Synthesis of a novel bistriazene reagent 4,4′-bis[3-(4-phenylthiazol-2-yl)triazenyl]biphenyl and its highly sensitive color reaction with mercury(II)

We report the synthesis of a novel bistriazene, 4,4′-bis(3-(4-phenylthiazol-2-yl)triazenyl)biphenyl (BPTTBP), and its highly sensitive color reaction with Hg2+. The new reagent was synthesized in good yield by coupling 2-amino-4-phenylthiazole with 4,4′-biphenyldiamine bisdiazonium salt. Using a blend of surfactants N-cetylpyridinium chloride (CPC) and polyethylene glycol n-octanoic phenyl ether (OP) as a micelle sensitizer, the red colored reagent assembles with Hg2+ in pH 9.8 borate buffer according to a 1:1 stoichiometry, forming a blue oligomeric/polymeric chelating complex with a high apparent stability constant (1.1 × 108 M−1). Whereas the maximum absorption of reagent occurs at 510 nm with an extinct coefficient of 1.35 × 104 M−1 cm−1, the complex absorbs at 611 nm, with an apparent extinct coefficient of 1.04 × 105 M−1 cm−1. Beer's law is obeyed in the range of 0–15 μg/25 mL Hg2+, and Sandell's sensitivity is 1.92 × 10−3 μg/cm2. In the presence of thiourea and Na4P2O7 as masking agents, the method was found free from interferences of foreign ions commonly occurring with mercury. The optimized protocol has been successfully applied to spectrophotometric determination of mercury in waste water samples. The features of the new reagent associated with its special structure were discussed, and an unprecedented “domino effect” was proposed to account for its unique chelating stoichiometry with Hg2+.