Comparison of the macrocyclic effect for ether hosts in aqueous and organic solvents

Thermodynamics of complexation of aqueous 18-crown-6 with potassium ion: apparent molar volumes and apparent molar heat capacities of aqueous 18-crown-6 and of the (18-crown-6+potassium chloride) complex at temperatures (278.15 to 393.15) K, at molalities (0.02 to 0.3) mol·kg−1, and at the pressure 0.35 MPa

“…The differences between our surface and all literature values range between (9 and À2) kJ AE mol À1 , and the average of these differences is 0.9 kJ AE mol À1 . Values of ðD r H m ; T Þ at m* = 0 that we obtained from our results are given in table 8. Figure 8 shows the (log Q, m, T) surface for reaction (3) calculated with the vanÕt Hoff equation using the D r H m shown in figure 7.…”

“…Because reaction (3) is isoelectric, we have assumed that Q = K and D r H m ¼ D r H m at all m t at T* = 298.15, and we used log K = (2.042 ± 0.006) (± standard deviation of the mean) and D r H m = (À25.57 ± 0.53) kJ AE mol À1 (± standard deviation of the mean). These values are the average of four literature values for reaction (3) obtained by calorimetry with Cl À as the anion [7][8][9][10].…”

“…We obtained regression parameters for C p,/ (18C6: K + ) by regressing equation (2) Values of V / (18C6: K + ,Cl À ) were calculated by equation (5) using the speciation results obtained above. We used values of V / (KCl) from the literature [36] and values of V /,t were obtained using equation (8),…”

“…Figure 7 shows the surface (D r H m , m, T) for reaction (3) using KirchhoffÕs law and the D r C p,m shown in figure 6. As mentioned earlier, we used D r H m,2 = À25.57 kJ AE mol À1 (the average of four literature values determined by calorimetry with Cl À as the anion [7][8][9][10]) as the integration constant at T* = 298.15 in the YoungÕs Rule calculation of C p,/ (18C6: K + ,Cl À ). These four values are shown in figure 7 as open symbols.…”

“…Because the extent of complexation of 18C6 with K + is dependent on temperature, it was necessary to apply YoungÕs Rule in an iterative calculation procedure to resolve V / and C p,/ for the complex (18C6: K + ,Cl À )(aq). We have also calculated estimates of the change in volume D r V m , the change in heat capacity D r C p,m , the change in enthalpy D r H m , and the equilibrium quotient log Q for the complexation reaction over the same ranges of T and m. Numerous reports of log K and D r H m have been reported in the literature for the formation of the complex (18C6: K + ) in water at 298.15 K [7][8][9][10][11][12][13][14][15][16][17][18]. Only a few papers report thermodynamic measurements at other temperatures [7,17,18].…”