Elucidation of specific ion association in non-aqueous solution environments

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  • Masashi
    Faculty of Science, Kochi University

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  • 非水溶媒環境下における特異なイオン会合現象とその解明
  • ヒスイヨウバイ カンキョウ カ ニ オケル トクイ ナ イオン カイゴウ ゲンショウ ト ソノ カイメイ

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Abstract

In aqueous solution, alkali metal and alkaline earth metal salts are regarded to be "indifferent salts" or supporting electrolytes, which should change the activity coefficients of ionic species. Although higher ion aggregates from 1 : 1 type electrolytes in low-permittivity media (εr<10) are widely accepted, only few chemists have recognized higher ion aggregation in higher permittivity media. However, we have clarified that the chemical interaction, such as coordination, can operate between anions and cations in non-aqueous solvents (20<εr<65) of low solvation ability. Acids (HA) and their conjugate base anions (A−) may react with each other to form homoconjugated species, such as A−(HA)2, in acetonitrile or benzonitrile, protophobic aprotic solvents with low hydrogen-bonding donor and acceptor abilities. After observing the direct reaction of some anions (e.g. Cl−) and cations (e.g. Li+) toward a certain species, we comprehensively interpreted the salt effects in chemical equilibria, based on distinct chemical interactions and not merely a vague term, "medium effect". A reaction manner similar to that in non-aqueous solution can take place, even in some "aqueous" solution, if the water structure of the aqueous solution is completely destroyed, because the properties of bulk water should arise from a huge network of water molecules by hydrogen bonding; otherwise, the properties of water must be reduced to just those of isolated H2O molecules, termed, "dihydrogen ether". The chemical interaction between ions has been proved in "aqueous" solution of low water-structuredness with the addition of concentrated salts and non-aqueous solvents; a minor increase of the intermediate species that would never be observed in the chemical equilibrium sense could be multiplied into a measurable change in the chemical kinetics.<br>

Journal

  • BUNSEKI KAGAKU

    BUNSEKI KAGAKU 53 (11), 1279-1293, 2004

    The Japan Society for Analytical Chemistry

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