JPH0570794A - Process for controlling hydrolysis of triethanolamine salt of n-acylaspartic acid - Google Patents

Abstract

PURPOSE:To provide a stable aqueous solution of a triethanolamine salt of N-acylaspartic acid whose surface activity is not reduced even after a long-term storage. CONSTITUTION:The pH of an aqueous solution of a triethanolamine salt of N-acylaspartic acid with a 10-16 C acyl group is maintained at 5.3-6.5 so as to control the hydrolysis of the amine salt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inhibiting hydrolysis of N-acyl aspartic acid triethanolamine salt which is suitable as a raw material for liquid detergents such as detergents for kitchen dishes, shampoos and body shampoos.

[0002]

2. Description of the Related Art Alkyl sulfates and alkyl ether sulfates have hitherto been used in kitchen dishwashing detergents, shampoos and body shampoos. However, there is a problem with the irritation to the skin, and a milder raw material is desired. In recent years, amino acid-based surfactants such as N-acyl glutamate have been attracting attention as detergents that are mild and safe to the skin and have good biodegradability. Among the amino acid-based surfactants, N-acyl aspartate-based detergents have better foaming power and detergency than those using N-acyl glutamate, and are also effective on the skin. It has been reported that there is no remaining tendency, so-called "slickness", and that it has a performance advantage of good rinsability (Japanese Patent Laid-Open No. 2-268113).

[0003]

As an ingredient of liquid detergents for kitchen dishwashing detergents, shampoos, body shampoos, etc., anionic surfactants are used as salts with triethanolamine for the purpose of increasing the solubility of the surfactants. Is commonly used. However, according to the research conducted by the present inventors,
When the N-acyl aspartic acid triethanolamine aqueous solution is stored at a relatively high temperature of 40 ° C. or higher for a long period of time, there is a problem that the performance such as foaming power is deteriorated due to partial hydrolysis. all right.

Therefore, as a result of intensive investigations by the present inventors on a method of suppressing the hydrolysis of N-acyl aspartic acid triethanolamine salt, the problem of the present invention was solved by maintaining the pH of the aqueous solution within a certain range. N- that does not reduce the surface activity even during long-term storage
It has been found that an acyl aspartic acid triethanolamine salt can provide.

[0005]

The present invention provides an aqueous solution containing 0.1 to 50% by weight of N-acyl aspartic acid triethanolamine salt having an acyl group having 10 to 16 carbon atoms. Is maintained in the range of 5.3 to 6.5, which is a method for suppressing hydrolysis of N-acylaspartic acid triethanolamine salt.

The N-acyl aspartic acid triethanolamine salt aqueous solution used in the present invention is N-acyl in an aqueous solvent.
-It is obtained by reacting acylaspartic acid with triethanolamine. Raw material N
-The acyl group in the acyl aspartic acid has 10 to 16 carbon atoms. If the carbon number is less than 10, the surfactant activity as a detergent is remarkably reduced, and if the carbon number exceeds 16, it becomes sparingly soluble in water. Specific examples thereof include single-composition acyl groups such as lauroyl group, myristoyl group, palmitoyl group, stearoyl group and oleoyl group, and mixed acyl groups such as cocoyl group and taroyl group. As aspartic acid, D-aspartic acid, L
Either aspartic acid or D, L-aspartic acid may be used, but L-aspartic acid is preferable because it is easily available and inexpensive.

In the method of the present invention, the concentration of the aqueous solution of triethanolamine N-acyl aspartate is 0.1.
The amount is in the range of ˜50% by weight, but the effect is particularly remarkable in the range of 10 to 40% by weight.

In order to suppress the hydrolysis of the N-acyl aspartic acid triethanolamine salt, it is extremely important to adjust the pH of the aqueous solution. The pH of the aqueous solution is 5.3
Must be maintained in the range of ~ 6.5. A more preferable range is 5.5 to 5.8. PH of aqueous solution is 5.3
If it is less than 60 ° C., the hydrolysis of the acylamide group becomes remarkable when the product is stored at a relatively high temperature such as 45 ° C. for a long period of time, and the performance is lowered, and especially the foaming force is lowered. Also, the pH is 6.
If it exceeds 5, the surfactant activity as a detergent is lowered, and the foaming power and hard water resistance are significantly impaired.

In the method of the present invention, the pH of the aqueous solution of triethanolamine salt of N-acyl aspartic acid is adjusted by
Specifically, the molar ratio of N-acyl aspartic acid to triethanolamine in the aqueous solution is maintained at 1: 1.2 to 1: 1.6, or the aqueous solution contains alkali metal hydroxide or alkaline earth metal. It can be carried out by adding a metal hydroxide or a base such as triethanolamine or an acid such as a mineral acid such as hydrochloric acid, sulfuric acid or nitric acid, or an organic acid such as acetic acid or lactic acid. When adding the acid or base, it is preferable to add them as an aqueous solution of 20% by weight or less. The amount of the acid or base to be added is usually 10 with respect to the N-acyl aspartic acid triethanolamine salt.
It is less than or equal to weight%.

[0010]

The present invention will be described in more detail with reference to the following examples. [Examples 1 to 9 and Comparative Examples 1 to 6] Carbon number 12 (Example 1
~ 3), 14 (Examples 4-6), 16 (Examples 7-9)
In a 30% aqueous solution of N-acyl-L-aspartic acid triethanolamine salt (100% linearity) of
The pH was adjusted by changing the ratio of acyl-L-aspartic acid (AAS) and triethanolamine (TEA), and the amount of free amine acid at 45 ° C by the following method:
The daily changes in the hydrolysis rate and foaming power were evaluated. The results are shown in Tables 1 to 3.

Measurement of free amino acid amount The measurement was performed by high performance liquid chromatography. [Conditions] Column: Sympac ISC-07 / S1504 4φ × 150 mm Eluent: 0.2 M sodium dihydrogen phosphate 0.25% phosphoric acid Flow rate: 1 ml / min Detector: UV detector 210 nm

Hydrolysis Rate The hydrolysis rate R was calculated by the following formula. R ′ = [(Ax−Ao) × MW] ÷ 133 R = [R ′ ÷ 30] × 100 Ao: N-acyl aspartic acid triethanolamine Free aspartic acid amount (% by weight) immediately after preparation Ax: x days later Amount of free aspartic acid in aqueous solution of triethanolamine N-acyl aspartate (% by weight) MW: Molecular weight of triethanolamine N-acyl aspartate R ′: N-acyl aspartate triethanolamine hydrolyzed over x days Salt amount (% by weight)

Foaming power N-acyl aspartic acid triethanolamine salt aqueous solution (concentration immediately after adjustment = 30% by weight) was diluted 30 times with 3DH tap water, and the diluted aqueous solution was stirred at 40 ° C. Foam strength was measured by the Loss Miles method. The foaming force value represents the foam height after 5 minutes in mm.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

Examples 10 to 12 and Comparative Examples 7 to 8 70% by weight of N-lauroyl-L-aspartic acid having 12 carbon atoms and 30% by weight of N-myristoyl-L-aspartic acid having 14 carbon atoms. Triethanolamine salt of 3
In a 0% by weight aqueous solution, the molar ratio of N-acyl-L-aspartic acid and triethanolamine was changed to 45
The daily changes in the amount of free amino acid, the hydrolysis rate and the foaming power at ° C were evaluated. The results are shown in Table 4.

[0018]

[Table 4]

[Examples 13 to 15 and Comparative Examples 9 to 10] A mixture of 70% by weight of N-lauroyl-L-aspartic acid having 12 carbon atoms and 30% by weight of N-myristoyl-L-aspartic acid having 14 carbon atoms. In a 30% by weight aqueous solution of triethanolamine salt of N-acyl-L-aspartic acid triethanolamine at a molar ratio of 1: 1,
Furthermore, when an aqueous solution of sodium hydroxide was added to this to adjust the pH of the aqueous solution to 5.6, 5.7, and 5.8, the amount of free amino acid at 45 ° C, the hydrolysis rate calculated from this, and the hydrolysis rate at that time The change with time in foaming power was evaluated. The results are shown in Table 5.

[0020]

[Table 5]

Claims (1)

[Claims] 1. An N-acyl aspartic acid triethanolamine salt whose acyl group has 10 to 16 carbon atoms is 0.1 to
A method for inhibiting hydrolysis of N-acylaspartic acid triethanolamine salt, which comprises maintaining the pH of the aqueous solution in the range of 5.3 to 6.5 in an aqueous solution containing 50% by weight.