Rotating Ring-Disk Electrodes

Hydroxylamine oxidation in acidic media at the rotating platinum, gold, and glassy carbon electrodes was investigated. It was found that the reaction occurred only at the platinum electrode. A single oxidation peak ͑instead of a wave͒ was observed at the rotating platinum electrode. Evidence for a kinetic hindrance of the reaction caused by the platinum oxide layer present at the electrode surface was shown. The reaction proceeds via NHOH, NOH, nitrous acid, and the final products are nitrate ions. The process involves hydroxylamine adsorption, which is the reason for the absence of the electrochemical signal in the case of gold and carbon, materials of lower catalytic activity. Hydroxylamine oxidation was accompanied by various homogeneous chemical reactions. The reaction of hydroxylamine with nitrous acid ͑intermediate product of hydroxylamine oxidation͒, yielding N 2 O, had a rate constant, estimated on the basis of the ring-disk experiments, equal to (6.4 Ϯ 0.4) 10 4 mol Ϫ1 cm 3 s Ϫ1 .Hydroxylamine can exist in water solutions in two forms: above pH 5.9 as simple NH 2 OH and, below this pH, in protonated form,Those two forms have different electrochemical behavior and NH 3 OH ϩ is assumed to be less active. 2,3 Moeller and Heckner, 2 who investigated the electrode reactions of hydroxylamine at the rotating platinum electrode, observed a single oxidation peak in acidic solutions. According to the authors the reaction consists of several steps and the final products are nitrites. In strongly acidic solutions (pH Ӎ 0), the oxidation reaction stops at the electroinactive NHOH ϩ .Karabinas et al. 3 studied NH 2 OH oxidation in 0.5 M H 2 SO 4 solution at the rotating platinum electrode with differential electrochemical mass spectroscopy ͑DEMS͒, a method which enables one to measure the rate of formation of a volatile product as a function of potential. They found that in 0.5 M H 2 SO 4 solution hydroxylamine is less active than in buffered neutral solution. The reaction proceeds at the potential of the platinum oxide layer formation and probably Pt-OH is involved in the process. A single oxidation peak was observed. The following DEMS signals were found 1. N 2 O signal was formed at the potential corresponding to the rising part of the hydroxylamine oxidation peak, indicating that the reaction proceeds via HNO 2 . According to the authors the formation of N 2 O is due to the following chemical reaction2. NO formation was suppressed within the anodic scan, which showed NOH formed to a small extent. The NO signal was strong in the cathodic scan on a freshly reduced ͑more active͒ Pt surface. The authors considered the existence of NO as a proof of NOH formation3. Small amounts of NO 2 were formed at peak potentials ͑i.e., in the range of HNO 3 formation͒. The authors concluded that in acidic solutions at least part of the reaction proceeds via NO 2 , which quickly disproportionatesThe main aim of this work was to study the electrochemical behavior of protonated hydroxylamine at the rotating platinum, gold and glassy c...

Section: Resultsmentioning

confidence: 99%

Oxidation of Hydroxylamine on the Rotating Solid Electrodes

Piela

Wrona

2004

“…2. [2] and [3]) and excludes mechanisms II (it is possible that a nuance of mechanism II [see (2) case IId, Fig. [2] and [3]) and excludes mechanisms II (it is possible that a nuance of mechanism II [see (2) case IId, Fig.…”

Section: Dimethylmentioning

confidence: 99%

“…In this paper we extend the study of the mechanism of electrohydrodimerization to the compounds dimethyl fumarate, cinnamonitrile, and fumaronitrile, with special emphasis on the application of rotating ring-disk electrode (RRDE) techniques, which have been shown to be particularly useful in distinguishing among mechanisms I, II, and III (2). Previous studies of these compounds [ (3)(4)(5)(6) and references therein] have verified that hydrodimers are the major products of the electroreduction.…”

mentioning

confidence: 96%

“…[1] 2R ~ 2e-b 2H + ~ R~H2 [1] The first paper in this series (1) R + e--> R ~ [2] k~ 2R= > R22- [3] rather than by reaction of the radical anion with parent and subsequent electron transfer (mechanism II) ks' [1] 2R ~ 2e-b 2H + ~ R~H2 [1] The first paper in this series (1) R + e--> R ~ [2] k~ 2R= > R22- [3] rather than by reaction of the radical anion with parent and subsequent electron transfer (mechanism II) ks'…”

mentioning

confidence: 99%

See 1 more Smart Citation

Electrohydrodimerization Reactions

Puglisi

Bard

1972

Self Cite

The reduction of the activated olefins dimethyl fumarate, cinnamonitrile, and fumaronitrile in tetra-n-butylammonium iodide-dimethylformamide solutions at a platinum electrode has been studied by rotating ring-disk electrode (RRDE) voltammetry, cyclic voltammetry, and coulometry. The results indicate that each compound undergoes a one-electron reduction to the anion radical which then undergoes a dimerization reaction. Rate constants for this dimerization reaction were found to be 110 (dimethyl fumarate), 880 (cinnamonitri]e), and 7 • l0 s (fumaronitrile) 1/mole-sec. Evidence of some bulk polymerization reaction was obtained from the coulometric results. * Electrochemical Society Active Member. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-03-30 to IP

“…2R " --> R2 ~- [2] It is also of interest to examine the hydrodimerization reaction of a disubstituted olefin in the presence of a second activated olefin (R') by RRDE voltammetry (3) and coulometric techniques. The aim was to explore the conditions under which formation of cross-coupled products can occur, thus obtaining more insight into the mechanism of electrolytic reductive coupling.…”

mentioning

confidence: 99%

Electrohydrodimerization Reactions

Puglisi¹,

Bard²

1973

Self Cite

The electrohydrodimerization reaction of dimethyl fumarate in the presence of cinnamonitrile and acrylonitrile was studied in dimethylformamide solution by rotating ring-disk emctrode, voltammetric and coulometric techniques. At potentials where only dimethyl fumarate is electroactive, the rate and mechanism of decay of the dimethyl fumarate anion radical are only slightly perturbed from the results obtained in the absence of cinnamonitrile and acrylonitrile. This is an indication that little or no cross-coupling was occurring. At potentials where both dimethyl fumarate and cinnamonitrile are electroactive evidence for the occurrence of a solution oxidation-reduction reaction consuming cinnamonitrile anion radical and dimethyl fumarate parent was obtained. In addition, the role of cis-trans isomerization of radical anions * Electrochemical Society Active Member.