Method for producing N-acylamines

Abstract

To provide a method for producing easily N-acylamine that resists coloring without using other components (such as catalysts) in addition to raw materials.SOLUTION: An method for producing N-acylamino acid includes a process in which, while irradiating an amino acid with microwaves, the amino acid is brought into contact with a fatty acid having a smaller amount of substance than that of the amino acid, to acylate the amino acid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing N-acylamines. [Background technology]

[0002] N-Acylamines such as N-acyl-N-methyltaurine salts are widely used as raw materials for various body cleansing agents such as shampoos, cosmetics, etc. Various methods are known for producing N-acylamines, such as a method for producing an N-acylamino acid by a dehydration reaction between an amino acid and a fatty acid, and a method for producing an N-acyl-N-methyltaurine salt by a dehydration reaction between an alkali metal salt of N-methyltaurine and a fatty acid (Patent Documents 1 and 2, etc.). However, these methods are known to have problems such as coloration of the product.

[0003] To solve this problem, a method has been proposed in which the dehydration reaction is carried out in the presence of a catalyst (Patent Document 3), and a method in which the dehydration reaction is carried out while blowing in nitrogen gas under specified conditions (Patent Document 4).

[0004] However, when N-acylamines are used as raw materials for cosmetics or body cleansers (such as shampoos), it is desirable that no catalyst or other components remain, and it is also desirable to be able to produce N-acylamines without requiring complicated operations. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] British Patent No. 1337782 [Patent Document 2] U.S. Patent No. 2,880,219 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-234868 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-8603 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above-mentioned problems in the prior art, an object of the present invention is to provide a method for producing N-acylamines with reduced coloration by a simple operation without using any components other than raw materials such as a catalyst. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the above problems can be solved by selectively and uniformly activating the desired components using microwaves, and have thus completed the present invention. The present invention relates to the following [1] to [3].

[0008] [1] A method for producing N-acylamino acids, comprising the step of acylating amino acids by contacting the amino acids with a fatty acid in a substance amount smaller than the substance amount of the amino acids while irradiating the amino acids with microwaves.

[0009] [2] The method for producing N-acylamino acids according to [1], wherein the step is a step of acylating the amino acids by irradiating microwaves to a mixture containing the amino acids and the fatty acids, wherein the amount of the amino acids is greater than the amount of the fatty acids.

[0010] [3] The method for producing N-acylamino acids according to [1] or [2] above, wherein the amino acids are amino acids, taurine compounds represented by the following formula (1), or salts thereof:

[0011] [ka]

[0012] [In the formula, R 1is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, R 2 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, R 3 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. [Effects of the Invention]

[0013] According to the production method of the present invention, N-acylamines with reduced coloration can be easily produced without using any components other than raw materials such as a catalyst, and therefore without the need for post-treatments such as removal of residual components or decolorization. [Brief explanation of the drawings]

[0014] [Figure 1] Figure 1 shows the microwave absorption characteristics (dielectric loss factor ε"-frequency curve) of an aqueous solution of sodium N-methyl taurine. [Figure 2] FIG. 2 shows the microwave absorption characteristics (dielectric loss factor ε″-frequency curve) of lauric acid. [Figure 3] FIG. 3 shows the microwave absorption characteristics of water (dielectric loss factor ε″-frequency curve). [Figure 4] FIG. 4 shows the microwave absorption characteristics (dielectric loss factor ε″-frequency curve) of an aqueous solution of sodium N-lauroyl-N-methyl taurate. [Figure 5] FIG. 5 shows the results of color quantification of sodium N-lauroyl-N-methyltaurine synthesized in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will now be described in further detail. The method for producing N-acylamino acids according to the present invention is characterized by comprising a step of acylating the amino acids by contacting the amino acids with a fatty acid in a substance amount smaller than the substance amount of the amino acids while irradiating the amino acids with microwaves.

[0016] The embodiment of the process may be, for example, (Aspect 1): A step of acylating the amino acids by irradiating a mixture containing the amino acids and the fatty acids, wherein the amount of the amino acids is greater than the amount of the fatty acids, with microwaves; and (Aspect 2): A step of acylating the amino acids by adding the fatty acid to the amino acids in a substance amount smaller than that of the amino acids while irradiating the amino acids with microwaves. Examples include:

[0017] The production method of the present invention will be described below, focusing on the first embodiment. (amino acids) Examples of the amino acids include amino acids, amino acid derivatives, and salts thereof.

[0018] The amino acid is a compound having one or more amino groups and one or more carboxyl groups in one molecule, preferably one amino group and one carboxyl group.

[0019] The amino group contained in the amino group is an amino group represented by NH2, NHR, or NRR' (R represents an alkyl group having 1 to 6 carbon atoms, preferably a methyl group, and R' represents an alkyl group having 1 to 6 carbon atoms, preferably a methyl group), and at least one amino group is an amino group represented by NH2 or NHR.

[0020] Examples of the amino acid include glycine, alanine, β-alanine, aminobutyric acid, aminovaleric acid, N-methylglycine, N-methylalanine, and N-methyl-β-alanine.

[0021] The amino acid derivative is a compound in which one or more carboxyl groups of the amino acid are replaced with a group selected from the group consisting of a sulfo group (SO3H) and a phosphate group (H2PO4).

[0022] The amino acid derivatives include, for example, taurine compounds represented by the following formula (1):

[0023] [ka]

[0024] [In the formula, R 1 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and is preferably a methyl group. R 2 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms (preferably 1 to 8, more preferably 1 to 4), and is preferably a hydrogen atom. R 3 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms (preferably 1 to 8, more preferably 1 to 4), and is preferably a hydrogen atom.

[0025] The taurine compound represented by the above formula (1) preferably includes N-methyltaurine.

[0026] Examples of salts of the amino acids or amino acid derivatives include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts and magnesium salts, and ammonium salts, with alkali metal salts being preferred and sodium salts being more preferred.

[0027] The amino acids are preferably N-methyl taurate sodium, N-methyl alanine, and N-methyl glycine, and more preferably N-methyl taurate sodium.

[0028] FIG. 1 shows the dielectric loss factor ε"-frequency curve of an aqueous solution of sodium N-methyl taurate, one of the amino acids, at 50°C, measured in the Examples described below. In the frequency measurement range shown in FIG. 1, sodium N-methyl taurate has a large dielectric loss factor ε" and high microwave absorption ability.

[0029] Amino acid molecules have carboxyl and amino groups, and therefore form zwitterions. Generally, microwave energy is converted into heat through either conductive, dielectric, or magnetic loss, depending on the molecule that absorbs it. Therefore, many amino acids, which are electrical conductors, have a very high microwave absorption capacity. Therefore, amino acids and their salts have a larger dielectric loss factor ε" than fatty acids.

[0030] (fatty acid) The fatty acid generally has 6 to 22, preferably 8 to 20, and more preferably 10 to 18 carbon atoms.

[0031] The fatty acids may be either saturated or unsaturated, and may have a straight or branched chain. The fatty acid may be a single fatty acid or a mixture of multiple fatty acids. The mixture of fatty acids may be naturally occurring or artificially prepared. An example of the mixture is coconut oil fatty acid (i.e., a mixture of multiple fatty acids obtained by hydrolysis of coconut oil).

[0032] Specific examples of the fatty acid include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid. Among these, lauric acid, myristic acid, palmitic acid, and oleic acid are preferred, and lauric acid is more preferred. As the fatty acid, lauric acid and coconut oil fatty acid are preferred.

[0033] FIG. 2 shows a dielectric loss factor ε"-frequency curve of lauric acid, one of the fatty acids, at 50°C, measured in the Examples described later. In the frequency measurement range shown in FIG. 2, lauric acid has a small dielectric loss factor ε" and an extremely low microwave absorption capacity.

[0034] It is known that molecular polarity affects dielectric properties. The polarity of fatty acid molecules is largely dependent on the COOH portion of the molecule. Even if the carbon chain length changes, the polarity remains almost constant, and therefore the dielectric loss factor remains almost constant. This point can be confirmed, for example, by the fact that "Dielectric properties of some edible and medicinal oils at microwave frequency" by Thomas Mathew, AD Vyas, and Deepti Tripathi, Canadian Journal of Pure and Applied Sciences, Vol. 3, No. 3, pp. 953-957, 2009, shows that the dielectric constant and dielectric loss factor of various fats and oils (triglycerides) remain almost unchanged even when the constituent fatty acids are changed. As described above, the microwave absorption capacity of the fatty acids is extremely low.

[0035] (mixture) In the production method of the present invention, the amino acids are contacted with the fatty acids in an amount smaller than the amount of substance of the amino acids while being irradiated with microwaves. For example, microwaves are irradiated to a mixture containing the amino acids and the fatty acids, in which the amount of substance of the amino acids is greater than the amount of substance of the fatty acids.

[0036] The ratio of the amino acids to the fatty acids is, for example, greater than 1:1 and not greater than 10, preferably greater than 1:1 and not greater than 5, and more preferably greater than 1.0 and not greater than 1.1:1.0, in terms of molar ratio (amino acids:fatty acids).

[0037] In the production of N-acylamines according to the present invention, the ratio of the amount of the fatty acid to the amount of the amino acids does not affect the coloration of the N-acylamines. That is, even if the amount of the fatty acid is equal to or greater than the amount of the amino acids, the N-acylamines produced by acylation of the amino acids do not suffer from coloration problems. However, if the amount of the fatty acid is equal to or greater than the amount of the amino acids, unreacted fatty acid remains in the N-acylamines. When N-acylamines are used in products such as commonly used water-based toiletries such as shampoos and oil-in-water cosmetics such as cleansing emulsions, the residual fatty acid, being water-insoluble, precipitates as crystals immediately after formulation or over time, not only impairing the appearance of the final formulation but also significantly affecting product quality, such as by breaking down emulsions. That is, when the amount of the fatty acid is equal to or greater than the amount of the amino acids, a step of removing the remaining fatty acid is essential. Distillation under high temperature and high vacuum is commonly used to remove fatty acids, but the heating during this process can cause discoloration and decomposition of N-acylamines.

[0038] On the other hand, when the amount of the fatty acid is smaller than the amount of the amino acids (i.e., when the amount of the amino acids is greater than the amount of the fatty acid), the production method of the present invention can suppress discoloration of N-acylamines and avoid the above-mentioned remaining unreacted fatty acids. In other words, when using N-acylamines in products such as cosmetics, a step of removing the remaining fatty acids is not required. Although unreacted amino acids remain in the N-acylamines produced by the method of the present invention, these amino acids are water-soluble, and therefore, when using N-acylamines in products such as the toiletries and cosmetics described above, it is not necessary to remove the remaining amino acids. Therefore, when N-acylamines are produced by the method of the present invention, cosmetics and other products using N-acylamines can be produced with a reduced number of steps, without the need for steps such as bleaching and fatty acid removal.

[0039] The mixture is prepared by mixing the amino acids and the fatty acids in the ratios described above. According to the production method of the present invention, N-acylamino acids with reduced coloration can be produced without adding components such as a catalyst to the mixture. Typically, components other than the amino acids and fatty acids that are raw materials, such as a catalyst, are not added to the mixture.

[0040] (Acylation step) Conventionally, a method for producing N-acylamino acids has been known, which includes a step of activating a mixture containing amino acids and fatty acids to acylate them (hereinafter also referred to as an "acylation step"). The production method of the present invention is characterized in that the acylation step is carried out by contacting the amino acids with fatty acids while irradiating the amino acids with microwaves, for example, by irradiating microwaves to a mixture containing amino acids and fatty acids, in which the amount of the amino acids is greater than the amount of the fatty acids.

[0041] The frequency of the microwaves to be irradiated may be, for example, within the range of 300 MHz to 20 GHz, or may be 434 MHz, 915 MHz, 2.45 GHz, 5.8 GHz, 10 GHz, or 24 GHz.

[0042] The temperature at which the acylation step is carried out (hereinafter also referred to as "reaction temperature") can be controlled by, for example, measuring the temperature of the reaction system and adjusting the microwave output based on the measured temperature.

[0043] Here, the reaction temperature refers to the temperature of the mixture as a whole. As mentioned above, in reality, amino acids and fatty acids have significantly different microwave absorption capacities, so the activation state and temperature differ for each component. However, since it is difficult to measure the temperature for each component, the reaction temperature is controlled based on the temperature of the mixture as a whole.

[0044] The reaction temperature is set appropriately depending on the types of amino acids and fatty acids within a range below the decomposition temperature of the N-acylamino acids, but from the viewpoint of ensuring a practical reaction rate and suppressing coloration of the N-acylamino acids, it is, for example, 200 to 250° C., preferably 210 to 230° C. The reaction temperature may be measured invasively using a thermocouple or the like, or non-invasively using infrared rays or the like.

[0045] A preferred method for raising the temperature of a mixture containing amino acids and fatty acids to the reaction temperature is to melt the fatty acids by any method, mix the amino acids with the melted fatty acids, and irradiate the resulting mixture with microwaves.

[0046] The time for carrying out the acylation step, that is, the time from when the temperature of the reaction system is raised to the desired reaction temperature until the microwave irradiation is finished, is appropriately set and is, for example, 0.1 to 3 hours.

[0047] The amino acids may be provided as an aqueous solution or as a dry powder, and are preferably provided as a dry powder or in a form from which moisture has been sufficiently removed. The atmosphere in which the acylation step is carried out is preferably an inert gas atmosphere (e.g., helium gas, nitrogen gas, argon gas), preferably a nitrogen gas atmosphere, from the viewpoint of suppressing coloration of the N-acylamino acid. The inert gas may be supplied to the headspace of a reactor in which the acylation step is carried out, or may be supplied directly into the mixture.

[0048] In the acylation step, the mixture is preferably stirred. The N-acylamines produced in the acylation step may be further purified by a conventionally known method.

[0049] The reason why N-acylamines with reduced coloration can be produced by the production method of the present invention is presumed to be as follows. As described above, the dielectric loss factor of the amino acids, which are one of the raw materials used in the production method of the present invention, is large, while the dielectric loss factor of the fatty acids, which are the other raw materials, is small. On the other hand, the activation temperature of the amino acids is higher than that of the fatty acids.

[0050] In the production method of the present invention, the raw materials are preferably supplied to the reaction system in a state in which moisture has been appropriately removed, since stirring efficiency of a mixture containing moisture is poor. When a powder or a reaction intermediate that has passed through a highly viscous state is heated by conventional heating methods, components located near a heat source such as a heater, an internal heat transfer coil, or a steam jacket tend to be locally heated. When a powder or a highly viscous liquid is heated by conventional methods, the contact time between the material and the heat transfer surface is relatively long. This can lead to the problem of partial or complete deterioration of the reaction intermediate and discoloration.

[0051] However, microwave irradiation enables heating inside the reactor without relying on contact with a heat transfer surface, as is the case with conventional heating methods. This is because microwaves transfer energy directly to microwave-absorbing components (molecules), heating the components as a result of the vibration of the molecules. Therefore, in the present invention, microwave-absorbing amino acids can obtain energy regardless of their position in the reactor, resulting in selective (i.e., amino acids are selected from the amino acids and fatty acids used as raw materials) and uniform heating. Therefore, when microwave irradiation is used, active stirring, as is usually required for heating, may not be necessary.

[0052] In the acylation reaction of the present invention, the microwave-absorbing components are amino acids and N-acylamino acids. Microwave irradiation achieves uniform internal heating of these components, thereby suppressing discoloration.

[0053] (Uses of N-acylamines, etc.) The production method of the present invention makes it possible to produce N-acylamines with reduced discoloration. The production method of the present invention can produce N-acylamines without adding any components other than the raw amino acids and fatty acids, such as catalysts, and therefore can produce N-acylamines that are free of undesirable residual components and are almost completely discolored through a simple process. When incorporated in large quantities into cosmetics, shampoos, and other toiletry products, the N-acylamines produced in this manner are easy to process, reducing the discoloration of the formulation in the final product form. Furthermore, when incorporated into quasi-drugs, they are particularly useful because there is no concern about the effects of residual components on the body. [Example]

[0054] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0055] [Microwave absorption characteristics of raw materials, etc.] (Complex dielectric constant measurement of sodium salts of amino acids) Sodium N-methyl taurate was dissolved in water to a concentration of 20% by mass. The complex permittivity of the resulting solution was measured using a liquid complex permittivity measurement probe over a frequency range of 0.2 GHz to 20 GHz. The measurement results (dielectric loss factor ε"-frequency curve) are shown in Figure 1. It was found that the microwave absorption of sodium N-methyl taurate was extremely high within the frequency range of the measurement. The dielectric loss factor ε"-frequency curve for water, used as a blank, is shown in Figure 3.

[0056] (Complex permittivity measurement of fatty acids) Lauric acid was heated to 50°C to melt it, and the complex permittivity was measured using a liquid complex permittivity measurement probe over the range of 0.2 GHz to 20 GHz. The measurement results (dielectric loss factor ε"-frequency curve) are shown in Figure 2. It was found that the microwave absorption by lauric acid was extremely low within the frequency range measured.

[0057] (Complex permittivity measurement of sodium N-acyl-N-methyltaurine) Sodium N-lauroyl-N-methyl taurate was dissolved in water to a concentration of 20% by mass. The complex permittivity of the resulting aqueous solution was measured using a liquid complex permittivity measurement probe over a frequency range of 0.2 GHz to 20 GHz. The measurement results (dielectric loss factor ε"-frequency curve) are shown in Figure 4. It was found that the microwave absorption of sodium N-lauroyl-N-methyl taurate was extremely high within the frequency range measured.

[0058] [Example 1] (Synthesis of sodium N-lauroyl-N-methyltaurate by microwave heating) 22.3 g of N-methyl taurine sodium powder and 25.0 g of lauric acid melted by heating to 60°C were added to a 100 mL three-neck glass flask. A reflux condenser was connected to the flask, and while dry nitrogen gas was supplied to the flask, the contents of the flask were heated by irradiating them with microwaves at a frequency of 2.45 GHz using a microwave reactor (μReactorEX, Shikoku Keisoku Kogyo Co., Ltd.). Stirring was started when the internal temperature of the flask reached 230°C, and the internal temperature was maintained at 230°C for 60 minutes, after which microwave irradiation was stopped. The internal temperature was measured with a thermocouple and maintained at 230°C by controlling the microwave output according to the measured temperature.

[0059] A portion of the resulting reaction product (a mixture containing the target substance) was collected and dissolved in water to a concentration of 10% by mass, and the content of the target substance (sodium N-lauroyl-N-methyl taurine) was quantified. The quantification was performed using a high-performance liquid chromatograph (manufactured by Shimadzu Corporation) equipped with an evaporative light scattering detector and a UV detector. The content was 72.3% by mass.

[0060] A portion of the resulting reaction product (a mixture containing the target substance) was collected and dissolved in water to a concentration of 10% by mass. The color of the resulting solution was quantified using an L*a*b color system. Quantification was performed using a UV-visible spectrophotometer (JASCO Corporation, V-750). The results are shown in Figure 5.

[0061] [Comparative Example 1] (Synthesis of sodium N-lauroyl-N-methyl taurate by heat transfer) 22.3 g of sodium N-methyl taurate and 25.0 g of lauric acid that had been heated to 60°C and melted were added to a 100 mL three-neck glass flask. A reflux condenser was connected to the flask, and while supplying dry nitrogen gas into the flask, the flask was heated using an aluminum block heater until the internal temperature of the flask reached 230°C. Stirring was started when the internal temperature of the flask reached 230°C, and the internal temperature was maintained at 230°C for 60 minutes, after which heating was stopped. The internal temperature was measured with a thermocouple, and maintained at 230°C by controlling the heater output according to the measured temperature.

[0062] A portion of the resulting reaction product (a mixture containing the target substance) was collected and dissolved in water to a concentration of 10% by mass, and the content of the target substance (sodium N-lauroyl-N-methyltaurine) was quantified in the same manner as in Example 1. The content was 77.5% by mass.

[0063] A portion of the resulting reaction product (a mixture containing the target substance) was collected and dissolved in water to a concentration of 10% by mass, and the color tone of the aqueous solution was quantified based on the L*a*b color system in the same manner as in Example 1. The results are shown in Figure 5.

[0064] In Example 1, in which heating was performed by microwave irradiation, the lightness L* value was higher in both the L*-a* plane and the L*-b* plane in the color tone quantification of the produced sodium N-lauroyl-N-methyl taurine, as compared with Comparative Example 1, in which heating was performed by a heater, and it was found that coloration was suppressed.

Claims

1. The method includes a step of acylating the amino acids without adding a catalyst by contacting the amino acids with a fatty acid in an amount smaller than the amount of the amino acids while irradiating the amino acids with microwaves, The amino acid is a taurine compound represented by the following formula (1) or a salt thereof: A method for producing N-acylamino acids. 【Chemical 1】 [wherein R 1 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R 2 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms; R 3 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms.

2. 2. The method for producing N-acylamino acids according to claim 1, wherein the step is a step of acylating the amino acids by irradiating microwaves to a mixture containing the amino acids and the fatty acids, wherein the amount of the amino acids is greater than the amount of the fatty acids.

3. 3. The method for producing N-acylamino acids according to claim 2, wherein the fatty acid is melted, and the amino acid and the melted fatty acid are mixed to obtain the mixture.

4. The method for producing N-acylamino acids according to any one of claims 1 to 3, wherein the amino acid is sodium N-methyltaurate and the fatty acid is lauric acid.

5. The method for producing N-acylamino acids according to any one of claims 1 to 4, wherein the acylation step is carried out at 200 to 250°C.

6. The method for producing N-acylamino acids according to any one of claims 1 to 5, wherein the amino acids in a reactor are irradiated with microwaves, and the reactor is a flask.

7. 1. A method for producing a product selected from water-based toiletries or oil-in-water cosmetics using N-acylamino acids, comprising: The method comprises the step of producing N-acylamino acids by the method according to any one of claims 1 to 6, does not include a step of removing fatty acids after the step. How the product is manufactured.

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