X-ray and Raman scattering studies of the MSE (p-dimethylaminobenzenesulfonate) solid-state transformation

A methyl p-dimethylaminobenzenesulfonate (MSE) single crystal is converted to the zwitterionic product p-trimethylammoniumbenzenesulfonate (ZWT) by an intermolecular methyl transfer reaction. We investigate the evolution of t his thermally induced transformation in the solid state and the lattice ins tability which takes place at about 60% conversion by X-ray diffraction wit h the precession method and Raman scattering. For times before the structur al change measurements give evidence of growth of long ZWT chains in a mono clinic matrix which progressively but weakly distorts. After the lattice in stability at which ZWT molecules rearrange to an orthorhombic antiferroelec tric array, one observes coexistence of monoclinic and orthorhombic domains in the mixed MSE-ZWT crystal. Both MSE and ZWT molecules are present in mo noclinic and orthorhombic domains.