Usefulness of charge–transfer complexation for the assessment of sympathomimetic drugs: Spectroscopic properties of drug ephedrine hydrochloride complexed with some π-acceptors

• Ephedrine assessment based on charge–transfer complexation.
• The newly synthesized complexes have been characterized spectroscopically.
• The physical spectroscopic data have been determined using the Benesi–Hildebrand method.
• Thermal decomposition behavior of these complexes was studied.
• The kinetic thermodynamic parameters were calculated.

Recently, ephedrine (Eph) assessment in food products, pharmaceutical formulations, human fluids of athletes and detection of drug toxicity and abuse, has gained a growing interest. To provide basic data that can be used to assessment of Eph quantitatively based on charge–transfer (CT) complexation, the CT complexes of Eph with 7′,8,8′-tetracyanoquinodimethane (TCNQ), dichlorodicyanobenzoquinone (DDQ), 1,3-dinitrobenzene (DNB) or tetrabromothiophene (TBT) were synthesized and spectroscopically investigated. The newly synthesized complexes have been characterized via elemental analysis, IR, Raman, 1H NMR, and UV–visible spectroscopy. The formation constant (KCT), molar extinction coefficient (εCT) and other spectroscopic data have been determined using the Benesi–Hildebrand method and its modifications. The sharp, well-defined Bragg reflections at specific 2θ angles have been identified from the powder X-ray diffraction patterns. Thermal decomposition behavior of these complexes was also studied, and their kinetic thermodynamic parameters were calculated with Coats–Redfern and Horowitz–Metzger equations.