Single-run determination of the saturation vapor pressure and enthalpy of vaporization/sublimation of a substance undergoing successive solid-solid and solid-liquid phase transitions: the case of $N$-methyl acetamide

We report on the dynamical measurement of the saturation vapor pressure of $N$-methyl acetamide in the temperature range $-{30}^{\circ }$C to ${34}^{\circ }$C. This is achieved by monitoring the pressure inside a vacuum chamber in which a precooled sample of the substance slowly thermalizes to the chamber temperature, undergoing first a phase transition between two crystalline structures around $1^{\circ }$C and then a solid-liquid phase transition around ${30}^{\circ }$C. Such a measurement provides in a single run accurate data for the saturation vapor pressure and the enthalpies of sublimation and vaporization of the different phases of the investigated substance.