JP2804132B2 - Purification method of carbamate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for purifying a crude carbamate. More specifically, the present invention relates to a method for purifying an aromatic ester of aliphatic polycarbamic acid used as a polyurethane raw material as an intermediate for producing an aliphatic polyisocyanate and as a block polyisocyanate in which the polyisocyanate is protected with a phenol.

[Conventional technology]

Conventionally, aliphatic polyisocyanates have been produced by the reaction of aliphatic primary polyamines with phosgene.However, the use of highly toxic phosgene, the production of a large amount of corrosive hydrogen chloride as a by-product, and the There is a problem such as containing hydrolyzable chlorine which is difficult to separate and remove, and it is desired to establish an industrial method for producing polyisocyanate without using phosgene. For example, a method of synthesizing an aliphatic isocyanate from an aliphatic nitro compound and carbon monoxide, and a method of converting an aliphatic amide compound to an isocyanate by Hoffman decomposition are known, but the yield is poor with any of the methods. This is insufficient for industrial implementation. Another method is to decompose the corresponding carbamic acid ester into isocyanate and phenol or alcohol. Although this method can achieve a high yield relatively easily than the above-mentioned method, H.SHIFF (Ber. 1870 , p.649, etc.), E.DYE
R and GCW-RIGHT [J. Am. Chem. Soc, 81 , 2138 (195
As shown in the study of 9)], side reactions such as carbodiimidization by decarboxylation, isocyanuration by trimerization, and formation of allophanate are inevitable during the decomposition reaction. In particular, these reactions are accelerated at high temperatures, but are described by G. Oertel in “Po
As shown in the lyurethane Handbook, p. 84, 1985 (published by Hanser), generally, aliphatic esters among aliphatic carbamates require a higher decomposition temperature than aromatic esters, The effects of side reactions are inherently significant, especially when considering the production of polyisocyanates,
It is extremely difficult to prevent a situation such as a decrease in the yield and a clogging of the reactor due to a polymer produced by a side reaction.

On the other hand, the aromatic ester of aliphatic carbamic acid can be said to be an advantageous method for producing the corresponding isocyanate because the decomposition proceeds without a catalyst even under relatively low temperature conditions.
The method for producing the aromatic ester of aliphatic carbamic acid includes a nitro compound, a nitroso compound, an azo compound,
A method of reductively synthesizing an azoxy compound or the like with carbon monoxide (for example, JP-A-54-415601), a method of oxidatively synthesizing a primary amine, carbon monoxide and an oxidizing agent (for example, JP-A 55-120551), a method of synthesizing from diphenyl carbonate and an amine [J. Pol. Sc
i. Polymer Chem. ED, 17,835 (1979)] and the like have been known for some time. Furthermore, the present inventors have proposed a method of synthesizing primary amine, urea and aromatic hydroxy compound while removing ammonia (Japanese Patent Application No. 63-232278). In any of the methods, the carbamate was reduced to about 10%.
It is difficult to obtain at a yield of 0%. Usually, urea bond (-NHCONH-) and urea terminal (-NHCONH-
_2), high boiling by-products having active hydrogen capable of binding to the -NCO groups, such as amine-terminated (-NH ₂₎ coexist. If the aromatic ester of carbamic acid is thermally decomposed in the presence of a large amount of these by-products, the resulting polyisocyanate is combined with the by-products, which not only reduces the yield but also causes the generation of a polymer-like substance, This will cause serious problems in long-term operation such as sticking to vessels and blockage of piping.

According to the inventor's detailed study, in the process of producing the corresponding aliphatic polyisocyanate by pyrolysis of the aromatic ester of the aliphatic polycarbamic acid, the amount of the high boiling by-product having active hydrogen is proportional to It has been found that the yield of polyisocyanate decreases, and the amount of generated polymeric substances increases, and the content of high-boiling by-products having active hydrogen in the carbamate has never been reduced. , Preferably 2% by weight or less, more preferably 1.
By adjusting the content to 5% by weight or less, a high-yield operation can be performed for a long time when the corresponding aliphatic polyisocyanate is produced by thermal decomposition of the carbamic acid ester.

Further, even when the carbamic acid ester is used as a block isocyanate, the presence of impurities deteriorates the physical properties of the urethane to be formed, and therefore, a high purity urethane is required.

[Problems to be solved by the invention]

Since the carbamic acid ester has a high boiling point and is unstable at high temperatures, it is extremely difficult to purify it by distillation, and it seems reasonable to purify it by crystallization. However, up to now, as a method for purifying the crude carbamate ester, it is possible to carry out high purification, which enables long-term operation of a high yield when producing the corresponding aliphatic polyisocyanate by thermal decomposition, There are no disadvantages such as a small loss associated with purification, large-scale use of the solvent due to the large amount of solvent used, and a large amount of energy required for the recovery of the used solvent. In other words, a crystallization purification method that is economical has been known. Had not been. For example, J. Polymer
Science: Polymer Chemistry Edition Vol.17,835 (197
9) describes a method for synthesizing a phenyl ester of carbamic acid corresponding to diphenyl carbonate and polyamine, and a method for crystallizing a crude reaction product from a mixed solvent of water and ethanol is described. However, the results of elemental analysis are not satisfactory in terms of purity. As an example of a similar compound, in Example 7 of JP-B-63-12059, an alkyl ester of an aromatic carbamic acid is oxidized from an aromatic amime compound, an alcohol and carbon monoxide, and crystallized from an alcohol solution. However, this method uses a large amount of alcohol, and in addition, the purity and loss associated with crystallization have not been clarified. In addition,
No. 15499 discloses primary aliphatic, alicyclic and heterocyclic polyamines, a technique for producing the corresponding carbamic acid ester from urea and alcohol,
The carbamic acid ester is precipitated from a solvent such as alcohol, but the purity and yield cannot be said to be satisfactory. An object of the present invention is to provide a method for obtaining a high-purity ester from a crude product of the ester containing a large amount of a high-boiling by-product having active hydrogen by an industrially advantageous method.

[Means for solving the problem]

The present inventors have conducted intensive studies to achieve the above object, and as a result, have finally reached the present invention. That is, the present invention
In a method of purifying a crude carbamic acid ester represented by the following formula (I) by crystallization, the ratio of the aromatic hydroxy compound to the aromatic hydroxy compound and the soluble organic solvent is 3:97 to 70: A method for purifying a carbamic acid ester, wherein crystallization is performed using a mixed solvent of 30.

R- (NHCOOAr) _n (1) (wherein, R is an aliphatic or alicyclic hydrocarbon group having 2 to 20 carbon atoms, or a part of hydrogen atoms of these hydrocarbon groups is a halogen group or a nitro group. Represents a group substituted with a nitroso group, and Ar represents an aromatic hydrocarbon group having 6 to 20 carbon atoms, or a hydrocarbon group in which a part of hydrogen atoms is substituted with a halogen group, a nitro group, or a nitroso group. And n is 1 to 10.
Represents an integer. The carbamate crude product used in the present invention is:
A mixture mainly composed of esters and by-products produced by the above-mentioned various aromatic polycarbamic acid aromatic ester synthesis methods. Depending on the synthesis method, insoluble components such as catalysts used as needed are filtered. -Removal by a method such as centrifugation or the like, and in some cases, removal of a solvent or an excessively used raw material having a low boiling point by a method such as evaporation is also included.

The aromatic hydroxy compound used in the present invention refers to a monohydroxy compound having 12 or less carbon atoms, and may be a halogenated compound, and particularly preferred are phenol, o-, m-, p-cresol, Monochlorophenol can be exemplified.

The organic solvent which can be dissolved in the aromatic hydroxy compound used in the present invention means a solvent which is uniformly dissolved and mixed with the aromatic hydroxy compound. Examples of such organic solvents include:
Aliphatic and alicyclic hydrocarbons such as hexane, cyclohexane, octane, nonane, and decane; aromatic hydrocarbons such as benzene, toluene, and xylene; halogenated hydrocarbons such as dichloromethane, chloroform, trichloroethane, trichloroethylene, chlorobenzene, and dichlorobenzene ;
Alcohols such as methanol, ethanol, isopropanol, butanol and ethylene glycol; ethers such as 1.4-dioxane; acetone, methyl ethyl ketone;
Ketones such as methyl isobutyl ketone and acetophenone; nitriles such as acetonitrile and propionitrile; esters such as ethyl acetate, amyl acetate, isobutyl acetate and diethyl carbonate; and one or more of these are used. They can be used in combination.

The proportion of the aromatic hydroxy compound and the organic solvent that can be dissolved with the aromatic hydroxy compound is such that the purity of the ester obtained by crystallization and the yield of crystallization, and the processes such as energy required for recovery of the used solvent are satisfied. Should be determined. The ratio between the aromatic hydroxy compound and the organic solvent soluble therewith is used in a weight ratio of 3:97 to 70:30, preferably 5:95 to 50:50. When the proportion of the aromatic hydroxy compound in the mixed solvent used is less than 3% by weight, the purity of the obtained crystallized product is low, or high purity cannot be achieved unless a large amount of solvent is used. Requires a lot of energy. On the other hand, when the proportion of the aromatic hydroxy compound is 70% by weight or more, the solubility of the target carbamic acid ester is increased, so that the crystallization yield is reduced.

In other words, high-purity carbamates can be produced economically only by using an aromatic hydroxy compound, which is a good solvent for by-products, and an aromatic hydroxy compound, which is a poor solvent for carbamates, and a soluble organic solvent in an appropriate ratio. Can be obtained in an advantageous manner.

The crystallization equipment and operation method are described in, for example, Ken Toyokura and Yoshio Aoyama, Chemical Equipment Design and Operation Series No. 3 “Revision and Crystallization” (19
1988, published by Chemical Industry Co., Ltd.), pages 75 to 173. The amount of the mixed solvent to be used varies depending on the kind and ratio, but usually the same amount or more than the carbamic acid ester to be purified is used. Crystallization using an excessively small amount of the mixed solvent is not preferable because the viscosity of the slurry after crystallization becomes high and the subsequent solid-liquid separation operation becomes difficult. On the other hand, use of an excessively large amount of the solvent is not preferable because a large amount of heat energy is required for recovering the solvent after crystallization.

The upper limit of the operating temperature is usually about 150 ° C. as long as the carbamate is stable, and the lower limit is a temperature higher than the temperature at which the mixed solvent used solidifies itself.

 The operating pressure may be any of reduced pressure, normal pressure, and pressurized.

The precipitated solid is separated into solid and liquid by a general-purpose method such as filtration and centrifugation, and if necessary, washed with a small amount of solvent and dried.

In the usual case, the aromatic hydroxy compound and the organic solvent which can dissolve the aromatic hydroxy compound in the separated and recovered solvent are purified and recovered by a method such as distillation and reused.
At this time, a mixture of a carbamic acid ester, a by-product, and the like is obtained as a recovery residue, but in some cases, a secondary use such as recycling a part of the mixture to the carbamic acid ester synthesis step is also possible.

〔Example〕

Next, the present invention will be specifically described with reference to examples. still,
The compositions of the carbamates and the like in the examples were analyzed and quantified using GPC (gel permeation chromatography) and HLC (high performance liquid chromatography).

 The crystallization yield in the examples was calculated by the following equation.

Crystallization yield = (weight of carbamic acid ester in purified product) / (weight of carbamic acid ester in crude product) x 100 Example 1-Production of carbamic acid ester 1,6-hexamethylenediamine, urea and phenol Then, a hexamethylene dicarbamic acid diphenyl ester (hereinafter abbreviated as HDU) composition was synthesized by the following method.

5.31% by weight of hexamethylenediamine, 3.14% by weight of urea, 91.55% by weight of phenol from the upper end of a vertical packed column reactor with an inner diameter of 2 inches and a height of 4m equipped with a cooling reflux condenser and a gas-liquid separator at the top and an evaporator at the bottom Of raw material liquid consisting of
The feed was continuously performed at a speed of r, and at the same time, nitrogen gas was introduced from the evaporator at the bottom of the reaction tube at 100 (converted to a standard state) per hour. Continuously recover the reaction solution from the evaporator at the bottom of the reaction tube,
A reaction gas containing NH ₃ and N ₂ was recovered from the cooling reflux condenser. Nitrogen gas was flowed at a reaction temperature of 238 ° C. and a reaction pressure of 3.15 kg / cm ² -G, and the reaction was carried out while maintaining the temperature of the cooling reflux device at 160 ° C.
Excess phenol was recovered from the resulting reaction solution by distillation under reduced pressure at 125 ° C., and 87.78% by weight of HDU and phenyl carbamate ( 4.80% by weight) A polyurea compound having the structure Products consisting mainly of made-terminal -NH ₂ compound of structure like (hereinafter, referred to as by-products C) 2.42 wt% and phenol 5.
A crude product A consisting of 00% by weight was obtained.

-Purification of carbamic acid ester To a stirred tank (1) were added 255 parts of the crude product I, 596 parts of methyl isobutyl ketone and 136 parts of phenol, and the mixture was heated to about 90 ° C and dissolved under stirring to form a uniform solution (phenol / phenol). Methyl isobutyl ketone = 20/80). The temperature was lowered to 20 ° C. over about 5 hours to precipitate a solid. The obtained slurry was filtered, and about 250 gr of methyl isobutyl ketone was used in five times to wash the solid. Then, this was vacuum-dried to obtain 205 parts of a purified HDU product having a purity of 99.0% by weight (others had 1.0% by weight of by-product C) (crystallization yield: 90.7%).

Example 2 Crystallization was carried out in the same manner as in Example 1 except that a mixed solvent of 279 parts of methyl isobutyl ketone and 267 parts of phenol was used (phenol / methyl isobutyl ketone = 50).
/ 50). As a result, purified HDU 247 with a purity of 99.9% by weight or more
Was obtained (crystal yield: 82.2%).

Example 3 Crystallization was carried out in the same manner as in Example 1 except that 222 parts of crude product I, 739 parts of methyl isobutyl ketone and 28 parts of phenol were used (phenol / methyl isobutyl ketone =
5/95). As a result, 187 parts of a purified HDU having a purity of 98.5% by weight (others were 1.4% by weight of by-product A and 0.1% by weight of by-product C) were obtained (crystallization rate: 94.8%).

Comparative Example 1 Crystallization was carried out in the same manner as in Example 3 except that 767 parts of methyl isobutyl ketone was used and phenol was not used (phenol / methyl isobutyl ketone = 1/99). As a result, purified HDU with a purity of 96.2% by weight (others
194 parts (2.3% by weight, by-product C 1.5% by weight) were obtained (crystallization yield).
96.0%).

Comparative Example 2 Crystallization was carried out in the same manner as in Example 1 except that 66.5 parts of crude A, 924 parts of methyl isobutyl ketone and 12.6 parts of phenol were used (phenol / methyl isobutyl ketone = 1/99). As a result, 49.7 parts of a purified HDU product having a purity of 98.6% by weight (others C1.4% by weight as byproducts) were obtained (crystallization yield).
84%).

Comparative Example 3 Crystallization was carried out in the same manner as in Example 1 except that 150 parts of methyl isobutyl ketone and 583 parts of phenol were used (phenol / methyl isobutyl ketone = 80/20). As a result, 120 parts of a purified HDU having a purity of 99.9% by weight or more was obtained (crystallization yield: 40.0%).

Example 4 Crystallization was carried out in the same manner as in Example 1 except that 633 parts of isopropanol and 99 parts of phenol were used (phenol / isopropanol = 15/85). As a result, purity 9
207 parts by weight of a 9.2% by weight purified HDU product were obtained (crystallization yield: 91.9%).
%).

Comparative Example 4 Crystallization was carried out in the same manner as in Example 3 except that 767 parts of isopropanol was used and phenol was not used (phenol / isopropanol = 1/99). As a result, the purity
96.6% by weight of purified HDU (others are by-product A2.1% by weight,
194 parts of by-product C1.3% by weight were obtained (crystallization yield: 96.4).
%).

Comparative Example 5 Crystallization was carried out in the same manner as in Example 1 except that 150 parts of isopropanol and 583 parts of phenol were used (phenol / isopropanol = 80/20). As a result, purity 9
124 parts of a purified HDU of 9.9% by weight or more was obtained (crystallization yield: 41.
3%).

Example 5 Crystallization was carried out in the same manner as in Example 1 except that 522 parts of 1,4-dioxane and 211 parts of phenol were used (phenol / 1,4-dioxane = 30/70). As a result, purity 99.
257 parts of a 2% by weight purified HDU product was obtained (crystallization yield: 85.0%).
%).

Example 6 Crystallization was carried out in the same manner as in Example 1 except that 522 parts of xylene and 211 parts of phenol were used (phenol / xylene = 30/70). As a result, 98.6% by weight of HDU
274 parts of a purified product were obtained (crystallization yield: 90.1%).

Example 7 Crystallization was carried out in the same manner as in Example 1 except that 522 parts of propionitrile and 211 parts of phenol were used (phenol / propionitrile = 30/70). As a result, purity 9
262 parts of a purified 8.8 wt% HDU product was obtained (crystallization yield: 89.2%).
%).

Example 8 Crystallization was carried out in the same manner as in Example 1 except that 522 parts of isobutyl acetate and 211 parts of phenol were used (phenol / isobutyl acetate = 30/70). As a result, purity 99.0
265 parts by weight of a purified HDU product were obtained (crystallization yield: 90.4%).

Example 9 Production of Carbamate A crude product of hexamethylenedicarbamic acid diphenyl ester was synthesized from 1,6-hexamethylenediamine and diphenyl carbonate by the following method.

14.5 parts of hexamethylenediamine, 53.5 parts of diphenyl carbonate and toluene 1 were charged into a two-necked flask equipped with a stirrer and reacted for 20 hours at 40 ° C. with stirring. The toluene and the formed phenol were removed under reduced pressure, and HDU 90.44% by weight, by-product C 4.56% by weight, phenol
A crude product b of 5.00% by weight was obtained.

-Purification of carbamic acid ester Crystallization was carried out in the same manner as in Example 1 except that 163 parts of crude product b, 586 parts of methyl isobutyl ketone and 243 parts of phenol were used (phenol / methyl isobutyl ketone = 30/70). . As a result, 119 parts of a purified HDU product having a purity of 98.8% by weight (and 1.2% by weight of by-product C) were obtained (crystallization yield: 79.6%).
%).

Example 10 Production of Carbamate Isophoronediamine represented by the following formula (II) (hereinafter, H ₂ N
Abbreviated as -Ri-NH _2. Ri represents a hydrocarbon group portion of isophoronediamine. ) And diphenyl carbonate by the following method to give 3-phenoxycarbonylaminomethyl-
3,5,5-trimethyl-1-phenoxycarbonylaminocyclohexane ( Hereinafter, it is abbreviated as IPDU. Ri represents a hydrocarbon group portion of isophoronediamine. ) The composition was synthesized.

H ₂ N-Ri-N was added to a _two -necked three-necked flask equipped with a stirrer.
21.2 parts of H ₂ , 53.5 parts of diphenyl carbonate and toluene 1 were added thereto, and reacted at 40 ° C. for 30 hours with stirring. Remove toluene and phenol formed under reduced pressure to obtain IPDU
91.05% by weight, A by-product D3.95 mainly composed of a polyurea compound having the following structure (Ri represents a hydrocarbon group portion of isophoronediamine).
By weight, a composition C having a phenol content of 5.00% by weight was obtained.

-Purification of carbamic acid ester Crystallization was carried out in the same manner as in Example 1 except that 255 parts of the composition, 633 parts of isopropanol and 99 parts of phenol were used (phenol / isopropanol = 15/85).
As a result, 196 parts of a purified IPDU having a purity of 99.0% by weight were obtained (crystallization yield: 83.6%).

〔The invention's effect〕

According to the present invention, a high-purity carbamic acid ester can be obtained by an economically advantageous method, and the high-purity carbamic acid ester obtained by the present invention can be thermally decomposed to obtain a target polyisocyanate. It can be obtained in high yield. Further, the adhesion of the by-product polymer to the pyrolysis reactor and the piping is reduced, and industrially significant long-term operation becomes possible.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C07C 271/40-271/58 C07C 269/08

Claims (5)

(57) [Claims] A method for purifying a crude carbamic acid ester represented by the following formula (I) by crystallization, wherein the weight ratio of the aromatic hydroxy compound to the aromatic hydroxy compound and the soluble organic solvent is 3% by weight. : A method for purifying a carbamic acid ester, comprising using a mixed solvent of 97 to 70:30. R- (NHCOOAr) _n (1) (wherein, R is an aliphatic or alicyclic hydrocarbon group having 2 to 20 carbon atoms, or a part of hydrogen atoms of these hydrocarbon groups is a halogen group or a nitro group. Represents a group substituted with a nitroso group, and Ar represents an aromatic hydrocarbon group having 6 to 20 carbon atoms, or a hydrocarbon group in which a part of hydrogen atoms is substituted with a halogen group, a nitro group, or a nitroso group. And n is 1-10.
Represents an integer. ) 2. The method according to claim 1, wherein the aromatic hydroxy compound is a monohydroxy compound having 12 or less carbon atoms or a halogenated monohydroxy compound having 12 or less carbon atoms. Method. 3. An organic solvent which is soluble in an aromatic hydroxy compound and comprises an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbon, a halogenated hydrocarbon, an alcohol, a ketone,
2. The method according to claim 1, wherein the solvent is a mixed solvent comprising at least one combination selected from nitrites and esters. 4. The method according to claim 1, wherein the carbamate crude product is produced from a primary amine, urea and an aromatic hydroxy compound. The method described in. 5. The method according to claim 1, wherein the carbamate crude product is produced from a primary amine and diphenyl carbonate.
A method according to any of the preceding clauses.