scholarly journals On the Mechanism of Electrochemical Generation and Decomposition of Phthalimide N-oxyl (PINO)

2021 ◽  
Author(s):  
Cheng Yang ◽  
Luke Farmer ◽  
Derek Pratt ◽  
Stephen Maldonado ◽  
Corey Stephenson
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Catalytic Efficiency ◽  
Hydrogen Atom Transfer ◽  
Second Order ◽  
Atom Transfer ◽  
Multiple Site ◽  
Mechanistic Studies ◽  
Electrochemical Generation ◽  
Bulk Electrolysis

Phthalimide <i>N</i>-oxyl (PINO) is a potent hydrogen atom transfer (HAT) catalyst that can be generated electrochemically from <i>N</i>-hydroxyphthalimide (NHPI). However, catalyst decomposition has limited its application. This paper details mechanistic studies of the generation and decomposition of PINO under electrochemical conditions. Voltammetric data, observations from bulk electrolysis, and <a>computational</a> studies suggest two primary aspects. First, base-promoted formation of PINO from NHPI occurs via multiple-site concerted proton-electron transfer (MS-CPET). Second, PINO decomposition occurs by at least two second-order paths, one of which is greatly enhanced by base. Optimal catalytic efficiency in PINO-catalyzed oxidations occurs in the presence of bases whose corresponding conjugate acids have <a>p<i>K</i><sub>a</sub></a>s in the range of 12-15, which strike a balance between promoting PINO formation and minimizing its decay.

scholarly journals On the Mechanism of Electrochemical Generation and Decomposition of Phthalimide N-oxyl (PINO)

2021 ◽  
Author(s):  
Cheng Yang ◽  
Luke Farmer ◽  
Derek Pratt ◽  
Stephen Maldonado ◽  
Corey Stephenson
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Catalytic Efficiency ◽  
Hydrogen Atom Transfer ◽  
Second Order ◽  
Atom Transfer ◽  
Multiple Site ◽  
Mechanistic Studies ◽  
Electrochemical Generation ◽  
Bulk Electrolysis

Phthalimide <i>N</i>-oxyl (PINO) is a potent hydrogen atom transfer (HAT) catalyst that can be generated electrochemically from <i>N</i>-hydroxyphthalimide (NHPI). However, catalyst decomposition has limited its application. This paper details mechanistic studies of the generation and decomposition of PINO under electrochemical conditions. Voltammetric data, observations from bulk electrolysis, and <a>computational</a> studies suggest two primary aspects. First, base-promoted formation of PINO from NHPI occurs via multiple-site concerted proton-electron transfer (MS-CPET). Second, PINO decomposition occurs by at least two second-order paths, one of which is greatly enhanced by base. Optimal catalytic efficiency in PINO-catalyzed oxidations occurs in the presence of bases whose corresponding conjugate acids have <a>p<i>K</i><sub>a</sub></a>s in the range of 12-15, which strike a balance between promoting PINO formation and minimizing its decay.

The kinetics of Oxidation of N-Methylacridan: A Model for Coenzyme 1

1953 ◽  
Vol 6 (4) ◽  
pp. 409 ◽  
Author(s):  
SJ Leach ◽  
JH Baxendale ◽  
MG Evans
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Molecular Oxygen ◽  
Hydrogen Atom Transfer ◽  
Second Order ◽  
Atom Transfer ◽  
Hydrogen Atoms ◽  
Kinetics Of Oxidation ◽  
Conjugate Acid ◽  
Kinetics Of

The rates of oxidation of N-methylacridan by 2,6-dichlorophenolindophenol have been measured between pH 2.74 and 6.91 at 20 to 22 �C in the presence of 8 to 22 per cent. ethanol. The reaction was of the second order and was found to proceed by ' two simultaneous mechanisms, both involving the conjugate acid of N-methylacridan. The oxidation of this cation by the indophenol anion proceeded at a rate which was 19 times greater than the oxidation by the uncharged indophenol molecule. It is shown that oxidation probably occurs by hydrogen atom transfer rather than electron transfer. A similar mechanism for the oxidation of dihydro-coenzyme I would account for its slow reactivity towards molecular oxygen and the biological necessity for mediating systems involving both hydrogen atoms and electrons.

Hydrogen Atom Transfer Reaction Free Energy as a Predictor of Abiotic Nitroaromatic Reduction Rate Constants: A Comprehensive Analysis

2019 ◽  
Author(s):  
Dominic Di Toro ◽  
Kevin P. Hickey ◽  
Herbert E. Allen ◽  
Richard F. Carbonaro ◽  
Pei C. Chiu
Keyword(s):  
Free Energy ◽  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Energy Model ◽  
Second Order ◽  
Transfer Model ◽  
Atom Transfer ◽  
Order Rate ◽  
Linear Free Energy ◽  
Free Energy Model

<div>A linear free energy model is presented that predicts the second order rate constant for the abiotic reduction of nitroaromatic compounds (NACs). For this situation previously presented models use the one electron reduction potential of the NAC reaction. If such value is not available, it has been has been proposed that it could be computed directly or estimated from the electron affinity (EA). The model proposed herein uses the Gibbs free energy of the hydrogen atom transfer (HAT) as the parameter in the linear free energy model. Both models employ quantum chemical computations for the required thermodynamic parameters. The available and proposed models are compared using second order rate constants obtained from five investigations reported in the literature in which a variety of NACs were exposed to a variety of reductants. A comprehensive analysis utilizing all the NACs and reductants demonstrate that the computed hydrogen atom transfer model and the experimental one electron reduction potential model have similar root mean square errors and residual error probability distributions. In contrast, the model using the computed electron affinity has a more variable residual error distribution with a significant number of outliers. The results suggest that a linear free energy model utilizing computed hydrogen transfer reaction free energy produces a more reliable prediction of the NAC abiotic reduction second order rate constant than previously available methods. The advantages of the proposed hydrogen atom transfer model and its mechanistic implications are discussed as well.</div>

Atmospheric formation of the NO3 radical from gas-phase reaction of HNO3 acid with the NH2 radical: proton-coupled electron-transfer versus hydrogen atom transfer mechanisms

2014 ◽  
Vol 16 (36) ◽  
pp. 19437-19445 ◽  
Author(s):  
Josep M. Anglada ◽  
Santiago Olivella ◽  
Albert Solé
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Phase Reaction ◽  
Electron Transfer Mechanism ◽  
Proton Coupled Electron Transfer ◽  
No3 Radical ◽  
Transfer Mechanisms ◽  
Atmospheric Formation

The amidogen radical abstracts the hydrogen from nitric acid through a proton coupled electron transfer mechanism rather than by an hydrogen atom transfer process.

The water–boryl radical as a proton-coupled electron transfer reagent for carbon dioxide, formic acid, and formaldehyde — Theoretical approach

2013 ◽  
Vol 91 (2) ◽  
pp. 155-168
Author(s):  
Waled Tantawy ◽  
Ahmed Hashem ◽  
Nabil Yousif ◽  
Eman Flefel
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Bond ◽  
Electron Transfer ◽  
Hydrogen Atom ◽  
Transfer Process ◽  
Carbonyl Compounds ◽  
Hydrogen Atom Transfer ◽  
Transfer Reactions ◽  
Atom Transfer ◽  
Proton Coupled Electron Transfer

The thermochemistry of the hydrogen atom transfer reactions from the H2O–BX2 radical system (X = H, CH3, NH2, OH, F) to carbon dioxide, formic acid, and (or) formaldehyde, which produce hydroxyformyl, dihydroxymethyl, and hydroxymethyl radicals, respectively, were investigated theoretically at ROMP2/6–311+G(3DF,2P)//UB3LYP/6–31G(D) and UG3(MP2)-RAD levels of theory. Surprisingly, in the cases of a strong Lewis acid (X = H, CH3, F), the spin transfer process from the water–boryl radical to the carbonyl compounds was barrier-free and associated with a dramatic reduction in the B–H bond dissociation energy (BDE) relative to that of isolated water–borane complexes. Examining the coordinates of these reactions revealed that the entire hydrogen atom transfer process is governed by the proton-coupled electron transfer (PCET) mechanism. Hence, the elucidated mechanism has been applied in the cases of weak Lewis acids (X = NH2, OH), and the variation in the accompanied activation energy was attributed to the stereoelectronic effect interplaying in CO2 and HCOOH compared with HCHO. We ascribed the overall mechanism as a SA-induced five-center cyclic PCET, in which the proton transfers across the so-called complexation-induced hydrogen bond (CIHB) channel, while the SOMOB–LUMOC=O′ interaction is responsible for the electron migration process. Owing to previous reports that interrelate the hydrogen-bonding and the rate of proton-coupled electron-transfer reactions, we postulated that “the rate of the PCET reaction is expected to be promoted by the covalency of the hydrogen bond, and any factor that enhances this covalency could be considered an activator of the PCET process.” This postulate could be considered a good rationale for the lack of a barrier associated with the hydrogen atom transfer from the water-boryl radical system to the carbonyl compounds. Light has been shed on the water–boryl radical reagent from the thermodynamic perspective.

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