JPH0238582B2 - - 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:
400 in the presence of a Lewis acid such as ferric chloride
A method conducted in a gas phase at a high temperature of ~600°C (Japanese Patent Publication No. 46-17773), a method using heavy metals or polymeric compounds (Japanese Patent Publication No. 51-19721), B, B, A,
A method using a catalyst in which compounds of group metals A, B, B and group metals are dissolved in a solvent (Japanese Patent Application Laid-Open No. 1986-
19624) and a method using an alkaline earth metal or an inorganic compound (Japanese Patent Application Laid-Open No. 1988-88201). However, even when these methods are used, there are drawbacks such as high boiling point by-products and significant corrosion of the material.Also, when a metal compound substantially dissolved in a solvent is used as a catalyst, the It has drawbacks such as difficulty in separating the product and catalyst when producing boiling point isocyanates. Therefore, the present inventors developed a method for producing isocyanates by thermally decomposing carbamate esters, which allows for easy separation of the product and catalyst, and also eliminates high-boiling substances due to side reactions of the produced isocyanates. As a result of extensive research into a method for suppressing the formation and obtaining isocyanate in good yield, the present invention was achieved. That is, in the presence of one or more catalysts selected from (a) carbides of titanium, zirconium, hafnium, and silicon, and (b) nitrides of titanium, zirconium, hafnium, silicon, and germanium, A method for producing isocyanates is characterized in that carbamate esters are thermally decomposed in a solvent that is inert to isocyanates and does not substantially dissolve the catalyst. Carbamate esters used as raw materials in the present invention are compounds represented by the general formula R(NHCOOR') _o or (R'NHCOO) _o R or R(NHCOSR') _o or (R'NHCOS) _o R. be. 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-
dimethyl ester of phenylenedicarbamic acid,
Phenylene dicarbamic acid diesters such as diethyl ester and diphenyl ester; tolylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester and diphenyl ester of 2,4- or 2,6-tolylene dicarbamic acid ; Methylenebisphenylenedicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester of 2,2'- or 2,4'- or 4,4'-methylenebisphenylenedicarbamic acid; formula (R' is as described above, m is an integer of 1 to 5) Polymeric aromatic carbamic acid esters; methyl ester, ethyl ester, butyl ester, phenyl ester of 1- or 2-naphthylcarbamic acid Naphthylcarbamate esters such as; 1,4- or 1,5- or 1,
Naphthylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester of 6- or 2,6-naphthylene dicarbamic acid; ethylene biscarbanilate, propylene carbanilate, glyceryl tricarbanilate, Carbanilates of polyhydric alcohols such as pentaerythryl tetrakis carbanilate; alkyl carbamates such as methylcarbamate, ethylcarbamate, propylcarbamate, butylcarbamate, amylcarbamate, hexylcarbamate, octylcarbamate, octadecylcarbamate, etc. Alkyl carbamate esters such as acid methyl ester, ethyl ester, propyl ester, butyl ester, phenyl ester; alicyclic carbamic acid such as methyl ester, ethyl ester, phenyl ester, etc. of cyclopentyl carbamate, cyclohexyl carbamate, etc. Esters; ethylenedicarbamic acid, trimethylenedicarbamic acid, tetramethylenedicarbamic acid, pentamethylenedicarbamic acid, hexamethylenedicarbamic acid, 2,
Alkylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester such as 2,4- or 2,4,4-trimethylhexamethylene dicarbamic acid; methylcyclohexane-2,4- or 2, Alicyclic dicarbamic acids such as dimethyl esters, diethyl esters, diphenyl esters such as 6-dicarbamic acid, methyl 3-carbamate-3,5,5-trimethylcyclohexylcarbamic acid, and 4,4'-methylenebiscyclohexylcarbamic acid Esters; 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 Examples include methyl esters such as 3,5-dichlorophenylcarbamic acid, halogenated phenylcarbamate esters such as ethyl ester and phenyl ester; and thiolcarbamate esters corresponding to these. These carbamate esters may be a single type or a mixture of two or more types. The catalyst used in the present invention is selected from (a) carbides of titanium, zirconium, hafnium, and silicon, and (b) nitrides of titanium, zirconium, hafnium, silicon, and germanium. Specifically, TiC, ZrC, HfC,
Carbides such as Si-C, TiN, ZrN,
Zr ₃ N ₂ , HfN, Si ₂ N ₃ , SiN, Si ₃ N ₄ , Ge ₃ N ₂ ,
Nitrides such as Ce ₃ N ₄ are used. When these carbides and nitrides are used as catalysts, they may be used alone or in combination of two or more. Furthermore, it may be a composite carbide or a composite nitride. 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 usually 0.001 to 100 times the weight of the carbamate ester. The process of the present invention is carried out in a solvent that does not substantially dissolve these catalysts and is inert to the isocyanate produced. Since it is insoluble, most solvents that are inert to isocyanates can be used. Such solvents include aliphatic, cycloaliphatic or aromatic substituted or unsubstituted hydrocarbons or mixtures thereof, and also include 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, bromnaphthalene, 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. One feature 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-phenylcarbamate ethyl ester is methylenated with a methylenating reagent such as formaldehyde, trioxane, or methylal in the presence of an acid catalyst, a benzene ring is added in addition to methylene-bis-(4-phenylcarbamate ethyl). A polycarbamate containing three or more polycarbamates 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 a simple operation such as filtration, so that the catalyst component can be easily separated from the product by a simple process such as filtration. Contamination of ingredients can be prevented. Further, since the catalyst of the present invention is not substantially dissolved in the reaction solution, it is also possible to react the catalyst components in a fixed bed type, which is one of the preferred embodiments of the present invention. In the case of a fixed bed type reaction, no special operation is required for separating the catalyst component and the reaction solution, so it is particularly advantageous when carried out industrially. When carrying out the process of the present 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 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 a mixture, into the reaction system. Low-boiling organic solvents that have similar effects include 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, more preferably 150 to 300°C. The reaction time is
Although it varies depending on the type of carbamate used, catalyst, reaction temperature, etc., it is usually 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. EXAMPLES 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 9 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
A decomposition reaction was carried out at 250° C. for 2 hours with stirring while nitrogen was introduced into the reaction mixture at a rate of 30/hour. 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] Note that the reaction solution of these Examples was uniformly transparent and substantially free of catalyst components. Bromnaphthalene was distilled off from the liquid of Example 1 and the boiling point was reduced to 195 by performing vacuum distillation.
6.9g of MDI distilled at ~200℃/5mmHg (yield 94
%) was obtained. Example 10 Hexamethylene diisocyanate (HMDI)
10g of dicarbamic acid dimethyl ester, 50g of n-hexadecane as a solvent, 2g of SiC as a catalyst
The decomposition reaction was carried out at 260°C for 2 hours in the same manner as in Example 1, except that . By analyzing the product liquid using gas chromatography,
It was found that HMDI was produced with a yield of 60%. When the same decomposition reaction was carried out without a catalyst, only 22% of HMDI was produced, and the majority remained undecomposed. Example 11 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. 2 g of Si ₃ N ₄ 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, nitrogen gas is
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. 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 87% tolylene-2,4-diisocyanate.
Obtained with a yield of 5% ethyl-4-methyl-3-isocyanatocarbanilate and 8% undecomposed diethyltolylene-2,4-dicarbamate.
It was included. The recovery rate of ethanol was 90%. 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 12 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 4 using 3 g of TiC as a catalyst, and the resulting liquid was analyzed by infrared absorption spectrum, and 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 13 A solution in which 10% by weight of dicarbamic acid diethyl ester of 4,4'-diphenylmethane diisocyanate was dissolved in orthodichlorobenzene was dissolved at 150 to
After preheating to 160°C, it was introduced from the top of a decomposition reactor with an inner diameter of 2 cm and a height of 2 m maintained at 240°C at a rate of 10 ml/min. The inside of the reaction tube is filled with granular SiC, and preheated nitrogen is supplied from the bottom of the reaction tube.
It was introduced at 0.5N/min. Decomposition reaction is 15Kg/cm ²
It was carried out continuously under pressure. As a result, an orthochlorobenzene solution of MDI containing no unreacted carbamate ester was obtained from the lower part of the reaction tube. Example 14 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.
20 g of diphenylmethanedicarbamate dimethyl ester obtained by reacting 2 g of SiC powder as a catalyst and methyl N-phenylcarbamate as a carbamate ester with formalhyde in the presence of an acid catalyst; A mixture consisting of 10 g of polymethylene polyphenylene polycarbamic acid methyl ester was added to the core. under stirring while introducing nitrogen into the reaction mixture at 50/h.
The decomposition reaction was carried out at 250°C for 3 hours. After the reaction, the catalyst was separated by filtration, and the bromnaphthalene was distilled off under reduced pressure. Next, by performing vacuum distillation, 7.2 g of MDI distilled at 195-200°C/5 mmHg was obtained. The remaining liquid contains an additional 6.8g of MDI,
Its NCO content, including PMPPI, was 30.8%. Comparative Example 1 The same reaction as in Example 14 was carried out except that 0.5 g of cobalt naphthenate was used instead of SiC powder, and then the solvent was distilled off under pressure. Next, vacuum distillation was performed in exactly the same manner to distill 6.5 g of MDI, but the residual liquid had changed into a highly viscous substance.
Only about 3 g of MDI was present, and the NCO content 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, MDI
In the case of , the NCO content is 33.6%. )

Claims (1)

[Claims] 1. Presence of one or more catalysts selected from (a) carbides of titanium, zirconium, hafnium, and silicon; and (b) nitrides of titanium, zirconium, hafnium, silicon, and germanium. Below, a method for producing isocyanates, which comprises thermally decomposing carbamate esters in a solvent that is inert to isocyanates and does not substantially dissolve the catalyst.