Surfactant composition containing n-acyl amino acid or salt thereof, and method for producing same

Abstract

Provided are: a surfactant composition containing an N-acylamino acid or a salt thereof; and a method for producing the surfactant composition. Provided is a novel technique with which it is possible to suppress odor and further improve hue stability in a surfactant composition containing an N-acylamino acid or a salt thereof. Provided is a surfactant composition which contains an N-acylamino acid represented by formula (1) (in formula (1), R1CO represents an aliphatic acyl group having 8-22 carbon atoms, R2 represents a hydrogen atom or a linear or branched alkyl group having 1-4 carbon atoms and optionally having one hydroxyl group, or a salt thereof, the content ratio of the amino acid represented by formula (2) and a salt thereof being 1% by weight or less, and in formula (2) (in formula (1), R1CO represents an aliphatic acyl group having 8-22 carbon atoms, R2 represents a hydrogen atom or a linear or branched alkyl group having 1-4 carbon atoms and optionally having one hydroxyl group; in formula (1), R2 represents-COOH or-SO3H, R3 represents-COOH or-SO3H, n represents 1, 2 or 3, and in formula (2), R2, R3 and n are as defined above.

Description

Technical Field

[0001] This invention relates to surfactant compositions containing N-acyl amino acids or their salts.

[0002] Compared to conventional alkylbenzene sulfonic acids and their salts, N-acyl amino acids and their salts, as amino acid-type surfactants, are less irritating and have higher safety, while also producing pleasant foam and a pleasant texture. Therefore, N-acyl amino acids and their salts are widely used as base agents in liquid cleansers such as facial cleansers, shower gels, hand soaps, and shampoos, as well as cosmetics, or for improving the user experience.

[0003] As a method for manufacturing N-acyl amino acids and their salts, the Schotten-Baumann process, which involves reacting fatty acyl chlorides in an alkaline aqueous solution of amino acids, is widely used. Patent Documents 1 and 2, which illustrate improvements to this method, describe a method of reacting fatty acyl chlorides in an amino acid water bath containing a hydrophilic solvent in the presence of an alkali.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 46-8685;

[0007] Patent Document 2: Japanese Patent Publication No. 51-38681. Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] One of the objectives of this invention is to provide a novel technology that can suppress odor and further improve color stability for surfactant compositions containing N-acyl amino acids or their salts.

[0010] Technical means to solve technical problems

[0011] Compared to conventional surfactants, N-acyl amino acid surfactants are prone to color change over time and sometimes have a distinctive odor. Therefore, the addition of preservatives such as antioxidants to prevent color change and the addition of large amounts of fragrances to cosmetics to mask the distinctive odor are considered. However, in the design of cosmetics that are liquid, highly transparent, and free of preservatives, given the increasing demand for high-value-added hair and body washes in recent years, products with low odor and high color stability even without added preservatives are preferred.

[0012] To solve the aforementioned technical problems, the inventors conducted in-depth research and surprisingly discovered a strong correlation between the aforementioned odor and color stability and the trace amounts of amino acids used as raw materials. Therefore, the inventors developed a technology capable of reducing the residual amount of amino acids used as raw materials, thus completing this invention.

[0013] The technical concept of this invention is as follows.

[0014] (A) A surfactant composition containing an N-acyl amino acid of formula (1) or a salt thereof, wherein the amino acid of formula (2) or its salt is contained in a proportion of less than 1% by weight.

[0015]

[0016] In formula (1), R1CO represents an aliphatic acyl group with 8 to 22 carbon atoms, R2 represents a hydrogen atom or a straight-chain or branched alkyl group with 1 to 4 carbon atoms that can have one hydroxyl group, R3 represents -COOH or -SO3H, and n represents 1, 2 or 3.

[0017]

[0018] In equation (2), R2, R3, and n are the same as defined above.

[0019] (B) A method for manufacturing a surfactant composition containing an N-acyl amino acid or a salt thereof as shown in formula (1), comprising the following steps:

[0020] In the presence of a base, in a reaction solution containing water as a solvent, a fatty acyl chloride reacts with the amino acid shown in formula (2) to generate the N-acyl amino acid shown in formula (1).

[0021] The pH of the reaction solution containing the N-acyl amino acid shown in formula (1) is adjusted to below 2.

[0022] The reaction solution, with its pH adjusted to below 2, is separated at a temperature above 80°C.

[0023] The phase containing the N-acyl amino acid represented by formula (1) was washed with water.

[0024]

[0025] In formula (1), R1CO represents an aliphatic acyl group with 8 to 22 carbon atoms, R2 represents a hydrogen atom or a straight-chain or branched alkyl group with 1 to 4 carbon atoms that can have one hydroxyl group, R3 represents -COOH or -SO3H, and n represents 1, 2 or 3.

[0026]

[0027] In equation (2), R2, R3, and n are the same as defined above.

[0028] (C) The manufacturing method according to (B) wherein, for a phase containing an N-acyl amino acid as shown in formula (1), the phase is washed with water in an amount of 1 to 30 times that of the phase.

[0029] (D) A method for suppressing odor and improving color stability of a surfactant composition containing an N-acyl amino acid or a salt thereof as shown in formula (1), comprising the following steps:

[0030] In the presence of a base, in a reaction solution containing water as a solvent, a fatty acyl chloride reacts with the amino acid shown in formula (2) to generate the N-acyl amino acid shown in formula (1).

[0031] The pH of the reaction solution containing the N-acyl amino acid of formula (1) is adjusted to below 2. The reaction solution with pH adjusted to below 2 is separated at a temperature above 80°C. The phase containing the N-acyl amino acid or its salt of formula (1) is washed with water.

[0032]

[0033] In formula (1), R1CO represents an aliphatic acyl group with 8 to 22 carbon atoms, R2 represents a hydrogen atom or a straight-chain or branched alkyl group with 1 to 4 carbon atoms that can have one hydroxyl group, R3 represents -COOH or -SO3H, and n represents 1, 2 or 3.

[0034]

[0035] In equation (2), R2, R3, and n are the same as defined above.

[0036] (E) The method according to (D), wherein, for a phase containing an N-acyl amino acid as shown in formula (1), the phase is washed with water in an amount of 1 to 30 times that of the phase.

[0037] Invention Effects

[0038] The present invention provides a novel technique for suppressing odors and further improving color stability in surfactant compositions containing N-acyl amino acids or their salts. Detailed Implementation

[0039] Hereinafter, one embodiment of the present invention will be described. However, the present invention is not limited to the following embodiment.

[0040] This embodiment relates to a surfactant composition containing an N-acyl amino acid or a salt thereof as shown in formula (1).

[0041]

[0042] In formula (1), R1CO represents an aliphatic acyl group with 8 to 22 carbon atoms, R2 represents a hydrogen atom or a straight-chain or branched alkyl group with 1 to 4 carbon atoms that can have 1 hydroxyl group, R3 represents -COOH or -SO3H, and n represents 1, 2 or 3.

[0043] The aliphatic acyl group of R1CO with 8 to 22 carbon atoms can be an acyl group derived from saturated or unsaturated fatty acids with 8 to 22 carbon atoms, or an acyl group derived from a mixture of two or more fatty acids containing these fatty acids. Examples of aliphatic acyl groups with 8 to 22 carbon atoms include octanoyl, hexanoyl, lauroyl, myristoyl, palmitoyl, stearyl, oleoyl, behenyl, coconut oil fatty acid acyl, and palm kernel oil fatty acid acyl, with lauroyl, myristoyl, oleoyl, coconut oil fatty acid acyl, and palm kernel oil fatty acid acyl being preferred.

[0044] Furthermore, the surfactant composition of this embodiment may contain an amino acid or a salt thereof as shown in formula (2). Examples of amino acids and their salts containing formula (2) include, for example, the precursor of the N-acyl amino acid shown in formula (1) and the amino acid and its salt.

[0045]

[0046] In formula (2), R2 represents a hydrogen atom or a straight-chain or branched alkyl group with 1 to 4 carbon atoms that can have 1 hydroxyl group, R3 represents -COOH or -SO3H, and n represents 1, 2 or 3.

[0047] Examples of straight-chain or branched alkyl groups having 1 to 4 carbon atoms and capable of having one hydroxyl group include methyl, ethyl, propyl, butyl, isopropyl, isobutyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxyisopropyl, hydroxybutyl, and hydroxyisobutyl.

[0048] Furthermore, R2 is preferred because hydrogen atoms, methyl groups, and hydroxyethyl groups have high foaming properties and low irritation.

[0049] Examples of specific compounds containing the amino acid represented by formula (2) include sarcosine, β-alanine, N-methyl-β-alanine, N-hydroxyethyl-β-alanine, and N-methyl-taurine. Furthermore, examples of specific compounds containing the N-acyl amino acid represented by formula (1) include acylsarcosine, acyl-β-alanine, acyl-N-methyl-β-alanine, acyl-N-hydroxyethyl-β-alanine, and acyl-N-methyl-taurine.

[0050] As described above, the surfactant composition of this embodiment may contain a salt of an N-acyl amino acid as shown in formula (1) and / or a salt of an amino acid as shown in formula (2). Specifically, salts formed with alkali metals, alkaline earth metals, ammonia, or organic ammonium compounds may be cited. Examples of alkali metals include potassium and sodium. Examples of alkaline earth metals include calcium and magnesium. Examples of organic ammonium compounds include alkanolamines and alkylamines. In the case of salts formed with divalent alkali metals and alkaline earth metals, half-salts (1 / 2 salts) may be formed.

[0051] Among them, compositions that are highly foaming, low in irritation, and transparent are preferred by selecting salts formed with potassium and / or sodium as alkali metal salts or salts formed with alkanolamines as organic ammonium salts.

[0052] In the surfactant composition of this embodiment, the content of the amino acid and its salt represented by formula (2) is reduced, resulting in the suppression of odor and the improvement of color stability.

[0053] From the viewpoint of suppressing odor and improving color stability, the proportion of the compound of formula (2) as an amino acid and its salt in the surfactant composition of this embodiment is preferably 1% by weight or less, more preferably 0.5% by weight or less, and even more preferably 0.3% by weight or less.

[0054] Furthermore, without particular limitation, the content ratio of the N-acyl amino acid or its salt represented by formula (1) in the surfactant composition of this embodiment can be, for example, 15% by weight or more and 100% by weight or less, preferably 25% by weight or more and 100% by weight or less. Furthermore, when the surfactant composition of this embodiment is an aqueous solution, the content ratio of the N-acyl amino acid or its salt represented by formula (1) is more preferably 25% by weight or more and 35% by weight or less. By adjusting the concentration of the aqueous solution to 25% or more, the relationship with the amount of water that can be used during formulation is easily improved in terms of operability. Furthermore, by adjusting it to 35% or less, gelation and curing under low-temperature winter conditions can be suppressed. The surfactant composition of this embodiment can also be prepared into solvent-free powder or blocks using known methods such as spray drying or freeze drying.

[0055] The surfactant composition of this embodiment may contain other components in addition to the N-acyl amino acid or its salt shown in formula (1) and the amino acid or its salt shown in formula (2), within the scope of achieving the purpose of the present invention, and is not particularly limited thereto.

[0056] For example, the surfactant composition of this embodiment may contain free fatty acids. The amount of free fatty acids contained in the surfactant composition of this embodiment is not particularly limited, but their inclusion contributes to a refreshing feel during washing and helps improve foam density. Furthermore, by keeping the free fatty acid content at 10% by weight or less, improved stability can be achieved by reducing odor and inhibiting gelation, as well as improved low-temperature transparency when the surfactant composition is transparent; therefore, this is preferred.

[0057] The surfactant composition of this embodiment exhibits higher hue stability over time even without the use of preservatives. On the other hand, the surfactant composition of this embodiment may also contain preservatives. Examples of such preservatives include antioxidants and chelating agents, such as diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), N-(2-acetamide)iminodiacetic acid (ADA), N-(2-hydroxyethyl)iminodiacetic acid (HIDA), hydroxyethylidene diphosphonic acid (HEDP), pyrophosphate, neridonic acid, alendronic acid, 2-pyridinol-1-oxide (HPNO), and juniper alcohol.

[0058] The surfactant composition of this embodiment can be manufactured, for example, by a method comprising the following steps:

[0059] In the presence of a base, in a reaction solution containing water as a solvent, a fatty acyl chloride is reacted with the amino acid shown in formula (2) to generate the N-acyl amino acid shown in formula (1).

[0060] The pH of the reaction solution containing the N-acyl amino acid shown in formula (1) was adjusted to below 2.

[0061] Separate the reaction solution with a pH adjusted to below 2 at a temperature above 80°C.

[0062] The phase containing the N-acyl amino acid shown in formula (1) is washed with water.

[0063] Specifically, the surfactant composition of this embodiment can be manufactured, for example, as follows.

[0064] First, an N-acyl amino acid of formula (1) is generated as an acylated product derived by acylation of an amino acid of formula (2) with a fatty acid derivative. This step can be a so-called Schott-Baumann reaction in which an amino acid equivalent to formula (2) and a fatty acyl chloride are condensed in the presence of a base, and water can be used as a reaction solvent, for example. On the other hand, if the amino acid of formula (2) has low dispersibility in water and the reaction does not proceed, an inactive hydrophilic organic solvent can be added to the fatty acyl chloride to prepare a mixed solvent with water. Examples of such inactive hydrophilic organic solvents include acetone, methyl ethyl ketone, and tetrahydrofuran. Since the content of the amino acid and its salt of formula (2) can be further reduced, the amount of hydrophilic organic solvent added is preferably 50% by weight or less, more preferably 10% by weight or less, and more preferably 0% by weight, relative to the water used as solvent.

[0065] Fatty acids from which R1CO in formula (1) originate are preferred because they are renewable raw materials with low environmental impact, thus having a low likelihood of depletion and being able to be used stably. In the case of mixed fatty acids, one or more fatty acids can be used in combination, and any mixing ratio of fatty acids can be used to achieve the desired user experience.

[0066] The amount of fatty acyl chloride relative to the amino acid belonging to formula (2) in the Shoten-Baumann reaction is preferably 0.9 equivalents or more and less than 1 equivalent. By adjusting to 0.9 equivalents or more, the economic advantage can be maintained, and by adjusting to less than 1 equivalent, the decrease in transparency caused by the increase of free fatty acids when the composition is transparent can be suppressed. If the amount of base used in the reaction is 1 equivalent or more and less than 1.2 equivalents relative to the acyl chloride used, it can be added in advance, or it can be added in conjunction with the addition of the acyl chloride. By adding 1 equivalent or more of base, the increase of free fatty acids caused by the slow reaction can be suppressed. In addition, by adding less than 1.2 equivalents, the need for a large amount of acid during neutralization in the next step can be avoided. The base used is not particularly limited as long as it can neutralize the chlorine generated in the Shoten-Baumann reaction, and readily available sodium hydroxide or potassium hydroxide can be used.

[0067] The reaction temperature can be arbitrarily selected within the range of 10℃ to 60℃, and is therefore preferred. By adjusting the temperature to 10℃ or higher, the increase in free fatty acids caused by the hydrolysis of fatty acyl chlorides, which is due to the slowing of the reaction, can be suppressed. Furthermore, by adjusting the temperature to 60℃ or lower, the increase in free fatty acids caused by the rapid hydrolysis of fatty acyl chlorides can be suppressed. From the viewpoint of suppressing the amount of free fatty acids generated after the acylation reaction, the reaction temperature is preferably 20℃ or higher and 50℃ or lower, and more preferably 30℃ or higher and 45℃ or lower. The reaction time is not particularly limited as long as it is within the range where heat generation can be controlled, and a ripening time can be set as needed after the reaction is completed.

[0068] After the acylation reaction, the pH of the reaction solution is adjusted to below 2 using acid, and the mixture is separated at a temperature above 80°C. The phase containing the acyl amino acid shown in formula (1) is then washed with water. By performing these steps after the acylation reaction, the proportion of the amino acid shown in formula (2) can be reduced.

[0069] The acid used to adjust the pH is preferably sulfuric acid and / or hydrochloric acid, which can minimize the amount of water loss from stratification. Sulfuric acid is particularly preferred, as it is a divalent acid with little odor derived from acid.

[0070] As described above, the separation can be carried out at a temperature above 80°C.

[0071] The amount of water used in the washing process is appropriately set by those skilled in the art and is not particularly limited. The proportion of the amino acid and its salt shown in formula (2) can be further reduced, and from the viewpoint of increasing yield, it is preferably 1 to 30 times more than the amount of the phase containing the acyl amino acid shown in formula (1). In addition, the temperature in the washing process is not particularly limited, and for example, it can be adjusted to the same temperature as the separation process.

[0072] After washing, the acyl amino acid shown in formula (1) can be neutralized with alkali metals, alkaline earth metals or organic ammonium, depending on the purpose.

[0073] According to this embodiment, the odor of the surfactant composition containing N-acyl amino acids can be suppressed, and the color stability can be improved.

[0074] In the surfactant composition of this embodiment, for example, no fragrance is added for masking, which helps to provide preservative-free shampoos, shower gels, facial cleansers and other toiletries that are of high concern to general consumers.

[0075] Example

[0076] The present invention will now be specifically described through examples and comparative examples, but the present invention is not limited to these examples in any way. Furthermore, unless otherwise specified, the raw materials used in the following examples or comparative examples are reagents manufactured by Kanto Chemical Co., Ltd. or Sigma-Aldrich Co., Ltd.

[0077] Method for determining the amino acid content of formula (2) in surfactant compositions

[0078] In a sealed flask, 30 g of distilled water and caustic soda (48%, 1.1 g (1.8 equivalents relative to benzoyl chloride)) were mixed with 1.0 g of a surfactant composition containing an N-acyl amino acid. Then, 1.0 g of benzoyl chloride was added, and the mixture was stirred in a bath at 30–45°C for at least 1 hour. Afterwards, the mixture was analyzed by high-performance liquid chromatography (HPLC) using an Inertsil ODS-2 chromatograph (manufactured by Nippon Spectrophotometers). The analysis was performed using the following methods: column temperature: 40℃, 0.1M NaH2PO4 (pH 2.1) / CH3OH = 65 / 35, flow rate: 1.0 mL / min, sample volume: 20 μL, UV wavelength: 220 nm. The amino acid represented by formula (2) was converted to an N-acyl amino acid represented by formula (1) using the same procedure, extracted with ethyl acetate, concentrated and dried. The product purified by column chromatography with hexane / ethyl acetate (MB-4B manufactured by Fuji Silysia Chemicals) was used as a standard. Quantification was performed using the absolute standard curve method, and the content of the amino acid represented by formula (2) remaining in the surfactant composition was calculated according to the following formula. For determination methods not specifically described, the determination was performed according to the "General Test Method" "2.01 Liquid Chromatograph" in "18th Amendment to the Japanese Pharmacopoeia, Supplement 1".

[0079] The content of amino acids shown in formula (2) (wt%) = the content of amino acids shown in formula (2) (g) / (the content of amino acids shown in formula (2) (g) + the content of N-acyl amino acids shown in formula (1) (g)) × 100

[0080] Evaluation of the odor of surfactant compositions

[0081] The odor of the surfactant composition is evaluated in four levels, starting from the weakest: "almost no odor", "barely perceptible odor", "weak odor with some smell" and "easily perceptible odor".

[0082] As a control, Comparative Example 5, described later, was used. For the evaluation of the level of odor being weaker than the control, it was evaluated as odor suppression. Furthermore, the cases evaluated as "almost no odor" and "barely perceptible odor" were evaluated as preferred results because, for example, the odor was so mild that it could be said that the formulation did not require fragrance to mask the odor from the amino acids shown in Formula (2).

[0083] Evaluation of the color stability of surfactant compositions

[0084] 100g of the surfactant composition was sealed in a glass vial (manufactured by Toyo Glass Co., Ltd., S-112), and left to stand in a constant temperature bath at 80°C for 18 hours. The Hasen unit color number (APHA) was then measured using a Spectrometer SE7700 (Nippon Denshoku Kogyo Co., Ltd.).

[0085] As a control, Comparative Example 5, described later, was used. A lower APHA value compared to this control was considered an improvement in hue stability.

[0086] Example 1

[0087] 156 g of a 27 wt% aqueous solution of N-methyl-β-alanine sodium, 210 g of tap water, and 13 g of 48 wt% sodium hydroxide were added to a 1 L four-necked flask equipped with a stirrer and the mixture was brought to 30 °C in a water bath. 72 g of lauroyl chloride and 13 g of 48 wt% sodium hydroxide were added dropwise over 1 hour at a temperature range of 30–40 °C, followed by aging over the same temperature range for 0.5 hours after each addition. After aging, 50 g of 75 wt% sulfuric acid was added to adjust the pH to 1.5, and the mixture was heated to 80 °C and allowed to stand for 1 hour before separation. 120 g of water was added to the upper layer, and the mixture was heated to 80 °C and allowed to stand for 1 hour, with two more separation operations performed. Then, 200 g of water and 26 g of 48% sodium hydroxide were added to obtain 310 g of a 30 wt% aqueous solution of N-lauroyl-N-methyl-β-alanine sodium as the surfactant composition. The residual amount of N-methyl-β-alanine sodium in the 30% wt% aqueous solution of N-lauroyl-N-methyl-β-alanine sodium was 0.02% wt%, with almost no odor, and the APHA after the color stability test was 10.

[0088] Example 2

[0089] Except that lauroyl chloride in Example 1 was replaced with coconut oil fatty acyl chloride, the reaction was carried out in the same manner as in Example 1 to obtain 330 g of a 25 wt% aqueous solution of N-cocoyl-N-methyl-β-alanine sodium as a surfactant composition. The residual amount of N-methyl-β-alanine sodium in the obtained 25 wt% aqueous solution of N-cocoyl-N-methyl-β-alanine sodium was 0.1 wt%, it had almost no odor, and the APHA after the color stability test was 10.

[0090] Example 3

[0091] Except that the amount of sulfuric acid used in neutralization in Example 1 was adjusted to 35g and the pH was adjusted to 2, the reaction was carried out in the same manner as in Example 1, yielding 310g of a 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium as the surfactant composition. The residual amount of N-methyl-β-alanine sodium in the obtained 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium was 1% by weight, with a barely perceptible odor, and an APHA of 20 after a color stability test.

[0092] Example 4

[0093] Except that the water used for washing in Example 1 was set to 175g, the reaction was carried out in the same manner as in Example 1, yielding 310g of a 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium as the surfactant composition. The residual amount of N-methyl-β-alanine sodium in the obtained 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium was 0.2% by weight, it had almost no odor, and the APHA after the color stability test was 15.

[0094] Example 5

[0095] Except for replacing the sodium N-methyl-β-alanine in Example 2 with 123 g of a 30 wt% aqueous solution of sodium β-alanine, replacing the 48 wt% sodium hydroxide used in salt formation with 34 g of 48 wt% potassium hydroxide after washing, and changing the N-acyl amino acid concentration to 25 wt%, the reaction was carried out in the same manner as in Example 2 to obtain 370 g of a 25 wt% aqueous solution of potassium N-cocoyl-β-alanine as a surfactant composition. The residual amount of potassium β-alanine in the obtained 25 wt% aqueous solution of potassium N-cocoyl-β-alanine was 0.1 wt%, it had almost no odor, and the APHA after the color stability test was 20.

[0096] Example 6

[0097] The sodium N-methyl-β-alanine in Example 1 was replaced with 150 g of a 30 wt% aqueous solution of sodium N-hydroxyethyl-β-alanine, and 100 g of tetrahydrofuran was added as an organic solvent for reaction. After washing with water, the solution was degelatinized and neutralized as in Example 1, thereby obtaining 300 g of a 30 wt% aqueous solution of sodium N-lauroyl-N-hydroxyethyl-β-alanine as a surfactant composition. The residual amount of sodium N-hydroxyethyl-β-alanine in the obtained 30 wt% aqueous solution of sodium N-lauroyl-N-hydroxyethyl-β-alanine was 1.0 wt%, with almost no odor, and an APHA of 10 after a color stability test.

[0098] Example 7

[0099] Except that the sodium N-methyl-β-alanine in Example 1 was replaced with 90 g of a 30 wt% aqueous solution of sodium sarcosinate, the reaction was carried out in the same manner to obtain 350 g of a 30 wt% aqueous solution of sodium N-lauroyl sarcosinate as a surfactant composition. The residual amount of sodium sarcosinate in the obtained 30 wt% aqueous solution of sodium N-lauroyl sarcosinate was 0.05 wt%, it had almost no odor, and the APHA after the color stability test was 10.

[0100] Comparative Example 1

[0101] The amount of 75% sulfuric acid used in Example 1 was adjusted to 28g, and the pH was adjusted to 3. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain 220g of a 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium as the surfactant composition. The resulting 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium contained 1.5% by weight of residual N-methyl-β-alanine sodium, had a weak odor (not noticeable), and an APHA of 15 after a color stability test.

[0102] Comparative Example 2

[0103] The 75% sulfuric acid in Example 1 was replaced with glacial acetic acid, the amount used was adjusted to 20g, and the pH was adjusted to 4. Otherwise, the procedure was performed in the same manner as in Example 1 to obtain 250g of a 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium as the surfactant composition. The resulting 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium contained 5% by weight of residual N-methyl-β-alanine sodium, had an easily perceptible odor, and an APHA of 30 after a color stability test.

[0104] Comparative Example 3

[0105] The separation temperature of Example 1 was adjusted to 60°C. Otherwise, the operation was the same as in Example 1. However, a large amount of intermediate layer was generated, making separation impossible. When cooled to room temperature, a large amount of salt precipitated, so the analysis was abandoned.

[0106] Comparative Example 4

[0107] The amount of sulfuric acid used in Example 6 was adjusted from 75% by weight to 28 g, and the pH was adjusted to 3. Otherwise, the procedure was performed in the same manner as in Example 6 to obtain 220 g of a 30% aqueous solution of N-lauroyl-N-hydroxyethyl-β-alanine sodium as the surfactant composition. The resulting 30% by weight aqueous solution of N-lauroyl-N-hydroxyethyl-β-alanine sodium contained 3% by weight of residual N-hydroxyethyl-β-alanine sodium, had a readily perceptible odor, and an APHA of 50 after a color stability test.

[0108] Comparative Example 5

[0109] The same procedures were performed before the first separation step in Example 1, but without the water washing step, and the process was transferred to the neutralization step. 320 g of a 30 wt% aqueous solution of N-lauroyl-N-methyl-β-alanine sodium as the surfactant composition was obtained. The residual amount of N-methyl-β-alanine sodium in the obtained 30 wt% aqueous solution of N-lauroyl-N-methyl-β-alanine sodium was 1.5 wt%, it had a weak odor with no perceptible smell, and the APHA after the color stability test was 25.

[0110] Reference Example

[0111] In Comparative Example 2, 100 ppm of hydroxyethylidene diphosphonic acid was added to a 30% by weight aqueous solution of N-lauroyl-N-methyl-β-alanine sodium, and a color stability test was conducted. The APHA value after the color stability test was 10.

[0112] As can be understood from the above test results of the examples and comparative examples, the odor is suppressed and the color stability is improved due to the reduced content of the amino acid of formula (2) in the surfactant composition. In addition, if the content of the amino acid of formula (2) is 1% or less, a surfactant composition containing N-acyl amino acid or its salt can be obtained with less odor and higher color stability.

[0113] Hair cleaning agent composition formulation example

[0114] The following fragrance-free shampoo is manufactured. The shampoo composition exhibits minimal odor and no color change during stability testing.

[0115] (Formula Example 1)

[0116]

[0117] (Formula Example 2)

[0118]

[0119] The following fragrance-free shampoo is manufactured. This shampoo composition has an odor derived from the raw amino acids and undergoes a color change during stability testing.

[0120] (Formula Comparison Example 1)

[0121]

[0122]

[0123] (Formula Comparison Example 2)

[0124]

Claims

1. A surfactant composition containing an N-acyl amino acid represented by formula (1) or a salt thereof, and an amino acid represented by formula (2) and a salt thereof at a content ratio of 1% by weight or less, ###0001### (1) ###0002### (2) wherein R1CO in formula (1) represents an aliphatic acyl group having 8 to 22 carbon atoms, R2 represents a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms which can have one hydroxyl group, R3 represents -COOH or -SO3H, and n represents 1, 2 or 3, and R2, R3 and n in formula (2) are the same as defined above.

2. A method for producing a surfactant composition containing an N-acyl amino acid represented by formula (1) or a salt thereof, comprising the following steps: reacting a fatty acid chloride and an amino acid represented by formula (2) in a reaction solution containing water as a solvent in the presence of a base to produce the N-acyl amino acid represented by formula (1), ###0001### (1) ###0002### (2) adjusting the pH of the reaction solution containing the N-acyl amino acid represented by formula (1) to 2 or less, separating the reaction solution having a pH of 2 or less at 80°C or higher, and washing the phase containing the N-acyl amino acid represented by formula (1) with water, wherein R1CO in formula (1) represents an aliphatic acyl group having 8 to 22 carbon atoms, R2 represents a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms which can have one hydroxyl group, R3 represents -COOH or -SO3H, and n represents 1, 2 or 3, and R2, R3 and n in formula (2) are the same as defined above.

3. The method according to claim 2, wherein the phase containing the N-acyl amino acid represented by formula (1) is washed with water in an amount of 1 times or more and 30 times or less relative to the phase.

4. A method for suppressing odor and improving color phase stability of a surfactant composition containing an N-acyl amino acid represented by formula (1) or a salt thereof, comprising the following steps: reacting a fatty acid chloride and an amino acid represented by formula (2) in a reaction solution containing water as a solvent in the presence of a base to produce the N-acyl amino acid represented by formula (1), ###0001### (1) ###0002### (2) adjusting the pH of the reaction solution containing the N-acyl amino acid represented by formula (1) to 2 or less, separating the reaction solution having a pH of 2 or less at 80°C or higher, and washing the phase containing the N-acyl amino acid represented by formula (1) or a salt thereof with water, wherein R1CO in formula (1) represents an aliphatic acyl group having 8 to 22 carbon atoms, R2 represents a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms which can have one hydroxyl group, R3 represents -COOH or -SO3H, and n represents 1, 2 or 3, and R2, R3 and n in formula (2) are the same as defined above.

5. The method according to claim 4, wherein the phase containing the N-acyl amino acid represented by formula (1) is washed with water in an amount of 1 times or more and 30 times or less relative to the phase. ​ ​ ​ ​ ​ 3. The manufacturing method according to claim 2, wherein, ​ ​ ​ ​ ​ ​ ​ ​ 5. The method of claim 4, wherein, ​

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