Monoelectronic Transfer Research Articles

Electrooxidation mechanism of glyoxylic acid on Au polycrystalline electrodes in acidic medium

AbstractThe electrooxidation mechanism of glyoxylic acid has been investigated on an Au polycrystalline electrode in acidic medium. The kinetic parameters deduced: Tafel slope, reaction order with respect to glyoxylic acid concentration, reaction order with respect to the pH, apparent activation enthalpy, entropy and Gibbs energy, and the final products detected after oxidation are in agreement with an electrooxidation mechanism beginning with an adsorption and a rate determining step in which the adsorbate becomes oxidized in a monoelectronic transfer reaction.

Trimesityl phosphoniumyl cation radical: electrogeneration and evolution

The electrochemical oxidation of tris (2,4,6-tri-methyl-phenyl) phosphine (TMP) in acetonitrile was investigated on a platinum electrode. A fast mono-electronic transfer ( E p = 0.71 V vs sce) gives rise to the corresponding long-lived phosphoniumyl cation radical. This electrochemically generated radical undergoes a slow reaction with residual water, generating the corresponding phosphine oxide (TMPO) and hydro phosphonium (TMPH +). The kinetics of the decay of the cation radical has been studied, and a reaction mechanism is proposed. When TMP is oxidized on a platinum electrode at potentials higher than 1.5 V vs sce, a fast surface reaction involving residual water takes place. This process was studied by voltammetry at a rotating ring-disk electrode; the same products, TMPO and TMPH + were formed.

Formation and scission of the sulfur–sulfur bond: a new approach to reactions between sulfur/polysulfide ions and thiolate ions/disulfides in N,N-dimethylacetamide

The reactivity of sulfur towards a series of thiolate ions RS–[R = phenyl (1), 4-methylphenyl (2), benzyl (3) ethyl (4), propyl (5), butyl (6), sec-butyl (7), tert-butyl (8)] has been studied by spectroelectrochemistry in N,N-dimethylacetamide. Apparently, sulfur reacts in two parallel ways: (i) oxidation of RS– leading to RS2R and S3˙– ions; (ii) preponderant S-nucleophilic process yielding stable RSx– ions (x= 2–5). RSx– species, whose spectrophotometric characteristics have been determined, are successively obtained in the course of sulfur addition with R = alkyl, whereas equilibria between arylpolysulfide ions were observed. At the junction of these two parallel pathways, the slow key equilibrium 2RS4–⇌ RS2R + 2S3˙– has been investigated by addition of RS2R R = 1–8 to S3˙– solutions. In fact, our study is consistent with at first, a monoelectronic transfer between RS–(or RS2–) ions and the very reactive S2 molecules in equilibrium with S8. The fast and competing couplings of the radicals RS˙(or RS2˙), S2˙–(or S3˙–) agree with the simultaneous formation of RS2R, RSx– and polysulfide ions. More generally, the S2/S2˙– redox system is believed to be involved in thiophilic reactions of a number of anions such as RS– towards sulfur rather than the initial opening of the cyclic S8 form.

Cyclic voltammetry, ESR and spectral investigation of the electrochemical reduction of some acetyl diphenylsulphides and sulphones

The electrochemical reduction in dimethylsulphoxide of five mono- and diacetyl derivatives of diphenylsulphide and diphenylsulphone was investigated by means of cyclic voltammetry, ESR spectroscopy and optical spectroscopy. In all cases the first reduction step corresponds to a reversible monoelectronic transfer and leads to the formation of an anion radical which is stable enough to be detected by in-situ ESR and optical spectroscopy. The electronic structure of the anion radical and the follow-up reactions are determined by the acetyl substituent and only influenced slightly by the degree of oxidation of the sulphur atom. Semi-empirical MO calculations in the frame of the AM1 method provide a good description of the main trends observed experimentally.

SRN1 Synthesis of vic-dinitro compounds containing a nitrodioxane subunit

vic-Dinitro compounds containing a nitrodioxane subunit can be obtained by SRN1 reactions between either open chain gem-chloronitro derivatives as substrates and an anion from nitrodioxane as the nucleophile or ‘reversed’ reagents namely gem-chloronitrodioxane (substrate) and anions from nitro derivatives. The former access is more efficient and is rationalized on the basis that the structure of the radical anion generated by mono electron transfer to the respective substrates allows an appropriate choice of reagents for optimizing the yield of the title compounds to be made.

Etude comparative des réactions par transfers monoeĺectronique entre les germylamines primaires, secondaires et tertiaires et la 3,5-di-tert-butylorthoquinone

Several germylamines were treated with 3,5-di-t-butylorthoquinone ( 1). Competitive 1,2 and 1,4 additions resulted using the tertiary amine Et 3GeNPh 2. The thermally unstable 1,4 adduct gives 2,2-dialkyl-4,5-(6,8-di-t-butyl)benzo-2-germa-1,3-dioxolanne. The 1,2 adduct leads via intermolecular redistribution to bis(triethylgermyl)oxide ((Et 3Ge) 2O), and aminal with partial regeneration of the initial quinone. These reactions seem to proceed solely via a mono-electron transfer mechanism; the aminyl radical Ph 2N . and the transitory o-semiquinonic germylated radical formed in the reaction have been characterized by ESR spectroscopy. The o-semiquinonic radical then gives O-germyl-3,5-di-t-butylcatechol by hydrogen abstraction. As ethylene and isobutene have been characterized, these hydrogen abstractions occur from ethyl groups linked to germanium and from t-butyl groups belonging to the organic moieties. In the reaction of the secondary amine Et 3GeN(H)Ph, a germylaminyl radical is mainly formed instead of an o-semiquinonic germylated radical, which can explain the lesser amount of germadioxolanne obtained. The quinone 1 is partially transformed in o-diphenol under the action of Mes 3GeNH 2. No germylated adducts are observed. Aminyl radicals characterized in several reactions between germylamines and 1 were also obtained via monoelectronic transfer between lithium amids and tri-t-butylnitrozobenzene (BNB), thus providing a new, useful method for obtaining such species. constitue une nouvelle bl]

ChemInform Abstract: Synthesis of Methyl‐ or Arylsulfonylhydroxybiphenyls Catalyzed by Monoelectronic Transfer and Related Compounds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Electrochemistry of 9,9′-bifluorenylidene: Detection of the radical species by spectroelectrochemical and EPR methods

It is shown by cyclic voltammetry and differential pulse polarography that 9,9′-bifluorenylidene (BFD) undergoes two successive reduction waves in ap a reversible ( E 1 = −1.10 V SCE) followed by a quasi-reversible ( E 2 = −1.50 V SCE) couple. These were monitored by spectrochemical m monoelectronic transfers. The monoradical was detected by EPR, and the spectrum interpreted in terms of delocalization of the unpaired electron on the

Synthesis of methyl or aryl sulfonyl hydroxy biphenyls catalyzed by monoelectronic transfer and related compounds

Abstract Methyl or aryl sulfonyl hydroxy biphenyls could be electrosynthesized in liquid ammonia via a SRN1 reaction, from chlorophenyl sulfones and 2,6-ditertbutylphenoxide. Further transformations such as tertbutyl groups elimination, alkylation at the α carbon of the sulfone, or at the oxygen are described.

Evidence for a mono-electron transfer process in the BF 3-promoted reaction of 4′-nitrobenzenesulphenanilide (NBSA).

ESR spectroscopy shows the formation of a radical species in the BF 3-promoted reaction of NBSA, an acid/base Lewis-type reaction.

Electrochemical properties of bridged and non-bridged dinuclear copper complexes using a flexible ligand

We have investigated the redox behavior of a series of dinuclear copper(II) complexes Cu 2L 4+, Cu 2(μ- OH)L 3+ and Cu 2(μ-Im)L 3+ where L is 1,4-bis((1-oxa- 4,10-dithia-7-azacyclododec-7-yl)methyl)benzene, a ligand which is capable of holding two copper centers in close proximity. Electrochemical studies of the three dinuclear complexes in propylene carbonate reveal that Cu 2L 4+ exhibits a sequential two-electron reduction at the same positive potential whereas in Cu 2(μ-OH)L 3+ and Cu 2(μ-Im)L 3+ which involve bridging groups, reduction to their dinuclear Cu I species occurs via two successive monoelectronic transfers at positive potentials. The relevance of these studies to those found for type III copper proteins is briefly discussed.

One-step electrochemical immobilization of keggin-type heteropolyanions in poly(3-methylthiophene) film at an alectrode surface: Electrochemical and electrocatalytic properties

Immobilization of Keggin-type heteropolyanions (HPA), such as PW 12O 40 −3, SiW 12O 40 4− and PMo 12O 40 3−, in poly(3-methylthiophene is performed by electropolymerization of the thiophene derivative in the presence of the corresponding HPA acid. The polymerization was possible even in the presence of a large amount of water because of the formation of a complex between the HPA and the 3-methylthiophene. The cyclic voltammetry curves in acetonitrile during polymerization are described and also of the polymer films doped with HPA. In the case of the phosphomolybdate anions, we observed in addition to the redox system of the polymer, six monoelectronic transfer from the HPA. These multiple electron transfers can explain the possibilities of such modified electrodes in electrocatalysis. Effectively, we observe an electrocatalytic reduction of oxygen in acetonitrile (0.5 M HClO 4) by comparison with an unmodified bare glassy carbon electrode.

Electrochemical studies of the adsorption of propargyl alcohol on a smooth platinum electrode in acid medium

The electrooxidation of the intermediate species produced by the adsorption of propargyl alcohol on a smooth platinum electrode has been studied in 0.5 M H2SO4 medium. At 25°C, the maximum amount of adsorbed intermediates was observed for Eads=0.2 V/rhe and the alcohol re-adsorption was avoided using a sweep rate ranging from 3 to 10 V s−1. The adsorption process is well described by a Temkin isotherm, with an interaction factor, f≈16, and an adsorption energy Δadso≈-49 kJ mol−1. The experimental data shown that the electrooxidation of propargyl alcohol proceeds through a reaction pathway involving an initial monoelectronic transfer step. In the temperature range from 20 to 80°C, the apparent activation energy for the electrooxidation of the adsorbed intermediates resulting from propargyl alcohol was determined, ΔHa*≈12 kJ mol−1.

Réaction de dérivés à liaison germanium-azote (germylamines, cyclogermazanes et germa-imines transitoires) avec la di-t-butyl-3,5-orthoquinone

Several germanium-nitrogen compounds were treated with 3,5-di-t-butylorthoquinone ( 1). In the case of the germylamines R 3GeNMe 2 (R = Et, Ph), 1,2 and 1,4 adducts were formed, as shown by 1H NMR spectroscopy. The thermally unstable 1,4 adduct, decomposes with nitrene elimination to give 2,2-dialkyl or 2,2-diaryl (6,8-di-t-butyl)-4,5-benzo-2-germa-1,3-dioxolane. The 1,2 adduct, through intermolecular redistribution, leads to digermyloxide (R 3Ge) 2O and a gem-diamine with partial regeneration of the starting quinone 1. These addition reactions proceed through a monoelectronic transfer mechanism, with formation of a transient o-semiquinonic radical identified by ESR spectroscopy. This transient radical leads to O-germyl 3,5-di-t-butylcatechol by hydrogen abstraction from the solvent. The proposed mechanism explains the formation of the germylated compounds as well as the organic by-products. Similar reactions were observed between cyclodigermazanes and 1. The 1,4 cycloaddition generates germadioxolanes with nitrene expulsion, whereas the 1,2-cycloaddition leads to the germoxane and conjugated ketoimine, or diimine. The latter is a good trapping agent for the nitrene formed in the decomposition of the 1,4 adduct. Both the 1,4 and 1,2 cycloadduct decompositions imply transient germaimine formation. The same germaimine, formed at room temperature from intramolecular dehydrohalogenation of the hindered R 2ClGeNHR′ by 1,8-diaza[5.4.0]bicyclo-7-undecene) gives the same reaction products.

Determination par CPG/IRTF de la structure et de la stereochimie des produits obtenus par action du sodium sur un ceto-ether allylique

GC/FTIR has shown that monoelectronic transfer reaction between sodium and the allylic keto-ether 1 is carried out by a radical mechanism to yield a five-carbon ring with two functional groups. The structure and the stereochemistry of the reaction products have been determined.

Addition 1, 4 de divers organo- et organohaloge´no-hydrogermanes sur la di-t-butyl-3, 5 orthoquinone

The thermal 1, 4 addition of triorganohydrogermanes R 3GeH (R = Et, Ph) with 3, 5-di-t-butylorthoquinone leads to their corresponding mono- O-germylated catechols in good yields. Similarly, the organohalohydrogermanes give the 2, 2-diorgano- (or 2, 2-organohalo)(6, 8-di-t-butyl)-4, 5-benzo-2-germa-1, 3-dioxolanes after dehydrochlorination of transient mono- O-chlorogermylated catechols. Since these reactions are only slightly dependent on solvent and radical initiators, the mechanism probably involves monoelectronic transfer with the formation of a radical anion pair in the first step. The ESR measurements show the transient formation of a paramagnetic o-semiquinonic species which supports the proposed mechanism.

Di-heteroarylethyl enes: synthesis and donor properties

The Wittig-Horner condensation of N-methylpyrrole-2-, and 2,5-dicarbaldehydes with diethyl heteroarylmethylphosphonates (heteroary =N-methylpyrrol-2-yl or 2-thienyl and the corresponding 2,5-diyl) leads to the (E)-1,2-diheteroarylethylenes (1) and (2), and the triheteroaryl derivatives respectively. A new entry into diethyl pyrrolylmethylphosphonates is described starting from the pyrrol-2-ylmethyltrimethylammonium iodide and the sodium salt of diethyl phosphite: the rate and the regiochemistry of the reaction is solvent dependent. The heteroarylethylenes (1)–(5) are electron-rich substrates affording charge transfer (c.t.) complexes with iodine and TCNQ (tetracyano-1,4-quinodimethane): the d.c. conductivities of the c.t. complexes are relatively low and fall in the range of semiconductors. I.r. frequencies of the CN stretching relative to the TCNQ moiety are used to evaluate the degree of charge transfer between the donor and the acceptor. It is believed that the radical cation of (5) arising by monoelectron transfer to TCNQ is the most stable charged species among the series considered.

The Adsorption and the Potentiodynamic Electro‐Oxidation of Acetylene on Platinized Platinum

The adsorption and the potentiodynamic electro‐oxidation of acetylene on platinized platinum in have been studied in the 16°–80°C temperature range. The perturbation conditions were chosen to avoid the influence of acetylene readsorption. The steady‐state coverage by the adsorbed species was studied as a function of the potential and the hydrocarbon partial pressure. The estimated values of the average number of electrons per adsorption site and the number of the electrocatalyst sites blocked per adsorbed species are 4.7 and 2.1, respectively. Aging effects of the adsorbed species are also reported. The kinetic parameters obtained under potentiodynamic conditions suggest that the electro‐oxidation of the adsorbed acetylene proceeds through a reaction pathway involving a slow initial monoelectronic transfer step.

Cyclic Voltammetry of Neptunium in Different Media

can be determined simultancously with Np4+ at the glassy carbon electrode in HClO4 and HNO3 solutions, because there is only one monoelectronic change transfer for . In acetate buffer medium and in sulfuric acid the determination of possible at the glassy carbon electrode, but in presence of Np4+ we found out an interaction between and Np4+. Considering this effect the determination of is possible.

The anodic behavior of saturated hydrocarbons in fluorosulfuric acid Part I. Study of the oxidation mechanism

The mechanism of anodic oxidation of saturated hydrocarbons in fluorosulfuric acid has been established with cyclopentane and cyclohexane. Two monoelectronic transfers are separated by a chemical reaction which is a deprotonation: RH→[RH] ⋎+ + e − E [RH] ⋎+ →R ⋎ +H + C R ⋎ →R + + e − E This ECE mechanism is supported by cyclic voltammetry and coulometries performed at cryogenic temperatures. It is shown that R is chemisorbed at low temperature: R radicals are hard and can give a complex with the platinum atoms of the anode which are also hard (because they are strongly deficient in electrons). Such a complex formation can explain why R is more difficult to oxidize than the parent hydrocarbon RH.