Organophosphorus complexones

Abstract

The advances of synthetic methods resulted in the development of a series of new and highly effective organophosphorus complexones operating in a broad range of pH values and exhibiting high selectivity. The principal method of producing these substances (polyaminopolyphosphonic acids) is condensation of carbonyl compounds with di- and polyamines and trivalent phosphorus compounds capable.of diad tautomerism. The components of this reaction were widely varied, thus yielding a variety of complexones of the general type ([OH]2P[O]CR2NCH2CH2)2X where X is a heteroatom. The range of synthetic complexones was increased by including complex-forming groups as well as P[III] in the molecules. The specific behaviour of organophosphorus complexones stems from the peculiar structure and properties of the phosphoryl group P(O)(OH)2: the considerable difference between the first and second ionization stages, the high polarizability of the PO3 dianion, and the tetrahedral structure of the phosphonate anion, which distinguish organophosphorus complexones from their carbon analogues. Studies of the complex-forming properties of the substances synthesized revealed their specific properties of which the most characteristic are as follows: ability to form di- and polynuclear complexes, including hetero-nuclear ones, as well as ‘hydrogen complexes, preferential formation of strong complexes with multi-charge cations of a small atomic radius (beryllium, iron, germanium); ability to form strong complexes with large radius cations (rare-earth elements, uranium, thorium and zirconium). Alkaline earth metals form rather weak complexes with organophosphorus complexones. It has been shown that complexone selectivity may be improved by the introduction of ‘rigid unit’ sites into the molecules. © 1975, Walter de Gruyter. All rights reserved.