Protonation behavior and intramolecular interactions of alpha,omega-alkanediaminepolymethylenepolyphosphonates

The protonation equilibria of two types of aminopolyphosphonates ((CH3)(2-p)(CH2PO3)(p)N(CH2)(m)N(CH2PO3)(p), (CH3)(2-p')) in aqueous solution were investigated by means of potentiometry and P-31 NMR spectroscopy. The protonation behavior of diaminotetramethylenetetraphosphonate (p = p' = 2) is significantly altered by a change in the number of methylene chains (rn = 2, 3, 6), The protonations of the imino fragments of hdtmp, which is connected with a six methylene chain (m = 6), are essentially independent of each other, whereas edtmp, which is connected with a two methylene chain (m = 2), forms a hydrogen bond between both nitrogen atoms (NH+... N) in the mono protonated species. The ethylenediaminepolyphosphonates (In = 2), having an iminodiphosphonate, group do = 2, p' = 0-2), show a peculiar P-31 NMR behavior in which the signal shows a downfield shift at higher protonated species. However, eddmp (N,N'), having one methylenephosphonate group at each imino fragment (p = p' = 1), does not show such an anomaly. These results indicate the existence of an intramolecular interaction between both fragments, such as a hydrogen bond of a protonated nitrogen atom with unprotonated phosphonates of another imino fragment, where two methylenephosphonate groups in one imino fragment are required to operate such an interaction.