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EDTA

  • Page ID
    526
  • construction of EDTA complete.png
    Figure 2: An EDTA molecule binds a total of six times to a generic central metal, labeled M. Notice that the atoms with the unpaired electrons (the two nitrogens and four oxygens) make these coordinate covalent bonds. Credits go to Wikipedia for picture.

    Industrial Uses

    As it is so good at displacing molecules in coordination complexes, EDTA can be used to prevent undesired metals in trace amounts from reacting and having detrimental effects on products. This is known as sequestering. For instance, in regards to cosmetics, EDTA serves to increase the cosmetic product's resistance towards molecules in the air. Simmilarly, in personal care and skin care products, EDTA binds to free metal ions and serves as a purifying agent and perservative. It basically reduces the "hardness" (or presence of metal cations) in tap water so that other ingredients in shampoos and soaps can work to cleanse more efficiently. Along the same lines, EDTA is used in laundry detergents to soften water that comes into contact with it so the other active ingredients can cleanse better. In textiles, EDTA prevents the discoloring of dyed fabrics by removing harmful free metal ions and it also gets rid of residue left on industrial equipment that must be used at high temperatures (i.e., broilers). In general, EDTA reduces the reactivity of a metal, preventing any unwanted effects that may result from its presence. EDTA is used in a salt form, most likely in disodium or calcium disodium EDTA.

    See the video below explaining chelation:

    Medicinal and Health-Science Uses

    In addition to its usefulness in industries, EDTA can also be utilized in medicine. Doctors can prescribe EDTA treatments for patients suffering from lead poisoning. Such a treatment is known as chelation therapy, in which EDTA renders the toxic ions present in the body harmless. The EDTA is administered intravenously and makes its way through the blood stream. Given its hexadentate nature, EDTA has a molecular structure much like a claw. Because of this very structure, the EDTA pulls toxic heavy metals detected in the bloodstream towards itself and attaches itself to these metal ions. This attachment forms a compound that can be excreted from the body through urine, not allowing them to bind to enzymes and cytochromes. A chelation therapy may take many sittings and may last anywhere from one to three hours per sitting. Not only can chelation therapy aid in excreting harmful lead ions from the body, but it can also aid in safely getting rid of mercury, chromium, cobalt, nickel, zinc, arsenic and thallium ions from the bloodstream. In cases of excess consumption of digoxin, a medication used to treat atrial fibrillation, atrial flutter and even heart failure, EDTA has been used to clear the bloodstream of the unused ions.

    Environmental Concerns

    EDTA is very useful as a polydentate ligand. Unfortunately, it is now so overused that it is considered to be an environmental pollutant. Left alone, it degrades eventually to ethylenediaminetriacetic acid, losing one acidic group and becoming toxic after it forms diketopiperizide. EDTA levels are currently being monitored with mass-spectrometry analysis procedures, though it is considered to have very low level acute toxicity.

    Questions

    1. How many times does EDTA bind in a coordination complex?
    2. List in order of most to least thermodynamically stable as a ligand: ONO, en (ethylenediamine), EDTA.
    3. What are the most common forms of EDTA?
    4. Why is EDTA so overused? Why is this a problem?
    5. What does Professor Larsen commonly refer to EDTA as?

    Answers

    1. EDTA is a hexadentate ligand, which means that it binds six times. It binds twice at the nitrogens and four at the oxygens.
    2. EDTA (which binds six times), en (which binds two times), ONO (which binds one time)
    3. EDTA is used most commonly as salts and in a dry form.
    4. EDTA is a great chelating agent, allowing multiple bindings in a coordination complex. This gives it the ability to displace other undesirable ligands due to entropy and thermodynamics, and is thus used in laboratories, factories, and in medicine. The problem with its overuse is that it degrades into a toxin. By having excess of this, more toxin is created and left in the environment.
    5. "The Kraken" because it is the ultimate ligand (it binds six times, which is a very large amount for ligand binding).

    References

    1. Fujii, Roger. "The complexing and adsorption of cadmium in soils in the presence of EDTA and NTA." (1978): 2-11.
    2. Darwish, Nazek. "The action of ethylenediaminetetraacetic acid (EDTA) in increasing zinc utilization in poultry.." (1963).
    3. Oxtoby, David, H. Gillis, and Alan Campion. Principles of modern chemistry. Sixth. Arden Shakespeare, The, 2008.
    4. Petrucci, Ralph. General chemistry. Ninth. Upper Saddle River, New Jersey: Prentice Hall, 2007.

    Contributors

    • Allen Zeng, UC Davis, SSReno, Parul Jandir, UC Davis