JPH0987239A - Production of isocyanate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an isocyanate useful as a raw material for paints in high yield and selectivity with side reactions suppressed. SOLUTION: In the presence of a catalyst such as triphenyltin acetate, a carbamate such as 1,4-bit(methoxycarbonylamino)butane is thermally decomposed in a solvent inactive to isocyanate such as dibenzyl-toluene and a stabilizer of the formula: Xn -Ar-SO2 -Y (Ar is benzene; X is a lower alkyl; Y is hydroxyl or the like; n is an integer of 0-3; in case that n>=2, Xs may be independently different or may be same) for example, a sulfanylamide, to give the corresponding isocyanate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing isocyanates by thermally decomposing carbamic acid esters. Isocyanates are useful as raw materials for producing paints, insecticides, herbicides, polyurethanes, polyureas, etc., and are commercially produced on a large scale.

[0002]

2. Description of the Related Art The reaction between primary amines and phosgene is most widely used industrially as a method for producing isocyanates. This production method uses phosgene, which is extremely toxic, and produces a large amount of highly corrosive hydrogen chloride as a by-product.
Therefore, an industrial production method of isocyanates that does not use phosgene is desired.

As one of the methods for producing isocyanates,
A thermal decomposition method of carbamic acid esters has been proposed.
The thermal decomposition reaction of carbamic acid esters is a reversible reaction, and its equilibrium is advantageous at the high temperature side for isocyanate formation. For this reason, the thermal decomposition reaction is carried out at a high temperature, but due to the severe reaction conditions, various side reactions occur simultaneously, and for example, ureas, amides, carbodiimides, uretidiones and isocyanurates are produced. This side reaction is
In addition to lowering the yield and selectivity of the desired isocyanates, it may cause the formation of high-boiling by-products, which may obstruct long-term operation such as clogging of the reactor and piping. Therefore, various methods of using a catalyst, a stabilizer and the like have been proposed as a method for increasing the thermal decomposition reaction rate of carbamic acid esters and suppressing side reactions to obtain a good isocyanate yield.

That is, as a method for producing isocyanates by thermally decomposing carbamic acid esters using a catalyst, for example, Japanese Examined Patent Publication (Kokoku) No. 57-45736 has a periodic table I of elements.
Disclosed is a catalyst in which one or more metals selected from the group consisting of B, IIB, IIIA, IVA, IVB, VB and VIII metal atoms or a compound thereof is dissolved in a solvent. . JP-A-54-88201 describes a method of using an alkaline earth metal and its metal compound as a catalyst. Japanese Patent Laid-Open No. 57-158747 discloses the copper group, zinc group, and
A method of using one or more kinds selected from the group consisting of aluminum group, carbon group other than carbon, and titanium group elements and oxides or sulfides of these elements as a heterogeneous catalyst in a solvent. It is disclosed. However,
Many metals and metal compounds that have catalytic activity for the thermal decomposition reaction of carbamic acid esters also have a catalytic effect on side reactions such as buret formation, allophanate formation, and cyanurate formation. It is difficult to obtain a good isocyanate yield by suppressing side reactions in the thermal decomposition reaction of compounds.

Further, in order to suppress the formation of by-products in the thermal decomposition of carbamic acid esters and obtain isocyanates in good yield, as a stabilizer, in JP-A-57-123159, carboxylic acid chlorides, sulfonic acid esters and alkylated compounds are used. JP-A-1-125359 proposes a method using a phosphorous acid triester as an agent. However, these methods are still unsatisfactory with many high-boiling by-products.

[0006]

The object of the present invention is to obtain a high yield of isocyanates stably over a long period of time by suppressing side reactions and the formation of high boiling by-products during the thermal decomposition of carbamic acid esters. To provide.

[0007]

Means for Solving the Problems As a result of intensive studies on the method for producing isocyanates having the above-mentioned problems, the present inventors have added compounds of aromatic sulfonic acids and aromatic sulfonamides as stabilizers. The present invention was found by the fact that if pyrolyzed, the production of by-products is reduced and the yield of isocyanates is significantly improved.

That is, the present invention provides a catalyst, a solvent inert to isocyanates, and a compound of the general formula: X _n -Ar-SO _2- , in a method for producing corresponding isocyanates by thermally decomposing carbamic acid esters. Y [Ar is an aromatic nucleus such as benzene or naphthalene, X is a lower alkyl group, a hydroxyl group or an amino group, Y is a hydroxyl group or an amino group, and n is 0.
It is an integer of 3 to 3, and when n is 2 or more, X may be the same or different from each other], and is thermally decomposed in the presence of a stabilizer.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention will be specifically described below. In the method of the present invention, usually, in the presence of a catalyst, a stabilizer and a solvent inert to isocyanates, carbamic acid esters are thermally decomposed at a temperature of 150 to 350 ° C. to produce isocyanates and alcohols. Are collected separately.

The carbamic acid ester used as a raw material in the method of the present invention is not particularly limited, but is usually represented by the following formula. R ¹ (NHCOOR ² ) _n [R ¹ and R ² are organic groups selected from saturated or unsaturated aliphatic groups, alicyclic groups, aromatic groups and aralkyl groups, and R ¹ and R ² are They may be the same or different from each other. n is an integer of 1 to 4].

Specific examples of the carbamic acid esters used as the raw material include, for example, 1,4-bis (methoxycarbonylamino) butane, 1,6-bis (methoxycarbonylamino) hexane, and 1,8- (methoxy). Carbonylamino) octane and other aliphatic carbamic acid esters; 1,
3- or 1,4-bis (methoxycarbonylamino) cyclohexane, 1,3- or 1,4-bis (methoxycarbonylaminomethyl) cyclohexane, 3-methoxycarbonylaminomethyl-3,5,5-trimethyl-1- Alicyclic carbamate esters such as methoxycarbonylaminocyclohexane, bis (4-methoxycarbonylaminocyclohexyl) methane, 1-methyl-2,4-bis (methoxycarbonylamino) cyclohexane; 1,3- or 1,4- Bis (methoxycarbonylamino) benzene, 1-methyl-2,4-bis (methoxycarbonylamino) benzene, 1-methyl-2,6-bis (methoxycarbonylamino) benzene, 2,4'- or 4,
Aromatic carbamic acid esters such as 4'-bis (methoxycarbonylamino) diphenylmethane, 4,4'-bis (methoxycarbonylamino) biphenyl, 1,5- or 2,6-bis (methoxycarbonylamino) naphthalene; 1 Aralkylcarbamic acid esters such as 1,3- or 1,4-bis (methoxycarbonylaminomethyl) benzene, 1,5- or 2,6-bis (methoxycarbonylaminomethyl) naphthalene; and methoxycarbonylamino substitution of each compound Carbamates having an ethoxycarbonylamino substituent or a phenoxycarbonylamino substituent in place of the group are exemplified. These carbamic acid esters can be used alone or as a mixture of two or more kinds.

Solvents inert to isocyanates used in the present invention are aliphatic, alicyclic and aromatic substituted or unsubstituted hydrocarbons, esters, ketones, ethers and the like. Specific examples include hexane, heptane,
Aliphatic hydrocarbons such as nonane and decane; aromatic hydrocarbons such as benzene, toluene, xylene, biphenyl, naphthalene, benzyltoluene, pyrene, triphenylmethane, phenylnaphthalene, benzenenaphthalene; dibutyl phthalate, dioctyl phthalate, phthalate Examples thereof include esters such as acid didecyl; ketones such as methyl ethyl ketone and acetophenone; ethers such as anisole and diphenyl ether. The amount of such a solvent used is in the range of 0.05 to 20 times by weight, preferably 0.1 to 10 times by weight that of the carbamic acid ester.

In the present invention, the catalyst is not particularly limited and, for example, the periodic table of elements IB, IIB, III.
One or more metals selected from the group consisting of A, IVA, IVB, VB and VIII group metal atoms, or a compound thereof is used. That is, copper, zinc, aluminum, tin, titanium, vanadium, iron, cobalt, copper naphthenate, zinc acetate, aluminum benzoate, tin acetate, titanium phenolate, nickel naphthenate, etc .; MgO, CaO, BaO, MgCl
₂ , alkaline earth metals such as MgS and metal compounds thereof; and CuO, ZnO, Al ₂ O ₃ , PbO ₂ ,
_{SnO, Cu 2 S, In 2} S 3, PbS, copper of the Periodic Table such as SnS, zinc group, aluminum group, carbon group except carbon, simple and oxides or sulfides of these elements of titanium group elements And so on. The catalyst concentration in the above solvent is 0.0001 to 10% by weight, preferably 0.001 to 1% by weight.
Range.

The stabilizer used in the present invention has the general formula: X _n
-Ar-SO ₂ -Y [Ar is a benzene, aromatic nucleus of naphthalene, X is a lower alkyl group, a hydroxyl group or an amino group, Y represents a hydroxyl group or an amino group, n is an integer of 0 to 3, n is 2 In the above cases, X may be the same or different from each other]. Specific examples of such compounds include benzenesulfonic acid, toluenesulfonic acid, ethylbenzenesulfonic acid, mesitylenesulfonic acid, xylenesulfonic acid, phenolsulfonic acid, sulfanilic acid, aminotoluenesulfonic acid, naphthalenesulfonic acid, aminonaphthalenesulfonic acid. , Aminohydroxynaphthalene sulfonic acid, benzene sulfonamide,
Toluenesulfonamide, sulfanilamide, hydroxynaphthalenesulfonamide and the like can be mentioned. A mixture of two or more of the above compounds can be used as a stabilizer. The amount of the stabilizer used is 0.0001 to the above solvent.
10% by weight, preferably 0.001-1% by weight,
If the amount used is too large, the formation of isocyanates may be hindered.

The reaction temperature for the thermal decomposition of carbamic acid esters is in the range of 150 to 350 ° C, preferably 200 to 300 ° C. When the reaction temperature is lower than 150 ° C, the thermal decomposition rate is low, and when the reaction temperature is higher than 350 ° C, side reactions are promoted, which is not preferable. The reaction pressure is usually under reduced pressure, but if necessary, it is also under normal pressure or under increased pressure. The reaction time varies depending on the reaction temperature, pressure, reaction type, etc., but is usually in the range of 0.2 to 10 hours.

In the method of the present invention, the carbamic acid esters are thermally decomposed into the corresponding isocyanates and alcohols, but the isocyanates and the alcohols are separated from each other in order to prevent recombination to return to the carbamic acid esters. To collect. As this recovery method, there is a method of separating and removing only the low boiling point component by distillation or the like among the components produced as the reaction proceeds. In order to promote the separation, an inert gas such as nitrogen, argon and methane or an organic solvent having a low boiling point and inert such as benzene and hexane can be introduced into the reaction system. As another method, there is also a method in which vapors of isocyanates and alcohols produced as the reaction progresses are taken out of the system by distillation or the like to be condensed by utilizing the difference in condensation temperature and separately recovered.

The reaction operation for thermally decomposing carbamic acid esters can be carried out by a batch system, but in practice, a flow system using a complete mixing type reactor or a tubular reactor is preferable. In the flow system, for example, a multi-stage distillation column is used as a pyrolysis reactor, and a raw material solution consisting of carbamic acid esters, a solvent, a stabilizer and the like is continuously supplied to a reactor held under reduced pressure, and the reaction is performed. It can be preferably carried out by condensing vapors of the produced isocyanates and alcohols outside the system. The isocyanate fraction obtained here is purified to a high-purity product by distillation or the like, if necessary. On the other hand, the retained liquid is discharged from the reactor continuously or intermittently,
For example, after removing the Harz component by distillation or the like, the fraction containing isocyanates, unreacted carbamic acid ester, solvent and the like is circulated to the raw material system.

[0018]

Next, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples.

Example 1 A 500 ml five-necked flask equipped with a capillary, a thermometer, a raw material supply nozzle, a reaction solution withdrawing nozzle, and a packed column with a fractionating head (Dixon packing; about 8 stages) was used as a reactor. . Using Burrell Therm 400 (main component; dibenzyltoluene) as a solvent, 350 ml of a solution containing 50 ppm of triphenyltin acetate catalyst and 50 ppm of sulfanilamide dissolved in the solvent was charged into a reactor and placed in a mantle heater. The fractionating tower was equipped with a receiver for collecting metaxylylene diisocyanate (hereinafter referred to as MXDI) and a reflux condenser, and hot water at 60 ° C was circulated in the reflux condenser.
The upper part of the reflux condenser was connected to a vacuum line through a trap for collecting methanol cooled with dry ice. The reaction liquid extraction nozzle was separately connected to a vacuum line through a control valve and then a receiver. After charging 1,3-bis (methoxycarbonylaminomethyl) benzene (hereinafter referred to as MXDU) and Burrell Therm 400 at a weight ratio of 1: 3 into a constant-temperature raw material tank purged with nitrogen, adjust the concentration to 50 ppm with respect to the solvent. Was prepared by adding triphenyltin acetate catalyst and sulfanilamide. Next, a small amount of nitrogen was flown into the constant temperature raw material tank in order to prevent the deterioration of MXDU. While maintaining the reaction solution temperature at 250 ° C and the system pressure at 22 mmHg, the raw material solution was supplied to the reactor from the nozzle at a flow rate of 120 g / h using a metering pump. MXDI and methanol produced by the reaction were collected by each receiver. The liquid retained in the reactor was continuously withdrawn to a receiver so that the liquid surface was maintained at a constant level. After the reaction was started, the amount of liquid in each receiver was measured every predetermined time, and the composition was analyzed using a liquid chromatograph and a gas chromatograph. 12
As a result of continuous operation for a period of time and analyzing data in a steady state, MXDI decomposition rate 98.8%, MXDI selectivity 91.7%, intermediate monoisocyanate (hereinafter referred to as MX
(Called MI) selectivity 7.6%, MXDI and MXMI
The total selection rate of is 99.3%. No solid matter was attached to the reactor or receiver, and sedimentation was not observed.

Comparative Example 1 In the same manner as in Example 1, M was added without adding a stabilizer.
Thermal decomposition of XDU was performed. As a result of analyzing steady-state data, MXDI selectivity of 95.7% and MXDI selectivity of 9
0.3%, MXMI selectivity of 1.0%, and MX
The total selectivity of DI and MXMI is 91.3%.

Comparative Examples 2-3 In the same manner as in Example 1, thermal decomposition was carried out using triphenyl phosphite (Comparative Example 2) and phthalic acid dichloride (Comparative Example 3) as stabilizers. The data in steady state was analyzed and the results are shown in Table 1.

Examples 2-3 In the same manner as in Example 1, thermal decomposition was carried out using paratoluenesulfonamide (Example 2) and paraphenolsulfonic acid (Example 3) as stabilizers. The data in steady state was analyzed and the results are shown in Table 1.

[0023]

[Table 1] Stabilizer MXDU MXDI MXMI MXDI + MXMI concentration Decomposition rate Selectivity Selectivity Selectivity [ppm] [%] [%] [%] [%] Comparative Example 1-95.7 90.3 1.0 91.3 Comparative Example 2 2100 94.9 87.2 8.9 96.1 Comparative Example 3 1300 96.1 91.2 3.9 95.1 Example 1 50 98.8 91.7 7.6 99.3 Example 2 50 97.2 92.1 6.0 98.1 Example 3 50 98.4 91.8 5.4 97.2

Examples 4 to 6 Pyrolysis experiments were conducted in the same manner as in Example 1 except that iron naphthenate (Example 4), cobalt acetylacetonate (Example 5) and zinc acetate (Example 6) were used as the catalysts. went. The data in the steady state was analyzed and the results are shown in Table 2.

[0025]

[Table 2] Catalyst MXDU MXDI MXMI MXDI + MXMI concentration Decomposition rate Selectivity Selectivity Selectivity [ppm] [%] [%] [%] [%] Example 4 1400 99.1 93.8 3.5 97.3 Example 5 250 98.9 90.1 8.1 98.2 Example 6 100 99.5 94.8 3.3 98.1

Examples 7 to 9 The concentration of the catalyst and the stabilizer was 25 ppm, and methyl isophorone dicarbamate was used as the raw material carbamate ester.
(Example 7) 1,3-bis (methoxycarbonylmethyl)
Cyclohexane (Example 8) and 1-methyl-2,4-bis
Using (ethoxycarbonylamino) benzene (Example 9), thermal decomposition was performed under the same conditions as in Example 1. The data in the steady state was analyzed and the results are shown in Table 3. In Table 3, the diisocyanate body was designated as DI, and the intermediate moisocyanate body was designated as MI.

[0027]

[Table 3] Carbamic acid DI MI DI + MI ester decomposition rate Selectivity Selectivity Selectivity [%] [%] [%] [%] Example 7 99.1 97.6 1.5 99.1 Example 8 99.2 97.2 2.1 99.3 Example 9 97.4 92.1 4.8 96.9

[0028]

As shown in the above examples, in the method of the present invention, side reactions and the like are suppressed, isocyanates can be obtained in high yield and high selectivity, and almost no polymer is produced. Since it does not exist, stable operation can be performed for a long time.
Therefore, the isocyanates can be industrially produced very advantageously by the method of the present invention, and the industrial significance of the present invention is great.

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[Procedure amendment]

[Submission date] May 9, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

Examples 7 to 9 The concentration of the catalyst and the stabilizer was 25 ppm, and methyl isophorone dicarbamate was used as the raw material carbamate ester.
(Example 7), 1,3-bis (methoxycarbonylamino main <br/> chill) cyclohexane (Example 8) and 1-methyl-2,4
-Bis (ethoxycarbonylamino) benzene (Example 9) was used to perform thermal decomposition under the same conditions as in Example 1.
The data in the steady state was analyzed and the results are shown in Table 3.
In Table 3, the diisocyanate body was designated as DI, and the intermediate moisocyanate body was designated as MI.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Takashi Okawa 182 Tayuhama, Niigata City, Niigata Prefecture Mitsubishi Gas Chemical Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a corresponding isocyanate by thermally decomposing carbamic acid esters, a catalyst,
Solvents inert to isocyanates and general formula: X
_n -Ar-SO ₂ -Y [Ar is a benzene, aromatic nucleus, X is a lower alkyl group, a hydroxyl group or an amino group, Y is a hydroxyl group or an amino group such as naphthalene, n is an integer of 0 to 3, n is 2 In the above case, X may be the same or different from each other], the method for producing isocyanates is characterized by thermally decomposing in the presence of a stabilizer.