Polyelectrolyte Catalysis in Ionic Reactions

of Polymer Chemistry, Kyoto University, Kyoto, Japan 

Recently, keen attention has been paid to the catalytic action of high molecular weight compounds [1]. It has been found that, under appropriate conditions, these compounds are much more efficient in accelerating chemical reactions than corresponding low molecular weight compounds. In our group, intensive studies have been carried out mainly on interionic reactions and polyelectrolyte influence thereon. In this article, we would like to review the recent progress of our work the present review is by no means comprehensive. The relevant contributions from other laboratories will be mentioned sufficiently to place our research in perspective. 

Electrostatic interactions give a large deviation from ideality in equilibrium properties of solutions containing low molecular weight electrolytes. This deviation was most successfully disposed of by the Debye-Huckel theory [2]. According to this theory, the ionic species are not distributed in solution in a random manner, but form an ionic atmosphere structure, and the thermodynamic properties such as the activity coefficient of solvent (or the osmotic coefficient), the mean activity coefficient of solute, and the heat of dilution, decrease linearly with the square root of the concentration, in conformity with experimental observations. 

The electrostatic interactions are also responsible for unusual, kinetic features of interionic reactions. The change of the rate constants of these reactions with ionic concentration was accounted for by Bronsted in terms of the Debye-Hiickel theory and an activated complex theory [3]. For a reaction between two ions, A- -B Z- Ch-D, (X the activated complex, C and Z) the products), the rate constant is 

Alan Rembaum and Eric Sdlegny (eds ), Polyelectrolytes and Their Applications, 71-96 All Rights Reserved Copyright 1975 by D Reidel Publishing Company, Dordrecht-Holland 

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In a continuation of their work on polyelectrolyte catalysis in ionic reactions, Ise and co-workers studied the effect of some cationic polyelectrolytes 20 in the hydrolysis of dinitrophenylphosphate dianion 21 (30). The dianion undergoes spontaneous decomposition [cf. Eq. (3—3)] (31, 32). The polycations employed are... 

The polyelectrolyte catalysis of chemical reactions involving ionic species has been the subject of extensive investigations since the pioneering studies of Morawetz et al. [12] and Ise et al. [13-17]. The catalytic effect or the ability of poly-electrolytes to enhance or retard reaction rates is mainly due to concentration or exclusion of either or both of the ionic reactants by the polyions added to the reaction systems. For example, the chemical reaction between ionic species carrying the same charge is enhanced in the presence of polyions carrying the opposite charge. This enhancement can be attributed to an increase in the local concentration... 

Morawetz, H., and Vogel, B. Catalysis of ionic reactions by polyelectrolytes, reaction of pentaamminechlorocobalt(iii) ion and pentaamminebromocobalt(iii) ion with mercuric ion in poly(sulfonic acid) solution. Journal of the American Chemical Society, 1969, 91, No. 3, p. 563-568. 

Morawetz and coworkers have also studied the catalysis of ionic reactions by polyelectrolytes [26—28]. These authors argue that the fluctuations of the electrostatic potential in a polyelectrolyte solution may in principle be studied by monitoring the effect a polyelectrolyte has upon the rate of reaction involving two small species. Qualitatively, if the charge of these two species is opposite to that of the polyion, the reagents... 

In summary, suppressed diffusion of nanoparticles in highly viscous media, such as ionic liquids, leads to an increase in the lifetime by a factor of 10-1000 comp>ared to classic low viscous solvents, contributing significantly to the stabilization of colloidal nano-sized particles. As mentioned above, ionic liquids can also serve as electrostatic and steric stabilizers. The physicochemical properties of ionic liquids and, thus, the properties of ionic liquid stabilized nanoparticles can be readily adjusted by changing cations and anions. Compared to polymers, ionic liquids as stabilizers for nanoparticles provide some particular advantages. Non-ionic polymers (in contrast to polyelectrolytes) have no ionic nature (only steric stabilization applies) and their ability to dissolve various compounds, for instance, metal precursors or substrates is limited vide infra). Thus, often an orj nic solvent is required, where both polymer, metal precursor and the substrate are soluble e.g., in case of applications in catalysis). The use of organic solvents can be avoided, when catalytic reactions are performed in neat ionic liquids (with dispersed nanoparticles). Reactions can also be conducted in neat substrate, where small amount of ionic liquid stabilized nanoparticles are added. 

The second chapter handles various problems regarding catalysis by ion-exchange resins. Mechanisms of reactions involving acidic and basic resins are discussed. In respect of the wide use of anion-exchange resins as interfacial transfer catalysts, attention is paid to the spedHc nature of this reaction. Similarities and differences in the catalysis of non-ionic resins and linear polyelectrolytes are shown. 

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