The acid catalyzed hydrolysis of hexafluorophosphate

Abstract

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 H 0 the rate law is formulated as: −d[PF 6 −]/dt = k[PF 6 −] total10 −H 0 . From the variation of the observed rate constant with the acidity function H 0, 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 PF 6 −, and available experimental evidence, the neutral species is an ion pair rather than the free acid HPF 6. 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.