Handbook of Solvents - George Wypych - ChemTech - Ventech!

32 Estanislao Silla, Arturo Arnau and Iñaki Tuñón
Figure 2.1.14. Schematic representation of the relative
energies (in Kcal/mol) for the products P1 and P2, in
vacuo (ε = 1), DMF ( ε = 36.7), or EtOH (ε = 24.3), and
in water (ε = 78.4).
Figure 2.1.15. Schematic representation of the relative
energies of activation (in Kcal/mol) for the transition
states TS1 and TS2, in vacuo (ε = 1), DMF (ε = 36.7),
or EtOH (ε = 24.3), and in water (ε = 78.4).
increases, favoring thermodynamically the path leading to P1. On the other hand, an
opposite influence is evident in the case of the transition states, so an increase of the
dielectric constant kinetically favors the path leading to P2.
All this data makes evident the crucial role which the solvent plays both in the thermodynamics
and in the kinetics of the chemical reaction analysed.
2.1.5 SOLVENT CATALYTIC EFFECTS
Beyond the solvent as merely making possible an alternative scenery to the gas phase, beyond
its capacity to alter the thermodynamics of a process, the solvent can also act as a
catalyst of some reactions, and can reach the point of altering the mechanism by which the
reaction comes about.
An example of a reaction in which the
solvent is capable of altering the mechanism
through which the reaction takes place
is that of Meyer-Schuster, which is much
utilized in organic synthesis. 66-71 This con-
Figure 2.1.16. Reaction of Meyer-Schuster.
sists of the isomerization in an acid medium