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Microemulsions electrochemical reactions

Hernandez J, Solla-Gullon J, Herrero E. 2004. Gold nanoparticles synthesized in a water-in-oil microemulsion Electrochemical characterization and effect of the surface structure on the oxygen reduction reaction. J Electroanal Chem 574 185-196. [Pg.589]

A wide variety of reactions other than substitutions and hydrolyses have been performed in microemulsions. Examples include alkylations [29], Knoevenagel condensations [13], oxidations [30,31], reductions [32], formation and decomposition of Meisenheimer complexes [33], aromatic substitution reactions such as nitration and bromination [34-36], nitrosation [37] and lactone formation, i.e. esterification [38-40]. Microemulsions have also been used for photochemical and electrochemical reactions [41-45]. [Pg.61]

Vaze, A. and Rusling, J.F. (2006) Microemulsion-controlled reaction sites in biocatalytic films for electrochemical reduction of vicinal dibromides. Langmuir 22, 10788-10795. [Pg.305]

A recent SECM study of electrochemical catalysis at the ITIES was based on a similar concept (23). The ITIES was used as a model system to study catalytic electrochemical reactions in microemulsions. Microemulsions, i.e., microheterogeneous mixtures of oil, water, and surfactant, appear attractive for electrochemical synthesis and other applications (63). The ITIES with a monolayer of adsorbed surfactant is of the same nature as the boundary between microphases in a microemulsion. The latter interface is not, however, directly accessible to electrochemical measurements. While interfacial area in a microemulsion can be uncertain, the ITIES is well defined. A better control of the ITIES was achieved by using the SECM to study kinetics of electrochemical catalytic reduction of //zms-l, 2-dibromo-cyclohexane (DBCH) by Co(I)L (the Co(I) form of vitamin B12) ... [Pg.337]

Let us now discuss some applications of microemulsions in catalytic processes. It has been shown in [298] that the use of microemulsions instead of organic solvents for electrochemical reactions is advantageous from both economical and ecological reasons. The electrode/fluid interface in microemulsions probably consists of a dynamic layer of surfactant molecules packed more loosely on the electrode than in aqueous solutions. Microemulsions provide good yields of carbon-carbon addition products in reactions catalysed by cobalt complexes when preparing vitamin B 2. Excellent stereo-selective control in microemulsions made with the cationic surfactant cetyl trimethyl ammonium bromide was demonstrated for the catalytic cyclisation of 2-(4-bromobutyl)-2-cycIohexene-l-one to 1-decalone. Electrochemical synthesis may be a viable future approach to environmentally friendly chemical methods. [Pg.592]

The aim of this chapter is to describe electrochemistry in micelles and microemulsions in fundamental and practical terms. A major focus is on the use of these media to purposely influence the desired outcome of electrochemical reactions. The chapter also describes how electrochemical methods can be used for structural characterization of these fluids. In the next section (Sect. 4.4.2), we discuss structures, properties, and dynamics of micelles and microemulsions. Subsequent sections present relevant aspects of direct electrochemistry and electrochemical catalysis in micelles and microemulsions. [Pg.951]

The catalytic conversion of trons-1,2-dibromocyclohexane (DBCH) to cyclohexene with macrocyclic cobalt complexes [6, 58] was used as a probe to investigate the kinetics of mediated electrochemical reactions in microemulsions. The P/Q catalyst couples were macrocyclic cobalt complexes Co L/Co L such as cobalt corrins, salen, porphyrins, and phthalocyanines. [Pg.967]

This chapter describes the electrochemistry of small reactants dissolved in micellar solutions and microemulsions. A major influence of these microheteroge-neous fluids on reversible reactants is slowing down mass transport. These phenomena enable electrochemical probes to be used to characterize aggregate mass transport and size in the fluids. Tuning the compositions of micelles and microemulsions can control pathways and kinetics of direct organic reactions, polymerizations, and mediated electrochemical reactions. [Pg.971]

The ITIES with an adsorbed monolayer of surfactant has been studied as a model system of the interface between microphases in a bicontinuous microemulsion [39]. This latter system has important applications in electrochemical synthesis and catalysis [88-92]. Quantitative measurements of the kinetics of electrochemical processes in microemulsions are difficult to perform directly, due to uncertainties in the area over which the organic and aqueous reactants contact. The SECM feedback mode allowed the rate of catalytic reduction of tra 5-l,2-dibromocyclohexane in benzonitrile by the Co(I) form of vitamin B12, generated electrochemically in an aqueous phase to be measured as a function of interfacial potential drop and adsorbed surfactants [39]. It was found that the reaction at the ITIES could not be interpreted as a simple second-order process. In the absence of surfactant at the ITIES the overall rate of the interfacial reaction was virtually independent of the potential drop across the interface and a similar rate constant was obtained when a cationic surfactant (didodecyldimethylammonium bromide) was adsorbed at the ITIES. In contrast a threefold decrease in the rate constant was observed when an anionic surfactant (dihexadecyl phosphate) was used. [Pg.321]

The original work was on ionic reactions in normal micelles in water, but subsequently there has been extensive work on reactions in reverse micelles (O Connor et al., 1982, 1984 Kitahara, 1980 O. A. El Seoud et al., 1977 Robinson, et al., 1979). There also has been a great deal of work on photochemical and radiation induced reactions in a variety of colloidal systems, and microemulsions have been used as media for a variety of thermal, electrochemical and photochemical reactions (Mackay, 1981 Fendler, 1982 Thomas, 1984). [Pg.218]

In activated sludge, 80.6% degraded after a 47-h time period (Pal et al., 1980). Chemical/Physical. Zhang and Rusling (1993) evaluated the bicontinuous microemulsion of surfactant/oil/water as a medium for the dechlorination of polychlorinated biphenyls by electrochemical catalytic reduction. The microemulsion (20 mL) contained didodecyldi-methylammonium bromide, dodecane, and water at 21, 57, and 22 wt %, respectively. The catalyst used was zinc phthalocyanine (2.5 nM). When PCB-1221 (72 mg), the emulsion and catalyst were subjected to a current of mA/cm on 11.2 cm lead electrode for 10 h, a dechlorination yield of 99% was achieved. Reaction products included a monochlorobiphenyl (0.9 mg), biphenyl, and reduced alkylbenzene derivatives. [Pg.897]

Transfer equilibria of halide ions between bulk water and association colloids have been followed electrochemically, e.g., by use of specific ion electrodes or conductimetrically [61,62], or by chemical trapping (Sec. Ill) [65]. Bromide ion is an effective nucleophile in S, 2 displacements at all l centers, and rate constants in aqueous and alcohol-modified micelles and in O/W microemulsions have been analyzed quantitatively in terms of local concentrations of substrate and Br in the interfacial region of the colloid microdroplets [99,105]. The local second-order rate constants are typically slightly lower in the colloidal pseudophases than in water but are similar for micelles and microemulsions prepared with CTABr, indicating that interfacial regions provide similar kinetic media for these Ss2 reactions. However, reactions with the same overall concentrations of Br , or other ionic reactant, are slower in microemulsions or alcohol-modified micelles than in normal micelles for two reasons (1) The fractional ionization, a, is lower in the normal micelles and (2) the increased volume of the reaction region, due to the presence of cosurfactant, dilutes Br in the pseudophase provided by the association colloid [66,69,105]. [Pg.469]

A rapidly growing field of application for microemulsions is as media for a variety of chemical reactions including electrochemical, photochemical, enzymatic, and polymerization reactions. The existence of microdomains or droplets with large interfacial area per unit... [Pg.653]

The reactions of polyaromatic hydrocarbons (PAHs) in DDAB bicontinuous microemulsions followed the ECE (electrochemical-chemical-electrochemical) mechanism at low scan rates [81,82]. The three-step ECE process consists of electron transfer to the PAH to form an anion radical, protonation of the anion radical to yield a neutral radical,... [Pg.670]

Electrochemical catalysis constitutes a general synthesis route that is amenable to rate control and enhancement in microemulsions [5,6]. Owlia et al. [36] were the first to investigate electrochemical catalysis in oil-continuous microemulsions. The kinetics of reduction of several allQ l vicinal dibromides was studied in the presence of vitamin B12 as catalyst. The following reaction mechanism was suggested ... [Pg.671]


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See also in sourсe #XX -- [ Pg.204 ]




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