Thermal behaviour of mandelic acid, sodium mandelate and its compounds with some bivalent transition metal ions

Characterization, thermal stability and thermal decomposition of transition metal mandelates, M(C6H5CH(OH)CO2)2 (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), as well as the thermal behaviour of mandelic acid C6H5CH(OH)CO2H and its sodium salt were investigated employing simultaneous thermogravimetry and differential scanning calorimetry (TG–DSC), TG–DSC coupled to FTIR, infrared spectroscopy (FTIR), elemental analysis and complexometry. All the compounds were obtained in the anhydrous state and the thermal decomposition occurs in two or four consecutive steps. The final residue up to 320 °C (Mn), 345 °C (Fe), 400 °C (Co), 405 °C (Ni), 355 °C (Cu) and 575 °C (Zn) is Mn3O4, Fe2O3, Co3O4, NiO, CuO and ZnO, respectively. The results also provided information concerning the ligand's denticity, thermal behaviour and identification of gaseous products evolved during the thermal decomposition of these compounds.

► There are few thermoanalytical studies with bivalent transition metal mandelates on solid sate were found in the literature.
► From TG, complexometry and elemental analysis results, a general formula could be established for the synthesized compounds.
► The TG–DSC curves provided previously unreported information about the thermal stability and thermal decomposition.