Reactions of hexamethylenetetramine (urotropine) with ethylenediaminetetraacetic acid. Molecular structure of diammonium ethylenediaminetetraacetate trihydrate (NH4)2H2L∙3H2O

The interaction of ethylenediaminetetraacetic acid (H4L, EDTA) with hexamethylenetetramine (CH2)6N4 (HMTA) in aqueous medium leads to formation of hexamethylenetetraminium ethylenediaminetetraacetate monohydrate [(CH2)6N4H]+(H3L)-∙H2O (1) and diammonium ethylenediaminetetraacetate trihydrate (NH4)2H2L∙3H2O (2). The diammonium salt is obtained by reaction of 2 moles of aqueous ammonia solution formed by dissociation of HMTA in aqueous methanol medium to formaldehyde and ammonia and reaction of the latter with EDTA, yielding 32% after recrystallization. The reaction with the ratio NH3 : H4L equaling 4 : 1 does not lead to formation of pure products of tetra- or triammonium salts (NH4)nH4-nL∙mH2O (n = 3,4). The mixture is a triammonium salt with an unreacted acid. However, recrystallization from aqueous methanol gives a pure sample of the diammonium salt (NH4)2H2L∙3H2O. The structure of the synthesized complexes was investigated by IR spectroscopy and elemental analysis. The structure of complex 2 was proved by the X-ray method. The analysis has shown that the dianion of ethylenediaminetetraacetate in 2 is a zwitterion in which hydrogen atoms are located on nitrogen atoms and all four carboxyl groups are deprotonated. General regularities concerning the interaction of quadruplebutyric acids EDTA and OEDP with HMTA and aqueous ammonia have been revealed, and the analogy of the course of these reactions has been shown. It is established that the diammonium salts can be synthesized directly from acids and aqueous ammonia solutions.