Kinetic medium effects on organic reactions

Kinetic medium effects on organic reactions in aqueous coiioidai soiutions... 

Kinetic medium effects on organic reactions in aqueous colloidal solutions, 43, 1 Kinetics, and mechanisms of reactions of organic cation radicals in solution, 20, 55 Kinetics and mechanism of the dissociative reduction of C—X and X—X bonds... 

Buurma NJ. Kinetic medium effects on organic reactions in aqueous coUoidA solutions. Adv Phys Org Chem. 2009 43 1—37. 

It will be clear that encapsulation of the reactant(s) is a prerequisite for vesicle-induced rate effects. In case of unimolecular organic reactions, the change in rate constant relative to the rate constant in bulk aqueous solution, is determined by the change in reaction environment going from water to the reactant binding sites in the vesicle. Several studies have suggested that the reaction environment in the vesicular phase is often less polar than that in micelles. Of course, the kinetic effect is a function of the distribution of the reactant over the aqueous and vesicular pseudophases. If the medium effects on the reaction are understood in some detail, the vesicle-induced rate effects provide information about the nature of the reactant encapsulation process. 

A micelle-bound substrate will experience a reaction environment different from bulk water, leading to a kinetic medium effect. Hence, micelles are able to catalyse or inhibit organic reactions. Research on micellar catalysis has focused on the kinetics of the organic reactions involved. An overview of the multitude of transformations that have been studied in micellar media is beyond the scope of this chapter. Instead, the reader is referred to an extensive set of review articles and monographs" ... 

Radiation techniques, application to the study of organic radicals, 12, 223 Radical addition reactions, gas-phase, directive effects in, 16, 51 Radicals, cation in solution, formation, properties and reactions of, 13, 155 Radicals, organic application of radiation techniques, 12,223 Radicals, organic cation, in solution kinetics and mechanisms of reaction of, 20, 55 Radicals, organic free, identification by electron spin resonance, 1,284 Radicals, short-lived organic, electron spin resonance studies of, 5, 53 Rates and mechanisms of solvolytic reactions, medium effects on, 14, 1 Reaction kinetics, polarography and, 5, 1... 

It is easy to understand the lower reactivity of non-ionic nucleophiles in micelles as compared with water. Micelles have a lower polarity than water and reactions of non-ionic nucleophiles are typically inhibited by solvents of low polarity. Thus, micelles behave as a submicroscopic solvent which has less ability than water, or a polar organic solvent, to interact with a polar transition state. Micellar medium effects on reaction rate, like kinetic solvent effects, depend on differences in free energy between initial and transition states, and a favorable distribution of reactants from water into a micellar pseudophase means that reactants have a lower free energy in micelles than in water. This factor, of itself, will inhibit reaction, but it may be offset by favorable interactions with the transition state and, for bimolecular reactions, by the concentration of reactants into the small volume of the micellar pseudophase. 

Solvolytic reactions, medium effects on the rates and mechanisms of, 14, 1 Spectroscopic detection of tetrahedral intermediates derived from carboxylic acids and the investigation of their properties, 21, 37 Spectroscopic observations ofalkylcarbonium ions in strong acid solutions, 4, 305 Spectroscopy, 13C NMR in macromolecular systems of biochemical interest, 13, 279 Spectroscopy of substituted phenylnitrenes, kinetics and, 36, 255 Spin alignment, in organic molecular assemblies, high-spin organic molecules and,... 

A kinetic model for the deactivation by coke deposition of a catalyst (based on a HZSM-5 zeolite) used in the transformation of aqueous ethanol into hydrocarbons has been proposed. The experiments have been carried out in an isothermal fixed bed reactor by feeding the reactor with ethene, ethanol/water with different mass ratios and diethyl ether. The kinetic model quantifies the effect on coke deposition of the concentration of the organic components in the reaction medium, and takes into account the attenuating effect of water on coke deposition. 

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