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Polarographic Reduction of Sulfonamoyl Azopyrazoles in Nonionic and Cationic Surfactant Media: Double Layer, Micellar Hydration, and pH-Dependent H⁺, e⁻, e⁻, H⁺ Mechanisms at the DME
DOI:18.A003.aarf.J14I01.200001.887683
Dr. Jyoti Bhadauria
Abstract:
The polarographic reduction of 1-(carboxymethyl)trimethylammoniumchloride-3-aminophenyl-5-methyl-4-(4'-sulphonamoyl)azopyrazoles was studied in Britton-Robinson buffers with Tween-20 and CTAC surfactants. At pH 4.7, four derivatives showed well-defined waves: guanylsulphonamoyl (E₁/₂ = -0.70 V), dimethylpyrimidinyl (-0.72 V), methoxazolylsulphonamoyl (-0.80 V), thiazolylsulphonoyl (-0.84 V). Surfactants adsorb on mercury, increasing double layer thickness and decreasing dielectric constant, reducing diffusion current (_i_d_) and heterogeneous rate constant (k°_f,h).
With CTAC (0→0.8%), _i_d_ decreased 3.2→1.0 µA and –E₁/₂ increased 0.90→1.14 V, marking CMC and IHP saturation. Tween-20 (1.0×10⁻²→10.0×10⁻² M) decreased αnₐ (0.45→0.28) and k°_f,h (2.4×10⁻⁴→3.0×10⁻¹³ cm s⁻¹), indicating extreme irreversibility. At low pH, both surfactants shift E₁/₂ negative; at mid-pH, Tween-20 catalyzes protonation more than CTAC. Substituent hydrophobicity controls micellar partitioning: thiazolyl > methoxazolyl > dimethylpyrimidinyl > guanyl.
