Development of a sensitive extraction–spectrophotometric method for Cu(II) based on 1-(o-tolylamino)- and 1-(phenylamino)propane-2-thiol complexes

Abstract

The reactions of copper(II) with 1-(o-tolylamino)-propane-2-thiol (L¹, TPT) and 1-(phenylamino)-propane-2-thiol (L², PPT) was studied by the extraction-photometric method. The ligands were characterized with IR and NMR spectroscopy. The influence of aqueous phase pH on the formation of CuL₂ complexes and thermal decomposition were studied. Chloroform was chosen as the best extractant. A single extraction with chloroform extracted 98.6–97.9 % of Cu(II). The yield of CuL₂ was maximum at c_L = 9 × 10^-3 M and did not decompose for 48 hours or more than 45 days after extraction. Phase volume ratios of 5 : 5–140 : 5 did not affect the recovery. The optimum acidity is in the range of pH_opt 3.1 – 5.3 (pH_form 1.0 – 7.1). The molar absorption coefficients are ε_450–470 = (3.4 – 3.8) × 10⁴. Compliance with the fundamental law of light absorption is achieved at c_Cu(II) = 0.08 – 19 μg mL^-1. Thermal decomposition of CuL₂ complexes ([C₂₀H₂₈N₂S₂Cu] and [C₁₈H₂₄N₂S₂Cu]; Cu²⁺ : L = 1 : 2) occurs stepwise due to the different stability of the Cu–S and Cu–N bonds. In the range of 65–135 ⁰C, a mass loss of 2.78–2.84 % is observed, associated with the removal of weakly coordinated water. At 345–400 ⁰C, profound destruction of the ligand occurs with the rupture of coordination bonds and the destruction of the chelate cycle (mass loss of 87.06–87.35 %). The proposed methods were successfully applied to determine copper in various complex samples.