Dramatic Enhancement of Enone Epoxidation Rates in Nonionic Microemulsions

Effects of a Multicomponent Perfume Accord and Dilution on the Formation of ST2S/CAPB Mixed-Surfactant Microemulsions

Perfume mixtures contain perfume raw materials (PRMs) with varying structures and hydrophobicities, which influence PRM localization within a surfactant-based formulation and thereby affect the phase behavior. In rinse-off products, the addition of water can further affect the phase behavior. In this study, a mixture of 12 PRMs was used as the oil phase in an aqueous system consisting of sodium trideceth-2 sulfate as a primary surfactant, cocamidopropyl betaine as a cosurfactant, and dipropylene glycol as a cosolvent. A series of phase diagrams were constructed with increasing water content, simulating the use conditions for rinse-off products, to determine how the phase boundaries shift with dilution. Using these phase diagrams, the compositions of interest in the micelle without perfume, micelle with perfume, microemulsion, and micelle-microemulsion transition regions were identified at each dilution level. The structural changes were probed through combined small-angle neutron scattering (SANS) and cryo-transmission electron microscopy analyses. The SANS results showed that ellipsoidal micelles were maintained as the perfume content and the dilution level increased. With ≥50 wt % water, increasing the perfume content increased the micelle volume. Interestingly, a higher rate of volume increase was observed at ≥70 wt % water. Notably, the volumes of the micelles with and without perfume increased steadily with dilution, whereas the volumes of the assemblies in the transition region and the microemulsion region increased more rapidly once diluted to 70 and 80 wt % water, respectively.

Interplay of Polarity and Confinement in Asymmetric Catalysis with Chiral Rh Diene Complexes in Microemulsions

Microemulsions provide a unique opportunity to tailor the polarity and liquid confinement in asymmetric catalysis via nanoscale polar and nonpolar domains separated by a surfactant film. For chiral diene Rh complexes, the influence of counterion and surfactant film on the catalytic activity and enantioselectivity remained elusive. To explore this issue chiral norbornadiene Rh(X) complexes (X=OTf, OTs, OAc, PO2 F2 ) were synthesized and characterized by X-ray crystallography and theoretical calculations. These complexes were used in Rh-catalyzed 1,2-additions of phenylboroxine to N-tosylimine in microemulsions stabilized either exclusively by n-octyl-β-D-glucopyranoside (C8 G1 ) or a C8 G1 -film doped with anionic or cationic surfactants (AOT, SDS and DTAB). The Rh(OAc) complex showed the largest dependence on the composition of the microemulsion, yielding up to 59 % (90 %ee) for the surfactant film doped with 5 wt% of AOT as compared to 52 % (58 %ee) for neat C8 G1 at constant surfactant concentration. Larger domains, determined by SAXS analysis, enabled further increase in yield and selectivity while the reaction rate almost remained constant according to kinetic studies.

Investigating the effect of a simplified perfume accord and dilution on the formation of mixed-surfactant microemulsions

The phase analysis of a mixed surfactant system is much more complex than that for a single surfactant system. The addition of fragrance further enhances the complexity of such colloidal systems. The wide variation in structure and log P values of perfume raw materials influence its partitioning into the micellar phase. Herein, we have created a simplified perfume accord consisting of three perfume raw materials (3-PRM) and investigated its loading within a mixed-surfactant system consisting of sodium trideceth-2 sulfate/ST2S and cocamidopropyl betaine/CAPB, along with citric acid and dipropylene glycol. We performed a systematic phase diagram analysis and identified the isotropic phases and compositions of interest. Select compositions from the phase diagram were further investigated to learn how the geometry of the surfactant self-assembly and the localization of the PRMs within the surfactant self-assembly changed when water or perfume is added. A combined small-angle neutron scattering/SANS and NMR methodology was used to identify variation in colloidal domains and positioning of perfume molecules at varying dilutions/rinse off scenarios. The results obtained were utilized to better distinguish distorted micelles from true microemulsions. The systematic investigation here provides a fundamental understanding about the self-assembly, encapsulation and perfume release from a commercially relevant mixed surfactant system.

A Journey toward Sulfolane Microemulsions Suggested as Inert, Nonaqueous Reaction Media

Recently, it turned out that nanostructured reaction media containing highly inert solvents as tetrahydrothiophen-1,1-dioxide (sulfolane) are beneficial for strongly oxidizing or reductive reactions. Because of their ability of solubilizing polar and nonpolar solvents with a large nanostructured interface in particular microemulsions provide such interesting reaction media. Starting from the pseudoternary microemulsion H2O-n-octane-C12E4/C12E5 (polyoxyethylene n-alkyl ether), water was successively replaced by the highly inert tetrahydrothiophen-1,1-dioxide (sulfolane). We found that an increasing sulfolane content drives the system beyond the tricritical point. Replacing the already long chain surfactants C12E4 and C12E5 by a mixture of the even longer chain surfactants C18E6 and C18E8, we were able to prepare nonaqueous sulfolane microemulsions for the first time. We also teach how in a second step the phase behavior of the hydrophilic sulfolane-n-octane-C18E8 system can be tuned at constant temperature (as required by the reaction conditions) by addition of the hydrophobic cosurfactant 1-octanol (C8E0). The change in curvature that occurs by adding 1-octanol is demonstrated measuring the size of reverse micelles by DLS. We found that the radius varies from at least 8 to 16 nm, a suitable sizes for inverse nanoreaction vessels.

Microemulsion systems for catalytic reactions and processes

This mini-review shows the diversity of microemulsion systems for catalytic reactions with the potential for process development.