A Fast and Additive Free C-C Homo/Cross-Coupling Reaction in Reverse Micelle: An Understanding of Role of Surfactant, Water Content and Base on the Product Yield and Reaction Site

Structural Transitions at the Water/Oil Interface by Ionic-Liquid-like Surfactant, 1-Butyl-3-methylimidazolium Dioctyl Sulfosuccinate: Measurements and Mechanism

Reverse micelle (RM) aggregates have a wide range of applications in various areas of science and technology. A continuous demand exists to replace interfacial surfactant molecules with various nonconventional amphiphiles. Ionic liquid (IL)-like surfactants (IL-surf's) constitute a class of such molecules that are being researched extensively. Here, we have formulated several water/IL-surf/oil microemulsions by optimizing the core droplet size with varying oil phases. The best composition of water/[BMIM][AOT]/IPM ([BMIM][AOT]: 1-butyl-3-methylimidazolium dioctyl sulfosuccinate; IPM: isopropyl myristate) was then analyzed in detail through experimental and computer simulations. Our results from DLS measurements suggest a structural transition from spherical aggregates in the parent water/[Na][AOT]/IPM solution to cylindrical droplets in the IL-surf-based system. The Raman and ATR-FTIR spectral analysis suggest a variation in the microstructure of the water/oil interface due to the differential interaction of the counterions with AOT headgroups and water. Molecular dynamics simulation results provided the direct image of the interface showing a structured versus uneven water/oil interface in [Na][AOT] versus [BMIM][AOT] RMs, where the larger [BMIM] cations weakly bind with the AOT headgroups due to their low charge density. Finally, an application of this IL-surf-based formulation was tested by carrying out a Heck cross-coupling reaction that showed significantly higher yield under milder reaction conditions.

Hydration of bromide at reverse micelle interfaces studied by X-ray absorption fine structure

Nanoconfined water exhibits various interesting properties, which are not only of fundamental importance but also of practical use. Because reverse micelles (RMs) provide versatile ways to prepare nanoconfined water, the understanding of their physicochemical properties is essential for developing efficient applications. Although the water properties in the RMs could be affected by its interaction with the RM interface, the details have not been well understood. This study focuses on the local structures of Br^- in hexadecyltrimethylammonium bromide (HTAB) RMs formed in chloroform and 10% hexanol/heptane. The dependence in Br^- hydration on the molar ratio of water to HTAB (w) is investigated using X-ray absorption fine structure (XAFS). These systems cover a wide range of w values (0-30) and allow us to study the impact of this parameter on the local structure of Br^- at the RM interface, which comprises water, surfactant headgroups, and organic solvent components. The presence of multiple scattering paths complicates the XAFS spectra and makes it difficult to analyze them using standard fitting methods. The linear combination of the spectra corresponding to the individual scattering paths captures the molecular processes that occur at the RM interface upon increasing w. The maximum hydration number of Br^- is found to be 4.5 at w > 15, suggesting that although most of the ions remain at the interface as partly hydrated ions, some of them dissociate as completely hydrated ones.