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

Abstract

The lanthanide 4-amino-benzenesulfonate salts (or sulfanilates) were obtained by the reaction of lanthanide carbonates (La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+ and Gd3+) 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 LnL3·nH2O, where Ln represents trivalent lanthanide ions (La–Gd), L is the 4-amino-benzenesulfonate anion (NH2C6H4SO3 −) 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 Ln2O2SO4 characterized by X- ray diffraction, which in the sequence decomposed to the respective oxides. For the La3+, Nd3+ and Pr3+ sulfanilates, the residual oxide formation occurs only after 1573 K.