Kinetics of degradation of long chain polyphosphates

The rates of hydrolytic degradation of long chain polyphosphates into shorter chains, and also into trimetaphosphate rings, have been studied at pH 5, 7, and 9 and at 40, 60, and 80°. Both processes follow first-order kinetics. The degradation into trimetaphosphate, whilst pH-dependent, is affected less by pH than is the hydrolytic degradation into shorter chains. At 60° and pH 7, the specific rate constant for the formation of trimetaphosphate, kD, is 0·81 × 10–5 min.–1, whilst that for the formation of shorter chains, kH, is 2·23 × 10–5 min.–1. The activation energies for the two processes have been found to be 23·5 ± 1·5 and 20·5 ± 1·0 kcal. mole–1 respectively. The half lives at 25° for the two processes have been calculated by extrapolation of the specific rate constants to be about 12 and 3·5 yr. respectively.