Trisodium dicarboxymethyl alaninate

Trisodium N-(1-carboxylatoethyl)iminodiacetate, methylglycinediacetic acid trisodium salt (MGDA-Na3) or trisodium α-DL-alanine diacetate (α-ADA), is the trisodium anion of N-(1-carboxyethyl)iminodiacetic acid and a tetradentate complexing agent. It forms stable 1:1 chelate complexes with cations having a charge number of at least +2, e.g. the "hard water forming" cations Ca²⁺ or Mg²⁺. α-ADA is distinguished from the isomeric β-alaninediacetic acid by better biodegradability and therefore improved environmental compatibility.^[3]

Trisodium dicarboxymethyl alaninate

Names
Other names * N,N-Bis(carboxymethyl)-DL-alanine trisodium salt N-(1-Carboxyethyl)-iminodiacetic acid α-Alanindiacetic acid α-ADA MGDA-Na3 Trilon M
Identifiers
CAS Number	164462-16-2
3D model (JSmol)	Interactive image
ChemSpider	9197166
ECHA InfoCard	100.120.943
EC Number	605-362-9
PubChem CID	11021984
UNII	784K2O81WY
CompTox Dashboard (EPA)	DTXSID2044555
InChI InChI=1S/C7H11NO6.3Na/c1-4(7(13)14)8(2-5(9)10)3-6(11)12;;;/h4H,2-3H2,1H3,(H,9,10)(H,11,12)(H,13,14);;;/q;3*+1/p-3 Key: OHOTVSOGTVKXEL-UHFFFAOYSA-K
SMILES CC(C(=O)[O-])N(CC(=O)[O-])CC(=O)[O-].[Na+].[Na+].[Na+]
Properties
Chemical formula	C7H8NNa3O6
Molar mass	271.111 g·mol^−1
Density	* 0.690 g/cm^3^[1] as powder 1.31 g/cm^3^[1] as ~40% aqueous solution at 20 °C 1.464 g/cm^3^[2] as 56-58% aqueous solution at 20 °C
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H290
Precautionary statements	P234, P390, P404
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Production

The patent literature on the industrial synthesis of trisodium N-(1-carboxylatoethyl)iminodiacetate describes the approaches for solving the key requirements of a manufacturing process that can be implemented on an industrial scale, characterized by

• Achieving the highest possible space-time yields
• Simple reaction control at relatively low pressures and temperatures
• Realization of continuous process options
• Achieving the lowest possible levels of impurities, particularly nitrilotriacetic acid, which is suspected of being carcinogenic
• Use of inexpensive raw materials, e.g. instead of pure L-alanine the raw mixture of Strecker synthesis from methanal, hydrogen cyanide and ammonia
• Avoidance of complex and yield-reducing isolation steps; instead, direct further use of the crude reaction solutions or precipitates in the following process step.

An obvious synthesis route to α-alaninediacetic acid is from racemic α-DL-alanine, which provides racemic α-ADA by double cyanomethylation with methanal and hydrogen cyanide, hydrolysis of the intermediately formed diacetonitrile to the trisodium salt and subsequent acidification with mineral acids in a 97.4% overall yield.^[4] In a later patent specification, however, only an overall yield of 77% and an NTA content of 0.1% is achieved with practically the same quantities of substances and under practically identical reaction conditions.^[5]

 

This later patent specification^[5] also indicates a process route via alaninonitrile, which is obtained by Strecker synthesis from hydrogen cyanide, ammonia and methanal and converted to methylglycinonitrile-N,N-diacetonitrile by double cyanomethylation (step 1). The three nitrile groups are then hydrolyzed with sodium hydroxide to α-ADA (step 2). The total yield is given as 72%, the NTA content as 0.07%.

 

One variant of the reaction involves iminodiacetonitrile or iminodiacetic acid (step 1'), which reacts in a weakly acidic medium (pH 6) with hydrogen cyanide and ethanal to form methylglycinonitrile-N,N-diacetic acid, the nitrile group of which is hydrolyzed with sodium hydroxide to trisodium N-(1-carboxylatoethyl)iminodiacetate (step 2'). The reactant iminodiacetic acid is accessible at low cost by dehydrogenation of diethanolamine. Again, the total yield is given as 72%, the NTA content as 0.07%.

 

A further variant is suitable for continuous production, in which ammonia, methanal and hydrogen cyanide react at pH 6 to form iminodiacetonitrile, which in a strongly acidic medium (pH 1.5) reacts with ethanal to produce trinitrile methylglycinonitrile-N,N-diacetonitrile in a very good yield of 92%. (step 1).

 

Alkaline hydrolysis (step 2) results in a total yield of 85% trisodium N-(1-carboxylatoethyl)iminodiacetate with an NTA content of 0.08%. This process variant seems to fulfil the above-mentioned criteria best.

A low by-product synthesis route for trisodium N-(1-carboxylatoethyl)iminodiacetate has recently been described, in which alanine is ethoxylated with ethylene oxide in an autoclave to form bis-hydroxyethylaminoalanine and then oxidized to α-ADA at 190 °C with Raney copper under pressure.^[6]

 

The yields are over 90% d.Th., the NTA contents below 1%. The process conditions make this variant rather less attractive.

Properties

The commercially available trisodium N-(1-carboxylatoethyl)iminodiacetate (84% by weight) is a colourless, water-soluble solid whose aqueous solutions are rapidly and completely degraded even by non-adapted bacteria. Aquatic toxicity to fish, daphnia and algae is low.^[7] Trisodium N-(1-carboxylatoethyl)iminodiacetate is described as readily biodegradable (OECD 301C) and is eliminated to >90 % in wastewater treatment plants.^[8] Trisodium N-(1-carboxylatoethyl)iminodiacetate has not yet been detected in the discharge of municipal and industrial sewage treatment plants. In addition to their very good biodegradability, trisodium N-(1-carboxylatoethyl)iminodiacetate solutions are characterized by high chemical stability even at temperatures above 200 °C (under pressure) in a wide pH range between 2 and 14 as well as high complex stability compared to other complexing agents of the aminopolycarboxylate type.^[1][9]

The following table shows the complexing constants log K of α-ADA compared to tetrasodium iminodisuccinate and ethylenediaminetetraacetic acid (EDTA) versus polyvalent metal ions:

Metal ions	MGDA	IDS^[10]	EDTA^[11]
Ba^2+	4,9	3,4	7,9
Ag^+		3,9	7,3
Sr^2+	5,2	4,1
Ca^2+	7,0	5,2	10,6
Mg^2+	5,8	6,1	8,7
Mn^2+	8,4	7,7	13,8
Fe^2+	8,1	8,2	14,3
Cd^2+	10,6	8,4	16,5
Cr^3+		9,6
Co^2+	11,1	10,5	16,3
Zn^2+	10,9	10,8	16,5
Pb^2+	12,1	11,0	18,0
Ni^2+	12,0	12,2	18,6
Cu^2+	13,9	13,1	18,8
Al^3+		14,1	16,1
Hg^2+		14,9	21,8
Fe^3+	16,5	15,2	25,1

The complex formation constants of the biodegradable chelators α-ADA and IDS are in a range suitable for industrial use, but clearly below those of the previous standard EDTA.

In solid preparations, trisodium N-(1-carboxylatoethyl)iminodiacetate is stable against oxidizing agents such as perborates and percarbonates, but not against oxidizing acids or sodium hypochlorite.

Use

Like other complexing agents in the aminopolycarboxylic acid class, trisodium N-(1-carboxylatoethyl)iminodiacetate (α-ADA) finds due to its ability to form stable chelate complexes with polyvalent ions (in particular the water hardening agents Ca²⁺ and Mg²⁺, as well as transition and heavy metal ions such as Fe³⁺, Mn²⁺, Cu²⁺, etc.) use in water softening, in detergents and cleaning agents, in electroplating, cosmetics, paper and textile production. Due to its stability at high temperatures and pH values, α-ADA should be particularly suitable as a substitute for the phosphates banned in the EU from 2017, such as sodium tripolyphosphate (STPP)^[12] in tabs for dishwashers.

BASF SE is the most important manufacturer of α-ADA under the brand name Trilon M, has large-scale plants in Ludwigshafen and Lima, Ohio, and is currently expanding its existing capacities with another large-scale plant at Evonik's site in Theodore, Alabama.^[13]

References

1. BASF SE, Technical Information: Trilon M Types
2. National Industrial Chemicals Notification and Assessment Scheme (NICNAS): , File No: STD/1092, August 2004.
3. Environmental Protection Agency, DfE's Safer Chemical Ingredients List, Chelating Agents, Alanine, N,N-bis(carboxymethyl)-, sodium salt (1:3).
4. WO 9429421, J. Schneider et al., "Use of glycine-N,N-diacetic acid derivatives as biodegradable complexing agents for alkaline earth metal ions and heavy metal ions, and methods of preparing them", issued 1994-12-22, assigned to BASF AG 
5. US 5849950, T. Greindl et al., "Preparation of glycine-N,N-diacetic acid derivatives", issued 1998-12-15, assigned to BASF AG 
6. EP 2547648, R. Baumann et al., "Verfahren zur Herstellung nebenproduktarmer Aminocarboxylate", issued 2013-01-23, assigned to BASF SE 
7. BASF, Sicherheitsdatenblatt: Trilon M Powder MSDS
8. Hessisches Landesamt für Umwelt und Geologie, 6.12 Komplexbildner. 2003, S. 12/6.
9. Kołodyńska, Dorota; Hubicka, Halina; Hubicki, Zbigniew (2009). "Studies of application of monodisperse anion exchangers in sorption of heavy metal complexes with IDS". Desalination. 239 (1–3): 216–228. doi:10.1016/j.desal.2008.02.024..
10. Lanxess AG, General Product Information: Baypure
11. BASF SE, Technical Information: (Dec 2013)
12. SEPAWA, Rückblick 2013, Abstracts: Wasch- und Reinigungsmittel Session Reinigen und Hygiene, Jürgen Kielholz: Phosphatfreie Reiniger für maschinelle Geschirrspüler 2014-07-14 at the Wayback Machine
13. BASF SE: No more tea stains and chalky deposits^{[permanent dead link]}