Electrochemical Reduction of Some Benzotriazoles in Protic and Aprotic Media.

Pedersen, Steen Uttrup; Lund, Henning; Mattinen, Jorma; Göndös, György; Wittman, Gyula; Gera, Lajos; Bartók, Mihály; Pelczer, István; Dombi, György

doi:10.3891/acta.chem.scand.42b-0319

Cited by 9 publications

(12 citation statements)

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“…[32] Pedersen et al performed electrochemical reduction on substituted benzotriazoles in aprotic DMF solutions and observed two reversible peaks (E p red ) for 2-phenylbenzotriazole at À 1.65 V and À 2.27 V vs. Ag/AgI. [33] Hence, it is postulated that the oxidation and reduction peaks are independent processes occurring at different parts of the molecule, with the reduction peaks due to processes at the benzotriazole moiety. As this study was conducted to focus on the investigation of the oxidation mechanism of the phenolic BZTs, further discussion on reductive CVs is omitted.…”

Section: Cyclic Voltammetrymentioning

confidence: 99%

Electrochemical Oxidation of the Phenolic Benzotriazoles UV‐234 and UV‐327 in Organic Solvents

Chan

Webster

2018

ChemElectroChem

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The electrochemical behavior of selected phenolic benzotriazoles (BZTs), namely 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐bis(1‐methyl‐1‐phenylethyl)phenol and 2,4‐di‐tert‐butyl‐6‐(5‐chlorobenzotriazol‐2‐yl)phenol (commercial names UV234 and UV327, respectively) were examined with cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in acetonitrile and dichloromethane solutions. CV indicated that both phenolic BZTs undergo a chemically irreversible oxidation process at approximately Ep°x=+1.0 V vs. Fc/Fc+ (where Ep°x is the anodic peak potential and Fc=ferrocene) to form compounds that cannot be electrochemically converted back to the starting material on the voltammetric timescale. In basic conditions, cyclic voltammetry experiments indicated that the corresponding phenolates (prepared by reacting the phenols with equiv. mols of n‐Bu4NOH) were oxidized at Ep°x∼−0.2 V vs. Fc/Fc+ via a one‐electron diffusion controlled process with anodic (ip°x) to cathodic (ipred) peak current ratios (ip°x/ipred)≫1, suggesting that the produced phenoxyl radicals decomposed rapidly via a chemical step. However, electron paramagnetic resonance (EPR) experiments performed on the bulk electrolyzed solutions of the phenolates after one‐electron bulk oxidation indicated long lifetimes of the UV234. and UV327. phenoxyl radicals. Therefore, the long timescale CPE and spectroscopic (UV‐vis and EPR) studies provided good evidence of a reversible dimerization mechanism between the phenoxyl radicals, which explained the apparent discrepancy with the short timescale CV experiments.

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Section: Cyclic Voltammetrymentioning

confidence: 99%

Electrochemical Oxidation of the Phenolic Benzotriazoles UV‐234 and UV‐327 in Organic Solvents

Chan

Webster

2018

ChemElectroChem

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“…In 1968, Lund et al studied the polarographic reduction of BTA as well as derivatives to disclose the electrochemical transformation mechanism [22]. Pedersen et al investigated the polarographic reduction of some BTAs in protic medium in 1988 [23]. The results indicated that BTA was reduced to 1,2,3-triacetyldihydrobenzotriazole in the presence of acetic anhydride.…”

Section: Introductionmentioning

confidence: 96%

Voltammetric behaviors of an emerging pollutant benzotriazole on multiwall carbon nanotubes (MWNTs)—Nafion modified electrode in various pH mediums

Zheng

Zhang

et al. 2016

Ionics

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The electrochemical behaviors of an emerging pollutant, benzotriazole (BTA), at multiwall carbon nanotubes and Nafion modified glassy carbon electrode (MWNTsNafion/GCE) were investigated systematically. The electrochemical reduction of BTA was significantly improved by MWNTs-Nafion compared to bare GCE, ascribed to the excellent adsorption capacity and electrocatalytic activity of MWNTs. BTA presented well-defined reduction peaks only at pH <3.0, suggesting the involvement of lots of protons in the reduction process. Peak potential shifted negatively and peak current decreased significantly with pH increase. BTA showed various UV-Vis absorption spectra in acidic and alkaline mediums. Cathodic peak current increased linearly with square root of sweep rate as well as with the concentration of BTA from 3.0 × 10 −6 to 1.6 × 10 −4 mol L −1 . This suggests a diffusion-controlled and irreversible electrode process.Diffusion coefficient of BTA on MWNTs-Nafion/GCE was obtained as 2.67 × 10 −2 cm 2 s −1 with four orders of magnitude larger than that on GCE. MWNTs-Nafion/GCE showed a good selectivity between BTA and O 2 but poor selectivity between BTA and tolyltriazole.

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“…The solution must be kept cold or the blue color fades rapidly with loss of the EPR signal, signifying loss of the anion radical. The rapid loss of anion radical upon warming or within a few hours of it formation may explain why others were unable to detect Bt-Ph • – . Attempts were made to reduce the observed peak-to-peak line width in the spectral data by lowering the solution concentration of Bt-Ph • – .…”

Section: Resultsmentioning

confidence: 99%

“…The rapid loss of anion radical upon warming or within a few hours of it formation may explain why others were unable to detect Bt-Ph •− . 17 Attempts were made to reduce the observed peak-topeak line width in the spectral data by lowering the solution concentration of Bt-Ph •− . These experiments did show some improvement although the signal detected was still broad.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Influence of Annulation on the Electron Spin within the 1,2,3-Triazole Ring in Annulenotriazole Anion Radicals

Peters

Maybell

2018

J. Org. Chem.

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The low temperature (-100 °C) single electron reduction of N1-phenylbenzotriazole in liquid ammonia, and the room temperature reduction of N1-phenylcyclooctatetraenotriazole in hexamethylphosphoramide, yields stable solutions of both anion radicals, which were studied via EPR spectroscopy. The amount of electron spin localized within the triazole ring, and how spin is distributed within this ring, is greatly influenced by the size of the annulene ring attached. UB3LYP/6-31++G(d,p) geometry optimizations using DFT methods were carried out for both anion radicals, and the calculated coupling constants (and electron spin densities) are in good agreement with the EPR spectroscopic results. Both theory and experiment show that much of the unpaired electron spin in the N1-phenylbenzotriazole anion radical is delocalized over the entire π system of benzotriazole ring including the phenyl ring attached, but that a significant percentage of total spin is found to reside within triazole ring with much of it located on the second nitrogen (N2). With the N1-phenylcyclooctatetraenotriazole anion radical, the majority of spin is localized over the π system of the COT ring, however a relatively small amount of total spin, found within the triazole moiety, is largely concentrated on two of the nitrogens (N1 and N3) within the ring.

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Electrochemical Reduction of Some Benzotriazoles in Protic and Aprotic Media.

Cited by 9 publications

References 0 publications

Electrochemical Oxidation of the Phenolic Benzotriazoles UV‐234 and UV‐327 in Organic Solvents

Electrochemical Oxidation of the Phenolic Benzotriazoles UV‐234 and UV‐327 in Organic Solvents

Voltammetric behaviors of an emerging pollutant benzotriazole on multiwall carbon nanotubes (MWNTs)—Nafion modified electrode in various pH mediums

Influence of Annulation on the Electron Spin within the 1,2,3-Triazole Ring in Annulenotriazole Anion Radicals

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