Pintu Sar

Best combination of promoter and micellar catalyst for the rapid conversion of sorbitol to glucose

Kinetic data for oxidation of D-sorbitol to glucose by hexavalent chromium in aqueous medium and aqueous surfactant medium (SDS, TX-100) have been reported. Effect of promoter such as PA, bipy and phenanthroline on the reaction has been investigated. The reaction is performed under pseudo first order condition with an excess of substrate over the oxidant. The reaction is first order with respect to substrate and oxidant. The micelles have a catalytic effect on the reaction. Combination of phen and TX-100 produces almost twelve times increase in rate of oxidation.

A review on the advancement of ether synthesis from organic solvent to water

Ethers have been synthesized by the different protocols such as Williamson ether synthesis, the Mitsunobu reaction, bimolecular dehydration, the Ullmann method, a transition metal-free coupling reaction between aliphatic alcohols and unsymmetric diaryliodonium salts, room temperature ionic liquid promoted synthesis, Cu(II) catalyzed synthesis, microwave assisted synthesis, and synthesis under solvent free micellar conditions. A good number of homogeneous Bronsted acids and Lewis acid based transition metals have also been reported as catalysts in the etherification of alcohols. The above mentioned pathway has exhibited some drawbacks including their deactivation through decomposition caused by the water formed during the course of the reaction. In many cases these methods also reveal the accumulation of a significant amount of acid at the end of the reaction due to the hydrolysis of Lewis acid catalysts such as metal oxides, which upon neutralization give a considerable amount of salts. A literature survey shows some reports on the use of phase transfer and polymer and clay supported catalysts for the synthesis of symmetrical and unsymmetrical ethers. To a synthetic chemist, an aqueous micellar solution is a good choice as a reaction medium for synthesizing several organic compounds. Micellar conditions are a new direction of study for ether synthesis as they are simple, efficient, economical and environmentally friendly.

Combined effect of promoter and surfactant on the chromium(VI) oxidation of D-ribose in aqueous media at room temperature

ABSTRACT Effect of polypyridine derivatives on chromium(VI) oxidation of D-ribose in aqueous media was studied spectrophotometrically. The oxidized product D-erythrose was detected by paper chromatography. The promoters 1,10-phenanthroline, 2,2΄-bipyridine, 2-picolinic acid, and 2,3-dipicolinic acid accelerated the oxidation, whereas isomeric 4,7-phenanthroline, 4,4΄-bipyridine, 4-picolinic acid, and 2,6-dipicolinic acid did not influence the oxidation. Formation of Cr(VI)-promoter complex was identified through fluorescence spectroscopy. Rate constants depended on promoter concentration. SDS and TX-100 enhanced the D-ribose oxidation, while CPC retarded the reaction. Location of D-ribose inside micelles was observed through 1H NMR. DLS study showed that the relative size of SDS and TX-100 micelles expanded in presence of chromium(VI). GRAPHICAL ABSTRACT

Rate enhancement via sodium dodecyl sulfate (SDS) encapsulation of metal-mediated cerium(IV) oxidation of d-mannitol to d-mannose at room temperature and pressure: a kinetic and mechanistic approach

Abstractd-mannitol is a sweet-tasting hexitol widely distributed in nature, and is found in olive trees, plane trees, fruits, and vegetables. However, production of mannitol and mannose by extraction of plant raw materials is no longer economical. Selective oxidation of d-mannitol gives d-mannose. Oxidation kinetics of d-mannitol by Ce(IV) in an aqueous medium in the presence of sodium dodecyl sulfate (SDS) has been carried out to observe the micellar effect on rate. The oxidation kinetics was studied by UV–Vis spectrophotometry. Five different metal ions Cr(III), Mn(II), Fe(II), Cu(II), and Ag(I) are used. Both Cr(III) and Mn(II) are active catalysts for the d-mannitol oxidation in the presence and absence of anionic surfactants. The substrate undergoes effective collision with the expected positive reactive species Ce(SO4)2+ resulting enhancement of rate. The presence of SDS surfactant was found to accelerate the reaction rate and this effect has been explained by the partitioning of the reactants in micelle. The effect of sodium dodecyl sulfate (SDS) on rate also indicate that Ce(SO4)2+ was the main reactive form of cerium(IV). The main product d-mannose was identified by the FTIR spectroscopy and spot test. The combination of Mn(II) and SDS is the most suitable combination for the conversion of d-mannitol to d-mannose.

Employment of different spectroscopic tools for the investigation of chromium(VI) oxidation of acetaldehyde in aqueous micellar medium

Different spectroscopic methods have been applied to investigate the chromic acid oxidation of acetaldehyde in aqueous media, catalysed by surfactants. Three representative heteroaromatic nitrogen base promoters, 2-picolinic acid (PA), 2,2’-bipyridine (bpy) and 1,10-phenanthroline (phen), have been associated along with surfactants as promoters to the kinetic study. Comparative studies of unpromoted and promoted reactions invoked that 2,2’-bipyridine produced maximum rate enhancement. The mechanism of the reaction path has been proposed with the help of kinetic results and spectroscopic studies. The observed net enhancement of rate effects has been explained with scientific manipulations and data obtained. The combination of TX-100 and1,10-phenanthroline is found to be most effective for acetaldehyde oxidation.Graphical AbstractChromium(VI) oxidation of acetaldehyde in aqueous micellar media has been carried out. Micellar catalysis by TX-100 in association with a ‘phen’ promoter increases the rate of the reaction almost 60 fold. The combination of TX-100 and ‘phen’ is the most suitable one for chromic acid oxidation of acetaldehyde to acetic acid in aqueous media.