Spectrophotometric study of interaction of iodine with 4'-aminobenzo-15-crown-5 in chloroform, dichloromethane and 1,2-dichloroethane solutions.

The formation of charge transfer complex between 4'-aminobenzo-15-crown-5 (AB15C5) and iodine is investigated spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 degrees C. The continuous variation method clearly revealed the formation of 1:1 charge transfer complex in solution. The observed time dependence of the charge transfer band and subsequent formation of I 3- in solution were related to the slow transformation of the initially formed 1:1 AB15C5.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. The pseudo-first-order rate constants for the transformation process were evaluated from the absorbance-time data and found to vary in the order of 1,2-DCE>DCM>CHCl3. The values of the formation constant, KDA, for each complex are evaluated from Benesi-Hilebrand equation. Stability of the resulting complex in three solvents was also found to vary in the order of 1,2-DCE>DCM>CHCl3.