JPS6317051B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a process for producing isocyanates from N-monosubstituted formamides. Although various methods for producing isocyanates have been proposed, most of the methods that have been carried out industrially involve the reaction of amines or their salts with phosgene. However, since phosgene is extremely poisonous and can be hydrolyzed and corrosive even in the presence of trace amounts of moisture, there is a desire to develop a method for producing isocyanates using other methods. As one such method, a method for producing isocyanate from formamide has recently been proposed in JP-A-54
-Disclosed by No. 39018. According to this,
N-monosubstituted formamide in the gas phase at approximately 300 ~
by oxidation at a temperature of about 600° C. in the presence of a catalyst of copper and/or one or more metals of Groups B and Groups 5 and 6 of the Periodic Table of the Elements. Although it has been described that isocyanates are produced, this method has poor isocyanate yields and selectivity when platinum group metals are used as catalysts, and is only satisfactory when silver is used. It is clear that results are being obtained. Therefore, the present inventors have conducted extensive research on a method for producing isocyanate from N-monosubstituted formamide in good yield and selectivity, and as a result, have arrived at the present invention. That is, the present invention provides a method for producing isocyanate by oxidizing N-monosubstituted formamide using an oxygen-containing gas at a temperature in the range of 200 to 600°C. The method of producing isocyanate from formamide is characterized by using a catalyst comprising an oxide of one or more metals. When metals such as Ru, Rh, Pd, Ir, and Pt are used as catalysts, the yield of isocyanate is several percent to
It is stated in JP-A-54-39018 that the selectivity is at most 10-odd percent, and the selectivity is a few percent to 10-odd percent at most. It has been found that according to the method of the present invention using a metal oxide as the main component of the catalyst, isocyanate can be obtained in good yield with a high selectivity of 50% or more. The oxides of Ru, Rh, Pd, Ir, and Pt used in the present invention include RuO ₂ , Rh ₂ O ₃ , PdO, IrO ₂ ,
Examples include PtO and Pt ₃ O ₄ , but of course oxides in other oxidation states may also be included. These metal oxides can be used alone, or two
More than one species can also be used. Moreover, it is also possible to use as a catalyst a mixture of these metal oxides with other metals or metal oxides which may or may not be active as catalysts, if necessary. These catalysts can also be used without a support, but
More preferably, it is supported on a carrier. The carrier should be selected from those that have no or low activity to cause decomposition or side reactions of the raw materials and products under the reaction conditions; examples of such carriers include silicon carbide, titanium carbide, and titanium dioxide. , silicon nitride, boron carbide, zirconium oxide, calcined silica gel, mixtures thereof, etc. are preferred, and particularly preferred is a carrier containing silicon carbide as a main component. A common method for supporting catalyst components on these carriers is to immerse the carrier in a solution of salts of these metals, dry it, and then heat treat it at a high temperature in an air or oxygen stream to form an oxide. However, it can of course be supported by any other method. There is no limit to the amount of catalyst components supported on the carrier, but it is usually 0.005% by weight or more. Among the oxides of Ru, Rh, Pd, Ir, and Pt, palladium oxide is particularly highly active in this reaction and shows no decrease in activity over time, making it a preferred catalyst species. The N-monosubstituted formamide used as a starting material in the present invention has the general formula In the formula, n represents an integer of 1 to 3. Further, R means an n-valent organic residue,
Represents a substituted or unsubstituted aliphatic group, alicyclic group, aromatic group, and aralkyl group. Any substituent may be used as long as it does not decompose or cause side reactions under the reaction conditions.
For example, N-monosubstituted formamides having substituents such as chlorine, fluorine, nitrile groups, alkyl groups, alkoxy groups, acyl groups, and ester groups can be used in the present invention. As unsubstituted N-monosubstituted formamide,
For example, N-methylformamide, N-ethylformamide, N-propylformamide, N-
Butylformamide, N-pentylformamide, N-hexylformamide, N-heptylformamide, N-octylformamide, N-nonylformamide, N-decylformamide, N
- N-alkyl monoformamides such as undecylformamide, N-dodecylformamide, N-octadecylformamide, N-isopropylformamide, N-isobutylformamide, N-t-butylformamide, N-neopentylformamide; N-cyclopentylformamide ,
N-alicyclic monoformamides such as N-cyclohexylformamide and N-methylcyclohexylformamide; N-phenylformamide, N-
- Naphthylformamide, N-pyridylformamide, N-indenylformamide, N-triazinylformamide, N-tolylformamide,
N-aryl monoformamides such as N-quinolylformamide and N-oxazolylformamide; N-aralkyl monoformamides such as N-benzylformamide and N-phenethylformamide; N,N'-ethylene diformamide, N,
N'-trimethylene diformamide, N,N'-tetramethylene diformamide, N,N'-hexamethylene diformamide, N,N'-octamethylene diformamide, N,N'-undecamethylene diformamide, N, N,N'-alkylene diformamides such as N'-dodecamethylene diformamide; N,N'-1,4-cyclohexyldiformamide, N,N'-1,4-dimethylcyclohexylformamide, N,N'- N,N'-alicyclic diformamides such as isophorone diformamide, N,N'-cyclohexylmethylene diformamide, N,N'-4,4'-dicyclohexylmethane diformamide; N,N'-1,4 -phenylene diformamide, N,N'-2,4-tolylene diformamide, N,N'-2,6-tolylene diformamide, N,N'-4,4'-diphenylmethane diformamide, N, N'-4,4'-diphenyl ether diformamide, N,N'-1,4
-Naphthylene diformamide, N,N'-1,5
-Naphthylene diformamide, N,N'-2,6
-N,N'-aryl diformamides such as naphthylene diformamide; monoformamides and diformamides such as N,N'-aralkylene diformamides such as N,N'-xylylene diformamide. Other triamines such as triformamides such as 1,8-diamino-4-aminomethyloctane, 1,2,3-triaminopropane, melanin, and tris(2-aminoethyl)amine may also be used in the present invention. I can,
It can be converted to the corresponding triisocyanate. Of course, formamides obtained by substituting these unsubstituted formamides with the above-mentioned substituents can also be used. For example, formamide, an ester derivative of amino acids, can also be used. These include formamides such as methyl and ethyl esters of alanine, valine, and leucine, formamides such as dimethyl and diethyl esters of aspartic acid and glutamic acid, diformamides such as methyl and ethyl esters of lysine, alanine, Diformamide such as 2-aminoethyl ester of valine and leucine, di(2-aminoethyl) of aspartic acid and glutamic acid.
Triformamide such as ester, 2- of lysine
Examples include triformamide such as aminoethyl ester. These formamides can be easily obtained by reacting the corresponding primary amine with a formic acid derivative such as a formate ester such as methyl formate or ethyl formate, or by reaction with carbon monoxide, but of course other methods can also be used. It may also be one that has been manufactured by The oxygen-containing gas used in the present invention may be air as long as it contains a predetermined amount of oxygen, or other gases that do not adversely affect the reaction with air or oxygen.
For example, it may be diluted with an inert gas such as nitrogen, argon, helium, or carbon dioxide. In some cases, it may also contain gases such as hydrogen, carbon monoxide, hydrocarbons, halogenated hydrocarbons, and thiols. The ratio of N-monosubstituted formamide and oxygen fed onto the catalyst is 0.5 to 50 equivalents, preferably 1 to 20 equivalents of oxygen per formamide group.
This is because if the amount of oxygen is too small, the yield of isocyanate will be low, and if it is too large, oxidative decomposition, combustion, etc. will occur, resulting in a decrease in the yield and selectivity of isocyanate. It is also preferable to dilute the reaction system with an inert gas such as nitrogen, argon, helium, carbon dioxide, etc. In this case, the concentration of N-monosubstituted formamide is preferably 1 to 30%. These inert gases are also used as carriers for raw materials. The N-monosubstituted formamide supplied to the reaction system may be as is or may be diluted with an inert solvent. Examples of such solvents include hydrocarbons such as benzene, toluene, xylene, biphenyl, pentane, hexane, cyclopentane, cyclohexane, methylcyclohexane, tetralyl, decalin, methylnaphthalene, benzonitrile, tolnitrile, adiponitrile, valeronitrile. , nitriles such as butyronitrile, esters such as ethyl acetate, octyl acetate, and octyl propionate, and halogenated hydrocarbons such as chlorobenzene and dichlorobenzene. The temperature range used in the method of the invention is:
The reaction temperature is preferably 200 to 600° C., although it varies depending on the catalyst system used, the type of N-monosubstituted formamide and its proportion with oxygen, and the reaction conditions such as the concentration of formamide in the gas stream, residence time, and gas velocity. 200
This is because substantially no reaction proceeds at temperatures lower than 600°C, and side reactions such as decomposition occur at temperatures higher than 600°C, reducing the yield and selectivity of isocyanate. Furthermore, a more preferable temperature range is 250 to 500°C. The reaction of oxidizing N-monosubstituted formamide to form an isocyanate by the method of the present invention can be carried out either continuously or batchwise, but it is preferable to carry out the reaction continuously, and more preferably, N-monosubstituted formamide is oxidized into isocyanate. ―
This is a so-called gas phase flow reaction method in which monosubstituted formamide and oxygen are brought into continuous contact with a catalyst layer.
In this case, the contact time with the catalyst layer is preferably 0.05 to 20 seconds, more preferably 0.1 to 5 seconds. The reaction is usually carried out under normal pressure, but may of course be carried out under reduced pressure or increased pressure. In particular, when using N-monosubstituted formamide with a high boiling point, the temperature is in the range of 200 to 600°C, more preferably 250°C.
It is preferable to carry out under reduced pressure for vaporization in the range of ~500°C. The isocyanate production reaction according to the method of the present invention is expressed by the following general formula. Therefore, water is produced as a by-product at the same time as isocyanate is produced, but when using the catalyst of the present invention,
Since amine R-(NH ₂ ) _o , which is thought to be produced by a secondary reaction between this water and isocyanate, is hardly detected, it appears that almost no reaction between the products occurs until the exit of the reactor. It seems that it is not. This water can be removed from the product by separating the water from the gaseous isocyanate that has come out of the reaction zone, or by using a good solvent for isocyanate to dissolve most of the water. It has been found that water can be removed relatively easily using methods such as introducing the reaction product gas into a solvent that does not contain water. Such solvents include hydrocarbons such as benzene, toluene, xylene, tetralin, decalin, kyumene, α-methylnaphthalene,
Halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene, trichloroethane, chlorobenzene, dichlorobenzene, bromobenzene, α-chloronaphthalene, α-bromonaphthalene, nitriles such as adiponitrile and benzonitrile, ethyl acetate, octyl acetate, etc. Esters and the like are preferred. 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 in any way. These examples were generally performed in the following manner. A quartz reaction tube with a length of 40 cm and a diameter of 2 cm was
The reaction was carried out in a flow-through type reactor in which the catalyst layer was fixed in a vertical electric furnace with a catalyst layer located approximately at the center, and raw materials and oxygen-containing gas were supplied from the top. The upper part of the catalyst layer was filled with quartz sand as a preheating layer. The reaction temperature was measured by inserting a quartz tube containing a thermocouple into the catalyst layer. Raw material N
- Monosubstituted formamide was preheated by a preheating device and introduced into the reaction tube in the form of a gas or a hot liquid. Identification and quantitative determination of the product can be carried out using gas chromatography on the gaseous substance at the outlet of the reaction tube, or gas chromatography on the liquid substance obtained by absorbing the reaction product in 1-bromonaphthalene. there was. Furthermore, the presence of isocyanate groups was also confirmed by IR and by adding alcohol or amine to the product solution to make urethane or urea derivatives. Example 1 A palladium oxide catalyst containing 0.5% by weight of palladium was obtained by immersing silicon carbide in a hydrochloric acid solution of palladium chloride, drying, and heating it to 600° C. while flowing air. A raw material gas having a molar ratio of Nn-butylformamide:oxygen:nitrogen=4:8:82 was introduced into this catalyst layer at a space velocity of SV=about 6000 hr ^-1 . N-n- at reaction temperature 290℃
The conversion rate of butylformamide was 70%, the yield of n-butyl isocyanate was 50%, and the selectivity to isocyanate was 71%. Approximately 10% n-butyronitrile and 2% dibutyl urea were produced as by-products. The yield and selectivity of n-butyl isocyanate when the reaction temperature was changed were as follows.

[Table] Example 2 N-n-butylformamide: oxygen: nitrogen =
The reaction was carried out by introducing raw material gases in a molar ratio of 7:7:86 into the same catalyst layer as in Example 1 at a space velocity of SV=about 4000 hr ^-1 . reaction temperature
The yield of n-butyl isocyanate at 300℃ is 43
%, and the selection rate was 68%. Also, as a by-product n
- Approximately 5% butyronitrile was produced. Example 3 Add ammonia water to palladium chloride and heat to about 70℃
A palladium oxide catalyst containing 0.7% by weight of palladium was obtained by immersing silicon carbide in an ammine complex solution of palladium obtained by heating the solution to a temperature of 100.degree. C., drying it, and heat-treating it at 600.degree. A raw material gas having a molar ratio of formanilide:oxygen:nitrogen=4:8:82 was introduced into this catalyst layer at a space velocity of SV=5000 hr ^-1 . At a reaction temperature of 310°C, the conversion rate of formanilide was 75%, the yield of phenyl isocyanate was 58%, and the selectivity was 77%. 20 again
No decrease in activity was observed during the time reaction. Example 4 Mixture of hexamethylene diformamide, adiponitrile and biphenyl (weight ratio 1:2:5)
was supplied to the same catalyst layer as in Example 3. The molar ratio of hexamethylene diformamide:air:nitrogen was 1:1:50 and SV=2000hr ^-1 . 390
At °C, the conversion of hexamethylene diformamide was nearly 100% and the yield of hexamethylene diisocyanate was 38%. Example 5 A palladium oxide catalyst using titanium dioxide as a carrier was obtained in the same manner as in Example 3. When the reaction was carried out in the same manner as in Example 1 except for using N-cyclohexylformamide, N-cyclohexyl isocyanate was obtained at 320°C with a selectivity of 53% and 68%. Example 6 A rhodium oxide catalyst containing 0.5% by weight of rhodium in silicon carbide was obtained in the same manner as in Example 1 using an aqueous solution of rhodium trichloride. Using this catalyst, the same raw material gas as in Example 2 was reacted under the same conditions. In the case of this catalyst, a considerable amount of n-butyronitrile was produced, but the yield and selectivity of n-butyl isocyanate were as follows at each temperature.

[Table] Example 7 A reaction was carried out under the same conditions as in Example 1 using an aqueous solution of ruthenium trichloride and a ruthenium oxide catalyst prepared in the same manner as in Example 1. The yield of n-butyl isocyanate was 12%, and the selectivity was 65%. Example 8 A platinum oxide catalyst prepared using a chloroplatinic acid solution in the same manner as in Example 1 (but the heat treatment was carried out at 500°C) was used under the same conditions as in Example 2. When the reaction was carried out at 300℃, n-
Butyl isocyanate yield is 23%, selectivity is 54
It was %. Example 9 Silicon carbide was immersed in a hydrochloric acid solution containing palladium chloride and ruthenium trichloride, and after drying, heat treatment was performed at 600°C for 4 hours in an air stream, resulting in a concentration of 0.3% by weight.
A palladium oxide and ruthenium monoxide catalyst containing 0.1% of palladium and 0.1% of ruthenium was obtained. Using this catalyst, a reaction of N-phenethylformamide was carried out. Formamide: oxygen: nitrogen = 1:2:40
The molar ratio was SV = 5000 hr ^-1 . The yield of 2-phenylethyl isocyanate at 350℃ is 45
%, and the selection rate was 78%. Example 10 A palladium oxide catalyst supported on silicon carbide containing 0.4% by weight of palladium was prepared by the method of Example 3. The corresponding triformamide was obtained by reacting 1,8-diamino-4-aminomethyloctane with ethyl formate. Raw materials having a molar ratio of triformamide:oxygen:nitrogen=2:3:45 were introduced into the catalyst layer at 420°C. The contact time with the catalyst was about 1 second. The product was isolated by distillation and IR confirmed the presence of isocyanate groups and also the absence of formamide groups. When determined by titration with dibutylamine, 1,8-diisocyanate
The yield of 4-isocyanatomethyloctane was 28%, and the selectivity was 35%. Example 11 A reaction was carried out under the same conditions as in Example 1 using an aqueous solution of iridium chloride and an iridium oxide catalyst prepared in the same manner as in Example 1. The yield was 15% and the selectivity was 53%.

Claims (1)

[Claims] 1. A method for producing isocyanate by oxidizing N-monosubstituted formamide using an oxygen-containing gas at a temperature in the range of 200 to 600°C, comprising:
A method for producing isocyanate from formamide, characterized by using a catalyst comprising an oxide of one or more metals selected from Ru, Rh, Pd, Ir, and Pt. 2. The method for producing isocyanate according to claim 1, wherein the catalyst is palladium oxide. 3. The method for producing isocyanate according to claim 1, wherein the catalyst is palladium oxide supported on silicon carbide.