Solutions of Fe-EDTA are produced by combiningferrous salts and aqueous solutions of EDTA known as Jacobson's solution. Near neutral pH, the principle complex is −, although most sources ignore the aquo ligand. The − anion has been crystallized with many cations, e.g., the trihydrateNa.2H2O. The salts as well as the solutions are yellow-brown. Provided the nutrient solution in which the − complex will be used has a pH of at least 5.5, all the uncomplexed iron, as a result of incomplete reaction, will still change into the chelated ferric form.
Uses
In contact with aerated natural waters, iron salts convert to the ferric form. Near neutral pH, ferric ions form insoluble solids and are thus not bioavailable. EDTA address this problem, by forming soluble complexes that resist formation of hydroxides. Together with pentetic acid, EDTA is widely used for sequesteringmetal ions. Otherwise these metal ions catalyze the decomposition of hydrogen peroxide, which is used to bleach pulp in paper making. Several million kilograms EDTA are produced for this purpose annually. 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. 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. 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. 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. Ferric EDTA is also used to control some broadleaf weeds in lawns. On the other hand these molecular ions may serve as plant available iron nutrients in modified Hoagland and Long Ashton solutions.
Related derivatives
Aside from ferric EDTA, iron complex of EDDHA is used to make the iron soluble in water and, for the purposes of agriculture, accessible to plants. In iron chelation therapy, deferoxamine, has been used to treat excess iron stores, i.e. haemochromatosis.
