VARIABLE-TEMPERATURE AND VARIABLE-PRESSURE NA-23 NMR-STUDY ON DISSOCIATION REACTION OF SODIUM(I) CRYPTATES IN ETHYLENEDIAMINE

The dissociation rates of the sodium(I) cryptates of 4,7,13,16,21-pentaoxa-1,10-diazabicyclo[8.8.5]tricosane (C221) and 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (C222) in ethylenediamine have been measured at various temperatures and pressures by the Na-23 NMR line-broadening method. The dissociation rate constant at 298 K (k(d)298), activation enthalpy (DELTAH(double dagger)), activation entropy (DELTAS(double dagger)), and activation volume (DELTAV(double dagger)) are as follows: k(d)298 = 7.2 s-1, DELTAH(double dagger) = 45.9 +/- 1.8 kJ mol-1, and DELTAS(double dagger) = -74.5 +/- 5.4 J mol-1 K-1 for Na+ C221, and k(d)298 = 272 s-1, DELTAH(double dagger) = 43.2 +/- 1.1 kJ mol-1, DELTAS(double dagger) = -53.6 +/- 3.7 J mol-1 K-1, and DELTAV(double dagger) = 8.9 +/- 0.4 cm3 mol-1 for Na+ C222. The large positive value of DELTAV(double dagger) for Na+C222 indicates the dissociative transition state accompanied by the expansion of the cavity of C222. The electrostatic interaction of the sodium cation with ethylenediamine in the transition state has been discussed in connection with the other solvents by comparison of the values of DELTAH(double dagger).