Method for producing isocyanate

Abstract

Disclosed is a method for stably producing an isocyanate with high yield for a long time without using phosgene. This method for producing an isocyanate does not cause the problems involved in the prior art. Specifically disclosed is a method for producing an isocyanate, which comprises a step wherein a carbamic acid ester is reacted with an aromatic hydroxy compound, thereby obtaining an aryl carbamate having a group derived from the aromatic hydroxy compound, and a step wherein the aryl carbamate is subjected to a decomposition reaction. This method for producing an isocyanate is characterized in that the aromatic hydroxy compound is an aromatic hydroxy compound represented by the formula (1) below, which has a substituent R<1> at at least one ortho-position of the hydroxyl group. In the formula, ring A represents an optionally substituted monocyclic or heterocyclic aromatic hydrocarbon ring having 6-20 carbon atoms; R<1> represents a group other than a hydrogen atom, which is an aliphatic alkyl group having 1-20 carbon atoms, an aliphatic alkoxy group having 1-20 carbon atoms, an aryl group having 6-20 carbon atoms, an aryloxy group having 6-20 carbon atoms, an aralkyl group having 7-20 carbon atoms or an aralkyloxy group having 7-20 carbon atoms, each containing an atom selected from a carbon atom, an oxygen atom and a nitrogen atom; and R<1> and A may combine together to form a ring structure.

Description

technical field [0001] The present invention relates to a method for producing isocyanates. Background technique [0002] Isocyanates are widely used as raw materials for the manufacture of polyurethane foams, coatings, joints, etc. The main industrial production method of isocyanate is the reaction of amines and phosgene (phosgene method), and almost all of the world's production is produced by the phosgene method. However, the phosgene method has many problems. [0003] First, a large amount of phosgene is used as a raw material. Phosgene is extremely toxic, and its handling requires special care in order to prevent phosgene from reaching workers, as well as special devices for decontaminating waste. [0004] Second, in the phosgene method, since a large amount of highly corrosive by-product hydrogen chloride is produced, a process for detoxifying the hydrogen chloride is required. In addition, most of the produced isocyanate contains hydrolyzable chlorine, and the use ...

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Problems solved by technology

[0004] Second, in the phosgene method, since a large amount of highly corrosive by-product hydrogen chloride is produced, a process for detoxifying the hydrogen chloride is required. In addition, most of the produced isocyanate contains hydrolyzable chlorine, and the use of phosgene When the isocyanate produced by the method is used, it may adversely affect the weather resistance and heat resistance of polyurethane products.

However, even for this aromatic polyaryl carbamate, the above-mentioned side reactions often occur at high temperatures such as transesterification and thermal decomposition reactions, and the improvement of the yield of isocyanate is still unfinished. topic

Also, it is known that when N-substituted aromatic carbamates are thermally decomposed in a gas phase or in a liquid phase, various undesired side reactions often occur (for example, refer to the specification of Patent Document 3)

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