Synthesis, characterization and thermal behavior of some trivalent lanthanide 4-amino-benzenesulfonate salts

The lanthanide 4-amino-benzenesulfonate salts (or sulfanilates) were obtained by the reaction of lanthanide carbonates (La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ and Gd 3+ ) and 4-amino-benzenesulfonic (or sulfanilic) acid in aqueous solution. Simultaneous thermogravimetry, differential thermal analysis and differential scanning calorimetry, elemental analysis, X-ray powder diffractometry and infrared spectroscopy (FTIR) were used to characterize and to study the thermal behavior of these compounds. The general formula could be established as LnL 3 · n H 2 O, where Ln represents trivalent lanthanide ions (La–Gd), L is the 4-amino-benzenesulfonate anion (NH 2 C 6 H 4 SO 3 − ) and n = 8 (La–Gd) and n = 7 only for Ce. The thermal behavior indicates that dehydration occurs in a single step up to 443 K, characterized by an endothermic peak, and the enthalpy of dehydration was evaluated by DSC. Thermal decomposition takes place above 523 K producing a stable intermediate Ln 2 O 2 SO 4 characterized by X- ray diffraction, which in the sequence decomposed to the respective oxides. For the La 3+ , Nd 3+ and Pr 3+ sulfanilates, the residual oxide formation occurs only after 1573 K.