P-31 NMR Study of organophosphonate protonation equilibrium at high pH

A P-31 NMR technique was used to determine the protonation constants of the organophosphonates 1-hydroxyethane-1,1-diphosphonic acid (HEDPA, H4L) nitr ilotri(methylenephosphonic acid) (NTPH, H6L) and 1,2-diaminoethane-N,N,N',N '-tetra(methyl acid) (EDTPH, H8L) at 24 degrees C and I = 3.4-3.5 mol dm(-3 ) (CH3)(4)NCl over the range pH 11-14.5. For the dissociation of the alipha tic hydroxy group of HEDPA log K(H-1L + H reversible arrow L) greater than or equal to 14.6 while for NTPH and EDTPH log K(L + H reversible arrow HL) was found to be 14.2(0.1) and 13.8(0.1), respectively. The influence of(CH3 )(4)NCl content on P-31 NMR chemical shifts was demonstrated.