EDDS

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This article is about the chemical. For the ICAO code EDDS, see Stuttgart Airport.
EDDS
File:EDDS racemic.PNG
IUPAC name
ethylenediamine-N,N’-disuccinic acid
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number 20846-91-7
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula C10H16N2O8
Molar mass 292.24 g mol−1
Density 1.44 g/cm3
Melting point

220-222 °C

Solubility in water slightly soluble
Acidity (pKa) 2.4, 3.9, 6.8, 9.8
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Ethylenediamine-N,N'-disuccinic acid (EDDS) is a chelating agent that may offer a biodegradable alternative to EDTA, which is currently used on a large scale in numerous applications. Research into the synthesis and application of EDDS is mainly focused on the (S,S) stereoisomer.[citation needed]

Structure and properties

EDDS has two chiral centers, and as such three stereoisomers exist.[1] These are the enantiomeric (R,R) and (S,S) isomers and the achiral meso (R,S) isomer. As a biodegradable replacement for EDTA, only the (S,S) stereoisomer is of interest, as the (R,S) and (R,R) stereoisomers are less biodegradable, whereas the (S,S) stereoisomer has been shown to be very effectively biodegraded even in highly polluted soils.[2]

Synthesis

EDDS was first reported by Barbier, M. et al. in 1963, in which they synthesized EDDS from maleic acid and ethylenediamine.[3] EDDS was patented in the US by Charles Kezerian and William M. Ramsey of Stauffer Chemical Co. in 1964.[4] (S,S)-EDDS is produced stereospecifically by the alkylation of an ethylenedihalide with L-aspartic acid. Racemic EDDS is produced by the reaction of ethylenediamine with fumaric acid or maleic acid. Some microorganisms have been manipulated for industrial-scale synthesis of (S,S)-EDDS from ethylenediamine and fumaric acid or maleic acid, which proceeds as follows:[5]

2 HO2CCH=CHCO2H + H2NCH2CH2NH2 →→→ [CH2NHCH(CO2H)CH2CO2H]2

Coordination Chemistry

File:EDDS metal complex.PNG
As shown above, the six-membered rings are in the equatorial positions in the EDDS metal chelate complex. Shown here is the (R,R) enantiomer.

In comparing the effectiveness of (S,S)-EDDS versus EDTA for its role as a chelating agent, and thus its efficacy as a replacement, we can compare the formation constants for the metal chelate complexes. Focusing on iron(III) as a very common metal iron that would typically be targeted through chelation, we can compare the following reactions:

Formation Reaction Formation Constant
[Fe(H2O)6]3+ + (S,S)-EDDS4- → Fe[(S,S)-EDDS]- + 6 H2O KEDDS = 1020.6
[Fe(H2O)6]3+ + EDTA4- → Fe(EDTA)- + 6 H2O KEDTA = 1025.1

Because of the lower stability constant for (S,S)-EDDS than EDTA, the useful chelating range for (S,S)-EDDS is narrower than that for EDTA, with the useful range being roughly 3<pH(S,S)-EDDS<9 and 2<pHEDTA<11. However, this range is sufficient for most applications.[6]

Another comparison that can be made between (S,S)-EDDS and EDTA is the structure of the chelated complex that each compound forms. EDTA’s six donor sites form five five-membered chelate rings around the metal ion, four NC2OFe rings and one C2N2Fe ring. The C2N2Fe ring and two of NC2OFe rings define a plane, and two NC2OFe rings are perpendicular to the plane that contains the C2-symmetry axis. The five-membered rings are slightly strained. EDDS’s six donor sites form both five- and six-membered chelate rings around the metal ion: two NC2OFe rings, two NC3OFe rings, and one C2N2Fe ring. Studies of the crystal structure of the Fe[(S,S)-EDDS]- complex show that the two five-membered NC3OFe rings project out of the plane of the complex, reducing the equatorial ring strain that exists in the Fe[EDTA]- complex.[7] The complex also has C2 symmetry.

Uses

(S,S)-EDDS is a biodegradable chelating agent that offers an alternative to EDTA, of which 80 million kilograms are produced annually. Under natural conditions, EDTA has been found to convert to ethylenediaminetriacetic acid and then cyclize to the diketopiperizide, which accumulates in the environment as a persistent organic pollutant.[8] As an environmentally friendly alternative, (S,S)-EDDS can thus be used as a substitute for EDTA in its myriad applications. These uses usually revolve around removing or deactivating metal cations.[9] When EDDS is applied in chemical-enhanced soil remediation in excessive case (e.g. when applied for ex-situ soil washing), higher extraction efficiency for heavy metals can be achieved and the amount of extraction is less independent with the EDDS dosage;[10] On the other hand, during soil remediation which involves continuous flushing, metal extraction is often limited by the amount of EDDS. Under EDDS deficiency, initial unselective extraction of heavy metals was observed, followed by heavy metal exchange and re-adsorption of heavy metals that have lower stability constant with EDDS.[11]

External links

References

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de:Ethylendiamindibernsteinsäure
  1. ↑ Neal, J. A.; Rose, N. J. (1968). "Stereospecific Ligands and Their Complexes. I. A Cobalt(III) Complex of Ethylenediaminedisuccinic Acid". Inorganic Chemistry. 7 (11): 2405–2412. doi:10.1021/ic50069a043. 
  2. ↑ Tandy, S.; Ammann, A.; Schulin, R.; Nowack, B. (2006). "Biodegredation and speciation of residual SS-ethylenediaminedisuccinic acid (EDDS) in soil solution left after soil washing". Environmental Pollution. 142 (2): 191–199. doi:10.1016/j.envpol.2005.10.013. PMID 16338042. 
  3. ↑ Barbier, M.; et al. (1963). "Synthese und Eigenschaften eines Analogen des Lycomarasmins und der Aspergillomarasmine". Liebigs Annalen. 668: 132. doi:10.1002/jlac.19636680115. 
  4. ↑ US patent 3158635, Kezerian, Charles; Ramsey, William M., "Bisadducts of diamines and unsaturated acids", issued 1964-11-24 
  5. ↑ Takahashi, R.; et al. (1999). "Production of (S,S)-Ethylenediamine-N,N'-disuccinic Acid from Ethylenediamine and Fumaric Acid by Bacteria". Biosci. Biotechnol. Biochem. 63 (7): 1269–1273. doi:10.1271/bbb.63.1269. 
  6. ↑ Orama, M.; Hyvönen, H.; Saarinen, H.; Aksela, R. (2002). "Complexation of [S,S] and mixed stereoisomers of N,N'-ethylenediaminedisuccinic acid (EDDS) with Fe(III), Cu(II), Zn(II) and Mn(II) ions in aqueous solution". J. Chem. Soc., Dalton Trans.: 4644–4648. doi:10.1039/b207777a. 
  7. ↑ Pavelčík, F and Majer, J. (1978). "The crystal and molecular structure of lithium [(S,S)-N,N'-ethylenediaminedisuccinato]cobaltate(III) trihydrate". Acta. Crystallogy., Sect. B. 34 (12): 3582–3585. doi:10.1107/S0567740878011644. 
  8. ↑ Yuan, Z. and VanBriesen, J. M. (2006). "The Formation of Intermediates in EDTA and NTA Biodegradation". Environmental Engineering Science. 23 (3): 533–544. doi:10.1089/ees.2006.23.533. 
  9. ↑ Yip, T.C.M.; Tsang, D.C.W.; Ng, K.T.W.; Lo, I.M.C. (2009). "Kinetic interactions of EDDS with soils. 1. Metal resorption and competition under EDDS deficiency". Environ. Sci. Technol. 43 (3): 831–836. doi:10.1021/es802030k. PMID 19245023. 
  10. ↑ Yip, T.C.M.; Tsang, D.C.W.; Ng, K.T.W.; Lo, I.M.C. (2009). "Empirical modeling of heavy metal extraction by EDDS from single-metal and multi-metal contaminated soils". Chemosphere. 74 (2): 301–307. doi:10.1016/j.chemosphere.2008.09.006. PMID 18851868. 
  11. ↑ Tsang, D.C.W.; Yip, T.C.M.; Lo, I.M.C. (2009). "Kinetic interactions of EDDS with soils. 2. Metal-EDDS complexes in uncontaminated and metal-contaminated soils". Environ. Sci. Technol. 43 (3): 837–842. doi:10.1021/es8020292. PMID 19245024. 
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