Effect of selenium‐position on the redox responsivity of isomeric selenium‐containing anionic surfactants

Abstract

The effect of Se-position on the redox responsivity of three isomeric seleniumcontaining surfactants (C m SeC n SO 4 Na, n = 3, 8, and 11, m + n = 15) was investigated under the conditions of monomer, micelle, and adsorbed layer at the liquid paraffin-water interface. The divalent selenide group in C m SeC n SO 4 Na (the reduction form, C m SeC n SO 4 Na-Re) was oxidized to a more hydrophilic tetravalent selenoxide by the oxidation with H 2 O 2 to afford C m SeOC n SO 4 Na (the oxidation form, C m SeC n SO 4 Na-Ox), and the selenoxide group of C m SeC n SO 4 Na-Ox could be reduced to selenide by the reduction with Na 2 SO 3 to form C m SeC n SO 4 Na-Re again. In the oxidation process of the monomeric C m SeC n SO 4 Na in water, no obvious difference in the oxidation responsivity among three Se-position isomers was observed. In contrast, a remarkable effect of the Se-position on the oxidation responsivity was observed in the cases of C m SeC n SO 4 Na self-assemblies, including micelles and adsorbed layers at the liquid paraffin-water interface. Both the steric hindrance of the well-organized self-assemblies and the hydrophobic microenvironment of the selenide group in the self-assemblies hindered the Se atom from reacting with H 2 O 2 . The greater n, the harder was the oxidation of Se with H 2 O 2 . In the reduction process of C m SeC n SO 4 Na-Ox, the hydrophilic selenoxide group was exposed outright to water, allowing the selenoxide group to readily react with Na 2 SO 3 regardless of whether C m SeC n SO 4 Na-Ox was self-assembled or not.