PROCESS FOR MAKING A CRYSTALLINE ALKALI METAL SALT OF A COMPLEXING AGENT, AND CRYSTALLINE COMPLEXING AGENT

Abstract

Process for manufacturing a crystalline alkali metal salt of the general formula (I) [R.sup.1CH(COO)N(CH.sub.2COO).sub.2]M.sup.1.sub.3 (I) wherein M.sup.1 is selected from alkali metal cations, same or different, R.sup.1 is selected from C.sub.1-C.sub.4-alkyl and CH.sub.2CH.sub.2COOM.sup.1, comprising the step of (b) crystallizing said alkali metal salt from an aqueous solution containing in the range of from 5 to 30% by weight of alkali metal hydroxide, referring to said aqueous solution.

Claims

1. A process for manufacturing a crystalline alkali metal salt of formula (I):
[R.sub.1CH(COO)N(CH.sub.2COO).sub.2]M.sup.1.sub.3(I) wherein each M.sup.1 is independently an alkali metal cation, and R.sup.1 is a C.sub.1-C.sub.4-alkyl or CH.sub.2CH.sub.2COOM.sup.1, the process comprising (b) crystallizing said alkali metal salt from an aqueous solution comprising in the range of from 5 to 30% by weight of alkali metal hydroxide, based on the weight of said aqueous solution.

2. The process according to claim 1, wherein said alkali metal salt is racemic or a mixture of enantiomers comprising predominantly the respective L-isomer with an enantiomeric excess (ee) in the range of from 0.1 to 85%.

3. The process according to claim 1, wherein R.sup.1 is methyl and M.sup.1 is sodium.

4. The process according to claim 1, wherein (b) comprises providing an aqueous solution of alkali metal salt of formula (I) in an aqueous solution of alkali metal hydroxide, said solution having a temperature of at least 50 C., and cooling down said solution to 35 C. or less at a cooling rate of 0.1 to 1.5 C./min.

5. The process according to claim 1, wherein said crystallizing comprises cooling crystallization.

6. The process according to claim 1, further comprising (a1): (a1) saponification of at least one nitrile according to formula (II a) or (II b)
R.sup.2CH(COOM.sup.2)-N(CH.sub.2CN).sub.2(II a)
R.sup.2CH(CN)N(CH.sub.2CN).sub.2(II b) wherein R.sup.2 is C.sub.1-C.sub.4-alkyl, CH.sub.2CH.sub.2COOH or CH.sub.2CH.sub.2COOM.sup.1, and M.sup.2 is an alkali metal or hydrogen, with an excess of aqueous alkali metal hydroxide solution before subjecting the resultant solution to (b).

7. The process according to claim 1, further comprising (a2) and (a3): (a2) saponification of at least one nitrile according to formula (II a) or (II b)
R.sup.2CH(COOM.sup.2)-N(CH.sub.2CN).sub.2(II a)
R.sup.2CH(CN)N(CH.sub.2CN).sub.2(II b) wherein R.sup.2 is C.sub.1-C.sub.4-alkyl, CH.sub.2CH.sub.2COOH or CH.sub.2CH.sub.2COOM.sup.1, and M.sup.2 is an alkali metal or hydrogen, with a stoichiometric amount of alkali metal hydroxide solution, and (a3) adding aqueous alkali metal hydroxide solution before subjecting the resultant solution to (b) or during (b).

8. The process according to claim 1, wherein the aqueous solution that is subjected to (b) is free from ammonia.

9. The process according to claim 6, wherein a mother liquor is at least partially used for saponification of the nitrile according to formula (II a) or (II b).

10. The process according to claim 1, wherein the crystallization is initiated by addition of seed crystals.

11. A solid alkali metal salt of formula (I):
[R.sub.1CH(COO)N(CH.sub.2COO).sub.2]M.sup.1.sub.3(I) wherein each M.sup.1 is independently an alkali metal cation, and R.sup.1 is a C.sub.1-C.sub.4-alkyl or CH.sub.2CH.sub.2COOM.sup.1, said solid alkali metal salt having a crystallinity in the range of from 90 to 99%, determined by X-ray diffraction.

12. The solid alkali metal salt according to claim 11, wherein said alkali metal salt is racemic or a mixture of enantiomers comprising predominantly the respective L-isomer with an enantiomeric excess (ee) in the range of from 0.1 to 85%.

13. The solid alkali metal salt according to claim 11, wherein said alkali metal salt is a mixture of enantiomers containing predominantly the respective L-isomer with an enantiomeric excess (ee) in the range of from 10 to 35%.

14. The solid alkali metal salt according to claim 11, wherein R.sup.1 is methyl and M.sup.1 is sodium.

15. A solid laundry detergent composition comprising the solid alkali metal salt according to claim 11.

Description

GENERAL REMARKS

Working Examples

[0157] The X-ray powder diffractometer measurements were carried out on a D8 Advance diffractometer from Bruker AXS (Karlsruhe). In reflection with Cu-K -radiation was measured with a variable diaphragm adjustment on the primary side and on the secondary side. The measurement range was 2 to 80 2-theta, the step width 0.01 and the measurement time per angle step 3.6 seconds.

[0158] With exception of ee values and of degrees of crystallinity, percentages in the context of the examples refer to percent by weight unless expressly indicated otherwise.

[0159] Normal pressure: 1013 mbar

I.1 Synthesis of a Solution of a Partially Neutralized L-Alanine Bis-Acetonitrile

[0160] A 5-litre 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 of sodium hydroxide solution the temperature raised to 60 C. After complete addition of the sodium hydroxide solution the slurry was stirred at 60 for 30 minutes. A clear solution was obtained.

[0161] A 5-litre 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. A solution was obtained that contained partially neutralized L-alanine bis-acetonitrile.

[0162] The resulting aqueous solution, step (a.1), contained 40.00 wt % MGDA-Na.sub.3 and 0.08 wt % nitrilotriacetic acid (NTA). The enantiomeric excess of L-MGDA-Na.sub.3 (31.6%) was determined by the aforementioned HPLC method.

[0163] The resulting aqueous solution, step (a.1), contained 40.00 wt % MGDA-Na.sub.3 and 0.08 wt % nitrilotriacetic acid (NTA). The enantiomeric excess of L-MGDA-Na.sub.3 (31.6%) was determined by the aforementioned HPLC method.

Step (b.1):

[0164] A 0.75-litre jacket stirred vessel made of glass was charged with 918 g of a 40% by weight aqueous (L)-MGDA-Na.sub.3 solution (1.35 mole, 31.6% ee, obtained according to (a.1), see above) at room temperature. The resultant solution was heated to 80 C. under stirring. Then, the pressure was lowered. At 300 mbar, 71.1 g water was evaporated within 30 minutes. The reaction mixture was brought to normal pressure and 335 mL of a 50% by weight aqueous sodium hydroxide solution (4.19 mole) were added within 1 hour. The clear solution was seeded with 3.7 g MGDA-Na.sub.3 powder (approx. 1% by weight calculated on solid content) and cooled at a rate of 40 K/h to 60 C. After 30 minutes at 60 C., the slurry was cooled with 40 K/h to 40 C. and stirred for 30 minutes. An end-temperature of 20 C. was reached after further cooling using the same rate. The suspension was filtered over a suction filter and the filter cake washed with mother liquid.

[0165] The wet filter cake was dried at 90 C. and 0.1 mbar to yield 204 g of white crystalline powder, inventive salt (S.1), containing 86 wt % MGDA-Na.sub.3 with 98% crystallinity (modification 1), 12.8% ee and 0.04 wt % NTA.

Step (a.2):

[0166] A flask was charged with 608 g (3.04 mol) of 20% by weight sodium hydroxide solution. Within about two hours, an amount of 148 g (1.0 mol) of pure racemic MGDN were introduced at approx. 25 C. Subsequently, the mixture was stirred further under nitrogen first at 30 C. for 3 h and then at 40 C. for 2 h. The mixture was then heated to 170-180 C. in a tubular reactor at approx. 25 bar for 15 minutes. Afterward, the mixture was stripped with nitrogen at 100 to 104 C. within approx. 5 hours. During stripping the solids contents were kept below 45 percent by weight by adding water. This resulted in a yellow-orange solution (Hazen color number: 105) with the following composition: MGDA-Na.sub.3: 257 g (0.95 mol, 95% yield), corresponding to 643 g of a 40 wt % MGDA-Na.sub.3 solution, with 0.07 wt % nitrilo-triacetic acid (NTA).

Step (b.2)

[0167] A 0.75-litre jacket stirred vessel made of glass was charged with 862.8 g of a 40% by weight aqueous (D,L)-MGDA-Na.sub.3 solution (1.27 mole, 0% ee) at room temperature. The resultant solution was heated to 80 C. under stirring. Then, the pressure was lowered. At 340 mbar, 82.2 g water was evaporated within 30 minutes. The reaction mixture was brought to normal pressure and 200 mL of a 50% by weight aqueous sodium hydroxide solution (3.80 mole) were added within 1 hour. The clear solution was seeded with 3.6 g MGDA-Na.sub.3 powder (approx. 1% by weight calculated on solid content) and cooled with 30 K/h to 70 C. After 1 hour at 70 C., the slurry was cooled at a rate of 40 K/h to 50 C. and stirred for 30 minutes. An end-temperature of 30 C. was reached after further cooling using the same rate. The slurry was filtered over a suction filter and the filter cake washed with mother liquid.

[0168] The wet filter cake was dried at 90 C. and 0.1 mbar to give 255.8 g of white crystalline powder, inventive salt (S.2) containing 84 wt % (D,L)-MGDA-Na.sub.3 with 98% crystallinity (modification 1), and 0.04 wt % NTA.

[0169] Inventive salts (S.1) and (S.2) showed only very low hygroscopicity. In addition, their stability against percarbonate was excellent.