Synthesis of 1-(6-hydroxy-2-pyrine)-3-(4-phenylazo-phenyl)-triazene and its chromogenic reaction with cadmium

The synthesis of reagent 1-(6-hydroxy-2-pynne)-3-(4-phenylazo-phenyl)-Triazene (HPAPT) and the condition of its reaction with Cadmium are reported. The composition and structure of the reagent are determined by elemental analysis and IR spectroscopy. Its dissociation constants are: pKa_1=4.1,pKa_2 =7.2,pKa_3=10.7, nm. In the presence of Triton X-100 the reagent reacts with cadmium (Ⅱ) to form a red complex with the molar ratio of 2∶1 in pH9.0～11.0 Na_2B_4O_7-NaOH buffer solution. The maximum absorption of the complex is at 530 nm and the apparent molar absorptivity is 2.25×10~5 L~(-1)·mol~(-1)·cm~(-1), Beer′s law is obeyed for Cadmium (Ⅱ) in the range of 0～0.6 mg/L. The method has been applied to the direct determination of Cadmium (Ⅱ) in practical samples with satisfactory results.