Synthesis and Hydrolysis of Hexakis(imidazolyl)cyclotriphosphazene

The reaction of imidazole with hexachlorocyclotriphosphazene (I) has yielded hexakis(imidazolyl)cyclotriphosphazene (II). Compound II has been studied as a model for the analogous linear high polymer which is a prospective biodegradable carrier macromolecule. Compound II is hydrolytically unstable and decomposes to hydroxyphosphazenes, imidazole, and phosphate in aqueous media. A kinetic analysis of the removal of the first imidazolyl group from II in unbuffered 20% aqueous tetrahydrofuran within the pH range of 6.5-7.8 has shown that the hydrolysis is autocatalyzed by the free imidazole liberated in this step. Initially, the displacement of imidazole is a first-order process with respect to [II], but the release of imidazole gives rise to faster, second-order reaction in which the rate depends on the first powers of [II] and [imidazole]. The evidence favors the influence of free imidazole as a general-base catalyst and not via the formation of hydroxide ion. TV-Methylimidazole reacts with I to form an unusual series of highly reactive yellow salts of the general formula [N3P3Cl6-x(C4H6N2)x]x+xCl (VII). The chemistry of II and VII is discussed in terms of its relationship to the synthesis and reactions of the analogous linear high polymeric phosphazenes.