Gas phase hydrolysis of sulfur tetrafluoride: A comparison of the gaseous and liquid phase rate constants

The second-order gas phase reaction rate constant for SF4 hydrolysis to SOF2 has been determined by mass spectrometry and found to be in the range (0.9--2.6) x 10-19 cm3 s-1 at 350 K. The hydrolysis of SOF2 in the gas phase is 3 to 4 orders of magnitude slower than that of SF4. Since only liquid phase rate constant data exist for SF4 and none for SOF2, our gas phase rate constant for SF4 was extrapolated to liquid H2O density for comparison to the literature and was found to be consistent with the rate constant for complete aqueous hydrolysis of SF4, which was indirectly determined by the conductivity change in a pulse radiolysis study of SF6 in aqueous solution. The agreement between these values provides direct support for the conclusion of the pulse radiolysis study, namely, that the rate-determining step involves water attack on SF4. The present data further indicate that SOF2 cannot be an intermediate in the aqueous hydrolysis of SF4. A reaction is proposed for both gaseous and liquid phase hydrolyses which involve a common intermediate