High temperature phase transitions in the crystal of p-trimethylammoniumbenzenesulfonate zwitterion

Crystals of p-trimethylammoniumbenzenesulfonate (ZWT) have been obtained fr om the thermally induced solid-state reaction of methyl p-dimethylaminobenz enesulfonate (MSE) or by recrystallization in aqueous solution. The charact erization of four crystalline phases has been performed by calorimetric, bi refringence, X-ray and Raman scattering studies. An unknown phase transitio n at room temperature yielding a new crystallographic phase has been round by calorimetric measurements. ZWT crystalline samples obtained from the MSE --> ZWT solid state reaction are disordered as compared to ZWT single crys tals obtained by growing from aqueous solution. This disorder is related to different arrangements of the phenyl ring orientations.