Electrochemical reduction of pyrazine in aqueous media

Klatt, Leon N.; Rouseff, Russell L.

doi:10.1021/ja00776a009

Cited by 52 publications

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“…The rate constant k, of the homogeneous decomposition of dihydropyrazine depends on pH more clearly, most probably having a minimum at pH 2.5. This behaviour, which is very close to the results of Klatt and Rouseff [8], indicates the occurrence of acid-base catalysed hydrolysis of protonated dihydropyrazine to yield the aminoaldehyde NH,-CH=CH-NH-CH,-CHO.…”

Section: (V) Discussion and Conclusionsupporting

confidence: 88%

“…Likewise, the high value of cfII indicates a major contribution of a following chemical step to the kinetics in the second charge-transfer step. These steps could be protonations, which might be involved according to Process I: P,+H+ +P,H+ (RI) PvH+ + e---, P,H (R2) PvH + H+ + PvH; (R3) Process II : P,H: + e-4 PYHZ (R4) P,H, + H++ P,H; (R9 where P,Hl is the stable intermediate radical cation [8] and PvHl is the protonated 1,4_dihydropyrazine.…”

Section: (V) Discussion and Conclusionmentioning

confidence: 99%

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Analysis of the interfacial admittance in the case of a two-step two-electron electrode reaction with a diffusing intermediate, with application to the reduction of pyrazine

Rueda

Sluyters‐Rehbach

Sluyters

1987

Journal of Electroanalytical Chemistry and Interfacial Electroc

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A critical evaluation is presented of the analysis of impedance or admittance data in the case of an electrode reaction proceeding by two consecutive one-electron transfers with a stable, solution-soluble intermediate. It is shown that the expression for this case, as derived by Armstrong and Firman, has four limiting forms that have the same frequency dependence as the expression describing a single charge+ transfer reaction ("pseudo-&mlles behaviour"). Also, the conditions for another simplification, which leads to quarter circles in the complex plane diagram ("Armstrong's equivalent circuit"), are considered. It follows that the special case, where the quarter circle is in the negative quadrant, cannot occur when the system is dc reversible or at equilibrium. For dc irreversible systems, this phenomenon can show up under rather narrow conditions. In addition, it is found that, if these limiting cases are not fulfiied, the general equation often has a frequency dependence that within the practically useful frequency range is hardly distinguishable from that of the single charge-transfer case ("apparent Randles behaviour"). Consequently, the presence of the consecutive mechanism has to be detected from the dc potential dependence of the admittance parameters rather than from the frequency dependence. Finally, it is shown that the general expression corresponds to an equivalent circuit consisting of five elements which, however, have no sensible physical meaning.These views are applied to the reduction of pyraxine at a DME from 1 M aqueous NaClO, solutions of pH 4.8, 5.4 and 6.1. Although only one wave is observed in the dc polarogram, the potential dependence of the transfer resistance and the Warburg coefficient (found as parameters in a case of "apparent Randles behaviour") indicates two consecutive oneelectron transfers. The standard rate constants and the transfer coefficients of these two electron transfers are calculated, as well as the rate constant of a homogeneous chemical reaction following the second electron transfer. It is concluded that slow protonation steps largely determine the kinetics of the electron transfers.The reactants are found to be weakly adsorbed in contrast with the strong adsorption found earlier in strongly acidic solutions.l Dedicated to the memory of Don Smith.

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Section: (V) Discussion and Conclusionsupporting

confidence: 88%

Section: (V) Discussion and Conclusionmentioning

confidence: 99%

Analysis of the interfacial admittance in the case of a two-step two-electron electrode reaction with a diffusing intermediate, with application to the reduction of pyrazine

Rueda

Sluyters‐Rehbach

Sluyters

1987

Journal of Electroanalytical Chemistry and Interfacial Electroc

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“…All attempts to observe the parent 1,4-dihydropyrazine have failed so far: electrochemical procedures have led either to the N-protonated form [206] (without the possibility of cyclic electron delocalization) or, in basic solution, to ringopened products [207]. Attempts to generate 7 in the gas phase were also unsuccessful due to the highly reducing nature of these species [208].…”

Section: Figurementioning

confidence: 99%

Heterocycles with 7 and 8π electrons. Models for flavin and pteridine intermediates and candidates for novel inorganic rings

Kaim

1987

Reviews of Chemical Intermediates

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“…The solubility of 1 is too low to carry out a raphy in hydroorganic mediums (2,3) but with preparative electrolysis. the exception of pyrazine itself in acidic medium, The polarograms at different p H and the U.V.…”

Section: 25-diphenylpyrazine ( I )mentioning

confidence: 99%

Electrochemical Reduction of Pyrazines into Dihydropyrazines. Preparation of Dihydropyrazines

Armand¹,

Chekir²,

Pinson³

1974

Can. J. Chem.

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. Can. J. Chem. 52,3971 (1974). The electrochemical reduction of several pyrazines in an alkaline hydroorganic medium leads t o 1,4-dihydropyrazines too easily oxidizable to be isolated. These derivatives isomerize into 1,2-or 1,6-dihydropyrazines, the rate of this reaction depending among other things on the p H and on the cosolvent. The different chemical and electrochemical preparations of dihydropyrazines are discussed. It is shown that 3,6-dihydro-2,5-diphenylpyrazine and 1,6-dihydro-2,5-diphenylpyrazine are in thermodynamic equilibrium.JOSEPH ARMAND, KHALED CHEKIR et JEAN PINSON. Can. J. Chem. 52,3971 (1974). La rkduction electrochimique de diverses pyrazines en milieu hydroorganique alcalin fournit des dihydro-1,4 pyrazines, trop oxydables pour pouvoir @tre isolCes. Ces dCrives s'isomkrisent en dihydro-l,2 ou dihydro-1,6 pyrazines avec une vitesse dependant en particulier du p H et de la nature du cosolvant Les differents modes d'obtention, chimiques et electrochimiques des dihydropyrazines sont discutes. I1 est montre que la dihydro-3,6 diphenyl-2,5 pyrazine forme un Cquilibre thermodynamique avec la dihydro-1,6 diphenyl-2,5 pyrazine.The reduction of pyrazines, by the usual chemical reagents, generally leads to hexahydro derivatives, i.e. to piperazines. Few semihydrogenated derivatives, dihydro-and tetrahydropyrazines, are known.The electrochemical reduction of pyrazines in an alkaline hydroorganic medium was investigated to determine the intermediates involved in the reduction of pyrazine5 into piperazines and to find out whether the electrochemical reduction could be of interest for the preparation of dihydro-and tetrahydropyrazines.Besides, a large number of organic compounds of biological or pharmaceutical interest possess the pyrazine ring. Oxido reduction reactions seemingly involving the pyrazine ring often take place in these compounds (1). Therefore there is an additional interest of a detailed knowledge of the electrochemical behavior of pyrazines.This investigation is divided into two parts. This first paper deals with the reduction of pyrazines into dihydropyrazines and with the preparation of dihydropyrazines.As the dihydropyrazines are unstable in acidic medium, this investigation was carried out in alkaline medium. The following pyrazines were investigated: 2,5-diphenylpyrazine (1); 2,3-diphenylpyrazine (2); tetramethylpyrazine (3); 2,5-di-2'-pyridylpyrazine (4); 2,3-di-2'-pyridylpyrazine (5); tetra-2'-pyridylpyrazine (6). I . 2,5-Diphenylpyrazine ( I )Between p H 1 and 13, 1 exhibits a single 2e cathodic wave, its E l l , depends on the pH: Ell, = -0.38 -0.079pH (50% DMF).During the electrolysis of a dilute solution of 1 in a water-DMF medium (0.5 N NaOH; c = 2 x M; E = -1.45 V) an anodic wave appears with an E l i , very close to that of the cathodic wave of 1 (Fig. 1). Then this anodic wave decreases at the expense of another anodic wave, at a less negative potential, and of a cathodic wave, at a potential slightly more negative than that of 1.In a water-methanol medium (80% CH,OH; 0.2...

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Electrochemical reduction of pyrazine in aqueous media

Cited by 52 publications

References 0 publications

Analysis of the interfacial admittance in the case of a two-step two-electron electrode reaction with a diffusing intermediate, with application to the reduction of pyrazine

Analysis of the interfacial admittance in the case of a two-step two-electron electrode reaction with a diffusing intermediate, with application to the reduction of pyrazine

Heterocycles with 7 and 8π electrons. Models for flavin and pteridine intermediates and candidates for novel inorganic rings

Electrochemical Reduction of Pyrazines into Dihydropyrazines. Preparation of Dihydropyrazines

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