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Synthesis and spectroscopic studies of charge transfer complex between dihydroxy-p-benzoquinone and 4-dimethylaminopyridine in different solvents
Abstract:Charge transfer (CT) complex formation between 4-dimethylaminopyridine (4-DMAP) as the electron donor and 2,5-dihydroxy-p-benzoquinone (DHBQ) as the π-electron acceptor has been investigated spectrophotometrically in methanol (MeOH), ethanol (EtOH) and acetonitrile (AN). The stoichiometry of the complex has been identified by Job’s and photometric titration methods to be 1:1. The Benesi–Hildebrand equation has been applied to estimate the formation constant (KCT) and molecular extinction coefficient (ε). It was found that the value of KCT is larger in AN than in MeOH and EtOH. The thermodynamic parameters are in agreement with the KCT values in that the enthalpy of formation (?ΔH) has a larger value both in EtOH and MeOH than in AN, suggesting higher stability of the complex in EtOH. The complex formed between 4-DMAP and DHBQ has been isolated as a solid and characterised using elemental analysis, FTIR and 1H NMR measurements. Moreover, it has been found that the formed complex involves proton transfer in addition to CT.
Keywords:spectrophotometry  CT-complex  4-dimethylaminopyridine  2,5-dihydroxy-p-benzoquinone
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