Phosphorus Nuclear Magnetic Resonance in Polyphosphates and Determination of Their Hydrolysis Rate Constants

The phosphorus nuclear magnetic resonance spectra of several condensed phosphates (polyphosphates) were measured in aqueous solutions. The NMR spectra generally consist of three peaks which correspond to the phosphorus atoms at the end and middle of the molecular chain and in orthophosphoric acid which is the final product of the hydrolysis. The chemical shift and, for some phosphates, spin-spin coupling constants were obtained. Both depend on pH of the solution. The chemical shifts for the end and middle phosphorus atoms depend also on the chain length of the molecule. The hydrolysis process of the phosphates can be traced by the observation of the time dependence of spectral line intensities. From this observation the rate constant of the hydrolysis is obtained for several phosphates. The values are comparable with those obtained by other methods.