JPS6052693B2 - Method for producing isocyanate from carbamate ester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing isocyanates from carbamate esters.

Isocyanates such as tolylene diisocyanate are extremely useful as raw materials for polyurethane.

Conventionally, for example, as an industrial method for producing tolylene diisocyanate, a method has been known in which tolylene diamine is nitrated and further reduced to form a hydrochloride, and then reacted with phosgene. However, this method not only requires a complicated process, but also has problems such as the use of phosgene, which is a harmful gas, and severe corrosion of the equipment by hydrogen chloride generated during phosgenation.

Therefore, in recent years, a method for producing isocyanate that does not use phosgene has been desired, and several methods have been proposed.

For example, a nitro compound is reacted with alcohol or phenol and carbon monoxide in the presence of a platinum group metal or selenium-based catalyst to obtain a carbamate ester;
A method has been proposed in which isocyanate is obtained by thermally decomposing this at a high temperature of, for example, 150 to 550°C.
This method does not pose many problems if a suitable catalyst is used in the process of producing the carbamate ester, but it has the drawback that various side reactions occur in the thermal decomposition process and a large amount of high-boiling byproducts are produced. This is because under high temperature conditions such as thermal decomposition conditions, the reactivity of isocyanates becomes particularly high, and isocyanates may oligomerize with each other in the reaction system, or reactions may occur between isocyanates and carbamate esters or intermediates. This is thought to be due to the following. This trend is
This is significant when using a conventionally known catalyst for thermal decomposition. That is, when a known catalyst is used, the rate of thermal decomposition becomes faster, but the amount of high-boiling by-products produced increases almost in proportion to this. Conventionally, as a catalyst for thermal decomposition, for example, IB)■B)■A)■A)■
B) Method using group ■ metal compounds (Japanese Unexamined Patent Publication No. 52-1
No. 9624), but even when these catalysts are used, the amount of high-boiling by-products produced is still high.
The present inventors investigated various methods for decomposing carbamate esters that produce very few high-boiling point byproducts, and found that when carrying out the reaction using a specific catalyst,
The present invention was completed by discovering that the reaction rate is fast and the amount of by-products is extremely small. That is, the gist of the present invention is a method of thermally decomposing a carbamate ester to obtain a vapor containing isocyanate and alcohol or phenol, and then condensing and separating the isocyanate, using an alkaline earth metal and/or as a catalyst for thermal decomposition. The present invention relates to a method for producing isocyanate from carbamate ester, characterized by using the inorganic compound.

The present invention will be explained in detail below. Carbamate esters used as raw materials in the present invention include monovalent to trivalent aliphatic, aromatic, or alicyclic isocyanates, and monovalent to tetravalent isocyanates. Examples include adducts with aliphatic, aromatic, and alicyclic alcohols or phenols.

In addition, these carbamate esters contain halogen atoms,
It may have a substituent that does not react with the isocyanate group, such as a nitro group, a cyano group, an alkyl group, an alkoxy group, an acyl group, an acyloxy group, a carbonyl group, or the isocyanate group itself. Specific examples of carbamate esters include:
For example, methyl carbanilate, ethyl carbanilate,
Propyl carbanilate, butyl carbanilate, ethylene dicarbanilate, trimethylene dicarbanilate, ethylnaphthalene-1-carbamate, diethylanthracene-9/10-dicarbamate, ethylene bis(P-phenylcarbanilate), Methyl-Sec-
Butyl carbutter. Examples include ethyl-4-methyl-3-nitrocarbanilate, dimethyltoluene-2●4-dicarbamate, and diethyl-4-chlorobenzene-1●3-dicarbamate. In the present invention, carbamate esters, which are addition products of aromatic polyhydric isocyanates and monohydric alcohols, are preferably used. This is carried out by contacting the carbamic acid ester, and the heat medium used in this case is preferably one that is liquid under the reaction conditions and is inert to the reaction raw materials and products.

Examples include triaryl dimethane isomers, diphenyl sulfone, silicone oil, diphenyl sulfoxide, and diphenyl methane, which are commonly used as heat transfer media. The present invention requires the use of an alkaline earth metal and/or its inorganic compound as a catalyst.

Specific examples of these catalysts include metals such as magnesium, calcium, barium, strontium, beryllium, and radium, as well as inorganic compounds such as oxides, halides, sulfides, and inorganic acid salts of these metals such as sulfates and nitrates. Among them, metals or oxides of magnesium and calcium are preferred. Two or more of these catalysts may be used in combination. For example, when the thermal decomposition reaction is carried out in a batch method, the amount of the catalyst of the present invention used is usually 0.001 to 10% by weight, preferably 0.01 to 10% by weight based on the heat medium. In addition, in the case of a continuous method, the amount is 0.001 to 10 n101 per 1 m01 of carbamate ester supplied to the reaction system per unit time.

In the present invention, the catalyst hardly dissolves in the heat medium and is in a suspended state, and it is usually preferable to use a powdered catalyst pulverized to an average particle size of 50 μm or less. Thermal decomposition conditions in the present invention are not particularly limited, but usually the reaction temperature is 18
0 to 350°C, preferably 230 to 280°C, under normal pressure or reduced pressure, for example, 100W! Under reduced pressure of 1Hg or less,
The reaction is carried out with a residence time of 1 minute or less, preferably 5 minutes or less.

To carry out the present invention, for example, a carbamic acid ester dissolved in a heating medium containing a predetermined amount of catalyst is supplied under stirring, and thermally decomposed at a predetermined temperature and pressure, and the generated isocyanate and alcohol are A method is adopted in which the vapor containing isocyanate is extracted from the upper part of the reactor, and then the isocyanate is condensed and recovered.

As explained above, according to the present invention, by using a specific catalyst for thermal decomposition of carbamate ester, the generation of high-boiling by-products is extremely reduced, and isocyanate can be obtained efficiently and economically. It is advantageous for

Further, according to the present invention, there is less contamination of the heat medium, which is preferable from the viewpoint of manufacturing. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 A round-bottom flask having a raw material supply port, a gas discharge port, and a nitrogen gas inlet pipe was placed in an oil bath equipped with a thermoregulator, and a Dimroth condenser was installed at the gas discharge port.

Heat medium (manufactured by Hüls Chemical Co., Ltd., trade name: Marotherm S) 95y and magnesium oxide powder 0.1 as a catalyst
Charge 51y into the flask and add nitrogen gas to the liquid.
It was circulated at 5ccImin, and the internal temperature was raised to 250°C.

Next, 5V of diethyltoluenedicarbamate was added to the heating medium from the raw material supply port to initiate a thermal decomposition reaction.
I was in between. The vapor generated by the reaction was cooled to 25° C. in the cooler, and tolylene diisocyanate, monocarbamate, etc. were recovered in liquid form. On the other hand, non-condensable gas was continuously sampled and the amount of ethanol in the gas was measured using gas chromatography. From the measured amount of ethanol, the thermal decomposition rate for the amount of raw material supplied for the three powders was calculated. Further, after the reaction was completed, the heating medium was cooled and filtered to separate the solid content, and the ratio of the solid content to the amount of raw material supplied (Hartz production rate) was calculated. These results were as shown in Table 1. Examples 2 to 5 Thermal decomposition was carried out in the same manner as in Example 1, except that various catalysts shown in Table 1 were used instead of magnesium oxide.

The results are shown in Table 1. Comparative Examples 1 to 5 In Example 1, various catalysts other than the catalysts of the present invention shown in Table 1 were used instead of magnesium oxide, or the same method as Example 1 was used except that no catalyst was used. Thermal decomposition was carried out.

The results are shown in Table 1. From the above results, it can be seen that the catalysts of the present invention have no Hartz formation at all and the thermal decomposition rate is high, and in the case of the comparative example, even when the thermal decomposition rate is low or high, the amount of Hartz formation is low. It turns out that there are many.

Example 6 The reaction was carried out in the same manner as in Example 1 except that the thermal decomposition temperature was changed to 201'C. The thermal decomposition rate was 27.4% and the Hartz production rate was 0%.

Claims (1)

[Claims] 1. Using an alkaline earth metal and/or its inorganic compound as a catalyst for thermal decomposition in a method of thermally decomposing a carbamate ester to obtain a vapor containing isocyanate and alcohol or phenol, and then condensing and separating the isocyanate. A method for producing isocyanate from carbamate ester, characterized by: