JPH0260662B2 - - 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 ester 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 heavy metal compounds (Japanese Patent Publication No. 51-19721), B, B, A,
A method using a catalyst in which compounds of A, B, B, and group metals are dissolved in a solvent (Japanese Unexamined Patent Application Publication No. 1983-1999)
19624) and a method using an alkaline earth metal or its 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 isocyanates in good yield, the present invention was achieved. That is, the present invention provides a catalyst that is inactive with respect to isocyanates and in the presence of one or more catalysts selected from the following groups (a) and (b). This is a method for producing isocyanates, which is characterized by thermally decomposing carbamate esters in a solvent that does not dissolve 1 ppm or more. (a) Elements selected from silicon, germanium, and zirconium (b) Oxides and composite oxides of elements selected from aluminum, silicon, germanium, titanium, and zirconium What are the carbamate esters used as raw materials in the present invention? , a compound represented by the general formula R(NHCOOR') _o or (R'NHCOO) _o R or R(NHCOSR') _o or (R'NHCOS) _o R. 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. Further, these organic groups may contain other substituents that do not react with the isocyanate group, such as a halogen atom, a nitro group, a cyano group, an alkyl group, an alkoxy group, an acyl group, an acyloxy group, a carbamoyl group, etc. , may contain the 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, 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;
Esters of polymeric aromatic carbamic acids represented by the formula K0261 (R' is as described above, m is an integer of 1 to 5); methyl ester, ethyl ester, butyl ester of 1- or 2-naphthylcarbamic acid , phenyl ester, and other naphthylcarbamic acid esters; 1,4- or 1,5- or 1,6- or 2,6-naphthylenedicarbamic acid dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester, etc. Naphthylene dicarbamic acid diesters; 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 type, or two
It may be a mixture of more than one species. The catalyst used in the present invention is (a) an element selected from silicon, germanium, and zirconium; and (b) an oxide and composite oxide of an element selected from aluminum, silicon, germanium, titanium, and zirconium. It is something that More specific compounds of group (b) include Al ₂ O ₃ , SiO, SiO ₂ , GeO,
Oxides such as _GeO2 , TiO, _{TiO2 , Ti2O3 , ZrO2} ; ZnO- _SiO2 , ZnO- _{Al2O3 , Al2O3} - _ZrO2 ,
ZnO− _ZnO2 , _SiO2 − _{Al2O3 , SiO2} − _{Ga2O3 , SiO2}
−ZrO ₂ , SiO ₂ −TiO ₂ , ZrO ₂ −CdO, TiO ₂ −
CuO, _TiO2 -ZnO, TiO2 _- CdO, _TiO2 - _{Al2O3 ,}
Composite oxides such as _TiO2 - _ZrO2 , _TiO2 -PbO, and PbO- _SiO2 can be mentioned. When these single substances, oxides, and sulfides are used as catalysts, they may be used alone or in combination of two or more kinds. Further, although the quantitative ratio between these catalysts and the carbamate ester may be arbitrary, it is preferable to use the catalyst in an amount usually 0.0001 to 100 times the weight of the carbamate ester. The method of the present invention is carried out in a solvent that does not dissolve these catalysts above 1 ppm and is inert to the isocyanate produced. However, most of the catalysts of the present invention are dissolved in common organic solvents at a concentration of 1 ppm or above. Most solvents can be used as long as they are inert to 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 substituent naphthalene, dodecylbenzene; chlorobenzene, dichlorobenzene, bromobenzene , dibromunzene, chlornaphthalene, bromnaphthalene, nitronzene, nitronaphthalene, and other aromatic compounds substituted with nitro groups and halogens; diphenyl, substituted diphenyl, diphenylmethane, terphenylanthracene, phenanthrene, various isomers of benzyltoluene, 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 ether , ethers and thioethers such as diphenyl sulfide; sulfoxides such as dimethyl sulfoxide and diphenyl sulfoxide; and silicone oil. 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, formaldehyde, trioxane, N-phenylcarbamic acid ethyl ester in the presence of an acid catalyst,
In the case of methylenation using a methylenation reagent such as methylal, a polycarbamate ester of a polynuclear substance containing three or more benzene rings is produced as a by-product in addition to methylene-bis-(ethyl 4-phenylcarbamate). 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. For fixed bed reactions,
Since no special operation is required to separate the catalyst component and the reaction solution, this method is particularly advantageous when carried out industrially. 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 point components by distillation or the like among these components that are generated as the reaction progresses. 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, and 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, 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 13 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 spectrum, and the results shown in Table 1 were obtained.

【table】

[Table] The following results were obtained. The reaction solutions of these Examples were separated by filtration and were homogeneous and transparent and substantially free of catalyst components. Bromnaphthalene was distilled off from the liquid of Example 5 and the boiling point was reduced to 195-195 by performing vacuum distillation.
6.5g of MDI distilled at 200℃/ ^5mmHgcm2 (yield 90
%) was obtained. Example 14 Hexamethylene diisocyanate (HMDI)
10g of dicarbamic acid dimethyl ester, 50g of n-hexadecane as a solvent, powdered as a catalyst
A decomposition reaction was carried out at 260° C. for 2 hours in the same manner as in Example 1 except that 2 g of Al ₂ O ₃ was used.
HMDI was determined by gas chromatography analysis of the product liquid from which Al ₂ O ₃ was separated by filtration.
It was found that the product was produced at a yield of 68%. Furthermore, when the same decomposition reaction was carried out without a catalyst, 22
Only % of HMDI was produced, and most of it remained undegraded. Example 15 In a 100 ml four-necked flask equipped with a raw material introduction tube, a nitrogen introduction tube, a column-filled vacuum jacket distillation tube (length 30 cm), a thermometer, and a stirring device, 50 ml of dibenzyltoluene (boiling point 390°C) was added as a solvent. 1 g of germanium 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
It was blown into the reaction solution from the inlet 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. 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 92
%, ethyl-4-methyl-3-isocyanatocarbanilate with a yield of 6.5%, and contained 1.5% of undecomposed diethyltolylene-2,4-dicarbamate. Ethanol recovery rate is 94
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 16 Using 15 g of a mixture containing tricarbamic acid triethyl ester represented by the formula K0262 and dicarbamic acid diethyl ester of MDI in a molar ratio of 1:1,
Using 1 g of SiO ₂ as a catalyst, thermal decomposition was carried out for 4 hours in the same manner as in Example 4. After separating the catalyst, the resulting liquid was analyzed by infrared absorption spectrum, and it was found that it had been almost completely decomposed into isocyanates. I understand. Furthermore, when this reaction solution was analyzed by high performance liquid chromatography, it was found that triisocyanate was detected.
It turns out that MDI is generated on a one-to-one basis.
A mixture of isocyanates was obtained by distilling off the solvent from this reaction solution. Example 17 A solution of 10% by weight of dicarbamic acid diethyl ester of 4,4-diphenylmethane diisocyanate dissolved in oligodichlorobenzene 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 Ge, and preheated nitrogen was introduced from the bottom of the reaction tube at a rate of 0.5 N/min. Decomposition reaction is 15Kg/
It was carried out continuously under pressure of 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 18 Into a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet extending below the liquid surface, and an air cooler, 300 g of bromonaphthalene was placed as a solvent.
20 g of diphenylmethane dicarbamate dimethyl ester obtained by reacting 2 g of zirconium powder as a catalyst and methyl N-phenylcarbamate as a carbamate ester with formaldehyde in the presence of an acid catalyst, and 3-nuclear A mixture consisting of 10 g of polymethylene polyphenylene polycarbamic acid methyl ester was added.
while introducing nitrogen into the reaction mixture at 50/hr.
The decomposition reaction was carried out at 250°C for 3 hours with stirring. After the reaction, the catalyst was separated by filtration, and the bromnaphthalene was distilled off under reduced pressure. Then, by performing vacuum distillation, it is distilled at 195-200℃/5mmHg.
Obtained 7g MDI. The residual liquid contains an additional 7g of MDI, and its NCO content including PMPPI is 30.5%.
It was hot. Comparative example 1 Cobalt naphthenate instead of zirconium powder
The reaction was carried out in exactly the same manner as in Example 34, except that 0.5 g was used, and then the solvent was distilled off under reduced pressure. Next, vacuum distillation was performed in exactly the same manner,
Although 6.5 g of MDI was distilled out, the residual liquid had changed into a highly viscous substance, with only about 3 g of MDI present and an NCO content of 15.8%. This means that
This is thought to be because the isocyanate groups were reduced by cyclization and polymerization reactions during the distillation operation and the molecular weight 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. In the presence of one or more catalysts selected from the following groups (a) and (b), the catalyst is inert to isocyanates and A method for producing isocyanates, which comprises thermally decomposing carbamate esters in a solvent that does not dissolve 1 ppm or more of isocyanates. (a) Elements selected from silicon, germanium, and zirconium (b) Oxides and composite oxides of elements selected from aluminum, silicon, germanium, titanium, and zirconium.