COMBINED DSC AND VIBRATIONAL STUDIES ON SOLID-SOLID TRANSITIONS OF ISOMERIC (HYDROXYTHIOPHENOXY)BENZOIC ACIDS

The thermal transitions of 4-(3-hydroxythiophenoxy)benzoic acid and 3- (4-hydroxythiophenoxy)benzoic acid have been investigated by combined DSC and vibrational studies. From analysis of the IR bandshapes and of their relative intensity as a function of temperature, changes in the distribution of the H-bonds have been revealed and related to the tra nsitions indicated by the DSC scanning profiles for the two compounds. The study was completed by Raman spectroscopy at room temperature and on samples submitted to thermal treatments. The results indicate that solid-solid transitions in compounds containing H-bonded molecules ca n be fully clarified by a combination of thermal analysis with vibrati onal studies, carried out in situ during proper temperature cycles and with analysis of the band dichroism in anisotropic samples.