Handbook of Solvents - George Wypych - ChemTech - Ventech!

3
Production Methods,
Properties,
and Main Applications
3.1 DEFINITIONS AND SOLVENT CLASSIFICATION
George Wypych
ChemTec Laboratories, Inc., Toronto, Canada
Several definitions are needed to classify solvents. These are included in Table 3.1.1
Table 3.1.1 Definitions
Solvent
Polarity
Polarizability
Normal
Term Definition
A substance that dissolves other material(s) to form solution. Common solvents
are liquid at room temperature but can be solid (ionic solvents) or gas (carbon dioxide).
Solvents are differentiated from plasticizers by limiting their boiling
point to a maximum of 250 o C. To differentiate solvents from monomers and
other reactive materials - a solvent is considered to be non-reactive.
Polarity is the ability to form two opposite centers in the molecule. The concept is
used in solvents to describe their dissolving capabilities or the interactive forces
between solvent and solute. Because it depends on dipole moment, hydrogen
bonding, entropy, and enthalpy, it is a composite property without a physical definition.
The dipole moment has the greatest influence on polar properties of solvents.
Highly symmetrical molecules (e.g. benzene) and aliphatic hydrocarbons
(e.g. hexane) have no dipole moment and are considered non-polar. Dimethyl
sulfoxide, ketones, esters, alcohol are examples of compounds having dipole moments
(from high to medium, sequentially) and they are polar, medium polar, and
dipolar liquids.
The molecules of some solvents are electrically neutral but dipoles can be induced
by external electromagnetic field.
A normal solvent does not undergo chemical associations (e.g. the formation of
complexes between its molecules).