A chromatographic study of the acidic hydrolysis of cyclo-hexa- and cyclo-octaphosphate

The hydrolysis rate of inorganic cyclo-hexa- and cyclo-octaphosphate in 0.1 mol dm−3 HCl was determined by means of anion-exchange chromatography. The phosphorus content in the column effluent was determined automatically by the use of the MoV–MoVI reagent. The hydrolysis reactions were first-order. The rate constant decreases from cyclo- tri- to cyclo-hexaphosphate with the increased ring, however, that of cyclo-octaphosphate increases again. This increase is thought to be due to the stronger proton affinity of cyclo-octaphosphate. The Arrhenius activation energies for cyclo-hexa- and cyclo-octaphosphate hydrolysis were 91.5 and 96.9 kJ mol−1 respectively.