Handbook of Solvents - George Wypych - ChemTech - Ventech!

2.3 Basic physical and chemical properties 61
Hildebrand solubility parameter, cal 1/2 cm -3/2
15
14
13
12
11
10
9
8
7
20 25 30 35 40 45
Surface tension, dynes cm -2
Figure 2.3.22. Hildebrand solubility parameter vs.
surface tension for four groups of solvents.
The CAS number identifies the
chemical compound or composition without
ambiguity.
RTECS number is the symbol given
by Registry of Toxic Effects of Chemical
Substances (e.g. AH4025000) to identify
toxic substances.
Composition is given for solvents
which are manufactured under trade name
and have a proprietary composition (if such
information is available).
Solvent purity (impurities) is given
as a percent and known impurities and their
concentrations are provided.
Hygroscopicity and water solubility
of solvents is an important characteristic in
many applications. The data are given in
the database either in mg of water per kilo-
gram of solvent or in a generic statement (e.g. miscible, slight). Many solvents are hygroscopic,
especially those which contain hydroxyl groups. These solvents will absorb water
from their surrounding until equilibrium is reached. The equilibrium concentration depends
on the relative humidity of air and the temperature. If solvents must maintain a low concentration
of water, vents of storage tanks should be fitted with silica gel or molecular sieves
cartridges or tanks should be sealed and equipped with pressure and vacuum relief vents
which open only to relieve pressure or to admit a dry inert gas to replace the volume pumped
out. Preferably prevention of water from contacting solvents or the selection of solvents
with a low water content is more economical than the expensive operation of drying a wet
solvent.
Surface tension and solubility parameter have been related in the following equation:
⎡ γ
δ = 21 . K
⎣
⎢ /
V
13
⎤
⎦
⎥
a
alcohols
aromatic CH
esters
ketones
[2.3.14]
where:
δ Hildebrand solubility parameter
K, a constants
γ surface tension
V molar volume of the solvent
However, Figure 2.3.22 shows that the parameters correlate only for aromatic hydrocarbons.
For three other groups the points are scattered. The equation has a very limited predictive
value.
Viscosity. Figure 2.3.2 shows that viscosity of solvents correlates with their boiling
point. There are substantial differences in the viscosity - boiling point relationship among
alcohols and other groups of solvents. These are due to the influence of hydrogen bonding
on the viscosity of alcohols.