A CHROMATOGRAPHIC STUDY OF THE ACIDIC HYDROLYSIS OF CYCLO-HEXA-OCTAPHOSPHATE AND CYCLO-OCTAPHOSPHATE

The hydrolysis rate of inorganic cyclo-hexa- and cyclo-octaphosphate in 0. 1 mol dm** minus **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 Mo**V-Mo**V**I 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** minus **1 respectively.