Handbook of Solvents - George Wypych - ChemTech - Ventech!

9
Mixed Solvents
Y. Y. Fialkov, V. L. Chumak
Department of Chemistry
National Technical University of Ukraine, Kiev, Ukraine
9.1 INTRODUCTION
One of the basic problems in conducting a chemical process in solution is control of the process
parameters. The most important is the yield of the reaction products and process rates.
The equilibrium constants and the rate constants of processes in solutions are multi-factor
dependencies, that is, they depend on temperature and many solvent properties. The realization
of the process in individual solvent often complicates such controls, and in some cases
makes it completely impossible. At the same time, it is possible to choose properties determining
the process characteristics in mixed solvents directly. Such properties relate, first of
all, to the density, ρ, viscosity, η, permittivity, ε, and specific solvation energy.
In this chapter, the term “mixed solvent” refers to binary solvents - regardless of the
relation of their components.
The use of mixed solvents in scientific and industrial practice began at the beginning
of the 20 th century. But systematic theoretical-experimental research began in the sixties,
and its intensity has been growing ever since. There are two basic reports on physical properties
of mixed solvents. One is the published in four-volume reference edition by
Timmermans 1 in the fifties and published at that period by Krestov and co-author’s monograph.
2 The detailed substantiation of information as well as the corresponding bibliography
are included in the monograph. 3
9.2 CHEMICAL INTERACTION BETWEEN COMPONENTS IN MIXED
SOLVENTS
The developments in physical chemistry and chemical physics of liquid state substantiated
common viewpoint that liquids are associated. Assuming this approach as a limit, we may
consider the individual solvent as divided into non-associated molecules having smaller energy
of intermolecular interaction than the energy of molecules in thermal motion, and to
molecules, having energy higher than kT.
9.2.1 PROCESSES OF HOMOMOLECULAR ASSOCIATION
In mixed solvents formed of associated component A and non-associated component B
(does not interact with component A), the following equilibrium takes place: