Method for producing acetal compound

Abstract

Provided is a method for producing an acetal compound, with which an acetal compound can be produced at an excellent yield while suppressing use of a catalyst. In a method for producing an acetal compound according to one embodiment of the present invention, a reaction liquid containing a carbonyl group-containing compound and an alcohol compound is irradiated with infrared radiation having an absorption wavelength of the carbonyl group-containing compound, thereby causing the carbonyl group-containing compound to react with the alcohol compound.

Description

Method for producing acetal compounds

[0001] The present invention relates to a method for producing an acetal compound.

[0002] It is known that acetal compounds are used in various industrial products such as pharmaceuticals. As a method for producing such acetal compounds, for example, a method for reacting a carbonyl group-containing compound with an alcohol compound in the presence of an acidic reagent has been proposed (see, for example, Non-Patent Document 1).

[0003] Synlett 2004(6), P. 1074-1076, DOI: 10.1055 / s-2004-820038

[0004] Acidic reagents such as those described in Non-Patent Document 1 may be harmful to the human body, and care must be taken when handling them. Furthermore, when an acidic reagent is used, the acetal compound is contaminated with the acidic reagent, necessitating neutralization treatment of the acetal compound or removal of the reagent. These factors may complicate the production of acetal compounds. Therefore, studies have been conducted on producing acetal compounds without using an acidic reagent. However, without using an acidic reagent, it is difficult to react a carbonyl group-containing compound with an alcohol compound, resulting in a problem of a reduced yield of the acetal compound. The main object of the present invention is to provide a method for producing an acetal compound that can produce an acetal compound in an excellent yield while minimizing the use of a catalyst.

[0005] [1] In one embodiment of the method for producing an acetal compound according to the present invention, a reaction solution containing a carbonyl group-containing compound and an alcohol compound is irradiated with infrared light having an absorption wavelength of the carbonyl group-containing compound to react the carbonyl group-containing compound with the alcohol compound. [2] In the method for producing an acetal compound according to [1] above, the reaction solution may be irradiated with the infrared light in the presence of carbon dioxide. [3] In the method for producing an acetal compound according to [2] above, the temperature of the reaction solution may be 60°C or less and the environmental pressure may be 0.2 MPa or less when the reaction solution is irradiated with the infrared light. [4] In the method for producing an acetal compound according to any one of [1] to [3] above, the reaction solution may be substantially free of a catalyst. [5] In the method for producing an acetal compound according to any one of [1] to [4] above, the carbonyl group-containing compound may have an aromatic ring and a carbonyl group bonded to the aromatic ring. [6] In the method for producing an acetal compound according to any one of [1] to [5] above, the infrared wavelength peak may be located in the range of 5.7±0.5 μm. [7] In another aspect of the method for producing an acetal compound according to the present invention, a carbonyl group-containing compound and an alcohol compound are reacted in the presence of carbon dioxide at 0.2 MPa or less.

[0006] According to an embodiment of the present invention, an acetal compound can be produced in an excellent yield while suppressing the use of a catalyst.

[0007] FIG. 1 is an IR spectrum of benzaldehyde used in the examples and comparative examples.

[0008] A. Overview of the Method for Producing Acetal Compounds In one embodiment of the method for producing an acetal compound according to the present invention, a reaction solution containing a carbonyl group-containing compound and an alcohol compound is irradiated with infrared light having an absorption wavelength of the carbonyl group-containing compound, thereby reacting the carbonyl group-containing compound with the alcohol compound. In another embodiment of the method for producing an acetal compound according to the present invention, the carbonyl group-containing compound and the alcohol compound are reacted at 0.2 MPa or less in the presence of carbon dioxide as an acidic gas. The present inventors discovered that even in an acetalization reaction that typically requires an acidic reagent as a catalyst, the acetalization reaction can proceed smoothly even with a sufficient reduction in the amount of catalyst by irradiating the carbonyl group-containing compound with infrared light having an absorption wavelength of the carbonyl group-containing compound or by reacting the carbonyl group-containing compound with the alcohol compound in the presence of carbon dioxide, thereby completing the present invention. More specifically, irradiating a reaction solution containing a carbonyl group-containing compound with infrared light having an absorption wavelength of the carbonyl group-containing compound can vigorously activate the molecules of the carbonyl group-containing compound. As a result, the inherent equilibrium state of a substance having a proton can be changed, and a state in which the proton is easily dissociated can be formed. Furthermore, when a carbonyl group-containing compound and an alcohol compound are reacted in the presence of carbon dioxide at 0.2 MPa or less, an acetal compound can be synthesized in a higher yield than in a reaction in the absence of carbon dioxide. As a result, the desired acetalization reaction can proceed smoothly without substantially using a catalyst. As a result, an acetal compound can be produced in an excellent yield.

[0009] B. First Embodiment First, as a first embodiment, a method for producing an acetal compound by irradiating a reaction solution with infrared rays will be described.

[0010] In the first embodiment, first, a reaction liquid containing a carbonyl group-containing compound and an alcohol compound is prepared. Typically, the reaction liquid is prepared by dissolving the carbonyl group-containing compound in the alcohol compound.

[0011] The carbonyl group-containing compound is not particularly limited as long as it has at least a carbonyl group. In one embodiment, the carbonyl group-containing compound has an aromatic ring and a carbonyl group bonded to the aromatic ring.

[0012] Examples of aromatic rings include a benzene ring, a naphthalene ring, an anthracene ring, and a biphenyl ring, and preferably a benzene ring. A hydrogen atom or any suitable substituent is typically bonded to the carbonyl carbon of the carbonyl group. Examples of substituents include an alkyl group; an aryl group such as a phenyl group; an alkoxy group such as a methoxy group; and a nitro group. A hydrogen atom is preferably bonded to the carbonyl carbon of the carbonyl group. In other words, the carbonyl group-containing compound preferably has an aromatic ring and an aldehyde group bonded to the aromatic ring.

[0013] The carbonyl group-containing compound has an absorption wavelength corresponding to the wavelength of the infrared light irradiated onto the reaction solution. In this specification, "absorption wavelength" refers to a wavelength at which the transmittance measured in accordance with JIS K0117:2017 is 60% or less. More specifically, the transmittance of the carbonyl group-containing compound measured in accordance with JIS K0117:2017 is 60% or less with respect to the infrared light irradiated onto the reaction solution. As shown in Figure 1, when the carbonyl group-containing compound has an aldehyde group, the carbonyl group-containing compound has an absorption wavelength of 5.5 μm to 6.5 μm, which corresponds to the aldehyde group.

[0014] Specific examples of such carbonyl group-containing compounds include benzaldehyde, p-anisaldehyde, piperonal, etc. The carbonyl group-containing compounds may be used alone or in combination.

[0015] Any suitable alcohol compound used in an acetalization reaction may be used. The alcohol compound may have, for example, 1 to 10 carbon atoms. Examples of such alcohol compounds include primary alcohols, secondary alcohols, and dihydric alcohols. Examples of primary alcohols include methanol, ethanol, 1-propanol, isopropanol, and 1-butanol. Examples of secondary alcohols include propan-2-ol (C3) butan-2-ol. Examples of dihydric alcohols include ethylene glycol and propylene glycol. The alcohol compounds may be used alone or in combination. Among such alcohol compounds, primary alcohols are preferred, and methanol, ethanol, and 1-propanol are more preferred.

[0016] In one embodiment, the carbonyl group-containing compound includes benzaldehyde and the alcohol compound includes methanol. The acetalization reaction that proceeds in this embodiment is shown in the following formula (1): In this case, benzaldehyde dimethyl acetal is produced.

[0017] The reaction solution may further contain an organic solvent in addition to the carbonyl group-containing compound and the alcohol compound. Examples of the organic solvent include ketones and ethers. In one embodiment, the reaction solution is substantially free of organic solvents other than the alcohol compound. If the reaction solution does not contain an organic solvent other than the alcohol compound, absorption of infrared rays by the organic solvent can be suppressed.

[0018] Furthermore, the reaction solution typically contains substantially no catalyst. Here, "substantially no catalyst" includes not only cases where the reaction solution does not contain any catalyst, but also cases where the catalyst content in the reaction solution is 1% by mass or less. The catalyst content in the reaction solution is preferably 0% by mass. According to such a method, post-treatment (e.g., neutralization) of the acetal compound produced is unnecessary, and the desired acetal compound can be produced more smoothly. Therefore, in recent years, there has been a demand for synthesis techniques that minimize the impact on the earth and ecosystems, and the method for producing an acetal compound according to one embodiment can be a very useful technique. Examples of catalysts include acidic catalysts and basic catalysts. The catalyst is typically a liquid or solid at room temperature and normal pressure (25°C, 0.1 MPa).

[0019] The content of the carbonyl group-containing compound in the reaction solution is, for example, 0.1% by mass or more, preferably 1% by mass or more. On the other hand, the content of the carbonyl group-containing compound in the reaction solution is, for example, 20% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less. The content of the alcohol compound in the reaction solution is, for example, 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. On the other hand, the content of the alcohol compound in the reaction solution is, for example, 99.9% by mass or less, preferably 99.0% by mass or less. When the content of the carbonyl group-containing compound and / or alcohol compound is within such a range, the acetalization reaction can be induced more stably.

[0020] Next, the reaction solution is irradiated with infrared light having an absorption wavelength of the carbonyl group-containing compound. When the carbonyl group-containing compound has an aldehyde group, the reaction solution is irradiated with infrared light having a wavelength peak in the range of 5.7±0.5 μm. In this way, irradiating the reaction solution with infrared light having a wavelength corresponding to the reactive site (carbonyl group) of the carbonyl group-containing compound can sufficiently activate the molecules of the carbonyl group-containing compound.

[0021] The infrared wavelength peak refers to the wavelength at which the infrared normal emissivity is maximum. The wavelength peak can be determined, for example, from an infrared emissivity curve obtained by plotting the infrared wavelength versus normal emissivity. The maximum infrared normal emissivity is, for example, 0.80 or more, preferably 0.85 or more, and more preferably 0.90 or more. Meanwhile, the upper limit of the maximum infrared normal emissivity is typically 1.0. Note that the infrared normal emissivity is calculated, for example, by applying Kirchhoff's law with transmittance set to 0, using the following formula (I). Note that the normal reflectivity is measured, for example, using a Fourier transform infrared spectrometer (FT-IR) equipped with an integrating sphere: (Normal emissivity) = 1 - (Normal reflectivity) (I). The half-width of the infrared peak is, for example, 2.0 μm or less, preferably 1.5 μm or less, and more preferably 1.0 μm or less. Meanwhile, the lower limit of the half-width of the peak is typically 0 μm.

[0022] In one embodiment, the reaction solution is irradiated with infrared rays from a surface light source. Compared to an infrared laser, a surface light source can irradiate a wider range of reaction solutions with infrared rays. Furthermore, such a surface light source can easily adjust the wavelength of the emitted infrared rays compared to an infrared laser oscillator. As a result, the reaction solution can be stably irradiated with infrared rays having a desired wavelength, and appropriate energy can be stably imparted to the carbonyl group-containing compound. An example of such a surface light source is the infrared heater described in Japanese Patent No. 6272589. The disclosure of this publication is incorporated herein by reference. The irradiation area of ​​the infrared rays irradiated from the surface light source to the reaction solution is, for example, 0.5 cm square to 10 cm square, and preferably 1.0 cm square to 5 cm square. The irradiation energy per unit area of ​​the infrared rays is, for example, 0.1 W / cm ２ or more, preferably 0.3 W / cm ２ That's all. When infrared rays have such irradiation energy, the yield of the acetal compound can be improved. In addition, infrared irradiation similar to that described above can be performed by combining an infrared lamp with one or more bandpass filters.

[0023] The reaction solution is typically stirred and mixed during infrared irradiation. The temperature of the reaction solution (reaction temperature) during infrared irradiation is, for example, 0°C or higher, preferably 10°C or higher. On the other hand, the reaction temperature is, for example, 90°C or lower, preferably 80°C or lower, more preferably 60°C or lower, and even more preferably 30°C or lower. When the reaction temperature is within this range, the acetalization reaction can proceed with less energy. Furthermore, during infrared irradiation, the environmental pressure in the space in which the reaction solution exists is, for example, 0.30 MPa or lower, preferably 0.20 MPa or lower, and more preferably 0.15 MPa or lower. On the other hand, the lower limit of the environmental pressure during infrared irradiation is typically 0.10 MPa. When the environmental pressure is within this range, the acetalization reaction can proceed with less energy, and the yield of the acetal compound can be sufficiently improved.

[0024] In one embodiment, the reaction solution is irradiated with the infrared rays in the presence of carbon dioxide. This method can significantly improve the yield of the acetal compound. The carbon dioxide concentration in the space where the reaction solution exists is, for example, 10% by volume to 100% by volume, preferably 50% by volume to 100% by volume, and more preferably 80% by volume to 100% by volume. The carbon dioxide partial pressure in the space where the reaction solution exists is, for example, 0.05 MPa to 0.30 MPa, and preferably 0.10 MPa to 0.20 MPa.

[0025] To introduce carbon dioxide into the space where the reaction solution is present, for example, CO ２ A balloon filled with CO was connected to the reaction solution. ２ These may be used to stably improve the reaction effect.

[0026] The infrared irradiation time is, for example, 10 minutes or more. The shorter the infrared irradiation time, the more preferable it is as long as it can induce the acetalization reaction.

[0027] This induces an acetalization reaction, in which the alcohol compound nucleophilically attacks the carbonyl carbon of the carbonyl group-containing compound, resulting in the elimination of water, thereby producing an acetal compound.

[0028] In one embodiment, water (H ２ O) is removed from the reaction system, which can promote the reaction between the alcohol compound and the carbonyl group-containing compound and improve the yield of the acetal compound.

[0029] As a method for removing water generated in the acetalization reaction from the reaction system, for example, a dehydrating agent can be used. Examples of the dehydrating agent include physical dehydrating agents and chemical dehydrating agents. The physical dehydrating agent is a dehydrating agent that removes water (H ２ Physical dehydrating agents typically have a porous structure. Examples of physical dehydrating agents include molecular sieves, silica gel, and zeolites. Chemical dehydrating agents can adsorb water (H ２ O). Examples of chemical dehydrating agents include chlorides of alkaline earth metals such as calcium chloride; sulfates of alkaline earth metals such as magnesium sulfate; and sulfates of alkali metals such as sodium sulfate. The dehydrating agents may be used alone or in combination. Among the dehydrating agents, preferred are physical dehydrating agents, more preferred are molecular sieves. Examples of molecular sieve types include 3A and 4A, with 3A being preferred. When the molecular sieve type is 4A, water (H ２ In addition to carbon dioxide (CO ２ Therefore, it is assumed that the type 4A molecular sieve is less effective in promoting the acetalization reaction than the type 3A molecular sieve.

[0030] To remove water using a dehydrating agent, for example, a drying tube filled with the above-mentioned dehydrating agent is connected to a reaction vessel containing the reaction solution. This allows the water produced in the acetalization reaction to be smoothly removed from the reaction system. Furthermore, since water can be removed without direct contact between the reaction solution and the dehydrating agent, it is possible to prevent the properties of the dehydrating agent from affecting the acetalization reaction, and the acetalization reaction can be stably promoted.

[0031] The yield of the acetal compound is, for example, 10 mol% or more, preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 70% or more, particularly preferably 80% or more, and particularly preferably 90% or more. On the other hand, the upper limit of the yield of the acetal compound is typically 100 mol% or less. When the yield of the acetal compound is in this range, the acetal compound can be produced efficiently, and the content of by-products in the reaction product can be reduced. Therefore, the efficiency of post-treatment (e.g., purification treatment) of the reaction product can be improved.

[0032] C. Second Embodiment In the first embodiment, the reaction solution is irradiated with infrared rays. In contrast, if the carbonyl group-containing compound and the alcohol compound are reacted in the presence of carbon dioxide at a pressure of 0.2 MPa or less, the desired acetalization reaction can be sufficiently carried out without infrared irradiation.

[0033] In the second embodiment, a reaction liquid is first prepared in the same manner as in the first embodiment. The reaction liquid is then adjusted to the above-described reaction temperature and stirred and mixed in the presence of carbon dioxide. At this time, the environmental pressure in the space in which the reaction liquid exists is 0.20 MPa or less. Meanwhile, the lower limit of the environmental pressure is typically 0.10 MPa. The carbon dioxide concentration in the space in which the reaction liquid exists is, for example, 10% by volume to 100% by volume, preferably 50% by volume to 100% by volume, and more preferably 80% by volume to 100% by volume. The partial pressure of carbon dioxide in the space in which the reaction liquid exists is, for example, 0.05 MPa to 0.30 MPa, preferably 0.10 MPa to 0.20 MPa. When the environmental pressure and / or the carbon dioxide concentration (partial pressure) are within these ranges, an acetal compound can be sufficiently produced without a catalyst or infrared irradiation.

[0034] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0035] (1) Infrared Absorption Spectroscopy (IR) Spectra The IR spectra of benzaldehyde used in the examples and comparative examples were obtained from a database (NIST Chemistry webbook, https: / / webbook.nist.gov / chemistry / ). The IR spectrum of benzaldehyde is shown in FIG.

[0036] Example 1 2.5 mmol of benzaldehyde (0.27 g: manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in methanol (15.0 mL: manufactured by Kanto Chemical Co., Ltd.) and the solution was placed in a reaction vessel. Under normal pressure (0.1 MPa), the reaction vessel was immersed in a thermostatic water bath, and the reaction solution was maintained at 20°C. The reaction vessel was irradiated with infrared light of 5.2 to 6.2 μm, with a peak at 5.7 μm, from the top of the reaction vessel (5 W: infrared irradiation area 3 cm square / irradiation energy per unit area: approximately 0.5 W / cm). ２ ) was started, and the solution was stirred to initiate the reaction. 70 hours after the start of the reaction, stirring was stopped, and the state of the reaction solution was analyzed using an HPLC analyzer (manufactured by Nihon Waters) under the following conditions. <HPLC conditions> Detector: ultraviolet absorbance detector Detection wavelength: 210 nm Eluent: 50% CH ３ CN Flow rate: 0.5 mL / min Injection volume: 5 μL Column: L-column 3 HP type C18 As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to the reaction substrate benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal (i.e., the yield of the acetal compound) was calculated from a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 1.

[0037] Example 2 Benzaldehyde and ethanol were reacted in the same manner as in Example 1, except that methanol was replaced with ethanol. The state of the reaction solution was then analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that benzaldehyde diethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde diethyl acetal was calculated using a calibration curve prepared using a commercially available standard sample of benzaldehyde diethyl acetal. The results are shown in Table 1.

[0038] Example 3 Benzaldehyde and 1-propanol were reacted in the same manner as in Example 1, except that methanol was replaced with 1-propanol. The state of the reaction solution was then analyzed in the same manner as in Example 1 above, using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that (dipropoxymethyl)benzene was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to (dipropoxymethyl)benzene was calculated using a calibration curve prepared using a standard sample of (dipropoxymethyl)benzene synthesized separately. The results are shown in Table 1.

[0039] [Example 4] Infrared irradiation energy per unit area was set to about 0.2 W / cm ２ Benzaldehyde and methanol were reacted in the same manner as in Example 1, except that the temperature was changed to 100°C. Thereafter, the state of the reaction solution was analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated from a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 1.

[0040] [Example 5] The reaction vessel was pre-filled with CO ２ Next, 2.5 mmol of benzaldehyde (0.27 g: manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in methanol (15.0 mL: manufactured by Kanto Chemical Co., Ltd.) and charged into the reaction vessel. ２A balloon filled with CO was connected to the reaction vessel, and the reaction vessel was immersed in a thermostatic water bath to maintain the reaction solution at 20°C, while stirring the solution to initiate the reaction. The pressure inside the reaction vessel was adjusted to 0.1 MPa. ２ The concentration was 100% by volume. 70 hours after the start of the reaction, stirring was stopped, and the state of the reaction solution was analyzed using an HPLC analyzer (manufactured by Nihon Waters) in the same manner as in Example 1 above. As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated using a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 1.

[0041] [Example 6] The reaction vessel was pre-filled with CO ２ Next, 2.5 mmol of benzaldehyde (0.27 g, manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in methanol (15.0 mL, manufactured by Kanto Chemical Co., Ltd.) and charged into the reaction vessel. CO was introduced into the reaction vessel from a gas cylinder. ２ The pressure inside the reaction vessel was increased to about 0.2 MPa, and the reaction vessel was immersed in a thermostatic water bath to maintain the reaction solution at 20°C. ２ The concentration was 100% by volume. In this state, the solution was stirred to initiate the reaction. Stirring was stopped 70 hours after the start of the reaction, and the state of the reaction solution was analyzed in the same manner as in Example 1 above using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated using a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 1.

[0042] Example 7 Benzaldehyde and methanol were reacted in the same manner as in Example 5, except that the temperature of the reaction solution was changed to 60°C. The state of the reaction solution was then analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated using a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 1.

[0043] [Example 8] Infrared rays of 5.2 to 6.2 μm with a peak at 5.7 μm were irradiated from the top of the reaction vessel (5 W: infrared irradiation area 3 cm square / irradiation energy per unit area: approximately 0.5 W / cm ２ Benzaldehyde and methanol were reacted in the same manner as in Example 5, except that the reaction mixture was thawed. The reaction mixture was then analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). The results confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated from a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 1.

[0044] Example 9: Benzaldehyde and methanol were reacted in the same manner as in Example 8, except that a drying tube was connected to the top of the reaction vessel. The drying tube was filled with 1 g of molecular sieve (product name: Molecular Sieves 3A 1 / 16, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a dehydrating agent. The dehydrating agent (molecular sieve) was used to remove H produced by the reaction of benzaldehyde and methanol. ２O was adsorbed and removed from the reaction system. The state of the reaction solution was then analyzed using an HPLC analyzer (manufactured by Nihon Waters) in the same manner as in Example 1 above. As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated from a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 3.

[0045] Example 10: Benzaldehyde and methanol were reacted in the same manner as in Example 9, except that the dehydrating agent packed in the drying tube was changed to calcium chloride. The state of the reaction solution was then analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated using a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 3.

[0046] Comparative Example 1: Benzaldehyde was dissolved in methanol and stirred in the same manner as in Example 1, except that infrared radiation was not applied. The state of the solution was then analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated using a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 2.

[0047] Comparative Example 2: Benzaldehyde was dissolved in ethanol and stirred in the same manner as in Example 2, except that infrared radiation was not applied. The state of the solution was then analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that benzaldehyde diethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde diethyl acetal was calculated using a calibration curve prepared using a commercially available standard sample of benzaldehyde diethyl acetal. The results are shown in Table 2.

[0048] Comparative Example 3: Benzaldehyde was dissolved in 1-propanol and stirred in the same manner as in Example 3, except that infrared radiation was not irradiated. The state of the solution was then analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that (dipropoxymethyl)benzene was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to (dipropoxymethyl)benzene was calculated using a calibration curve prepared using a standard sample of (dipropoxymethyl)benzene synthesized separately. The results are shown in Table 2.

[0049] Comparative Example 4 Benzaldehyde and methanol were reacted in the same manner as in Comparative Example 1, except that the temperature of the reaction solution was changed to 60°C. The state of the reaction solution was then analyzed in the same manner as in Example 1 using an HPLC analyzer (manufactured by Nihon Waters). As a result, it was confirmed that benzaldehyde dimethyl acetal was produced in addition to benzaldehyde. The conversion rate of benzaldehyde to benzaldehyde dimethyl acetal was calculated from a calibration curve prepared using a commercially available standard sample of benzaldehyde dimethyl acetal. The results are shown in Table 2.

[0050]

[0051]

[0052]

[0053] <Evaluation> As is clear from Tables 1 to 3, it was confirmed that the acetalization reaction can be promoted without using a catalyst and the yield of the acetal compound can be improved by irradiating a reaction solution containing benzaldehyde and an alcohol compound with infrared light having an absorption wavelength of benzaldehyde, or by reacting benzaldehyde and an alcohol compound in the presence of carbon dioxide at 0.2 MPa or less.

[0054] The method for producing an acetal compound according to an embodiment of the present invention can be suitably used for producing various industrial products in which an acetal compound is used.

Claims

1. A method for producing an acetal compound, comprising irradiating a reaction solution containing a carbonyl group-containing compound and an alcohol compound with infrared light having an absorption wavelength of the carbonyl group-containing compound, thereby reacting the carbonyl group-containing compound with the alcohol compound.

2. The method for producing an acetal compound according to claim 1, wherein the reaction solution is irradiated with infrared rays in the presence of carbon dioxide.

3. The method for producing an acetal compound according to claim 2, wherein the temperature of the reaction solution is 60°C or less and the environmental pressure is 0.2 MPa or less when the reaction solution is irradiated with the infrared rays.

4. The method for producing an acetal compound according to claim 1, wherein the reaction liquid is substantially free of a catalyst.

5. The method for producing an acetal compound according to claim 1, wherein the carbonyl group-containing compound has an aromatic ring and a carbonyl group bonded to the aromatic ring.

6. The method for producing an acetal compound according to claim 1, wherein the infrared wavelength peak is located in the range of 5.7±0.5 μm.

7. A method for producing an acetal compound, comprising reacting a carbonyl group-containing compound with an alcohol compound in the presence of carbon dioxide at a pressure of 0.2 MPa or less.

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