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 (NH₂C₆H₄SO ⁻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 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.