The relative stability of xylazine hydrochloride polymorphous forms.

All four known xylazine hydrochloride polymorphous forms were obtained and their relative stabilities were compared directly at three different temperatures. At higher temperatures, it is possible to determine the relative stability of all forms directly by measuring the changes in the composition of the mixtures of two polymorphous forms using powder x-ray diffraction methods. At lower temperatures, a solvent was added to the mixture and the changes in composition were determined. Polymorph transition temperatures were determined directly. To predict the transition temperature which was not found using the direct method, the polymorph melting data and determined transition temperatures were used. A phase stability diagram was constructed from the acquired data. The stability of all anhydrous polymorphous forms was compared in the presence of water vapor pressure that was higher than the equilibrium pressure.

Hydration and dehydration kinetics of xylazine hydrochloride.

From the experiments where mixture of xylazine hydrochloride hydrate H and anhydrous X were held at constant conditions, the stable form of xylazine hydrochloride can be found out. To determine equilibrium relative humidity, the unstable form of xylazine hydrochloride was inserted in thermostated humidity chamber and its weight was recorded by weighing the sample outside the chamber. The kinetic model and the rate constant for each condition were determined. The rate constants give information regarding the speed of the process at every experimentally used relative humidity. Thus using the data in coordinates k-p for each temperature it is possible to determine the water vapor pressure of the equilibrium. With this method the phase boundary for xylazine hydrochloride was determined and hydration enthalpy was calculated. The hydration rates of xylazine polymorphs A and X were investigated.