红外光谱电化学法研究对苯二酚的电化学氧化还原过程

Investigation on Electrochemical Redox of Hydroquinone-FT-IR Spectroelectrochemistry Techniques

利用现场红外光谱电化学、循环伏吸、导数循环伏吸法及其重构的电流-电位(i-E)曲线,研究对苯二酚(QH2)在不同溶剂中的电化学行为,得到可能的氧化还原机理。结果表明,在乙腈和中性非缓冲溶液中,QH2氧化终产物是对苯醌(Q)。在中性非缓冲溶液的还原的过程中,一部分Q在较正的电位下还原成QH2,另一部分Q在较负的电位下还原成Q2"。碱性溶液中,当加入1倍QH2量的OH-,循环伏安图(CV)出现2个电流相当的氧化峰(Q2",QH2);加入2倍OH-后,只出现一对氧化还原峰(Q2"/Q),从红外谱图上可清晰观察到电化学过程中氢键的变化。

The in situ spectroelectrochemistric method which is a combination of spectroscopy and electrochemistry can provide more information of redox reaction mechanism than traditional electrochemical methods alone. Based on the IR absorption at the detected wavenumbers, we can track simultaneously the concentration changes of relevant redox species during electrochemical process. In this paper, the electrochemical behavior of hydroquinone （QH：） was studied by cyclic vohammetry in acetonitrile media, neutral unbuffer solution, basic solution. During electrochemical process, the changes of each species （reactant, intermediate, final product） were tracked by FT-IR spectroelectrochemistry. Based on cyclic vohabsorptometry （CVA）, derivative cyclic vohabsorptometry （DCVA）, and reconstructed i-E curves, reasonable redox mechanism was proposed. In acetonitrile media, the electrochemical behavior of hydroquinone showed a couple of irreversible redox peaks in cyclic voltammogram. One negative-going band at 1510 cm^-1 and three positive-going bands at 1656, 1595, 1318 cm^-1, corresponding to QH2, Q respectively, were observed in FT-IR 3 D map. It suggested that the oxidation of QH2 was two electrons, two protons process and the final oxidized product was benzoquinone （Q）. In neutral unbuffer solution, it displayed an anodic peak （A1 ） and two cathode peaks （C1, C2 ） for one cycle. For continuous three cycles, an oxidation peak （A2）, corresponding to the negative potential reduction peak （C2）, appeared. In IR 3D map, six IR absorption peaks, 1510; 1656, 1318; 1341; 1495, 1272 cm^-1 which were associated with QH2, Q, Q- , Q^2- respectively, were observed. The results indicated that the final oxidation product was also Q. In reduction process, one part of Q was reduced to QH2 in more positive potential （ C1 ） and the other was to Q^2- in more negative potential （C2）. When 1 equiv of OH- was added into the unbuffer solution, two anodic peaks which were related to QH2, Q^2-, appeared in CV. Then 2 equiv of OH- was added, and only a couple of redox peaks （Q2-/Q） appeared. In addition, we can observe the change of hydrogen bond by the negative-going bands at 2140 cm-Xwhich was due to the absorption of Q^2-...D20 or Q- ... D20. So the results indicated that this process was H-bonding coupled-electron transfer. Based on reconstructed current-potential （i-E） curve, we can conclude that the electron transfer of Q^2- showed two-step one-electron transfer process.