619. The polarographic reduction of pyridine, quinoline, and phenazine

Kaye, R. C.; Stonehill, H. I.

doi:10.1039/jr9520003240

Cited by 18 publications

(12 citation statements)

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“…Cyclic voltammograms (CVs) indicate that the redox properties of GCC sites are fundamentally different than those in molecules. CVs of GCC-phenazine in 0.1 M NaOH display a broad redox feature at −0.65 V (all potentials are vs the normal hydrogen electrode (NHE)) (Figure ), previously attributed to the two-proton, two-electron reduction of the surface pyrazine unit to dihydropyrazine. , This wave occurs 0.35 V positive of the redox feature associated with the two-proton, two-electron reduction of phenazine to dihydrophenazine in solution …”

Section: Proton Transfer At Gccs Is Coupled To Electron Transfermentioning

confidence: 81%

“…59,60 This wave occurs 0.35 V positive of the redox feature associated with the two-proton, two-electron reduction of phenazine to dihydrophenazine in solution. 66…”

Section: Proton Transfer At Gccs Is Coupled To Electron Transfermentioning

confidence: 99%

“…60,61 This wave occurs 0.35 V positive of the redox feature associated with the two-proton, two-electron reduction of phenazine to dihydrophenazine in solution. 67 Interestingly, the electrochemical behaviors of GCC-phen-COOH and GCC-phen-NH 2 are strikingly different than those of the molecular analogues. In CVs of GCC-phen-COOH in 0.1 M NaOH, the pyrazine wave is still observed at −0.65 V, but we also observe a second reversible wave at −0.46 V (Figure 3a).…”

Section: ■ Introductionmentioning

confidence: 99%

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Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces

2019

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Proton-coupled electron-transfer (PCET) steps play a key role in energy conversion reactions. Molecular PCET reactions are well-described by “square schemes” in which the overall thermochemistry of the reaction is broken into its constituent proton-transfer and electron-transfer components. Although this description has been essential for understanding molecular PCET, no such framework exists for PCET reactions that take place at electrode surfaces. Herein, we develop a molecular square scheme framework for interfacial PCET by investigating the electrochemistry of molecularly well-defined acid/base sites conjugated to graphitic electrodes. Using cyclic voltammetry, we first demonstrate that, irrespective of the redox properties of the corresponding molecular analogue, proton transfer to graphite-conjugated acid/base sites is coupled to electron transfer. We then show that the thermochemistry of surface PCET events can be described by the p K a of the molecular analogue and the potential of zero free charge (zero-field reduction potential) of the electrode. This work provides a general framework for analyzing and predicting the thermochemistry of interfacial PCET reactions.

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Section: Proton Transfer At Gccs Is Coupled To Electron Transfermentioning

confidence: 81%

“…59,60 This wave occurs 0.35 V positive of the redox feature associated with the two-proton, two-electron reduction of phenazine to dihydrophenazine in solution. 66…”

Section: Proton Transfer At Gccs Is Coupled To Electron Transfermentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces

2019

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“… a E° (2H + /2 e – ) for hydroquinones and dihydrophenazine under aqueous conditions from previous literature reports. ,, b Average A- H BDFE values were calculated from reported E° values under aqueous conditions. …”

Section: Discussionmentioning

confidence: 99%

“… a E° (2H + /2 e – ) for hydroquinones and dihydrophenazine under aqueous conditions from previous literature reports. ,, …”

Section: Discussionmentioning

confidence: 99%

Hydrogen on Cobalt Phosphide

Delley

Mundy

et al. 2019

J. Am. Chem. Soc.

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Cobalt phosphide (CoP) is one of the most promising earthabundant replacements for noble metal catalysts for the hydrogen evolution reaction (HER). Critical to HER is the binding of H atoms. While theoretical studies have computed preferred sites and energetics of hydrogen bound to transition metal phosphide surfaces, direct experimental studies are scarce. Herein, we describe measurements of stoichiometry and thermochemistry for hydrogen bound to CoP. We studied both mesoscale CoP particles, exhibiting phosphide surfaces after an acidic pretreatment, and colloidal CoP nanoparticles. Treatment with H 2 introduced large amounts of reactive hydrogen to CoP, ca. 0.2 H per CoP unit, and on the order of one H per Co or P surface atom. This was quantified using alkyne hydrogenation and Hatom transfer reactions with phenoxy radicals. Reactive H atoms were even present on the as-prepared materials. On the basis of the reactivity of CoP with various molecular hydrogen donating and accepting reagents, the distribution of binding free energies for H atoms on CoP was estimated to be roughly 51−66 kcal mol −1 (ΔG°H ≅ 0 to −0.7 eV vs H 2 ). Operando X-ray absorption spectroscopy gave preliminary indications about the structure of hydrogenated CoP, showing a slight lattice expansion and no significant change of the effective nuclear charge of Co under H 2flow. These results provide a new picture of catalytically active CoP, with a substantial amount of reactive H atoms. This is likely of fundamental relevance for its catalytic and electrocatalytic properties. Additionally, the approach developed here provides a roadmap to examine hydrogen on other materials.

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Physical Properties and Chemical Reactivity of Alternant Hydrocarbons and Related Compounds VII. The polarographic reduction of pyridine‐like heterocycles

Párkányi¹,

Zahradník²

1964

Bulletin des Soc Chimique

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The polarographic reduction of pyridine-like heterocycles in 5 . 10-2 M tetraethy lammonium iodide in 95 % dimethylformamide gives well pronounced two-electron waves. Half-wave potentials of seven heterocyclic compounds have been determined in this medium. The data have been found to fit the correlation with energies of the lowest free. x-molecular orbitals in the HMO approximation. A similar correlation has also been obtained for half-wave potentials of some heterocycles taken from the literature.A number of polarographic works has been devoted to the study of half-wave reduction potentials of aromatic hydrocarbons and their derivatives in organic solvents. In this connection, Maccoll(3) and Lyons (4) have shown that there is a correlation between the energies of the lowest free Tc-molecular orbitals of aromatic hydrocarbons and (*) Presented at the symposium

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619. The polarographic reduction of pyridine, quinoline, and phenazine

Cited by 18 publications

References 0 publications

Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces

Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces

Hydrogen on Cobalt Phosphide

Physical Properties and Chemical Reactivity of Alternant Hydrocarbons and Related Compounds VII. The polarographic reduction of pyridine‐like heterocycles

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