Chemistry Reference
In-Depth Information
2
Physico-Chemical Properties
of Organosuperbases
Davor Margetic
Rudjer Boskovic Institute, Bijenicka c. 54, 10001 Zagreb, Croatia
2.1
Introduction
From the physical-organic point of view, the most interesting physico-chemical property of
neutral organosuperbases is their exceptional basicity associated with high kinetic activity
in proton exchange reactions. Because of their high basicity and relatively weak nucleo-
philicity, these nonionic compounds have found wide application as catalysts for organic
reactions. By definition [1] the superbases are stronger bases than a
[1,8-bis
(dimethylamino)naphthalene: DMAN], that is, they have an absolute proton affinity (APA)
larger than 245.3 kcal mol
1
and a gas phase basicity (GB) over 239 kcal mol
1
.
The basicity of organic molecules can be measured by various physical methods, in gas
phase or condensed media experiments, or calculated by quantum chemical methods.
Several solvents, including dimethyl sulfoxide (DMSO), acetonitrile (MeCN), and tetra-
hydrofuran (THF), have found wide application as media for studies of strong bases.
Acetonitrile has been the most popular solvent and a vast number of basicity measurements
in acetonitrile have been carried out. Nevertheless, various reference bases have been used
for gas phase measurements. Hence, a variety of results obtained by different authors and by
different methods has been collected in this review. Material collected in tables has been
arranged in descending order of basicity. A number of other organobases approaching a
superbasicity threshold have been also measured; however, due to limitations in space here,
these molecules have been omitted. This review is divided according to the chemical classes
proton sponge
