JPS6317052B2 - - 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 satisfactory results are obtained only when silver is used. It is clear that only . In any case, this method uses expensive silver or platinum group metals as catalysts. Therefore, the present inventors have conducted extensive research on a method for producing isocyanates from N-monosubstituted formamides in relatively high yields and with high selectivity without using such expensive catalysts. As a result,
We 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 300 to 600°C. A method for producing isocyanate from N-monosubstituted formamide, characterized by using a catalyst comprising a metal or/and an oxide of a metal. Iron, cobalt, and nickel used in the present invention are respectively in a metallic state and an oxide. Examples of oxides include Fe ₂ O ₃ , Fe ₃ O ₄ , Co ₂ O ₃ , CoO,
An example is NiO, but of course oxides in other oxidation states may also be included. These metals and metal oxides can be used alone or in combination of two or more. Further, it is also possible to use, as a catalyst, a mixture of these metals and metal oxides with other metals or metal oxides which may or may not be catalytically active. These catalysts may be used without a carrier or may be 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 dioxide, and silicon nitride. , boron carbide, zirconium oxide, calcined silica gel, titanium carbide, and mixtures thereof are preferred. Particularly preferred is a carrier containing silicon carbide as a main component. Common methods for supporting catalyst components on these carriers include immersing the carrier in a solution of salts of these metals, drying, and then subjecting the carrier to high-temperature heat treatment in air or an oxygen stream to form oxides. There is a method in which the material is made into a metallic state by heat treatment and then further heat treatment in a reducing atmosphere such as hydrogen or carbon monoxide, but of course any other method may be used to support the material. On these supports, the catalyst component may be a mixture of a metal state and various oxidation states. These catalyst components are preferably supported in an amount of 0.1% by weight or more on the carrier. 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
- N-aryl monoformamides such as quinolylformamide and N-oxazolylformamide;
N-aralkyl monoformamides such as N-benzylformamide and N-phenethylformamide; N,N'-tetramethylene diformamide,
N,N'-hexamethylene diformamide, N,
N'-octamethylene diformamide, N,N'-
N,N'-alkylene cyformamides such as undecamethylene diformamide and N,N'-dodecamethylene diformamide; N,N'-1,4-cyclohexyldiformamide, N,N'-1,4
-dimethylcyclohexylformamide, N,
N'-isophorone diformamide, N,N'-cyclohexylmethylene diformamide, N,N'-
N,N'-alicyclic diformamides such as 4,4'-dicyclohexylmethane diformamide; N,
N'-1,4-phenylenediformamide, 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;
N, such as N,N'-xylylene diformamide,
Examples include monoformamides and diformamides such as N'-aralkylene diformamides. In addition, triamines such as 1,8-diamino-4-aminomethyloctane, 1,2,3
- Triaminopropane, melamine, Tris (2-
Triformamides such as aminoethyl)amine can also be used in the present invention and 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, which is 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; Diformamides such as 2-aminoethyl esters 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 N-monosubstituted formamides can be easily obtained by reacting the corresponding primary amine with a formic acid derivative such as a formic acid ester such as methyl formate or ethyl formate, or by reaction with carbon monoxide. It may also be manufactured by other methods. The oxygen-containing gas used in the present invention includes a predetermined amount of oxygen, and may be air or other gases that do not inhibit the reaction of air or pure oxygen, such as nitrogen, argon, helium, carbon dioxide, etc. It may be diluted with an inert gas. In some cases, it may also contain gases such as hydrogen, carbon monoxide, hydrocarbons, and halogenated hydrocarbons. 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.
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 of isocyanate. It is also a preferred method to dilute the reaction system with an inert gas such as nitrogen, argon, helium, carbon dioxide, etc. In this case, these inert gases are also used as carriers for the raw materials. The N-monosubstituted formamide supplied to the reaction system may be supplied 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, tetralin, 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 300 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. 300
At temperatures lower than 600°C, virtually no reaction proceeds; at temperatures higher than 600°C, side reactions such as decomposition occur, reducing the yield and selectivity of isocyanate. Furthermore, a more preferable temperature range is 350°C. ~
The temperature is 550℃. 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 preferably carried out continuously, and more preferably in a gaseous state. This is a so-called gas phase flow reaction method in which N-monosubstituted formamide and oxygen are brought into continuous contact with a catalyst layer. In this case, the contact time with the catalyst layer is 0.05
-20 seconds is preferable, and 0.1-10 seconds is more preferable. 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 should be within the range of 300 to 600°C, more preferably
It is preferable to carry out under reduced pressure in order to vaporize at a temperature in the range of 350 to 550°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 up to the exit of the reaction zone. 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,
Number of halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene, trichloroethane, chlorobenzene, dichlorobenzene, bromobenzene, α-chloronaphthalene, α-bromonaphthalene, number of nitriles such as adiponitrile, benzonitrile, etc., 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 in 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 quantification 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 Silicon carbide is immersed in a nickel chloride aqueous solution,
After drying, a nickel oxide catalyst containing 2% by weight of nickel was obtained by treating at 600° C. for 3 hours 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=3000 hr ^-1 . At a reaction temperature of 450°C, the conversion rate of N-n-butylformamide was 55%, the yield of n-butyl isocyanate was 38%, and the selectivity to isocyanate was 69%. 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 1:1:10 into the same catalyst layer as in Example 1 at a space velocity of SV=2000 hr ^-1 . At a reaction temperature of 430°C, the yield of n-butyl isocyanate was 35% and the selectivity was 78%. Example 3 Immersing silicon carbide in a cobalt nitrate aqueous solution,
After drying, a cobalt oxide catalyst containing 0.5% by weight of cobalt was obtained by treating at 600° C. for 3 hours while flowing air. A raw material gas with a molar ratio of N-n-butylformamide:oxygen:nitrogen = 1:2:15 was introduced into this catalyst layer at a space velocity of SV = 6000 hr ^-1 , and the N-n- The conversion of butylformamide was 52%, the yield of n-butyl isocyanate was 23%, and the selectivity was 44%. Example 4 Using 3 g of a catalyst made of nickel powder molded into a tablet, raw material gas with a molar ratio of formanilide:oxygen:nitrogen = 1:2:20 was applied to this catalyst layer at SV=
It was introduced at a space velocity of 4000hr ^-1 . Reaction temperature 420℃
The yield of phenyl isocyanate was 35% and the selectivity was 84%. Example 5 A reaction was carried out under the same conditions as in Example 1 using iron powder as a catalyst. The yield and selectivity of n-butyl isocyanate at 380℃ and 440℃ are respectively
10%, 39%; 14%, 20%. Example 6 Mixture of hexamethylene diformamide, adiponitrile and biphenyl (weight ratio 1:2:5)
was supplied to the same catalyst layer as in Example 1. The molar ratio of hexamethylene diformamide:oxygen:nitrogen was 1:2:30 and SV = 1500 hr ^-1 . 450
The yield of hexamethylene diisocyanate at °C is
The selection rate was 38%. Example 7 A nickel oxide catalyst using titanium dioxide as a carrier was prepared in the same manner as in Example 1. The reaction was carried out in the same manner as in Example 1 except for using N-cyclohexylformamide, and the reaction temperature was 420°C.
yield of N-cyclohexyl isocyanate is 31.
%, with a selectivity of 63%. Example 8 A mixed powder of iron and nickel (weight ratio 1:2) molded into a tablet was used as a catalyst. The corresponding triformamide was obtained by reacting 1,8-diamino-4-aminomethyloctane with methyl formate. Triformamide:Oxygen:Nitrogen = 2:5:45 molar ratio of raw materials at 470℃
was introduced into the catalyst layer. The contact time with the catalyst was about 2 seconds. The product was isolated by distillation and IR confirmed the presence of isocyanate groups and also the absence of formamide groups. Quantification by titration with dibutylamine revealed that 1,8-diisocyanato-4-isocyanatomethyloctane was obtained in a yield of 13% and a selectivity of 18%. Example 9 Phenyl isocyanate was synthesized in the same manner as in Example 4 except that cobalt powder was used. The yield was 20% and the selectivity was 60%.

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 300 to 600°C, comprising:
1. A method for producing isocyanate from N-monosubstituted formamide, which comprises using a catalyst comprising one or more metals selected from iron, cobalt, and nickel and/or oxides of metals. 2. The method for producing isocyanate according to claim 1, wherein the catalyst is nickel or/and nickel oxide.