Determination of the Association Constants of Charge-Transfer Complexes Between N,N-Diethylaniline and Nitro Explosives Using High Performance Thin Layer Chromatography with Scanning Video Densitometry and Spectrophotometry

Abstract

Charge-transfer (CT) or electron donor-acceptor (EDA) complex formation between organic donors and acceptors has been extensively studied by spectrophotometry and other methods. High performance thin layer chromatography (HPTLC), although extensively used for the identification and quantification of drugs and explosives, has not been used until now to determine the extent of association and the association constants K DA of charge transfer or EDA complexes between donor (D) and acceptor (A). This paper describes the use of the HPTLC technique with scanning densitometry to identify and determine the association constants K DA of charge-transfer complexes of N,N-diethylaniline (DEA) with different nitro explosives, namely 1,4-dinitrobenzene (DNB), 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), in chloroform. Advantages of the HPTLC method are highlighted. The association constants K DA of the complexes determined using the HPTLC method have been verified and validated spectrophotometrically when the concentrations of D and A are in their stoichiometric ratio. The thermodynamics of the complex formation reaction were obtained spectrophotometrically from measurements of the association constants K DA at five different temperatures ranging from 293 to 313 K, when D and A are in their stoichiometric ratio and also when A≫D. The vertical ionization potential ( $I_{\mathrm{D}}^{\mathrm{V}}$ ) and vertical electron affinity ( $E_{\mathrm{A}}^{\mathrm{V}}$ ) of DEA were also calculated using Mulliken’s theory employing the semi-empirical AM1 method.