JPH03157357A - Recovering method of diphenylmethane dicarbamic acid esters - Google Patents

Abstract

PURPOSE:To readily obtain 4,4'-modification of the subject compound in high purity and high recovery by adding specific solvent to alcoholic mother solution after recrystallization and separation of solid product in production of the subject compound from an N-phenyl carbamic acid ester with using an acid catalyst. CONSTITUTION:In the presence of an acid catalyst, a N-phenyl carbamic acid ester is condensed with methylenation agent and a resultant solid product is separated from a reacting solution, then washed with water or hot water, thus further recrystallized in an alcohol to produce a diphenylmethane dicarbamic acid ester useful as starting material for producing a raw material of polyure thane. In said process, an aliphatic hydrocarbon and/or an alicyclic hydrocarbon solvent liquid at normal temperature is added to an alcoholic mother solution after recrystallization of the above-mentioned product and product other than N-benzyl compound is separated from said mother solution with simple opera tion, then, 4,4'-modification is recovered in high purity and high recovery.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for recovering diphenylmethanedicarbamate esters, and more specifically, a method for recovering the product from an alcohol mother liquor after recrystallization separation with high purity and high recovery rate. The present invention relates to a method for recovering diphenylmethanedicarbamate ester.

[Conventional technology]

Diphenylmethane dicarbamates and their higher homologues, polymethylene polyphenyl carbamates, are starting materials for producing diphenylmethane diisocyanate (MDI) and polymethylene polyphenylisocyanate, which are known as raw materials for polyurethane. It is useful as In particular, demand for 4,41-diphenylmethane diisocyanate (pure MDI) has increased significantly in recent years as a raw material for polyurethane elastomers, elastic fibers, coating materials for artificial leather, and the like. Therefore, an industrially advantageous manufacturing method containing abundant diphenylmethanedicarbamate esters, especially 4,41-diphenylmethanedicarbamate esters (hereinafter also abbreviated as 4,4"), which is the raw material, is recommended. Development is desperately needed.

Conventionally, the isocyanates have been described, for example, in U.S. Pat.
It is produced by phosgenating a diamine and a polyamine obtained by condensing aniline with formaldehyde in an acid aqueous solution as described in No. 14,914. However, since phosgene is highly poisonous, special attention must be paid to safety, and safety equipment is expensive, and a large amount of hydrogen chloride is produced as a by-product, causing environmental deterioration. For this reason, methods for producing isocyanates that do not use phosgene have been investigated.

US Pat. No. 2,946,768 discloses a method in which N-phenylcarbamate is reacted with formaldehyde or a compound that eliminates formaldehyde by heating in an aqueous acid solution. However, in this method, according to JP-A No. 54-59264, condensation generally occurs at the N-position of the N-phenylcarbamate 15
~50% by weight of (alkoxycarbonyl)phenylaminomethylphenyl compounds and their various polynuclear forms (
(hereinafter abbreviated as N-benzyl compound) is produced as a by-product. N
- The benzyl compound is a combination of diphenylmethane dicarbamate ester and diphenylmethane diisocyanate (MDI).
), it is not converted to MDI by non-catalytic heat treatment and reacts with the generated MDI, significantly reducing product purity.

Further, the N-benzyl compound cannot be separated from diphenylmethanedicarbamate and MDI by ordinary separation operations such as distillation and crystallization. Therefore, it is necessary to suppress the by-product of this compound as much as possible, and methods have been proposed to suppress the production of this compound as much as possible.

JP-A-55-57550 discloses a protic acid having a strength of at least 75% sulfuric acid in a concentration of 0.1 to 25% by weight based on the reaction mixture or at least 0.5% by weight based on the reaction mixture. A method is described for rearranging N-hensyl compounds to carbamate esters in the presence of a certain concentration of Lewis acid. In particular, when an organic sulfonic acid is used as the acid, it is advantageous because it becomes a better solvent than sulfuric acid for N-phenylcarbamate ester, enabling a single-phase reaction, and because sulfonation does not occur due to the use of high concentration sulfuric acid. . In addition, N-phenylcarbamate is removed from formaldehyde or formaldehyde using a carboxylic acid with a pKa of less than 4 (Japanese Unexamined Patent Publication No. 56-158752) or in the coexistence of a carboxylic acid and a strong acid (Japanese Unexamined Patent Publication No. 56-65864). A similar result can be obtained by reacting with a compound that releases the compound. Furthermore, JP-A-5!11-1
Publication No. 064539 discloses that the first stage reaction is carried out by reacting N-phenylcarbamate esters with a methylenating agent in a 20 to 70% heavy weight acid aqueous solution, and the second stage reaction is carried out in a reaction with a pKa of 4 or less. 1 by reacting in carboxylic acid of
A two-stage synthesis method in which the N-hensyl compound produced as a by-product in each stage is rearranged to diphenylmethanedicarbamate esters, and a method in which unreacted products obtained at each stage are separated and recycled are shown.

In general, in the production of diphenylmethanedicarbamate ester, in addition to 4.4′ monomer, 2.4゛ and 2.2′ monomer positional isomers are produced; The production ratio of integral and 2゜2' integral is approximately 4
= 1 and 20:1, which is about 78% 4,4'
This shows an isomer distribution of 18% 2.4'' and 4% 2,2''. Such a product mixture, when pyrolyzed in a solvent, changes the isomer ratio. Although it is useful as a commercially valuable diphenylmethane diisocyanate having a 4,4-dicarbamate content, it is preferable for the above-mentioned specific uses to use a diphenylmethane dicarbamate rich in 4,4-monocarbons. JP-A-55-1292
No. 60 discloses that in an acid-catalyzed single-phase system, N-phenylcarbamate is limited to 0.1 to 50% by weight based on the solvent, and diphenylmethanedicarbamate is prepared in an inert solvent having a dielectric constant of at least 20. When producing esters,
The 4,4′ integrated sound volume increased significantly, and the above isomer distribution decreased to 9.
It has been shown that the improvement is as high as 4.5%, 4.7% and 0.8%.

In the synthesis of diphenylmethane dicarbamates, a higher homologue, polymethylene polyphenyl carbamate, is also produced at the same time. This is a carbamate ester having three or more benzene rings interconnected by methylene bridges. This polynuclear body has already formed diphenylmethane dicarbamate and N-
Phenylcarbamate ester is produced by sequential reaction with formaldehyde, and the selectivity of polynuclear bodies among carbamate esters is usually 10 to 50%. In order to suppress the formation of polynuclear bodies, the reaction is generally carried out using N-phenylcarbamate in an amount greater than the stoichiometric amount of formaldehyde, for example, the molar ratio of N-phenylcarbamate to formaldehyde is Sat. At such a molar ratio, the conversion rate of N-phenylcarbamate ester becomes low, and furthermore, the formation of polynuclear bodies cannot necessarily be efficiently suppressed for the following reasons. That is, in reactions using organic solvents, the reactants are in a homogeneous phase, so it is difficult to suppress the formation of polynuclear bodies and increase the selectivity of 4,4'' bodies. However, since the reaction proceeds with the organic phase emulsified in the aqueous phase, the produced diphenylmethanedicarbamate ester reacts with the N-phenylcarbamate ester, making it difficult to suppress the production of polynuclear bodies.

As a method to solve such problems, Japanese Patent Laid-Open No. 62-67
Publication No. 059 discloses that the concentration of N-phenylcarbamate is set to be below the solubility at the reaction temperature, and the ratio of the solubility of diphenylmethanedicarbamate to the solubility of N-phenylcarbamate is 0.1 or below at the reaction temperature. A method has been shown in which the production of polynuclear bodies is significantly suppressed by using a certain inorganic acid aqueous solution, and 4.4' monomers are produced with high selectivity. However, this method has the disadvantage that the raw material processing capacity is small.

[Problem to be solved by the invention]

In production by a non-phosgene method, diphenylmethane dicarbamate (MDU) 19 can be synthesized in high yield, and unlike MDI, MDU is characterized in that there is no fear of hydrolytic polymerization.

After the MDUs produced in this way are separated from the aqueous catalyst solution as a solid product, most of the unreacted raw material N-phenylcarbamate (NPU) and the catalyst are removed by washing with water or hot water. It is further recrystallized in alcohol, and most of the 4°4° product is recovered. In addition to 4 and 4 degrees, the alcohol mother liquor at this time contains 2
, 4° integral, polynuclear bodies, NPU, N-benzyl compounds, etc. are contained in small amounts. However, as mentioned above, it is difficult to separate the N-benzyl compound from products such as 4.4° by normal separation operations, and the N-benzyl compound is difficult to separate from products such as 4.
It was only possible to recover the 4° unit with high purity.

The purpose of the present invention is to solve the above-mentioned problems of the prior art, to separate products other than N-benzyl compounds from the alcohol mother liquor after recrystallization separation with a simple operation, and to recover 4゜4' with high purity. An object of the present invention is to provide a method for recovering diphenylmethanecarbamate esters that can be recovered at a high rate.

(Means for Solving the Problems) The present invention involves condensing N-phenylcal/z)miso acid esters with a methylenating agent using an acid catalyst to produce diphenylmethanedicarbamic acid esters. After separating the resulting solid product from the reaction solution and washing it with water or hot water, the product is recrystallized in alcohol, and aliphatic hydrocarbons and/or fats that are liquid at room temperature are added to the alcohol mother liquor. The present invention relates to a method for recovering diphenylmethanecarbamate esters, which comprises adding a cyclic hydrocarbon solvent and recovering the product remaining in the alcohol mother liquor.

In the present invention, diphenylmethanecarbamate esters are produced, for example, as follows.

N-phenylcarbamate (NPU), for example, a lower alkyl ester of N-phenylcarbamate such as ethyl N-phenylcarbamate, is heated to 150°C from the temperature at which the N-phenylcarbamate melts or higher.
At the following reaction temperature, a methylenating agent such as formaldehyde, paraformaldehyde, or trioxane is gradually added to an aqueous inorganic acid solution containing phosphoric acid and/or its salt and an organic carboxylic acid and/or its salt, and the mixture is thoroughly stirred. While reacting. In such a method, N-
It is possible to suppress the by-product of benzyl compounds, and if the molar ratio of N-phenylcarbamate and methylenating agent is kept at the theoretical reaction amount ratio, even when the solubility of N-phenylcarbamate is exceeded, N-phenyl The conversion rate of carbamate ester can be significantly increased, and in particular, the formation of polymethylene polyphenyl carbamate ester can be significantly suppressed.

Furthermore, the 4.4' monolithic selectivity among diphenylmethanedicarbamate ester isomers can be increased.

As the N-phenylcarbamate ester, a compound having one or more types of acid esters 5 (-NHCOOR group) is used. However, R in the formula means an alkyl group having 8 or less carbon atoms, a phenyl group, or an alkyl-substituted phenyl group having 4 or less carbon atoms in the alkyl substituent. The N-phenyl group of the carbamate ester may contain a substituent such as an alkyl group, an alkoxy group, or a halogen at the 0- and/or m-positions. Suitable N-phenylcarbamate esters include methyl N-phenylcarbamate, ethyl N-phenylcarbamate, propyl N-phenylcarbamate, N-o-
Methyl tolylcarbamate, N-.

Examples include ethyl tolylcarbamate, methyl N-2,6-dimethylphenylcarbamate, and ethyl N-o-cucorphenylcarbamate.

Said methylenating agents include formaldehyde or compounds which eliminate formaldehyde in the presence of acids, such as paraformaldehyde, trioxane or special formaldehyde derivatives. Examples of the above formaldehyde derivatives include general 2X-CH, -X (wherein X represents OR', SR1 or 0COR', R1
means an alkyl group having 1 to 3 carbon atoms)
Examples include compounds represented by:

As the acid condensation catalyst, inorganic mineral acids other than phosphoric acid, such as hydrochloric acid and sulfuric acid, are used. The acid concentration varies depending on the N-phenylcarbamate concentration, the molar ratio of N-phenylcarbamate and formaldehyde, the reaction temperature, the concentration of the acid or its salt described below, etc., but is in the range of 3 to 13.5 mol/l. is preferable, more preferably 4 to 7 mol/
The range is 1. If the acid concentration is too low, the conversion rate of N-phenylcarbamate ester will be low, and if the acid concentration is too high, the selectivity of 4,4'' will decrease and it will be difficult to separate the condensation product from the acid aqueous solution. There is a tendency.

Examples of the phosphoric acid and its salts added to the inorganic acid aqueous solution include orthophosphoric acid, birophosphoric acid, metaphosphoric acid and its salts, and organic carboxylic acids and its salts include formic acid, oxalic acid, chloroacetic acid, Examples include dichloroacetic acid, trichloroacetic acid, fluoroacetic acid, difluoroacetic acid, trifluoroacetic acid, and the like. As the cation of the salt, sodium, lithium, ammonium, magnesium, rubidium, cesium, etc. are used. The concentration of phosphoric acid, organic carboxylic acid, etc. is related to the concentration of inorganic acids other than phosphoric acid, but it is 0.1 to 6 mol/I! A range of , is preferred.

The concentration of N-phenylcarbamate ester is 1 mol/
It is preferably 1 or less. If the concentration is too high, the selectivity of 44' monomer in diphenylmethane dicarbamate ester decreases (JP-A-55-129260), and the formation of polynuclear bodies tends to increase (JP-A-62-6705).
No. 9), furthermore, the molar ratio of N-phenylcarbamate to formaldehyde is not particularly limited, but may be 1
．． A range of 5 to 4.0, particularly a stoichiometric ratio of 2.0, is preferred from the viewpoint of increasing the conversion rate of N-phenylcarbamate ester and increasing the selectivity of 4,4''.

The reaction is carried out at a temperature of 150°C or less from the temperature at which the raw material N-phenylcarbamate ester melts. At high temperatures, N-phenylcarbamate hydrolyzes to produce amines (German Patent Application Publication No. 2,831).
, No. 379), and the temperature is usually in the range of 60°C to 100°C. The reaction is also generally carried out under atmospheric pressure, although high pressures may be used at high reaction temperatures. If necessary, it can be carried out at a pressure lower than atmospheric pressure.

The reaction time varies depending on the N-phenylcarbamate ester used, reaction temperature, catalyst concentration, type of catalyst, etc., and also depending on whether the reaction is carried out continuously or batchwise, but is generally 15 minutes to 6 hours. , 3 hours is usually sufficient.

In the reaction using an acid catalyst as described above, the product is obtained as a solid. Since this product contains other by-products, the 4,4° isomer is separated and recovered by the following method. That is, after the reaction is completed, the precipitated solid product is separated from the acid aqueous solution by filtration or the like, washed with water or warm water, and dried if necessary. The aqueous solution containing unreacted raw materials and catalyst can be recycled and reused. The separated solid product is dissolved in alcohol below its boiling point, and most of the 4,4" product is recovered by a recrystallization method that utilizes the difference in dissolution temperature. For example, a product with a purity of 99% or more can be obtained in one operation. 4,4' can be recovered with a recovery rate of approximately 85%.Next, a poor solvent for aliphatic hydrocarbons and/or alicyclic hydrocarbons, which are liquid at room temperature, is added to the alcohol mother liquor until no precipitates are formed. Add gradually.

In this way, products other than N-benzyl are completely separated from the alcohol mother liquor as a precipitate. After distilling off the poor solvent, the 4.4° solids are crystallized again from the alcohol, and for example, about 96% of the 4.4° solids are recovered in total.

As described above, according to the present invention, the N-benzyl compound can be separated from the product remaining in the alcohol mother liquor by a simple method such as filtration. This N-benzyl compound can be converted into diphenylmethanedicarbamate ester, for example, according to the method disclosed in JP-A-58-194852. 4,41 Increasing the overall recovery rate can be achieved by repeating recrystallization from alcohol several times, but increasing the number of repetitions is not a good idea in terms of utility, and the recovery operation is performed twice. is sufficient. Thereafter, the 2,46 monomer, polynuclear in some cases, and raw material N-phenylcarbamate ester remaining in the alcohol can be separated by an appropriate method, such as distillation, and returned to the reaction system for use. The remaining condensate can also be used as a raw material for so-called crude MDI.

As the alcohol used for the recrystallization, an aliphatic alcohol or an alicyclic alcohol is used. Particularly preferred are methanol, ethanol and inpropertool.

As the poor solvent, aliphatic hydrocarbons such as pentane and hexane, which are liquid at room temperature, aliphatic halogenated hydrocarbons such as carbon tetrachloride, chloroform, and dichloroethane, and alicyclic hydrocarbons such as cyclopenkune and cyclohexane are used,
These can also be used in combination.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in detail with reference to examples, but the present invention is not limited to the following examples. Note that all analyzes were performed using a high performance liquid chromatograph.

Example 1 Take 12.26 g (0.27 mol) of formic acid and 34.82 g (0.36 mol) of orthophosphoric acid in a pot, add an appropriate amount of water and 188.20 g (1.83 mol) of concentrated sulfuric acid.
was added to dissolve, transferred to a measuring cylinder for 500m+42, and further water was added to make 333mf. This is the internal volume 2
The mixture was added to Erlenmeyer flask No. 1 and kept at 90°C. 16.50 g (0.1 mol) of ethyl N-phenylcarbamate was added with stirring and melted.

4.05 g (0.05 mol) of 37% formaldehyde was gradually added dropwise to this to start condensation, and the reaction was stopped in 3 hours. Separate the precipitated solid from the catalyst aqueous solution and heat at 60°C.
Washed with warm water and dried. Dry weight was 16.19 g. This was dissolved in hot ethanol at about 50 mA and cooled to room temperature, yielding 10.30 g of crystals. The purity of the 44° crystal obtained as a crystal was 99%, and the recovery rate was 8.
It was 4%. N-pentane was gradually added to the ethanol mother liquor, and a small amount of lopentane was further added to the supernatant liquid that was allowed to stand still until scuttling no longer occurred. This precipitate was filtered, n-pentane was distilled off, and the weight was 5.
．． It was 12 g. The precipitate was recrystallized from as little ethanol as possible to obtain 1.22 g of 4,4° monomer. The purity of this 4,4' monomer was over 99%. When this was combined with the first crystal, the recovery rate was 96%. In addition, unreacted ethyl N-phenylcarbamate is 90% in the catalyst hot water and 10% in the final alcohol mother liquor.
It was transitioning.

Example 2 The same experiment as in Example 1 was conducted except that ethanol was replaced with isopropanol and n-pentane was replaced with cyclopentane, and the recovery rate was 95%.

4.4" N-phenylcarbamic acid was sometimes confirmed as a trace impurity in the product.

〔Effect of the invention〕

According to the present invention, products other than the N-benzyl compound can be separated from the alcohol mother liquor after recrystallization with a simple operation, making it possible to recover high-purity 44" monomers at a high recovery rate. It is.

Claims (1)

[Claims] (1) N-phenylcarbamates are condensed with a methylenating agent using an acid catalyst to produce diphenylmethanedicarbamates, and the resulting solid product is separated from the reaction solution and washed with water or hot water. After washing with water, recrystallize the product in alcohol, add an aliphatic hydrocarbon and/or alicyclic hydrocarbon solvent that is liquid at room temperature to the alcohol mother liquor, and add the aliphatic hydrocarbon and/or alicyclic hydrocarbon solvent that remains in the alcohol mother liquor. A method for recovering diphenylmethanedicarbamate esters, the method comprising recovering the product.