A Conductometric Study of Complexation of Macrocyclic Polyethers with Sodium Salts

Abstract

AbstractThe complexation of sodium ions with the macrocyclic polyethers dibenzo‐18‐crown‐6 (DBC), cis‐4,4′‐dinitro‐dibenzo‐18‐crown‐6 (NDBC) and cis‐4,4′‐diamino‐dibenzo‐18‐crown‐6 (AmDBC) has been investigated conductometrically in the temperature range 10–40°C. A computer program based on iteration procedure has been used for the calculation of the equilibrium constants. In DMF, KNDBC < KDBC ≅ KAmDBC (at 30°, KNDBC = 100 M−1, KAmDBC = 580M−1). In dimethoxyethane (DME), values of K's for the complexation of DBC with free sodium ions and with the sodium tetraphenylboron ion pairs have been shown to be nearly identical (at 30° Kf = 4.5 × 103M−1, Kip = 4.2 × 103M−1). The complexation reaction in DME is both entropy and enthalpy driven. Fuoss plots has been used in the calculations of the dissociation constants of the complexed and of the solvated sodium tetraphenylboron in DME at 10–40°C. The apparent ionic radius of the sodium ion complexed with DBC has been found to be about 4.5Å. A significant contribution of the DME molecules to the solvation of sodium ions complexed with DBC seem to be ruled out on the basis of the analysis of the thermodynamic parameters of the system.