对硝基苯酚在质子惰性溶剂中的氧化还原机理

利用现场红外光谱电化学法、红外光谱循环伏吸法(CVA)和导数循环伏吸法(DCVA)研究了对硝基苯酚(PNP)在乙腈中的氧化还原机理,并结合B3LYP方法在6-311++G*水平上计算得出反应中自由基阴离子和二聚体可能的结构.通过循环伏安曲线(CV)和快速扫描红外光谱验证了在电化学还原过程中PNP在乙腈溶剂中发生较复杂的自质子化反应,并且PNP的电化学行为受其浓度的影响.当PNP浓度较高时,PNP在还原成自由基阴离子后发生自质子化作用,然后自由基阴离子与质子化产物得到电子发生二聚反应,随后PNP阴离子还原成二价阴离子;当PNP浓度较低时,电化学还原机理会发生改变,二聚现象消失,阴离子自由基继续还原.

Investigation on Redox Mechanism of p-Nitrophenol in Aprotic Media

The mechanism of electrochemical reduction of p-nitrophenol in acetonitrile was explored by means of in situ FTIR spectroelectrochemistry, cyclic voltabsorptometry ( CVA ) and derivative cyclic voltabsorptometry( DCVA) . Also, the possible structures of free radical anions and dimers in the reaction were calculated by the B3LYP method at the 6-311++G? level. Electrochemical experimental results showed that CV curve changed with the change of p-nitrophenol concentration. When increasing the number of CV scan turns, the entire electrochemical process was chemically reversible by observing 3D IR spectra. Both CV and rapid-scan IR spectra( CVA and DCVA) supported that for p-nitrophenol in acetonitrile solvent, complex self-protonation reaction occured during electrochemical reduction. The self-protonation reaction took place after PNP was reduced to free radical anion;when the PNP concentration was high, the dimerization reaction hap-pened from the free radical anion and products of self-protonation reaction, followed by the p-nitrophenol anion being reduced to the corresponding radical dianion. At the same time, when the concentration of p-nitrophenol was decreased, the electrochemical process would also change, that is, the dimerization phenomenon disap-peared, and the anion free radical would continue to reduce.