JPH10168045A - Production of ethylenediamine-n,n'-disuccinic acid and its ferric complex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce ethylenediamine-N,N'-disuccinic acid that has biodegradability and is useful as a photographic agent, etc., separately, as meso isomer and racemic isomer. SOLUTION: This production of meso and racemic isomers of ethylenediamine-N,N'- disuccinic acid (hereinafter abbreviated as EDDS) and their ferric complexes respectively isolated condition comprises making the isomer mixture of EDDS react with triiron tetroxide in an aqueous solution of NH3 or alkali metal hydroxide by taking advantage of difference of the reaction rates of both isomers in condition that the reaction is carried out using triiron tetroxide of approximately the same molarity as that of the racemic isomer of EDDS and NH3 , etc., of the same molarity as total of both the meso and racemic isomers at pH of 3-7 at 30-80 deg.C to form the ferric complex of the racemic isomer, filtering the aqueous solution in the process of formation of the ferric complex of the racemic isomer, adding triiron tetroxide of approximately the same molarity as that of the meso isomer in the precipitation on the basis of Fe content, and NH3 , etc., of approximately the same molarity as that of the meso isomer, and making the meso isomer react with the triiron tetroxide at pH at 3-7 at 60-90 deg.C, to form the ferric complex of the meso isomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ethylenediamine-N, N'-disuccinic acid (hereinafter abbreviated as EDDS).
The present invention relates to a method for producing each isomer and a ferric complex salt thereof in an isolated state from a mixture of isomers of a meso form and a racemic form.

[0002]

EDDS is conventionally known as a biodegradable compound, and its ferric complex salt also has excellent biodegradability. Further, it has been revealed that the ferric complex salt of EDDS can be used as a photographic processing agent for processing an exposed silver halide photographic light-sensitive material (Japanese Patent Application Laid-Open No. Hei 4 (1994)).
No. 313752). Further, the method of producing the EDDS ferric complex salt is described in, for example, JP-A-7-2745.

[0003] By the way, it is known that the [S, S] form of EDDS can be produced from L-aspartic acid and 1,2-dibromoethane, which are natural products, by the following reaction, for example, Inorganic Chemi.
It is also described in the 7th volume of the story (1968), pages 2405 to 2412.

[0004]

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In this method, L-aspartic acid is expensive as an industrial raw material, and 1,2-dibromoethane is a compound designated as a mutagen and has a problem in its handling. Lack of versatility as a typical manufacturing method.

Accordingly, as a synthesis method using raw materials which are inexpensive and easily available, a method has been proposed in which maleic anhydride and ethylenediamine are reacted in the presence of an alkali as shown in the following formula (US Pat. No. 158,635).

[0007]

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However, in this method, the synthesized EDD
S is formed as a mixture of three kinds of optical isomers of racemic [S, S], [R, R] and meso form [R, S] due to the presence of two asymmetric carbon atoms. To do
In order to effectively utilize the action and effect unique to each isomer, it must be separated, but since no industrially practical separation method has been established, it is only used as an optical isomer mixture. The same applies to the ferric complex salt of the optical isomer. Further, the present inventors have confirmed that, among the EDDS or the ferric complex salt thereof, the racemic EDDS or the ferric complex salt thereof is particularly excellent in biodegradability. If it can be manufactured in an isolated state, it is considered that its properties can be more effectively utilized.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide an EDDS which has biodegradability and is useful as a photographic processing agent and the like. An object of the present invention is to provide a method capable of producing a meso form and a racemic form of a ferric complex salt in a state of being isolated as respective isomers.

[0010]

Means for Solving the Problems The production method according to the present invention which can solve the above-mentioned problems includes (1) a mixture of a meso-isomer and a racemic-isomer of EDDS, and (2) an F
e equimolar amount of triiron tetroxide in terms of e, (3) a substantially equimolar amount of ammonia or an alkali metal hydroxide with respect to the sum of the meso form and the racemic form in an aqueous solution, followed by heat reaction, The ferric complex salt is separated as an aqueous solution, or the aqueous solution is further concentrated and / or cooled, and the ED
The gist lies in obtaining the DS racemic ferric complex salt as crystals.

Another manufacturing method according to the present invention is as follows: (1) EDD
A mixture of isomers of the meso- and racemic forms of S, (2) an approximately equimolar amount of iron tetroxide in terms of Fe with respect to the racemic body, and (3) an approximately equimolar amount of the total of the meso- and racemic forms. Of ammonia or alkali metal hydroxide in an aqueous solution to separate the racemic ferric complex salt as an aqueous solution.
An equimolar amount or more of triiron tetroxide, and an equimolar amount or more of ammonia or an alkali metal hydroxide are reacted with heat in an aqueous solution to separate the meso ferric complex salt as an aqueous solution, Alternatively, the gist lies in that the aqueous solution is concentrated and / or cooled to obtain the EDDS meso ferric complex salt as crystals.

Further, the process for producing EDDS according to the present invention comprises the following steps: (1) a mixture of a meso-isomer and a racemic isomer of EDDS; and (2) an approximately equimolar amount of 43 Iron oxide, (3) a substantially equimolar amount of ammonia or an alkali metal hydroxide with respect to the sum of the meso form and the racemic form is heated and reacted in an aqueous solution, and the racemic ferric complex salt is separated as an aqueous solution, After adding an excessive amount of alkali to the aqueous solution to remove the Fe component as iron hydroxide, the filtrate is acidified to obtain a racemic EDDS, or a solid remaining as an insoluble substance after the heating reaction is treated with ammonia or alkali metal hydroxide. The feature lies in that a soluble substance is eluted by treating with an aqueous solution of a substance, and the resulting alkaline aqueous solution is acidified to obtain a meso-form of EDDS.

[0013]

DETAILED DESCRIPTION OF THE INVENTION As described above, in the present invention, a mixture of a meso-isomer and a racemic-isomer of EDDS produced by a reaction of maleic anhydride and ethylenediamine, etc. It is characterized in that the iron complex salt is produced in a substantially isolated state, and is characterized by the fact that the meso-form of EDDS and racemic ammonia or triiron tetroxide in an aqueous solution of an alkali metal hydroxide are used. Utilizing a new property that has not been confirmed so far, that there is a difference in the reaction rate of the EDDS and the meso form and the racemic form of the ferric complex salt using the difference in the reaction rate,
It can be manufactured in an isolated state.

That is, the present inventors have confirmed that when an isomer mixture containing a meso-form and a racemic-form of EDDS is reacted with triiron tetroxide in an aqueous solution of ammonia or an alkali metal hydroxide, A ferric complex salt of each isomer is formed, and the formation reaction rate is considerably different between the meso form and the racemic form. In particular, the ferric oxide used for the above treatment and the ED of ammonia or alkali hydroxide are used.
If the amount used for DS is properly adjusted, first ED
Only the racemate of DS forms a ferric complex and solubilizes. Therefore, when this aqueous solution is separated from the insoluble meso-form of EDDS and the like, only the racemic EDDS-ferric complex salt can be obtained in a substantially isolated state. Also,
When the remaining insolubles are heat-treated again in an aqueous solution containing an appropriate amount of ferric oxide and ammonia or an alkali metal hydroxide, the meso-form of EDDS contained in the insolubles forms a ferric complex salt Thus, the EDDS meso ferric complex salt can be obtained in a substantially isolated state.

When an excess amount of alkali is added to the aqueous solution of the meso- or racemic EDDS ferric complex salt obtained as described above, the complex salt is decomposed and Fe precipitates as iron hydroxide. The meso form or the racemic form is solubilized as an alkali salt. Therefore, when the aqueous solution after removing the precipitate of iron hydroxide is made acidic with an acid such as hydrochloric acid or sulfuric acid, the meso form or the racemic form becomes EDDS.
・ Because it precipitates as 4H, it is possible to obtain EDDS ・ 4H meso form from EDDS meso ferric complex salt and EDDS ・ 4H racemic form from EDDS racemic ferric complex salt respectively. Becomes possible. This method is called ED
The method for producing the racemic DS or the ferric complex thereof, and the method for producing the EDDS meso form or the ferric complex thereof will be described in more detail.

First, in preparing a racemic EDDS ferric complex salt, (1) a mixture of a meso-form of EDDS and a racemic isomer, and (2) a substantially equimolar amount of tetrameric equivalent of Fe to the above-mentioned racemic form. (3) A substantially equimolar amount of ammonia (or an alkali metal hydroxide) with respect to the sum of the meso form and the racemic form is heated and reacted in an aqueous solution. Then, the racemate in the above-mentioned isomer mixture is preferentially changed to ferric oxide and ammonia (or alkali metal hydroxide).
Reacts with a ferric complex, for example [EDDS racemate]
^It forms ⁴ -.Fe ³⁺ .NH ₄ ⁺ and solubilizes in water. The EDDS meso form contained in the mixture of isomers hardly forms a complex salt even when a part thereof forms a 1-ammonium salt, and remains as an insoluble substance. The unreacted iron tetroxide remains as an insoluble substance. Since the remaining reaction solution is filtered to remove insolubles, substantially only the EDDS racemic ferric complex salt can be obtained as an aqueous solution.

In the formation reaction of the racemic EDDS ferric complex salt, tri-iron tetroxide is used in an approximately equimolar amount in terms of Fe with respect to the racemic form in the EDDS isomer mixture, and the meso form and the racemic form are mixed. Approximately equimolar amounts of ammonia (or alkali metal hydroxide) relative to the total are used and they are heated and reacted in an aqueous solution. Here, if the amount of triiron tetroxide is too large, even the EDDS meso form forms a complex salt to be solubilized, and the purity of the obtained EDDS racemic second complex salt becomes low. Some EDDS racemates remain unreacted as insolubles without forming a complex salt, and the yield of the EDDS racemic ferric complex salt decreases. If the amount of ammonia (or alkali metal hydroxide) used is too large, a part of the EDDS meso form may be converted into a ammonium salt (or alkali metal salt).
Is formed and solubilized to decrease the purity of the racemic ferric EDDS complex, and conversely, when the purity is insufficient, the pH is lowered to decrease the EDD.
Since the reactivity of the S meso form also increases, the selective complex salt formation reaction is inhibited, and the yield of the racemic EDDS ferric complex salt decreases.

Therefore, when the racemic EDDS ferric complex salt formation reaction is carried out, substantially equimolar amounts of triiron tetroxide and ammonia (or alkali metal hydroxide) are added to the racemic EDDS in the above isomer mixture. Product) is best used in equimolar amounts with respect to the sum of the meso and racemic forms, but when industrialized, it may deviate slightly from equimolar amounts,
About ± 10% by weight is acceptable. The complex salt formation reaction is carried out in the range of pH 3 to 7, more preferably in the range of pH 4 to 6.
If the pH is too high, the complex salt formation reaction rate will be slow and a satisfactory yield will not be obtained, and if the pH is too low, the selective complex salt formation reaction of the racemic EDDS will be inhibited. As a result, even the meso form forms a complex salt and is easily solubilized, thereby lowering the purity of the target product. The reaction temperature is not particularly limited, but at room temperature, the above-mentioned complex salt formation reaction rate is slow and requires a long time for the treatment, and when it is too high,
Since the rate of the complex salt formation reaction becomes too high to inhibit the above-mentioned selective complex salt formation reaction and the purity of the target product tends to decrease, it is preferably 30 to 80 ° C, more preferably 50 to 80 ° C.
It is good to carry out in the range of -70 ° C.

The aqueous solution obtained by removing the insolubles in this step is an aqueous solution containing substantially a racemic ferric EDDS complex salt and a small amount of ammonia (or an alkali metal hydroxide). Or when cooled, the ED
The racemic DS ferric complex salt can be obtained as high-purity crystals.

When it is desired to obtain a racemic EDDS / 4H, an excess amount of an alkali is added to the aqueous solution containing the racemic EDDS ferric complex to decompose the complex, insolubilize the Fe component as iron hydroxide and separate and remove it. After that, when the aqueous solution is acidified with an acid such as hydrochloric acid, sulfuric acid, nitric acid, etc., EDDS · 4H
Since the racemate is insolubilized and precipitates, the EDDS.4H racemate can be obtained as a highly purified product by filtering it.

On the other hand, in the step of obtaining the racemic ferric complex salt, insolubles obtained as a residue after filtration of the aqueous solution containing the solubilized EDDS racemic ferric complex salt include:
It contains insoluble matter and a small amount of triiron tetroxide which may be mixed in as impurities, and EDDS meso form which does not form a complex salt. The EDDS meso form in the precipitate (insoluble matter) is converted to Fe equivalent. When approximately equimolar amount or more of triiron tetroxide and approximately equimolar amount or more, preferably 2 times or more of ammonia or alkali metal hydroxide are added, and the mixture is heated and reacted in an aqueous solution, the EDDS meso form becomes Since a ferric complex salt is formed and solubilized in water, it is filtered off from the insoluble residual ferric oxide to obtain a ferric complex salt of the EDDS meso form as an aqueous solution, which can be concentrated and / or concentrated. Upon cooling, the EDDS meso ferric complex salt can be obtained as high purity crystals.

In producing the EDDS mesoferric ferric complex salt, since the racemic EDDS is not substantially contained in the system, the reaction conditions may be set mainly based on the complex salt production efficiency. The preferred pH is in the range of 3-7, more preferably 4-6, and the preferred temperature is 60-90 ° C, more preferably 70-80 ° C.

When it is desired to obtain an EDDS / 4H meso form, an excess amount of alkali is added to the aqueous solution containing the ferric complex salt of the EDDS meso form to decompose the complex salt, insolubilize the Fe component as iron hydroxide and separate and remove it. After that, the aqueous solution is acidified with an acid such as hydrochloric acid, sulfuric acid, nitric acid, or the like.
The insoluble matter remaining after separating the racemic S-ferric complex salt as an aqueous solution is treated with an aqueous solution containing an excessive amount of ammonia or an alkali metal hydroxide, and the EDDS meso form is solubilized as an alkali salt. Insoluble impurities and iron hydroxide are separated and removed, and the resulting alkaline aqueous solution is acidified with an acid such as hydrochloric acid, sulfuric acid, or nitric acid.
Since the 4H meso form is insolubilized and precipitates, the EDDS-4H meso form can be obtained as a highly purified product by filtering it.

Thus, according to the present invention, the difference in the reaction rate of complex salt formation between iron tetroxide and ammonia (or an alkali metal hydroxide) from an EDDS isomer mixture obtained using maleic anhydride and ethylenediamine as raw materials is utilized. By doing so, the meso form and the racemic form of EDDS or their ferric complex salts can be efficiently produced as high-purity substances, respectively.

[0025]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, but may be appropriately adjusted within a range that can conform to the purpose of the preceding and following examples. Modifications can be made and all are included in the technical scope of the present invention.

Example 1 A 1-liter four-necked flask equipped with a stirrer and a thermometer was charged with EDDS.4H (meso-form / racemic-form = 45.
4 / 54.6 weight ratio) 200 g (purity 87.0%, meso form: 0.27 mol, racemic form: 0.33 mol) and 25
% Ammonia water 40.5 g (0.60 mol), water 813
g and 25.3 g of Fe ₃ O ₄ (0.33 mol as Fe) were added, a reaction was carried out at 60 ° C. for 3 hours, and air was blown into the reaction solution at the same temperature to oxidize iron in the iron complex salt. . After completion of the reaction, the reaction solution was separated into a soluble substance and an insoluble substance by filtration.

The obtained soluble matter (filtrate) is concentrated under reduced pressure until the liquid volume becomes 200 g, and when the liquid temperature is cooled to 20 ° C., crystals are precipitated. The crystals are separated by a centrifuge. After washing with a small amount of water and drying at 60 ° C. for 15 hours, 63.4 g of pale yellow crystalline powder was obtained.

This crystal powder is a racemic EDDS ferric ammonium complex salt as is apparent from the following analysis results, and the charged EDDS.
The yield based on 4H was 28.4%. Analysis result: EDDS Fe NH ₄ adhering water content 76.9% 15.1% 4.5% 3.8% molar ratio 1.0 1.0 0.9 0.8 racemic purity (liquid chromatogram: see FIG. 1): meso / racemic = 0.5% / 99.5% IR spectrum (KBr method): See FIG.

Example 2 In the same manner as in Example 1 described above, an EDDS-4H meso / racemic mixture, ammonia water, water and Fe ₃ O ₄ were heated and reacted, and after the reaction was completed, the reaction solution was filtered. 20% NaOH aqueous solution (NaO
H) (1.3 mol) was added, and the resulting precipitate (iron hydroxide) was filtered off. The filtrate was adjusted to pH 2.5 by adding hydrochloric acid. A white precipitate was deposited. After drying, 61.7 g of a white powder was obtained.
As a result of IR analysis and liquid chromatography analysis of the white powder, 99.5% of EDDS · 4H racemate was obtained,
EDDS prepared with 0.5% DS / 4H meso body
It was confirmed that the recovery of the racemic EDDS / 4H in the isomer mixture was 65%.

Example 3 A 500 ml four-necked flask equipped with a stirrer and a thermometer was charged with the insoluble matter (unreacted E) filtered off in Example 1 above.
100 g (0.34 mol) of DDS meso compound was added, and then 23.1 g (0.34 mol) of 25% aqueous ammonia, 400 g of water and 25.5 g of Fe ₃ O ₄ (0.1% in terms of Fe).
34 mol) and reacted at 80 ° C. for 10 hours, and then air was blown into the reaction solution at 60 ° C. to oxidize iron in the iron complex salt.

After the completion of the reaction, insolubles were removed by filtration, and the filtrate was concentrated under reduced pressure until the amount of the reaction solution reached 200 g. Then, when the liquid temperature is cooled to 20 ° C., crystals precipitate. The crystals are separated by a centrifugal separator, washed with a small amount of water, and then cooled.
After drying at 15 ° C. for 15 hours, 66.4 g of pale yellow crystalline powder was obtained.
was gotten.

This crystal powder is a ferric ammonium complex of a meso-form of EDDS, as is clear from the following analysis results.
The yield based on H was 53.9%. Analysis result: EDDS Fe NH ₄ attached water content 77.6% 15.6% 5.0% 1.8% Molar ratio 1.0 1.0 1.1 0.4 Meso-form purity (liquid chromatogram: see FIG. 3): meso-form / racemic-form = 92.5% / 7.5% IR spectrum (KBr method): See FIG.

For reference, L-aspartic acid and 1,1
EDDS ・ 4 synthesized from 2-dibromoethane
FIG. 5 shows a liquid chromatogram of ferric ammonium EDDS obtained using the [S, S] isomer of H, and FIG. 6 shows an IR spectrum (KBr method) of EDDS · 4H obtained above.

Example 4 The insoluble matter obtained by filtering the soluble matter in Example 1 was reduced to 25%
93.1 g of aqueous ammonia was added and dissolved, and the remaining insolubles were removed by filtration, and then diluted hydrochloric acid was added to adjust the pH to 2.5. A white precipitate was deposited, and this was washed with water and dried. 54.7 g of a white powder were obtained. As a result of IR analysis and liquid chromatography analysis of the white powder, 92.5% of an EDDS · 4H meso compound was obtained.
7.5% DDS / 4H racemate, charged ED
It was confirmed that the recovery of the EDDS-4H meso form in the DS isomer mixture was 69%.

Comparative Example EDDS · 4H (meso-form / racemic-form = 45.times.) Was placed in a 2-liter four-necked flask equipped with a stirrer and a thermometer.
4 / 54.6 weight ratio) 200 g (purity 87.0%, meso form: 0.27 mol, racemic form: 0.33 mol) and 25
% Ammonia water 40.5 g (0.60 mol), water 813
g and FeCl ₃ 232 g (0.6 mol as Fe)
And reacted at 25 ° C. for 1 hour. When this reaction solution was analyzed by liquid chromatography, unreacted EDDS
Was not confirmed, so the reaction solution was reduced in pressure as it was and concentrated until the reaction solution amount reached 300 g. Since a small amount of crystals were precipitated in the concentration step, the components were examined by filtration and confirmed to be ammonium chloride. Thereafter, the mixture was further concentrated under reduced pressure, but no EDDS ferric complex salt crystals could be obtained.

Example 5 EDDS-4H meso-form and EDDS depending on temperature and time
To investigate the reactivity of the second complex salt with the racemic 4H,
The following experiment was performed. That is, in a 500 ml four-necked flask equipped with a stirrer and a thermometer, 30.0 g (0.10%) of EDDS.4H having a meso body purity of 99.8% was added.
Mol), 99.5% racemic purity EDDS.4H: 3
0.0G (0.10 mol), Fe ₃ O ₄ : 16.0 g
(0.20 mol), 25% aqueous ammonia: 14.0 g
(0.20 mol) and water: 400 g, and after stirring at the temperature shown in Table 1 for the time shown in the same table, the concentration of the EDDS ferric complex salt in the solution dissolved as the ferric complex salt and the result of liquid chromatography analysis From, the reaction rates of the meso form and the racemic form at each temperature and time were examined.

The results are shown in Table 1. The reaction rate between the meso form and the racemic form is considerably different depending on the reaction temperature and the reaction time. In each case, the reaction rate of the racemic form is higher than that of the meso form. The reaction rate is shown. In particular, when the reaction temperature is increased, almost all of the racemate is reacted and the conversion of the meso form is increased. As a result, the racemic purity of the second complex salt formed by the reaction is reduced. Therefore, in order to increase the racemic purity of the product by selectively reacting the racemate while ensuring a high reaction rate to some extent, it is desirable to employ appropriate reaction temperatures and reaction times.

[0038]

[Table 1]

Considering the results in Table 1, the reaction temperature was set at 70
℃, set the reaction temperature to 60 ℃ within 0.5 hours
The reaction rate of the meso form is set to about 2 hours when the reaction temperature is set, about 3 to 4 hours when the reaction temperature is set to 50 ° C., and about 4 hours or more when the reaction temperature is set to 30 ° C. It can be seen that the reaction rate of the racemate can be sufficiently increased without significantly increasing the

Table 1 shows that each of the obtained reaction solutions was 60%
And the meso- and racemic purity of the ferric complex salt of the crystal formed by concentrating and cooling to 20 ° C. As is clear from this value, the crystal formed by concentration and cooling is also shown. Is significantly higher than the racemic purity of the reaction solution. This is racemic
It is considered that when crystallization is performed from the second complex salt of the meso mixture, the racemic ferric complex salt is preferentially precipitated. However, if the racemic purity of the reaction solution falls below 85%,
Since the meso form in the reaction solution acts as an impurity with respect to the racemate, the ferric complex salt crystal does not precipitate even when the reaction solution is concentrated. When the concentration of the meso form in the reaction solution is up to about 15%, it can be understood that the racemic iron complex salt crystals can be obtained by concentration and cooling, and the purpose of the racemic form isolation can be sufficiently achieved.

[0041]

As described above, according to the present invention, EDD obtained by using maleic anhydride and ethylenediamine as raw materials
Using a mixture of S optical isomers, a meso form and a racemic form of EDDS or a ferric complex salt thereof can be obtained by a simple method.
Each of them can be manufactured individually as a high-purity product. In particular, according to the present invention, it is possible to produce a racemate or a ferric complex thereof having excellent biodegradability among the above isomers in an isolated state, and to further enhance the features of EDDS or a ferric complex thereof. It can be used effectively.

[Brief description of the drawings]

FIG. 1 is a liquid chromatogram of racemic EDDS ferric ammonium salt obtained in Example 1.

FIG. 2 is an IR spectrum of EDDS · 4H obtained in Example 1.

FIG. 3 is a liquid chromatogram of a ferric ammonium salt of an EDDS meso compound obtained in Example 2.

FIG. 4 is an IR spectrum of EDDS · 4H obtained in Example 2.

FIG. 5 is a liquid chromatogram of ferric ammonium EDDS obtained using the [S, S] isomer of EDDS · 4H synthesized from L-aspartic acid and 1,2-dibromoethane.

FIG. 6 is an IR spectrum of EDDS · 4H synthesized from L-aspartic acid and 1,2-dibromoethane.

Claims (6)

[Claims] (1) a mixture of a meso-form and a racemic-form isomer of ethylenediamine-N, N'-disuccinic acid; (2) an approximately equimolar amount of triiron tetroxide in terms of Fe with respect to the racemic form; 3) A substantially equimolar amount of ammonia or alkali metal hydroxide with respect to the sum of the meso form and the racemic form is heated and reacted in an aqueous solution, and the racemic ferric complex salt is separated as an aqueous solution. , Ethylenediamine-N,
A method for producing a racemic N'-disuccinic acid ferric complex salt. 2. An ethylenediamine-N, N, characterized in that the racemic ferric complex aqueous solution separated as an aqueous solution in the above (1) is concentrated and / or cooled to obtain the ferric complex salt as crystals. Preparation of racemic ferric complex salt of '-disuccinic acid. (3) a mixture of a meso- and a racemic isomer of ethylenediamine-N, N'-disuccinic acid; (2) a substantially equimolar amount of triiron tetroxide in terms of Fe with respect to the racemic body; 3) A substantially equimolar amount of ammonia or alkali metal hydroxide with respect to the sum of the meso form and the racemic form is heated and reacted in an aqueous solution, and the racemic ferric complex is separated as an aqueous solution, and the resulting insoluble The product is reacted with the meso form in the insoluble material by heating in an aqueous solution with approximately three or more equimolar amounts of iron tetroxide, and approximately equimolar amount or more of ammonia or alkali metal hydroxide in terms of Fe. A process for producing a meso ferric complex of ethylenediamine-N, N'-disuccinic acid, comprising separating a meso ferric complex salt as an aqueous solution. 4. An ethylenediamine-N, N, characterized in that the meso ferric complex aqueous solution separated as an aqueous solution is concentrated and / or cooled to obtain the ferric complex salt as crystals. Preparation of ferric complex salt of '-disuccinic acid meso compound. (5) (1) a mixture of isomers of a meso form and a racemic form of ethylenediamine-N, N'-disuccinic acid; (2) a substantially equimolar amount of triiron tetroxide in terms of Fe with respect to the racemic form; 3) A substantially equimolar amount of ammonia or an alkali metal hydroxide with respect to the total of the meso form and the racemic form is heated and reacted in an aqueous solution, and the racemic ferric complex salt is separated as an aqueous solution, and the excess is added to the aqueous solution. After removing the Fe component as iron hydroxide by adding an alkali in an amount, the filtrate is acidified to obtain a racemate of ethylenediamine-N, N'-disuccinic acid, wherein ethylenediamine-N, N'-disuccinic acid is obtained. Manufacturing method. 6. An isomeric mixture of a meso-form and a racemic-form of ethylenediamine-N, N'-disuccinic acid, (2) an approximately equimolar amount of triiron tetroxide in terms of Fe, 3) A substantially equimolar amount of ammonia or an alkali metal hydroxide is reacted in an aqueous solution with respect to the total of the meso form and the racemic form in an aqueous solution, and the racemic ferric complex salt is filtered off as an aqueous solution, followed by filtration. Is treated with an aqueous solution of ammonia or an alkali metal hydroxide to elute soluble substances, and the resulting alkaline aqueous solution is acidified to obtain ethylenediamine-N,
A process for producing ethylenediamine-N, N'-disuccinic acid, characterized in that a meso-form of N'-disuccinic acid is obtained.