JPS6338986B2 - - 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 pesticides, especially 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 this method is difficult to manufacture due to the use of highly toxic phosgene and the production of large amounts of corrosive hydrogen chloride. There is a need for a method for producing isocyanates relatively easily and inexpensively without using phosgene. 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 conducted 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. 1989-52
-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, in the presence of a catalyst containing one or more elements selected from rare earth elements, antimony, bismuth, and oxides, sulfides, and salts of these elements,
This is a method for producing isocyanate, which is characterized by thermally decomposing carbamate esters. 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 represents an organic group selected from an n-valent (n is an integer of 1 to 4) saturated or unsaturated aliphatic group, alicyclic group, aromatic group, and aralkyl group,
R' represents an organic group selected from monovalent saturated or unsaturated aliphatic groups, alicyclic groups, aromatic groups, and aralkyl groups. In addition, 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,
It may contain an alkoxy group, an acyl group, an acyloxy group, a carbamoyl group, etc., or may contain an isocyanate group itself. It may also contain divalent functional groups that do not react with isocyanate groups, such as ether groups, thioether groups, carbonyl groups, carboxyl groups, and sulfone groups. 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, and 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 above, m is an integer from 1 to 5)
Polymeric aromatic carbamic acid esters represented by: naphthylcarbamic acid esters such as methyl ester, ethyl ester, butyl ester, phenyl ester of 1- or 2-naphthylcarbamic acid; 1,4- or 1,5- or naphthylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester of 1,6- or 2,6-naphthylene dicarbamic acid; ethylene biscarbanilate, propylene biscarbanilate,
Carbanilates of polyhydric alcohols such as glyceryl tricarbanilate and pentaerythryl tetrakiscarbanilate; methylcarbamate, ethylcarbamate, propylcarbamate, butylcarbamate, amylcarbamate, hexylcarbamate, octylcarbamate, octadecyl Alkyl carbamate esters such as methyl ester, ethyl ester, propyl ester, butyl ester, phenyl ester of alkyl carbamate such as carbamic acid; methyl ester, ethyl ester, phenyl ester, etc. of cyclopentyl carbamate, cyclohexyl carbamate, etc. alicyclic carbamic acid esters; ethylenedicarbamic acid, trimethylenedicarbamic acid,
Dimethyl esters, diethyl esters, dibutyl esters, diphenyls such as tetramethylene dicarbamic acid, pentamethylene dicarbamic acid, hexamethylene dicarbamic acid, 2,2,4- or 2,4,4-trimethylhexamethylene dicarbamic acid Alkylene dicarbamic acid diesters such as esters; methylcyclohexane-2,4-
Or alicyclic esters such as dimethyl ester, diethyl ester, diphenyl ester, etc. of 2,6-dicarbamic acid, methyl 3-carbamate-3,5,5-trimethylcyclohexylcarbamate, 4,4'-methylenebiscyclohexylcarbamic acid, etc. Group dicarbamic acid diesters; dimethyl ester, diethyl ester of xylylene dicarbamic acid,
Aralkyl dicarbamic acid diesters such as diphenyl esters; o- or m- or p-chlorophenylcarbamic acid, 2,5- or 3,4
- or halogenated phenylcarbamate esters such as methyl ester, ethyl ester, and phenyl ester such as 3,5-dichlorophenylcarbamate; and thiolcarbamate esters corresponding to these. These carbamate esters may be a single one,
It may be a mixture of two or more types. The catalyst used in the present invention is selected from rare earth elements, antimony, bismuth, and their oxides, sulfides, and salts. Rare earth elements include scandium, yttrium, lanthanum, cerium, prosedium, neodymium, promethium, samarium,
Eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium are used, and the oxides and sulfides of these elements include oxides and sulfides of these elements alone; CeO ₂ -
Composite oxides containing only rare earth elements such as La ₂ O ₃ ;
Composite oxides of rare earth elements and other elements such as LaAlO ₃ , La ₂ SiO ₅ , LaCrO ₃ , and CeAlO ₃ are used. Salts of rare earth elements include halides such as fluorides and chlorides; nitrates, sulfates, carbonates,
Salts of inorganic acids such as phosphates, borates; formates, acetates, oxalates, organic phosphates, aminopolyacetic acids (e.g. ethylenediaminetetraacetic acid, nitrilotriacetic acid, N-hydroxyethylenediaminetriacetic acid), etc. Salts of organic acids; complex salts coordinated with chelating agents such as acetylacetone, ethyl acetoacetate, benzoylacetone; halides, nitrates, etc. with ethylenediamine, dimethylformamide, dimethylacetamide, 2,
Complex salts coordinated with 2'-bipyridine, 1,10-phenanthroline, etc. are used. As oxides and sulfides of antimony and bismuth, Sb ₂ O ₃ , Sb ₂ S ₃ , Bi ₂ O ₃ , Bi ₂ S ₃ are used, and salts of these elements include trichloride and tribromide. halides such as; salts of inorganic acids such as nitrates, sulfates, carbonates, phosphates, borates;
Salts of organic acids such as formates, acetates and oxalates; salts of sulfonic acids such as methanesulfonic acid and benzenesulfonic acid; salts of carbamic acids corresponding to the carbamate esters used in the present invention, etc. . These simple substances and their oxides, sulfides,
Salts may be used alone or in combination of two or more. In addition, these simple substances or compounds,
A catalyst supported on a carrier such as SiO ₂ , Al ₂ O ₃ , SiO ₂ -Al ₂ O ₃ , activated carbon, graphite, diatomaceous earth, or zeolite can also be used. In the method of the present invention, the ratio of these catalysts to the carbamate ester can be adjusted to any desired ratio, but the ratio by weight to the carbamate ester is usually
It is preferable to use 0.0001 to 100 times the amount of catalyst. 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. . 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, promnaphthalene, nitrobenzene, nitronaphthalene; diphenyl, substituted diphenyl, diphenylmethane, terphenyl, anthracene, phenanthrene, various isomers of dibenzyltoluene , 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; diphenyl Examples include ethers and thioethers such as ether and diphenyl sulfide; sulfoxides such as dimethyl sulfoxide and diphenyl sulfoxide; and silicone oil. When carrying out the process of the invention, esters of carbamic acid are converted into the corresponding isocyanates and alcohols, but one component is removed from the reaction system to prevent recombination back to carbamate esters. It is necessary to remove it from In this case, it is preferable to remove and separate low-boiling components by distillation or the like from among the components that will be generated as the reaction progresses. An inert gas, such as nitrogen, helium, argon, carbon dioxide, methane, ethane, propane, etc., is used alone to facilitate this separation.
Alternatively, it is also a preferable method to mix them and introduce them 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, and ethers such as tetrahydrofuran and dioxane. You can also use 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 carbamate used, the type of catalyst, the reaction temperature, etc., but usually
The duration ranges from several minutes to several tens of hours. Further, although this method is usually carried out at normal pressure, it may be carried out under increased pressure or reduced pressure as necessary. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. Examples 1 to 27 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
g 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 Table 1 were obtained.

【table】

[Table] Regarding the reaction mixture of Example 21, the boiling point was 195-200℃/5mm by filtering the Bi powder and distilling off the brominenaphthalene, and then performing vacuum distillation.
6.7 g of MDI (yield 92%) was obtained by distilling with Hg. Example 28 Hexamethylene diisocyanate (HMDI)
10 g of dicarbamic acid dimethyl ester, 50 g of n-hexadecane as solvent, SbCl ₃ 1 as catalyst
The decomposition reaction was carried out at 260° C. for 2 hours in the same manner as in Example 1, except that g was used. By analyzing the product liquid using gas chromatography,
It was found that HMDI was produced with a yield of 78%. When the same decomposition reaction was carried out without a catalyst, only 22% of HMDI was produced, and the majority remained undecomposed. Example 29 50 ml of dibenzyltoluene (boiling point 390°C) was added as a solvent to a 100 ml four-necked flask equipped with a raw material introduction tube, a nitrogen introduction tube, a column-filled vacuum jacket type distillation tube (length 30 cm), a thermometer, and a stirring device. 1 g of bismuth powder was charged as a catalyst and heated to 250°C. At this temperature, a tetrahydrofuran solution (0.1 g/ml) of diethyltolylene-2,4-dicarbamate was introduced into the flask at a rate of 50 ml/hr from the raw material introduction tube. At the same time, add nitrogen gas to 30
It was blown into the reaction solution from the inlet tube at a rate of /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. After reaching steady state 2
After a period of time, the isocyanate fraction was analyzed by high performance liquid chromatography and infrared absorption spectroscopy, and it was found that tolylene-2,4-diisocyanate 90
%, ethyl-4-methyl-3-isocyanatocarbanilate with a yield of 6.5%, and contained 3.5% of undecomposed diethyltolylene-2,4-dicarbamate. Ethanol recovery rate is 92
It was %. Further, 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 30 formula SbO ₃ 3
Thermal decomposition was carried out for 4 hours in the same manner as in Example 4 using g as a catalyst, and the resulting liquid was analyzed by infrared absorption spectroscopy, and it was found that it was almost completely decomposed into isocyanate. Furthermore, when this reaction solution was analyzed using high performance liquid chromatography,
It was found that triisocyanate and MDI were produced in a 1:1 ratio.

Claims (1)

[Claims] 1. Carbamate esters are thermally decomposed in the presence of a catalyst containing one or more elements selected from rare earth elements, antimony, bismuth, and oxides, sulfides, and salts of these elements. A method for producing isocyanate, characterized by: