Structure and Fertilizer Properties of Byproducts Formed in the Synthesis of EDDHA

Abstract

The synthesis of commercial EDDHA produces o,o-EDDHA as the main reaction product, together with a mixture of regioisomers (o,p-EDDHA and p,p-EDDHA) and other unknown byproducts also able to complex Fe3+. These compounds have been obtained by direct synthesis, and their structures have been determined by ESI-MS analysis as oligomeric EDDHA-like products, formed by polysubstitution in the phenolic rings. Short-term experiments show that the iron complexes of samples enriched in these oligomeric byproducts have adequate stability in solution, but a significant amount of them is lost after interaction with soils and soil materials. Mildly chlorotic cucumber plants are able to reduce iron better from o,p-EDDHA/Fe3+ than from the iron complexes of the oligomeric byproducts. In hydroponics, the chlorotic soybean susceptible plants have a lower potential for Fe absorption from these byproducts than from o,o-EDDHA/Fe3+ and from o,p-EDDHA/Fe3+. In the studied conditions, the iron chelates of EDDHA byproducts do not have the long-lasting effect shown by o,o-EDDHA/Fe3+ and present a less efficient fast-action effect than the o,p-EDDHA/Fe3+.

Novel chelating agents as manganese and zinc fertilisers: characterisation, theoretical speciation and stability in solution

“…Several chelates have been studied to prepare fertilisers. Synthetic polyamino polyphenolic polycarboxylic iron chelates are the most efficient soil fertilisers to treat iron chlorosis in plants growing in calcareous soil, the iron chelates derived from EDDHA/Fe 3+ being the standard treatment to alleviate this plant disease (Chen and Barak, 1982;Mengel and Kirby, 2001 (Cremonini et al, 2001;Hernández-Apaolaza et al, 2006). Although o,p-EDDHA/Fe 3+ can be used as an effective Fe source for plant nutrition Rojas et al, 2008), it presents lower stability than o,o-EDDHA/Fe 3+ (Yunta et al, 2003a) so other micronutrients can compete with Fe to bind with o,p-EDDHA.…”

FeEDDHA-facilitated Fe uptake in relation to the behaviour of FeEDDHA components in the soil-plant system as a function of time and dosage

“…The first two characteristics have been addressed in a number of interaction studies with soil (AlvarezFernandez et al 1997(AlvarezFernandez et al , 2002Garcia-Marco et al 2006;Hernandez-Apaolaza et al 2006;Schenkeveld et al 2007). These studies show that racemic o,oFeEDDHA is superior in maintaining Fe in solution, followed by meso o,o-FeEDDHA, while restFeEDDHA and particularly o,p-FeEDDHA are largely removed from solution.…”

The behaviour of EDDHA isomers in soils as influenced by soil properties

“…1), labelled as follows: (1) racemic o,o-EDDHA (referring to the (R,R) and (S,S) o,o-EDDHA enantiomers; the enantiomers are mirror images, differing in the direction they deviate polarized light but identical in binding strength), (2) meso o,o-EDDHA (referring to the (R,S) = (S,R) enantiomer; due to the internal mirror plane of the molecule, the (R,S) and (S,R) configurations are identical (Bailey et al 1981;Hill-Cottingham 1962;Ryskievich and Boka 1962)), (3) o,p-EDDHA (referring to the four o,p-EDDHA enantiomers) and (4) rest-EDDHA (referring to the 3 p, p-EDDHA enantiomers and a variety of polycondensates and half-products (Cremonini et al 2001;Hernandez-Apaolaza et al 2006)). In general these four groups are referred to as the different EDDHA isomers.…”

“…To improve the understanding on the interaction of FeEDDHA isomers with soil and soil constituents, several studies have been done (Alvarez-Fernandez et al 1997Cantera et al 2002;Garcia-Marco et al 2006;Garcia-Mina et al 2003;Hernandez-Apaolaza et al 2006;Hernandez-Apaolaza and Lucena 2001;Siebner-Freibach et al 2004). Soil organic matter (acid peat) and iron (hydr)oxides (ferrihydrite) have been identified as the most reactive, and calcium carbonate and clay (Ca-montmorillonite) as less reactive soil constituents with respect to FeEDDHA sorption (Alvarez-Fernandez et al 1997.…”