Investigation of the phase-transition behaviour in solid tetramethylene sulphoxide

Abstract

The phase-transition behaviour of tetramethylene sulphoxide has been investigated by differential scanning calorimetry (DSC) and vibrational spectroscopy (infrared and Raman). Tetramethylene sulphoxide exhibits a phase transition at 223.9 K and melts at 231.8 K. The entropy changes associated with these processes are 26.1 and 2.2 J K^–1 mol^–1, respectively. A metastable phase, phase II′, is formed when the high-temperature phase supercools. The vibrational spectra of phase I exhibited broad, featureless bands, characteristic of highly disordered phases, and the absence of discrete external modes indicated that the molecules were undergoing isotropic rotation. The spectra of phases II and II′ contained sharp, narrow bands, indicating that both phases are ordered. Many of the bands observed in the spectrum of phase II were doubled in the spectrum of phase II′, which is consistent with a doubling of the number of molecules per unit cell. The frequencies of the SO stretching and bending modes and ring-puckering vibrations were highly phase dependent.