Contributed in honour of the 70th Birthday of Professor L. Horner.The rate constant of the heterogeneous electron transfer from a platinum electrode to aromatic disulfides is low, whereas the homogeneous electron transfer from suitable aromatic anion radicals is much faster. Anion radicals of such aromatic compounds can thus be generated electrochemically at potentials more negative than the normal standard reduction potential of the disulfide, but less negative than its observed reduction potential. An attempt is made to estimate E, of the aromatic disulfides from the rates of the homogeneous electron transfer from a number of donors and the reversible redox potential of these donors. Elektrochemisch induzierte, homogene Elektroneniibertragung auf aromatische DisulfideDie Geschwindigkeitskonstante der heterogenen Elektroneniibertragung von einer Platinelektrode auf aromatische Disulfide ist klein, wahrend die homogene Elektroneniibertragung von geeigneten aromatischen Radikalanionen wesentlich rascher stattfindet . Derartige Radikalanionen von aromatischen Verbindungen kBnnen elektrochemisch bei Potentialen erhalten werden, die zwar negativer als das Standard-Reduktionspotential des Disulfids, aber nicht negativer als die beobachteten Reduktionspotentiale der Disulfide sind. Es wird der Versuch unternommen, Eo-Werte von aromatischen Disulfiden aus den Geschwindigkeiten homogener Elektroneniibertragungen durch einige Donoren und den reversiblen Redoxpotentialen dieser Donoren zu ermitteln.Electrochemical measurements of organic sulfur compounds at mercury electrodes are in many cases complicated by the formation of mercury compounds before orland during the electrochemical reaction'). The polarographic half-wave potentials for the reduction of disulfides and oxidation of mercaptans are influenced by reactions with mercury and do not allow the measurement of the redox potentials of these systems by this method.Cyclic voltammetric peak potentials (E,) of aromatic disulfides depend strongly on the electrode material as illustrated in Figure 1, showing cyclic voltammetric (CV)curves of bis(4chlorophenyl) disulfide in N,N-dimethylformamide/tetrabutylammonium iodide (DMF/TBAI) at vitreous carbon, platinum, and copper electrodes. The systems are irreversible at all sweep rates ( u ) accessible at present ( v < 103V s-l) even at vitreous carbon which has the highest heterogeneous rate constant of all three Liebigs Ann. Chem. 1981
Die heterogene Elektronenübertragung von einer Pt‐Elektrode auf Diphenyldisulfide (Substituenten symmetrisch an beiden Phenylringen:‐H, p‐NHz , o‐Me, p‐Cl, o‐CO‐OEt) verläuft langsam, der homogene Elektronentransfer von geeigneten aromatischen Radikalanionen ( ;z.B. der Verbindungen Perylen, Chinoxalin , Acridin, Azobenzol, Fluoren) auf die Diphenyldisulfide dagegen wesentlich schneller.
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