Handbook of Solvents - George Wypych - ChemTech - Ventech!

576 S. Bistac, M. Brogly
from -0.013 to 0.20. Calculation for various solid polymers could be found in a paper of
Lee. 16
10.2.1.2.4 Effect of ionocity and covalency: Drago’s concept
Similar to the perturbation theory, Drago and Wayland 17 proposed a four-parameter equation
for predicting reactions enthalpies between acid and base species. Both species are each
characterized by two independent parameters: an E value which measures their ability to
participate in electrostatic bonding, and a C value which measures their ability to participate
in covalent bond. Both E and C values are derived empirically to give the best curve fit of
calculated to experimental heats of formation for the largest possible number of adducts,
leading to:
AB
− ΔH = E E + C C
A B A B [10.2.6]
where:
ΔH AB
enthalpy of acid-base adduct formation
EA ability of the acid to participate in electrostatic bonding
EB ability of the base to participate in electrostatic bonding
CA ability of the acid to participate in covalent bonding
CB ability of the base to participate in covalent bonding.
A self-consistent set of E and C values is now available 18 for 33 acids and 48 bases, allowing
ΔH prediction for over 1584 adducts. It is assumed that the conditions under which
measurements are made (gas phase or poorly coordinating solvents) give rather constant entropy
contribution and that most of adducts are of one-to-one stoichiometry. Table 10.2.2
gathers Drago’s parameters, given in (kcal/mol) 0.5 of some common solvents.
Table 10.2.2. Drago’s parameters of some common solvents [after reference 18]
Acid CA EA Base CB EB
Phenol 0.442 4.330 Acetone 2.330 0.987
Chloroform 0.159 3.020 Benzene 0.681 0.525
Water 2.450 0.330 Ethyl acetate 1.740 0.975
tert-Butyl alcohol 0.300 2.040 Pyridine 6.400 1.170
Iodine 1.000 1.000 Methylamine 5.880 1.300
Pyrrole 0.295 2.540 Tetrahydrofuran 4.270 0.978
Trifluoroethanol 0.451 3.88 Dimethylformamide 2.480 1.230
The major importance of the above four parameters is their relationship with the
HSAB principle. Actually, through the plot of E A versus C A for several liquids on a solid,
one can obtain indirectly the values of the chemical softness 1/η from the slope of C/E, as
represented by the following equation :
E
A
H
C
E
C
AB
Δ
=− − A
E
B
B
B
[10.2.7]