EDTA

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EDTA
Chemical name	EDTA
Other names	EDTA H4EDTA Diaminoethanetetraacetic acid Edetic acid Edetate Ethylenedinitrilotetraacetic acid Versene
Chemical formula	C10H16N2O8
Molecular mass	292.25 g/mol
CAS number	[60-00-4]
Density	0.86 g/cm³
Melting point	237-245 °C (dec.)
SMILES	OC(CN(CC(O)=O)C- CN(CC(O)=O)CC(O)=O)=O
Hazards
MSDS	External MSDS
Main hazards	irritant
NFPA 704	0 1 0
R/S statement	R: 36 S: 26
RTECS number	AH4025000
Disclaimer and references

EDTA is a popular acronym for the chemical compound ethylenediaminetetraacetic acid. EDTA refers to the chelating agent that is widely used to sequester di- and trivalent metal ions. EDTA features four carboxylic acid and two amine groups that can all bind to metals. EDTA forms specially strong complexes with Mn(II), Cu(II), Fe(III), and Co(III).^[1]

[edit] Popular vs. chemical nomenclature

To describe EDTA and its various protonated forms, chemists use a more cumbersome but more precise acronym that distinguishes between EDTA⁴⁻, the conjugate base that is the ligand, and H₄EDTA, the precursor to that ligand.

[edit] Coordination chemistry principles

In coordination chemistry, H₄EDTA is a member of the aminocarboxylate family of ligands that includes imidodiacetic acid ("H₂IDA") and nitrilotriacetic acid ("H₃NTA"). More specialized relatives include N,N'-ethylenediaminediacetic acid ("H₂EDDA") and 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid ("H₄CyDTA"). These ligands are all formally derived from the amino acid glycine.

H₄EDTA forms highly stable coordination compounds that are soluble in water. In these complexes, the ligand is usually either hexa- or pentadentate, EDTA⁴⁻ or HEDTA³⁻, respectively. Such complexes are chiral, and [Co(EDTA)]⁻ has been resolved into enantiomers.^[2]

Metal-EDTA chelate

[edit] Uses

Annual consumption of EDTA is about 35,000 tons in 1999 in Europe and 50,000 tons in the US.^{[citation needed]} The most important uses are:

• Industrial cleaning: complexation of Ca²⁺ and Mg²⁺ ions, binding of heavy metals.
• Detergents: complexation of Ca²⁺ and Mg²⁺ (reduction of water hardness).
• Photography: use of Fe(III)EDTA as oxidizing agent.
• Pulp and paper industry: complexation of heavy metals during chlorine-free bleaching, stabilization of hydrogen peroxide.
• Textile industry: complexation of heavy metals, bleach stabilizer.
• Agrochemicals: Fe, Zn and Cu fertilizer, especially in calcareous soils.
• Hydroponics: iron-EDTA is used to solubilize iron from in nutrient solutions.

More specialised uses of EDTA are:

• Food: added as preservative to prevent catalytic oxidation by metal ions or stabilizer and for iron fortification.
• Personal care: added to cosmetics to improve product stability.
• Oil production: added into the borehole to inhibit mineral precipitation.
• Dairy and beverage industry: cleaning of bottles from milk stains.
• Flue gas cleaning: removal of NO_x.
• Medicine: used in chelation therapy (brand name Endrate®, marketed by Hospira; generic product is also on the market) for acute hypercalcemia and mercury poisoning and has been used for lead poisoning.
• Dentistry as a root canal irrigant to remove organic and inorganic debris (smearlayer).
• Soft drinks containing ascorbic acid and sodium benzoate, to mitigate formation of benzene (a carcinogen).
• Recycling: recovery of used lead acid batteries.^{[citation needed]}

In laboratory science, EDTA is also used for:

• Scavenging metal ions: in biochemistry and molecular biology, ion depletion is commonly used to inactivate metal-dependent enzymes which could damage DNA or proteins
• Complexometric titrations.
• Buffer solutions.
• Determination of water hardness.
• Used in medical and laboratory equipment as an anticoagulant.

[edit] Environmental behavior

EDTA coordinating a Cu²⁺ ion

Widespread use of EDTA and its slow removal under many environmental conditions has led to its status as the most abundant anthropogenic compound in many European surface waters. River concentrations in Europe are reported as 10-100 ìg/L, and lake concentrations are in the 1-10 ìg/L range. EDTA concentrations in U.S. groundwater receiving wastewater effluent discharge have been reported at 1-72 ìg/L, and EDTA was found to be an effective tracer for effluent, with higher concentrations of EDTA corresponding to a greater percentage of reclaimed water in drinking water production wells.

EDTA is not degraded or removed during conventional wastewater treatment. However, an adjustment of pH and sludge residence time can result in almost complete mineralization of EDTA. A variety of microorganisms have been isolated from water, soils, sediments and sludges that are able to completely mineralize EDTA as a sole source of carbon, nitrogen and energy.

Recalcitrant chelating agents such as EDTA are an environmental concern predominantly because of their persistence and strong metal chelating properties. The presence of chelating agents in high concentrations in wastewaters and surface waters has the potential to remobilize heavy metals from river sediments and treated sludges, although low and environmentally relevant concentrations seem to have only a very minor influence on metal solubility. Elevated concentrations of chelating agents enhance the transport of metals (e.g. Zn, Cd, Ni, Cr, Cu, Pb, and Fe) in soils, and enhance the undesired transport of radioactive metals away from disposal sites. Low concentrations of chelating agents may either stimulate or decrease plankton or algae growth, while high concentrations always inhibit activity. Chelating agents are nontoxic to many forms of life on acute exposure; the effects of longer-term low-level exposure are unknown. EDTA at elevated concentrations is toxic to bacteria due to chelation of metals in the outer membrane. EDTA ingestion at high concentrations by mammals changes excretion of metals and can affect cell membrane permeability.

[edit] Trivia

• EDTA played a role in the O.J. Simpson trial when one of the blood samples collected from Simpson's estate was found to contain traces of the compound. This was used by the defense to indicate that the sample had been planted from one of the vials collected during the investigation. Prosecution claimed EDTA might have appeared in the sample as a result of eating McDonald's foods (either through bloodstream or, more likely, via contamination of blood flowing over the hand used in grabbing the food)
• "Ethylenediaminetetraacetates" is the longest hypothetically legal Scrabble word (hypothetical because it exceeds 15 letters, the width of a Scrabble board) in North American play
• EDTA was used in the movie Blade as a weapon against vampires.

[edit] See also

• EGTA
• NTA
• Phosphonate
• DTPA

[edit] References

1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
2. ^ Kirchner, S. Barium (Ethylenediaminetetracetato) Cobalt(III) 4-Hydrate" Inorganic Syntheses, McGraw-Hill: New York, 1957; Vol. 5, pages 186-188.

[edit] External links

• pH-Spectrum of EDTA complexes
• EDTA: Molecule of the Month
• http://www.chem.utk.edu/~chem319/Experiments/Exp6.pdf
• Links to external chemical sources

Categories: Articles with unsourced statements since February 2007 | All articles with unsourced statements | Articles lacking sources from October 2006 | All articles lacking sources | Chelating agents | Antidotes | Carboxylic acids | Amines

 

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