Method for producing unsaturated alcohol

Abstract

The purpose of the present invention is to provide a method for producing an unsaturated alcohol, the method making it possible to produce an unsaturated alcohol with high selectivity and high yield even at high temperatures. A method for producing an unsaturated alcohol according to the present invention is characterized by comprising a step for reducing an unsaturated carboxylic acid ester to an unsaturated alcohol by using an alkali metal and an alcohol, the alkali metal being alkali metal particles having an average particle diameter of 100 μm or less.

Description

Method for producing unsaturated alcohol

[0001] The present invention relates to a method for producing an unsaturated alcohol.

[0002] Conventionally, unsaturated alcohols have been used as fragrances and flavors. For example, cis-3-hexen-1-ol, also known as leaf alcohol, is widely used as a fragrance and flavor. Many methods exist for producing unsaturated alcohols, but the Bouveault-Blanc reduction, in which an unsaturated carboxylic acid ester is reduced to an unsaturated alcohol by reacting it with an alkali metal in the presence of an alcohol as a proton donor, is known as an effective method.

[0003] It is known that the Bouveault-Blanc reduction can produce not only the target unsaturated alcohol but also a saturated alcohol (saturate) in which the carbon-carbon double bonds in the unsaturated alcohol are also reduced, in an amount equal to or greater than the target alcohol. Such saturated compounds usually have a boiling point close to that of the unsaturated alcohol, which poses a problem in that it is difficult to separate the unsaturated alcohol and the saturated compound by distillation.

[0004] To address these problems, a technique has been proposed for suppressing the production of saturated compounds and increasing the selectivity (purity) of unsaturated alcohols when producing unsaturated alcohols by Bouveault-Blanc reduction. For example, Patent Document 1 discloses a technique for increasing the selectivity of unsaturated alcohols by performing Bouveault-Blanc reduction at a low temperature of −10° C. to −50° C.

[0005] Special Publication No. 62-54090

[0006] However, low-temperature facilities are costly, and the above-mentioned conventional techniques, which require low-temperature conditions, have the problem that it is difficult to produce unsaturated alcohols on an industrial scale at low cost and in high yield.

[0007] Therefore, an object of the present invention is to provide a method for producing unsaturated alcohols that can produce unsaturated alcohols with high selectivity and high yield even at high temperatures (for example, above −10° C.).

[0008] The present inventors have conducted extensive research to solve the above problems, and have found that when producing unsaturated alcohols by Bouveault-Blanc reduction, if alkali metal particles having an average particle size of a predetermined value or less are used, unsaturated alcohols can be produced with high selectivity and in high yield even at high temperatures, and have completed the present invention.

[0009] The present invention aims to advantageously solve the above-mentioned problems. The present invention provides a method for producing an unsaturated alcohol, comprising: [1] reducing an unsaturated carboxylic acid ester to an unsaturated alcohol using an alkali metal and an alcohol, wherein the alkali metal is alkali metal particles having an average particle size of 100 μm or less. By using alkali metal particles having an average particle size of a predetermined value or less, unsaturated alcohols can be produced with high selectivity and high yield even at high temperatures. In the present invention, the average particle size of the alkali metal particles can be measured by the method described in the Examples.

[0010] [2] In the method for producing an unsaturated alcohol according to [1] above, the unsaturated carboxylic acid ester is preferably an aliphatic unsaturated carboxylic acid ester. By using the aliphatic unsaturated carboxylic acid ester, the corresponding aliphatic unsaturated alcohol can be easily obtained.

[0011] [3] In the method for producing an unsaturated alcohol according to [1] or [2] above, the alcohol is preferably a saturated aliphatic secondary alcohol, an unsaturated aliphatic secondary alcohol, a saturated aliphatic tertiary alcohol, or an unsaturated aliphatic tertiary alcohol. Use of a saturated or unsaturated secondary aliphatic alcohol or a saturated or unsaturated tertiary aliphatic alcohol as the alcohol can further increase the selectivity and yield of the unsaturated alcohol.

[0012] [4] In the method for producing an unsaturated alcohol according to any one of the above [1] to [3], the alcohol is preferably a cyclic alcohol. Use of a cyclic alcohol can further increase the selectivity and yield of the unsaturated alcohol.

[0013] [5] In the method for producing an unsaturated alcohol according to any one of the above [1] to [4], the molar ratio of the unsaturated carboxylic acid ester to the alcohol (unsaturated carboxylic acid ester / alcohol) is preferably 1 / 30 or more and 1 / 2 or less. When the molar ratio of the unsaturated carboxylic acid ester to the alcohol is within the above-mentioned range, the selectivity and yield of the unsaturated alcohol can be further improved.

[0014] [6] In the method for producing an unsaturated alcohol according to any one of the above [1] to [5], the molar ratio of the unsaturated carboxylic acid ester to the alkali metal (unsaturated carboxylic acid ester / alkali metal) is preferably 1 / 5 or more and 1 / 4 or less. When the molar ratio of the unsaturated carboxylic acid ester to the alkali metal is within the above-mentioned range, the selectivity and yield of the unsaturated alcohol can be further improved.

[0015] [7] In the method for producing an unsaturated alcohol according to any one of [1] to [6] above, the temperature when the unsaturated carboxylic acid ester is brought into contact with the alkali metal is preferably −8° C. or higher and 10° C. or lower. When the temperature when the unsaturated carboxylic acid ester is brought into contact with the alkali metal is equal to or higher than the lower limit, the unsaturated alcohol can be produced industrially on a large scale at low cost. Furthermore, when the temperature when the unsaturated carboxylic acid ester is brought into contact with the alkali metal is equal to or lower than the upper limit, the selectivity and yield of the resulting unsaturated alcohol can be further improved.

[0016] [8] In the method for producing an unsaturated alcohol according to any one of the above [1] to [7], the reduction is preferably carried out in the presence of a hydrocarbon solvent. The use of a hydrocarbon solvent makes the reduction reaction easy.

[0017] According to the present invention, it is possible to provide a method for producing an unsaturated alcohol, which is capable of producing an unsaturated alcohol with high selectivity and high yield even at high temperatures.

[0018] Hereinafter, embodiments of the present invention will be described in detail.

[0019] (Method for Producing Unsaturated Alcohol) The method for producing an unsaturated alcohol of the present invention (hereinafter also simply referred to as the "production method of the present invention") includes a step of reducing an unsaturated carboxylic acid ester to an unsaturated alcohol using an alkali metal and an alcohol (reduction step), and may optionally include other steps. According to the production method of the present invention, the production of saturated alcohol is suppressed, and unsaturated alcohol can be produced with high selectivity and high yield even at high temperatures.

[0020] <Reduction Step> In the reduction step, an unsaturated carboxylic acid ester as a starting material (raw material) is reduced to an unsaturated alcohol using an alkali metal and an alcohol. Specifically, in the reduction step, the unsaturated carboxylic acid ester is reacted with an alkali metal in the presence of an alcohol and an optional solvent to produce an unsaturated alcohol, a so-called Bouveault-Blanc reduction is carried out.

[0021] The reaction is not particularly limited, and can be carried out, for example, by adding (dropping) a mixed solution of an unsaturated carboxylic acid ester and an alcohol to a dispersion containing an alkali metal (alkali metal dispersion) at a predetermined temperature for a predetermined time while stirring (main reaction). Here, instead of using a mixed solution of an unsaturated carboxylic acid ester and an alcohol, the unsaturated carboxylic acid ester and the alcohol may be added (dropped) separately and simultaneously to the alkali metal dispersion. After the main reaction, it is preferable to perform a post-reaction by further stirring and mixing the resulting mixed solution at a predetermined temperature for a predetermined time.

[0022] [Main Reaction Temperature] The temperature at which the unsaturated carboxylic acid ester and the alkali metal are reacted in the reduction step (main reaction temperature) is preferably above −10° C., more preferably at −8° C. or higher, and preferably at 10° C. or lower, and more preferably at 5° C. or lower. When the main reaction temperature is equal to or higher than the above-mentioned lower limit, the cost of low-temperature equipment can be reduced, and the unsaturated alcohol can be produced industrially on a large scale at low cost. Furthermore, when the main reaction temperature is equal to or lower than the above-mentioned upper limit, the selectivity and yield of the resulting unsaturated alcohol can be further improved. Here, the "main reaction temperature" refers to the temperature at which the unsaturated carboxylic acid ester and the alkali metal are brought into contact with each other. Specifically, as described above, when a mixed solution of an unsaturated carboxylic acid ester and an alcohol is added (dropwise) to an alkali metal (alkali metal dispersion), or when an unsaturated carboxylic acid ester and an alcohol are added (dropwise) separately and simultaneously to an alkali metal (alkali metal dispersion), the "main reaction temperature" refers to the temperature of the reaction solution (mixture) during the addition (dropwise addition).

[0023] [Post-reaction temperature] When the mixed solution (reaction solution) is further stirred and mixed for a predetermined time after the main reaction (after the addition) as described above to carry out a post-reaction, the post-reaction temperature (the temperature of the reaction solution during stirring and mixing) is not particularly limited and may be the same as or different from the main reaction temperature. The post-reaction temperature can be, for example, −8° C. or higher and lower than 40° C.

[0024] [Reaction Time] The time for the main reaction of the unsaturated carboxylic acid ester with the alkali metal in the reduction step (main reaction time) is not particularly limited, but from the viewpoint of further increasing the selectivity and yield of the resulting unsaturated alcohol, it is preferably 120 minutes or less, and more preferably 30 minutes or less. Here, the "main reaction time" refers to the time for contacting the unsaturated carboxylic acid ester with the alkali metal, and specifically refers to the time of addition (dropwise addition) when a mixed solution of the unsaturated carboxylic acid ester and the alcohol is added (dropwise added) to the alkali metal (alkali metal dispersion) as described above, or when the unsaturated carboxylic acid ester and the alcohol are added (dropwise added) separately and simultaneously to the alkali metal (alkali metal dispersion).

[0025] [Post-reaction time] As described above, when the mixed solution obtained after the main reaction (after the addition) is further stirred and mixed for a predetermined period of time to carry out the post-reaction, the post-reaction time (the time during which stirring and mixing is continued after the main reaction) is not particularly limited, and is preferably 60 minutes or less, more preferably 30 minutes or less.

[0026] [Alkali Metal] The alkali metal is a component that can function as an electron reducing agent in the Bouveault-Blanc reduction. In the production method of the present invention, it is necessary to use alkali metal particles having an average particle size of 100 μm or less as the alkali metal. By using alkali metal particles having an average particle size of 100 μm or less, it is possible to suppress the production of saturated alcohols even at high temperatures (e.g., above −10° C.), and to produce unsaturated alcohols with high selectivity and high yield.

[0027] From the viewpoint of further increasing the selectivity and yield of the unsaturated alcohol, the average particle size of the alkali metal particles is preferably 50 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. The lower limit of the average particle size of the alkali metal particles is not particularly limited, but can be, for example, 0.1 μm or more.

[0028] The alkali metal is not particularly limited, and examples thereof include lithium, sodium, and potassium. Among them, sodium is preferred from the viewpoint of further increasing the selectivity and yield of the obtained unsaturated alcohol. The alkali metal may be used alone or in combination of two or more kinds.

[0029] Although there are no particular limitations on the alkali metal particles, they are preferably used in the form of an alkali metal dispersion in which they are dispersed in a solvent as described below. Here, the alkali metal dispersion may optionally further contain a known dispersant.

[0030] [Unsaturated Carboxylic Acid Ester] The unsaturated carboxylic acid ester used as a starting material is not particularly limited and can be selected depending on the type of unsaturated alcohol to be produced. As the unsaturated carboxylic acid ester, for example, an aliphatic unsaturated carboxylic acid ester can be used.

[0031] -Aliphatic unsaturated carboxylic acid ester- The aliphatic unsaturated carboxylic acid ester is not particularly limited, and both an aliphatic chain carboxylic acid ester having an unsaturated chain hydrocarbon group and an aliphatic cyclic carboxylic acid ester having an unsaturated alicyclic hydrocarbon group can be used. Among these, an aliphatic chain carboxylic acid ester having an unsaturated chain hydrocarbon group is preferred.

[0032] Specifically, the aliphatic unsaturated carboxylic acid ester is represented by the formula: R １ COOR ２ (In the formula, R １ represents an unsaturated chain hydrocarbon group or an unsaturated alicyclic hydrocarbon group, R ２ represents an aliphatic saturated hydrocarbon group or an aliphatic unsaturated hydrocarbon group. １ COOR ２ (In the formula, R １ represents an unsaturated chain hydrocarbon group, R ２ represents an aliphatic saturated hydrocarbon group.

[0033] The above R １The unsaturated chain hydrocarbon group represented by the formula (I) is not particularly limited and may be linear or branched. The unsaturated chain hydrocarbon group may be, for example, an unsaturated chain hydrocarbon group having from 3 to 10 carbon atoms, and is preferably an unsaturated chain hydrocarbon group having from 3 to 6 carbon atoms. Examples of the unsaturated chain hydrocarbon group include alkenyl groups. Specific examples of the alkenyl group include a 2-propenyl group, a 2-butenyl group, a 3-butenyl group, a 1-methyl-2-propenyl group, a 2-methyl-2-propenyl group, a 2-pentenyl group, a 3-pentenyl group, a 4-pentenyl group, a 1-methyl-2-butenyl group, a 1-methyl-3-butenyl group, a 2-methyl-2-butenyl group, a 2-methyl-3-butenyl group, a 3-methyl-2-butenyl group, a 3-methyl-3-butenyl group, a 1,1-dimethyl-2-propenyl group, a 1,2-dimethyl-2-propenyl group, a 1-ethyl-2-propenyl group, a 2-hexenyl group, and a 3-hexenyl group. Examples of alkenyl groups having 3 to 10 carbon atoms include an alkenyl group, such as an aryl group, a 4-hexenyl group, a 5-hexenyl group, a 2-octenyl group, a 3-octenyl group, a 4-octenyl group, a 5-octenyl group, a 6-octenyl group, a 7-octenyl group, a 2-nonenyl group, a 3-nonenyl group, a 4-nonenyl group, a 5-nonenyl group, a 6-nonenyl group, a 7-nonenyl group, an 8-nonenyl group, a 2-decenyl group, a 3-decenyl group, a 4-decenyl group, a 5-decenyl group, a 6-decenyl group, a 7-decenyl group, an 8-decenyl group, a 9-decenyl group, and cis isomers and trans isomers thereof. １ is preferably a cis-2-pentenyl group from the viewpoint of obtaining a leaf alcohol (cis-3-hexen-1-ol) as the target product.

[0034] In addition, the above R １ The unsaturated alicyclic hydrocarbon group represented by the formula (I) is not particularly limited and can be an unsaturated alicyclic hydrocarbon group having from 3 to 10 carbon atoms, and among these, an unsaturated alicyclic hydrocarbon group having from 4 to 6 carbon atoms is preferred. Specific examples of unsaturated alicyclic hydrocarbon groups include cycloalkenyl groups. Specific examples of cycloalkenyl groups include cycloalkenyl groups having from 3 to 10 carbon atoms, such as cyclobutenyl, cyclopentenyl, cyclohexenyl, and cycloheptenyl.

[0035] The above R ２ The aliphatic saturated hydrocarbon group represented by the formula (I) is not particularly limited and may be linear or cyclic. Examples of the aliphatic saturated hydrocarbon group include linear, branched, and cyclic alkyl groups having from 1 to 10 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an isohexyl group, an n-heptyl group, an isoheptyl group, an n-octyl group, an isooctyl group, an n-nonyl group, an isononyl group, an n-decyl group, an isodecyl group, a cyclopentyl group, a cyclohexyl group, and a cyclooctyl group.

[0036] The above R ２ The aliphatic unsaturated hydrocarbon group represented by the formula (I) is not particularly limited and may be linear or cyclic. Examples of the aliphatic unsaturated hydrocarbon group include linear, branched, or cyclic alkenyl groups having from 1 to 10 carbon atoms. Specific examples of the alkenyl group include vinyl, 1-propenyl, 2-propenyl, 2-butenyl, 3-butenyl, 3-pentenyl, 4-pentenyl, 1-hexenyl, 5-hexenyl, 7-octenyl, cyclohexenyl, cyclohexadienyl, and cyclooctatrienyl groups.

[0037] Among them, R ２ is preferably a chain-like aliphatic saturated hydrocarbon group, more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably a methyl group, an ethyl group, or a butyl group.

[0038] Among these, the above formula: R １ COOR ２ In this case, R １ is an alkenyl group having 3 to 5 carbon atoms, and R ２ is an alkyl group having 1 to 6 carbon atoms, and methyl cis-3-hexenoate, ethyl cis-3-hexenoate, or butyl cis-3-hexenoate is more preferred.

[0039] —Mole Ratio of Unsaturated Carboxylic Acid Ester to Alkali Metal— From the viewpoint of further increasing the selectivity and yield of the obtained unsaturated alcohol, the molar ratio of the unsaturated carboxylic acid ester to the alkali metal (unsaturated carboxylic acid ester / alkali metal) is preferably 1 / 5 or more, more preferably 1 / 4.8 or more, and even more preferably 1 / 4.5 or more, and is preferably 1 / 4 or less, and more preferably 1 / 4.2 or less.

[0040] [Alcohol] The alcohol is a component that supplies protons in the Bouveault-Blanc reduction. The alcohol is not particularly limited, and for example, a monohydric alcohol or a dihydric alcohol can be used, but it is preferable to use a monohydric alcohol. Furthermore, the alcohol may be used alone or in combination of two or more types.

[0041] Here, the number of carbon atoms of the alcohol is not particularly limited, but from the viewpoint of further increasing the selectivity and yield of the obtained unsaturated alcohol, the number of carbon atoms is preferably 3 or more, more preferably 4 or more, and is preferably 10 or less, more preferably 6 or less.

[0042] -Monohydric Alcohol- As the monohydric alcohol, for example, a monohydric aliphatic alcohol can be used.

[0043] The monohydric aliphatic alcohol is not particularly limited, and both monohydric aliphatic chain alcohols and monohydric aliphatic cyclic alcohols can be used. The monohydric aliphatic chain alcohols may be either linear or branched. The monohydric aliphatic alcohols may be either saturated or unsaturated. That is, the monohydric aliphatic alcohols may be either monohydric saturated aliphatic alcohols or monohydric unsaturated aliphatic alcohols. The monohydric aliphatic alcohols may be primary, secondary, or tertiary.

[0044] --Monohydric saturated aliphatic alcohols-- Specific examples of monohydric saturated aliphatic alcohols include saturated aliphatic chain primary alcohols such as 1-propanol, 1-butanol, 1-amyl alcohol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, isobutyl alcohol, isoamyl alcohol, isohexanol, isooctanol, 2-ethylhexanol, isononanol, 2-methyloctanol, isodecanol, isooctadecanol, and 2-decyl-1-tetradecanol; saturated aliphatic chain secondary alcohols such as 2-propanol (isopropanol), 2-butanol (sec-butyl alcohol), 2-pentanol, 4-methyl-2-pentanol (sec-hexanol), 2-heptanol, 2-octanol, 2-nonanol, 2-decanol, and 2-undecanol; Examples of the saturated aliphatic chain tertiary alcohol include t-butanol, t-pentyl alcohol, and t-hexyl alcohol; saturated aliphatic cyclic primary alcohols such as cyclobutanemethanol, cyclopentanemethanol, cyclohexanemethanol, and cycloheptanemethanol; saturated aliphatic cyclic secondary alcohols such as cyclobutanol, cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, cyclononanol, cyclodecanol, 4-methylcyclohexanol, 4-ethylcyclohexanol, and 4-t-butylcyclohexanol; saturated aliphatic cyclic tertiary alcohols such as 1-methylcyclopentanol and 1-methylcyclohexanol. These monohydric saturated aliphatic alcohols may be used alone or in combination of two or more.

[0045] --Monohydric Unsaturated Aliphatic Alcohols-- Specific examples of monohydric unsaturated aliphatic alcohols include unsaturated aliphatic chain primary alcohols such as allyl alcohol, methallyl alcohol, and cis-3-hexen-1-ol; unsaturated aliphatic chain secondary alcohols such as 3-buten-2-ol, 4-penten-2-ol, and 5-hexen-2-ol; unsaturated aliphatic chain tertiary alcohols such as 2-methyl-3-buten-2-ol and 3-methyl-1-penten-3-ol; unsaturated aliphatic cyclic primary alcohols such as cyclopenten-1-methanol and cyclohexen-1-methanol; unsaturated aliphatic cyclic secondary alcohols such as 2-cyclopenten-1-ol and 2-cyclohexen-1-ol; and unsaturated aliphatic cyclic tertiary alcohols such as 1-methyl-2-cyclopenten-1-ol and 1-methyl-2-cyclohexen-1-ol. These monohydric unsaturated aliphatic alcohols may be used alone or in combination of two or more.

[0046] -Dihydric Alcohol- The dihydric alcohol is not particularly limited, and a dihydric aliphatic alcohol can be used. The dihydric aliphatic alcohol is not particularly limited, and both a dihydric aliphatic chain alcohol and a dihydric aliphatic cyclic alcohol can be used. The dihydric aliphatic chain alcohol may be either linear or branched. The dihydric aliphatic alcohol may be either saturated or unsaturated. That is, the dihydric aliphatic alcohol may be either a dihydric saturated aliphatic alcohol or a dihydric unsaturated aliphatic alcohol. The dihydric aliphatic alcohol may be primary, secondary, or tertiary. In the present invention, dihydric aliphatic alcohols in which one hydroxyl group is secondary and the other hydroxyl group is primary are also considered to be dihydric secondary aliphatic alcohols, and dihydric aliphatic alcohols in which one hydroxyl group is tertiary and the other hydroxyl group is primary or secondary are also considered to be dihydric tertiary aliphatic alcohols.

[0047] --Dihydric saturated aliphatic alcohols-- Specific examples of dihydric saturated aliphatic alcohols include saturated aliphatic chain primary alcohols such as 1,2-ethanediol (ethylene glycol), 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; saturated aliphatic chain secondary alcohols such as 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-hexanediol, 1,2-octanediol, 1,2-decanediol, and 1,2-dodecanediol; saturated aliphatic chain tertiary alcohols such as 2-methyl-2,4-pentanediol; Examples of the saturated aliphatic cyclic primary alcohols include cycloheptane dimethanol, cycloheptane diethanol, cyclohexane dimethanol, and cyclohexane diethanol; saturated aliphatic cyclic secondary alcohols such as 1,2-cycloheptane diol, 1,2-cyclohexane diol, and 1,4-cyclohexane diol; and saturated aliphatic cyclic tertiary alcohols such as 1-methyl-1,2-cyclohexane diol. These dihydric saturated aliphatic alcohols may be used alone or in combination of two or more.

[0048] --Dihydric Unsaturated Aliphatic Alcohols--Specific examples of dihydric unsaturated aliphatic alcohols include unsaturated aliphatic chain primary alcohols such as cis-3-hexene-1,6-diol; unsaturated aliphatic chain secondary alcohols such as cis-3-hexene-1,2-diol; unsaturated aliphatic chain tertiary alcohols such as 2-methyl-cis-3-hexene-1,2-diol; unsaturated aliphatic cyclic primary alcohols such as cyclohexene dimethanol and cyclohexene diethanol; unsaturated aliphatic cyclic secondary alcohols such as 3-cyclohexene-1,2-diol; and unsaturated aliphatic cyclic tertiary alcohols such as 3-cyclohexene-1-methyl-1,2-diol. These dihydric unsaturated aliphatic alcohols may be used alone or in combination of two or more.

[0049] Among these alcohols, from the viewpoint of further increasing the selectivity and yield of the obtained unsaturated alcohol, monohydric saturated aliphatic secondary alcohols (monohydric saturated aliphatic chain secondary alcohols, monohydric saturated aliphatic cyclic secondary alcohols), monohydric unsaturated aliphatic secondary alcohols (monohydric unsaturated aliphatic chain secondary alcohols, monohydric unsaturated aliphatic cyclic secondary alcohols), monohydric saturated aliphatic tertiary alcohols (monohydric saturated aliphatic chain tertiary alcohols, monohydric saturated aliphatic cyclic tertiary alcohols), or monohydric unsaturated aliphatic tertiary alcohols (monohydric unsaturated aliphatic chain tertiary alcohols, monohydric unsaturated aliphatic cyclic tertiary alcohols) are preferred, and from the viewpoint of further increasing the selectivity and yield of the saturated alcohol while suppressing an increase in viscosity of the reaction solution and increasing the reaction efficiency, monohydric saturated aliphatic secondary alcohols or monohydric unsaturated aliphatic secondary alcohols are more preferred, and monohydric saturated aliphatic secondary alcohols are even more preferred.

[0050] Furthermore, from the viewpoint of further increasing the selectivity and yield of the unsaturated alcohol obtained, the alcohol is preferably a cyclic alcohol. The cyclic alcohol may be the monohydric aliphatic cyclic alcohol described above (i.e., a monohydric saturated aliphatic cyclic primary alcohol, a monohydric unsaturated aliphatic cyclic primary alcohol, a monohydric saturated aliphatic cyclic secondary alcohol, a monohydric unsaturated aliphatic cyclic tertiary alcohol, or a monohydric unsaturated aliphatic cyclic tertiary alcohol). The cyclic alcohol is preferably a monohydric saturated aliphatic cyclic secondary alcohol or a monohydric unsaturated aliphatic cyclic secondary alcohol, more preferably a monohydric saturated aliphatic cyclic secondary alcohol, even more preferably cyclopentanol or cyclohexanol, and particularly preferably cyclopentanol.

[0051] As the alcohol, from the viewpoint of further increasing the selectivity and yield of the obtained unsaturated alcohol, isopropanol, 4-methyl-2-pentanol, cyclopentanol, and cyclohexanol are preferred, cyclopentanol or cyclohexanol is more preferred, and cyclopentanol is even more preferred.

[0052] —Mole Ratio of Unsaturated Carboxylic Acid Ester to Alcohol— From the viewpoint of further increasing the selectivity and yield of the obtained unsaturated alcohol, the molar ratio of unsaturated carboxylic acid ester to alcohol (unsaturated carboxylic acid ester / alcohol) is preferably 1 / 30 or more, more preferably 1 / 5 or more, and even more preferably 1 / 4.5 or more, and is preferably 1 / 2 or less, more preferably 1 / 3 or less, and even more preferably 1 / 4 or less.

[0053] - Molar Ratio of Alcohol to Alkali Metal - From the viewpoint of further increasing the selectivity and yield of the unsaturated alcohol obtained, the molar ratio of alcohol to alkali metal (alcohol / alkali metal) is preferably 1:1.

[0054] [Solvent] In the reduction step, in addition to the alcohols described above, any solvent may be used. The solvent is not particularly limited as long as it does not affect the reduction reaction, and for example, a hydrocarbon solvent can be used. The hydrocarbon solvent is not particularly limited, and examples thereof include aliphatic hydrocarbon solvents such as n-pentane, isopentane, n-hexane, isohexane, n-heptane, isoheptane, 2,2,4-trimethylpentane, n-octane, isooctane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, trimethylbenzene, methylethylbenzene, n-propylbenzene, isopropylbenzene, diethylbenzene, isobutylbenzene, triethylbenzene, diisopropylbenzene, and n-amylnaphthalene. Among these, aromatic hydrocarbon solvents are preferred, and toluene is more preferred. The solvent may be added to a mixed solution of an unsaturated carboxylic acid ester and an alcohol, or may be used as a dispersion medium for dispersing alkali metal particles to prepare an alkali metal dispersion. However, it is preferable to use the solvent as a dispersion medium for dispersing alkali metal particles to prepare an alkali metal dispersion.

[0055] <Other Steps> Other steps that may be included in the production method of the present invention are not particularly limited, and include a step of preparing a solution containing the unsaturated carboxylic acid ester as a starting material (preparation step) and a step of purifying the reaction liquid (reaction mixture) obtained in the reduction step (purification step). Note that these other steps may be carried out in a line separate from the reduction step, or may be carried out as a series of steps together with the reduction step (i.e., in-line).

[0056] [Preparation Step] In the preparation step, a solution containing an unsaturated carboxylic acid ester to be subjected to the reduction step is prepared. The solution containing an unsaturated carboxylic acid ester can be prepared, for example, by dissolving the unsaturated carboxylic acid ester in the above-mentioned alcohol. The prepared solution containing the unsaturated carboxylic acid ester may be purified by known purification methods such as filtration by column chromatography or recrystallization. The preparation step may also be omitted. For example, as described above, the above-mentioned unsaturated carboxylic acid ester and the above-mentioned alcohol may be simultaneously added (dropwise) to and mixed with an alkali metal (alkali metal dispersion).

[0057] [Purification Step] In the purification step, the reaction solution obtained in the reduction step (a reaction mixture containing the target unsaturated alcohol, by-products, etc.) is purified to isolate the produced unsaturated alcohol. The purification method is not particularly limited, and for example, purification can be performed by adding water to the reaction solution obtained in the reduction step, discharging the reaction solution from the reaction vessel, and then performing distillation, filtration by column chromatography, etc., recrystallization, etc. After purification, the target unsaturated alcohol can be recovered by a known method.

[0058] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. The qualitative and quantitative analyses of the alcohols obtained in the examples and comparative examples were all carried out using gas chromatography (8860 gas chromatograph: Agilent Technologies, GC column: TC-WAX, GC detector: FID). For quantitative analysis, measurements were carried out using cyclopentyl methyl ether as an internal standard, and the yield, selectivity of the reaction target product, etc. were calculated by the internal standardization method.

[0059] <Average Particle Diameter of Alkali Metal (Sodium) Particles> Under a nitrogen atmosphere, the metallic sodium dispersions prepared in the Examples and Comparative Examples were placed in a sealable glass container and shaken until uniform. A drop of metallic sodium dispersion was immediately collected using a pipette and dripped onto a glass slide. A small amount of liquid paraffin was then added and the resulting slide was covered with a cover glass to prepare a preparation. Next, the prepared preparation was magnified using a transmission electron microscope and analyzed using image processing computer software in accordance with JIS Z-8827-1:2018 Particle Size Analysis - Image Analysis Method - Part 1: Static Image Analysis Method to determine the average particle diameter. Here, the "average particle diameter" is the arithmetic mean of the circumscribed circle equivalent diameters (diameters of the circles circumscribing the particles) of the projected images of the particles obtained. The magnification should be such that at least 100 to 200 particles, preferably 300 to 400 particles, and more preferably 500 to 600 particles can be measured. The average particle size can be controlled, for example, by changing the rotation speed of a homogenizer and / or the disintegration time when preparing the metallic sodium dispersion. As computer software for image processing, WinRoof manufactured by Mitani Shoji Co., Ltd. can be used.

[0060] Example 1 Preparation of Metallic Sodium Dispersion A three-neck glass vessel was used as a reactor, equipped with a homogenizer (KINEMATICA Homogenizer PT1300D / shaft outer diameter 12 mm), a septum, and a Dimroth condenser. 4.5 g of metallic sodium and 22 g of toluene were placed in the glass vessel, and the glass vessel was heated to 120°C to reflux the toluene and melt the metallic sodium. Subsequently, 0.1 g of dispersant was added, and the metallic sodium was crushed with the homogenizer for 20 minutes to disperse it in the form of fine particles in the toluene. Specifically, the metallic sodium was crushed for 20 minutes using the homogenizer at a rotation speed of 30,000 rpm, and then the dispersion was cooled to room temperature to solidify (particulate) the metallic sodium, thereby obtaining a metallic sodium dispersion. Reduction A glass vessel was used as a reactor. A portion of the metallic sodium dispersion (metallic sodium: 0.37 g, average particle size of metallic sodium: 10 μm) and toluene were mixed so that the total amount of toluene was 13.3 g. To this mixture, a mixture of cyclopentanol (1.36 g) as an alcohol and ethyl cis-3-hexenoate (0.50 g) as an unsaturated carboxylic acid ester was added dropwise over 5 minutes while stirring so that the internal temperature (temperature of the reaction solution; the same applies hereinafter) reached 5°C (main reaction). After completion of the dropwise addition, the resulting mixture was stirred at 0°C for 5 minutes (post-reaction). Distilled water (10 g) was then added. Gas chromatography of the separated organic layer revealed that the yield of the target product, cis-3-hexen-1-ol, was 85.2%, and the production ratio of the saturated form (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 1.5%.

[0061] Example 2 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the alcohol used in Example 1 was changed from cyclopentanol (1.36 g) to isopropanol (0.95 g). The yield of cis-3-hexen-1-ol was 83.5%, and the production ratio of the saturated product (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 2.6%.

[0062] Example 3 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the alcohol used in Example 1 was changed from cyclopentanol (1.36 g) to 4-methyl-2-pentanol (1.62 g). The yield of cis-3-hexen-1-ol was 76.4%, and the production ratio of saturated compound (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 8.4%.

[0063] Example 4 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the alcohol used in Example 1 was changed from cyclopentanol (1.36 g) to cyclohexanol (1.59 g). The yield of cis-3-hexen-1-ol was 82.5%, and the production ratio of the saturated product (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 2.3%.

[0064] Example 5 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the unsaturated carboxylic acid ester used in Example 1 was changed from ethyl cis-3-hexenoate (0.50 g) to methyl cis-3-hexenoate (0.51 g). The yield of cis-3-hexen-1-ol was 81.4%, and the production ratio of saturated compound (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 3.6%.

[0065] Example 6 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the unsaturated carboxylic acid ester used in Example 1 was changed from ethyl cis-3-hexenoate (0.50 g) to butyl cis-3-hexenoate (0.60 g). The yield of cis-3-hexen-1-ol was 84.6%, and the production ratio of saturated compound (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 2.3%.

[0066] Example 7 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the average particle size of the alkali metal particles was changed from 10 μm to 15 μm. The yield of cis-3-hexen-1-ol was 83.1%, and the production ratio of saturated form (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 1.9%.

[0067] Example 8 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the average particle size of the alkali metal particles was changed from 10 μm to 50 μm in Example 1. The yield of cis-3-hexen-1-ol was 63.0%, and the production ratio of saturated form (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 5.8%.

[0068] Example 9 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that a mixture of cyclopentanol and ethyl cis-3-hexenoate was added dropwise to a liquid prepared by dispersing a metallic sodium dispersion in toluene under stirring over 5 minutes so that the internal temperature became −3° C. The yield of cis-3-hexen-1-ol was 80.2%, and the production ratio of the saturated form (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol]×100(%)) was 1.2%.

[0069] Example 10 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that a mixture of cyclopentanol and ethyl cis-3-hexenoate was added dropwise to a toluene dispersion of a metallic sodium dispersion over 15 minutes so that the internal temperature became 5° C. The yield of cis-3-hexen-1-ol was 82.4%, and the production ratio of the saturated form (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol]×100(%)) was 2.8%.

[0070] Comparative Example 1 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the average particle size of the alkali metal particles was changed from 10 μm to 140 μm in Example 1. The yield of cis-3-hexen-1-ol was 57.2%, and the production ratio of saturated form (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 7.0%.

[0071] Comparative Example 2 Cis-3-hexen-1-ol was produced in the same manner as in Example 1, except that the average particle size of the alkali metal particles was changed from 10 μm to 110 μm in Example 2. The yield of cis-3-hexen-1-ol was 46.6%, and the production ratio of saturated form (1-hexanol) to cis-3-hexen-1-ol ([1-hexanol / cis-3-hexen-1-ol] × 100(%)) was 64.5%.

[0072] The results shown in Table 1 show that in Examples 1 to 10, in which the reduction of the unsaturated carboxylic acid ester was carried out using alkali metal particles having an average particle size of 100 μm or less, the unsaturated alcohol could be produced with high selectivity and in high yield even at high temperatures.

[0073] According to the present invention, it is possible to provide a method for producing an unsaturated alcohol, which is capable of producing an unsaturated alcohol with high selectivity and high yield even at high temperatures.

Claims

1. A method for producing an unsaturated alcohol, comprising the step of reducing an unsaturated carboxylic acid ester to an unsaturated alcohol using an alkali metal and an alcohol, wherein the alkali metal is alkali metal particles having an average particle size of 100 μm or less.

2. The method for producing an unsaturated alcohol according to claim 1, wherein the unsaturated carboxylic acid ester is an aliphatic unsaturated carboxylic acid ester.

3. The method for producing an unsaturated alcohol according to claim 1, wherein the alcohol is a saturated aliphatic secondary alcohol, an unsaturated aliphatic secondary alcohol, a saturated aliphatic tertiary alcohol, or an unsaturated aliphatic tertiary alcohol.

4. The method for producing an unsaturated alcohol according to claim 1, wherein the alcohol is a cyclic alcohol.

5. The method for producing an unsaturated alcohol according to claim 1, wherein the molar ratio of the unsaturated carboxylic acid ester to the alcohol (unsaturated carboxylic acid ester / alcohol) is 1 / 30 or more and 1 / 2 or less.

6. The method for producing an unsaturated alcohol according to claim 1, wherein the molar ratio of the unsaturated carboxylic acid ester to the alkali metal (unsaturated carboxylic acid ester / alkali metal) is 1 / 5 or more and 1 / 4 or less.

7. The method for producing an unsaturated alcohol according to claim 1, wherein the temperature when the unsaturated carboxylic acid ester is brought into contact with the alkali metal is -8°C or higher and 10°C or lower.

8. The method for producing an unsaturated alcohol according to any one of claims 1 to 7, wherein the reduction is carried out in the presence of a hydrocarbon solvent.

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