Electronic and steric effects: how do they work in ionic liquids? The case of benzoic acid dissociation

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Abstract

The need to have a measure of the strength of some substituted benzoic acids in ionic liquid solutionled us to use the protonation equilibrium of sodium p-nitrophenolate as a probe reaction, which wasstudied by means of spectrophotometric titration at 298 K. In order to evaluate the importance ofelectronic effect of the substituents present on the aromatic ring, both electron-withdrawingand -donor substituents were taken into account. Furthermore, to have a measure of the importanceof the steric effect of the substituents both para- and ortho-substituted benzoic acids were analyzed.The probe reaction was studied in two ionic liquids differing for the ability of the cation to givehydrogen bond and π-π interactions, namely [bm2im][NTf2] and [bmpyrr][NTf2]. Data collectedshow that benzoic acids are less dissociated in ionic liquid than in water solution. Furthermore, theequilibrium constant values seem to be significantly affected by both the nature of ionic liquid cationand the structure of the acid. In particular, the ortho-steric effect seems to operate differently in waterand in the aromatic ionic liquid, determining in this solvent medium a particular behavior for orthosubstitutedbenzoic acids.
Lingua originaleEnglish
pagine (da-a)4828-4834
Numero di pagine7
RivistaJournal of Organic Chemistry
Stato di pubblicazionePublished - 2010

All Science Journal Classification (ASJC) codes

  • Organic Chemistry

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