Mixtures of MGDA enantiomers, and process for making such mixtures

Abstract

Mixture of L- and D-enantiomers of methyl glycine diacetic acid (MGDA) or its respective mono-, di or trialkali metal or mono-, di- or triammonium salts, said mixture containing predominantly the respective L-isomer with an enantiomeric excess (ee) in the range of from 10 to 75%.

Claims

1. A mixture of L- and D-enantiomers of methyl glycine diacetic acid (MGDA) or its respective mono-, di or trialkali metal or mono-, di- or triammonium salts, the mixture comprising predominantly the respective L-isomer with an enantiomeric excess (ee) in the range of from 10 to 75%.

2. The mixture according to claim 1, the enantiomers being selected from the trisodium salts of MGDA.

3. The mixture according to claim 1, the mixture being predominantly the L-isomer with an enantiomeric excess (ee) in the range of from 12.5 to 60%.

4. The mixture according to claim 1, comprising of from 0.1 to 10% by weight of one or more optically inactive impurities, at least one of the impurities being selected from the group consisting of iminodiacetic acid, formic acid, glycolic acid, propionic acid, acetic acid and their respective alkali metal or mono-, di- or triammonium salts.

5. An aqueous solution comprising of from 40 to 60% by weight of a mixture according to claim 1.

6. The aqueous solution according to claim 5, wherein the aqueous solution is free from organic polymer.

7. The aqueous solution according to claim 5, wherein the aqueous solution additionally comprises at least one inorganic salt selected from the group consisting of alkali metal hydroxides and alkali metal carbonates.

8. A process for making a mixture according to claim 1, comprising (a) dissolving a mixture of L-alanine and its alkali metal salt in water, (b) converting the mixture of L-alanine and its alkali metal salt with formaldehyde and hydrocyanic acid or alkali metal cyanide to a dinitrile, (c) performing saponification of the dinitrile resulting from (b) in two steps (c1) and (c2) at different temperatures, employing stoichiometric amounts of hydroxide or an excess of 1.01 to 1.5 moles of hydroxide per molar sum of COOH groups and nitrile groups of the dinitrile from (b).

9. The process according to claim 8, wherein (c1) is carried out at a temperature in the range of from 20 to 80° C. and (c2) is carried out at a temperature in the range of from 175 to 195° C.

10. The process according to claim 8, wherein (c2) has an average residence time in the range of from 20 to 60 minutes.

11. The process according claim 8, wherein (c2) is carried out with an excess of base of 1.01 to 1.2 moles of hydroxide per molar sum of COOH and nitrile groups of the dinitrile from (b).

12. The process according to claim 8, wherein (c2) is carried out at a higher pressure than (c1).

13. The aqueous solution according to claim 5, wherein the aqueous solution is suitable for the manufacture of laundry detergent compositions and of detergent compositions for cleaners.

14. The aqueous solution according to claim 1, wherein the aqueous solution is suitable in fully or partially neutralized form for the manufacture of laundry detergent compositions or of detergent compositions for cleaners, the neutralization being performed with an inorganic acid.

15. The aqueous solution according to claim 1, wherein the aqueous solution is suitable in fully or partially neutralized form for the manufacture of laundry detergent compositions or of detergent compositions for cleaners, the neutralization being performed with an organic acid.

Description

(1) The Invention is Further Illustrated by Working Examples.

(2) General Remarks:

(3) The ee value was determined by HPLC using a Chirex 3126 column; (D)-penicillamine, 5 μm, 250×4.6 mm. The mobile phase (eluent) was 0.5 mM aqueous CuSat-solution. Injection: 10 μl, flow: 1.5 ml/min. Detection by UV light at 254nm. Temperature: 20° C. Running time was 25 min. The ee value was determined as difference of the area % of the L- and D-MGDA peak divided by the sum of area % of L- and D-MGDA peak. Sample preparation: A 10 ml measuring flask was charged with 5 mg of test material and then filled mark with the eluent and then homogenized.

(4) In each case, the solubility was calculated to refer to pure MGDA, without hydrate water.

(5) I. Syntheses of Inventive Mixtures

(6) With exception of ee values, percentages in the context of the examples refer to percent by weight unless expressly indicated otherwise.

(7) I.1 Synthesis of a Solution of Partially Neutralized of L-alanine, Step (a.1)

(8) A 5-liter stirred flask was charged with 2,100 g of de-ionized water and heated to 40° C. 1,200 g of L-alanine (13.47 mol, 98% ee) were added. To the resultant slurry 700 g of 50% by weight aqueous sodium hydroxide solution (8.75 mol) were added over a period of 30 minutes. During the addition the temperature raised to 60° C. After complete addition of the sodium hydroxide the slurry was stirred at 60° for 30 minutes. A clear solution was obtained.

(9) Samples of aqueous L-MGDA-Na3 were prepared according to WO 2012/150155, page 4, lines 26 ff.

(10) I.2 Syntheses of Aqueous Solutions of L-MGDA-Na.sub.3, Steps (b.1) and Saponification

(11) A 5-liter stirred flask was charged with 500 ml of water and heated to 40° C. Then, 2,373 g of L-alanine solution according to step (a.1) (8.00 mole), 1627 g of 30% by weight aqueous formaldehyde solution (16.27 mole) and 220 g of hydrogen cyanide (8.15 mol) were added simultaneously within 60 minutes. Then, additional 220 g of hydrogen cyanide (8.15 mol) were added at 40° C. within 60 minutes. Upon completion of the addition the reaction mixture was stirred for additional 60 minutes at 40° C. The resulting solution of dinitrile (B) and 1,600 g of sodium hydroxide (50% aqueous solution, 20 mol) were simultaneously added over 160 minutes into another 5-liter stirred flask at a constant rate. During that addition, the temperature was maintained at 28 to 32° C. by external cooling. Upon completion of the addition, the reaction mixture was refluxed for 6 hours at 90 to 95° C. to complete the saponification and to remove any excess of ammonia. The resultant reaction mixture was treated with activated carbon. The resulting aqueous solution contained 38.00 wt % L-MGDA-Na.sub.3 and 0.08 wt % trisodium nitrilotriacetate (NTA-Na.sub.3). The enantiomeric excess of L-MGDA-Na.sub.3 (94.3%) was determined by the aforementioned HPLC method.

(12) The above aqueous solution of MGDA was taken as starting material to investigate the racemization behavior of L-MGDA-Na.sub.3: 6 g of the solution were filled into a pressure tube. This tube was sealed and then tempered for a defined period of time (table 2) at 120° C. or 180° C., respectively. Then the solution was cooled to room temperature and the enantiomeric excess was determined by HPLC.

(13) TABLE-US-00002 TABLE 2 Heating of L-MGDA-Na.sub.3 (6 g of 38% aqueous solution, excess of 0.15 mol NaOH/mol MGDA) in a sealed pressure tube: Temperature Period L-MGDA-Na.sub.3 D-MGDA-Na.sub.3 ee # [° C.] [min] [%] [%] [%] C-0 — — 97.1 2.9 94.3 C-(c2.1) 120 60 94.4 5.6 88.8 (c2.2) 180 20 78.3 21.7 56.6 (c2.3) 180 40 61.3 38.7 22.6 (c2.4) 180 60 55.8 44.2 11.6

(14) C-0 and C-(c2.1) are comparison experiments.

(15) The inventive mixtures so obtained typically have an NTA-Na3 content of 0.05% by weight with respect to the total solution. Unlike the mixture obtained from C-(c2.1), inventive mixtures displayed an excellent olfactory behavior, and they had a low tendency of yellowing.

(16) I.2 Synthesis of Aqueous Solutions of Inventive Mixtures, Steps (b.1) and (c1.1) and (c2.5) to (c2.7), Continuous Process

(17) The continuous syntheses of ca. 40% solutions of inventive mixtures were carried out in cascade of 6 stirred tank reactors, total volume of 8.5 I. The reaction mixture passed all 6 stirred tank reactors (STR.1 to STR.6) consecutively. The last stirred tank reactor to be passed, STR.6, was connected to a tubular reactor, TR.7. In the first three stirred tank reactors, STR.1 to STR.3, dinitrile (B) was synthesized, and STR.1 to STR.3 were operated at 40° C. The average residence time in STR.1 to STR.3 was 45 to 90 min in total. In the three stirred tank reactors STR.4 to STR.6 the saponification was carried out. STR.4 to STR.6 were operated at 60° C. The average residence time in STR.4 to STR.6 was 170 to 400 min in total. The saponification was then completed in tubular reactor TR.7 which was operated with a temperature profile of 130 to 195° C. The final ammonia stripping is done in a column under normal pressure using steam.

(18) Formaldehyde (30% aqueous solution), an aqueous solution of L-alanine (I) and its sodium salt obtained according to 1.1 and 80 mol-% of the required HCN were added to STR.1, the remaining 20% of the required HCN were added to STR.2, the required sodium hydroxide solution was added in STR.4.

(19) The molar ratios of the feed materials were as follows: Sum of L-alanine and its sodium salt: 1.00, Formaldehyde=1.95 to 2.05, HCN=1.95 to 2.10 and Sodium hydroxide=3.15 (total amount of sodium hydroxide, including sodium hydroxide added in step (a.1).

(20) The 40% by weight solutions of inventive mixtures so obtained typically had an NTA-Na3 content of 0.05-0.10% with respect to the total respective solution. They displayed excellent olfactory behavior, and they had a low tendency of yellowing.

(21) TABLE-US-00003 TABLE 3 Influence of temperature and residence time of step (c2.5) to (c2.7) Temperature Residence time for ee [° C.] step (c2) [min] [%] (c2.5) 180 70 10.0 (c2.6) 180 30 30.6 (c2.7) 178 30 36.2
II. Determination of Solubility

(22) The solubility of inventive mixtures and of comparison experiments was determined with an apparatus that allowed heating and cooling down liquid solutions. The temperature (or concentration) of beginning solubility was determined by first cooling down a 50% by weight solution of the respective inventive mixture (or of pure L-MGDA, or of racemic MGDA) to beginning precipitation of MGDA, cooling rate: 30° C./h. Then, the slurry of crystals of MGDA so obtained was again heated at a speed of 1° C./h until a clear solution was obtained. The slurry/solution was checked for solid particles by visible light scattering detection.

(23) The above tests furnished the minimum temperature, T.sub.sol, for forming a kinetically stable 50% by weight solution of the respective mixture of isomers. A higher temperature T.sub.sol correlates with a lower solubility at ambient temperature.

(24) TABLE-US-00004 TABLE 4 correlation ee value versus T.sub.sol ee value (%) T.sub.sol [° C.] zero 103.8 10.1 74.5 20.0 74.0 50.0 68.1 70.0 59.5 97.7 37.0
Ill. Determination of Stability Against Strong alkali

(25) The following tolerance tests were performed: 25 g of a 40% by weight aqueous solution of the respective inventive mixture (or of racemic MGDA) were mixed under one hour of stirring with the amount of solid NaOH beads according to table 5. The mixture so obtained was stored at ambient temperature over the period of up to 96 hours. Then, the appearance was characterized by visual inspection. The results are summarized in table 5.

(26) TABLE-US-00005 TABLE 5 Appearance of test solutions after 96 h of storage NaOH added [g] Racemic MGDA MGDA: 50% ee 0 clear liquid clear liquid 0.5 clear liquid clear liquid 1.0 clear liquid clear liquid 1.5 turbid* liquid clear liquid 2.0 turbid* liquid clear liquid 2.5 turbid, precipitate** clear liquid *after 48 hours **immediately after addition of NaOH