GB2344587A - Producing (s,s)-alkylenediamine-n,n'-disuccinic acid - Google Patents

Abstract

A method for producing (S,S)-alkylenediamine-N,N'-disuccinic acid, comprises allowing ammonium L-aspartate to contact with an alkali metal hydroxide compound, removing ammonia and then allowing the resulting compound to react with a dihaloalkane, wherein concentration of residual ammonia in an aqueous medium after the removal of ammonia is 4.0% by weight or less of the aspartic acid-based amount of the aspartic acid salt in the aqueous medium. The present method does not spoil the product quality, is inexpensive and efficient and can be practically used industrially.

Description

METHOD FOR PRODUCING (S, S)-ALKYLENEDIAMINE-N, N' DISUCCINIC ACID FIELD OF THE INVENTION This invention relates to a method for the production of (S, S)-alkylenediamine-N, N'-disuccinic acid which is useful as a biodegradable chelating agent.

More particularly, it relates to an industrially practical production method in which (S, S)-alkylenediamine N, N'-disuccinic acid is produced by allowing L-aspartic acid ammonium salt to contact with an alkali metal hydroxide compound and then to react with a dihaloalkane.

BACKGROUND ART It is known that various useful derivatives such as specialty chemicals and pharmaceutical and agricultural chemical intermediates are produced by allowing the nitrogen atom of aspartic acid to react with various carbon electrophilic agents in an aqueous medium, and (S, S) form of alkylenediamine-N, N'-disuccinic acid is particularly drawing attention as a biodegradable chelating agent which can be used as a substitute for generally used chelating agents such as ethylenediaminetetraacetic acid (EDTA).

Various studies have been carried out on the production method of alkylenediamine-N, N'-disuccinic acid, such as 1) a method in which maleic acid is allowed to react with ethylenediamine (Zhurnal Obshchei Khinii., 49, 659 (1978)) and 2) a method in which a dihaloalkane is allowed to react with L-aspartic acid (Inorg. Chem., 7, 2405 (1968), Chem. Zvesti., 20,414 (1966), WO 9512570 and WO 9601803).

The aforementioned method 1) is not practical because of low reactivity, large by-product formation and inability to control stereo effect of asymmetric carbon, and, in the case of the method 2), L-aspartic acid is generally obtained through complex steps of carrying out acid precipitation from L-aspartic acid ammonium salt aqueous solution and its subsequent isolation and purification, so that the material cost is high and industrial realization of this method is difficult to achieve when the factors such as yield, price of the final products and the like are taken into consideration.

On the other hand, it is known that, when aspartic acid ammonium salt is used as the material and allowed to react with a carbon electrophilic agent, salt exchange of an alkali metal compound with ammonia is desirable, and removal of the salt-exchanged ammonia from the system improves the yield due, for example, to the enhancement of the subsequent reaction with the carbon electrophilic agent (JP-B-7-71490; the term"JP-B"as used herein means an "examine Japanese patent publication").

Taking these factors into consideration, a method has been reported in which an L-aspartic acid metal salt having reduced residual ammonia concentration of 20 ppm is produced from L-aspartic acid ammonium salt, by carrying out ammonia distillation (JP-A-9-202754; the term"JP-A"as used herein means an"unexamined published Japanese patent application").

However, when a derivative is produced from L- aspartic acid ammonium salt by its reaction with a carbon electrophilic agent, it is considered that the level of reduced ammonia concentration after salt exchange of an alkali metal with ammonia exerts great influence upon the factors such as the subsequent yield and the like, and sharp increase in the cost cannot be avoided due, for example, to a large load required for the distillation step and the necessity to use additives such as a chelating agent, so that industrial realization of this method is still difficult to achieve.

The present invention contemplates providing a method for the production of (S, S)-ethylenediamine-N, N'-disuccinic acid which is one of the aforementioned aspartic acid derivatives and useful as a biodegradable chelating agent, as an inexpensive and efficient method which does not spoil the product quality and can be practically used industrially.

SUMMARY OF THE INVENTION With the aim of resolving the aforementioned problems, the inventors of the present invention have conducted extensive studies and found as a result of the efforts that, when residual ammonia concentration in an aqueous medium, after contact of ammonium L-aspartate with an alkali metal hydroxide compound and subsequent removal of ammonia, is within a specified range, yield and product quality are not spoiled by the subsequent reaction with a dihaloalkane, thus resulting in the accomplishment of the present invention.

Accordingly, the gist of the present invention resides in a method for the production of (S, S)alkylenediamine-N, N'-disuccinic acid, which comprises allowing ammonium L-aspartate to contact with an alkali metal hydroxide compound, removing ammonia and then allowing the resulting compound to react with a dihaloalkane, wherein concentration of residual ammonia in an aqueous medium after the removal of ammonia is 4.0% by weight or less of the aspartic acid-based amount of the aspartic acid salt in the aqueous medium.

BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a graph showing a relationship between the ammonia content based on aspartic acid and the EDDS yield.

DETAILED DESCRIPTION OF THE INVENTION The ammonium L-aspartate to be used in the present invention is not particularly limited, but it is generally obtained by a method in which aspartase and/or an aspartase-containing microorganism is allowed to react upon fumaric acid and ammonia or ammonium fumarate.

The aforementioned methods are well known and not particularly limited when carried out in accordance with them. Also, said ammonium fumarate may be produced in accordance with a known method in which maleate isomerase and/or a microorganism containing the same is allowed to react upon maleic acid and ammonia, and, in that case, enzymatic isomerization reaction using the maleate isomerase and the reaction with aspartase can be carried out in one pot.

The microorganism to be used in the aforementioned enzyme reaction is not particularly limited, with the proviso that it has the aspartase activity, and its examples include microorganisms belonging to the genera Brevibacterium, Escherichia, Pseudomonas and Bacillus.

Illustrative examples include Brevibacterium flavum MJ-233 (FERM BP-1497), Brevibacterium flavum MJ-233-AB-41 (FERM BP-1498), Brevibacterium ammoniagenes ATCC 6872, Escherichia coli ATCC 11303 and Escherichia coli ATCC 27325.

When microbial cells are used, cultured cells of each strain are washed for example with a phosphate buffer (pH 7) and used as such in the reaction. Desirable concentration of the washing phosphate buffer to be used is approximately from 0. 05 to 0. 2 M. Alternatively, the cells may be used by increasing their permeability in advance through their freezing or treatment with a surface active agent such as Triton X-100 or Tween 20.

Also useful are disrupted cells obtained by treating the cells by ultrasonic disintegration or the like means; a cell extract obtained by centrifuging the disrupted cells; a partially purified enzyme obtained by purifying the cell extract by ammonium sulfate fractionation, ion exchange column, gel filtration column or the like means; or an immobilized preparation thereof.

In the aforementioned enzyme reaction, preferred pH is generally from 7.5 to 10. The reaction temperature is within such a range that the enzyme reaction can be carried out efficiently, which is generally from 10 to 80 C, preferably from 20 to 60 C. In adjusting the reaction pH, it is most desirable to use ammonia which is one of the L- aspartic acid production materials, but an alkali metal hydroxide or the like such as sodium hydroxide or potassium hydroxide may be jointly used, with the proviso that it is 10% by weight or less based on ammonia.

Amount of ammonia to be used in the aforementioned reaction is not particularly limited, with the proviso that the enzyme treatment can be effected, but is within the range of generally from 1.0 to 3.0, preferably from 2.0 to 2.6, as molar ratio to fumaric acid. When the molar ratio is too small or too large, the reaction pH deviates from the optimum pH of aspartase, which is from 7.5 to 9.5, so that the reaction becomes slow.

The reaction solution obtained by this enzyme reaction mainly contains ammonium L-aspartate, and this ammonium salt is a mixture of mono-salt and di-salt. In addition, the reaction solution may also contain unreacted ammonium fumarate and ammonium maleate, and, in that case, it is desirable to control their amounts to 2 g/L or less, preferably 1 g/L or less, by optimization of the reaction conditions.

Also, concentration of L-aspartic acid in the reaction solution is within the range of generally from 50 to 800 g/L, preferably from 100 to 500 g/L. When the concentration is too low, a large amount of water is required which is disadvantageous from the process point of view, and when the concentration is too high, progress of the enzyme reaction is disturbed.

Regarding the reaction method of the enzyme reaction, it may be either a batch system or a continuous system with no particular limitation, but a continuous system is more efficient. Illustrative examples of the continuous system include a method in which a material aqueous solution is passed through a packed layer of immobilized cells and a method in which, while a material aqueous solution is added continuously to a cell suspension, the reaction mixture containing the cells and L-aspartic acid is drawn out at the same time and treated, for example, with ultrafiltration membrane or centrifuge and the thus separated cells are recycled.

In the method of the present invention, removal of ammonia is carried out after allowing ammonium L-aspartate to contact with an alkali metal hydroxide compound.

Examples of the just described alkali metal hydroxide compound include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide; and alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, of which alkali metal hydroxides are preferable and sodium hydroxide is particularly preferable.

Said alkali metal hydroxide compound may be contacted in its aqueous solution form with ammonium L-aspartate or in its solid state with ammonium L-aspartate aqueous solution.

Amount of the alkali metal hydroxide compound to be used is from 0.5 to 4 moles, preferably from 0.65 to 3 moles, more preferably from 0.8 to 2.5 moles, of the Laspartic acid-based amount of the L-aspartic acid salt.

The amount if too small would exert bad influence upon the reaction with dihaloalkane due to increased amount of residual ammonia and if too large would entail undesirable handling because of increased viscosity and basic nature of the liquid.

The method for adding an alkali metal hydroxide compound to ammonium L-aspartate aqueous solution may be effected by either a continuous process or a batch process, and either a mixing vessel equipped with an agitator or a mixing apparatus such as line mixing may be used.

The thus obtained mixture of ammonium L-aspartate and an alkali metal hydride compound can be substantially converted into an L-aspartic acid alkali metal salt by removing ammonia by, for example, distillation, stripping, etc. (to be called sometimes to be"ammonia-removing operation"or"removal of ammonia"herein).

The method of the present invention is characterized in that the concentration of residual ammonia after the ammonia-removing operation is 4.0% by weight or less of the aspartic acid-based amount of the aspartic acid salt. The concentration of residual ammonia is preferably 3.5% by weight or less, more preferably 3.0% by weight or less.

The concentration of residual ammonia if larger than 4.0% by weight would rapidly worsen yield of the reaction with a dihaloalkane.

From the practical point of view, the concentration of residual ammonia is from 20 ppm to 4.0% by weight, preferably from 200 ppm to 3.5% by weight and more preferably from 400 ppm to 3.0% by weight. The concentration of residual ammonia if smaller than 20 ppm would result in increased cost due to large load in the distillation or stripping step.

Particularly, when the reaction with dichloroethane is carried out, the concentration of residual ammonia is within the range of preferably from 0.1 to 4% by weight, more preferably from 0.3 to 3.5% by weight.

The ammonia-removing operation may be carried out either under ordinary pressure or under a reduced pressure at a liquid temperature of from 30 to 100 C, preferably from 40 to 80 C. The ammonia-removing operation if carried out at a lower temperature would entail increased operational limitation due to the necessity to increase decompression degree and if carried out at a higher temperature would cause thermal deterioration of the reaction solution. In this case, temperature of the supply solution is not particularly limited, but, when the reaction and operation temperature of each step are taken into consideration, it may be from 5 to 80 C, preferably from 10 to 50 C. The residence time, though it varies depending on the tower bottom temperature, is within the range of generally from 0.01 to 5 hours, preferably from 0.02 to 4 hours.

The ammonia-removing operation may be either a batch system or a continuous system, but a continuous system which can carry out the treatment within a short period of time is desirable.

Examples of the ammonia-removing apparatus to be used in the present invention include a flash distillation column and a distilling column having appropriate number of plate, which are used in general chemical industry. Also, in order to avoid thermal deterioration as feasible as possible, an apparatus which can carry out the treatment within a short period of time, such as a thin film distiller, may be used. In this ammonia-removing operation, ammonia and water are separated as steam, so that the aqueous ammonia obtained by cooling the steam by a condenser can be recycled into the ammonium L-aspartate production step.

Concentration of the L-aspartic acid alkali metal salt after the ammonia-removing operation is, by taking the subsequent reaction with a dihaloalkane into consideration, adjusted to a level of from 5 to 50% by weight, preferably from 10 to 40% by weight, more preferably from 15 to 30% by weight, as L-aspartic acid.

By allowing the thus obtained L-aspartic acid alkali metal salt to further react with a dihaloalkane, the product of interest (S, S)-alkylenediamine-N, N'-disuccinic acid can be obtained.

Examples of the dihaloalkane to be used in the present invention include dihaloalkanes having 2 to 6 carbon atoms, such as 1,2-dichloroethane, 1,2dibromoethane, 1,2-dichloropropane, 1,2-dibromopropane, 1,3-dichloropropane, 1,3-dibromopropane, 1,2dichlorobutane, 1,4-dichlorobutane, 1,2-dibromobutane, 1,4dibromobutane, 1,5-dichloropentane, 1,5-dibromopentane, 1,6-dichlorohexane and 1,6-dibromohexane, of which a dihaloalkane having 2 or 3 carbon atoms, such as 1,2dichloroethane, 1,3-dichloropropane or 1,2-dibromoethane is preferred from the viewpoint of reactivity, 1,2dichloroethane or 1,3-dichloropropane is more preferred and 1,2-dichloroethane is most preferred.

The dihaloalkane is used within the range of from 0.3 to 1.0 mole, preferably from 0.5 to 0.7 mole, more preferably from 0.5 to 0.6 mole, based on the L-aspartic acid alkali metal salt. The amount if smaller than 0.3 mole would cause considerable reduction of purification efficiency due to increased amount of unreacted L-aspartic acid and if larger than 1.0 mole would entail increased amount of by-products.

Regarding the reaction solvent, water is desirable but the reaction rate can be improved by the joint use of other water-soluble organic solvents such as alcohols (e. g., methanol, glycol, etc.). The"aqueous medium" includes such a mixed solvent as well as a wholly aqueous solvent (i. e., water). It is desirable to use the solvent in such an amount that concentration of the L-aspartic acid alkali metal salt becomes from 5 to 50% by weight.

This reaction is carried out under a basic condition, and the reaction solution has a pH value of preferably from 9 to 13. As occasion demands, an alkali metal hydroxide compound may be added for adjusting the reaction solution to the basic range. Examples of the alkali metal hydroxide compound include alkali metal hydroxides and alkaline earth metal hydroxides, of which sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide or a mixture thereof is preferred.

Regarding the method for the addition of the alkali metal hydroxide compound, a compound hardly soluble in water may be added in one portion prior to the commencement of the reaction, but, in the case of a compound easily soluble in water, it is desirable to add in portions in order to suppress decomposition of the dihaloalkane.

The reaction is carried out at a temperature of from 50 to 140 C, preferably from 80 to 120 C, more preferably from 90 to 110 C. The temperature if lower than 50 C would cause considerable reduction of the reaction rate and if higher than 140 C would reduce selectivity of the product of interest and also entail a problem of causing racemization of L-aspartate. The reaction can be carried out under ordinary pressure or under compression, and the reaction time is within the range of from 0.5 to 50 hours, though it varied depending on other conditions.

After completion of the reaction, unreacted dihaloalkane is evaporated from the reaction solution and then the product of interest is precipitated by adding an inorganic acid. If necessary, prior to the addition of the inorganic acid, the product of interest in the reaction solution may be adjusted to a concentration of from 1 to 50% by weight, preferably from 3 to 30% by weight, more preferably from 5 to 20% by weight, by adding water. The concentration if too low would entail poor precipitation efficiency and if too high would cause operational problems such as a difficulty in carrying out uniform agitation of the system due to precipitated crystals.

Hydrochloric acid or sulfuric acid is desirable as the acid to be used, and it is desirable to dilute the acid to a concentration of from 3 to 50% by weight from the viewpoint of preventing excess exothermic reaction.

It is desirable to add the acid in portions in such a manner that the difference between the pH value when the product of interest starts to precipitate by the acid addition and the pH value increased by the precipitation, namely A pH, becomes small. Illustratively, the A pH value is 0.5 or less, preferably 0.3 or less. When the A pH value is 0.5 or less, product having a crystal size of 10 zm or more can be obtained, which is easy to handle.

In the crystallization step, the reaction solution is finally adjusted to a pH value of from 2.0 to 5.0, preferably from 2.5 to 4.0.

The crystallization temperature is from 5 to 80 C, preferably from 20 to 60 C. In comparison with the crystallization temperature, period for the addition of acid varies depending on the scale but is within the range of from 0.1 to 30 hours. After completion of the acid addition, aging may be carried out at a temperature of from 0 to 50 C, preferably from 20 to 40 C, for a period of approximately from 1 to 10 hours.

The thus precipitated crystals can be isolated by separating them using a usual filtration means such as pressure filtration, filtration under reduced pressure or centrifugation, washing the separated crystals several times with water and then drying them.

In the aforementioned crystallization operation, the filtrate after separation of the product of interest by filtration may be subjected to the pH and temperature treatment directly or after concentration of the filtrate, so that the unreacted material L-aspartate can be precipitated, recovered and used again as the material.

In this specification, the term"L-aspartic acidbased amount (or concentration) of the L-aspartic acid salt means the amount (or concentration) of L-aspartic acid salt measured as L-aspartic acid. That is, the amount or concentration of the L-aspartic acid salt was measured by converting the L-aspartic acid salt into L-aspartic acid and measuring the amount or concentration of L-aspartic acid by the conventional way, such as the liquid chromatography.

The present invention is described more illustratively in the following with reference to the Examples, Comparative Examples and Reference Examples, though the invention is not restricted by these Examples unless overstepping its scope.

Products, L-aspartic acid, fumaric acid and maleic acid were determined by a high performance liquid chromatography (LC-1OA manufactured by Simadzu Corp.), ammonia and sodium were determined by an ion chromatography (IC-500 manufactured by Yokokawa Analytical), and the moisture content by a Karl Fischer apparatus (CA-05 manufactured by Mitsubishi Chemical Industries).

EXAMPLE 1 Brevibacterium flavum MJ-233-AB-41 (FERM BP-1498) having aspartase activity was cultured in the usual way, the resulting cells were concentrated using an ultrafiltration membrane (ACV-3050 manufactured by Asahi Chemical Industry), and 50 kg of the thus concentrated cells (40% by weight as wet cells) were added to a material (an aqueous solution prepared by adding water to 45 kg of fumaric acid and 61 kg of aqueous ammonia to a total volume of 200 liters; pH, about 9) to carried out the reaction at 45 C for 30 hours. After completion of the reaction, the cells were removed using the ultrafiltration membrane and the thus obtained filtrate was analyzed to find that it contained 259 g/liter of L-aspartic acid (to be referred to as"ASP"hereinafter), 0.5 g/liter of fumaric acid and 45.5 g/liter of NH4+ (NH4+/ASP molar ratio was 1.30, the ammonia content based on aspartic acid was 17.6% by weight) and its pH was 9 (25 C).

A 100 ml portion of said reaction solution (25.9 g as L-aspartic acid, 0.195 mol) and 16. 08 g (0.39 mol) of granular 97% sodium hydroxide were put into a 300 ml capacity eggplant type flask and stirred at room temperature for 30 minutes. Thereafter, ammonia distillation was carried out using an evaporator at 30 C and under 50 mm Hg for 0.2 hour. The recovered solution after distillation contained 241 g/liter of L-aspartic acid and 4.1 g/liter of ammonia (1.7% by weight based on aspartic acid). This solution was put into a 300 ml capacity autoclave, mixed with 9.9 g (0.1 mol) of 1,2dichloroethane and stirred at 100 C to carry out the reaction. The reaction pressure was about 0.2 MPa. After 4 hours of the reaction, the reaction solution was cooled and mixed with 20 g of 20% by weight sodium hydroxide aqueous solution (NaOH 0.1 mol), and the reaction was continued for 6 hours under the same conditions (total reaction time, 10 hours). After completion of the reaction, a portion of the reaction solution was withdrawn and analyzed to find that the conversion ratio of Laspartic acid was 75.6% and the yield of (S, S)- ethylenediamine-N, N'-disuccinic acid (EDDS) was 57.0% based on L-aspartic acid.

Thereafter, trace amount of unreacted 1,2dichloroethane was recovered under a reduced pressure.

When the remaining solution was transferred into a beaker and 40% by weight sulfuric acid aqueous solution was added thereto while stirring at room temperature, white crystals were precipitated at pH 4.5. The liquid temperature at this stage was 29 C. The crystallization was continues by gradually adding the sulfuric acid aqueous solution dropwise while keeping the pH value between 3.7 and 4.5.

When increase in the pH value was not observed after standing, the sulfuric acid addition was stopped and the stirring was continued for 30 minutes as such, and then the thus precipitated crystals were collected by filtration under a reduced pressure. The crystals were washed three times with 30 ml of water and then dried under a reduced pressure. The thus recovered crystals were 15.3 g and contained, when analyzed by a high performance liquid chromatography, 13.4 g of EDDS (87.6% by weight, yield 54.5% calculated as L-aspartic acid), 0.11 g of L-aspartic acid, 100 ppm of sodium and 10.6% by weight of water.

COMPARATIVE EXAMPLE 1 (NO AMMONIA DISTILLATION) A 100 ml portion of the enzyme reaction solution described in Example 1 (the ammonia content based on Laspartic acid, 17.6% by weight), 16.08 g of granular 97% sodium hydroxide and 9.9 g of 1,2-dichloroethane were put into a 300 ml capacity autoclave and stirred at room temperature for 30 minutes and then the reaction was carried out under the same reaction conditions of Example 1.

After completion of the reaction, a portion of the reaction solution was withdrawn and analyzed to find that the conversion ratio of L-aspartic acid was 49. 2% and the yield of (S, S)-ethylenediamine-N, N-disuccinic acid (EDDS) was 8.3% based on L-aspartic acid.

REFERENCE 1 A 25.9 g (0.195 mol) portion of L-aspartic acid (manufactured by Wako Pure Chemical Industries, Lot No.

017-04835, the ammonia content 50 ppm or less), 16.08 g of granular 97% sodium hydroxide and 75 g of water were mixed while taking care of not increasing the temperature to 40 to 50 C or more due to exothermic reaction, by ice-cooling or the like means, and the mixture was put into a 300 ml capacity autoclave. After adding 9.9 g (0.1 mol) of 1, 2 dichloroethane, the reaction was carried out under the same reaction conditions of Example 1.

After completion of the reaction, a portion of the reaction solution was withdrawn and analyzed to find that the conversion ratio of L-aspartic acid was 74.2% and the yield of (S, S)-ethylenediamine-N, N'-disuccinic acid (EDDS) was 55.1% based on L-aspartic acid.

Thereafter, crystallization was carried out in the same manner as described in Example 1 to recover 14.9 g of crystals which, when analyzed, contained 13.1 g of EDDS (87.9% by weight, yield 53.3% calculated as L-aspartic acid), 0.09 g of L-aspartic acid, 100 ppm of sodium and 10.9% by weight of water.

EXAMPLE 2 The procedure of Example 1 was repeated, except that the period of ammonia-removing step was changes from 0.2 hour to 1.5 hours. The recovered solution after distillation contained 261 g/liter of L-aspartic acid and 0.15 g/liter of ammonia (0.057% by weight based on aspartic acid).

After completion of the reaction with 1,2dichloroethane, a portion of the reaction solution was withdrawn and analyzed to find that the conversion ratio of L-aspartic acid was 73.8% and the yield of (S, S)ethylenediamine-N, N'-disuccinic acid (EDDS) was 56.3% based on L-aspartic acid.

EXAMPLES 3 TO 5 A 100 ml portion of sodium L-aspartate solution containing 236 g/liter of L-aspartate and 7.08 g/liter of ammonia (3.0% by weight based on L-aspartic acid) was allowed to react with 1,2-dichloroethane by the same procedure of Example 1 After completion of the reaction, a portion of the reaction solution was withdrawn and analyzed to find that the conversion ratio of L-aspartic acid was 72.5% and the yield of (S, S)-ethylenediamine-N, N'-disuccinic acid (EDDS) was 53.9% based on L-aspartic acid.

In this connection, the same method was repeated using an L-aspartic acid salt solution having the ammonia content of 5.0% by weight or 13.0% by weight based on aspartic acid.

Results of Examples 1 to 5, Compara

TABLE 1 Ammonia content Conversion EDDS based on ratio of yield aspartic acid aspartic acid (%) (%) Reference Example 1 50 ppm or less 74.2 55.1 Example 1 1.70% by weight 75.6 57.0 Example 2 0.057% by weight 73.8 56.3 Example 3 3.0% by weight 72.5 53.9 Example 4 5.0% by weight 56.4 11.4 Example 5 13.0% by weight 48.1 9.5 Comparative Example 1 17.6% by weight 49.2 8.3 According to this invention, (S, S)-alkylenediamine- N, N'-disuccinic acid which is useful as a biodegradable chelating agent can be produced inexpensively and efficiently without spoiling yield and product quality.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

This application is based on Japanese patent application No. Hei.-10-348480, filed on December 8,1998, herein incorporated by reference.

Claims (10)

1. CLAIMS 1. A method for producing (S, S)-alkylenediamine-N, N'-disuccinic acid, which comprises allowing ammonium L-aspartate to contact with an alkali metal hydroxide compound, removing ammonia and then allowing the resulting compound to react with a dihaloalkane, wherein concentration of residual ammonia in an aqueous medium after the removal of ammonia is 4.0% by weight or less of the L-aspartic acid-based amount of the Laspartic acid salt in the aqueous medium.
2. 2. A method according to claim 1, wherein the concentration of residual ammonia is from 20 ppm to 4.0% by weight.
3. 3. A method according to claim 2, wherein the concentration of residual ammonia is 3.5% by weight or less.
4. 4. A method according to claim 2, wherein the concentration of residual ammonia is 3.0% by weight or less.
5. 5. A method according to any preceding claim, wherein amount of the alkali metal hydroxide compound is from 0.5 to 4 moles of the L-aspartic acid-based amount of the L-aspartic acid salt.
6. 6. A method according to any preceding claim, wherein the alkali metal hydroxide compound is sodium hydroxide or potassium hydroxide.
7. 7. A method according to any one of claims 1 to 6, wherein ammonium L-aspartate is produced from fumaric acid and ammonia or from ammonium fumarate using aspartase and/or an aspartase-containing micro-organism.
8. 8. A method according to any one of claims 1 to 6, wherein the dihaloalkane is dichloroethane.
9. 9. A method as claimed in claim 1, substantially as hereinbefore described in any one of Examples 1 to 5.
10. 10. (S, S)-alkylenediamine-N, N'-disuccinic acid when produced by a method as claimed in any preceding claim.