Method for producing isocyanate

Abstract

Disclosed is a method for producing an isocyanate, the method comprising a thermal decomposition step for thermally decomposing a carbamic acid ester in the presence of a catalyst that is selected from among a fatty acid metal salt and a phosphoric acid metal salt. The fatty acid metal salt is a compound that is represented by (R11COO)n1M11 or (R12COO)n2M12. (In the formulae, M11 represents a group 1 metal, a group 2 metal, a group 13 metal, or a lanthanoid metal; n1 represents the valence of M11; R11 represents an alkyl group or an alkenyl group; M12 represents a group 3-11 metal or zinc; n2 represents the valence of M12; and R12 represents an alkyl group or an alkenyl group.) The phosphoric acid metal salt is a compound that is represented by (M13)m(PO4)n3. (In the formula, M13 represents a group 1-11 metal, a group 13 metal, zinc, or a lanthanoid metal; and m and n3 satisfy (valence of M13) × m = 3 × n3.)

Description

Isocyanate manufacturing method

[0001] The present disclosure relates to a method for producing isocyanates.

[0002] Isocyanates are widely used as raw materials for polyurethanes, polyureas, etc. The main conventional industrial method for producing isocyanates is the phosgene method, which involves reacting amines with phosgene. However, phosgene is highly toxic and generates highly corrosive hydrochlorides during the reaction. Therefore, efforts have been made to develop methods for producing isocyanates that do not use phosgene.

[0003] As a method for producing an isocyanate without using phosgene, methods have been proposed to produce an isocyanate by thermal decomposition of a carbamic acid ester, using as a catalyst a silicate such as montmorillonite (Patent Document 1, Non-Patent Document 1), a tin catalyst such as dibutyltin dilaurate and tin octoate (Patent Documents 2 to 5), lead octoate (Patent Documents 4 and 5), or an organic sulfonic acid and an alkali metal salt thereof (Patent Document 6).

[0004] European Patent Application Publication No. 1160239 JP 2011-201795 A International Publication No. 2009 / 139062 International Publication No. 2018 / 212208 Japanese Patent Application Publication No. 2019-199426 Japanese Patent Application Publication No. 07-258194

[0005] Tetrahedron Letters, Volume 43, Issue 9, 2002, pp. 1673-1676

[0006] Among the catalysts proposed to date, some require the use of large amounts, and some exhibit a rapid decline in catalytic activity when the reaction temperature is lowered to about 200° C. or lower. Therefore, it has been desired to produce isocyanates by thermal decomposition of carbamic acid esters using a novel catalyst, preferably a catalyst whose catalytic activity does not decline even when the reaction temperature is lowered to about 200° C. or lower.

[0007] An object of the present disclosure is to provide a novel method for producing isocyanates from carbamates in the presence of a catalyst.

[0008] As a result of intensive research aimed at solving the above-mentioned problems, the inventors of the present disclosure have found that isocyanates can be produced by thermally decomposing carbamic acid esters in the presence of specific fatty acid metal salts.

[0009] [1] A method for producing an isocyanate, comprising a thermal decomposition step of thermally decomposing a carbamic acid ester in the presence of one or more catalysts selected from the group consisting of a fatty acid metal salt and a phosphate metal salt, wherein the fatty acid metal salt is a compound represented by the following general formula (IA) or the following general formula (IB), and the phosphate metal salt is a compound represented by the following general formula (IC). (R １１ COO) ｎ１ M １１ (IA) (In general formula (IA), M １１ is a metal of Group 1, Group 2, or Group 13 of the periodic table, or a lanthanide metal; １１ is the valence of R １１ is an alkyl group having 1 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms. １２ COO) ｎ２ M １２ (IB) (In general formula (IB), M １２ is a metal of Groups 3 to 11 of the periodic table or zinc; n2 is M １２ is the valence of R １２ is an alkyl group having 10 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms. １３ ) ｍ (P.O. ４ ) ｎ３ (IC) (In general formula (IC), M １３ is a metal of Groups 1 to 11 of the Periodic Table, a metal of Group 13 of the Periodic Table, zinc, or a lanthanide metal; m and n3 are M １３ [2] The method for producing an isocyanate according to [1], wherein the carbamic acid ester is a compound represented by the following general formula (II): ２１ (NHCOOR ２２ ) ｐ (II) (In general formula (II), R２１ is a p-valent organic group; R ２２ are each independently a hydrocarbon group which may have a substituent; and p is an integer of 1 or more. [3] The method for producing an isocyanate according to [1] or [2], wherein the isocyanate produced by thermal decomposition of the carbamic acid ester is a compound represented by the following general formula (III): ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (III) (In general formula (III), R ３１ is a p-valent organic group; R ２２ are each independently a hydrocarbon group which may have a substituent; p is an integer of 1 or more; and q is an integer of 1 or more and p or less. [4] The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), and R in the general formula (IA) １１ is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms, １２ is an alkyl group having from 12 to 40 carbon atoms or an alkenyl group having from 12 to 40 carbon atoms. [5] The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), and M in the general formula (IA) １１ is a metal of Group 13 of the periodic table, and M in the general formula (IB) １２ is a metal of Groups 8 to 11 of the periodic table or zinc. [6] The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), and M in the general formula (IA) １１ is a metal of Group 13 of the periodic table, and M in the general formula (IB) １２is a metal of Group 8 of the periodic table, a metal of Group 9 of the periodic table, or zinc. [7] The method for producing an isocyanate according to any of [1] to [6], wherein the catalyst is the fatty acid metal salt represented by general formula (IA). [8] The method for producing an isocyanate according to any of [1] to [7], wherein the thermal decomposition is carried out in one or more reaction solvents selected from the group consisting of hydrocarbons and halogenated hydrocarbons.

[0010] According to the present disclosure, a novel method for producing an isocyanate from a carbamate ester in the presence of a catalyst can be provided.

[0011] The present disclosure will be described in detail below. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present disclosure, and the present disclosure is not limited to these contents, and can be implemented in various modifications within the scope of its gist.

[0012] One embodiment of the present disclosure is a method for producing an isocyanate, comprising a thermal decomposition step of thermally decomposing a carbamic acid ester in the presence of one or more catalysts selected from the group consisting of metal salts of fatty acids and metal salts of phosphates.

[0013] [Carbamic acid ester] In the production method according to this embodiment, the carbamic acid ester used as the raw material for the isocyanate is not particularly limited as long as it is a compound having a carbamic acid ester group (-NHCOO-) in one or more of the main backbone, side chain, and terminal of the molecule, and may be selected depending on the isocyanate to be produced. The carbamic acid ester may be a commercially available product or may be produced by a known production method or a production method similar thereto. Known methods for producing carbamic acid esters include, for example, those described in JP 2021-191742 A, JP 2022-022652 A, JP 2022-171090 A, or JP 2022-171090 A.

[0014] Suitable carbamic acid esters in this embodiment include carbamic acid esters represented by the following general formula (II). In this disclosure, unless otherwise specified, when a symbol in one general formula is used in another general formula, the definition of the symbol is the same in all general formulas. R ２１ (NHCOOR ２２ ) ｐ (II)

[0015] In general formula (II), R ２１ is a p-valent organic group. ２１ may have a carbamate group (—NHCOO—), but preferably does not have one.

[0016] The organic group is not particularly limited, and examples thereof include a hydrocarbon group which may have a substituent and a heterocyclic group which may have a substituent. In the present disclosure, the hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic, and may have a carbon-carbon unsaturated bond. -CH in the aliphatic hydrocarbon group ２ - represents -O-, -S-, or -SO ２ The cyclic aliphatic hydrocarbon group, aromatic hydrocarbon group, and heterocyclic group may be monocyclic, polycyclic, or fused ring.

[0017] Of these, the organic group is preferably a hydrocarbon group, more preferably an aromatic hydrocarbon group.

[0018] R ２１ There are no particular limitations on the number of carbon atoms in the hydrocarbon group represented by the formula: When the hydrocarbon group is an aliphatic hydrocarbon group, the number of carbon atoms is usually 1 or more, preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, and is usually 30 or less, preferably 24 or less, more preferably 16 or less, and even more preferably 12 or less. That is, suitable ranges for the number of carbon atoms in the aliphatic hydrocarbon group include 1 or more and 24 or less, 2 or more and 30 or less, 4 or more and 16 or less, and 6 or more and 12 or less.

[0019] In the present disclosure, the number of carbon atoms in a hydrocarbon group or heterocyclic group includes the number of carbon atoms in a substituent group in the case where the hydrocarbon group or heterocyclic group has a substituent.

[0020] Examples of the unsubstituted aliphatic hydrocarbon group include groups in which any p hydrogen atoms have been removed from an alkane such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, and n-eicosane; groups in which any p hydrogen atoms have been removed from a cycloalkane such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, and adamantane; and groups in which any p hydrogen atoms have been removed from an alkene such as ethylene, propylene, butylene, isobutylene, 1-hexene, and 1-octene.

[0021] R ２１ When the hydrocarbon group represented by the formula (I) is an aromatic hydrocarbon group, the number of carbon atoms therein is usually 6 or more, preferably 8 or more, more preferably 10 or more, and usually 30 or less, preferably 24 or less, more preferably 20 or less. That is, suitable ranges for the number of carbon atoms in the aromatic hydrocarbon group include ranges of 6 or more and 24 or less, 8 or more and 30 or less, and 10 or more and 20 or less.

[0022] Examples of the unsubstituted aromatic hydrocarbon group include groups in which any p number of hydrogen atoms have been removed from an aromatic ring such as benzene, naphthalene, phenanthrene, anthracene, fluorene, pyrene, and triphenylene. The aromatic hydrocarbon group also includes a single bond, —CH ２ It may also be a group obtained by removing any p hydrogen atoms from a compound in which a plurality of the above-mentioned cyclic compounds are connected via linking groups such as -, -O-, and -S-. Such a group may be a group obtained by removing one hydrogen atom from each of the p benzene rings in poly(phenylenemethylene).

[0023] R ２１The number of carbon atoms in the heterocyclic group represented by the formula (I) is not particularly limited, but is usually 3 or more, preferably 5 or more, more preferably 10 or more, and is usually 30 or less, preferably 24 or less, more preferably 20 or less. That is, suitable ranges for the number of carbon atoms in the heterocyclic group include ranges of 3 or more and 24 or less, 5 or more and 30 or less, and 10 or more and 20 or less.

[0024] Examples of the unsubstituted heterocyclic group include groups in which p arbitrary hydrogen atoms have been removed from a nitrogen-containing heterocycle such as pyrrolidone, imidazole, pyridine, pyrimidine, triazine, quinoline, phenazine, and carbazole; groups in which p arbitrary hydrogen atoms have been removed from an oxygen-containing heterocycle such as tetrahydrofuran, furan, dioxane, tetrahydropyran, benzofuran, and dibenzofuran; groups in which p arbitrary hydrogen atoms have been removed from a sulfur-containing heterocycle such as tetrahydrothiophene, thiophene, sulfolane, thiane, trithiane, benzothiophene, and dibenzothiophene; and groups in which p arbitrary hydrogen atoms have been removed from a heterocycle containing multiple heteroatoms such as oxazole, thiazole, morpholine, phenoxazine, phenothiazine, and phenoxathiin.

[0025] R ２１When the hydrocarbon group or heterocyclic group represented by the formula (I) has a substituent, the substituent is not particularly limited as long as it does not inhibit thermal decomposition. Examples of the substituent include a deuterium atom; an alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, and a tert-butyl group; a cycloalkyl group having 3 to 6 carbon atoms, such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group; an alkyl group having 1 to 4 carbon atoms, such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a sec-butoxy group, an isobutoxy group, and a tert-butoxy group. cycloalkyloxy groups having from 3 to 6 carbon atoms, such as a cyclopropyloxy group, a cyclobutoxy group, a cyclopentyloxy group, and a cyclohexyl group; aromatic hydrocarbon groups having from 6 to 12 carbon atoms, such as a phenyl group, a 1-naphthyl group, and a 2-naphthyl group; heterocyclic groups, such as a furanyl group, a thienyl group, a morpholino group, and a pyridyl group; aralkyl groups, such as a benzyl group and a 2-phenylethyl group; halogeno groups, such as a fluoro group, a chloro group, a bromo group, and an iodo group; a hydroxy group; and a nitro group.

[0026] In general formula (II), R ２２ are each independently a hydrocarbon group which may have a substituent. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic, and may have a carbon-carbon unsaturated bond. -CH in the aliphatic hydrocarbon group ２ - represents -O-, -S-, or -SO ２ The cyclic aliphatic hydrocarbon group, aromatic hydrocarbon group, and heterocyclic group may be monocyclic, polycyclic, or fused ring.

[0027] R ２２The number of carbon atoms in the hydrocarbon group represented by the formula (I) is not particularly limited, but when the hydrocarbon group is an aliphatic hydrocarbon group, the number of carbon atoms is usually 1 or more, preferably 2 or more, more preferably 3 or more, and usually 30 or less, preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. That is, suitable ranges for the number of carbon atoms in the aliphatic hydrocarbon group include 1 or more and 10 or less, 1 or more and 8 or less, 1 or more and 6 or less, 2 or more and 30 or less, and 3 or more and 6 or less.

[0028] R ２２ Examples of the unsubstituted aliphatic hydrocarbon group represented by the formula (I) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an isobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a 2-ethylhexyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, Examples thereof include an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, an n-icosyl group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclohexylmethyl group, a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a butenyl group, a 2-methylallyl group, a pentenyl group, an isopentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, and isomers thereof.

[0029] R ２２ When the hydrocarbon group represented by the formula (I) is an aromatic hydrocarbon group, the number of carbon atoms therein is usually 6 or more, preferably 8 or more, and usually 30 or less, preferably 20 or less, more preferably 10 or less. That is, suitable ranges for the number of carbon atoms in the aromatic hydrocarbon group include ranges of 6 or more and 10 or less, 6 or more and 20 or less, and 8 or more and 30 or less.

[0030] R ２２Examples of the unsubstituted aromatic hydrocarbon group represented by the formula (I) include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a 9-phenanthrenyl group, a 2-anthracenyl group, a 9-anthracenyl group, a 9-fluorenyl group, and isomers thereof.

[0031] R ２２ When the hydrocarbon group represented by the formula (I) has a substituent, the substituent may be R ２１ When the hydrocarbon group or heterocyclic group represented by the following formula (I) has a substituent, examples of the substituent include the same groups as those of the substituent.

[0032] When the carbamic acid ester is a compound represented by the general formula (II), the carbamic acid ester is thermally decomposed to give the compound R together with the isocyanate. ２２ An alcohol represented by OH is produced. ２２ OH is preferably an alcohol having a boiling point lower than that of the carbamic acid ester and the isocyanate, in that the alcohol produced can be easily removed by distillation when the thermal decomposition of the carbamic acid ester is carried out while the resulting alcohol is being distilled off, or when the alcohol is distilled off after the thermal decomposition. ２２ is preferably an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or an aromatic hydrocarbon group having from 6 to 10 carbon atoms, more preferably an aliphatic hydrocarbon group having from 1 to 8 carbon atoms or an aromatic hydrocarbon group having from 6 to 10 carbon atoms, and even more preferably an aliphatic hydrocarbon group having from 1 to 6 carbon atoms. However, when the alcohol is removed by a method other than distillation, R ２２ R, which has a high boiling point due to thermal decomposition ２２ Even if the group generates OH, there is no particular disadvantage in terms of operation.

[0033] In general formula (II), p is an integer of 1 or more, and its upper limit is not particularly limited. In terms of ease of production and handling and the production of a highly versatile isocyanate, p is preferably 1 or more and 6 or less, more preferably 1 or more and 3 or less, even more preferably 1 or 2, and particularly preferably 2.

[0034] The carbamic acid esters may be used alone or in any combination of two or more in any ratio.

[0035] [Isocyanate] In the production method according to the present embodiment, the isocyanate produced is not particularly limited, but is preferably an isocyanate represented by the following general formula (III). The isocyanate represented by general formula (III) is an isocyanate in which one or more carbamate groups of the carbamic acid ester represented by general formula (II) are converted to an isocyanate group. R ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (III)

[0036] In general formula (III), R ３１ is a p-valent organic group. ３１ is R ２１ or R ２１ R is a group derived from ２１ The group derived from R ２１ may be a group whose structure is changed under the reaction conditions of pyrolysis, and after pyrolysis, R ２１ The structural transformation may be a transformation of a part of the structure, such as the skeleton and functional groups, of the hydroxyl group. Examples of the structural transformation include halogenation, nitration, and hydrogenation, which can be carried out by a known method or a method similar thereto.

[0037] In general formula (III), R ２２ and p are R in general formula (II), respectively. ２２ and p have the same meanings, and the preferred embodiments thereof are also the same.

[0038] In general formula (III), q is an integer of 1 or more and p or less. q is preferably 1 or more and 6 or less, more preferably 1 or more and 3 or less, even more preferably 1 or 2, and particularly preferably 2. In the production method according to this embodiment, it is also preferable that all of the carbamate groups in the carbamic acid ester are converted to isocyanate groups, and therefore it is also preferable that q = p.

[0039] Specific examples of isocyanates produced by the production method of this embodiment include monoisocyanates such as n-butyl isocyanate, tert-butyl isocyanate, n-hexyl isocyanate, n-octyl isocyanate, n-octadecyl isocyanate, cyclohexyl isocyanate, adamantyl isocyanate, benzyl isocyanate, α-methylbenzyl isocyanate, phenyl isocyanate, o-tolyl isocyanate, m-tolyl isocyanate, p-tolyl isocyanate, o-nitrophenyl isocyanate, m-nitrophenyl isocyanate, p-nitrophenyl isocyanate, o-methoxyphenyl isocyanate, m-methoxyphenyl isocyanate, p-methoxyphenyl isocyanate, ethyl 4-isocyanatobenzoate, 2,6-dimethylphenyl isocyanate, 3,5-dimethylphenyl isocyanate, 1-naphthyl isocyanate, and 2-naphthyl isocyanate. Diisocyanates: hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), norbornene diisocyanate, 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 2,2'-diphenylmethane diisocyanate (2,2'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 4,4'-diphenylmethane diisocyanate (4,4'-MD 1), m-xylylene diisocyanate (m-XDI), p-xylylene diisocyanate (p-XDI), tetramethyl xylene diisocyanate (TMXDI), 1,5-naphthalene diisocyanate (1,5-NDI), hydrogenated diphenylmethane diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate (hydrogenated XDI), and polymethylene polyphenylene polyisocyanate; and isomers thereof.

[0040] [Catalyst] The thermal decomposition of the carbamic acid ester is carried out in the presence of one or more catalysts selected from the group consisting of fatty acid metal salts and phosphate metal salts, preferably in the presence of a fatty acid metal salt. The fatty acid metal salt is a compound represented by general formula (IA) or general formula (IB). The fatty acid metal salt may be a hydrate. (R１１ COO) ｎ１ M １１ (IA) (R １２ COO) ｎ２ M １２ (IB)

[0041] In general formula (IA), M １１ is a metal of Group 1 of the periodic table, a metal of Group 2 of the periodic table, a metal of Group 13 of the periodic table, or a lanthanide metal. １１ is preferably a metal of Group 2 of the periodic table, a metal of Group 13 of the periodic table, or a lanthanoid metal, more preferably magnesium, calcium, strontium, barium, aluminum, or cerium, and even more preferably magnesium, aluminum, or cerium. In addition, from the viewpoint of being able to suppress the generation of by-products such as allophanate and isocyanurate due to side reactions such as allophanation and polymerization of isocyanate, or from the viewpoint of low toxicity of fatty acid metal salts, M １１ is preferably a metal of Group 13 of the periodic table, and more preferably aluminum. １１ is preferably a metal of Group 2 or Group 13 of the periodic table, more preferably magnesium or aluminum, and even more preferably aluminum.

[0042] In the general formula (IA), n1 is M １１ and is preferably an integer of 1 or more and 4 or less.

[0043] In general formula (IA), R １１is an alkyl group having from 1 to 40 carbon atoms or an alkenyl group having from 2 to 40 carbon atoms, preferably an alkyl group having from 1 to 40 carbon atoms. That is, the fatty acid metal salt serving as the catalyst may be a saturated fatty acid metal salt or an unsaturated fatty acid metal salt, but is preferably a saturated fatty acid metal salt. The alkyl group and alkenyl group are not limited to linear groups and may have a branched structure or a cyclic structure, but linear groups are preferred in terms of high catalytic activity and ease of availability. Furthermore, the number, position, and bonding style (i.e., geometric isomerism) of the carbon-carbon double bonds in the alkenyl group are not particularly limited.

[0044] R １１ The number of carbon atoms in the alkyl group represented by R is preferably 2 or more, more preferably 12 or more, and even more preferably 16 or more, from the viewpoint of high catalytic activity and solubility, and is preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less. １１ Preferred ranges of the number of carbon atoms in the alkyl group represented by the formula (I) include, for example, 1 or more and 36 or less, 2 or more and 40 or less, 12 or more and 40 or less, 12 or more and 32 or less, and 16 or more and 28 or less.

[0045] R １１Specific examples of the alkyl group represented by the formula (I) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an isobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a 2-ethylhexyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, an n-icosyl group, Examples thereof include an n-heneicosyl group, an n-docosyl group, an n-tricosyl group, an n-tetracosyl group, an n-pentacosyl group, an n-hexacosyl group, an n-heptacosyl group, an n-octacosyl group, an n-nonacosyl group, an n-triacontyl group, an n-hentriacontyl group, an n-dotriacontyl group, an n-tritriacontyl group, an n-tetratriacontyl group, an n-pentatriacontyl group, an n-hexatriacontyl group, an n-heptatriacontyl group, an n-octatriacontyl group, an n-nonatriacontyl group, an n-tetracontyl group, and isomers thereof.

[0046] R １１ The number of carbon atoms in the alkenyl group represented by R12 is usually 2 or more and 40 or less, and from the viewpoint of high catalytic activity and solubility, it is preferably 8 or more, more preferably 12 or more, even more preferably 16 or more, and is preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less. That is, preferred ranges for the number of carbon atoms in the alkyl group and alkenyl group represented by R12 include, for example, 2 or more and 36 or less, 8 or more and 40 or less, 12 or more and 40 or less, 12 or more and 36 or less, 16 or more and 32 or less, and 16 or more and 28 or less.

[0047] R １１Specific examples of the alkenyl group represented by the formula (I) include a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a butenyl group, a 2-methylallyl group, a pentenyl group, an isopentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, a heptadecadienyl group, a heptadecatrienyl group, an octadecenyl group, a nonadecenyl group, a nonadecatetraenyl group, a nonadecapentaenyl group, an icosenyl group, and the like. Examples of the alkyl group include a henicosenyl group, a henicosahexaenyl group, a docosenyl group, a tricosenyl group, a tetracosenyl group, a pentacosenyl group, a hexacosenyl group, a heptacosenyl group, an octacosenyl group, a nonacosenyl group, a triacontenyl group, a hentriacontenyl group, a dotriacontenyl group, a tritriacontenyl group, a tetratriacontenyl group, a pentatriacontenyl group, a hexatriacontenyl group, a heptatriacontenyl group, an octatriacontenyl group, a nonatriacontenyl group, a tetracontenyl group, and isomeric groups thereof.

[0048] In general formula (IB), M １２ is a metal of Groups 3 to 11 of the periodic table or zinc. １２ is preferably a fourth period metal or a fifth period metal in terms of high catalytic activity, more preferably scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, or silver, and even more preferably iron, cobalt, nickel, copper, or zinc. Furthermore, M is a metal having a good balance of high catalytic activity, low toxicity of the fatty acid metal salt, and ability to suppress the generation of by-products such as allophanates and isocyanurates due to side reactions such as allophanation and polymerization of isocyanates. １２ is preferably a metal of Groups 8 to 11 of the periodic table or zinc, and more preferably a metal of Group 8 of the periodic table, a metal of Group 9 of the periodic table, or zinc. １２is preferably iron, cobalt, nickel, copper, or zinc, more preferably iron, cobalt, or zinc, and even more preferably iron or cobalt.

[0049] In general formula (IB), n2 is M １２ and is preferably an integer of 1 or more and 6 or less.

[0050] In general formula (IB), R １２ is an alkyl group having from 10 to 40 carbon atoms or an alkenyl group having from 2 to 40 carbon atoms, preferably an alkyl group having from 10 to 40 carbon atoms. That is, the fatty acid metal salt serving as the catalyst may be a saturated fatty acid metal salt or an unsaturated fatty acid metal salt, but is preferably a saturated fatty acid metal salt. The alkyl group and alkenyl group are not limited to linear groups and may have a branched structure or a cyclic structure, but linear groups are preferred in terms of high catalytic activity and ease of availability. Furthermore, the number, position, and bonding style (i.e., geometric isomerism) of the carbon-carbon double bonds in the alkenyl group are not particularly limited.

[0051] R １２ The number of carbon atoms in the alkyl group represented by R is preferably 12 or more, more preferably 14 or more, and even more preferably 16 or more, from the viewpoint of high catalytic activity and solubility, and is preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less. １２ Preferred ranges of the number of carbon atoms in the alkyl group represented by the formula (I) include, for example, 10 to 36, 12 to 40, 14 to 32, and 16 to 28.

[0052] R １２ The alkyl group represented by R １１ Among the examples of alkyl groups represented by the formula (I), those having 10 or more carbon atoms can be mentioned.

[0053] R １２The number of carbon atoms in the alkenyl group represented by R is preferably 8 or more, more preferably 12 or more, and even more preferably 16 or more, from the viewpoint of high catalytic activity and solubility, and is preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less. １２ Preferred ranges of the number of carbon atoms of the alkenyl group represented by the formula (I) include, for example, ranges of 2 or more and 36 or less, 8 or more and 40 or less, 12 or more and 32 or less, and 16 or more and 28 or less.

[0054] R １２ The alkenyl group represented by R １１ Examples of the alkenyl group represented by the following formula include those given as examples.

[0055] In summary, examples of fatty acid metal salts include salts of the above metals of fatty acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, erucic acid, linoleic acid, α-linolenic acid, γ-linolenic acid, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid.

[0056] Specific examples of fatty acid metal salts include cerium acetate, magnesium laurate, calcium laurate, strontium laurate, barium laurate, iron laurate, cobalt laurate, nickel laurate, copper laurate, zinc laurate, aluminum laurate, cerium laurate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, nickel stearate, copper stearate, zinc stearate, aluminum stearate, and cerium laurate. Examples of the oleic acid salt include cerium phosphate, magnesium palmitate, calcium palmitate, strontium palmitate, barium palmitate, iron palmitate, cobalt palmitate, nickel palmitate, copper palmitate, zinc palmitate, aluminum palmitate, cerium palmitate, magnesium oleate, calcium oleate, strontium oleate, barium oleate, iron oleate, cobalt oleate, nickel oleate, copper oleate, zinc oleate, aluminum oleate, and cerium oleate. Of these, the fatty acid metal salt is preferably cerium acetate, magnesium laurate, calcium laurate, strontium laurate, barium laurate, iron laurate, cobalt laurate, zinc laurate, aluminum laurate, cerium laurate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, zinc stearate, aluminum stearate, or cerium stearate, and more preferably cerium acetate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, zinc stearate, aluminum stearate, or cerium stearate.

[0057] The fatty acid metal salt may be a commercially available product, or may be synthesized by a known production method or a production method similar thereto, for example, by a neutralization reaction between a fatty acid and a base containing the above metal.

[0058] The metal phosphate used as a catalyst in the thermal decomposition step is represented by the following general formula (IC). The metal phosphate may be a hydrate. (M １３ ) ｍ (P.O. ４ ) ｎ３ (IC)

[0059] In the general formula (IC), M １３ is a metal of Groups 1 to 11 of the periodic table, a metal of Group 13 of the periodic table, zinc, or a lanthanide metal.

[0060] In the general formula (IC), m and n3 are M １３ The valence of m×m=3×n3 is preferably the minimum value among the values ​​that satisfy the above formula, and for example, M １３ is trivalent cerium, then m is 1 and n3 is 1.

[0061] Specific examples of metal phosphates include sodium phosphate, potassium phosphate, magnesium phosphate, calcium phosphate, barium phosphate, zinc phosphate, aluminum phosphate, and cerium phosphate.

[0062] Generally, homogeneous catalysts exhibit higher catalytic activity than heterogeneous catalysts. Therefore, when the thermal decomposition is carried out in a solvent, the catalyst in this embodiment is preferably selected from those which are highly soluble in the solvent and which are liquid under the reaction conditions. When the thermal decomposition is carried out without a solvent, the catalyst is preferably selected from those which are liquid under the reaction conditions. From this viewpoint, the catalyst used in the thermal decomposition step is preferably a fatty acid metal salt represented by general formula (IA) or general formula (IB), and is represented by general formula (IA) and R １１ is a long-chain fatty acid metal salt represented by general formula (IB), １２ is more preferably a metal salt of a long-chain fatty acid in which R is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms.

[0063] The catalyst may be used alone or in any combination of two or more in any ratio.

[0064] The amount of catalyst used in the thermal decomposition step may be appropriately selected depending on the type of carbamic acid ester, the type of catalyst, the reaction conditions, etc. When multiple types of catalysts are used, the amount of catalyst means the total amount thereof.

[0065] Specifically, the amount of catalyst relative to the carbamic acid ester (the amount of catalyst when the amount of carbamic acid ester is taken as 100.0 mol%) is not particularly limited, but is usually 0.5 mol% or more, preferably 1.0 mol% or more, more preferably 4.0 mol% or more, and even more preferably 5.0 mol% or more, and is usually 100.0 mol% or less, preferably 90.0 mol% or less, more preferably 70.0 mol% or less, and even more preferably 30.0 mol% or less. That is, preferred ranges of the catalyst amount include, for example, 0.5 mol% to 90.0 mol%, 1.0 mol% to 100.0 mol%, 4.0 mol% to 70.0 mol%, and 5.0 mol% to 30.0 mol%.

[0066] Alternatively, the amount of catalyst relative to the carbamic acid ester (the amount of catalyst when the amount of carbamic acid ester is taken as 100% by weight) is not particularly limited, but is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, and even more preferably 20% by weight or more, and is usually 100% by weight or less, preferably 80% by weight or less, more preferably 50% by weight or less, and even more preferably 30% by weight or less. That is, preferred ranges of the catalyst amount include, for example, from 1% by weight to 80% by weight or less, preferably from 5% by weight to 100% by weight, from 10% by weight to 50% by weight or less, and from 20% by weight to 30% by weight.

[0067] [Reaction Solvent] Pyrolysis may be carried out in a reaction solvent or without a solvent. When the pyrolysis is carried out in a reaction solvent, the carbamic acid ester, the catalyst, etc. are dissolved to make the reaction system homogeneous, and the concentration of each component can be easily adjusted. Therefore, pyrolysis in a reaction solvent is preferred in that the reaction is easily controlled. On the other hand, when the pyrolysis is carried out without a solvent, there are advantages such as an increased opportunity for contact between the carbamic acid ester and the catalyst, which improves the reaction rate and enables a shorter reaction time, or enables the catalytic reaction at a lower reaction temperature, and this is therefore preferred.

[0068] In the present disclosure, "solvent-free" means that no liquid other than the reaction substrates, catalyst, product, and compounds derived therefrom is used. Therefore, for example, even if a fatty acid metal salt that exists as a liquid under the reaction conditions also functions as a solvent, the fatty acid metal salt is not considered to be a reaction solvent, and the thermal decomposition is considered to be carried out "solvent-free."

[0069] When the thermal decomposition is carried out in a reaction solvent, the reaction solvent is preferably an inert solvent that does not react with the carbamic acid ester, the catalyst, and the isocyanate. Preferred examples of the inert solvent include hydrocarbons and halogenated hydrocarbons.

[0070] Examples of hydrocarbons include aliphatic hydrocarbons such as n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tetradecane, n-octadecane, bicyclohexyl, and decalin; aromatic hydrocarbons such as benzene, toluene, ethylbenzene, butylbenzene, dodecylbenzene, o-xylene, m-xylene, p-xylene, p-cymene, naphthalene, and biphenyl; and partially hydrogenated aromatic hydrocarbons such as cyclohexylbenzene and tetralin. Among aliphatic hydrocarbons, decalin is preferred. Furthermore, among aromatic hydrocarbons, linear alkylbenzenes such as butylbenzene and dodecylbenzene are preferred.

[0071] Examples of halogenated hydrocarbons include 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, 1,2,3-trichloropropane, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, 1,2,4-trichlorobenzene, and bromobenzene.

[0072] Among the above reaction solvents, the reaction solvent is preferably one or more selected from decalin, dodecylbenzene, o-xylene, m-xylene, p-xylene, and o-dichlorobenzene, and more preferably one or more selected from decalin and dodecylbenzene. Furthermore, when the reaction is carried out while distilling off alcohol produced together with the isocyanate, the reaction solvent preferably has a boiling point higher than that of the alcohol and lower than that of the isocyanate.

[0073] The reaction solvent may be used alone or in any combination of two or more in any ratio.

[0074] [Reaction Temperature] The reaction temperature in the pyrolysis step is usually 100°C or higher and 300°C or lower, and from the viewpoint of increasing the reaction rate while suppressing side reactions, it is preferably 150°C or higher and 280°C or lower, more preferably 180°C or higher and 260°C or lower, and even more preferably 200°C or higher and 240°C or lower.

[0075] [Reaction Time] The reaction time in the thermal decomposition step is not particularly limited and may be appropriately adjusted depending on the type of catalyst, reaction temperature, reaction scale, etc. Specifically, the reaction time is preferably 0.5 hours to 72.0 hours, more preferably 1.0 hours to 72.0 hours, even more preferably 5.0 hours to 60.0 hours, even more preferably 12.0 hours to 48.0 hours, and particularly preferably 16.0 hours to 36.0 hours. The reaction time may also be 0.5 hours to 48.0 hours, 1.0 hours to 24.0 hours, or 2.0 hours to 12.0 hours. By setting the reaction time within the above range, the thermal decomposition of the carbamic acid ester can be sufficiently promoted, and side reactions such as allophanation and polymerization of the produced isocyanate can be suppressed.

[0076] [Operation Procedure] The method for producing an isocyanate according to this embodiment can be carried out, for example, by the following procedure. First, a carbamic acid ester, a catalyst, and, if necessary, a reaction solvent are supplied to a reactor. This operation may be carried out under an air atmosphere or an inert gas atmosphere such as nitrogen or argon. However, since thermal decomposition is preferably carried out under an inert gas atmosphere, it is preferable to carry out the operation under an inert gas atmosphere. Next, the resulting reaction solution is heated to a predetermined temperature to carry out thermal decomposition of the carbamic acid ester. The reaction pressure is not particularly limited and may be set appropriately depending on the type of reaction solvent and the reaction temperature. It is preferable to stir the reaction solution during thermal decomposition. The method for stirring the reaction solution is not particularly limited, and for example, a method of stirring the reaction solution using a stirring means such as a magnetic stirrer or a stirring blade can be used. The thermal decomposition of the carbamic acid ester may be carried out while distilling off the produced alcohol.

[0077] The method for producing an isocyanate according to this embodiment may include any optional step in addition to the thermal decomposition step. For example, the optional step may include a purification step for increasing the purity of the isocyanate. Purification methods for the isocyanate in the purification step may be those commonly used in the field of organic synthesis, such as filtration, adsorption, column chromatography, and distillation.

[0078] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure. In the examples, "room temperature" refers to a temperature range of 15°C or higher and 35°C or lower.

[0079] [ １ H NMR measurement] １ The product yield was calculated by H NMR. １ The H NMR measurement conditions were as follows: Apparatus name: ADVANCE-III (manufactured by Bruker) Frequency: 400 MHz Solvent: (CD ３ ) ２ CO or (CD ３ ) ２ SO

[0080] [Example 1, Comparative Example 1]

[0081] In a glove box filled with nitrogen, a 100 mL three-neck flask was charged with the catalyst shown in Table 1, 500 mg of methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me), and 20 mL of dodecylbenzene. After sealing the three-neck flask, it was taken out of the glove box and a condenser and a diaphragm pump with a pressure controller were attached to the three-neck flask.

[0082] The reaction was carried out at 220°C while controlling the internal pressure of the three-neck flask at 20 torr, and then the reaction mixture was cooled to room temperature. 20 mL of N-methyl-2-pyrrolidone was added to the reaction mixture to dissolve the precipitated methylenediphenyl 4,4'-dimethylcarbamate. 200 mg of trimethoxybenzene was added to the resulting solution as an internal standard. １ The yield of the product and the recovery rate of the raw material were calculated by H NMR measurement. The results are shown in Table 1.

[0083]

[0084] From Example 1 and Comparative Example 1, it was confirmed that when cerium stearate was used as a catalyst under a temperature condition of 220°C, isocyanate was obtained in a yield similar to that when five times the amount (by weight) of montmorillonite was used as a catalyst. This indicates that cerium stearate has high catalytic activity.

[0085] [Examples 2-1 to 2-2, Comparative Example 2-1]

[0086] In a glove box filled with nitrogen, a 100 mL three-neck flask was charged with the catalyst shown in Table 2, 500 mg of methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me), and 20 mL of dodecylbenzene. After sealing the three-neck flask, it was taken out of the glove box and a condenser and a diaphragm pump with a pressure controller were attached to the three-neck flask.

[0087] The reaction was carried out at 190°C while controlling the internal pressure of the three-neck flask at 5 torr, and then the reaction mixture was cooled to room temperature. 20 mL of N-methyl-2-pyrrolidone was added to the reaction mixture to dissolve the precipitated methylenediphenyl 4,4'-dimethylcarbamate. 200 mg of trimethoxybenzene was added to the resulting solution as an internal standard. １ The yield of the product and the recovery rate of the raw material were calculated by H NMR measurement. The results are shown in Table 2.

[0088]

[0089] Examples 2-1 to 2-2 and Comparative Example 2-1 were used to investigate the reactivity of montmorillonite under low-temperature conditions (190°C), at which the catalytic activity of montmorillonite decreases. Table 2 shows that when cerium stearate is used as a catalyst, a product in which all carbamate groups are converted to isocyanate groups can be obtained in higher yield than when montmorillonite is used as a catalyst, even if the catalyst amount is smaller and the reaction time is shorter.

[0090] [Examples 3-1 to 3-6]

[0091] In a glove box filled with nitrogen, a catalyst shown in Table 3, 500 mg of methyl 4-butylphenylcarbamate, and 20 mL of decalin were placed in a 100 mL three-neck flask. After tightly sealing the three-neck flask, it was taken out of the glove box, and a condenser and a diaphragm pump with a pressure controller were attached to the three-neck flask.

[0092] The reaction was carried out at 190°C while controlling the internal pressure of the three-neck flask at 400 torr, and then the reaction mixture was cooled to room temperature. 20 mL of N-methyl-2-pyrrolidone was added to the reaction mixture to dissolve the precipitated methyl 4-butylphenylcarbamate. 200 mg of trimethoxybenzene was added to the resulting solution as an internal standard. １ The yield of the product and the recovery rate of the raw material were calculated by H NMR measurement. The results are shown in Table 3.

[0093]

[0094] Examples 3-1 to 3-6 confirmed that fatty acid metal salts, regardless of the metal species, exhibit catalytic activity in the reaction of decomposing carbamic acid esters to obtain isocyanates. Examples 3-1 to 3-6 also demonstrate that, among fatty acid metal salts, calcium salts and barium salts of fatty acids have particularly high catalytic activity. Furthermore, it was also demonstrated that the use of aluminum salts, zinc salts, iron salts, or cobalt salts of fatty acids as catalysts inhibits the allophanation and polymerization of isocyanates produced by thermal decomposition, allowing the target isocyanates to be selectively obtained.

[0095] [Examples 4-1 to 4-4]

[0096] In a glove box filled with nitrogen, a catalyst shown in Table 4 (1.25 mol % relative to 4-BuPhMeC), 1 g of methyl 4-butylphenylcarbamate (4-BuPhMeC), and 20 mL of decalin were placed in a 100 mL test tube. After sealing the test tube with a three-way stopcock and a septum, the tube was taken out of the glove box and a syringe needle connected to a mass flow controller was attached.

[0097] The reaction was carried out at 190°C while introducing nitrogen into the test tube so that nitrogen circulated above the reaction solution at 50 mL / min, and then the reaction mixture was cooled to room temperature. 15 mL of N-methyl-2-pyrrolidone was added to the reaction mixture, and the precipitated methyl 4-butylphenylcarbamate was dissolved. 300 mg of trimethoxybenzene was added to the resulting solution as an internal standard, and １ The yield of the product and the recovery rate of the raw material were calculated by H NMR measurement. The results are shown in Table 4.

[0098]

[0099] Examples 4-1 to 4-4 confirmed that fatty acid metal salts, regardless of the metal species, exhibit catalytic activity in the reaction of decomposing a carbamic acid ester to obtain an isocyanate. Furthermore, as can be seen from Examples 4-1 to 4-4, among fatty acid metal salts, zinc salts and copper salts of fatty acids have particularly high catalytic activity and can also suppress allophanation and polymerization of the resulting isocyanate. Therefore, by thermally decomposing a carbamic acid ester in the presence of a zinc salt and a copper salt of a fatty acid, the target isocyanate can be obtained selectively and in high yield.

[0100] [Examples 5-1 to 5-3]

[0101] In a glove box filled with nitrogen, a 100 mL two-neck flask was charged with the catalyst shown in Table 5, 500 mg of methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me), and 5 mL of decalin. After sealing the two-neck flask, it was taken out of the glove box and a condenser and a diaphragm pump with a pressure controller were attached to the two-neck flask.

[0102] The reaction was carried out at 210°C while controlling the internal pressure of the two-neck flask at 712 torr, and then the reaction mixture was cooled to room temperature. 20 mL of N-methyl-2-pyrrolidone was added to the reaction mixture to dissolve the precipitated methylenediphenyl 4,4'-dimethylcarbamate. 200 mg of trimethoxybenzene was added to the resulting solution as an internal standard. １The yield of the product and the recovery rate of the raw material were calculated by H NMR measurement. The results are shown in Table 5.

[0103]

[0104] Examples 5-1 to 5-3 show that as the reaction time is increased, the thermal decomposition of the carbamic acid ester progresses and the proportion of carbamate groups converted to isocyanate groups increases. This shows that by controlling the reaction time, it is possible to selectively produce a compound having a desired ratio of carbamate groups to isocyanate groups. It also shows that by carrying out the reaction for a long period of time, it is possible to selectively produce a compound in which all carbamate groups are converted to isocyanate groups.

[0105] According to the present disclosure, there is provided a method for producing an isocyanate by thermally decomposing a carbamic acid ester in the presence of one or more catalysts selected from the group consisting of a fatty acid metal salt and a phosphate metal salt. This production method can produce an isocyanate that can be used as a raw material for chemical products such as polyurethane and polyurea without using phosgene, and therefore has high industrial utility value.

Claims

1. A method for producing an isocyanate, comprising a thermal decomposition step of thermally decomposing a carbamic acid ester in the presence of one or more catalysts selected from the group consisting of a fatty acid metal salt and a phosphate metal salt, wherein the fatty acid metal salt is a compound represented by the following general formula (IA) or the following general formula (IB), and the phosphate metal salt is a compound represented by the following general formula (IC). (R １１ COO) ｎ１ M １１ (IA) (In general formula (IA), M １１ is a metal of Group 1, Group 2, or Group 13 of the Periodic Table, or a lanthanide metal; １１ is the valence of; R １１ is an alkyl group having 1 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms. １２ COO) ｎ２ M １２ (IB) (In general formula (IB), M １２ is a metal of Groups 3 to 11 of the Periodic Table or zinc; n2 is M １２ is the valence of; R １２ is an alkyl group having 10 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms. １３ ) ｍ (P.O. ４ ) ｎ３ (IC) (In general formula (IC), M １３ is a metal of Groups 1 to 11 of the Periodic Table, a metal of Group 13 of the Periodic Table, zinc, or a lanthanide metal; m and n3 are M １３ The valence of x m = 3 x n3 is satisfied.) 2. The method for producing an isocyanate according to claim 1, wherein the carbamic acid ester is a compound represented by the following general formula (II): ２１ (NHCOOR ２２ ) ｐ (II) (In general formula (II), R ２１ is a p-valent organic group; R ２２ each independently represents a hydrocarbon group which may have a substituent; and p is an integer of 1 or more.

3. The method for producing an isocyanate according to claim 2, wherein the isocyanate produced by thermal decomposition of the carbamic acid ester is a compound represented by the following general formula (III): ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (III) (In general formula (III), R ３１ is a p-valent organic group; R ２２ and p are each R in general formula (II). ２２ and p; q is an integer of 1 to p.

4. The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), １１ is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms, １２ The method for producing an isocyanate according to claim 1, wherein is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms.

5. The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), １１ is a metal of Group 13 of the periodic table, １２ The method for producing an isocyanate according to claim 1, wherein is a metal of Groups 8 to 11 of the periodic table or zinc.

6. The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), １１ is a metal of Group 13 of the periodic table, １２ The method for producing an isocyanate according to claim 1 , wherein is a metal of Group 8 of the periodic table, a metal of Group 9 of the periodic table, or zinc.

7. The method for producing an isocyanate according to claim 1, wherein the catalyst is the fatty acid metal salt represented by the general formula (IA).

8. The method for producing an isocyanate according to claim 1, wherein the thermal decomposition is carried out in one or more reaction solvents selected from the group consisting of hydrocarbons and halogenated hydrocarbons.

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