The Mechanism of the Hydrolysis of Condensed Phosphates. II. The Mechanism of the Degradation of Long-chain Polyphosphates

Abstract The hydrolysis of long-chain polyphosphates (Graham’s salt) was carried out in water and dioxane-water solvents at various pHs in the range from 3.0 to 11.0 and at 30, 50, and 70 °C. The rates of the hydrolytic degradation of the polyphosphates into shorter chains and into trimetaphosphate obeyed the first-order kinetics with respect to the concentration of the polyphosphates. In acidic media, a small solvent effect was perceived on the rates of both the processes. On the other hand, in basic media the effect was very remarkable; that is, the rates of both the processes in the dioxane-water solvent were more rapid than in water. The results show that the rate of the hydrolysis of both the processes in basic media may be very dependent on the step of the nucleophilic attack of a water molecule on the phosphorus atom of phosphates, while in acidic media other factor, for example, the folding of the chains to a helix, may affect the overall rate. The activation energies for the two processes have been found to be 22–26 kcal/mol in the pH range from 3.0 to 7.0.