PROCESS FOR MANUFACTURE OF A COMPLEXING AGENT

Abstract

A process for making a complexing agent with an enantiomeric excess of at least 60%, wherein said process comprises the following steps: (a) reacting an aqueous slurry of alanine with an enantiomeric excess of at least 60% with formaldehyde and hydrocyanic acid, thereby forming an aqueous solution of alanine-bisacetonitrile, (b) saponifying the alanine-bisacetonitrile from step (a) by combining the aqueous solution obtained in step (a) with an aqueous solution of alkali metal hydroxide.

Claims

1. A process for making a complexing agent with an enantiomeric excess of at least 60%, wherein said process comprises the following steps: (a) reacting an aqueous slurry of alanine with an enantiomeric excess of at least 60% with formaldehyde and hydrocyanic acid, thereby forming an aqueous solution of alanine-bisacetonitrile, (b) saponifying the alanine-bisacetonitrile from step (a) by combining the aqueous solution obtained in step (a) with an aqueous solution of alkali metal hydroxide.

2. The process according to claim 1, wherein alanine in step (a) is predominantly the L-isomer with an enantiomeric excess of at least 60%.

3. The process according to claim 1, wherein in step (b), the aqueous solution of step (a) is added to an aqueous solution of alkali metal hydroxide.

4. The process according to claim 1, wherein in step (b), the aqueous solution of step (a) and a solution of alkali metal hydroxide are simultaneously added to an aqueous solution of alkali metal hydroxide.

5. The process according to claim 1, wherein the alkali metal hydroxide is sodium hydroxide.

6. The process according to claim 1, wherein step (b) is performed at two different temperatures, (b1) in the range of from 20 to 80° C., (b2) in the range of from 90 to 190° C.

7. The process according to claim 1, wherein step (a) is performed by first adding the formaldehyde to said aqueous slurry of alanine followed by addition of hydrocyanic acid.

8. The process according to claim 1, wherein in step (b), the molar amount of alkali metal hydroxide corresponds to an excess, referring to the nitrile group and neutralization of the carboxylic acid group of alanine.

9. The process according to claim 1, in step (b), alkali metal hydroxide corresponds to an undercut, referring to the nitrile group and neutralization of the carboxylic acid group of alanine.

Description

I. EXAMPLE 1: SYNTHESIS OF D-MGDA-Na.SUB.3

I.1 Synthesis of an Aqueous Solution of D-Aban

[0067] A 2.5-litre stirred reactor was charged with 234 g of D-alanine (2.60 mol) and 480 g of deionized water. To the resultant slurry 520.3 g of formaldehyde (30.0% in water, 5.20 mol) were added at 25° C. over a time period of 10 minutes. The slurry did not show any significant temperature change during formaldehyde addition. After complete addition of formaldehyde, the temperature was raised to 40° C. Within 60 minutes, 142.0 g of hydrogen cyanide (99.0%, 5.20 mol) were added while keeping the temperature at 40° C. In the course of the HCN addition the white solid was completely dissolved, but during the second half of the HCN addition a white precipitate formation was observed again. At the end of the HCN addition, said white precipitate had dissolved completely. After complete addition of HCN the resultant solution was stirred at 40° C. for 60 minutes for completion of the reaction. During this stirring, no formation of solids was observed.

[0068] Analytics (HPLC): D-alanine-bisacetonitrile: 28.9 wt.-%, D-alanine mono-acetonitrile: 0.3 wt.-%, alanine: not detected

I.2 Synthesis of an Aqueous Solution of Complexing Agent D-Mgda-Na.SUB.3

[0069] A 2.5-litre stirred reactor was charged with 644.8 g of sodium hydroxide (50.0% in water, 8.06 mol). The obtained solution D-ABAN from step I.1 was dosed in the caustic solution during 60 minutes at a temperature of 60° C. After complete addition of the ABAN-solution the solution was stirred for 30 minutes at 60° C. Then, the reaction mixture was heated up to temperature 95 to 100° C. to finalize the saponification reaction. During this step the reactor was also charged with a continuous air flow to strip off the evolving ammonia. The aqueous solution was stirred for 240 minutes at this temperature level and then concentrated to 40% by weight (calculated on MGDA-Na.sub.3).

[0070] Analytics: Fe-binding capacity (titration): 40.0 wt.-% (calc. as MGDA-Na.sub.3); HPLC: NTA-Na.sub.3: 0.04 wt.-%, ee-value: 97.6

I.3 Synthesis of an Aqueous Solution of L-Aban

[0071] The protocol of I.1 was followed but L-alanine was used as starting material. Accordingly, an aqueous solution of L-ABAN was obtained.

[0072] Analytics (HPLC): L-alanine-bisacetonitrile: 30.3 wt.-%, L-alanine-monoacetonitrile: 0.5 wt.-%, alanine: not detected

I.4 Synthesis of an Aqueous Solutions Of Complexing Agent L-Mgda-Na.SUB.3

[0073] The protocol of 1.2 was followed but the aqueous solution of L-ABAN from I.3 was used as starting material. Accordingly, a 40% by weight (calculated as MGDA-Na.sub.3) aqueous solution of L-MGDA-Na.sub.3 was obtained.

II. COMPARATIVE EXAMPLE 1: SYNTHESIS OF (±)-MGDA-Na.SUB.3

II.1 Synthesis of an Aqueous Solution of (±)-Aban

[0074] A 2.5-litre stirred reactor was charged with 234 g of (±)-alanine (2.60 mol) and 480 g of deionized water. To the resultant slurry 520.3 g of formaldehyde (30.0% in water, 5.20 mol) were dosed at 25° C. within 10 minutes. The white slurry did not show any significant temperature change during formaldehyde addition. After complete addition of the formaldehyde the temperature was raised to 40° C. Within 60 minutes, 142.0 g of hydrogen cyanide (99.0%. 5.20 mol) were added. The temperature was maintained at 40° C. In the course of the addition of HCN the white solid dissolved completely and no solid was formed during the remaining addition of HCN. After complete addition of HCN the solution was stirred at 40° C. for 60 minutes. During this completion of the reaction no precipitate formation was observed. At the end of the reaction, the vessel was flushed with a small amount of de-ionized water.

[0075] Analytics (HPLC): (±)-alanine-bisacetonitrile: 28.9 wt.-%, alanine mono-acetonitrile: 0.6 wt.-%, alanine: not detected

II.2 Synthesis of an Aqueous Solution of Complexing Agent (±)-Mgda-Na.SUB.3

[0076] The protocol of 1.2 was followed but the aqueous solution of (±)-ABAN from II.1 was used as starting material. Accordingly, a 40% by weight (calculated as MGDA-Na.sub.3) aqueous solution of (±)-MGDA-Na.sub.3 was obtained.

[0077] Analytics: Fe-binding capacity (titration): 40.1 wt.-% (calc. as MGDA-Na.sub.3); HPLC: NTA-Na.sub.3: 0.09 wt.-%, ee-value: 0.0