Microemulsions of N-Alkylimidazolium Ionic Liquid and Their Performance as Microreactors for the Photocycloaddition of 9-Substituted Anthracenes

The phase behavior of the ternary system consisting of an ionic liquid (1-tetradecyl-3-methylimidazolium bromide [C(14)mim]Br), p-xylene, and water were investigated. Depending on the composition of the ternary system, formation of hexagonal and lamellar liquid crystals as well as microemulsions was observed. H-1 NMR spectroscopy study, 2D ROESY spectroscopic analysis, and rheological measurements of the microemulsions indicated that p-xylene is preferably located in the hydrophobic core and the palisade shells of the microemulsions. The sizes of the microemulsion droplets for the samples with water/[C(14)mim]Br ratio of 78:22 are measured by both dynamic light scattering (DLS) and transmission electron microscopy with the freeze-fracture technique (FF-TEM). Upon change of the mole ratio of the solubilized xylene to [C(14)mim]Br from 0 to 2.4, the diameters of the microemulsion droplets increase from ca. 20 to 90 nm and size distribution gets broad, These microemulsions can solubilize and preorientate anthracene derivatives with a polar 9-substituent, and thus may enhance the head-to-head cyclomers in the photocyclization of these substrates.