Electrochemical Reducation Studies On Quinone Molecules-In-Situ FTIR Spectroelectrochemistry

The paper introduced current research status and progress of quinone compounds, followed by the introduction of in-situ FTIR spectroelectrochemistry method. Cyclic voltammetry (CV), in-situ FTIR spectroelectrochemistry cyclic voltabsorptometry (CVA) and derivative cyclic voltabsorptometry (DCVA) techniques were utilized to study the electron transfer mechanism of three quinone compounds, Tetrachlorobenquinone(TCBQ),2,3-Ⅱchlorine-5,6-dicyano-benzoquinone (DDQ) and Tetramethyl-p-benzoquinone (TMBQ), and various species changes of these three compounds among their electrochemical redox process in proton inert solvent were described. Main results were summarized as follows:1. Through in-situ FTIR spectroelectrochemical techniques, it was concluded that TCBQ had a two-step single electron transfer mechanism in acetonitrile. The existence of the intermediate semiquinone radical TCBQ- observed in IR 3D map further proved the above conclusion which was consistent with two pairs of redox peaks in CV curves. Then several main characteristic IR absorption peaks in 3D map were attributed:1695 cm-1 and 1564 cm-1 were TCBQ's characteristic absorption peaks; 910cm-1,1140cm-1 and 1525cm"1 were the characteristic absorption peaks of TCBQ-; 886cm-1 and 1410cm-1 were the characteristic absorption peaks of TCBQ2-. In addition, the changes of various species of TCBQ in redox process could also be observed through CVA and DCVA curves.2. DDQ had a continuous two-step one-electron transfer mechanism in acetonitrile among the electrochemical redox process. The main IR absorption peaks of DDQ in 3D map were as follows:1171 cm-1,1264 cm-1 and 1702 cm-1 were characteristic peaks of DDQ; 1217 cm-1,1384 cm-1,1410 cm-1 and 1464 cm-1 were four positive direction absorption peaks which were attributed to be the resultant DDQ2-; 1194 cm-1,1548 cm-1 and 2210 cm-1 were attributed to be the intermediate DDQ-, also positive direction.3. The first step electrochemical reduction process of TMBQ in acetonitrile solution was accompanied with underwent chemical reactions, that is dimerization reaction, and the dimer was oxidized at-0.32V. The main IR absorption peaks in 3D map were as follows:1264 cm-1 was a C-CH3 stretching vibration peak; 1310 cm-1 and 1641 cm-1 were the characteristic peaks of TMBQ; 1356 cm-1,1479 cm-1 were the characteristic peaks of TMBQ'- free radical; 1679 cm-1 was C=O stretching vibration on the dimer.