Aerobic α-hydroxylation of 2-Me-1-tetralone in 1-alkyl-3-methylimidazolium ionic liquids

Abstract

The aerobic α-hydroxylation of 2-Me-1-tetralone was investigated in imidazol-based ionic liquids (ILs), where reactions in 1-alkyl-3-methylimidazolium tetrafluoroborates were found to generate considerable products. By correlating the conversion at 2 h with viscosity, relative permittivity and the E_T(30) value of ILs, we found that the local polarity in ILs represented by the E_T(30) value or the chemical shift of α-proton at the substrate was the critical factor influencing the reaction rate. Furthermore, two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) was used to characterize the distribution of 2-Me-1-tetralone in ILs. As a result, the mesoscopic structures in ILs were recommended to have crucial influences on the distribution of the substrate in ILs, and the caused local polarity could affect the activation of 2-Me-1-tetralone. These findings revealed the solvent effects of ILs with different structures on the α-hydroxylation of 2-Me-1-tetralone, and may encourage the explorations of more types of aerobic oxidations in ILs.