JPH0827097A - Production of aminosulfonic acid-n,n-diacetic acid and its alkali metal salts and biodegradable chelating agent containing the same - Google Patents

Abstract

PURPOSE:To provide a novel production method of aminosulfonic acid-N,N- diacetic acid or its alkali metal salt of high purity in high yield through efficient process using hydrocyanic acid and formalin in stead of chloroacetic acid in the conventional process. CONSTITUTION:An aminosulfonic acid such as taurine, aminomethanesulfonic acid, 2-aminobenzenesulfonic acid or cysteic acid is allowed to react with hydrocyanic acid and formaldehyde or with glycolonitrile in the presence of or in the absence of an alkali metal hydroxide to give an aminosulfonic acid-N,N- diacetic acid or its alkali metal salt. Additionally, a biodegradable chelating agent contains at least one selected from these aminosulfonic acid-N,N-diacetic acids and alkali metal salts thereof as an active ingredient.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing aminosulfonic acid-N, N-diacetic acid and its alkali metal salt from aminosulfonic acid, and more specifically to 2-aminoethanesulfonic acid and aminomethanesulfone. Acid, 2-
Aminosulfonic acid-N, N-diacetic acid and its alkali are obtained by reacting aminosulfonic acid such as aminobenzenesulfonic acid and 2-amino-2-carboxyethanesulfonic acid with hydrocyanic acid and formaldehyde or glycolonitrile. The present invention relates to a method for producing a metal salt.

Aminosulfonic acid-N, N-diacetic acid and its alkali metal salts are widely used as biodegradable chelating agents in detergent compositions, detergent builders, heavy metal sequestering agents, hydrogen peroxide stabilizers and the like.

[0003]

2. Description of the Related Art Various methods for producing aminosulfonic acid-N, N-diacetic acid and its alkali metal salts have been known. For example, by adding two molecules of chloroacetic acid to 2-aminoethanesulfonic acid (common name: taurine), 2
-Aminoethanesulfonic acid-Method for synthesizing N, N-diacetic acid (Helv. Chim. Acta. 1949 32: 1175)
, (L) -2-amino-2-carboxyethanesulfonic acid (trivial name (L) -cysteic acid) to which two molecules of chloroacetic acid are added to obtain (L) -2-amino-2-carboxyethanesulfonic acid- Method for synthesizing N, N-diacetic acid (US Pat. No. 3683014), and 2-aminobenzenesulfonic acid-N, N-diacetic acid by adding two molecules of chloroacetic acid to 2-aminobenzenesulfonic acid (Helv. Chim. Acta. 1947 40: 4312).

However, the prior art of using chloroacetic acid as an aminosulfonic acid such as 2-aminoethanesulfonic acid, aminomethanesulfonic acid, 2-aminobenzenesulfonic acid and 2-amino-2-carboxyethanesulfonic acid is known as aminosulfone. It cannot be said that the proper raw material is selected for the production of acid-N, N-diacetic acid. That is, chloroacetic acid is a raw material which is unstable in the alkalinity of the reaction conditions, and in order to avoid by-product to glycolic acid,
It must be added very slowly to the reaction solution under strict control of pH. Further, in the reaction product, in addition to sodium chloride in an amount equivalent to that of chloroacetic acid used, by-products such as glycolic acid are unavoidable. Therefore, in the prior art, not only is the reaction time unavoidably lengthened, but also complicated operations are involved in the addition reaction step and the purification step, so that the desired yield of aminosulfonic acid-N, N-diacetic acid and There was still a serious problem in terms of purity.

[0005]

The present invention has been made to solve the problems of the prior art, and provides an efficient method for producing aminosulfonic acid-N, N-diacetic acid and its alkali metal salt. Specifically, aminosulfonic acid-N, which is excellent in biodegradability and chelating ability, is produced by an efficient process using a raw material advantageous in an industrial process.
An object of the present invention is to provide a production method for obtaining N-diacetic acid and its alkali metal salt in high yield and high purity.

[0006]

Means for Solving the Problems As a result of intensive research aimed at achieving the above-mentioned object, the present inventors have found that 2-aminoethanesulfonic acid, aminomethanesulfonic acid, 2-aminobenzenesulfonic acid and 2-amino-2 An industrially available aminosulfonic acid such as carboxyethanesulfonic acid as a raw material, and by reacting hydrocyanic acid with formaldehyde or glycolonitrile, the desired aminosulfonic acid-N, N-diacetic acid and its Alkali metal salt
It has been found that an efficient process results in high yield and high purity. Further, the inventors have found that the aminosulfonic acid-N, N-diacetic acid and the alkali metal salt thereof thus obtained are chelating agents having excellent biodegradability, and arrived at the present invention.

That is, the first invention of the present invention is
Aminosulfonic acid-N, characterized by reacting aminosulfonic acid with hydrocyanic acid and formaldehyde or glycolonitrile in the presence of an alkali metal hydroxide.
The gist is a method for producing an alkali metal salt of N-diacetic acid.

The second invention is characterized in that aminosulfonic acid is reacted with hydrocyanic acid and formaldehyde or glycolonitrile in the absence of an alkali metal hydroxide, followed by acid precipitation crystallization with a mineral acid. Aminosulfonic acid-
The gist is the method for producing N, N-diacetic acid.

A third invention is to react aminosulfonic acid with hydrocyanic acid and formaldehyde or glycolonitrile in the absence of an alkali metal hydroxide, and then to hydrolyze with an alkali metal hydroxide. The gist is a method for producing a characteristic alkali metal salt of aminosulfonic acid-N, N-diacetic acid.

The fourth invention is to react aminosulfonic acid with hydrocyanic acid and formaldehyde or glycolonitrile in the absence of an alkali metal hydroxide, followed by hydrolysis with an alkali metal hydroxide. , Aminosulphonic acid-N, N-, characterized by acid precipitation crystallization with a mineral acid
The gist is the method for producing diacetic acid.

Further, the fifth invention is aminosulfonic acid-
The present invention relates to a biodegradable chelating agent containing, as an active ingredient, at least one selected from N, N-diacetic acid and its alkali metal salts.

The present invention will be described in detail below. In the method of the present invention, aminosulfonic acid is hydrolyzed by reacting hydrocyanic acid and formaldehyde or glycolonitrile in the presence of an alkali metal hydroxide to give an alkali of aminosulfonic acid-N, N-diacetic acid. It consists of a carboxymethylation step to obtain a metal salt.

Alternatively, a cyanomethylation step of reacting aminosulfonic acid with hydrocyanic acid and formaldehyde or glycolonitrile, and a reaction solution of the obtained N, N-biscyanomethylaminosulfonic acid are treated with a mineral acid or an alkali metal. It comprises a step of hydrolysis by stepwise hydrolysis with hydroxide to obtain aminosulfonic acid-N, N-diacetic acid or alkali metal salts thereof. Further, the alkali metal salt of aminosulfonic acid-N, N-diacetic acid obtained by the carboxymethylation step or the hydrolysis step is treated with a mineral acid to give crystals of aminosulfonic acid-N, N-diacetic acid. The resulting acid precipitation crystallization step.

The aminosulfonic acid which is a raw material in the present invention has at least one amino group and 1 or more amino groups in the molecule.
Any compound having two or more sulfonic acid groups can be used, but 2-aminoethanesulfonic acid,
Monoaminomonosulfonic acid such as aminomethanesulfonic acid, 2-aminobenzenesulfonic acid and 2-amino-2-carboxyethanesulfonic acid has a desired chelating power and biodegradation of aminosulfonic acid-N, N-diacetic acid. Particularly preferred from the viewpoint of sex.

As these aminosulfonic acids, industrially available solids having a purity of 70% or more, preferably 85% or more are generally used. The alkali metal salt obtained during the production or an aqueous solution of the alkali metal salt is directly used. It can also be used. When an aqueous solution of aminosulfonic acid alkali metal salt having low purity is used, it is desirable that the concentration of ammonia as an impurity is 3% or less. In particular, it should be noted that the presence of a high concentration of ammonia in the carboxymethylation step or the cyanomethylation step leads to an increase in the byproduct of nitrilotriacetic acid, which has been reported to be carcinogenic.

As the 2-amino-2-carboxyethanesulfonic acid, any optical isomer of D-form, L-form and D, L-form may be used, but the desired 2-amino-isomer is used. From the viewpoint of biodegradability of 2-carboxyethanesulfonic acid-N, N-diacetic acid, (L) -2-amino-2 was used as a raw material.
It is especially preferred to choose carboxyethanesulfonic acid.

The mixing molar ratio of each compound in the carboxymethylation step or the cyanomethylation step is 2.0 to 3.0 times the molar amount of prussic acid and formaldehyde with respect to any aminosulfonic acid selected as a raw material. It is good to use in a range of 2.0 to 2.5 times the molar amount. The same is true when using glycolonitrile instead of hydrocyanic acid and formaldehyde,
In the range of 2.0 to 3.0 times the molar amount, preferably 2.0
It is preferable to use it in the range of 2.5 to 2.5 times the molar amount.

The hydrocyanic acid used in the carboxymethylation step or the cyanomethylation step is a method of introducing hydrocyanic acid into the reaction solution, a method of using an alkali metal cyanide salt,
It can be used in various forms, such as a method of introducing hydrocyanic acid into an aqueous alkali metal hydroxide solution prepared in a reaction tank and capturing it as an alkali metal cyanide salt. When utilizing hydrocyanic acid in the form of an alkali metal cyanide salt, Li, Na or K, preferably Na or K, more preferably Na is selected as the type of alkali metal used.

The formaldehyde used in the carboxymethylation step or the cyanomethylation step may be in various forms such as a gaseous product, an aqueous solution product or a solid product such as paraformaldehyde. %, Preferably 20-50% by weight,
It is more preferable to use a 35-40 wt% aqueous solution.

In the carboxymethylation step or cyanomethylation step, glycolonitrile used in place of hydrocyanic acid and formaldehyde is usually treated with hydrocyanic acid in an aqueous solution in the presence or absence of an alkali catalyst such as an alkali metal hydroxide. It is obtained by mixing formaldehyde, but it is also possible to use it as a 10 to 70% by weight, preferably 30 to 60% by weight, aqueous solution prepared in advance.

Alkali metal hydroxides used in the carboxymethylation step are prussic acid and formaldehyde,
Or, a total of 3.0 to 5.5 for glycolonitrile
It is preferable to use it in a double molar amount range, preferably in a range of 3.0 to 4.0 times molar amount. The alkali metal hydroxide used is a hydroxide of Li, Na or K, preferably N.
a or K hydroxide, more preferably Na hydroxide, solid product having a purity of 80% or more, or a concentration of 1
An aqueous solution of 0 to 60% by weight is used.

The reaction temperature in the carboxymethylation step is 40 to 120 ° C., preferably 60 to 100 ° C.

There is no particular restriction on the order of mixing each compound in the carboxymethylation step, but in any mixing order, finally about 2 times the molar amount of ammonia based on the aminosulfonic acid used in the reaction is obtained. Occurs. Controlling the generation of ammonia at an appropriate rate is important for obtaining the target aminosulfonic acid-N, N-diacetic acid in high purity and high yield.
This is accomplished by adjusting the rate of addition of either alkali metal hydroxide, a mixture of prussic acid and formalin, or glycolonitrile. It is also an effective means to remove ammonia in the reaction mixture by introducing air, nitrogen gas, an inert gas or the like, or by carrying out continuous distillation.

When it is desired to obtain the desired aminosulfonic acid-N, N-diacetic acid with a particularly high purity, it is advantageous to carry out the cyanomethylation step and the hydrolysis step stepwise instead of the carboxymethylation step. is there. When 2-amino-2-carboxyethanesulfonic acid is selected as the raw material aminosulfonic acid and 2-amino-2-carboxyethanesulfonic acid-N, N-diacetic acid is obtained with high purity, a cyanomethylation step and Performing the hydrolysis step stepwise,
It is particularly advantageous. The cyanomethylation step is performed in the same manner as the carboxymethylation step except that it is performed in the absence of alkali metal hydroxide.

In the cyanomethylation step, highly crystalline N, N-biscyanomethylaminosulphonic acid is obtained as a synthetic intermediate, but it may be isolated once and then used in the next hydrolysis step or may be isolated. Instead, the hydrolysis step may be continuously performed.

The hydrolysis step is accomplished by reacting an aqueous solution of N, N-biscyanomethylaminosulfonic acid obtained in the cyanomethylation step with an alkali metal hydroxide or acid.

The alkali metal hydroxide used in the hydrolysis step is Li, as in the carboxymethylation step.
It is selected from the hydroxides of Na or K, preferably the hydroxides of Na or K, more preferably the hydroxides of Na.
When N, N-biscyanomethylaminosulfonic acid is once isolated, it is preferable to use 3.0 to 4.0 times the molar amount of the aminosulfonic acid selected as the raw material, and to carry out continuously from the cyanomethylation step. In this case, the molar amount is preferably 3.0 to 5.0 times, and more preferably 3.0 to 4.0 times.

The hydrolysis step with the alkali metal hydroxide is carried out at a temperature of 40 to 120 ° C, preferably 60 to 100 ° C. It is 0.5 to 8.5 hours, preferably 0.5 to 8.5 hours until ammonia corresponding to about twice the molar amount of the aminosulfonic acid selected as the raw material is finally generated.
It is better to carry out in 3.5 hours.

In the acid hydrolysis step, it is preferable to use sulfuric acid, hydrochloric acid, nitric acid or hydrochloric acid, preferably sulfuric acid or hydrochloric acid, more preferably sulfuric acid. Acid hydrolysis is performed at pH 0.
It is desirable to carry out in the range of 5-2.5, preferably pH 0.5-1.5. The reaction temperature is 60 to 120 ° C,
The temperature is preferably in the range of 80 to 100 ° C., and the reaction time is 1 to 20 hours, preferably 2 to 14 hours.

After the carboxymethylation step or the hydrolysis step with alkali metal hydroxide, if desired,
By crystallization of the reaction mixture by means such as evaporation to dryness or spray-drying, the desired aminosulfonic acid-
N, N-diacetic acid can be isolated as an alkali metal salt.

When crystals of aminosulfonic acid-N, N-diacetic acid are to be obtained, the reaction solution in the hydrolysis step is subjected to acid precipitation crystallization. The acid used in the acid precipitation crystallization step is sulfuric acid, hydrochloric acid, nitric acid or hydrochloric acid, preferably sulfuric acid or hydrochloric acid, more preferably sulfuric acid. Target aminosulfonic acid-N, N-
In order to obtain diacetic acid with high purity and high yield, the temperature during the addition of the acid to the reaction mixture is 5 to 90 ° C, preferably 15 to 90 ° C.
It is desirable to adjust the pH in the range of 50 ° C. to 0.5 to 3.5, preferably 1.5 to 2.5. The obtained crystals of aminosulfonic acid-N, N-diacetic acid are usually sufficiently high in purity without recrystallization except that a small amount of mother liquor adhering to the crystal surface is washed with a small amount of water. .

The aminosulfonic acid-N, N-diacetic acid thus obtained is treated with a predetermined amount of alkali metal hydroxide, alkaline earth metal hydroxide, base such as ammonia, organic amine, etc. By neutralizing or partially neutralizing,
The desired salt can be produced.

Conventionally, sulfonic acid, which is a strong acid group, has a weaker complex-forming power for cations than carboxylic acid, which is a weak acid group. Therefore, aminosulfonic acid-N, N
-The chelating power of diacetic acid is equivalent to that of the corresponding aminocarboxylic acid-
It was considered to be inferior to N, N-diacetic acid. For example, in J. Am. Chem. Soc. 1955, 77, p. 5512, the complexing power of aminomethanesulfonic acid-N, N-diacetic acid for copper ions is higher than that of its structural analogue nitrilotriacetic acid. The content of the inferior purpose is described. However, surprisingly, 2 synthesized by the method of the present invention
-Aminoethanesulfonic acid-N, N-diacetic acid, aminomethanesulfonic acid-N, N-diacetic acid, 2-aminobenzenesulfonic acid-N, N-diacetic acid, (L) -2-amino-2
-Carboxyethanesulfonic acid-N, N-diacetic acid and other calcium ion scavenging capacities were measured, and β-alanine-N, N-diacetic acid and anthranil-
When compared with N, N-diacetic acid, aspartic acid-N, N-diacetic acid, nitrilotriacetic acid, etc., the chelating power of a series of aminosulfonic acid-N, N-diacetic acid was found to be aminocarboxylic acid-N, N -It was shown to be comparable to diacetic acid.

Further, a series of these aminosulfonic acids
When the biodegradability of N, N-diacetic acid was measured and compared with aminocarboxylic acid-N, N-diacetic acid, which is a structural analog thereof, biodegradation was observed when a sulfonic acid group was introduced into the molecular structure. The tendency of improving the sex was recognized.

That is, 2-aminoethanesulfonic acid-N, N-diacetic acid, aminomethanesulfonic acid-N, N-diacetic acid, 2-aminobenzenesulfonic acid-N, N- synthesized by the method of the present invention. Diacetic acid and (L) -2-amino-2-carboxyethanesulfonic acid-N, N-diacetic acid, and their alkali metal salts can be used as biodegradable chelating agents.

[0036]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to the following examples. Example 1 In a reactor equipped with a stirrer, an automatic temperature controller, a dropping device, a prussic acid introducing device and a distillation device, 1.20 kg (9.6 mol) of 2-aminoethanesulfonic acid, 40% by weight sodium hydroxide aqueous solution. 3.03 kg (30.3 mol), followed by 37 wt% formaldehyde aqueous solution 1.87 kg (2
3.1 mol) were mixed. 0.56k of hydrocyanic acid in this mixed solution
Under a closed condition, g (20.7 mol) was added dropwise over 3 hours while gradually raising the reaction temperature in the range of 50 to 90 ° C. During this time, 25% by weight of ammonia condensed water of 0.
After distilling out 98 kg, the reaction mixture was aged for 3 hours, and 1.48 kg of condensed water containing 7.3% by weight of ammonia.
Was distilled off. After confirming that the generation of ammonia was completed, 4.17 kg of water was added to the reaction solution to dilute it, and the mixture was allowed to cool to 50 ° C. Next, 1.52 k of 98% sulfuric acid was added to this reaction solution.
g (15.2 mol) was added dropwise over 1.5 hours, while the temperature was raised to 80 ° C. The reaction solution was allowed to cool to 33 ° C. again, and the precipitated 2-aminoethanesulfonic acid-N, N-diacetic acid crystals were isolated by suction filtration, and further water at 10 ° C.
It was washed twice with 25 kg. 2-Aminoethanesulfonic acid-N, N-diacetic acid (2.10 kg, 8.7) after blast drying
Mol, yield 91%). The obtained 2-aminoethanesulfonic acid-N, N-diacetic acid was uniform white crystals (decomposition point 107 to 110 ° C) and had a purity of 99% or more.

Example 2 1.81 kg of water was used in place of 3.03 kg of 40% by weight sodium hydroxide aqueous solution, and hydrocyanic acid was added dropwise and the reaction mixture was aged at 50 to 70 ° C. without distilling ammonia.
The same operation as in Example 1 was carried out except that the reaction was carried out under the reaction temperature range. Next, this reaction liquid was cooled to 5 ° C., and 1.71 kg of precipitated wet crystals of N, N-biscyanomethyl-2-aminoethanesulfonic acid were isolated by suction filtration.
The isolated N, N-biscyanomethyl-2-aminoethanesulfonic acid was added to a 40% by weight aqueous sodium hydroxide solution 2.8.
After suspending in 8 kg (28.1 mol), the reaction temperature was gradually raised to 105 ° C., and after 3 hours, 1.60 kg of condensed water containing 15% by weight of ammonia was distilled off. After confirming that the generation of ammonia was completed, the slurry remaining in the reaction tank
Is dried and powdered at 120 ° C. by a spray-dry method,
A trisodium salt of 2-aminoethanesulfonic acid-N, N-diacetic acid was obtained (2.82 kg, 9.2 mol, yield 95).
%). Obtained 2-aminoethanesulfonic acid-N, N-
The trisodium salt of diacetic acid was uniform white crystals and had a purity of 99% or more.

Examples 3-5 Instead of 1.20 kg (9.6 mol) of 2-aminoethanesulfonic acid, 1.6 of 2-aminobenzenesulfonic acid was used.
6 kg (9.6 mol), (L) -2-amino-2-carboxyethanesulfonic acid 1.62 kg (9.6 mol),
Alternatively, aminomethanesulfonic acid 1.07 kg (9.6
Mol) was used in the reaction and the same operation as in Example 1 was carried out. The results are shown in Table 1.

Examples 6-8 Instead of 1.20 kg (9.6 mol) of 2-aminoethanesulfonic acid, 1.6 of 2-aminobenzenesulfonic acid was used.
6 kg (9.6 mol), (L) -2-amino-2-carboxyethanesulfonic acid 1.62 kg (9.6 mol) or aminomethanesulfonic acid 1.07 kg (9.6 mol) were used in the reaction. Other than that, the same operation as in Example 2 was performed. The results are shown in Table 1.

[0040]

[Table 1]

Examples 9 to 12 The calcium ion scavenging ability of the compounds synthesized in Examples 1, 3, 4, and 5 was determined by J. Am. Oil. Chem. Soc., 1970,
It was measured according to the method described in Volume 48, page 682. Table 2 shows the results.

Comparative Examples 1 to 4 Test compounds were added to β-alanine-N, N-diacetic acid, anthranyl-N, N-diacetic acid, (L) -aspartic acid-
Except that N, N-diacetic acid and nitrilotriacetic acid were used,
The calcium ion-capturing ability was measured in the same manner as in Examples 9 to 12. Table 2 shows the results.

[0043]

[Table 2]

The biodegradability test of the compounds synthesized in Examples 1, 3, 4, and 5 was conducted according to OECD Test Guideline 3
The test was carried out under the following conditions according to the 01C modified MITI test (I). The results are shown in Table 3. (Test conditions) Test sample concentration: 30 mg / l Activated sludge: Activated sludge in the Nitto Chemical Yokohama Works Activated sludge concentration: 100 mg / l Test temperature: 25 ± 1 ° C Test period: 28 days

Comparative Examples 5 to 8 Test compounds were added to β-alanine-N, N-diacetic acid, anthranyl-N, N-diacetic acid, (L) -aspartic acid-
Except that N, N-diacetic acid and nitrilotriacetic acid were used,
The biodegradability was measured in the same manner as in Examples 13 to 16. The results are shown in Table 3.

[0046]

[Table 3]

[0047]

INDUSTRIAL APPLICABILITY According to the present invention, industrially available raw materials such as 2-aminoethanesulfonic acid, aminomethanesulfonic acid, 2-aminobenzenesulfonic acid and 2-amino-2-carboxyethanesulfonic acid are used. By reacting hydrocyanic acid with formalin or glycolonitrile, aminosulfonic acid-N, N-diacetic acid and its alkali metal salt can be obtained in high yield and high purity. The present invention also has the following advantages. (1) The resulting aminosulfonic acid-N, N-diacetic acid and its alkali metal salt have excellent calcium ion-capturing ability and biodegradability, and can be used as a biodegradable chelating agent. (2) Since the reaction proceeds with a high yield and a high selectivity, almost no impurities are generated, and a highly pure target product can be obtained without a complicated production process. (3) There are almost no by-products other than ammonia in the process, and ammonia, which produces about twice the molar amount of the target substance, is efficiently recovered with high purity and high yield, and can be used as another industrial raw material. Can be done.

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Claims (7)

[Claims] 1. An alkali metal salt of aminosulfonic acid-N, N-diacetic acid, which comprises reacting aminosulfonic acid with hydrocyanic acid and formaldehyde or glycololonitrile in the presence of an alkali metal hydroxide. Manufacturing method. 2. Amino sulfone characterized by reacting aminosulfonic acid with hydrocyanic acid and formaldehyde or glycolonitrile in the absence of an alkali metal hydroxide, and then acidifying and crystallizing with a mineral acid. Method for producing acid-N, N-diacetic acid. 3. Amino acid characterized by reacting aminosulfonic acid with hydrocyanic acid and formaldehyde or glycolonitrile in the absence of an alkali metal hydroxide, followed by hydrolysis with an alkali metal hydroxide. A method for producing an alkali metal salt of sulfonic acid-N, N-diacetic acid. 4. Aminosulfonic acid is reacted with hydrocyanic acid and formaldehyde or glycolonitrile in the absence of an alkali metal hydroxide, then hydrolyzed with an alkali metal hydroxide and further with a mineral acid. A method for producing aminosulfonic acid-N, N-diacetic acid, which comprises crystallizing by acid precipitation. 5. A biodegradable chelating agent containing, as an active ingredient, at least one selected from aminosulfonic acid-N, N-diacetic acid and alkali metal salts thereof. 6. The aminosulfonic acid is 2-aminoethanesulfonic acid, aminomethanesulfonic acid, 2-aminobenzenesulfonic acid or 2-amino-2-carboxyethanesulfonic acid, 1, 2, 3 or 4. The method described. 7. Aminosulfonic acid-N, N-diacetic acid,
2-Aminoethanesulfonic acid-N, N-diacetic acid, aminomethanesulfonic acid-N, N-diacetic acid, 2-aminobenzenesulfonic acid-N, N-diacetic acid or (L) -2-amino-2- The biodegradable chelating agent according to claim 5, which is carboxyethanesulfonic acid-N, N-diacetic acid.