Multiple and sequential charge transfer interactions occurring in situ: A redox reaction of thiazolidine-2-thione with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

Interaction of thiazolidine-2-thione (T2T) as an electron donor with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an electron π-acceptor has been studied. Electronic absorption spectra of the system T2T-DDQ in several organic solvents of different polarities have been measured. A charge transfer (CT) complexation has occurred between T2T and DDQ. This CT interaction has led to a redox reaction in which T2T has been oxidized to the corresponding dehydrogenated T2T (T2T-2H), meanwhile DDQ has been fully reduced to the corresponding hydroquinone (DDQH2). However, the two new species, resulting in situ, have been interacted, whereas a CT complex having the formula (T2T-2H·DDQH2) has occurred. IR, 1H NMR and mass spectra were used for ascertaining the structural formula of the synthesized CT complex. Formation constants (KCT), molar absorption coefficients (ɛCT) and thermodynamic properties of this CT interaction in various organic solvents were determined and discussed. The obtained KCT and ɛCT values have indicated that T2T-2H is a weak CT donor, whereas the formed CT complex has a low stability and it is classified as a contact-type CT complex.