Ferric EDTA

Ferric EDTA is the coordination complex formed from ferric ions and EDTA. EDTA has a high affinity for ferric ions. It gives yellowish aqueous solutions.[1]

Ferric EDTA
Names
Other names
(ethylenedinitrilo)tetraacetatoferrate
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 241-171-3
  • InChI=1S/C10H16N2O8.Fe/c13-7(14)3-11(4-8(15)16)1-2-12(5-9(17)18)6-10(19)20;/h1-6H2,(H,13,14)(H,15,16)(H,17,18)(H,19,20);/q;+3/p-3
    Key: UOMQUZPKALKDCA-UHFFFAOYSA-K
  • C(CN(CC(=O)[O-])CC(=O)[O-])N(CC(=O)O)CC(=O)[O-].[Fe+3]
Properties
C10H12FeN2O8
Molar mass 344.057 g·mol−1
Appearance yellow
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319
P264, P280, P302+P352, P305+P351+P338, P321, P332+P313, P337+P313, P362
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Synthesis and structure

Solutions of Fe(III)-EDTA are produced by combining ferrous salts and aqueous solutions of EDTA known as Jacobson's solution (cf. chemical equation (1) under Table (1)).[2]

Near neutral pH, the principal complex is [Fe(EDTA)(H2O)]−, although most sources ignore the aquo ligand. The [Fe(EDTA)(H2O)]− anion has been crystallized with many cations, e.g., the trihydrate Na[Fe(EDTA)(H2O)].2H2O.[3] The salts as well as the solutions are yellow-brown. Provided the nutrient solution in which the [Fe(EDTA)(H2O)]− complex will be used has a pH of at least 5.5, all the uncomplexed iron, as a result of incomplete synthesis reaction, will still change into the chelated ferric form.[4]

Uses

EDTA is used to solubilize iron(III) in water. In the absence of EDTA or similar chelating agents, ferric ions form insoluble solids and are thus not bioavailable.[1]

Together with pentetic acid (DTPA), EDTA is widely used for sequestering metal ions. Otherwise these metal ions catalyze the decomposition of hydrogen peroxide, which is used to bleach pulp in papermaking. Several million kilograms EDTA are produced for this purpose annually.[5]

Iron chelate is commonly used for agricultural purposes to treat chlorosis, a condition in which leaves produce insufficient chlorophyll. Iron and ligand are absorbed separately by the plant roots whereby the highly stable ferric chelate is first reduced to the less stable ferrous chelate.[6] In horticulture, iron chelate is often referred to as 'sequestered iron' and is used as a plant tonic, often mixed with other nutrients and plant foods (e.g. seaweed). It is recommended in ornamental horticulture for feeding ericaceous plants like Rhododendrons if they are growing in calcareous soils. The sequestered iron is available to the ericaceous plants, without adjusting the soil's pH, and thus, lime-induced chlorosis is prevented.

Ferric EDTA can be used as a component for the Hoagland solution or the Long Ashton Nutrient Solution.[7] According to Jacobson (1951),[2] the stability of ferric EDTA was tested by adding 5 ppm iron, as the complex, to Hoagland's solution at various pH values. No loss of iron occurred below pH 6. In addition to Jacobson's original recipe and a modified protocol by Steiner and van Winden (1970),[4] an updated version for producing the ferric EDTA complex by Nagel et al. (2020)[8] is presented in Table (1).

Jacobson's solution

Table (1) to prepare the ferric EDTA stock solution

Component Quantities in solution
g/L mmol/L
FeSO4•7H2O25.0290
C10H16N2O8 (EDTA)26.3090
H2SO40.1962
KOH15.71280

The formation of Fe(III)-EDTA (FeY)− can be described as follows:

FeSO4∙7H2O + K2H2Y + 1/4 O2 → K[FeY(H2O)].H2O + KHSO4 + 5.5 H2O (1)[8]

Iron chelate has also been used as a bait in the chemical control of slugs, snails and slaters in agriculture in Australia and New Zealand. They have advantages over other more generally poisonous substances used as their toxicity is more specific to molluscs.[9]

Ferric EDTA is used as a photographic bleach to convert silver metal into silver salts, that can later be removed.

Aside from EDTA, the chelating agent EDDHA is used to solubilize iron in water. It also can be used for the purposes of agriculture, accessible to plants.[10]

In iron chelation therapy, deferoxamine, has been used to treat excess iron stores, i.e. haemochromatosis.[11]

See also

References
  1. Xue, Hanbin; Sigg, Laura; Kari, Franz Guenter (1995). "Speciation of EDTA in Natural Waters: Exchange Kinetics of Fe-EDTA in River Water". Environmental Science and Technology. 29 (1): 59–68. doi:10.1021/es00001a007. PMID 22200201.
  2. Jacobson, L. (1951). "Maintenance of Iron Supply in Nutrient Solutions by a Single Addition of Ferric Potassium Ethylenediamine Tetra-Acetate". Plant Physiology. 26 (2): 411–413. doi:10.1104/pp.26.2.411. PMC 437509. PMID 16654380.
  3. Solans, X.; Font Altaba, M.; Garcia-Oricain, J. (1984). "Crystal Structures of Ethylenediaminetetraacetato Metal Complexes. V. Structures Containing the [Fe(C10H12N2O8)(H2O)]− Anion". Acta Crystallographica Section C. 40 (4): 635–638. doi:10.1107/S0108270184005151.
  4. Steiner, A.A.; van Winden, H. (1970). "Recipe for Ferric Salts of Ethylenediaminetetraacetic Acid". Plant Physiology. 46 (6): 862–863. doi:10.1104/pp.46.6.862. PMC 396702. PMID 16657561.
  5. J. Roger Hart "Ethylenediaminetetraacetic Acid and Related Chelating Agents" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a10_095
  6. Van Driel, W. (1964). "The effect of iron ethylenediaminetetraacetic acid on the growth and metabolism of tomato plants in water culture". Plant and Soil. 20: 85–104. doi:10.1007/BF01378101. S2CID 28252630.
  7. Hewitt E. J. (1966). Sand and Water Culture Methods Used in the Study of Plant Nutrition. Farnham Royal, England: Commonwealth Agricultural Bureaux, pp. 547. Technical Communication No. 22 (Revised 2nd Edition) of the Commonwealth Bureau of Horticulture and Plantation Crops.
  8. Nagel, K.A.; Lenz, H.; Kastenholz, B.; Gilmer, F.; Averesch, A.; Putz, A.; Heinz, K.; Fischbach, A.; Scharr, H.; Fiorani, F.; Walter, A.; Schurr, U. (2020). "The platform GrowScreen-Agar enables identification of phenotypic diversity in root and shoot growth traits of agar grown plants". Plant Methods. 16 (89): 1–17. doi:10.1186/s13007-020-00631-3. PMC 7310412. PMID 32582364.
  9. Young CL, Armstrong GD (2001). "Slugs, Snails and Iron based Baits: An Increasing Problem and a Low Toxic Specific Action Solution". Australian Society of Agronomy. The Regional Institute. Retrieved 2009-10-18.
  10. Batra, P.P.; Maier, R.H. (1964). "Isolation and determination of the ferric iron chelate of ethylenediamine di(o-hydroxyphenylacetic acid) in plant tissues". Plant and Soil. 20: 105–115. doi:10.1007/BF01378102. S2CID 9873911.
  11. "Hemochromatosis: Monitoring and Treatment". National Center on Birth Defects and Developmental Disabilities (NCBDDD). 2007-11-01. Archived from the original on May 18, 2009. Retrieved 2009-10-18.
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