对硝基苯酚在质子惰性溶剂中的氧化还原机理

doi:10.7503/cjcu20170107

摘要/Abstract

摘要：

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.

关键词: 现场红外光谱电化学, 循环伏吸法, 导数循环伏吸法, 对硝基苯酚, 自质子化作用

Abstract:

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 happened 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 disappeared, and the anion free radical would continue to reduce.

Key words: In situ FTIR spectroelectrochemistry, Cyclic voltabsorptometry(CVA), Derivative cyclic voltabsorptometry(DCVA), p-Nitrophenol, Self-protonation reaction

中图分类号:

O646
O657.1

TrendMD:

李钰滢, 李丹, 程龙玖, 金葆康. 对硝基苯酚在质子惰性溶剂中的氧化还原机理. 高等学校化学学报, 2017, 38(11): 2023.

LI Yuying, LI Dan, CHENG Longjiu, JIN Baokang. Investigation on Redox Mechanism of p-Nitrophenol in Aprotic Media^†. Chem. J. Chinese Universities, 2017, 38(11): 2023.

图/表 9

Fig.1 Cyclic voltammogram(A), the corresponding 3D IR spectrum(B), CVAs(C) and selected DCVAs(D) in acetonitrile containing 10 mmol/L PNP and 0.2 mol/L Bu4NClO4 as the supporting electrolyteTo make the DCVA data readily comparable to CV, the partial data in DCVA were multiplied by -1. Au electrode as working electrode, Ag/AgCl as reference electrode. The potential scan rate was 10 mV/s.

Table 1 Attribution of IR absorption peaks of PNP in acetonitrile

$ν ˙$ /cm^-1	Assignment	$ν ˙$ /cm^-1	Assignment
1110	Cl $O 4 -$ from TBAP	1318	ν_N—O from ^-OC₆H₄NOOH^·
1156	ν_C—N from ^-OC₆H₄NOOH^·-	1341	$ν NO$ from PNP
1164	ν_C—N from HOC₆H₄NOOH^·	1472^[9]	ν_N—O from ^-OC₆H₄NOOH^·
1195	ν_C—N from ^-OC₆H₄NOOH^·	1533	ν_N—O from HOC₆H₄NOOH^·
1272^[29]	ν_C—O from ^-OC₆H₄NOOH^·-	1564	Benzene skeleton vibration from ^-OC₆H₄NOOH^·
1279	ν_C—O from HOC₆H₄NOOH^·	1587	Benzene skeleton vibration from HOC₆H4NOOH^·

Table 1 Attribution of IR absorption peaks of PNP in acetonitrile

$ν ˙$ /cm^-1	Assignment	$ν ˙$ /cm^-1	Assignment
1110	Cl $O 4 -$ from TBAP	1318	ν_N—O from ^-OC₆H₄NOOH^·
1156	ν_C—N from ^-OC₆H₄NOOH^·-	1341	$ν NO$ from PNP
1164	ν_C—N from HOC₆H₄NOOH^·	1472^[9]	ν_N—O from ^-OC₆H₄NOOH^·
1195	ν_C—N from ^-OC₆H₄NOOH^·	1533	ν_N—O from HOC₆H₄NOOH^·
1272^[29]	ν_C—O from ^-OC₆H₄NOOH^·-	1564	Benzene skeleton vibration from ^-OC₆H₄NOOH^·
1279	ν_C—O from HOC₆H₄NOOH^·	1587	Benzene skeleton vibration from HOC₆H4NOOH^·

Fig.2 CVAs(A) and selected DCVAs(B) in acetonitrile containing 15 mmol/L PNP

Fig.3 Consecutive CV(A) and the corresponding 3D IR spectra(B) in acetonitrile containing 10 mmol/L PNP The experimental conditions were the same as those of Fig.1.

Fig.4 CV(A), the corresponding 3D IR spectra(B), CVAs(C) and selected DCVAs(D) in acetonitrile containing 10 mmol/L PNPThe scan range was -0.3—-1.5—1.0 V. Experimental conditions were the same as those of Fig.1.

Fig.5 Optimization of dimer structures at the B3LYP/6-311++G** level of calculation

Fig.6 CV curves of PNP and +Na-OC6H4NO2 for comparisonAu electrode as working electrode, Ag/AgCl as reference electrode. The potential scan rate was 10 mV/s.

Fig.7 CV curves in acetonitrile containing different concentrations of PNPExperimental conditions were the same as those of Fig.1.

Fig.8 CV curve(A), 3D IR spectra(B), CVAs(C) and selected DCVAs(D) in acetonitrile containing 5 mmol/L PNPThe partial data in DCVA(D) were multiplied by -1 or divided by 2. Experimental conditions were the same as those of Fig.1.

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