Micellar Catalysis Research Articles

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

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 C16QAS micellar system (QAS with n-hexadecyl group) gave highest cyclohexanone conversion (90%) to desired product (82%) showing that C16QAS micellar system possesses optimum properties and/or microenvironment for this reaction. Furthermore, the micellar system with high surfactant concentration (C16QAS; >150mM) made the reaction faster giving >99% conversion to selectively desired product (>99%) within 30min The large interface created by C16QAS 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.

Evidence of co-operativity in the pre-micellar region in the hydrolytic cleavage of phenyl salicylate in the presence of cationic surfactants of CTAB, TTAB and CPC

The effects of cationic surfactants of cetyl trimethyl ammonium bromide (CTAB), tetradecyl trimethyl ammonium bromide (TTAB) and cetyl pyridinium chloride (CPC) on the kinetics of intramolecular general base catalyzed hydrolysis ([OH−] range 0.05–0.1molL−1) of phenyl salicylate have been studied at different temperatures. The rate is independent of [OH−] in the studied range. The anionic surfactant sodium dodecyl sulphate (SDS) has no effect on the rate. The presence of small amount of any of these cationic surfactants well below its critical micelle concentration markedly inhibits the rate of reaction suggesting a pre-micellar aggregation between the substrate and surfactant monomers. The kinetic data have been analyzed in terms of earlier reported models (Piszkiewicz's co-operativity model and Raghavan and Srinivasan's model) for micellar catalysis. The binding constants between the substrate and the surfactants evaluated from the two models are in good agreement. Three dimensional structure of the pre-micellar aggregate controls the approach of the nucleophile water molecule to the reaction center. The planar structure of the pyridinium head group of CPC provides less steric hindrance to the attacking water molecule that leads to the least enthalpy of activation for CPC among the three surfactants. The association between the negatively charged substrate and the cationic surfactant is favored owing to electrostatic as well as hydrophobic interactions. The binding between the substrate and pre-micelles follows the order: CPC>TTAB>CTAB.

ChemInform Abstract: Installation of Protected Ammonia Equivalents onto Aromatic & Heteroaromatic Rings in Water Enabled by Micellar Catalysis.

AbstractThe arylation of carbamates (I), ureas (IX), and sulfonamides (XI) in an aqueous solution of TPGS‐750‐M surfactant is elaborated.

Synthesis of sodium allyl sulfonate in an aqueous medium by micellar catalysis with methoxy polyethylene glycol methacrylates

Micellar catalysis with various polyoxyethylated compounds was used to synthesize sodium allyl sulfonate by the reaction of allyl chloride with an aqueous solution of sodium sulfite. It was shown that methoxy polyethylene glycol methacrylates and water soluble polymers based on these compounds are surfactants and can be used to intensify the synthesis of sodium allyl sulfonate, which is of interest in the case of its subsequent application to obtain copolymers with methoxy polyethylene glycol methacrylates.

Micellar catalysis of quinquivalent vanadium oxidation of methanol to formaldehyde in aqueous medium

The kinetics of oxidation of methanol by quinquivalent vanadium in aqueous sulfuric acid medium has been studied at 313 K under pseudo-first-order condition by UV–vis spectrophotometry. Nonfunctional sodium dodecyl sulfate (SDS) surfactant solution was used as a microheterogeneous micellar catalyst. The reaction rate and selectivity strongly depend on the chosen surfactant, and in some cases also on the surfactant concentration. The critical micelle concentration (CMC) values of the SDS surfactant in aqueous medium as well as in the presence of the substrate methanol were determined by the conductivity method, matching well with the kinetically determined CMC value. SDS was found to be an excellent catalyst for oxidation of methanol by vanadium(V) in aqueous sulfuric acid medium, leading to the corresponding oxidized product (formaldehyde), which was detected by 1H nuclear magnetic resonance (NMR). The micellar catalysis by SDS is due to strong binding of the cationic oxidant with the anionic surfactant. Formation of aggregates by the catalytic surfactant was studied using optical microscopy, and the change in shape and size of the aggregates in the reaction condition was studied by using scanning electron microscopy and the dynamic light scattering method. Mechanisms for this oxidation reaction in aqueous medium as well as with micellar catalyst are proposed, being completely supported by our experimental results.

Micelles into Glycerol Solvent: Overcoming Side Reactions of Glycerol

The ring-closing metathesis (RCM) of diethyl diallylmalonate in glycerol micellar conditions was studied using microwave irradiation. The micellization of different cationic surfactants in glycerol was first investigated. The results show the superiority of micellar catalysis in glycerol for a RCM reaction compared to glycerol alone, limiting byproduct formation. In comparison with the classical solution syntheses, the method here described allows safer reaction conditions, less hazardous chemical syntheses, and use of renewable feedstocks. The practical workup, separation, and purification operations minimize the use of materials.

Stereoselective Silylcupration of Conjugated Alkynes in Water at Room Temperature

Micellar catalysis enables copper-catalyzed silylcupration of a variety of electron-deficient alkynes, thereby providing access to isomerically pure E- or Z-β-silyl-substituted carbonyl derivatives. These reactions take place in minutes, afford high yields and stereoselectivity, and are especially tolerant of functional groups present in the substrates. The aqueous reaction medium has been successfully recycled several times, and a substrate/catalyst ratio of 10,000:1 has been documented for this methodology.

ChemInform Abstract: On the Way Towards Greener Transition‐Metal‐Catalyzed Processes as Quantified by E Factors

AbstractReview: 31 refs.

Kinetics of cetyl trimethyl ammonium bromide catalyzed substitution of tris(sulfonated triazine)iron(II) complexes by 1,10-phenanthroline, 2,2′-bipyridine and 2,2′,6,2″-terpyridine

The kinetics of substitution of tris(3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonic acid)-1,2,4-triazine)-iron(II), $$ {\text{Fe}}({\text{PDTS}})_{3}^{4 - } $$ , and tris(3-(4-(4-phenylsulfonic acid)-2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine)-iron(II), $$ {\text{Fe}}({\text{PPDTS}})_{3}^{7 - } $$ , by two polypyridyls, namely 2,2′-bipyridine (bpy) and 2,2′,6′,2″-terpyridine (terpy), have been studied at 25–55 °C under pseudo-first-order conditions, i.e., [ppy] ≫ $$ [{\text{Fe}}({\text{PDTS}})_{3}^{4 - } ] $$ or $$ [{\text{Fe}}({\text{PPDTS}})_{3}^{7 - } ] $$ in acetate buffers over the pH range 3.6–5.6 (ppy = bpy, terpy or phen). The reactions are first order in $$ {\text{Fe}}({\text{PDTS}})_{3}^{4 - } $$ or $$ {\text{Fe}}({\text{PPDTS}})_{3}^{7 - } $$ . The reaction rates increase with [ppy] and pH. Plots of k obs versus [ppy] and 1/[H+] are linear with positive intercepts on the rate axes, indicating that the reactions proceed by both ppy- and hydrogen ion-dependent and independent paths. Ionic strength has no influence on the rate of reaction. Cetyl trimethyl ammonium bromide (CTAB) catalyzes these substitution processes, including substitution by 1,10–phenanthroline (phen). The micelle-catalyzed reactions essentially follow the same general pattern as the uncatalyzed reactions. Micellar catalysis is ascribed to the binding of the anionic substrate on the surface of the cationic surfactant by hydrophilic and/or electrostatic interactions and significant electrostatic contribution to the binding of the positively charged quaternary ammonium head group to π-electron-rich polypyridyls. Kinetic data have been obtained at three different temperatures, and the specific rate constants (k 1 and k 2) and thermodynamic parameters (E a, ΔS # and ΔG #) have been computed. The binding constants between $$ {\text{Fe}}({\text{PDTS}})_{3}^{4 - } $$ / $$ {\text{Fe}}({\text{PPDTS}})_{3}^{7 - } $$ and CTAB have been evaluated. The near-equal values of ΔG # obtained in aqueous and CTAB media suggest that these reactions occur by essentially the same mechanism in either medium.

Installation of protected ammonia equivalents onto aromatic & heteroaromatic rings in water enabled by micellar catalysis.

A single set of conditions consisting of a palladium catalyst, a commercially available ligand, and a base, allow for several types of C-N bond constructions to be conducted in water with the aid of a commercially available "designer" surfactant (TPGS-750-M). Products containing a protected NH2 group in the form of a carbamate, sulfonamide, or urea can be fashioned starting with aryl or heteroaryl bromides, iodides, and in some cases, chlorides, as substrates. Reaction temperatures are in the range of room temperature to, at most, 50 °C, and result in essentially full conversion and good isolated yields.

Micellar Catalysis Using a Photochromic Surfactant: Application to the Pd-Catalyzed Tsuji–Trost Reaction in Water

The first example of a Pd-catalyzed Tsuji-Trost reaction, applied in a photochromic micellar media under conventional heating and microwave irradiation, is reported. The surfactant activity and recycling ability were investigated and compared with those of a few commercially available surfactants. The synthetic photochromic surfactant proved to be efficient, recyclable, and versatile for Pd-catalyzed coupling reactions.

On the way towards greener transition-metal-catalyzed processes as quantified by E factors.

Transition-metal-catalyzed carbon-carbon and carbon-heteroatom bond formations are among the most heavily used types of reactions in both academic and industrial settings. As important as these are to the synthetic community, such cross-couplings come with a heavy price to our environment, and sustainability. E Factors are one measure of waste created, and organic solvents, by far, are the main contributors to the high values associated, in particular, with the pharmaceutical and fine-chemical companies which utilize these reactions. An alternative to organic solvents in which cross-couplings are run can be found in the form of micellar catalysis, wherein nanoparticles composed of newly introduced designer surfactants enable the same cross-couplings, albeit in water, with most taking place at room temperature. In the absence of an organic solvent as the reaction medium, organic waste and hence, E Factors, drop dramatically.

CATALYTIC ACTIVITY OF CETYLTRIMETHYLAMMONIUM BROMIDE (CTAB) IN THE REACTION OF NINHYDRIN AND ZINC GLYCYLTYROSINE COMPLEX

The kinetics of interaction between ninhydrin and zinc-dipeptide (glycyl-tyrosine), [Zn(II)-Gly-Tyr] + complex have been studied in aqueous and in micelles formed by the cationic surface active material, cetyltrimethylammonium bromide (CTAB) at 80 °C and pH 5.0. The reaction follows first- and fractional- order kinetics with respect to [Zn(II)-Gly-Tyr] + and [ninhydrin], respectively, both in the absence and presence of cationic CTAB micelles. The catalytic role of [CTAB] can be related to the extent of incorporation or association of the [Zn(II)-Gly-Tyr] + complex and ninhydrin into the micelles. CTAB micelles decrease the activation enthalpy and make the activation entropy less negative. The micellar catalysis is explained in terms of the pseudo-phase model of the micelles. Binding constants K S for [Zn(II)-Gly-Tyr] + and K N for ninhydrin with micelles are calculated with the help of observed kinetic data.

Kinetics of micellar catalysis on oxidation of p-anisaldehyde to p-anisic acid in aqueous medium at room temperature

Oxidation of p-anisaldehyde by chromic acid produces p-anisic acid under kinetic condition [p-anisaldehyde]T≫[Cr(VI)]T. This oxidation reaction is performed also in presence of micellar catalysts in aqueous media at room temperature. The progress of the reaction is monitored spectrophotometrically by following the decay of Cr(VI) at 450nm wavelength. The product is confirmed by 1H NMR spectroscopy. Anionic surfactant sodium dodecyl sulfate (SDS) accelerated the reaction almost three-fold compared to uncatalyzed path, whereas cationic surfactant N-cetylpyridinium chloride (CPC) and neutral surfactant triton-X-100 (TX-100) inhibited the reaction.

ChemInform Abstract: Rhodium‐Catalyzed Asymmetric 1,4‐Additions, in Water at Room Temperature, with In‐Flask Catalyst Recycling.

Using the newly introduced designer surfactant polyethyleneglycol ubiquinol sebacate (PQS), as the platform for micellar catalysis, nonracemic BINAP has been covalently attached and rhodium(I) inserted to form PQS-BINAP-Rh. This species, the first example of a nonracemically-ligated transition metal catalyst-tethered amphiphile, can be utilized for Rh-catalyzed asymmetric conjugate addition reactions of arylboronic acids to acyclic and cyclic enones. These are performed in water at room temperature, while the catalyst can be recycled without its removal from water in the reaction vessel.

Micellar Catalysis of Chromic Acid Oxidation of Methionine to Industrially Important Methylthiol in Aqueous Media at Room Temperature

Abstract Oxidation of organic molecule by metal is very important. Selective oxidants require non aqueous media, which is toxic and hazardous. L-methionine is oxidized to industrially important methyl thiol in micellar media by chromic acid. The overall reaction follows a first order dependency on substrate and hexavalent chromium and second order dependency on hydrogen ion. Here, reverse micelle formation is observed. TX-100 increases the rate where as SDS retards the rate of oxidation.

Micellar Catalysis on 1,10-Phenanthroline Promoted Chromic Acid Oxidation of Ethane-1,2-diol in Aqueous Media at Room Temperature

Under pseudo-first order conditions, the monomeric species of Cr(VI) was found to be kinetically active in the absence of phenanthroline (phen) whereas in the phenpromoted path, the Cr(VI)-phen complex undergoes a nucleophilic attack by etane-1,2-diol to form a ternary complex which subsequently experience a redox decomposition leading to hydroxy ethanal and Cr(III)-phen com

Ullmann Homocoupling Catalysed by Gold Nanoparticles in Water and Ionic Liquid

AbstractThe gold‐catalysed Ullmann‐type homocoupling of aryl halides is carried out with two different methodologies: (i) under micellar catalysis conditions in water and (ii) using a molten tetralkylammonium ionic liquid as the reaction medium. Glucose is used as a clean and renewable reductant. Morphology, size, and chemical composition of the gold nanoparticles were ascertained by X‐ray photoelectron spectroscopy, transmission electron microscopy and dynamic light scattering analyses. A plausible reaction mechanism is proposed.

Micellar Catalysis on 1,10-Phenanthroline Promoted Chromic Acid Oxidation of Glycerol in Aqueous Media

Abstract On pseudo-first order conditions, the monomeric species of Cr(VI) was found to be kinetically active in the absence of phenanthroline (phen) whereas in the phen-promoted path, the Cr(VI)-phen complex undergoes a nucleophilic attack by glycerol to form a ternary complex which subsequently experience a redox decomposition leading to glyceraldehydes and Cr(III)-phen complex. The effect of the cationic surfactant, cetyl pyridinium chloride (CPC); anionic surfactant, sodium dodecyl sulphate (SDS) and nonionic surfactant, triton X-100 (TX-100) on the unpromoted and phen-promoted path have been studied. Micellar effects have been explained by considering the preferential partitioning of reactants between the micellar and aqueous phase.

Micellar catalysis of oxidation of glycolic acid by N-bromophthalimide

Catalysis of oxidation of glycolic acid by N-bromophthalimide by micelles of cetyltrimethylammonium bromide (CTAB) at 318 K was investigated. The observed value of critical micelle concentration of CTAB in the presence of other components was lower than those reported in the literature. The oxidation reaction was strongly catalyzed by cationic micelles of CTAB. The reaction rate increased with CTAB concentration until the steady state was achieved. The reaction kinetics corresponded to first, fractional and inverse fiactional orders with respect to changes of concentration of reaction components. Effects of solvent, phthalimide, mercuric acetate, and potassium chloride on the reaction kinetics were also studied. The micelle-catalyzed oxidation reaction was shown to fit Arrhenius equation. The experimental data were rationalized in terms of Menger-Portnoy model considering a distribution of the reactants between the micellar and aqueous phases.