Kinetic and thermodynamic studies of charge-transfer complex formation between imipramine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (ddq) in acetonitrile and dichloromethane solutions

Masoumeh Hasani,Masoud Shariati-Rad

doi:10.17159/0379-4350/2015/v68a28

Masoumeh Hasani, Masoud Shariati-Rad

Open Access

https://doi.org/10.17159/0379-4350/2015/v68a28

Copy DOI

Abstract

Spectro-kinetic studies revealed the formation of charge-transfer (CT) complex of imipramine as an electron donor with π acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in acetonitrile and dichloromethane solutions. The resulted CT complexes exhibit spectra that were remarkably different fromthose of the donor and acceptor. The stoichiometry of the resulting complex was found to be 1:1 by the method of Job‘s continuous variation. The formation constants and thermodynamic parameters of the resulting electron-donor-acceptor (DA) complexes were determined by Benesi-Hildebrand and van’t Hoff equations, respectively. The time-dependent spectra recorded after mixing donor and acceptor has been related to an immediate formation of DA complex, which is followed by two relatively slow consecutive reactions. The pseudo-first-order rate constants for the formation of the ionic intermediate and the final product have been evaluated at various temperatures by computer fitting of the absorbance-time data to appropriate equations. The activation parameters, i.e. activation energy, enthalpy, and entropy of activation were computed from temperature dependence of the rate constants. The observed results afford evidence concerning the critical role of solvent polarity on the kinetics and stability of the resulting charge transfer complexes. The ionization potential of the donor in the two solvents was estimated and compared with the theoretical values. KEYWORDS Charge-transfer complex, imipramine, DDQ, ionization potential, kinetic, thermodynamic.

Highlights

Charge-transfer phenomena was introduced by Mulliken[1,2] and widely discussed by Foster to define a new type of adducts
While none of the reactants show any considerable absorption in the 450–600 nm region, addition of imipramine to DDQ results in strong absorptions in this spectral region, presumably due to the occurrence of charge transfer during the formation of corresponding molecular complexes
Spectrophotometric studies revealed that the interaction of imipramine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to be proceed through the formation of a 1:1 CT-complexes

Summary

Introduction

Charge-transfer phenomena was introduced by Mulliken[1,2] and widely discussed by Foster to define a new type of adducts. Molecular interactions between electron donors and acceptors are generally associated with the formation of intensely coloured charge-transfer complexes either in the visible or UV region.[3,4] These complexes are commonly found as intermediates in a wide variety of reactions involving electron-rich species or donors (D), such as nucleophiles and bases, and electrondeficient acceptors (A). Weiss proposed[4] that all molecular complexes have an essentially ionic structure D+A–, and pointed out that a low ionization potential for the donor D, and a high electron affinity for the acceptor A, should favour a stable complex. He attributed the colour of molecular complexes to intense charge-resonance spectra arising within the ions in the complex. The ubiquitous CT absorptions are diagnostic of a very wide spectrum of intermolecular electron donor-acceptor (DA) interactions arising in extremely stable, isolable 1:1 complexes on one hand,[5] to highly transient complexes (with collisional lifetimes) at the other extreme.[6]

Objectives

Results

Conclusion