JP2962596B2 - Method for producing isocyanate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a process for producing isocyanates by pyrolysis of urethane in the presence of a catalyst.

[0002]

2. Description of the Related Art It has long been known that the thermal decomposition of urethane gives isocyanates and hydroxyl compounds (for example, H. Schiff, Ber., 3 , 635 (1870); AWH).
offmann, Ber., 3 , 653 (1870)), and its basic reaction is exemplified by the following equation. R (NHCOOR ') n → R (NCO) n + n R'OH or (R'NHCOO) nR → n R'NCO + R (OH) n (where R is an n-valent organic residue and R' is Monovalent organic residues,
n represents an integer of 1 or more. ) The thermal decomposition reaction represented by the above general formula is reversible, and its equilibrium is biased toward the urethane on the left side at low temperatures, but at high temperatures, the isocyanate and hydroxyl compounds are advantageous.

[0003] As described above, the thermal decomposition reaction of urethane requires severe reaction conditions, such as the reaction being performed at a high temperature, and causes various irreversible side reactions. Side reactions include the above-mentioned H. Schiff literature and
Research by E. Dyer and GCWright (J. Am. Chem. Soc., 81 , 2138)
(1959)), for example, the production of substituted ureas, burettes, carbodiimides, isocyanurates and the like. These side reactions not only reduce the yield and selectivity of the target isocyanate, but also cause the production of high molecular weight substances, especially in the production of polyisocyanates, and in some cases, the precipitation of solids in the reactor. This can lead to such situations as long-term operation becoming difficult, such as blockage of the building.

[0004] Most of the undesired side reactions are at high temperatures,
Also, the reaction time tends to increase as the time during which the produced isocyanate is in contact with each component of the reaction mixture is increased. Various methods have been proposed so far for suppressing the generation of undesired by-products in the thermal decomposition of urethane and obtaining a good isocyanate yield.

One of the methods is to reduce the thermal load by using a catalyst. For example, US Pat. Nos. 2,135,911, 2,692,275 and 2,727,020 and JP-A-54-88201 disclose basic methods. A process for producing isocyanates by pyrolyzing urethane in the presence of a catalyst is described. However, it has been reported that when these basic catalysts are used, the yield of solid by-products is increased and the yield of isocyanate is not so high (FWAbbate et.
al., J. Appl. Pol. Sci., 16 , 1213 (1972)), which is not preferred.

A thermal decomposition method using a Lewis acid as a catalyst is proposed in Japanese Patent Publication No. 46-17773, and various metal salts and halides are exemplified. As these improved patents, a number of thermal decomposition methods using various metal compounds as catalysts have been proposed.For example, Japanese Patent Application Laid-Open No. 51-19721 discloses heavy metal compounds, Japanese Patent Application Laid-Open Nos. 52-19624 and 56-56.
-166160 discloses Ib, IIb, IIIa, IVa,
Group IVb, Vb and VIII metal compounds are disclosed in
No. 9657 and JP-A-57-21356 disclose zinc chloride, which is a Lewis acid, in U.S. Pat.
In No. 41, acetylacetonate of aluminum and iron respectively, and in Japanese Patent Application Laid-Open No. 58-128354, thallium, tin,
There is a description that antimony and zirconium compounds effectively act as homogeneous pyrolysis catalysts, respectively.
As solid catalysts, JP-A-56-65856 and JP-A-56-65856
In JP-A-56-65857 and JP-A-56-65858,
Surface-rich metallic zinc, aluminum, titanium, iron,
The use of chromium, cobalt and nickel is described. Further, JP-A-57-158747 proposes a method of using oxides / sulfides of various metals as solid catalysts, and JP-A-57-158746 proposes a method of using carbides / nitrides of various metals as solid catalysts. I have.

However, for example, as shown in Hiratsuka and Yokoyama, "Polymer Processing", Vol. 34, p. 502 (1985) and Iwata, "Polyurethane Resin Handbook" (1987, published by Nikkan Kogyo Co., Ltd.), pp. 90-98. It is well known that many metals and metal compounds that exhibit catalytic activity in the thermal decomposition reaction of urethane also exhibit catalytic activity in side reactions such as allophanation, burette formation and trimerization, and have been proposed so far. The use of such catalysts has a limitation in suppressing the formation of undesired by-products in the thermal decomposition of urethane and obtaining a good isocyanate yield.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an isocyanate stably at a high yield for a long period of time.

[0009]

The inventors of the present invention have made intensive studies to overcome various problems in the prior art, and as a result, have completed the present invention. That is, the present invention is a method for producing an isocyanate, which comprises thermally decomposing urethane in the presence of a carbamic acid ester represented by the following formula (1).

[0010]

Embedded image

In the method of the present invention, specific examples of the carbamate represented by the formula (1) include phenyl carbamate, isomers of cresyl carbamate, isomers of xylyl carbamate, naphthyl carbamate, Methyl carbamate, ethyl carbamate, propyl carbamate isomers, butyl carbamate isomers, pentyl carbamate isomers, hexyl carbamate isomers, cyclohexyl carbamate, octyl carbamate isomers Examples thereof include those in which a part of hydrogen of the above hydrocarbon group is substituted with a halogen group, a nitro group, a nitroso group, or a nitrile group.

In the method of the present invention, the carbamic acid ester represented by the formula (1) is added to the urethane as a raw material in an amount of 0.1%.
It is used in the range of 1 to 50 mol%, preferably 0.5 to 30 mol%. If the amount is less than the above range, the effect of the reaction activity is small, and if the amount is larger than the above range, side reactions increase and the selectivity of the reaction deteriorates, and the generation of an insoluble polymer is not preferable.

The urethane used as a raw material in the present invention may be any type of N-mono-substituted urethane in which the boiling points of the isocyanate and the hydroxyl compound produced by decomposition differ by 5 ° C. or more under the reaction conditions. It may be something. Such a urethane is expressed by the following equation (2).

[0014]

Embedded image

Is a compound represented by the formula: Where R is n
A monovalent saturated or unsaturated aliphatic or alicyclic group, an aromatic group or an aralkyl group, wherein R ′ is a monovalent saturated or unsaturated Represents an organic group selected from an aliphatic group, an alicyclic group, an aromatic group, and an aralkyl group. Further, these organic groups are other substituents which do not react with the isocyanate group, for example, a halogen atom,
It may contain a nitro group, a cyano group, an acyl group, an acyloxy group, a carbamoyl group or the like, or may contain an isocyanate group itself. Further, it may contain a divalent functional group which does not react with the isocyanate group, for example, an ether group, a thioether group, a carbonyl group, a carboxyl group, a sulfone group and the like.

Examples of such urethanes include methyl carbanilate, ethyl carbanilate, propyl carbanilate, butyl carbanilate, cyclohexyl carbanilate, phenyl carbanilate, and the following formula (3)

[0017]

Embedded image

Carbanilates represented by the formula: o-, m- or p-tolyl carbamic acid methyl ester, ethyl ester, phenyl ester and other tolyl carbamic acid esters; o-, m- or p-phenylenedicarbamic acid Phenylenedicarbamic acid diesters such as dimethyl ester, diethyl ester and diphenyl ester; 2,4-
Or tolylene dicarbamic acid diesters such as dimethyl ester, diethyl ester and diphenyl ester of 2,6-tolylene dicarbamic acid; 2,2′-, 2,
Methylenebisphenylenedicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester and diphenyl ester of 4'-, 2,6'- or 4,4'-methylenebisphenylenedicarbamic acid; the following formula (4)

[0019]

Embedded image

Polymeric aromatic carbamates represented by the following formula (5):

[0021]

Embedded image

Esters of aromatic carbamic acid represented by the following: naphthyl carbamic acid esters such as dimethyl ester, diethyl ester, dibutyl ester and diphenyl ester of naphthyl carbamic acid; 1,4-, 1,5
Naphthylene carbamic esters such as dimethyl ester, diethyl ester, dibutyl ester and diphenyl ester of-, 1,6- or 2,6-naphthylene carbamic acid; ethylene biscarbanilate, propylene biscarbanilate, glyceryl triscal Polyhydric alcohols such as vanillate and pentaerythryltetrakiscarbanilate, and alkyls such as methylcarbamic acid, ethylcarbamic acid, propylcarbamic acid, butylcarbamic acid, amylcarbamic acid, hexylcarbamic acid, octylcarbamic acid and octadecylcarbamic acid Alkyl carbamates such as methyl ester, ethyl ester, propyl ester, butyl ester and phenyl ester of carbamic acid; cyclopentyl carbamic acid, cyclohexyl Alicyclic carbamates such as methyl ester, ethyl ester and phenyl ester such as rucarbamic acid; ethylene dicarbamic acid, trimethylene dicarbamic acid, tetramethylene dicarbamic acid, pentamethylene dicarbamic acid, hexamethylene dicarbamic acid , 2,2,4- or 2,4,4-trimethyldicarbamic acid and other methyl esters, ethyl esters, phenyl esters and other alkylene dicarbamic esters; methylcyclohexane-2,4 or 2,6
-Dicarbamic acid, methyl 3-carbamate-3,5,
Alicyclic dicarbamic acid diesters such as dimethyl ester, diethyl ester and diphenyl ester such as 5-trimethylcyclohexylcarbamic acid; aralkyldicarbamic acid diesters such as dimethyl ester, diethyl ester and diphenyl ester of xylylenedicarbamic acid; o- , M- or p-chlorophenylcarbamic acid,
Methyl esters such as 2,5-, 3,4- or 3,5-dichlorophenylcarbamic acid, and halogenated phenylcarbamic esters such as ethyl ester and phenyl ester. These carbamates may be used alone or as a mixture of two or more.

The reaction temperature may be any temperature as long as urethane as a raw material is decomposed, but is usually from 140 to 380 ° C.
Is maintained at an appropriate temperature within the range of More preferably 16
In the range of 0-350 ° C, even more preferred is 180-330 ° C
Range. As high a temperature as possible is desirable in order to increase the decomposition rate, but a low temperature is preferable in order to suppress a side reaction, so that an appropriate temperature should be adopted according to each urethane.

The reaction pressure must be such that the reaction temperature evaporates at least one of the decomposition products isocyanate or hydroxyl compound. When a solvent is used, it is necessary to select a pressure that is lower than the boiling point. If these conditions are satisfied, the pressure is reduced, for example, from 1 mmHg to the pressure, for example, 40 kg.
/ Cm ² under a wide range of pressures.

In the practice of the present invention, the reaction time varies depending on the reaction conditions and the like, but is usually 1 to 24 in average residence time.
A range of 0 minutes, preferably 3 to 150 minutes is used. In the method of the present invention, a solvent can be used. The solvent only needs to be substantially inert under thermal decomposition conditions, and it is necessary to select a solvent whose boiling point is higher than the boiling point of at least one of the isocyanate and the hydroxyl compound to be produced. Such solvents include aliphatic, cycloaliphatic or aromatic unsubstituted or substituted hydrocarbons or mixtures thereof, as well as certain oxygen compounds such as ethers, ketones and esters, phosphate esters And phosphorus-containing compounds such as phosphites and sulfur-containing compounds such as thioethers, sulfoxides and sulfones. Preferred solvents include alkanes such as hexane, heptane, octane, nonane, decane, n-hexadecane, n-octadecane, eicosane, squalane and alkenes corresponding thereto; benzene, toluene,
Aromatic hydrocarbons and alkyl-substituted aromatic hydrocarbons such as xylene, ethylbenzene, cumene, diisopropylbenzene, dibutylbenzene, naphthalene, lower alkyl-substituted naphthalene and dodecylbenzene; chlorobenzene,
Aromatic hydrocarbons substituted by nitro groups and halogen groups such as dichlorobenzene, bromobenzene, dibromobenzene, chlornaphthalene, bromonaphthalene, nitrobenzene, and 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; dibutyl phthalate, butyl benzyl phthalate;
Esters such as dioctyl phthalate; phosphorus-containing esters such as tributyl phosphate, tricresyl phosphate, tributyl phosphite and triphenyl phosphite; ethers and esters such as diphenyl ether and diphenyl sulfide; sulfoxides such as dimethyl sulfoxide and diphenyl sulfoxide. Sulfones such as dimethyl sulfone, diethyl sulfone, diphenyl sulfone, and sulfolane; and silicon oil.

When such a solvent is used in an excessively large amount, the space-time yield of isocyanate is deteriorated and the size of the reaction apparatus is increased, so that the weight of the solvent is usually 20 times or less, more preferably 10 times or less, based on the urethane as the raw material. It is used in the range of 2 times or less. The introduction of the solvent into the reaction system may be carried out as a mixture with urethane or separately. Further, a carrier may be used for the purpose of expelling the low-boiling components generated by thermal decomposition more quickly. Examples of such a carrier include inert gases such as nitrogen, argon, helium, carbon dioxide, methane, ethane, and propane; lower hydrocarbons such as pentane, hexane, heptane, and benzene; dichloromethane, chloroform, and carbon tetrachloride. And ethers such as tetrahydrofuran and dioxane.

It is also possible to use a reaction stabilizer as disclosed in, for example, JP-A-1-125359, JP-B-2-11581 and JP-A-1-125359. The method of the invention can be used in batch or continuous reactions,
As for the type of the reaction apparatus, any of those conventionally proposed as a method of thermal decomposition can be adopted. If the isocyanate formed by decomposition in the method of the present invention is obtained as a gas phase component, it is known to those skilled in the art as other gas phase components (for example, a formed hydroxyl compound and optionally a part of the reaction solvent). Separated by method. For example, a method in which a gas phase component is introduced into a distillation column to separate it, a method in which partial separation is performed by a partial condenser, and the like can be mentioned. On the other hand, when the target isocyanate has a high boiling point and can be obtained as a liquid phase component, it can be separated from other liquid phase components (for example, a reaction solvent) by, for example, evaporation after thermal decomposition.

[0028]

Next, the present invention will be described in more detail by way of examples. The present invention is not limited by these examples. In the examples, the molar concentration of the carbamic acid ester is based on urethane as a raw material.

[0029]

EXAMPLE 1 In a 300 cc flask equipped with a stirrer, a Liebig condenser and a thermometer, 45 g of hexamethylenediphenylurethane represented by Ph-OOCNH (CH ₂ ) ₆ NHCOO-Ph, 105 g of tricresyl phosphate and 105 g of PhOOCNH ₂ 1 g (5.8 mol%) of phenyl carbamate represented by the following formula, and the reaction temperature was reduced to 200 ° C. under reduced pressure of 10 mmHg.
It was allowed to react for 0 minutes. The yield of hexamethylene diisocyanate represented by the obtained OCN (CH ₂ ) ₆ NCO was 96%, and the selectivity was 99%. In addition, no solid content floating or adhering to the reaction solution or the reactor after the reaction was observed.

[0030]

Comparative Example 1 A reaction was conducted in the same manner as in Example 1 except that 1 g of phenyl carbamate was not added. Hexamethylene diisocyanate yield: 66%, selectivity: 96%
Met. In addition, no solid content floating or adhering to the reaction solution or the reactor after the reaction was observed.

[0031]

Comparative Example 2 A reaction was carried out in the same manner as in Example 1 except that 20 mg of ferric chloride was added instead of 1 g of phenyl carbamate. The yield of hexamethylene diisocyanate was 91% and the selectivity was 93%. The amount of solids suspended or attached to the reaction solution or the reactor after the reaction is 0.1%.
It was 5 grams.

[0032]

Example 2 As a raw material, 3-
Except that 45 g of phenoxycarbonylaminomethyl-3,5,5-trimethyl-1-phenoxycarbonylaminocyclohexane was used, and 3 g (20 mol%) of phenyl carbamate represented by PhOOCNH ₂ was used, and the reaction temperature was 230 ° C. Was reacted in the same manner as in Example 1. The yield of 3-isocyanatomethyl-3,5,5-trimethyl-1-isocyanatocyclohexane is 9
The selectivity was 2% and the selectivity was 98%. In addition, no solid content floating or adhering to the reaction solution or the reactor after the reaction was observed.

[0033]

Embedded image

[0034]

Example 3 As a raw material, 2,2 represented by the following formula (7):
A method similar to that of Example 1 was used except that 45 g of 4- (phenoxyaminocarbonyl) toluene was used, 105 g of butylbenzyl phthalate and 1 g (9.0 mol%) of ethyl carbamate represented by EtOOCNH ₂ were used. The reaction was performed. The yield of 2,4-diisocyanatotoluene was 92%, and the selectivity was 94%. In addition, no solid content floating or adhering to the reaction solution or the reactor after the reaction was observed.

[0035]

Embedded image

[0036]

According to the method of the present invention, an isocyanate can be obtained with a higher yield and a higher selectivity as compared with the prior art, and there is no precipitation of an insoluble polymer.

Claims (1)

(57) [Claims] 1. A method for producing an isocyanate, which comprises thermally decomposing urethane in the presence of a carbamic acid ester represented by the following formula (1). Embedded image