Micellar catalysis on picolinic acid promoted hexavalent chromium oxidation of glycerol

Potential application of Micellar nanoreactor for electron transfer reactions mediated by a variety of oxidants: A review

Surfactant, either natural or synthetic, forms a different type of aggregates among which 'Micelle' is truly an important dynamic surfactant aggregate, having a different region to interact with several organic, inorganic, and biomolecules; therefore the practical use of micelle is rapidly growing day-to-day. Surfactant-micelle, looks like a reactor of nano-dimension, govern a variety of reactions in aqueous media extensively. Oxidation is one of the vital reaction, take a part in the course of several organic transformations which are not very easy to execute in water media alone due to the solubility problem. Moreover, in order to achieve a quick transformation overcoming several difficulties the utility of micellar media became an excellent innovation, that's why nowadays, the surfactant and its aggregates are a focus of interest to the researcher of synthetic field and thus its practical applicability has been tremendously cultivated over the few decades. It is, therefore, useful to introduce some basic concepts regarding the aggregation of surfactants. Subsequently, we emphasize the importance of micellar media on the kinetics of oxidation reactions mediated by several metal ions with a special emphasis on their catalytic role.

Influence of Anions and Micelle and Submicellar Aggregates on the Alkaline Hydrolysis of Malachite Green: Tensiometric, Spectrophotometric, and Kinetic Investigations

The influence of mono- and bivalent anions and micelle/submicellar clusters of different ionic and nonionic surfactants on the hydrolysis of malachite green (MG⁺) was studied in the presence of low alkali concentrations. Large polarizable I^- ion and bivalent SO₄^2- ion show specific interaction toward MG⁺ with the formation of dye-anion ion-pair resulting in a retardation of the reaction rate. Tensiometric studies for anionic surfactants sodium dodecyl sulfate (SDS) and dioctyl sodium sulfosuccinate (AOT) in the presence of dye indicate the formation of ion-pair micelles which subsequently break down to form normal micelles. A change of the absorbance value accompanied by a red shift in the electronic spectra with increase in surfactant concentration also evidenced the formation of ion-pair. The observed rate inhibition by the anionic surfactants and the interaction behavior/nature of binding between the dye and surfactant in the premicellar region have been analyzed in terms of different kinetic models. The Piszkiewicz cooperativity index (n) suggests 1:1 association between the anionic surfactant monomer and MG⁺ in the submicellar cluster. A catalyzing effect for the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was noticed in the post-CMC region leading toward a limiting reaction rate, and the Menger-Portonoy pseudophase model was employed to explain the behavior with evaluation of the binding parameter. The nonionic surfactant poly(oxyethylene) (20) sorbitan monolaurate (Tween 20) exerts inhibition effect on the hydrolysis reaction which may be explained qualitatively by the dearth of HO^- ions in the vicinity of the micelle-bound dye and quantitatively in light of the pseudophase model. Different equilibrium constants and binding constant parameters suggest appreciable binding between the dye and surfactant monomer/micelles owing to electrostatic/hydrophobic interactions.

Promising Biocompatible, Biodegradable, and Inert Polymers for Purification of Wastewater by Simultaneous Removal of Carcinogenic Cr(VI) and Present Toxic Heavy Metal Cations: Reduction of Chromium(VI) by Poly(ethylene glycol) in Aqueous Perchlorate Solutions

A spectrophotometric technique has been applied for studying the reduction of chromium(VI) by poly(ethylene glycol) (PEG) as water-soluble and nontoxic synthetic polymer at a constant ionic strength of 4.0 mol dm^-3 in the absence and presence of the ruthenium(III) catalyst. In the absence of the catalyst, the reaction orders in [Cr(VI)] and [PEG] were found to be unity and fractional first orders, respectively. The oxidation process was found to be acid-catalyzed with fractional second order in [H⁺]. The addition of Ru(III) was found to catalyze the oxidation rates with observation of zero-order reaction in [CrO₄ ^2-] and fractional orders in both [PEG] and [Ru(III)], respectively. The PEG reduces the soluble toxic hexavalent Cr(VI) as a model pollutant to the insoluble nontoxic Cr(III) complex, which is known to be eco-friendly and more safer from the environmental points of view. The acid derivative of PEG was found to possess high affinity for the removal of poisonous heavy metal ions from contaminant matters by chelation. Formation of the 1:1 intermediate complex has been kinetically revealed. A consistent reaction mechanism of oxidation was postulated and discussed.

Green Methodology Development for the Surfactant Assisted Williamson Synthesis of 4-Benzyloxy Benzoic Acid (Ether) in Aqueous Media

Modern science and technology promote synthesis routes which are eco-friendly, chemicals which are promoted as “green” and solvents which are less toxic. A convenient method for the synthesis of ether by the reaction of 4-hydroxy benzoic acid and benzyl chloride using a surfactant as catalyst has been developed. The targeted ether is completely immiscible in water but in association with the interface active surfactants, the production of such a hydrophobic organic compound in water has been made possible. Micelles produce a pseudo-cellular organic environment to isolate species from the bulk solvent and favour the compartmentalization of reagents as well. Thus, the enhancement of the local concentration takes place and consequently the reactivity increases. The interaction of such unique chemo-, regio- and stereo-selectivity of surfactants made this reaction feasible. Organic species added to a micellar media are distributed between bulk water and micelles depending on their polarity, charge and dimension. This novel chemistry describes a set of green methods for carrying out this new generation Williamson reaction which can also be used for selective O-alkylation.

Synthesis of 2-(Prop-2-ynyloxy) Benzaldehyde using Salicyl Aldehyde and Propargyl Bromide in Aqueous Micellar Media

Advances in science and technology are promoting eco-friendly synthesis routes, green chemicals, and non-hazardous solvents. A suitable method for the synthesis of 2-(prop-2-ynyloxy) benzaldehyde was developed using three different aqueous micellar media. The targeted product ether is completely immiscible in water, but in combination with interface active surfactants it has been possible to produce the hydrophobic organic compound in water. Micelles function as a pseudocellular organic environment to isolate species from the main solvent and favor compartmentalization of reagents. There is an increase in the local concentration and consequently the reactivity increases. The use of such unique chemo-, regio-, and stereoselectivity renders this reaction new. Organic species added to a micellar media are distributed between water and micelles depending on polarity, charge, and size. In the experiments it was observed that salicylaldehyde and propargyl bromide interacted best in CTAB media and the yield of the formed product was 96 %.

Solvent-Free Acetalization of Glycerol with n-Octanal using Combined Brønsted Acid-Surfactant Catalyst

Glycerol, derived from biodiesel production, is a renewable feedstock for the production of value-added chemicals. Herein, we report an investigation of the acetalization of glycerol with n-octanal by homogeneous acid catalysis in the absence of a solvent, using p-dodecylbenzenesulfonic acid, p-toluenesulfonic acid, and sulfuric acid, respectively, as catalysts. p-Dodecylbenzenesulfonic acid, a surfactant-type Brønsted acid, proved to be an excellent catalyst capable of efficiently promoting the reaction under solvent-free conditions, and the yields of glycerol acetals reached 99% under the optimal conditions. The distribution of five- and six-membered cyclic acetal regioisomers varied depending on the reaction time and temperature. Moreover, the amphiphilic properties of the products, with different ratios of five- to six-membered cyclic acetals, have been evaluated by surface tension measurements.

Optimal Process Condition for Room Temperature Hetero-Aromatic Nitrogen Base Promoted Chromic Acid Oxidation of p-Chlorobenzaldehyde to p-Chlorobenzoic Acid in Aqueous Micellar Medium at Atmospheric Pressure

The present paper describes the kinetics of oxidation of p-chlorobenzaldehyde by chromic acid in aqueous and surfactant media in the presence of a promoter at 303 K. The rate constants were found to increase with introduction of hetero-aromatic nitrogen base promoters such as picolinic acid (PA), 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen). The product p-chlorobenzoic acid has been characterized by NMR. The mechanism of both unpromoted and promoted reaction paths has been proposed. In presence of the anionic surfactant sodium dodecyl sulfate (SDS), cationic surfactant N-cetylpyridinium chloride (CPC) and non-ionic surfactant Triton X-100 (TX-100) the reaction can undergo simultaneously in both aqueous and micellar phase with an enhanced rate of oxidation. Both SDS and TX-100 produce a normal micellar effect whereas CPC produces a reverse micellar effect in the presence of p-chlorobenzaldehyde.

Methanesulfonic Acid as a More Efficient Catalyst for the Synthesis of Lauraldehyde Glycerol Acetal

The purpose of this paper is to describe a more efficient catalyst for the synthesis of lauraldehyde glycerol acetal. Catalytic effect of methane sulfonic acid and p-toluenesulfonic acid were compared. With a mixture of 0.67 wt.% methanesulfonic acid in relation to lauraldehyde, equimolar amounts of glycerol and lauraldehyde being stirred at 110 °C for 2.5 h, the yield of the product was 76.32 %. When p-toluenesulfonic acid was used, the amount of the catalyst was 0.91 wt.% and the yield of the product was 62.91 % after reacting for 2.5 h at 120 °C. The result reveals that methane sulfonic acid is more efficient. Surface tension measurements showed that critical micelle concentration of the product catalyzed by methanesulfonic acid was 5.33 × 10−5 mol · L−1, and at this point the surface tension could achieve about 24 mN m−1.

Combination of best promoter and micellar catalyst for chromic acid oxidation of 1-butanol to 1-butanal in aqueous media at room temperature

In aqueous acidic media, picolinic acid, 2,2'-bipyridine and 1,10-phenanthroline promoted Cr(VI) oxidation of 1-butanol produces 1-butanal. 1-butanal is separated from mixture by fractional distillation. The anionic surfactant (SDS) and neutral surfactant (TX-100) accelerate the process while the cationic surfactant (CPC) retards the reaction. Combination of bipy and SDS is the best choice for chromic acid oxidation of 1-butanol to 1-butanal in aqueous media.

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

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.

Suitable combination of promoter and micellar catalyst for kilo fold rate acceleration on benzaldehyde to benzoic acid conversion in aqueous media at room temperature: a kinetic approach

The kinetics of oxidation of benzaldehyde by chromic acid in aqueous and aqueous surfactant (sodium dodecyl sulfate, SDS, alkyl phenyl polyethylene glycol, Triton X-100 and N-cetylpyridinium chloride, CPC) media have been investigated in the presence of promoter at 303 K. The pseudo-first-order rate constants (kobs) were determined from a logarithmic plot of absorbance as a function time. The rate constants were found to increase with introduction of heteroaromatic nitrogen base promoters such as Picolinic acid (PA), 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen). The product benzoic acid has been characterized by conventional melting point experiment, NMR, HRMS and FTIR spectral analysis. The mechanism of both unpromoted and promoted reaction path has been proposed for the reaction. In presence of the anionic surfactant SDS, cationic surfactant CPC and neutral surfactant TX-100 the reaction can undergo simultaneously in both aqueous and micellar phase with an enhanced rate of oxidation in the micellar phase. Both SDS and TX-100 produce normal micellar effect whereas CPC produce reverse micellar effect in the presence of benzaldehyde. The observed net enhancement of rate effects has been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. SDS and bipy combination is the suitable one for benzaldehyde oxidation.