Axial Hydration and Adsorption of Chloro(5,10,15,20-tetraphenylporphyrinato)manganese(III) at the Toluene/Water Interface, Studied by External Reflection Spectrophotometry

Abstract

Abstract Interfacial adsorption of chloro(5,10,15,20-tetraphenylporphyrinato)manganese(III), [Mn(tpp)Cl], at the interface of toluene/aqueous sodium hydrogensulfate was studied by means of an UV/vis external reflection (ER) spectroscopy and interfacial tension measurements. The s-polarized ER spectrum showed higher sensitivity than the p-polarized one at the incident angle of 70.8°. A linear correlation sililar to Beer’s law was obtained between the s-polarized ER absorbance and the interfacial concentration determined from the interfacial tension. The molar ER coefficient at the maximum wavelength of 478 nm was determined as −8.41×105 (mol−1 dm2). The effect of chloride ion concentration on the ER spectra suggested that the interfacial species at toluene/0.1 mol dm−3 sodium hydrogensulfate solution (pH 1.7) was Mn(tpp)(H2O)+i. The interfacial adsorption could be analyzed according to the Langmuir isotherm; the equilibrium constant for the adsorption reaction of Mn(tpp)Clo + H2O →← Mn(tpp)(H2O)+i + Cl− was determined as 59.6. Furthermore, it was suggested that chloride ions were preferentially distributing at the diffuse layer under low chloride ion concentrations.