Handbook of Solvents - George Wypych - ChemTech - Ventech!

10.1 General concept of acid-base interactions 567
Cl 2p 3/2 ,eV
Finally the plot of ΔH AB/AN vs. DN/AN gives K a and K b. Further details of this method are
described elsewhere. 4-9 It can be seen that the procedure is complicated. The various conditions
of experiments conducted in various laboratories were sufficiently different to prevent
correlation of data between laboratories. 10 To rectify this situation, a large body of data was
obtained for 45 solvents and 19 polymers tested under uniform conditions. 10
Fowkes 11 showed that the carbonyl stretching frequency shifts to lower values as the
dispersion component of surface tension increases. The following empirical relationship
was proposed:
AB
ΔH = 0. 236Δv
[10.1.8]
AB
where:
ΔHAB the enthalpy change on acid-base adduct formation
Δv AB
projection of carbonyl stretching frequency on dispersive line.
It should be noted that, as Figure 7.1.16 shows, the change in frequency of carbonyl
stretching mode is related to the process of crystallization. 12
XPS is emerging as very precise method for evaluating acid-base interactions based
on the works by Chehimi et al. 6-9 There is very good correlation between XPS chemical shift
and the change in exothermic enthalpy of acid-base interaction. Drago’s equation is used for
data interpretation: 13
where:
199.5
199
198.5
198
197.5
1 1.5 2 2.5 3 3.5
-ΔH, kcal mol -1
Figure 10.1.1. Correlation of binding energy and ΔH AB
for several polymers. [Adapted, by permission, from
J F Watts, M M Chehimi, International J. Adhesion
Adhesives, 15, No.2, 91-4 (1995).]
323.5
322.5
321.5
0 20 40 60 80 100 120 140
− ΔHAB = E AE B + CACB [10.1.9]
323
322
A, B subscripts for acid and base, respectively
EA,EB susceptibility of acid or base species to undergo an electrostatic interaction
CA,CB susceptibility of acid or base species to undergo a covalent interaction.
Binding energy, eV
-ΔH AB ,kJmol -1
Figure 10.1.2. Correlation of binding energy and ΔH AB
for several solvents. [Adapted, by permission, from
J F Watts, M M Chehimi, International J. Adhesion Adhesives,
15, No.2, 91-4 (1995).]