Selective oxidation has an important role in environmental and green chemistry (e.g., oxidative desulfurization of fuels and oxidative removal of mercury) as well as chemicals and intermediates chemistry to obtain high-value-added special products (e.g., organic sulfoxides and sulfones, aldehydes, ketones, carboxylic acids, epoxides, esters, and lactones). Due to their unique physical properties such as the nonvolatility, thermal stability, nonexplosion, high polarity, and temperature-dependent miscibility with water, ionic liquids (ILs) have attracted considerable attention as reaction solvents and media for selective oxidations and are considered as green alternatives to volatile organic solvents. Moreover, for easy separation and recyclable utilization, IL catalysts have attracted unprecedented attention as “biphasic catalyst” or “immobilized catalyst” by immobilizing metal- or nonmetal-containing ILs onto mineral or polymer supports to combine the unique properties of ILs (chemical and thermal stabili...

Ionic Liquids in Selective Oxidation: Catalysts and Solvents

The scope and limitations of surfactants as catalysts for the synthesis of quinoxalines using microreactors made of the surfactants in water has been assessed The catalytic potential followed the order: non-ionic surfactants > anionic surfactants > Bronsted acid surfactants > cationic surfactants The non-ionic surfactant, Tween 40, is the most effective catalyst affording excellent yields within a short reaction time at room temperature and is compatible with different variations of the 1,2-diketones and 1,2-diamines The reaction medium (spent water) containing the catalyst, as well as the catalyst itself (recovered Tween 40) can be reused for five consecutive reactions The better catalytic efficiency of the surfactant (Tween 40) compared to the various Lewis/Bronsted acids, as well as the surfactant combined Lewis acid, suggests that surfactants, which generate microreactor assemblies at the interface, are better suited as catalytic aids to promote organic reactions in water The inferior results obtained in organic solvents, which provide a homogeneous reaction mixture compared to those obtained in water, indicate the specific role of water This has been depicted as a synergistic dual activation through the hydrogen bond mediated formation of supramolecular assemblies involving a water dimer and the reactants The catalytic assistance of the surfactant could be ascribed to the ability of the surfactant molecule to undergo hydrophobic and hydrogen bond forming interactions with water and the reactants in orienting the reactants at the water interface and encapsulating inside the microreactors to facilitate the cyclocondensation

Surfactant micelles as microreactors for the synthesis of quinoxalines in water: scope and limitations of surfactant catalysis

Magnetic amphiphilic nanocomposites (MANCs) based on nanoalumina and carbon nanostructures were produced and applied as catalysts for biphasic reactions. These amphiphilic composites (MANCs) exhibit an excellent interaction at the interface of systems composed of immiscible liquids and can form stable emulsions between them. Being magnetic, the composites can also be used to break other stable emulsions or make the emulsions formed reversible. In this work, we report the first use of magnetic amphiphilic nanocomposites to promote biphasic reactions undergoing a magnetically reversible emulsion process. Fe and Mo catalysts were supported on the surface of nanoalumina to grow carbon nanostructures by a CVD process. To achieve the amphiphilic property, the carbon coating on the surface of the matrix is only partial. Thus, exposed iron sites can be active to catalysis. For this reason the biphasic selective oxidation of organic contaminants by hydrogen peroxide was studied. Fe species catalyze the decomposition of H2O2 into ˙OH very close to the substrate and intensify the biphasic reaction. The oxidized compounds are then extracted by the aqueous phase by polarity. The amphiphilic nanocomposites showed a high activity for the oxidation of model contaminants, reaching 100% of removal. The composites can be recovered by a magnetic field and reused several times with good efficiency.

Biphasic oxidation promoted by magnetic amphiphilic nanocomposites undergoing a reversible emulsion process

Highly efficient oxidation of organic halides to aldehydes and ketones with H5IO6 in ionic liquid [C12mim][FeCl4]

The importance of alkyl chain length and concentration of quaternary ammonium surfactants (QAS) in the micellar catalysis of cross aldol reaction was investigated The NaOH-micellar system catalyzed aldol reaction of benzaldehyde and cyclohexanone to α,α′-dibenzylidene cyclohexanone (di condensation/desired product) over mono condensation product was used as model reaction for this study The C 16 QAS micellar system (QAS with n -hexadecyl group) gave highest cyclohexanone conversion (90%) to desired product (82%) showing that C 16 QAS micellar system possesses optimum properties and/or microenvironment for this reaction Furthermore, the micellar system with high surfactant concentration (C 16 QAS; >150 mM) made the reaction faster giving >99% conversion to selectively desired product (>99%) within 30 min The large interface created by C 16 QAS micelles in the aqueous medium at high surfactant concentration makes the reaction faster by facilitating the interaction of hydrophobic reactants and water soluble catalyst (OH − ions) The activation of benzaldehyde molecules, their localization preferably near the interface and stabilization of enolate ions (reactive intermediates) by micellar system at high surfactant concentration were observed to be promoting the cross reaction selectively to the desired product

Molecular mechanism of micellar catalysis of cross aldol reaction: Effect of surfactant chain length and surfactant concentration

In this work, the chloromethylation reaction of aromatic compounds was performed successfully by micellar catalysis in oil/water biphasic system at high reactant loadings that exceeded the solubilization capacity of micellar solutions. The effects of cationic, nonionic and anionic surfactants on the reaction were compared. The mechanism of chloromethylation reaction and the mechanism of micellar catalysis were investigated. The results show that the micellar catalysis is an effective way to realize the chloromethylation. The chloromethylation reaction consists of electrophilic substitution reaction and nucleophilic substitution reaction. Cationic surfactants, especially those containing longer hydrophobic carbon chain, are more effective. Selectivity for mono-chloromethylation was remarkably improved and regioselectivity was found to be dependent on the nature of the surfactant. Under the optimal reaction conditions, chloromethylation of isopropylbenzene could obtain 97.5% selectivity in mono-chloromethylation and 8.28 para/ortho selectivity ratio at 89.8% conversion. In oil/water biphasic system, surfactant micelles can catalyze the chloromethylation reaction of aromatic compounds effectively and different types of surfactants have different catalytic abilities. Good conversion and high selectivity in mono-chloromethylation were obtained.

Chloromethylation of Aromatic Compounds Catalyzed by Surfactant Micelles in Oil-Water Biphasic System

Oxidation of Benzyl Halides to Aldehydes and Ketones with Potassium Nitrate Catalyzed by Phase-Transfer Catalyst in Aqueous Media

A small amount of organic electrolyte tetrabutylammonium bromide (TBAB) was added into the micellar catalysis system in which chloromethylation reaction of 2-bromoethylbenzene (BrEtBz) was carried out, and the effect of TBAB on the catalytic reaction was investigated. The decrease in critical micelle concentration (CMC) and the increase in solubilization of BrEtBz in the micelles formed by surfactant and TBAB were observed. The chloromethylation reaction of BrEtBz exhibited higher conversion and higher selectivity for mono-chloromethylation in the surfactant micelles containing TBAB than in the single surfactant micelle. The mechanism of chloromethylation reaction and the synergistic mechanism between organic electrolyte (TBAB) and three types of surfactants were discussed.

Effect of organic electrolyte on chloromethylation of 2-bromoethylbenzene in micellar catalytic system

The catalytic oxidation of benzyl halides to aldehydes and ketones in aqueous media was studied under relatively mild reaction conditions by using phase-transfer catalyst combined with potassium nitrate and 10% aqueous potassium hydroxide solution. As a result, a simple high-yield procedure has been developed.

Jiang Li

Papers

Chloromethylation of Aromatic Compounds Catalyzed by Surfactant Micelles in Oil-Water Biphasic System

Oxidation of Benzyl Halides to Aldehydes and Ketones with Potassium Nitrate Catalyzed by Phase-Transfer Catalyst in Aqueous Media

Effect of organic electrolyte on chloromethylation of 2-bromoethylbenzene in micellar catalytic system

Oxidation of Benzyl Halides to Aldehydes and Ketones with Potassium Nitrate Catalyzed by Phase‐Transfer Catalyst in Aqueous Media.