Kinetics and mechanism of the solid-state decomposition of propantheline bromide.

The kinetics of the solid-state hydrolysis of propantheline bromide (1) was studied with respect to the effect of temperature and water vapor pressure on the decomposition rate. For the hydrolysis at a relative humidity (RH) above the critical relative humidity (CRH), the percent decomposed (x) could be described by the empirical equation: x = ktn, where n is a constant independent of temperature and water vapor pressure, and k is related to temperature (T) and water vapor pressure (P) by the equation: k = k'e-Ea/RTPs (k' and s are constants). A mechanism in which the decomposition products serve to provide reaction nuclei is proposed. On the other hand, the hydrolysis at RH below the CRH could be described by a zero-order kinetic model with a lag time, and the dependence of the zero-order rate constant and the lag time on T and P was determined. The kinetic data suggested that decomposition occurs in an adsorbed moisture layer.