JP7849679B2 - Method for producing carbamic acid esters - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law: CO2 Resource Recycling Technologies for De-petroleum Regeneration - Focusing on Chemical and Biological Processes, pp. 165-171, CMC Publishing Co., Ltd., Publication Date: July 31, 2020.

This invention relates to a method for producing carbamic acid esters.

Carbamic acid esters are useful compounds with a wide range of applications in pharmaceuticals, agrochemicals, various fine chemicals, and as raw materials for their synthesis.

To date, methods for producing carbamic acid esters using carbon dioxide at atmospheric pressure have been proposed.
For example, Non-Patent Document 1 describes a multi-component synthesis method for carbamate derivatives, which involves the in situ synthesis of ammonium carbamate, equivalent amounts of triphenylphosphine, and equivalent amounts of trichloroisocyanuric acid (TCCA) from the reaction of an amine _as a carbonyl source with CO2. Non-Patent Document 1 uses _CO2 gas at 1 atmosphere and employs non-renewable sacrificial reagents.
Non-patent document 2 reports a method for synthesizing carbamic acid esters via carbamic acid using 1,8-diazabicyclo[5.4.0]undeca-7-ene as a catalyst, with _CO2 gas at 1 atmosphere. Non-patent document 2 uses _PBu3 and DBAD (azodicarboxylate di-tert-butyl) as non-renewable sacrificial reagents.
Non-patent document 3 reports the synthesis of carbamic acid esters from amines and _CO2 gas using non-renewable sacrificial reagents such as _KO2 / _Et4NBr .
Non-patent document 4 reports the synthesis of carbamic acid esters via the Mitsunobu reaction using _CO2 gas at 1 atmosphere and carbamic acid, with the sacrificial reagents _Ph3P and DEAD (diethyl azodicarboxylate).

S. S. E. Ghodsinia, B. Akhlaghinia, Phosphorus Sulfur Silicon Relat. Elem., 2016, vol.191, p.1-7 Scott L. Peterson, Sabrina M. Stucka, Christopher J. Dinsmore, Org. Lett. 2010, 12, p.1340-1343 Krishna Nand Singh, Synth. Commun. 2007, 37, p.2651-2654 Devdutt Chaturvedi, Nisha Mishra, Virendra Mishra, Monats. Chem. 2007, 138, p.57-60

All of the above methods for producing carbamic acid esters require either a sacrificial reagent or an alkyl halide with poor environmental compatibility.
The object of this invention is to provide a method for producing carbamic acid esters using carbamic acid salts as raw materials, without using sacrificial reagents or alkyl halides.

The inventors of this invention conducted extensive research to solve the above problems and, as a result, discovered that carbamate esters can be produced from carbamate salts and metal alkoxides, thus completing the present invention.
The present invention provides the following specific embodiments, etc.
[1] From a carbamate salt and a metal alkoxide, the following formula (a-1) or (a-2)
A method for producing a carbamic acid ester, characterized by producing a carbamic acid ester having the structure represented by .
(In the above formula, ^R1 independently represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, ^R2 and ^R3 independently represent an unsubstituted or substituted monovalent hydrocarbon group, and ^R20 represents an unsubstituted or substituted divalent hydrocarbon group.)
[2] The method for producing a carbamic acid ester according to [1], wherein the carbamic acid salt is a carbamic acid salt represented by formula (B-1), the metal alkoxide is a metal alkoxide represented by formula (C-1), and the carbamic acid ester having the structure represented by formula (a-1) is a carbamic acid ester represented by formula (A-1).
(In the above formula, R ¹¹ represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group; R ²¹ and R ³¹ each independently represent an unsubstituted or substituted monovalent hydrocarbon group; R ⁴¹ each independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand different from -OR ³¹ ; M represents a metal atom or metalloid atom; n represents the oxidation state of M, where (n-m) is an integer from 1 to 6; m represents an integer between 0 and (n-1), and Q represents a q-valent countercation; q is 1 or 2.)
[3] The method for producing a carbamic acid ester according to [2], wherein Q is a cation selected from the group consisting of ammonium cation, amidinium cation, guanidinium cation, phosphonium cation, phosphazenium cation, carbocation, alkali metal cation, and alkaline earth metal cation.
[4] The method for producing a carbamic acid ester according to [1], wherein the carbamic acid salt is a carbamic acid salt represented by formula (B-2), the metal alkoxide is a metal alkoxide represented by formula (C-2), and the carbamic acid ester having the structure represented by formula (a-2) is a carbamic acid ester represented by formula (A-2).
(In the above formula, R ¹² each independently represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group; R ²² represents an unsubstituted or substituted divalent hydrocarbon group; R ³² each independently represents an unsubstituted or substituted monovalent hydrocarbon group; R ⁴² each independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand different from -OR ³² ; M' represents a metal atom or metalloid atom, n' represents the oxidation state of M', (
n'-m') is an integer between 1 and 6; m' represents an integer greater than or equal to 0 and less than or equal to (n'-1); Q
' represents a (2/q') valent countercation; q' is 1 or 2.
[5] The method for producing a carbamic acid ester according to [4], wherein Q' is a cation selected from the group consisting of ammonium cation, amidinium cation, guanidinium cation, phosphonium cation, phosphazenium cation, carbocation, alkali metal cation, and alkaline earth metal cation.
[6] The method for producing a carbamic acid ester according to any one of [1] to [5], wherein the metal alkoxide is at least one selected from the group consisting of titanium compounds and silicon compounds.
[7] The method for producing a carbamic acid ester according to any one of [1] to [6], wherein the metal alkoxide is an alkoxysilane and the reaction step is carried out in the presence of a catalyst.
[8] The method for producing a carbamic acid ester according to [7], wherein the catalyst is at least one selected from the group consisting of organic base carboxylates, alkali metal salts, zinc compounds, titanium (IV) compounds, and zirconium (IV) compounds.
[9] A method for producing a carbamic acid ester according to any one of [1] to [8], wherein the reaction step is carried out in the presence of an aprotic solvent.
[10] A method for producing a carbamic acid ester according to any one of [1] to [9], further comprising a carbamic acid salt production step of producing the carbamic acid salt by contacting an amino group-containing organic compound with a carbon dioxide-containing mixed gas in a solvent in the presence of a base, wherein the volume of carbon dioxide in the carbon dioxide-containing mixed gas is 0.01% or more.

According to the present invention, a method for producing carbamic acid esters using carbamic acid salts as raw materials, without using sacrificial reagents or alkyl halides, can be provided.

In describing the details of this invention, specific examples will be given, but the invention is not limited to the following, and can be modified as appropriate, without departing from the spirit of the invention.

<1. Method for producing carbamic acid esters>
A method for producing a carbamic acid ester according to one embodiment of the present invention is characterized by including a reaction step (hereinafter sometimes referred to as the "reaction step") in which a carbamic acid ester having a structure represented by the following formula (a-1) or (a-2) is produced from a carbamic acid salt and a metal alkoxide.
(In the above formula, ^R1 independently represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, ^R2 and ^R3 independently represent an unsubstituted or substituted monovalent hydrocarbon group, and ^R20 represents an unsubstituted or substituted divalent hydrocarbon group.)

Reactions that produce carbamic acid esters having a structure represented by formula (a-1) or (a-2) from a carbamate salt and a metal alkoxide include, for example, the reaction between benzylammonium N-benzylcarbamate and titanium tetramethoxide, as shown below. The reaction mechanism in this case is presumed to be as follows.
The present invention enables the production of carbamic acid esters without using sacrificial reagents or alkyl halides, which have poor environmental compatibility. Furthermore, as will be described later, the present invention can also produce carbamate salts and carbamic acid esters using a low-concentration carbon dioxide mixed gas as a raw material, enabling the effective utilization of low-concentration carbon dioxide contained in exhaust gases, etc. Moreover, since the present invention uses metal alkoxides that can be recycled with alcohol, it is possible to produce carbamic acid esters with excellent environmental compatibility, where essentially only low-concentration carbon dioxide, amines, and alcohols are consumed. The method for producing carbamic acid esters according to the present invention will be described in detail below.

<1-1. Carbamic acid esters having a structure represented by formula (a-1) or (a-2)>
A carbamic acid ester having the structure represented by formula (a-1) or (a-2) can be obtained by a manufacturing method according to one embodiment of the present invention.
(R ¹ )
Each ^R1 independently represents a hydrogen atom or a monovalent hydrocarbon group that is either unsubstituted or substituted.
In this specification, the term "hydrocarbon group" is not limited to a linear saturated hydrocarbon group, but may also have carbon-carbon unsaturated bonds, branched structures, or cyclic structures.
The number of carbon atoms in ^R1 is not particularly limited, but is usually 1 or more, and is usually 30 or less, preferably 24 or less, and more preferably 20 or less.
The unsubstituted hydrocarbon groups represented by R ¹ include ethyl group, n-propyl group, iso-propyl group, n-butyl group, sec-butyl group, iso-butyl group, tert-butyl group, n-pentyl group, iso-pentyl group, neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n Examples include alkyl groups such as docosyl groups; cycloalkyl groups such as cyclopropyl groups, cyclobutyl groups, cyclopentyl groups, and cyclohexyl groups; aromatic hydrocarbon groups such as phenyl groups, 1-naphthyl groups, 2-naphthyl groups, 1-phenanthryl groups, 2-phenanthryl groups, 3-phenanthryl groups, 4-phenanthryl groups, 9-phenanthryl groups, 1-anthryl groups, 2-anthryl groups, 9-anthryl groups, 1-pyrenyl groups, 2-pyrenyl groups, 4-pyrenyl groups, 1-triphenylenyl groups, and 2-triphenylenyl groups.
When the hydrocarbon group represented by ^R1 has substituents, examples of substituents include deuterium atoms; C1-C4 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl groups; C3-C4 cycloalkyl groups such as cyclopropyl and cyclobutyl groups; C6-C10 aromatic hydrocarbon groups such as phenyl, 1-naphthyl, and 2-naphthyl groups; heterocyclic groups such as oxygen-containing heterocyclic groups like furanyl groups, sulfur-containing heterocyclic groups like thienyl groups, and nitrogen-containing heterocyclic groups like pyrrolyl and pyridyl groups; hydroxyl groups; and alkoxy groups. Therefore, when the hydrocarbon group represented by ^R1 has substituents, ^R1 can preferably be, for example, an aralkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, or a 2-naphthylmethyl group; a cycloalkylalkyl group such as a cyclohexylmethyl group; a hydrocarbon group having an oxygen-containing heterocycle such as a furfuryl group; a hydrocarbon group having a sulfur-containing heterocycle such as a thienylmethyl group; or a hydrocarbon group having a nitrogen-containing heterocycle such as a pyridylmethyl group, with a benzyl group being particularly preferred.
Furthermore, if the hydrocarbon group has substituents, the carbon number refers to the sum of the carbon numbers of the substituents and the hydrocarbon group.
For ^R1 , hydrogen is preferred from the viewpoint of the usefulness of the carbamate ester compound.

( ^R2 , ^R3 )
^R2 and ^R3 each independently represent an unsubstituted or substituted monovalent hydrocarbon group.
The number of carbon atoms in ^R2 is not particularly limited, but is usually 1 or more, and is usually 30 or less, preferably 24 or less, and more preferably 20 or less.
The number of carbon atoms in ^R3 is not particularly limited, but is usually 1 or more, and is usually 30 or less, preferably 24 or less, and more preferably 20 or less.
Unsubstituted hydrocarbon groups represented by ^R2 and ^R3 include ethyl group, n-propyl group, iso-propyl group, n-butyl group, sec-butyl group, iso-butyl group, tert-butyl group, n-pentyl group, iso-pentyl group, neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n Examples include alkyl groups such as docosyl groups; cycloalkyl groups such as cyclopropyl groups, cyclobutyl groups, cyclopentyl groups, and cyclohexyl groups; aromatic hydrocarbon groups such as phenyl groups, 1-naphthyl groups, 2-naphthyl groups, 1-phenanthryl groups, 2-phenanthryl groups, 3-phenanthryl groups, 4-phenanthryl groups, 9-phenanthryl groups, 1-anthryl groups, 2-anthryl groups, 9-anthryl groups, 1-pyrenyl groups, 2-pyrenyl groups, 4-pyrenyl groups, 1-triphenylenyl groups, and 2-triphenylenyl groups.
When the hydrocarbon groups represented by ^R2 and ^R3 have substituents, examples of substituents include deuterium atoms; C1-C4 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl groups; C3-C4 cycloalkyl groups such as cyclopropyl and cyclobutyl groups; C6-C10 aromatic hydrocarbon groups such as phenyl, 1-naphthyl, and 2-naphthyl groups; heterocyclic groups such as oxygen-containing heterocyclic groups like furanyl groups, sulfur-containing heterocyclic groups like thienyl groups, and nitrogen-containing heterocyclic groups like pyrrolyl and pyridyl groups. Therefore, when the hydrocarbon groups represented by ^R2 and ^R3 have substituents, ^R2 and ^R3 can preferably be, for example, aralkyl groups such as benzyl, phenethyl, 1-naphthylmethyl, and 2-naphthylmethyl groups; cycloalkylalkyl groups such as cyclohexylmethyl; hydrocarbon groups having oxygen-containing heterocycles such as furfuryl; hydrocarbon groups having sulfur-containing heterocycles such as thienylmethyl; or hydrocarbon groups having nitrogen-containing heterocycles such as pyridylmethyl. Particularly preferred is the benzyl group.
In the case of a branched alkyl group, the number of carbon atoms in the main chain is considered to be the number of carbon atoms in the hydrocarbon group. Furthermore, if the hydrocarbon group has substituents, the number of carbon atoms in the substituents is not included in the calculation of the hydrocarbon group's carbon count.
For ^R2 , from the viewpoint of ease of obtaining raw materials, it is preferably an alkyl group such as an n-hexyl group; a cycloalkyl group such as a cyclohexyl group; an aromatic hydrocarbon group such as a phenyl group; or an aralkyl group such as a benzyl group; more preferably a benzyl group, an n-hexyl group, a cyclohexyl group, or a phenyl group, and even more preferably a benzyl group or a phenyl group.
For ^R3 , from the standpoint of ease of obtaining raw materials, it is preferably an alkyl group, and more preferably a methyl group, an ethyl group, an n-propyl group, or an n-butyl group.

(R ²⁰ )
R ²⁰ represents an unsubstituted or substituted divalent hydrocarbon group.
Examples of divalent hydrocarbon groups include methylene groups; ethylene groups; linear, branched, or cyclic alkylene groups having 3 or more carbon atoms; or arylene groups having 6 or more carbon atoms.
The number of carbon atoms in the divalent hydrocarbon group is not particularly limited, but is preferably 2 or more, preferably 10 or less, and more preferably 7 or less. The divalent hydrocarbon group may also have unsaturated bonds. When the divalent hydrocarbon group has substituents, the number of carbon atoms in the divalent hydrocarbon group refers to the number of carbon atoms including those of the substituents. Examples of substituents are those exemplified in the explanation of item (R ¹ ).
R ²⁰ specifically refers to chain-like hydrocarbon groups such as methylene group, ethylene group, tetramethylethylene group, n-propylene group (trimethylene group), 1-methylpropylene group, 1,1-dimethylpropylene group, 2-methylpropylene group, 1,2-dimethylpropylene group, 2,2-dimethylpropylene group, 1,1,2-trimethylpropylene group, 1,1,3-trimethylpropylene group, n-butylene group (tetramethylene group), 2-methyl-1,4-butylene group, 3-methyl-1,4-butylene group, 2,2-dimethyl-1,4-butylene group, 2,3-dimethyl-1,4-butylene group, 2,2,3-trimethyl-1,4-butylene group, n-pentylene group (pentamethylene group), n-hexanylene group (hexamethylene group); 1,4- Examples of divalent groups include alicyclic hydrocarbon groups such as cyclohexylene groups, 1,4-phenylene groups, 1,2-phenylene groups, and 1,3-phenylene groups obtained by removing two hydrogen atoms from a benzene ring; aromatic hydrocarbon groups such as dimethylphenylene (xylyl group) obtained by removing two hydrogen atoms from the benzene ring of xylene, methylphenylene (trylene group) obtained by removing two hydrogen atoms from the benzene ring of toluene, and naphthalylene groups obtained by removing two hydrogen atoms from naphthalene; aliphatic hydrocarbon groups such as 1,4-phenylenebis(methylene) groups, 1,4-phenylenebis(ethylene) groups, groups obtained by removing one hydrogen atom from each of the two benzene rings of biphenyl, and groups obtained by removing one hydrogen atom from each of the two benzene rings of diphenylmethane.

Examples of carbamic acid esters represented by formula (a-1) or (a-2) include the following compounds.

<1-2. Carbamate>
The carbamate salt used in this embodiment can be any salt capable of producing a carbamate ester represented by formula (a-1) or (a-2). That is, it can be any carbamate salt containing a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group ^R1 and an unsubstituted or substituted monovalent hydrocarbon group ^R2 , or a carbamate salt containing an unsubstituted or substituted monovalent hydrocarbon group ^R1 and an unsubstituted or substituted divalent hydrocarbon group ^R20 . Preferably, a carbamate salt represented by formula (B-1) or formula (B-2) described later can be mentioned.

Carbamate salts may be obtained commercially or synthesized. When synthesized, the manufacturing method is not particularly limited, but for example, an amino group-containing organic compound having one or more primary or secondary amino groups, more specifically, one produced by the reaction of an aliphatic monoamine such as benzylamine or hexylamine, or an aliphatic diamine such as ethylenediamine, with carbon dioxide can be used. As for the carbon dioxide used in the reaction, pure carbon dioxide gas can be used, but a mixed gas containing carbon dioxide at a partial pressure of 1 atmosphere or less, for example, a mixed gas with a carbon dioxide content of 0.01% or more by volume, can also be used.
In one embodiment of the present invention, it is preferable to further include a carbamate salt production step in which an amino group-containing organic compound is brought into contact with a carbon dioxide-containing mixed gas in a solvent to produce a carbamate salt. The volume of carbon dioxide in the carbon dioxide-containing mixed gas is usually 0.01% or more, preferably 1% or more, more preferably 10% or more, even more preferably 15% or more, particularly preferably 20% or more, and preferably 50% or less. The solvent used in the carbamate salt production step is not particularly limited, but hydrocarbon solvents such as hexane, benzene, and toluene can be preferably used. The reaction time can be appropriately adjusted according to the partial pressure of carbon dioxide in the carbon dioxide-containing mixed gas and the reaction scale. For example, if the volume of carbon dioxide in the carbon dioxide-containing mixed gas is 15%, a carbamate salt can be synthesized with a yield of 80% or more by reacting 1 mmol of the amino group-containing organic compound as a raw material for 5 to 10 minutes. Also, when 40 mmol of the amino group-containing organic compound is used, a yield of 90 minutes or more can be achieved with a reaction time of about 180 minutes. The produced carbamate salt can be easily isolated by filtration.

The inventors have confirmed that carbamate salts can be produced in a high yield of, for example, 99% or more, by the reaction shown in the following scheme as a carbamate salt production step. Furthermore, carbamate salts were also obtained in a high isolation yield of 93% in synthesis using a mixed gas of low partial pressure carbon dioxide.

While methods for producing carbamic acid esters using carbon dioxide as a raw material have been reported previously, they all require either a sacrificial reagent or an alkyl halide, which has poor environmental compatibility. In contrast, the production method of this embodiment does not require a sacrificial reagent or an alkyl halide, and can even utilize a mixed gas containing carbon dioxide at a low partial pressure. For example, exhaust gas from thermal power plants typically contains about 15% carbon dioxide. This method of producing carbamate salts and then carbamic acid esters using such a low-concentration carbon dioxide-containing mixed gas is a reaction that enables the effective utilization of low-concentration carbon dioxide, is effective in reducing greenhouse gas emissions, and is an environmentally friendly production method.

<1-3. Metal Alkoxides>
The metal alkoxide used in this embodiment can be any metal capable of producing a carbamic acid ester represented by formula (a-1) or (a-2). That is, any metal alkoxide containing an alkoxide group ^-OR3 is acceptable. Preferably, the metal alkoxide represented by formula (C-1) or (C-2) described later is mentioned. The metal alkoxide may be obtained commercially or synthesized.
Furthermore, metal alkoxides are regenerative reagents that can be recycled with alcohol. After the reaction process, the residue can be recovered from the reaction product and recycled using alcohol. The recycled metal alkoxide can then be reused in the reaction process. Therefore, as one embodiment of the present invention, it is possible to provide an environmentally friendly method for producing carbamate esters using low-concentration carbon dioxide, where substantially only low-concentration carbon dioxide, amines, and alcohols are consumed.

<1-4. Method for producing carbamic acid ester represented by formula (A-1)>
In one embodiment of the present invention, it is preferable that the carbamate salt is a carbamate salt represented by formula (B-1), the metal alkoxide is a metal alkoxide represented by formula (C-1), and the carbamate ester having the structure represented by formula (a-1) is a carbamate ester represented by formula (A-1).
In the above formula, R ¹¹ represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group; R ²¹ and R ³¹ each independently represent an unsubstituted or substituted monovalent hydrocarbon group; R ⁴¹ each independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand different from -OR ³¹ ; M represents a metal atom or metalloid atom; n represents the oxidation state of M, where (n-m) is an integer from 1 to 6; m represents an integer from 0 to (n-1); Q represents a q-valent countercation; q is 1 or 2.

<1-4-1. Carbamic acid esters represented by formula (A-1)>
In formula (A-1), R ¹¹ represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, and R ²¹ and R ³¹ each independently represent an unsubstituted or substituted monovalent hydrocarbon group.
The details of R ¹¹ are as described in the above explanation for R ¹ .
For details of R ²¹ , the explanation of R ² above applies.
For details of R ³¹ , the explanation of R ³ above applies.

<1-4-2. Carbamate salts represented by formula (B-1)>
In formula (B-1), R ¹¹ represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, R ²¹ and R ³¹ each independently represent an unsubstituted or substituted monovalent hydrocarbon group, and Q represents a countercation.
R ¹¹ in equation (B-1) corresponds to R ¹¹ in equation (A-1). Also, R ²¹ in equation (B-1) corresponds to R ²¹ in equation (A-1). Furthermore, R ³¹ in equation (B-1) corresponds to R ³¹ in equation (A-1). Therefore, the above explanation of R ¹ applies to the details of R ^11. Also, the above explanation of R ² applies to the details of R ^21. The above explanation of R ³ applies to the details of R ³¹ .

(Q)
Q represents the countercation in the carbamate salt, and is not particularly limited as long as it is a monovalent or divalent cation, but examples include ammonium cation, amidinium cation, guanidinium cation, phosphonium cation, phosphazenium cation, carbocation, sulfonium cation, iodonium cation, alkali metal cation, alkaline earth metal cation, etc.
Examples of ammonium cations include primary ammonium cations such as n-butylammonium cation; secondary ammonium cations such as diethylammonium cation; tertiary ammonium cations such as triethylammonium cation; and quaternary ammonium cations such as tetramethylammonium cation, phenyltrimethylammonium cation, and tetrabutylammonium cation.
Examples of amidinium cations include formamidinium cation, acetamidinium cation, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,8-diazabicyclo[5.4.0]undecé-7-ene, which are protonated formsamidinium cation, acetamidinium cation, 1,5-diazabicyclo[4.3.0]non-5-enium cation, and 1,8-diazabicyclo[5.4.0]undecé-7-enium cation, as well as derivatives thereof having one or more substituents. Examples of substituents include hydrocarbon groups such as alkyl groups, cycloalkyl groups, and aromatic hydrocarbon groups, as exemplified in the description of item (R ¹ ).
Examples of guanidinium cations include 1,1,3,3-tetramethylguanidinine, 2-tert-butyl-1,1,3,3-tetramethylguanidinine, 1,5,7-triazabicyclo[4.4.0]deca-5-ene, and 7-methyl-1,5,7-triazabicyclo[4.4.0]deca-5-ene, which are protonated, as well as derivatives thereof having one or more substituents. Examples of substituents include hydrocarbon groups such as alkyl groups, cycloalkyl groups, and aromatic hydrocarbon groups as exemplified in the description of item (R ¹ ).
Examples of phosphonium cations include tertiary phosphonium cations such as triphenylphosphonium cation and tritert-butylphosphonium cation; and quaternary phosphonium cations such as tetraphenylphosphonium cation, tetra-p-tolylphosphonium cation, triphenylbenzylphosphonium cation, triphenylbutyl cation, tetraethylphosphonium cation, and tetrabutylphosphonium cation.
Phosphazenium cations include tert-butylimino-tris(dimethylamino)phosphorane, tert-butylimino-tri(pyrrolidino)phosphorane, 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine, 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino) ^{-2λ5,4λ5 -} catenadi(phosphazene), and 1-tert-butyl-4,
4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylideneamino] ^{-2λ5,4λ5 -} catenadi(phosphazene) are each protonated, resulting in tert-butylimino-tris(dimethylamino)phosphoranium cations, t
Examples include ert-butylimino-tri(pyrrolidino)phosphoranium cation, 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphospholinium cation, 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino) ^{-2λ5,4λ5 -} catenadi(phosphazene), and 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[ ^tris (dimethylamino)phosphoranylideneamino] ^-2λ5,4λ5 -catenadi(phosphazene)onium cation, as well as derivatives thereof having one or more substituents. Examples of the substituents include hydrocarbon groups such as alkyl groups, cycloalkyl groups, and aromatic hydrocarbon groups as exemplified in the description of item (R ¹ ).
Examples of carbocations include monovalent carbocations such as triphenylmethyl cation, tropylium cation, and azurenium cation.
Examples of sulfonium cations include triphenylsulfonium cation, 4-(phenylthio)phenyldiphenylsulfonium cation, bis[4-(diphenylsulfonio)phenyl] sulfide, and 4-hydroxyphenylmethylbenzylsulfonium cation.
Examples of iodonium cations include diphenyliodonium cation, di-p-tolyliodonium cation, and 4-isopropylphenyl(p-tolyl)iodonium cation.
Examples of alkali metal cations include lithium cations, sodium cations, and potassium cations.
Examples of alkaline earth metal cations include magnesium cations and calcium cations.
Preferably, from the viewpoint of ease of synthesis, the cations are ammonium cations, amidinium cations, guanidinium cations, phosphonium cations, phosphazenium cations, carbocations, alkali metal cations, and alkaline earth metal cations, and more preferably ammonium cations or amidinium cations. Among these, primary ammonium cations, tertiary ammonium cations, and 1,8-diazabicyclo[5.4.0]undecé-7-enium cations are preferred.
(q)
q is either 1 or 2. q represents the number of carbamate anions and is the same value as the valence of Q. Therefore, if Q is a monovalent cation, q is 1, and if Q is a divalent cation, q is 2.

Specific examples of carbamates represented by formula (B-1) include, but are not limited to, amidinium salts, guanidinium salts, phosphonium salts, phosphazenium salts, carbocation salts, alkali metal salts, or alkaline earth metal salts, where the counter cation of these is an amidinium cation other than the 1,8-diazabicyclo[5.4.0]undecé-7-enium cation, guanidinium salt, phosphonium salt, phosphazenium salt, carbocation salt, alkali metal salt, or alkaline earth metal salt.

<1-4-3. Metal alkoxides represented by formula (C-1)>
In formula (C-1), R ³¹ represents an unsubstituted or substituted monovalent hydrocarbon group; R ⁴¹ each independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand different from -OR ³¹ ; M represents a metal atom or metalloid atom; n represents the oxidation state of M, where (n-m) is an integer from 1 to 6; and m represents an integer between 0 and (n-1).
(M)
M represents a metallic atom or a metalloid atom.
The types of metal atoms and metalloid atoms are not particularly limited, but examples include metal atoms or metalloid atoms selected from the group consisting of silicon, titanium, zirconium, germanium, indium, tin, tantalum, zinc, and tungsten. Among these, silicon and titanium are preferred due to their availability.
(R ³¹ )
R ³¹ represents an unsubstituted or substituted monovalent hydrocarbon group.
R ³¹ in equation (C-1) corresponds to R ³¹ in equation (A-1). Therefore, the details of R ³¹ are explained in the above description of R ³ .
(R ⁴¹ )
Each R ⁴¹ independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand that is different from -OR ³¹ .
Unsubstituted hydrocarbon ligands include alkyl ligands such as methyl ligands and ethyl ligands, cycloalkyl ligands such as cyclohexyl ligands, phenyl ligands, naphthyl ligands, cyclopentadienyl ligands, cyclohexadienyl ligands, cyclooctadienyl ligands, cyclooctatetraenyl ligands, aryl ligands such as norvonadienyl ligands, benzyl ligands, methylcyclopentadienyl ligands, methylcyclohexadienyl ligands,
Examples of aralkyl ligands include methylcyclooctadienyl ligands and methylcyclooctatetraenyl ligands. Substituents that hydrocarbon ligands may have include, for example, oxygen-containing heterocyclic groups such as hydroxyl groups, ester groups (-COOR), amide groups (-CONRR'), halogen atoms, alkylthio groups (-SR), amino groups (-NRR'), carboxyl groups, nitro groups, sulfonic acid groups ( _-SO₃H ), and furanyl groups, sulfur-containing heterocyclic groups such as thienyl groups, and nitrogen-containing heterocyclic groups such as pyridyl groups.
Examples of unsubstituted alkoxy ligands different from -OR ³¹ include methoxy ligands, ethoxy ligands, propoxy ligands, butoxy ligands, pentoxy ligands, dodecyloxy ligands, and phenoxy ligands. Examples of substituents that alkoxy ligands may have include hydroxyl groups, ester groups (-COOR), amide groups (-CONRR'), halogen atoms, alkylthio groups (-SR), amino groups (-NRR'), carboxyl groups, nitro groups, sulfonic acid groups ( _-SO3H ), oxygen-containing heterocyclic groups such as furanyl groups, sulfur-containing heterocyclic groups such as thienyl groups, and nitrogen-containing heterocyclic groups such as pyridyl groups.
Examples of amide ligands include unsubstituted amide ligands ( _NH₂ ), methylamide ligands (NHMe), dimethylamide ligands ( _NMe₂ ), diethylamide ligands ( _NET₂ ), di-n-propylamide ligands ( _NPr₂ ), isopropylamide ligands, di-n-butylamide ligands, and di-t-butylamide ligands.
Examples of halide ligands include fluorine ligands, chlorine ligands, bromine ligands, and iodine ligands. When m is 2 to 5, the multiple R ^41s may be the same or different, but it is preferable that all R ^41s are the same for ease of availability.
(n)
n represents the oxidation number of M, and (n-m) is an integer from 1 to 6.
(m)
m represents an integer between 0 and (n-1), i.e., an integer between 0 and 5.

Specifically, the metal alkoxide represented by formula (C-1) is:
Tetramethoxysilane, tetraethoxysilane, tetra(n-propoxy)silane, tetra(iso-propoxy)silane, tetra(n-butoxy)silane, tetra(2-butoxy)silane, tetra(t-butoxy)silane, trimethoxy(iso-propoxy)silane, trimethoxy(n-butoxy)silane, trimethoxy(2-butoxy)silane, trimethoxy(t-butoxy)silane, trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, propyltrimethoxysilane, propyl Alkoxysilanes such as riethoxysilane, propyltrimethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, cyclohexyltripropoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, dimethoxydimethylsilane, diethoxydimethylsilane, dimethoxydiethylsilane, diethoxydiethylsilane, dimethoxymethylvinylsilane, dimethoxydiphenylsilane, dimethoxymethylphenylsilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane;
Tetramethoxytitanium (titanium tetramethoxide), tetraethoxytitanium, tetraallyloxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium (titanium tetra-iso-propoxide), tetra-n-butoxytitanium (titanium tetra-n-butoxide), tetraisobutoxytitanium, tetra-sec-butoxytitanium, tetra-t-butoxytitanium (titanium tetra-t-butoxide), tetra-n-pentyloxytitanium, tetracyclopentyloxytitanium, tetrahexyloxytitanium, tetracyclohexyloxytitanium, tetrabenzyloxytitanium, tetraoctyloxytitanium, tetrakis(2-ethylhexyloxy)titanium, tetradecyloxytitanium, tetradodecyloxytitanium, tetrastearyloxytitanium, tetrakis(8-hydroxyoctyloxy)titanium, diisopropoxybis(2-ethyl-1,3-hexanediolato)titanium, bis(2-ethylhexyloxy)bis(2-ethyl-1, 3-Hexanediolate)titanium, tetrakis(2-chloroethoxy)titanium, tetrakis(2-bromoethoxy)titanium, tetrakis(2-methoxyethoxy)titanium, tetrakis(2-ethoxyethoxy)titanium, butoxytrimethoxytitanium, dibutoxydimethoxytitanium, butoxytriethoxytitanium, dibutoxydiethoxytitanium, butoxytriisopropoxytitanium, dibutoxydiisopropoxytitanium, tetraphenoxytitanium, tetrakis(o-chlorophenoxy)titanium, tetrakis(m-nitrophenoxy)titanium, tetrakis(p-methylphenoxy)titanium, tetrakis(trimethylsilyloxy)titanium, triethoxytitanium, trimethoxytitanium, triisopropoxytitanium, tributoxytitanium, methyldimethoxytitanium, ethyltriethoxytitanium, methyltriisopropoxytitanium, tetradimethylaminotitanium, dimethyltitanium diacetylacetonate, ethyltitanium triacetylacetonate, and other alkoxytitaniums;
Tetramethoxyzirconium, tetraethoxyzirconium, tetraallyloxyzirconium, tetra-n-propoxyzirconium, tetraisopropoxyzirconium, tetra-n-butoxyzirconium, tetraisobutoxyzirconium, tetra-sec-butoxyzirconium, tetra-t-butoxyzirconium, tetra-n-pentyloxyzirconium, tetracyclopentyloxyzirconium, tetrahexyloxyzirconium, tetracyclohexyloxyzirconium, tetrabenzyloxyzirconium, tetraoctyloxyzirconium, tetrakis(2-ethylhexyloxy)zirconium, tetradecyloxyzirconium, tetradodecyloxyzirconium, tetrastearyloxyzirconium, tetrakis(8-hydroxyoctyloxy)zirconium, diisopropoxybis Alkoxyzirconiums such as (2-ethyl-1,3-hexanediolato)zirconium, bis(2-ethylhexyloxy)bis(2-ethyl-1,3-hexanediolato)zirconium, tetrakis(2-chloroethoxy)zirconium, tetrakis(2-bromoethoxy)zirconium, tetrakis(2-methoxyethoxy)zirconium, tetrakis(2-ethoxyethoxy)zirconium, butoxytrimethoxyzirconium, dibutoxydimethoxyzirconium, butoxytriethoxyzirconium, dibutoxydiethoxyzirconium, butoxytriisopropoxyzirconium, dibutoxydiisopropoxyzirconium, tetraphenoxyzirconium, tetrakis(o-chlorophenoxy)zirconium, tetrakis(m-nitrophenoxy)zirconium, tetrakis(p-methylphenoxy)zirconium, etc.
Alkoxygermaniums such as tetraethoxygermanium, tetrapropoxygermanium, tetraisopropoxygermanium, tetra(n-butoxy)germanium, tetra(2-butoxy)germanium, and tetra(t-butoxy)germanium;
Alkoxyindium such as tetra(n-butoxy)indium, tetra(2-butoxy)indium, tetra(t-butoxy)indium, trimethoxyindium, triethoxyindium, tri(n-propoxy)indium, triisopropoxyindium, tri(n-butoxy)indium, triisobutoxyindium, tri(t-butoxy)indium, tri(s-butoxy)indium, etc.
Alkoxytins such as dibutyldimethoxytin, dibutyldiethoxytin, and dibutyldipropoxytin;
Alkoxytantalums such as tetramethoxytantalum, tetraethoxytantalum, tetra(n-propoxy)tantalum, tetraisopropoxytantalum, tetra(n-butoxy)tantalum, tetra(2-butoxy)tantalum, tetra(t-butoxy)tantalum, and pentaethoxytantalum;
Alkoxyzincs such as isopropoxyzinc, tetra(n-butoxy)zinc, tetra(2-butoxy)zinc, and tetra(t-butoxy)zinc;
Alkoxytungstens such as pentamethoxytungsten, pentaethoxytungsten, pentaisopropoxytungsten, tungsten(V)pentabtoxytungsten, triisobutoxytungsten, and tri(t-butoxy)tungsten;
These are some examples.
The metal alkoxide represented by formula (C-1) is preferably at least one selected from the group consisting of titanium compounds and silicon compounds, from the viewpoint of availability, more preferably titanium tetramethoxide, titanium tetra-iso-propoxide, titanium tetra-n-butoxide, titanium tetra-t-butoxide, tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-n-butoxysilane, and even more preferably titanium tetramethoxide, titanium tetra-iso-propoxide, titanium tetra-n-butoxide, titanium tetra-t-butoxide, and tetramethoxysilane.
In this embodiment, a metal alkoxide compound may be added to the reaction system, or a metal alkoxide may be generated in the reaction system and used. For example, one method is to react zirconium tetrachloride ( _ZrCl₄ ) with sodium ethoxide to generate tetraethoxyzirconium. Another method is to react zirconocene dichloride ( _{Cp₂ZrCl₂ )} with sodium ethoxide to generate zirconocene diethoxide. Yet another method is to react dibutyldichlorotin ( _{Bu₂SnCl₂ )} with sodium ethoxide to generate dibutyldiethoxytin.

<1-5. Method for producing carbamic acid ester represented by formula (A-2)>
Furthermore, in another embodiment of the present invention, it is preferable that the carbamate salt is a carbamate salt represented by formula (B-2), the metal alkoxide is a metal alkoxide represented by formula (C-2), and the carbamate ester having the structure represented by formula (a-2) is a carbamate ester represented by formula (A-2).
In the above formula, R ¹² each independently represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group; R ²² each independently represents an unsubstituted or substituted divalent hydrocarbon group; R ³² each independently represents an unsubstituted or substituted monovalent hydrocarbon group; R ⁴² each independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand different from -OR ³² ; M' represents a metal atom or metalloid atom; n' represents the oxidation number of M', where (n'-m') is an integer from 1 to 6; m' represents an integer between 0 and (n'-1);Q'
represents a (2/q') valent countercation, where q' is 1 or 2.

<1-5-1. Carbamic acid esters represented by formula (A-2)>
In formula (A-2), each ^R12 independently represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, each ^R22 independently represents an unsubstituted or substituted divalent hydrocarbon group, and each ^R32 independently represents an unsubstituted or substituted monovalent hydrocarbon group.
The details of R ¹² are as described in the above explanation for R ¹ .
For details regarding R ²² , the explanation for R ²⁰ described above applies.
For details regarding R ³² , the explanation for R ³ described above applies.

<1-5-2. Carbamate represented by formula (B-2)>
In formula (B-2), ^R12 each independently represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, ^R22 represents an unsubstituted or substituted divalent hydrocarbon group, and Q' represents a countercation.
R ¹² in equation (B-2) corresponds to R ¹² in equation (A-2). Similarly, R ²² in equation (B-2) corresponds to R ²² in equation (A-2). Therefore, the details of R ¹² are explained in the description of R ¹ above. Similarly, the details of R ²² are explained in the description of R ² above.

(Q')
Q' represents the countercation in the carbamate salt and is not particularly limited as long as it is a monovalent or divalent cation, but examples include ammonium cation, amidinium cation, guanidinium cation, phosphonium cation, phosphazenium cation, carbocation, sulfonium cation, iodonium cation, alkali metal cation, and alkaline earth metal cation. Specific examples of these cations are those mentioned above in section (Q).
Preferably, from the viewpoint of ease of synthesis, the cations are ammonium cation, amidinium cation, guanidinium cation, phosphonium cation, phosphazenium cation, carbocation, alkali metal cation, and alkaline earth metal cation, and more preferably ammonium cation, amidinium cation, guanidinium cation, and phosphazenium cation. Among these, the most preferred are tert-butylimino-tri(pyrrolidino)phosphoranium cation and 1,8-diazabicyclo[5.4.0]undecé-7-enium cation.
(q')
q' is either 1 or 2. (2/q') indicates the number of countercations Q; that is, if Q is a monovalent cation, q' is 2, and if Q is a divalent cation, q' is 1.

Specific examples of carbamates represented by formula (B-2) include compounds represented by the following formulas and amidinium salts, guanidinium salts, phosphonium salts, phosphazenium salts, carbocation salts, alkali metal salts, or alkaline earth metal salts, where the counter cation of these compounds is an amidinium cation other than the 1,8-diazabicyclo[5.4.0]undecé-7-enium cation, as well as an amidinium cation, guanidinium cation, phosphonium cation, phosphazenium salt, carbocation salt, alkali metal salt, or alkaline earth metal salt.
Specific examples of carbamates represented by formula (B-2) include, but are not limited to, compounds represented by the following formula and their countercations being phosphazenium cations other than amidinium cation, guanidinium cation, phosphonium cation, tert-butylimino-tri(pyrrolidino)phosphoranium cation, carbocations, alkali metal cations, or alkaline earth metal cations, such as amidinium salts, guanidinium salts, phosphonium salts, phosphazenium salts, carbocation salts, alkali metal salts, or alkaline earth metal salts.

<1-5-3. Metal alkoxides represented by formula (C-2)>
In formula (C-2), R ³² represents an unsubstituted or substituted monovalent hydrocarbon group; R ⁴² each independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand different from -OR ³² ; M' represents a metal atom or metalloid atom, n' represents the oxidation state of M', (n'-m') is an integer from 1 to 6; and m' represents an integer between 0 and (n'-1).
M' represents a metal atom or a metalloid atom.
The types of metal atoms and metalloid atoms are not particularly limited, but examples include metal atoms or metalloid atoms selected from the group consisting of silicon, titanium, zirconium, germanium, indium, tin, tantalum, zinc, and tungsten. Among these, silicon and titanium are preferred due to their availability.
(R ³² )
R ³² in equation (C-2) corresponds to R ³² in equation (A-2). Therefore, the details of R ³² are explained in the above description of R ³ .
(R ⁴² )
Each R ⁴² independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand that is different from -OR ³² .
Specific examples of unsubstituted or substituted hydrocarbon ligands, unsubstituted or substituted alkoxy ligands, amide ligands, and halide ligands different from -OR ³² include the ligands exemplified in R ⁴¹ , respectively. When m is 2 to 5, the multiple R ^42s may be the same or different, but it is preferable that all R ^42s are the same for ease of availability.
(n')
n' represents the oxidation number of M', and (n' - m') is an integer from 1 to 6.
(m')
m' represents an integer between 0 and (n'-1), i.e., an integer between 0 and 5.
Examples of metal alkoxides represented by formula (C-2) include the metal alkoxides exemplified in formula (C-1). Preferably, from the viewpoint of availability, it is at least one selected from the group consisting of titanium compounds and silicon compounds, and more preferably titanium tetramethoxide, titanium tetra-iso-propoxide, titanium tetra-n-butoxide, titanium tetra-t-butoxide, tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, and tetra-n-butoxysilane.
More preferably are titanium tetramethoxide, titanium tetra-iso-propoxide, titanium tetra-n-butoxide, titanium tetra-t-butoxide, and tetramethoxysilane.

<1-6. Reaction Process>
The reaction process may involve, for example, placing the raw materials, a carbamate salt and a metal alkoxide, into a sealed reaction vessel and reacting them at 200°C for 48 hours. Alternatively, for example, an amine may be placed in a sealed reaction vessel, carbon dioxide-containing gas may be blown in to produce a carbamate salt, and then titanium alkoxide, a metal alkoxide, may be added and the mixture heated to react. The reaction conditions will be described below.

(Reaction solvent)
The reaction step may or may not use a reaction solvent, but it is preferable to use one. The type of reaction solvent is not particularly limited, but ethers such as diethyl ether, tetrahydrofuran, and 1,4-dioxane; nitriles such as acetonitrile and propionitrile; and aprotic polar solvents such as dimethylacetamide, N,N-dimethylformamide, N,N'-dimethylpropyleneurea, 1,3-dimethyl-2-imidazolidinone, and N-methylpyrrolidone are preferred. Aprotic solvents are more preferred as the reaction solvent, ethers and aprotic polar solvents are even more preferred, and 1,4-dioxane, an aprotic ether, and N-methylpyrrolidone, an aprotic polar solvent, are particularly preferred. Using the above reaction solvents allows for more efficient production of carbamic acid esters. Furthermore, if there is a large difference between the boiling point of the solvent and the boiling point of the product, purification is easy, and the solvent can be reused. One type of reaction solvent may be used, or two or more types may be used.
The amount of reaction solvent used is not particularly limited and can be appropriately selected depending on the target carbamic acid ester.

(catalyst)
In one embodiment of the present invention, the reaction step may be carried out in the presence of a catalyst. In particular, when an alkoxysilane is used as the metal alkoxide, it is preferable to carry out the reaction step in the presence of a catalyst. Examples of preferred catalysts include organic base carboxylates, alkali metal salts, zinc compounds, titanium (IV) compounds, and zirconium (IV) compounds.
Examples of organic base carboxylates include acetate of 1,8-diazabicyclo[5.4.0]undec-7-ene, acetate of 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,1
Examples include nitrates of 3,3-tetramethylguanidine.
Examples of alkali metal salts include alkali metal acetates such as lithium acetate, sodium acetate, potassium acetate, rubidium acetate, and cesium acetate; alkali metal carbonates such as lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, and cesium carbonate; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide; and alkali metal alkoxides such as lithium alkoxide, sodium alkoxide, potassium alkoxide, rubidium alkoxide, and cesium alkoxide.
Examples of zinc compounds include zinc halides such as zinc chloride and zinc bromide; zinc sulfate; zinc sulfonates such as zinc p-toluenesulfonate and zinc trifluoromethanesulfonate; zinc formate, zinc acetate, zinc propionate, zinc octanoate, zinc salicylate, zinc pivalate, zinc acrylate, p-chlorobenzoic acid, zinc phenolate, zinc chloroacetate, zinc acetylacetonate, zinc oxalate, and zinc carboxylate derivatives such as zinc trifluoroacetate and zinc(II)-1,10-phenanthroline complex.
Examples of titanium(IV) compounds include titanium(IV) oxysulfate n hydrate, _TiCl₄ , _{TiBr₄ ,} Ti( _OC₂H₅ ) _Cl₃ , Ti( _{OC₅H ₷ ) Cl₃} , and Ti(O-iso- _C₄H₇ ) _Cl₃ .
Examples of zirconium(IV) compounds include zirconium(IV) chloride and zirconium(IV) oxychloride octahydrate.
The catalyst may be prepared, for example, by generating it from two or more compounds. For instance, zinc acetate and 1,10-phenanthroline may be placed in a reaction vessel to form a zinc(II)-1,10-phenanthroline (phen) complex, which can then be used as the catalyst.
In particular, zinc compounds such as zinc acetate, zinc pivalate, zinc(II)-1,10-phenanthroline (phen) complex, zinc p-toluenesulfonate, and zinc trifluoromethanesulfonate are preferred, and zinc acetate and zinc(II)-1,10-phenanthroline (phen) complex are preferred.
The amount of catalyst used in the reaction process (charging amount) is not particularly limited and should be appropriately selected depending on the target carbamate ester, but is preferably 10 mol% or more, 70 mol% or less, and more preferably 50 mol% or less relative to the amount of carbamate salt. In addition, one type of catalyst may be used, or two or more types may be used.

(Reaction temperature)
The reaction temperature (sometimes referred to as "reaction temperature") is not particularly limited and can be adjusted as appropriate by the reaction scale, etc. It is usually 140°C or higher, preferably 150°C or higher, and usually 250°C or lower, preferably 210°C or lower.

(Reaction time)
The reaction time is not particularly limited and can be adjusted as appropriate depending on the reaction temperature, reaction scale, etc. Typically, it is 30 minutes or more, preferably 1 hour or more, and typically 48 hours or less, preferably 24 hours or less, and more preferably 20 hours or less.

(Reaction atmosphere)
The atmosphere during the reaction process may be an air atmosphere or an inert gas atmosphere such as nitrogen or argon. The reaction process may be carried out under either pressurized or reduced pressure conditions, usually 0.01 atm or higher, preferably 0.05 atm or higher, more preferably 0.1 atm or higher, and usually 10 atm or lower, preferably 5 atm or lower, more preferably 2 atm or lower.

(Reaction vessel)
The reaction vessel is not particularly limited and should be appropriately selected depending on whether it is a continuous process or a batch process. In one embodiment of the present invention, it may be a continuous process or a batch process. In the case of a batch process, it is preferably a sealed reaction vessel (closed reaction vessel), and more preferably a sealed reaction vessel that is equal in volume to the mixture of the carbamate salt, metal alkoxide, and, if necessary, the reaction solvent and catalyst.

(Other processes)
In the method for producing carbamic acid esters according to this embodiment, optional steps may be included in addition to the reaction steps described above. Optional steps include the carbamic acid salt production step described in the (Carbamic Acid) section, the regeneration of metal alkoxides with alcohol, and the purification step to increase the purity of the carbamic acid ester. In the purification step, purification methods commonly used in the field of organic synthesis, such as filtration, adsorption, column chromatography, and distillation, can be employed.

The present invention will be described in more detail below with reference to examples, but modifications may be made as appropriate without departing from the spirit of the invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

<Example 1-1>
Benzylammonium N-benzylcarbamate (2.0 mmol), titanium tetramethoxide (2.0 mmol), and 1,4-dioxane (5 mL) were added to a 5 mL sealed reaction vessel and reacted at 200 °C for 48 hours. The yield of the alkyl N-benzylcarbamate was 8%. The yield was determined by ^1H NMR using mesitylene (50 mg) as an internal standard.

<Example 1-2>
Alkyl N-benzylcarbamate was obtained in the same manner as in Example 1-1, except that the reaction temperature was changed as shown in Table 1. The yields are shown in Table 1.

<Examples 1 and 3>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Examples 1-2, except that the reaction time was changed as shown in Table 1. The yields are shown in Table 1.

<Example 1-4>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Example 1-1, except that the amounts of metal alkoxide and solvent were changed as shown in Table 1. The yields are shown in Table 1.

<Examples 1-5>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Examples 1-4, except that the reaction temperature was changed as shown in Table 1. The yields are shown in Table 1.

<Example 1-6>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Examples 1-5, except that the reaction temperature was changed as shown in Table 1. The yields are shown in Table 1.

<Example 1-7>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Example 1-1, except that the amounts of metal alkoxide and solvent were changed as shown in Table 1. The yields are shown in Table 1.

<Examples 1-8>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Examples 1-7, except that the reaction temperature was changed as shown in Table 1. The yields are shown in Table 1.

<Examples 1 and 9>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Examples 1-7, except that the reaction time and reaction temperature were changed as shown in Table 1. The yields are shown in Table 1.

<Example 1-10>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Examples 1-7, except that the reaction temperature was changed as shown in Table 1. The yields are shown in Table 1.

<Example 1-11>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Example 1-1, except that the amounts of metal alkoxide and solvent were changed as shown in Table 1. The yields are shown in Table 1.

<Example 1-12>
Alkyl N-benzylcarbamate was obtained in the same manner as in Examples 1-11, except that the reaction temperature was changed as shown in Table 1. The yields are shown in Table 1.

Examples 1-1 to 1-12 demonstrate that alkyl carbamates can be produced using various titanium compounds as metal alkoxides.

<Example 2-1>
Benzylammonium N-benzylcarbamate (2.0 mmol), tetramethoxysilane (2.0 mmol), zinc acetate (0.2 mmol), and 1,4-dioxane (4.5 mL) were added to a 5 mL sealed reaction vessel and reacted at 200 °C for 1 hour. The yield of methyl N-benzylcarbamate was 18%. The yield was determined by ^1H NMR using mesitylene (50 mg) as an internal standard.

<Example 2-2>
Alkyl N-benzylcarbamate was obtained in the same manner as in Example 2-1, except that the reaction temperature was changed as shown in Table 2. The yields are shown in Table 2.

<Example 2-3>
Alkyl N-benzylcarbamate was obtained in the same manner as in Example 2-2, except that the reaction time was changed as shown in Table 2. The yields are shown in Table 2.

<Example 2-4>
Alkyl N-benzylcarbamate was obtained in the same manner as in Example 2-3, except that the reaction temperature was changed as shown in Table 2. The yields are shown in Table 2.

<Example 2-5>
Alkyl N-benzylcarbamate esters were obtained in the same manner as in Examples 2-3, except that the catalyst was changed as shown in Table 2. The yields are shown in Table 2. In Table 2, phen represents 1,10-phenanthroline.

It was demonstrated that alkyl carbamates can be produced using silicon compounds as metal alkoxides.

<Example 3-1>
Benzylamine (2.0 mmol), 1,8-diazabicyclo[5.4.0]undeca-7-ene (2.0 mmol), and 1,4-dioxane (4.5 mL) were added to a 5 mL sealed reaction vessel, and a _CO2 / _N2 mixed gas (v:v = 15:85) was passed through for 15 minutes. Subsequently, titanium tetramethoxide (2.0 mmol) was added, and the reaction was carried out at 200 °C for 1 hour. The yield of N-benzylcarbamate methyl ester was 50%. The yield was determined by ^1H NMR using mesitylene (50 mg) as an internal standard.

<Example 3-2>
Alkyl N-benzylcarbamate was obtained in the same manner as in Example 3-1, except that the reaction temperature was changed as shown in Table 3. The yields are shown in Table 3.

<Example 3-3>
Alkyl N-benzylcarbamate was obtained in the same manner as in Example 3-1, except that the volume ratio of the _CO2 / _N2 mixed gas was changed as shown in Table 3. The yield is shown in 3.

<Example 4-1>
A mixture containing dicarbamate, prepared by aerating a mixture of hexamethylenediamine (116 mg, 1.0 mmol), 1,8-diazabicyclo[5.4.0]undec-7-ene (457 g, 3.0 mmol), and N-methylpyrrolidone (1.0 mL) with a carbon dioxide/nitrogen mixture (1 atm, v:v = 15:85) at a flow rate of 0.1 L/min for 20 minutes, was placed in a 5 mL sealed reaction vessel. Titanium tetrabutoxide (680 mg, 2.0 mmol) and N-methylpyrrolidone (3.6 mL) were added, and the mixture was reacted at 180 °C for 3 hours. The yield of N,N'-hexamethylenebis(dibutylcarbamate) was 60%. The yield was determined by ^1H NMR using mesitylene (50 mg) as an internal standard.

<Example 4-2>
A mixture containing carbamate, prepared by aerating a mixture of aniline (186 mg, 2.0 mmol), 1,8-diazabicyclo[5.4.0]undec-7-ene (1.52 g, 10.0 mmol), and N-methylpyrrolidone (1.5 ml) with a carbon dioxide/nitrogen mixture (1 atm, v:v = 15:85) at a flow rate of 0.1 L/min for 20 minutes, was placed in a 5 mL sealed reaction vessel. Titanium tetrabutoxide (680 mg, 2.0 mmol) and N-methylpyrrolidone (1.6 ml) were added, and the mixture was reacted at 180°C for 3 hours. The yield of butyl-N-phenylcarbamate was 40%. The yield was determined by ^1H NMR using mesitylene (50 mg) as an internal standard.

<Example 4-3>
A mixture containing dicarbamate, prepared by aerating a mixture of hexamethylenediamine (116 mg, 1.0 mmol), tert-butylimino-tri(pyrrolidino)phosphorane (1250 mg, 4.0 mmol), and N-methylpyrrolidone (2.0 ml) with a carbon dioxide/nitrogen mixture (1 atm, v:v = 15:85) at a flow rate of 0.1 L/min for 20 minutes, was placed in a 5 mL sealed reaction vessel. Titanium tetrabutoxide (680 mg, 2.0 mmol) and N-methylpyrrolidone (3.6 ml) were added, and the mixture was reacted at 180°C for 3 hours. The yield of N,N'-hexamethylenebis(dibutylcarbamate) was 52%. The yield was determined by ^1H NMR using mesitylene (50 mg) as an internal standard.

It was demonstrated that alkyl carbamates can be produced by adding titanium alkoxide, a metal alkoxide, to a reaction system in which carbamates are generated using amines and carbon dioxide as raw materials. Furthermore, it was shown that alkyl carbamates can be produced using a low-concentration carbon dioxide gas mixture containing 15% carbon dioxide by volume.

According to this invention, carbamate esters can be produced using carbamate salts and metal alkoxides as raw materials. Furthermore, this invention also allows for the production of carbamate salts and carbamate esters using a low-concentration carbon dioxide mixed gas as a raw material, enabling the effective utilization of low-concentration carbon dioxide contained in exhaust gases, etc. Moreover, since the metal alkoxide used in this invention can be recovered after the reaction and regenerated using alcohol, it is an environmentally friendly reaction that consumes essentially only low-concentration carbon dioxide, amines, and alcohol.

Claims (7)

A carbamate salt production step involves contacting an amino group-containing organic compound with a carbon dioxide-containing mixed gas in a solvent in the presence of a base to produce a carbamate salt represented by the following formula (B-1) or (B-2), and
The process includes a reaction step (excluding one carried out in the presence of a zinc compound) to produce a carbamic acid ester represented by the following formula (A-1) or (A-2) from the carbamate salt and alkoxysilane .
A method for producing a carbamate ester , wherein the volume of carbon dioxide in the carbon dioxide-containing mixed gas in the carbamate salt production step is 0.01% or more .


(In the above formula, R ¹¹ represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group; R ²¹ and R ³¹ each independently represent an unsubstituted or substituted monovalent hydrocarbon group; R ¹² each independently represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group; R ²² represents an unsubstituted or substituted divalent hydrocarbon group; R ³² each independently represents an unsubstituted or substituted monovalent hydrocarbon group; Q represents a q-valent countercation; q is 1 or 2; Q' represents a (2/q')-valent countercation; q' is 1 or 2.) A method for producing a carbamic acid ester according to claim 1, wherein the carbamic acid salt is a carbamic acid salt represented by formula (B-1), the alkoxysilane is an alkoxysilane represented by the following formula (C-1), and the carbamic acid ester is a carbamic acid ester represented by formula (A-1).

(In the above formula, each R ³¹ independently represents an unsubstituted or substituted monovalent hydrocarbon group; each R ⁴¹ independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand different from -OR ³¹ ; M represents silicon; n is 4; (n-m) is an integer from 1 to 4; m is an integer from 0 to 3.) The method for producing a carbamic acid ester according to claim 1 or 2, wherein Q is a cation selected from the group consisting of ammonium cation, amidinium cation, guanidinium cation, phosphonium cation, phosphazenium cation, carbocation, alkali metal cation, and alkaline earth metal cation. A method for producing a carbamic acid ester according to claim 1, wherein the carbamic acid salt is a carbamic acid salt represented by the formula (B-2), the alkoxysilane is an alkoxysilane represented by the following formula (C-2), and the carbamic acid ester is a carbamic acid ester represented by the formula (A-2).

(In the above formula, R ³² each independently represents an unsubstituted or substituted monovalent hydrocarbon group; R ⁴² each independently represents an unsubstituted or substituted hydrocarbon ligand, an unsubstituted or substituted alkoxy ligand, amide ligand, or halide ligand different from -OR ³² ; M' represents silicon, n' is 4; (n'-m') is an integer from 1 to 4; m' represents an integer from 0 to 3.) The method for producing a carbamic acid ester according to claim 1 or 4, wherein Q' is a cation selected from the group consisting of ammonium cation, amidinium cation, guanidinium cation, phosphonium cation, phosphazenium cation, carbocation, alkali metal cation, and alkaline earth metal cation. A method for producing a carbamic acid ester according to any one of claims 1 to 5, wherein the reaction step is carried out in the presence of an aprotic solvent. A method for producing a carbamic acid ester according to any one of claims 1 to 6, wherein the carbamic acid salt production step and the reaction step are carried out in a continuous process.