Title:Can the Lewis Basicity of an Isolated Solvent Molecule be Used for Characterizing Solvent Effects?
Volume: 17
Issue: 3
Author(s): Jean-François Gal*Pierre-Charles Maria
Affiliation:
- CNRS, Institut de Chimie de Nice, Université Côte d’Azur, UMR 7272, 06108 Nice,France
Keywords:
Donicity, donor number, lewis basicity, solute basicity, solvent basicity, solvent effects, trifluoroborane (boron
trifluoride).
Abstract:
Background: The ubiquitous Lewis acid/base interactions are important in solution processes.
Analytical chemistry may benefit from a better understanding of the role of Lewis basicity at
the molecular level or acting through a bulk solvent effect.
Objective: To delineate (i) the basicity at a molecular level, hereafter referred to as solute basicity,
and (ii) the solvent basicity, which is a bulk-liquid property.
Methods: The literature that relates Lewis basicity scales and solvent effects is analyzed. A special
focus is placed on two extensive scales, the Donor Number, DN, and the BF3 Affinity scale, BF3A,
which were obtained by calorimetric measurements on molecules as solutes diluted in a quasi-inert
solvent, and therefore define a molecular Lewis basicity. We discuss the validity of these solute
scales when regarded as solvent scales, in particular when the basicity of strongly associated liquids
is concerned.
Results: We demonstrate the drawbacks of confusing the Lewis basicity of a solvent molecule, isolated
as a solute, and that of the bulk liquid solvent itself.
Conclusion: Consequently, we recommend a reasoned use of the concept of Lewis basicity taking
clearly into account the specificity of the process for which a Lewis basicity effect may be invoked.
In particular, the action of the Lewis base, either as an isolated entity or as a bulk liquid, must be distinguished.