposition etc. under the above condensation reaction conditions,
Examples include trioxane, paraformaldehyde, methylal and other formals.

Usually, an aqueous formaldehyde solution (formalin) is used, mainly for economic reasons.

Acid catalysts include inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, polysulfuric acid, polyphosphoric acid, boric acid, hydrobromic acid, and perchloric acid;
Lewis acids such as boron trifluoride and organic acids such as methanesulfonic acid can be used, but sulfuric acid, which is a strong inorganic acid, is particularly preferred.

Hereinafter, to simplify the explanation, formaldehyde will be used as a methylenating agent, and sulfuric acid will be used as an acid catalyst.

Although the condensation reaction in the present invention can be carried out in the same manner as conventional methods, the reaction conditions will be briefly explained below.

There is no particular restriction on the supply ratio of formaldehyde and phenyl carbamate, but when the purpose is to produce binuclear MDLI, the molar ratio is usually 0.2 to 1. It is preferably within the range of O. If the amount of formaldehyde added is too small, the conversion rate of the raw material tends to be low, and if it is too large, the selectivity to the target product tends to decrease.

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 sulfuric acid concentration supplied is less than 20% by weight, or
If it exceeds 0% by weight, the selectivity to the desired condensation product tends to decrease.

The supply ratio of the sulfuric acid aqueous solution and phenyl carbamate is preferably 2 or more in molar ratio of sulfuric acid to phenyl carbamate. When the supply ratio is lower than this, the effect of accelerating the condensation reaction decreases.

Condensation reactions are usually carried out in the absence of organic solvents, unless they react with formaldehyde under the reaction conditions.
It can also be carried out in the coexistence of various organic solvents. However, if the organic solvent is not an aromatic solvent used in the crystallization process, the organic solvent should be removed by appropriate means such as phase separation or distillation after the reaction so as not to interfere with the crystallization process after the condensation reaction. It is preferable.

The reaction temperature is preferably 60 to 120°C, more preferably 80 to 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 products 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.If the zero reaction time is too short, the reaction will not be completed, and if it is too long, side reactions will occur significantly.

The condensation reaction can be carried out batchwise, continuously or semi-continuously. Although there are no particular restrictions on the addition of reaction components, it is generally preferable to carry out the reaction by adding a methylenating agent to a mixture of phenyl carbamate and an acid catalyst.

According to the present invention, an aromatic organic solvent is added to the reaction mixture obtained by the condensation reaction to dissolve the entire amount of the reaction product. Through this treatment, unreacted phenyl carbamate, reaction intermediates, and reaction product polycarbamate are extracted into the organic layer, and the acid catalyst and methylenating agent remain in the aqueous layer.

The aromatic organic solvent used in this treatment is not particularly limited, but it is preferable to use one in which the solubility of the reaction product is high and which preferentially crystallizes 4.4-MDU.

In this sense, preferred aromatic organic solvents are those substituted with an alkyl group such as a methyl group or an ethyl group, or a halogen such as chloro or bromo, and have a boiling point (normal pressure) of 250° C. or lower. Specific examples include toluene, xylene, chlorobenzene, dichlorobenzene, and chlorotoluene.

Thereafter, the organic layer containing the reaction product and the like is separated from the aqueous layer by layer separation (oil/water separation). Since this aqueous layer contains sulfuric acid as a catalyst and formaldehyde as a methylenating agent, it can be reused in the condensation reaction after concentration adjustment.

On the other hand, MDU crystals are precipitated from the separated organic layer by a method such as cooling crystallization or evaporation crystallization, and recovered as a product by an appropriate solid-liquid separation means. As shown in the examples below, this crystallization yields 4.4'-M with a purity of 95% or more.
DU crystals can be obtained, which can be thermally decomposed to yield pure MDI.

After separation of the precipitated MDU crystals, in addition to uncrystallized MDU,
An organic solution remains containing unreacted phenyl carbamate, polynuclear polycarbamate, and reaction intermediates. If this is thermally decomposed as it is, various problems will occur due to the reaction intermediates as described above.

According to the present invention, the amount of reaction intermediates is reduced and the yield of polycarbamate is improved by subjecting this organic solution to acid treatment as detailed below.

The organic solution includes not only the mother liquor after crystal separation (the filtrate in the case of filtration) but also the washing liquid when the crystals are washed with an appropriate organic solvent.

As the acid used in the acid treatment of the organic solution after crystal separation, an inorganic acid is used. Since the inorganic acid does not dissolve in the aromatic solvent, the treatment process is easy to operate, and the conversion effect from the intermediate to polycarbamate is high. Sulfuric acid, hydrochloric acid,
Inorganic acids such as perchloric acid are preferred, and sulfuric acid is particularly preferred.

A treatment method using sulfuric acid as the acid will be described below.

The concentration of sulfuric acid used in the treatment is 50% by weight or more, and 60% by weight or more.
It is preferably at least % by weight. When the concentration of sulfuric acid is less than 50%, the effect of reducing intermediates by acid treatment is small. In addition, if the acid concentration is lower than 75%, the treatment temperature should be adjusted to 70-10%.
Although it is preferable to raise the temperature to 0° C., high temperature treatment may cause deterioration of the polycarbamate and reduce the yield.

Therefore, 1111 degrees should be 75% by weight or more, preferably 75% by weight.
It is preferable to use as high as 5 to 90% by weight and carry out the treatment at a relatively low temperature of room temperature to 70°C, preferably 30 to 60°C, thereby improving the yield. In this case, if the processing temperature is below room temperature, the processing time will be longer and cooling equipment will also be required, which is not economical.

The amount of sulfuric acid used in this acid treatment step is 0.5 to 50 times, preferably 1 to 20 times, the total amount of the condensation product containing polycarbamate as a main component. If it is less than 0.5 times, it is difficult to complete the process.

The reaction time for acid treatment varies depending on the amount of condensation product to be treated, the concentration and amount of sulfuric acid, and also varies depending on whether the treatment method is continuous or batchwise, but generally it is 0.05~ It is lO time. Although it is not necessary to use an organic solvent in this process, a solvent may be used as long as it is chemically inert and stable to the components of the treatment system under the above conditions, and there are no particular restrictions on the amount. .

The above acid treatment conditions are an example when sulfuric acid is used, and the treatment conditions can be changed depending on the acid used to obtain the optimum result.

By this acid treatment, the condensation reaction intermediates having methylene amino bonds such as the benzylic compound (II/) and bisanilino compound (V) contained in the organic solution to be treated are transferred to polycarbamate, and the organic A tar insoluble in the solvent is formed. This tar is thought to be a substance that has an adverse effect on the next step, the thermal decomposition step, and has been changed by the acid treatment.

By this acid treatment, if optimal conditions are selected, reaction intermediates that are not converted to polyisocyanate can be completely converted to polycarbamate, as shown in the examples below, and thermal decomposition can be prevented as described above. Inhibiting substances can be converted into tar and removed from the polycarbamate product.

Therefore, the polycarbamate obtained from the organic solution after acid treatment is most suitable as a precursor for polymeric MDI, and by thermal decomposition thereof, polymeric MDI whose quality is significantly improved compared to the conventional one can be obtained.

After acid treatment, removal of the sulfuric acid by oil/water separation results in a solution containing the polycarbamate product with reduced intermediate content. The aromatic solvent is distilled off from this solution to isolate the polycarbamate product, which can then be thermally decomposed. When thermal decomposition of polycarbamate is carried out by liquid-phase thermal decomposition in an organic solvent, the polycarbamate solution obtained by separating sulfuric acid is recovered as a product and subjected to thermal decomposition as it is or after appropriate concentration adjustment. Good too.

The sulfuric acid recovered by oil-water separation can be reused as is for the next acid treatment, and the same effect as when fresh sulfuric acid is used can be obtained.

Sulfuric acid if necessary? It is closed with respect to the acid since the acid can be used repeatedly thereafter while adjusting the RK.

As described above, the acid treatment of the present invention can be carried out in a relatively short time under mild reaction conditions using a normal inorganic acid with a slightly high acidity, and the subsequent separation of the acid is easy. This method is very suitable for industrial implementation, as it can be used repeatedly and does not require waste liquid treatment, and its effects are also excellent.

The present invention will now be illustrated by examples. In the examples, % is by weight unless otherwise specified. The analysis was performed by high performance liquid chromatography using 0-phenylphenol as an internal standard. For polynuclear bodies and condensation reaction intermediates, calculations were performed using a factor of 1.0 for the internal standard.

Ethyl phenyl carbamate (
RPC) 200.0 g and 55% sulfuric acid 1078.
After heating the contents to 50°C in an oil bath without stirring, 49.1g of 37% formaldehyde aqueous solution (formalin) was added dropwise. After the completion of the dropwise addition, the mixture was heated to 90°C while stirring. The line combination reaction was carried out at this temperature for 2 hours.

After the reaction, 600 cj of toluene was added to the obtained product, the condensation product was dissolved in toluene, the sulfuric acid layer was separated, and the toluene solution containing the obtained condensation product was diluted with hot water. After washing, it was cooled. The precipitate was filtered off, washed with toluene (200 cd), and dried to collect 119.7 g of crystals. The composition of this crystal is 97.2% 4.4°-MDU, 0.1% 2,4°-MDU, and 1% polynuclear.
．． 0%, and contained no unreacted RPC.

A portion of the toluene solution obtained by combining the filtrate and washing liquid
．． By directly concentrating and drying 0 g without acid treatment, 11.64 g of oily substance was recovered. This is referred to as the "untreated" product.

The remainder of the above toluene solution was added to 100. Add 100 g of sulfuric acid aqueous solutions of various concentrations and perform acid treatment at 90°C for 2 hours with stirring. Then, sulfuric acid is separated by oil-water separation, and the remaining organic solution is evaporated to dryness in the same manner as above. The oil was collected. The composition and yield (oil recovery) of the "acid-treated" product thus obtained are shown in Table 1 below, together with the results for the untreated product.

Table 1 Value m when the amount of oil recovered during final treatment is taken as 100 Condensation reaction and crystallization treatment of the reaction product (solvent used: l.luene) were carried out in exactly the same manner as in Example 1, and 118 .1 g of polycarbamate crystals were obtained. Its composition is 4.4'
-MDU is 95.1%, 2.4'-MDU is not included, polynuclear is 1.4%, E I) C is 1.8%
100 g of 70% sulfuric acid was added to a portion of 100.0 g of the organic solution, which was a combination of the filtrate and washing liquid obtained in the crystallization treatment, and acid treatment was performed for 90 minutes while stirring at varying temperatures. Then, the acid was separated and the organic solution was concentrated to dryness in the same manner as in Example 1 to obtain an oily polycarbamate product. Its composition and yield are shown in Table 2 below, along with the results of the untreated product.

Table 2 117.6 g of polycarbamate crystals were obtained. Its composition is 95.5% 4.4'-M D U, 2,4"
-MDU is 0.2%, polynucleate is 1.2%, RPC is 1.
It was 8%.

The combination of the filtrate and washing liquid remaining after crystallization treatment is 1! !
Various amounts of 70% sulfuric acid were added to 100.0 g of a portion of the solution, and acid treatment was performed at 90°C for 90 minutes with stirring, followed by separation of the acid and concentration of the organic solution to dryness in the same manner as in Example 1. An oily polycarbamate product was obtained.

Its composition and yield are shown in Table 3 below, along with the results of the untreated product.

Table 3 Values when the amount of oil recovered when untreated is taken as 100 Condensation reaction and crystallization treatment of the reaction product (solvent used: toluene) were carried out in exactly the same manner as in Main Example 1. The condensation reaction and the crystallization treatment of the reaction product (solvent used: toluene) were carried out in exactly the same manner as in Example 1, and 105.5 g of polypropylene was obtained. Carbamate crystals were obtained. Its composition is 4.4'-M
DU was 95.3%, 2.4"-MDU was 0.2%, polynuclear was 1.3%, and RPC was 1.2%.

Add 100 g of 70% sulfuric acid to a portion of the organic solution, which is a combination of the filtrate and washing liquid obtained in the crystallization treatment, and perform acid treatment at 90 ° C. with stirring while varying the treatment time. f! The acid was separated and concentrated to dryness as in A1 to obtain an oily polycarbamate product. The composition, yield, and results of the untreated product are shown in Table 4 below.

Table 4: Using 300 g of untreated SWPc, and using 50 g of other reaction components in the same manner.
The condensation reaction and the crystallization treatment of the reaction product (solvent used: toluene) were carried out in the same manner as in Example 1, using an increased amount of 0%. The composition of the obtained 177.4 g polycarbamate crystals was 96.9% 4,4°-MDU, 2.4′-MDU
DU was not included, and polynuclear bodies and EPC were 1.0% and 1.3%, respectively.

Too much 70% sulfuric acid was added to 100.0 g of a portion of the organic solution obtained by combining the filtrate and washing liquid obtained in the crystallization treatment, and the mixture was heated at 90°C.
Acid treatment was carried out for 120 minutes, the acid was then recovered by separation, and the organic solution was concentrated to dryness to yield an oily polycarbamate product. The sulfuric acid thus recovered was reused as is, and the acid treatment of another 100.0 g of organic solution was repeated under the same conditions as above. The results of repeating the acid treatment five times by reusing sulfuric acid are shown in Table 5 below.

Table 5 *Values when the amount of oil recovered when untreated is set as 100 From Table 5, it can be seen that even if sulfuric acid is repeatedly reused, the performance of acid treatment does not deteriorate at all.

Separation of 4.4'-M DU (A) A hot toluene solution containing the condensation product obtained in the same manner as in Example 1 was cooled to 10° C. to precipitate crystals. The precipitated crystals were separated by suction a-filtration to obtain 544.3 g of crystals. When this crystal was analyzed by high performance liquid chromatography, it was found that it contained 96.4% of 44°-M D U and 2
．． 4''-MDLI and EPC were not detected.

After crystal separation, the mother liquor was evaporated to dryness to give the untreated product 497
．． 2 g was obtained. Its composition is unreacted RP C17,6
%, 4,4°-M D U25.2%, 2,4°-M
The DU was 16.4%.

(B) Sulfuric acid treatment of untreated product 50 g of the untreated product obtained in the above (A) and 350 g of 77% sulfuric acid aqueous solution were charged into a flask equipped with a stirrer, reflux condenser, and temperature system, and heated to 50°C. The mixture was heated and stirred. After 2 hours, 33 g of water was gradually added while cooling.

The reaction was stopped. After adding water, add toluene 500c
After dissolving the organic matter, the mixture was transferred to a separatory funnel, the toluene layer was separated, the sulfuric acid layer was washed twice with 200 CC of toluene, and this toluene layer was combined with the above toluene layer and washed with hot water. Toluene was separated from the toluene layer using an evaporator to obtain 48.0 g of an acid-treated product. When this acid-treated product was analyzed by high performance liquid chromatography, it was found that 7.2 g of unreacted EPC and 4.4'-MDUI4.
3 g, 2.4°-M D Ulo, 2 g, no intermediates were detected. Therefore, step (A),
(B) As a result of performing 4, the yields of 4,4''-MDU and 2,4°MDU were 66.7% and 10.1%, respectively, based on the EPC charged in (^), and the conversion rate of RPC was is 9
It becomes 2.8%.

From this acid-treated product, unreacted RPC was recovered by distillation, and 40.4 g of the acid-treated product was recovered. When this acid-treated product was analyzed by high-performance liquid chromatography, it was found that
4.4'-M D U3O, 1%, 2,4°-MDU
It contained 26.6%, and no RPC was detected.

(C) Pyrolysis reaction stirrer for acid-treated products, thermometer, pressure gauge, packed distillation column with 5 stages, cooling pipe and receiver for cooling and condensing the vapor distilled from the top of the column, preheating means 10 g of the acid-treated product obtained in (B) above and 270 g of o-dichlorobenzene were charged into a pressure-resistant container with an internal volume of 5001111 and equipped with a nitrogen gas blowing pipe and a solvent supply pipe, and reacted with nitrogen gas. The inside of the vessel was pressurized to 2.9 kg/cs'G, and the packed distillation column was
Heated to 0°C. Furthermore, while flowing nitrogen gas preheated to 170°C at a flow rate of 30w2/s+in, the pressure inside the reactor was maintained at 2.9 kg/c+m''G, and the outer wall temperature was 40°C.
The reaction was carried out while heating to 0°C. The temperature of the reaction system became constant at the solution temperature of 246°C, and the system reached a boiling state.
During the reaction, the reaction pressure was gradually increased so that the reaction temperature was increased at a rate of 0.1° C./win. Since ethanol is distilled out together with O-dichlorobenzene during the reaction, the same volume of O-dichlorobenzene preheated to 200°C as the distilled amount is added to the reaction system to keep the volume in the reaction system constant throughout the reaction. I made it so that

120 minutes after the boiling state, the heating was stopped and the contents were taken out when the temperature reached 80°C.A small amount of the contents was analyzed by high performance liquid chromatography.As a result, unreacted 4.
No 4'-MDU was detected, and the yield of intermediate monoisocyanate and 4.4°-MDI was lower than that of the starting 4.4
'-0.2 mol% and 95% relative to MDUI, respectively
．． It was 2 mol%. This reaction solution was heated at 70℃15~1Qm
The solvent was removed by vacuum distillation at mHg, leaving a brown liquid. This liquid dinuclear polyisocyanate (MDr
) The total content was 56%, and the NGO content was 31%.

This μM was obtained in Example 6 (B
) was treated with sulfuric acid in the same manner as in 47.
0 g was collected. Analysis of this solid by high performance liquid chromatography revealed that unreacted RPC was 3.6 g, 4.4
It contained 26.2 g of '-MDU and 4.3 g of 2.4-MDU, and no intermediate was detected. Thus, as a result of treating the entire amount of the condensation product with sulfuric acid without separating 4.4'-M D U by crystallization,
The yields of '-MDU and 2,4MDU were 54.5% each.
5% and 930%, and compared with Example 6, the M of the dinuclear body
The yield of DU, especially 4,4 MDU, decreased.

Comparison 1 (A) Treatment with trifluoroacetic acid Untreated product (4,4'-
50 g of the solution after MDU crystallization (as is or concentrated to dryness) and 250 g of trifluoroacetic acid were charged into a flask equipped with a stirrer, a reflux condenser, and a thermometer, and heated and stirred at a reaction temperature of 70°C for 30 minutes. I went for a minute. After cooling, trifluoroacetic acid was collected in an evaporation lake, and the solid matter was 49.8
I got g. When this solid was analyzed by liquid chromatography, it was found that unreacted EP C7.5g, 4.4'
-M D U12.3 g, 2.4'-M D tJ9
．． 3 g and 0.6 g of intermediate. From this solid, unreacted RPC is recovered by distillation, and the solid 41.
0 g was collected. When this solid was analyzed by high performance liquid chromatography, it was found to be 4.4'-M DU34.
2%, 2.4'-M D LJ and 23.5%, and no RPC was detected. Compared to the product obtained in Example 6(B) after EPCFA distillation, the content of MDU is lower.

(B) Thermal decomposition reaction of condensation product treated with trifluoroacetic acid Using the solid material not containing unreacted RPC obtained in (A) above, the same method as in (C) of Example 1 was carried out. A thermal decomposition reaction was carried out. When the reaction solution was analyzed by high performance liquid chromatography, unreacted 4.4°-MDU was not detected, and intermediate monoisocyanate and 4,4°-MDU were detected.
The yields of MDI were 0.5 mol % and 93.5 mol %, respectively, based on the 4.4°-MDU charged. The solvent was removed from this reaction solution by vacuum distillation to obtain a brown liquid. This liquid dinuclear polyisocyanate (MDI)
Total content is 39.6%, NGO content is 25.4%
The quality was inferior to that of the thermal decomposition product of Example 6(C).

(Effects of the Invention) According to the present invention, pure MD is obtained by condensing phenyl carbamate with a methylenating agent in the presence of an acid catalyst and then crystallizing and separating MDU crystals using an aromatic organic solvent.
In the method for producing polycarbamate in which the precursor polycarbamate of I and the precursor polycarbamate of PolymeLink MDI are separately recovered, thermal decomposition of the polycarbamate is inhibited by treating the organic solution after MDU crystal separation with an acid, or Substances that become impurities in thermal decomposition products can be effectively removed. Therefore, by thermally decomposing the polycarbamate obtained in the present invention, a polyisocyanate with excellent quality can be obtained.

Further, the acid treatment utilized in the present invention is easily performed under relatively mild treatment conditions using an easy-to-handle acid such as sulfuric acid. Furthermore, the acid separated and recovered after the acid treatment can be reused as is in the acid treatment step, and even if this reuse is repeated, the effect of the acid treatment will not deteriorate. Therefore, the process is closed with respect to acid, and acid treatment can be performed without troublesome waste liquid treatment, so it can be easily implemented industrially.

As described above, the present invention can solve the problems in the production of conventional polycarbamates using a simple method, and has great industrial significance.

Claims (2)

[Claims] (1) A method for producing polymethylene polyphenyl polycarbamate by reacting phenyl carbamate with a methylenating agent in the presence of an acid catalyst, in which (A) the resulting reaction mixture is treated with an aromatic organic solvent, Separated into an aqueous layer containing the acid catalyst and an organic layer containing the reaction products, (
B) Methylene diphenyl dicarbamate crystals are obtained from this organic layer by crystallization, and (C) the organic solution obtained after crystal separation is treated with an inorganic acid aqueous solution, and the product is separated from the above crystals from this solution. A method for producing polymethylene polyphenyl polycarbamate, characterized by recovering it in isolation or solution form. (2) The method according to claim 1, wherein in (C), the acid aqueous solution is recovered and reused after the treatment.