Absorptionsspektren, sichtbar und ultruciolett j Freie Radikale j p-Phenylendiamine 1 Thermodynamik Die Gleichgewichte zwischen einer Reihe von am Stickstoff oder am Ring substituierten p-Phenylendiaminen (R) und ihren protonierten Formen (RH', R H i + ) werden uber die pH-Abhingigkeit der Spektren gemessen. Die Verbindungen lassen sich mil Jod rasch und ohne Nebenreaktionen in einem pH-Bereich oxidieren. in dem die Chinondiimine (T') relativ stabil sind ( 5 < pH < 6). Auf diese Weise wird das Symproportionierungsgleichgewicht der Semichinondlimine ( S + ) : K = [S+]',[R] [T'] [ H + ] spektroskopisch bei 25'C ermittelt. Die Spektren von R. RH'. S' und T' werden im Bereich zwischen 220 und 640 nm aufgenommen und die Extinktionskoeffizienten bestimmt. Die Ergebnisse werden durch Versuche mit anderen Oxidationsmitteln (Hexacyanoferrat (III), Permanganat, Ce(IV), anodische Oxidation) uberpriift. The equilibria of some N-substituted and ring-substituted p-phenylenediamines (R) with their protonated forms (RH'. RH:') are calculated from the pH-dependence of their spectra. The symproportionation constants of the semipuinonediimines (St): K = [St]2/[R] [T'] [H']are measured spectroscopically at 25 C. Iodine was used as a reagent which is able to oxidiie the p-phenylenediamines quickly and without any side reactions within the region of maximum stability of the quinonediimines (T') (5 < pH < 6). The spectra of R, S'. T' are recorded between 230 and 620 nm. In case of short living reaction products the spectra :ire calculated stepwise from extinction-time curves, using a stopped flow technique. The respective extinction coefficients are tabulated. I lic results are checked by experiments with other oxidants inoferrate(lII). permanganate. Ce(IV), and anodic current.

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of the Oxidative Silver Chloride Formation on Silver etc. Brownian motion. As a result, the tracer source broadens asymmetrically, and the maximum of the profile drifts towards the side of higher oxygen potential, relative to its original position. In combination with the measured crystal shift, it was possible to obtain the self-diffusion coefficients of the defects, Dv and DI, the correlation factors for tracer diffusion, fv andfI, and the rate constant for the exchange of oxygen between magnetite and CO/C02 mixtures. This was possible because the chemical diffusion coefficient in magnetite is identical to the self-diffusion coefficients of the dominant defects in the vacancy and interstitial regimes, i. e. the enhancement factor is identical to one.Thanks are due to Prof. H. Schmalzried for his stimulating interest and due to the Deutsche Forschungsgemeinschaft for financial support. D. Dorris acknowledges the receipt of a National Science Foundation postdoctoral fellowship. 149, 77 (1986). Chemical Kinetics J Electrocatalysis J Electrochemistry / Methods and SystemsSilver chloride was formed on a rotating silver disc electrode by oxidation with [CO"'(NH,)~C~]*+ in acid solution and subsequently reduced galvanostatically in order to determine quantitatively the amount of silver(1) formed during the chemical oxidation. By varying both the oxidation time and the concentration of the cobalt complex as well as that of chloride the kinetics of the formation of silver chloride was studied indirectly. As long as the concentration of chloride exceeds that of the cobalt(II1) complex the reaction is first order in [CO"'(NH~)~CI]~+ and almost zero order in C1-. The diffusion controlled process can be explained with the theory of mixture potential and mixture current and may therefore be regarded as a corrosion process.