Effect of the tether on the Mg(ii), Ca(ii), Cu(ii) and Fe(iii) stability constants and pM values of chelating agents related to EDDHA

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Abstract
The effect of the length and the structure of the tether on the chelating ability of EDDHA-like chelates have not been established. In this work, PDDHA (propylenediamine-N,N′-bis(o-hydroxyphenyl)acetic acid), BDDHA (butylenediamine-N,N′-bis(o-hydroxyphenyl)acetic acid) and XDDHA (p-xylylenediamine-N,N′-bis(o-hydroxyphenyl)acetic acid) have been obtained and their chemical behaviour has been studied and compared with that of EDDHA following our methodology. The purity of the chelating agents, and their protonation, Ca(II), Mg(II), Fe(III) and Cu(II) stability constants and pM values have been determined. The stability constants and pM values indicate that EDDHA forms the most stable chelates followed by PDDHA. However, the differences among the pFe values are small when a nutrient solution is used, and in these conditions the XDDHA/Fe(III) chelate is the most stable. The results obtained in this work indicate that all the chelating agents studied can be used as iron chlorosis correctors and they can be applied to soil/plant systems.