Anions from Bronsted acids, reactivity

We can consider decarboxylation reactions in terms that are analogous to those in proton transfer reactions the reactivity of the carbanion in carboxylation reactions is analogous to internal return observed in proton transfer reactions from Bronsted acids. Kresge61 estimated that the rate constant for protonation of the acetylide anion, a localized carbanion (P A 21), is the same as the diffusional limit (1010 M s1). However, achieving this rate is highly dependent on the extent of localization of the carbanion. Jordan62 has shown that intermediates in thiazolium derivatives are also likely to be localized carbanions, which implies that protonation of these intermediates could occur at rates approaching those of other localized carbanions. 

The Bronsted parameter a varies substantially over the large range of ArG° covered by the experimental data collected in Fig. 10 it ranges from 0.2 for the most reactive enolates (phenylethynol anion) to about 0.8 for the least reactive compound (1-naphthol). The a-values calculated by Equation (20) are in satisfactory agreement with those determined experimentally from Bronsted plots of general acid catalysis (Table 2). 

Ionic liquids can be compared to any other liquid in that the reactivity of a species will depend upon its relative activity in solution. To this end it is important to consider the relative Lewis and Bronsted acids that can interact with the solutes to affect their activity. It is also important to remember that ionic liquids with discrete anions have wider potential windows and what we therefore hope to achieve with them is more susceptible to the presence of reactive species. The influence of impurities on the electrochemical behavior of an ionic liquid will depend upon the relative Lewis acidity/basicity of the liquid and of the redox process in question. Eutectic-based ionic liquids behave very differently from ionic liquids with discrete... 

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