JPH036136B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing isocyanates by thermally decomposing carbamate esters in the presence of a catalyst. Isocyanates are industrially useful substances as raw materials for polyurethane and carbamate concentrates, and in particular tolylene diisocyanate (TDI),
4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate, etc. are produced in large quantities. These isocyanates are usually produced by reacting the corresponding amines with phosgene, but there are many problems such as using highly toxic phosgene and producing large amounts of corrosive hydrogen chloride as a by-product. Therefore, a method for producing isocyanates relatively easily and inexpensively without using phosgene is desired. As one method for this, a method using thermal decomposition of carbamate esters has been proposed. A method for producing isocyanates by thermally decomposing carbamate esters using a catalyst is as follows:
For example, in the presence of a Lewis acid such as ferric chloride
Method carried out in a gas phase at a high temperature of 400 to 600°C (Japanese Patent Publication No. 46-17773), method using heavy metals or heavy metal compounds (Japanese Patent Publication No. 51-19721), B, B,
A method using a catalyst in which compounds of A, A, B, B, and group metals are dissolved in a solvent (Japanese Unexamined Patent Application Publication No. 52
-19624) and a method using alkaline earth metals or their inorganic compounds (Japanese Patent Application Laid-Open No. 1988-88201). However, even when these methods are used, there are drawbacks such as a large amount of high boiling point by-products and significant corrosion of the material. Therefore, the present inventors have developed a method for producing isocyanates by thermally decomposing carbamate esters, suppressing the production of high-boiling substances due to side reactions of the produced isocyanates, and producing isocyanates with good yield. As a result of careful consideration of how to obtain
We have arrived at the present invention. That is, the present invention provides a method for producing isocyanates by thermally decomposing carbamates, in which boron alone or/and at least one boron-containing compound selected from the following group (a) is used. Alkali metal borates (b) Alkaline earth metal borides (c) Zirconium borides, hafnium borides, tungsten borides (d) Boric acid esters (e) Boron carbide, boron silicide, boron nitride, oxides A method for producing isocyanates, which comprises thermally decomposing carbamate esters in the presence of a catalyst made of boron in a solvent that is inert to isocyanates and does not substantially dissolve the catalyst. . When boron and a boron-containing compound selected from the above groups (a), (b), (c), (d), and (e) are used to thermally decompose carbamate esters to produce isocyanates, Until now, it was completely unknown that it could be an excellent catalyst. These boron compounds are not mentioned at all in the above-mentioned prior patents, and moreover, their solubility in the reaction solution is virtually non-existent or very low. Not only Japanese Patent Application Publication No. 52-19624, but also Japanese Patent Application Publication No. 51-19721,
It is completely unexpected that such insoluble boron or boron compounds have excellent catalytic activity, since it has been reported that metal components dissolved in the reaction solution exhibit good catalytic effects. It was about that. The carbamate esters used as raw materials in the present invention have the general formula R(NHCOOR')n
or (R′NHCOO)nR, or R
It is a compound represented by (NHCOSR')n or (R'NHCOS)nR. Here, R is n value (n is 1 to
R′ represents a monovalent saturated or unsaturated aliphatic group and an organic group selected from a cyclic group, an aromatic group, and an aralkyl group (an integer of 4); Represents an organic group selected from a cyclic group, an aromatic group, and an aralkyl group. Furthermore, these organic groups may contain other substituents that do not react with the isocyanate group, such as halogen atoms, nitro groups, cyano groups, alkyl groups, alkoxy groups, acyl groups, acyloxy groups, carbamoyl groups, etc. It may also contain the isocyanate group itself. In addition, divalent functional groups that do not react with isocyanate groups, such as ether groups, thioether groups,
It may contain a carbonyl group, a carboxyl group, a sulfone group, etc. As such carbamate esters,
For example, methyl carbanilate, ethyl carbanilate, propyl carbanilate, butyl carbanilate, cyclohexyl carbanilate, phenyl carbanilate, etc.

Carbanilate represented by [Formula] (R' is as above); methyl ester of o- or m- or p-tolylcarbamic acid;
Tolylcarbamate esters such as ethyl ester and phenyl ester; o- or m- or p
- phenylenedicarbamic acid diesters such as dimethyl ester, diethyl ester, diphenyl ester of phenylenedicarbamic acid; 2,4
- or tolylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester of 2,6-tolylene dicarbamate; 2,2'- or 2,4'- or 4,4'-methylene Methylenebisphenylenedicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, and diphenyl ester of bisphenylenedicarbamic acid;
formula (R' is as described above, m is an integer of 1 to 5) Polymeric aromatic carbamic acid esters; 1- or 2-naphthylcarbamic acid methyl ester, ethyl ester, butyl ester, phenyl ester, etc. Naphthylcarbamate esters; 1,4- or 1,5- or 1,
Naphthylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, and diphenyl ester of 6- or 2,6-naphthylene dicarbamic acid; ethylene biscarbanilate, propylene biscarbanilate, chryceryl tricarbanilate, Carbanilates of polyhydric alcohols such as pentaerythryl tetrakis carbanilate; alkyl carbamates such as methylcarbamate, ethylcarbamate, propylcarbamate, butylcarbamate, amylcarbamate, hexylcarbamate, octylcarbamate, octadecylcarbamate, etc. Methyl ester, ethyl ester, propyl ester of acids,
Alkyl carbamate esters such as butyl ester and phenyl ester; Alicyclic carbamate esters such as methyl ester, ethyl ester, and phenyl ester such as cyclopentyl carbamate and cyclohexyl carbamate; ethylene dicarbamate and trimethylene dicarbamate Carbamic acid, tetrametalenedicarbamic acid, pentamethylenedicarbamic acid, hexamethylenedicarbamic acid,
Alkylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester such as 2,2,4- or 2,4,4-trimethylhexamethylene dicarbamic acid; methylcyclohexane-2,4- or Alicyclic groups such as dimethyl esters, diethyl esters, diphenyl esters such as 2,6-dicarbamic acid, methyl 3-carbamate-3,5,5-trimethylcyclohexylcarbamic acid, and 4,4'-methylenebiscyclohexylcarbamic acid. Dicarbamic acid diesters; aralkyl dicarbamic acid diesters such as dimethyl ester, diethyl ester, diphenyl ester of xylylene dicarbamic acid; o- or m- or p-chlorophenylcarbamic acid, 2,5- or 3,4 −
Or halogenated phenylcarbamate esters such as methyl ester, ethyl ester, phenyl ester such as 3,5-dichlorophenylcarbamate; and thiolcarbamate esters corresponding to these. These carbamate esters may be a single type or a mixture of two or more types. In the present invention, elemental boron is used as a catalyst; sodium borate, potassium borate,
Alkali metal borates such as rubidium borate and cesium borate; alkaline earth metal borides such as calcium boride, strontium boride, and barium boride; zirconium boride,
Hafnium boride, tungsten boride; boric acid esters such as triphenyl borate, tribenzyl borate, trinaphthyl borate, tributyl borate; boron carbide, boron silicide, boron nitride,
At least one selected from boron oxide. Moreover, although the quantitative ratio of these catalysts and the carbamate ester may be arbitrary, it is preferable to use the catalyst in an amount of 0.0001 to 100 times the weight of the carbamate ester. The process of the invention is preferably carried out in a solvent that is inert towards isocyanates. Such solvents include aliphatic, cycloaliphatic or aromatic substituted or unsubstituted hydrocarbons or mixtures thereof, and also certain oxygenated compounds such as ethers, ketones and esters. It will be done. Preferred solvents include hexane, heptane,
Octane, nonane, decane, n-hexadecane,
Alkanes such as n-octadecane, eicosane, squalane, and alkenes corresponding to these;
Aromatic hydrocarbons and alkyl-substituted aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, cumene, diisopropylbenzene, dibutylbenzene, naphthalene, lower alkyl-substituted naphthalene, dodecylbenzene; chlorobenzene, dichlorobenzene, bromobenzene, Aromatic compounds substituted with nitro groups and halogens such as dibromobenzene, chlornaphthalene, bromnaphthalene, nitrobenzene, nitronaphthalene; diphenyl, substituted diphenyl, diphenylmethane, terphenyl, anthracene, phenanthrene, various dibenzyltoluenes isomers, polycyclic hydrocarbon compounds such as triphenylmethane; alicyclic hydrocarbons such as cyclohexane and ethylcyclohexane; ketones such as methyl ethyl ketone and acetophenone; esters such as dibutyl phthalate, dihexyl phthalate, and dioctyl phthalate; Examples include ethers and thioethers such as diphenyl ether and diphenyl sulfide; sulfoxides such as dimethyl sulfoxide and diphenyl sulfoxide; and silicone oil. It is necessary that the elemental boron and the catalyst containing boron of the present invention be used in a substantially insoluble state in such a solvent under reaction conditions. Since such catalyst components are not substantially dissolved in the reaction solution, they can be easily separated from the reaction products and the reaction solvent used as necessary, for example, by an extremely simple operation. It is also possible to carry out the reaction using a fixed bed type catalyst component. In the case of a fixed bed reaction, no special operation is required for separating the catalyst and the reaction solution, so it is particularly advantageous when carried out industrially. As described above, one of the characteristics of the method of the present invention is that the catalyst is substantially insoluble in the reaction solution, so that it can be easily separated from the product. This is a particularly advantageous method when producing high-boiling point isocyanates that are difficult to distill by distillation or the like. For example, when N-phenylcarbamic acid ethyl ester is methylenated with a methylenating reagent such as formaldehyde, trioxane, or methylal in the presence of an acid catalyst, methylene-bis-
In addition to (ethyl 4-phenylcarbamate), a polynuclear polycarbamate ester containing three or more benzene rings is produced as a by-product. Crude MDI, which is industrially important, can be produced by thermally decomposing these mixed carbamic acid esters. However, these isocyanates have a high boiling point, and are distilled from the reaction solution containing the catalyst by distillation. It is difficult to separate the components. However, according to the method of the present invention, the catalyst component can be easily separated from the reaction solution by simple operations such as filtration, so that the catalyst component can be easily separated from the reaction solution by a simple operation such as filtration. Contamination of ingredients can be prevented. When carrying out the process of the present invention, esters of carbamic acid are converted into reacting isocyanates and alcohols, but one component is removed from the reaction system to prevent recombination and return to carbamate esters. It needs to be removed. in this case,
Among these components produced as the reaction progresses, it is preferable to remove and separate low-boiling components by distillation or the like. In order to promote this separation, it is also a preferred method to introduce an inert gas such as nitrogen, helium, argon, carbon dioxide, methane, ethane, propane, etc., singly or in combination, into the reaction system. Organic solvents with a similar effect include low-boiling point organic solvents, such as halogenated hydrocarbons such as dichloromethane, chloroform, and carbon tetrachloride; lower hydrocarbons such as pentane, hexane, and heptane;
Ethers such as tetrahydrofuran and dioxane can also be used. The method of the invention can be carried out either batchwise or continuously. The reaction temperature is usually preferably 100 to 350°C.
Furthermore, 150 to 300°C is more preferable. The reaction time varies depending on the type of carbamate used, catalyst, reaction temperature, etc., but is usually from several minutes to several tens of hours. Further, although this method is usually carried out under normal pressure, it may be carried out under increased pressure or reduced pressure as necessary. Next, the present invention will be further explained with reference to Examples, but the present invention is not limited to these Examples. Examples 1 to 11 Into a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet extending below the liquid level, and an air cooler, 100 g of bromnaphthalene as a solvent and 4,
Dicarbamic acid diethyl ester of 4'-diphenylmethane diisocyanate (abbreviated as MDI) 10
and 0.5 g of the specified catalyst, and heated at 250°C with stirring while introducing nitrogen into the reaction mixture at a rate of 30/hour.
The decomposition reaction was carried out for 2 hours. The generated ethanol was introduced into a dry ice trap from the top of the cooler and collected. The reaction solution was analyzed by high performance liquid chromatography, gel permeation chromatography, and infrared absorption spectroscopy, and the results shown in the table below were obtained.

[Table] For the reaction mixture of Example 6, B ₄ C
After distilling off the bromnaphthalene, the boiling point is 195-200℃/5 by performing vacuum distillation.
6.4 g (89% yield) of MDI distilled at mmHg was obtained. Example 12 Hexamethylene diisocyanate (HMDI)
A decomposition reaction was carried out at 250° C. for 2 hours in the same manner as in Example 1, except that 10 g of dicarbamic acid dimethyl ester, 50 g of n-hexadecane as a solvent, and 0.5 g of triphenyl borate were used as a catalyst. By analyzing the produced liquid by gas chromatography, it was found that HMDI was produced with a yield of 75%. When the same decomposition reaction was carried out without a catalyst, only 22% of HMDI was produced, and the majority remained undecomposed. Example 13 Dibenzyltoluene (boiling point 390°C) was added as a solvent to a 100ml four-necked flask equipped with a raw material introduction tube, a nitrogen introduction tube, a column-filled vacuum jacket type distillation tube (length 30cm), a thermometer, and a stirring device. 50ml,
3 g of tungsten boride powder was charged as a catalyst and heated to 250°C. At this temperature, add a solution of diethyltolylene-2,4-dicarbamate in tetrahydrofuran (0.1 g/ml) at 50%
It was introduced into the flask at a rate of ml/hr. At the same time, nitrogen gas was blown into the reaction solution from the introduction tube at a rate of 30/hr. The liquid and gas distilled from the upper part of the distillation tube were condensed in an air-cooled cooling tube (80 cm) to collect an isocyanate fraction, and then led to a dry ice trap to collect ethanol. Two hours after the steady state was reached, the isocyanate fraction was analyzed by high performance liquid chromatography and infrared absorption spectroscopy, and the results showed that it was 85% tolylene-2,4-diisocyanate, ethyl-4-methyl-3-
It was obtained with a yield of 10% of isocyanate carbanilate, and undecomposed diethyltolylene-2,4-
It contained 5% dicarbamate. The recovery rate of ethanol was 92%. In addition, the catalyst was recovered by filtering the reaction solution and the same experiment was repeated, but almost the same results as above were obtained, and no deterioration of the catalyst was observed. When a similar decomposition reaction was carried out without using a catalyst, the yield of the target tolylene-2,4-diisocyanate was 65%. Example 14 Formula Using 15 g of a mixture containing tricarbamic acid triethyl ester shown by and MDI dicarbamic acid diethyl ester in a molar ratio of 1:1, thermal decomposition was carried out for 4 hours in the same manner as in Example 1 using 1 g of boron carbide as a catalyst. When the produced liquid was analyzed by infrared absorption spectrum, it was found that it was almost completely decomposed into isocyanate. Furthermore, when this reaction solution was analyzed by high performance liquid chromatography, it was found that triisocyanate and MDI were produced in a 1:1 ratio. Example 15 A solution of 10% by weight of dicarbamic acid diethyl ester of 4,4'-diphenylmethane diisocyanate dissolved in orthodichlorobenzene was added to
Inner diameter 2cm, kept at 240℃ after preheating to 160℃,
It was introduced from the top of a 2 m high decomposition reactor at a rate of 10 ml/min. The inside of the reaction tube was filled with granular boron carbide, and preheated nitrogen was introduced from the bottom of the reaction tube at a rate of 0.5 N/min. The decomposition reaction was carried out continuously under a pressure of 15 Kg/cm ² . As a result, an orthodichlorobenzene solution of MDI containing no unreacted carbamate ester was obtained from the lower part of the reaction tube. Example 16 Into a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet extending below the liquid level, and an air cooler, 300 g of bromonaphthalene was placed as a solvent.
2 g of zirconium boride powder as a catalyst and 20 g of diphenylmethanedicarbamate dimethyl ester obtained by reacting methyl N-phenylcarbamate with formaldehyde in the presence of an acid catalyst as a carbamate ester; 3
A mixture consisting of 10 g of polymethylene polyphenylene polycarbamic acid methyl ester was added to the core. The decomposition reaction was carried out at 250° C. for 3 hours with stirring while introducing nitrogen into the reaction mixture at a rate of 50/hour.
After the reaction, the catalyst was separated by filtration, and the bromnaphthalene was distilled off under reduced pressure. Next, by performing vacuum distillation, 18 g of MDI distilled at 195-200°C/5 mmHg was obtained. The residual liquid further contained 6 g of MDI, and its NCO content including PMPPI was 30.3%. Comparative Example 1 The same reaction as in Example 16 was carried out except that 0.5 g of cobalt naphthenate was used instead of the zirconium boride powder, and then the solvent was distilled off under reduced pressure. Next, vacuum distillation was carried out using exactly the same method, and 6.5 g of MDI was distilled out, but the residual liquid had changed into a highly viscous substance, and only about 3 g of MDI existed, and the NCO content was It was 15.8%. This is considered to be because the isocyanate groups were reduced by cyclization reaction or polymerization reaction during the distillation operation, and the molecular weight was increased. Note that the NCO content represents the weight percent of NCO groups in the isocyanate compound. (For example, for MDI, the NCO content is
(33.6%).

Claims (1)

[Scope of Claims] 1 Boron alone or/and at least one compound containing boron selected from the following group (a) Borate of an alkali metal (b) Boride of an alkaline earth metal (c) Boron Zirconium oxide, hafnium boride, tungsten boride (d) Boric acid ester (e) In the presence of a catalyst consisting of boron carbide, boron silicide, boron nitride, boron oxide, inert to isocyanates and A method for producing isocyanates, which comprises thermally decomposing carbamate esters in a solvent that does not substantially dissolve a catalyst.