Interaction of Iodine with Hexaaza-18-crown-6 and Tetraaza-14-crown-4 in Chloroform Solution

Abstract

Interactions of hexaaza-18-crown-6 (HA18C6) and tetraaza-14-crown-4 (TA14C4) with iodine have been investigated spectrophotometrically in chloroform solution. The observed time dependence of the charge-transfer band and subsequent formation of I3 - in solution were related to the slow transformation of the initially formed 1:1 macrocycle. I2 outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion, as follows: macrocycle + I2→fast K f macrocycle.I2 (outer complex) macrocycle.I2 (outer complex) →slow (macrocycle.I+)I- (inner complex) macrocycle.I+)I- (inner complex) + I2→slow (macrocycle.I+)I3 -. The pseudo-first-order rate constants at various temperatures for thetransformation process were evaluated from the absorbance-time data. The activation parameters (Ea, Δ H‡, and Δ S‡) for thetransformation were obtained from the temperature dependence of the rate constants. The stoichiometry and formation constants of the resulting EDA complexes have also been determined. It was found that the (TA14C4.I+)I3 - is more stable the (HA18C6.I+)I3 - complex in chloroform solution.