JPH01135758A - Production of aromatic polycarbamate - Google Patents

Abstract

PURPOSE:To obtain the subject compound useful as an intermediate for medicines, agricultural chemicals, etc., in high conversion rate and quality without requiring recovery of the unreacted raw materials, by dividedly adding a relatively small excessive amount of a methylenating agent to an N- phenylcarbamate in the presence of an acid catalyst. CONSTITUTION:A methylenating agent (e.g., trioxane or paraformaldehyde) is reacted with an N-phenylcarbamate in the presence of an acid catalyst (e.g., H2SO4, HCl, phosphoric acid, polysulfuric acid or polyphosphoric acid) to provide polymethylene polyphenyl polycarbamate. In the process, the methylenating agent is used in an excessive amount of <=twice based on the stoichiometric amount and added in >=2 divided portions. In the divided addition, an almost stoichiometric amount (0.5mol. methylenating agent) or a somewhat smaller amount (e.g., 0.7-1.0 based on the stoichiometric amount) is previously added and the rest is added after a time of about half the total reaction time elapsed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing polymethylene polyphenyl polycarbamate (hereinafter abbreviated as polycarbamate) using N-phenyl carbamate and a methylenating agent as raw materials.

More specifically, in a method for producing polycarbamate by reacting a methylenating agent such as formaldehyde with N-phenyl carbamate in an acid aqueous solution of a catalyst, the raw material N
- An improved method capable of increasing the conversion rate of phenyl carbamate and obtaining a reaction product containing substantially no unreacted raw materials.

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 the dinuclear methylene diphenyl diisocyanate (MDI), are useful materials as raw materials for the production of polyurethane elastomers and coating materials, and the amount used in this application is problematic due to their high volatility and toxicity. At present, it has surpassed tolylene diisocyanate (TDI), and is being mass produced on an industrial scale.

(Prior Art) Conventionally, aromatic isocyanes (1) have generally been industrially produced by reducing an aromatic nitro compound with hydrogen to obtain an aromatic amine, and then treating this 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 isocyanates that do not use phosgene are being actively researched.

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, this method is difficult to apply to the production of the above-mentioned polyisocyanates such as MDI.

The second carbamate-mediated method involves reacting an aromatic nitro compound and an alcohol with carbon monoxide in the presence of a platinum group metal catalyst or a selenium catalyst to obtain an intermediate aromatic carbamate, which is then 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, polycarbamate (■) is produced by crosslinking N-phenyl carbamate (+) by condensation with a methylenating agent such as formaldehyde in the presence of an acid catalyst. .

4 4 (where m is 0 or the number of M from I to 6, R is the number of carbon atoms from 1 to 6)
lower alkyl group).

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

Upon pyrolysis, the resulting polycarbamate has the formula (Il
r) to the corresponding polyisocyanate.

(where m and R have the same meanings as above).

As a raw material for producing polyurethane, m =
The 2N; field of Q, ie, M D I, is most desirable.

However, in the above condensation reaction, the dinuclear polycarbamate (methylene diphenyl cicabamate,
Even if the reaction is carried out at a ratio of 2 moles of N-phenyl carbamate to 1 mole of formaldehyde to produce MDU), the formation of polynuclear bodies (m≧1) of trinuclear bodies or more is unavoidable, and the condensation reaction product necessarily contains a small amount of polynuclear polycarbamate, and as a result, the products obtained in the next thermal decomposition reaction also contain a small amount of polyisocyanate, along with side reaction products and intermediate products, in addition to MDI. Contain.

Therefore, in order to obtain a high-quality raw material for producing polyurethane, it is advantageous to obtain a polycarbamate product in which the proportion of binuclear MDU produced is as high as possible in the condensation reaction.

For a method for producing polycarbamates by crosslinking N-phenyl carbamate compounds by condensation with a methylenating agent in the presence of an acid catalyst, see, for example, U.S. Pat.
No. 6,768, JP-A-54-59264, JP-A No. 55-7
No. 9358, No. 55-81850, No. 55-8185
Many proposals have been made, such as No. 1 and No. 59-106453.

In addition, in order to improve the yield of the target product in the above condensation reaction, methods have been proposed to use co-catalysts and/or to promote the condensation reaction homogeneously (for example, JP-A No. 5
No. 6-100280, No. 56-167655, etc.).

However, these known methods have insufficient yields of condensation reaction products, particularly desirable binuclear MDU, and a method for separating the target product from the reaction products has not been established. The production of polycarbamates by the above-mentioned condensation reactions and the production of polyisocyanates by thermal decomposition thereof have not yet been commercially implemented.

(Problems to be Solved by the Invention) Before the polycarbamate product obtained by the condensation reaction is thermally decomposed into polyisocyanate, unreacted raw material N-phenyl carbamate is usually removed by means such as distillation. . If the unreacted amount is large, the equipment and energy required for its separation will be large, which is industrially disadvantageous. However, in the above reaction of N-phenyl carbamate and methylenating agent in the presence of an acid catalyst, even if the methylenating agent is used in an amount larger than the equivalent amount to N-phenyl carbamate, a considerable amount of unreacted N-phenyl remains. It is recognized that carbamate remains.

The following method can be considered to achieve complete conversion of N-phenyl carbamate.

■Use a large excess of methylenating agent.

■Use a large amount of acid catalyst.

■Increase the acid catalyst concentration in the reaction system.

However, in these methods, the condensation reaction progresses too much and the proportion of polynuclear bodies with m ≧ 1 or more trinuclear bodies in the above-mentioned -tubular formula (n) increases, or other side reactions occur simultaneously, resulting in unobtainable results. The composition of the resulting condensation reaction product is unsatisfactory from an industrial point of view. In particular, the most desirable reaction product, the dinuclear 4,4'-methylene diphenyl dicarbame) (
4,4'-MDIJ) production rate becomes low.

Therefore, an object of the present invention is to increase the conversion rate of raw material N-phenyl carbamate to close to 100% in the production of polycarbamate by the reaction of N-phenyl carbamate with a methylenating agent in the presence of an acid catalyst, and at the same time to Body MD
The object of the present invention is to provide a production process which makes it possible to give products containing a high proportion of U, in particular 4.4"-MDU.

This makes it possible to use the reaction product in subsequent pyrolysis without having to recover unreacted raw materials after production, and in pyrolysis, the desired product is a high-quality polymer with a high MDI content. An isocyanate product can be obtained.

(Means for Solving the Problem) The present inventors have found that it is effective to use a relatively small excess amount of the methylenating agent and add it to the reaction system in portions to achieve the above object. They found that this is the case, and completed the present invention.

Here, the gist of the present invention is a method for producing polymethylene polyphenyl polycarbamate by causing a methylenating agent to act on N-phenyl carbamate in the presence of an acid catalyst, in which the methylenating agent is added in a stoichiometric amount relative to the N-phenyl carbamate. This is a method for producing polymethylene polyphenyl polycarbamate, which is characterized in that an excess amount of not more than twice the stoichiometric amount is used and the amount is added in two or more portions.

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

The starting material for the polycarbamate production method of the present invention is N-phenylcarbamate represented by the above-mentioned formula (1). - In the tubular formula (1), it is particularly preferable that R is methyl or ethyl because the next thermal decomposition reaction becomes easy.

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, primarily for economic reasons, an aqueous formaldehyde solution (formalin) is used as the methylenating agent.

Examples of acid catalysts include sulfuric acid, hydrochloric acid, phosphoric acid, polysulfuric acid, and polysulfuric acid.
J IJ Inorganic acids such as phosphoric acid, boric acid, hydrobromic acid, 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, can be used as catalysts. Preferred from the viewpoint of activity. There is no particular restriction on the amount of catalyst used, but it is between 3 and 3 to N-phenyl carbamate.
It is preferably within the range of 5 times.

The above condensation reaction may be carried out in the presence of an organic solvent, if desired. The reaction temperature is generally 50 to 120°C, preferably 80 to 100°C, and the reaction time varies depending on the temperature, but is generally within the range of 1 to 5 hours. The reaction method may be either a batch method or a continuous method, and there is no particular restriction on the amount of reaction components added, but the reaction is generally carried out by adding a methylenating agent to a mixture of N-phenyl carbamate and an acid catalyst. It is preferable to implement it.

According to the present invention, the amount of the methylenating agent used is a relatively small excess of twice the stoichiometric amount or less.

When the purpose is to produce binuclear MDU, the stoichiometric amount is 0.5 mol of the methylenating agent per 1 mol of N-phenyl carbamate. If the methylenating agent is used in an amount exceeding twice the stoichiometric amount, the condensation reaction will proceed too much and the proportion of undesirable polynuclear products will increase. The preferred amount of methylenating agent to be used is about 1.2 times or less of the stoichiometric amount, and in particular, if a small excess of about 1.1 times is used, 2
This is advantageous because the yield of nuclear bodies is increased.

When the methylenating agent is used in a relatively small excess as described above, it is difficult to complete the reaction.

According to the present invention, the condensation reaction can be substantially completed by adding the methylenating agent in at least two portions.

Although there is no particular limitation on the amount of the methylenating agent to be added in portions, the following method is advantageous. The first addition amount at the start of the reaction is approximately 36 stoichiometric amounts (0.5 mol of methylenating agent per 1 mol of N-phenyl carbamate), or a slightly smaller amount, e.g. stoichiometric amount. 0.
7 to 1.0 times the amount (preferably about 1 times the amount), and add the rest during the second addition. There is no particular restriction on the timing of the second addition, but it is undesirable from the spirit of the present invention to add it too close to the first addition. When the addition is made in two portions, the second addition is carried out after at least 174, preferably 1/3, for example about half, of the total reaction time has elapsed.

The methylenating agent can be added in three or more parts, but in the above example, the conversion rate of the raw material N-phenyl carbamate usually reaches almost 100% by adding the methylenating agent the second time. Therefore, it is necessary to be careful because the third and subsequent additions may have the disadvantage of increasing the proportion of polynuclear bodies produced. In this sense, the object of the present invention can usually be fully achieved by adding in two portions.

When carrying out the reaction continuously, the methylenating agent can be added in portions by using two or more reactors and adding the methylenating agent to each reactor in appropriate portions as described above. Can be done.

The polycarbamate reaction product produced by condensation can be obtained as a solid by removing the catalyst, unreacted raw materials, water, and other reaction solvents from the condensation reaction mixture. If necessary, purification (eg, ion exchange resin treatment) may be performed to remove impurities. According to the present invention, by adding the methylenating agent in portions, unreacted N can be removed even though a relatively small excess amount of methylenating agent is used.
- A reaction product is obtained with a very low content of phenyl carbamate. Therefore, this reaction product can be used as it is in the next step of producing polyisonanate by thermal decomposition.

Generally, it is expected that adding an excess of the reactant will improve the conversion rate and reduce the amount of unreacted raw material, but it is difficult to improve the selectivity of the desired reaction product. In the present invention, by dividing the addition of the methylenating agent, the amount of addition is reduced, so the formation of polynuclear bodies can be suppressed, and a product containing a large amount of desirable dinuclear MDU can be obtained. The selectivity is improved at the same time, and the unexpected effect is that the quality of the product is significantly improved.

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

Conducted 100 times fitted with a thermometer, reflux condenser and dropping funnel.
8.28 g of ethyl N-phenyl carbamate, 25.52 g of 96% sulfuric acid, and 23.50 g of distilled water were placed in a CD volume three-necked flask and heated while stirring with a magnetic stirrer. When the temperature reached 50°C, 2.02 g of 37% formaldehyde aqueous solution (1.0 times the stoichiometric amount for the above carbamate) was started to be added dropwise. After the completion of the dropwise addition, the mixed solution was heated to 90°C while stirring, This temperature was maintained for 1 hour to allow a condensation reaction. Then, 0.2 g of 37% formaldehyde aqueous solution (0.1 times the stoichiometric amount) was added and the reaction was continued at 90°C for an additional hour. After the reaction was completed, it was cooled to room temperature, and the reaction product was added with methyl ethyl ketone. The organic matter containing 20% was extracted from the aqueous layer, and a portion of it was analyzed by high performance liquid chromatography.

As a result of analysis, the conversion rate of N-phenyl carbamate was 98.
．． The yield of dinuclear MDυ was 73.0%. 2
The breakdown of the nuclear bodies is 90.1% 4.4'-MDU, 2゜4
'-MDU accounted for 9.9%, and trace amounts of 2.2'-MDU were also detected.

8.29 g of ethyl N-phenyl carbamate on carbon, 9
The reaction was carried out in the same manner as in Example 1 using 6125.62 g of 6% sulfur, 23.53 g of distilled water, and 2.02 g of a 37% formaldehyde aqueous solution (roughly stoichiometric). However, the entire amount of the formaldehyde aqueous solution was added dropwise at 50°C, and the reaction time at 90°C was set to 2 hours as in Example 1.

The analysis results of the reaction product showed that the conversion rate of N-phenyl carbamate was 89.8% and the yield of dinuclear MDU was 67.8%, and the breakdown of the dinuclear bodies was 4.4'-M D U3O, 2
%, 2.4'-M DU was 9.8%. That is, when a nearly stoichiometric amount of the methylenating agent was added at once, both the conversion rate and the binuclear yield were significantly lower than in Example 1.

Comparison 5 I Ethyl N-phenyl carbamate 8.33 g, 9
6% sulfuric acid 25.50 g, distilled water 23.60 g,
The reaction was carried out in the same manner as in Example 1 using 2.23 g (approximately 1.1 times the stoichiometric amount) of 37% formaldehyde aqueous solution.

However, the entire amount of the formaldehyde aqueous solution was added dropwise at 50°C, and the reaction time at 90°C was set to 2 hours as in Example 1.

The analysis results of the reaction product showed that the conversion rate of N-phenyl carbamate was 99.5%, and the yield of binuclear MDU was 70.1%, and the breakdown of the binuclear product was 4.4'-MDU92. 2
%, 2.4°-MDU 7.8%.

In other words, even if the amount of methylenating agent used was approximately 1.1 times the stoichiometric amount as in Example 1, the conversion rate was slightly higher when it was not added in portions, but The yield was substantially lower than in Example 1, in which the mixture was added in portions, and the product quality deteriorated.

Comparing Comparative Example 2 with Comparative Example 1, it can be seen that simply adding an excessive amount of methylenating agent has little effect on improving the yield of the desired product, dinuclear MDU. On the other hand, when the same amount of methylenating agent as in Comparative Example 2 is added in portions, the dinuclear yield is improved as shown in Example 1, which is an unexpected effect.

8.28 g of ethyl N-phenyl carbamate, 25.50 g of 96% sulfuric acid, 23.50 g of distilled water, and 3
A reaction was carried out in the same manner as in Example 1 using 2.43 g (approximately 1.2 times the stoichiometric amount) of a 7% formaldehyde aqueous solution.

However, formaldehyde aqueous solution has a temperature of 2.
After adding 01 g and reacting for 30 minutes at 90°C,
The remaining 0.42g was added. After this addition, the reaction product was further reacted at 90°C for 30 minutes.The reaction product obtained by the reaction for a total of 1 hour was analyzed in the same manner as in Example 1, and the conversion rate of N-phenyl carbamate was 95.1%. nuclear body MDU
The yield was 69.1%, and the breakdown of dinuclear bodies was 4.4'
-M D U92.9%, 2.4' -M D U7.
It was 1%.

Based on Yuethyl N-phenyl carbamate 8.27 g, 9
25.50 g of 6% sulfuric acid, 23.50 g of distilled water, and 3
The reaction was carried out in the same manner as in Example 2 using 2.43 g of 7% formaldehyde aqueous solution. However, the entire amount of the formaldehyde aqueous solution was added when the temperature was 50°C, and the reaction time at 90°C was 1 hour as in Example 2.

The analysis results of the reaction product showed that the conversion rate of N-phenyl carbamate was 94.9%, and the yield of dinuclear MDU was 66.6%, and the breakdown of the dinuclear body was 4,4°-MDU93. 9%
, 2.4'-M DU was 6.1%.

Ethyl N-phenyl carbamate 8.27 g, 9
The reaction was carried out in the same manner as in Example 1 using 25.50 g of 6% sulfuric acid, 23.50 g of distilled water, and 2.93 g of 37% formaldehyde aqueous solution (approximately 1.45 times the stoichiometric amount).

However, formaldehyde aqueous solution has 2
．． After adding 19 g and reacting at 90°C for 1 hour, 0.74 g
was added, and the reaction was further carried out at 90°C for 1 hour.

The analysis results showed that the conversion rate of N-phenyl carbamate was 10
0%, the yield of dinuclear MDU is 67.9%, and the breakdown of dinuclear bodies is 4.4'-MDU92.3%, 2,4°
-MDU was 7.7%.

Compared to Example 1, the amount of methylenating agent used was larger, so the conversion rate was 100%, but the dinuclear yield was slightly lower.

(Effects of the Invention) As explained and exemplified above, according to the present invention, by a simple operation of adding a relatively small excess of methylenating agent in portions to the reaction, the conversion rate is improved and unreacted N-phenyl carbamate is A polycarbamate product with a greatly reduced fffi content can be obtained. Moreover, unexpectedly, when the methylenating agent is added all at once in a small excess amount, even though the conversion rate is improved, the desirable binuclear M in the reaction product is
While the yield of DU is not significantly improved, the yield of binuclear MDU can be considerably increased by adding portions according to the present invention compared to converting the same amount at once.

As a result, when the obtained polycarbamate is used as a raw material for producing polyisocyanate by thermal decomposition, separation and recovery operations of unreacted N-phenyl carbamate are not necessary, the reaction process is simplified, and the dinuclear A polyisocyanate product with a high content of MD+ can be obtained, improving the polyisocyanate yield and product quality.

Therefore, the present invention makes it possible to economically produce high-quality polyisocyanate in good yield by the above-mentioned carbamate-mediated method, and greatly contributes to its industrialization.

Claims (3)

[Claims] (1) In a method for producing polymethylene polyphenyl polycarbamate by allowing a methylenating agent to act on N-phenyl carbamate in the presence of an acid catalyst, the methylenating agent is used in an amount not more than twice the stoichiometric amount of N-phenyl carbamate. A method for producing polymethylene polyphenyl polycarbamate, the method comprising using an excess amount of , and adding the same in two or more portions. (2) Add the methylenating agent in an amount of 0.7 to 1.0 times the stoichiometric amount at the start of the reaction, and add it for at least 1.0 times the stoichiometric amount.
2. The manufacturing method according to claim 1, wherein the remaining methylenating agent is added after 30 minutes. (3) The total amount of methylenating agent used is about 1 of the stoichiometric amount.
．． 3. The method according to claim 1 or 2, wherein the amount is 1 to 1.2 times.