Water in Oil Microemulsions as Reaction Media for a Diels−Alder Reaction between N-Ethylmaleimide and Cyclopentadiene

Study of structure of nonaqueous reverse micelles with o-nitroaniline and methyl orange as molecular probes: comparison with an aqueous reverse micelles

Instead of water reversed micelles can also be formed with polar organic solvents possessed with high dielectric constant and very low solubility in oil phase. Nonaqueous reverse micelles or microemulsions represent an interesting microreactors for various reactions, especially for reactions, where reagents can react with water. Study of localization places of molecular probes in organic polar pockets of reverse micelles is topical. The solvatochromic behavior of optical probes ortho-nitroaniline (o-NA) and methyl orange (MO) was studied in nonaqueous reverse micelles on the basis of surfactants sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and polyoxyethylene (4) lauryl ether (C12E4) and polar organic solvents (acetonitrile, dimethylformamide, glacial acetic acid, etc.) insoluble in oil phase hexane. The strength of binding of o-NA and MO to AOT and C12E4 reversed micelles was assesssed via binding constant (K b ) and association degree (α) respectively. Donor, acceptor, or dipole-dipole interactions ability of the solvent to the head groups of surfactant was taken into account in order to explain results obtained with UV–visible spectroscopic method. The binding constants of o-NA with reverse AOT micelles in the presence of various solvents in the pockets of reversed micelles increase in the following row water < glacial acetic acid < acetonitrile < dimethylformamide < dimethyl sulfoxide, but this sequence is reversed when o-NA binds to C12E4 reverse micelles. The high value of the proton donor or acidity parameter in the water molecule (x d  = 0.37) determines the weak binding of o-NA to the head AOT groups (K b  = 20.8) in case of aqueous reverse micelles. The high value of the dipole parameter in the dimethylformamide molecule (x n  = 0.40) promotes its strong interaction with nonionic polyoxyethylene groups of C12E4, which results in low value of binding constant (K b  = 26.5) in case of optical probe o-NA and low value of association degree (α = 0.60) using MO as absorption probe. The results of this article will contribute to the improvement of the concept of interfacial processes, viz.: (i) some issues of supramolecular chemistry, (ii) revealing the contribution of parameters of donor, acceptor or dipole-dipole interaction in a polar organic solvent at the surfactant/nonpolar organic solvent interface, and (iii) features of the dissolution of optical probes in non-aqueous reverse micelles.

Organic Reactions in Microdroplets: Reaction Acceleration Revealed by Mass Spectrometry

The striking finding that reaction acceleration occurs in confined-volume solutions sets up an apparent conundrum: Microdroplets formed by spray ionization can be used to monitor the course of bulk-phase reactions and also to accelerate reactions between the reagents in such a reaction. This Minireview introduces droplet and thin-film acceleration phenomena and summarizes recent methods applied to study accelerated reactions in confined-volume, high-surface-area solutions. Conditions that dictate either simple monitoring or acceleration are reconciled in the occurrence of discontinuous and complete desolvation as the endpoint of droplet evolution. The contrasting features of microdroplet and bulk-solution reactions are described together with possible mechanisms that drive reaction acceleration in microdroplets. Current applications of droplet microreactors are noted as is reaction acceleration in confined volumes and possible future scale-up.

Liposomes Can Achieve Enantioselective C-C Bond Formation of an α-Amino Acid Derivative in Aqueous Media

We first report that a highly enantioselective C-C bond formation reaction was achieved with liposomes in aqueous media. Alkylation of N-(diphenylmethylene)glycine tert-butyl ester (DMGBE) with benzyl bromide was conducted in the presence of cetyltrimethylammonium bromide micelles, resulting in a high conversion of DMGBE but little enantiomeric excess (e.e.) of the product. The same reaction was then carried out in 1,2-dioleoyl-sn-glycero-3-phosphocholine liposome suspensions, where the e.e. values were high (at least 90 % (S)), indicating that the liposome membranes can behave as the promoter of the enantioselective reaction. Changing the type of lipid to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine to form a more ordered bilayer membrane lowered the reaction conversion but still maintained high e.e.% , that is, >90 (S), regardless of lipid chirality. It is indicated that multiple interactions between the DMGBE intermediate and lipid molecules promoted the migration of the intermediate into the interior of the membrane, whose bottom side (Si face) could be free for alkylation. These results suggest that liposomes can promote and regulate the alkylation of amino acid derivatives.

In-Oleo Microgasometry of Nanoliter-Scale Gas Volumes with Image-Based Detection

Gasometric assays involve measurements of the amounts of gases that are released during physical or chemical processes. The available instrumentation for gasometric analysis is generally difficult to use and requires large sample volumes. In some cases, toxic materials (mercury) are involved in the analysis process. Here, we propose a microscale gasometric assay using silicone oil as matrix. Microliter-volume (∼2.5 μL) aqueous droplets, containing sample and reagent and/or catalyst, are introduced to the oil matrix and merged. Nanoliters of gaseous products are released to the surrounding oil matrix forming tiny spherical bubbles. Due to the huge differences between refractive indices of the released gas and the surrounding liquids (aqueous assay solution, oil), the gas bubbles are clearly visible from the top, when the assay reservoir is illuminated from the bottom with light-emitting diodes. The released gas bubbles are documented by recording videos of the assay reservoir. Individual frames within these videos are then analyzed by a graphical software to obtain diameters of every gas bubble at each time point. Following a fixed period of time (typically, 5-90 s) after the sample/reagent droplet merger, the volume of the released gas scales with the amount of the substrate (analyte) present in the sample droplet. For example, hydrogen peroxide can be decomposed to oxygen by 0.44 U catalase enzyme and semiquantified in the range up to ∼1.0 μmol. Glutathione can be detected in a two-step procedure ((1) oxidation of glutathione by hydrogen peroxide; (2) decomposition of the hydrogen peroxide residue by catalase).

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.

Fusion of microlitre water-in-oil droplets for simple, fast and green chemical assays

Fusion of pipette-generated droplets in an oil matrix enables analyses using a minimum amount of equipment and reagents.

Polarity of the interface in ionic liquid in oil microemulsions

Ionic liquid based microemulsions were characterized by absorption solvatochromic shifts, (1)H NMR and kinetic measurements in order to investigate the properties of the ionic liquid within the restricted geometry provided by microemulsions and the interactions of the ionic liquid with the interface. Experimental results show a significant difference between the interfaces of normal water and the new ionic liquid microemulsions. Absorption solvatochromic shift experiments and kinetic studies on the aminolysis of 4-nitrophenyl laurate by n-decylamine show that the polarity at the interface of the ionic liquid in oil microemulsions (IL/O) is higher than at the interface of water in oil microemulsions (W/O) despite the fact that the polarity of [bmim][BF(4)(-)] is lower than the polarity of water. (1)H NMR experiments showed that an increase in the ionic liquid content of the microemulsion led to an increase in the interaction between [bmim][BF(4)(-)] and TX-100. The reason for the higher polarity of the microemulsions with the ionic liquid can be explained in terms of the incorporation of higher levels of the ionic liquid at the interface of the microemulsions, as compared to water in the traditional systems.

Ionic liquid/oil microemulsions as chemical nanoreactors

The phase diagram and microstructure of the ternary system ionic, liquid benzylpyridinium bis(trifluoromethanesulfonyl)imide)/nonionic surfactant (octylphenol ethoxylate)/toluene, were studied by using conductivity measurements, dynamic light scattering, pulse field gradient spin-echo NMR, and small-angle neutron scattering. Three microregions were identified by conductivity measurements according to the percolation theory. The sizes of IL-in-oil microemulsions with various IL fractions were then determined by NMR and DLS and were found to be in accordance with the radii of gyration (approximately 2 or 3 nm) determined by SANS. The reverse IL-in-oil microemulsions were used as nanoreactors to perform a Matsuda-Heck reaction between p-methoxyphenyl diazonium salt and 2,3-dihydrofurane in the presence of a palladium catalyst. The reaction yields obtained were greater in microemulsions (67%) than in bulk IL (33%), highlighting a strong effect of confinement. Moreover, a direct correlation between the quantity of IL and the reaction yield was observed.

AOT-Based Microemulsions Accelerate the 1,3-Cycloaddition of Benzonitrile Oxide to N-Ethylmaleimide

We studied the 1,3-dipolar cycloaddition of benzonitrile oxide to N-ethylmaleimide in AOT/isooctane/water microemulsions at 25.0 degrees C and found the reaction rate to be roughly 150 and 35 times greater than that in isooctane and pure water, respectively. The accelerating effect of the microemulsion is the combined result of an increase in the local concentrations of the reactants through incorporation into the interface and of the intrinsic rate of the process through electrostatic interactions with the headgroups in the surfactant.