Edetic acid
N,N’-1,2-Ethanediylbis[N-(carboxymethyl)glycine]
Ethylenediaminetetracetic acid (EDTA)

C10H16N2O8, mol wt 292.25

EDTA is the archetypal synthetic chelating agent. The coordinating groups in EDTA are two amine nitrogens and four carboxylic oxygens, which are capable of wrapping around a central metal ion, such as Fe(III), and satisfying the octahedral coordination requirements of Fe(III).

EDTA was the first synthetic chelating agent used for keeping Fe(III) soluble in nutrient solutions for hydroponics (1951, replacing tartaric and citric acids in earlier solutions), although it was early noted that its effectiveness was limited to pH 6.5 or lower. Soil applications of FeEDTA are likewise limited to acidic and slightly acidic soils, which restricts its usefulness since most micronutrient deficiencies that would call for chelate therapy appear in calcareous soils, with pH greater than 7.5. FeEDTA is occasionally used in foliar application of micronutrients. EDTA is permitted for use in human food and is often added to soft drinks as a preservative. EDTA is also used as a therapy for heavy metal and radionuclide poisoning in humans and has also been used experimentally and semi-commercially as a Pb-solubilizing agent as part of phytoextraction treatment for lead-contaminated fields.

Molecular coordinates were calculated by John Nash of Purdue University using HyperChem and are used here with permission.