ACID CATALYZED HYDROLYSIS OF HEXAFLUOROPHOSPHATE

The rate of hydrolysis of hexafluorophosphate has been determined in hydrochloric acid solutions whose concentrations ranged from 2 to 10 M. The reaction is acid catalyzed, and from the variation of the observed rate with the acidity functions H- and H0 the rate law is formulated as: -d[PF6-]/dt = k[PF6-]total10-H0 . From the variation of the observed rate constant with the acidity function H0, it is postulated that the transition state is formed by the addition of a proton to a neutral species. From Raman spectral investigations of the basicity of PF6-, and available experimental evidence, the neutral species is an ion pair rather than the free acid HPF6. An averaged apparent enthalpy of activation is 25·5±0·3 kcal/mole, which is less than that for the uncatalyzed reaction. An acid assisted dissociation mechanism is consistent with these experimental results. © 1969.