33624-86-1Relevant articles and documents
Electrochemical Study of the Heterogeneously Catalysed Reaction between N,N-Dimethyl-p-phenylenediamine and Co(III)(NH3)5Cl(2+) at Monometallic and Bimetallic Surfaces of Silver and Gold
Chen, Yao-Hong,Nickel, Ulrich,Spiro, Michael
, p. 617 - 624 (1994)
The mechanism of the heterogeneously catalysed reaction between N,N-dimethyl-p-phenylenediamine and Co(III)(NH3)5Cl(2+) at silver, gold and silver-on-gold (Ag/Au) discs has been studied by means of electrochemical methods.Both the mixed (or mixture) potentials and the mixture currents were determined by recording the current-potential curves of the reactants.Silver halide, formed during the reaction, was determined by subsequent galvanostatic reduction.The reaction at silver was strongly inhibited by the formation of silver halide whereas the reaction at gold was inhibited by adsorption of the organic compounds as well as by iodide.At Ag/Au discs almost no inhibition occurred.The explanation is that the reduction of the cobalt complex takes place predominantly at the silver surface whereas the simultaneous oxidation of the p-phenylenediamine occurs on the gold.In this way the formation of inhibiting silver halide is suppressed as well as the inhibition caused by the adsorption of p-phenylenediamine.
Scanning electrochemical microscopy: Kinetics of chemical reactions following electron-transfer measured with the substrate-generation-tip-collection mode
Martin, Rachel D.,Unwin, Patrick R.
, p. 753 - 759 (2007/10/03)
The substrate-generation-tip-collection (SG-TC) mode of the scanning electrochemical microscope (SECM) is used as a new approach to investigate the kinetics of EC processes. Under the conditions of interest, a species O is generated at a macroscopic substrate (generator) electrode, with potential-step control, through the diffusion-limited electrolysis of a solution species R (E step). As O diffuses away from the generator, it undergoes a first order chemical reaction in solution (C step). A fraction of O is collected by electrolysis back to R at an externally biased ultramicroelectrode (UME), positioned directly over the substrate. This promotes the diffusional feedback of R to the substrate. Theory for the problem, relating the time-dependent tip current response to the rate constant for the C step and the tip-substrate electrode separation is developed numerically. Results of the calculations illustrate how the characteristic features of the tip current transients: peak current, peak time and post-half-peak time, depend on the kinetics of the C step and the inter-electrode separation. It is shown that both the kinetics and tip-substrate separation can be determined independently from a single transient by simply measuring the peak current and peak time. The theoretical results are validated experimentally through model studies of the oxidative deamination of N,N,-dimethyl-p-phenylenediamine (DMPPD) in aqueous solution at high pH. The effective second-order rate constant for the deamination step is in excellent agreement with values measured by alternative methods.
Mechanism and Kinetics of the Photocatalyzed Oxidation of p-Phenylenediamines by Peroxydisulfate in the Presence of Tri-2,2'-bipyridylylruthenium(II)
Nickel, Ulrich,Chen, Yao-Hong,Schneider, Siegfried,Silva, Maria I.,Burrows, Hugh D.,Formosinho, Sebastiao J.
, p. 2883 - 2888 (2007/10/02)
The autocatalytic oxidation of p-phenylenediamines with peroxydisulfate can be strongly enhanced by irradiation in the presence of tri-2.2'-bipyridylylruthenium(II).Ru(bpy)32+ acts as photosensitizer and photocatalyst.First, Ru(bpy)33+ is formed by quenching excited Ru*(bpy)32+ with S2O82-.Then the ruthenium(III) complex oxidizes p-phenylenediamine.The resulting Ru(bpy)32+ can start the cycle again.The photocatalytic oxidation of N,N-diethyl-p-phenylenediamine as well as the dark reactions were studied with stopped-flow techniques.The mechanism of this complex reaction is discussed in detail.
INVESTIGATION OF ELECTRON TRANSFER REACTIONS BETWEEN AROMATIC AND QUINOID SYSTEMS.
Goez,Jaenicke,Nickel
, p. 459 - 467 (2007/10/02)
A classical organic redox reaction is the conversion of an aromatic compound from its reduced form R to a semioxidized state S, and further to a totally oxidized (quinoid) species T. Complex redox systems are present in a reaction of quinoid and aromatic forms derived from different parent compounds. In this case, the exchange of one or two electrons in one step between T and R can be distinguished experimentally. These reactions were investigated in a stopped-flow apparatus with optical detection. In the system N,N,N prime ,N prime -tetramethyl-para-phenylene-diamine/N,N-dimethyl-para- phenylenediamine the rate constants for all elementary reactions have been determined. Protonated, and unprotonated R were found to be reactive.
Mechanismus der quasi-homogenen Oxidation von p-Phenylendiaminen mit Silbernitrat
Nickel, U.,Ruehl, N.,Zhou, B. M.
, p. 33 - 52 (2007/10/02)
The redox reaction between p-phenylenediamines and silver nitrate in aqueous acid solution was observed optically in a double wavelength photometer.In presence of a nobel metal plate or larger clusters of silver, production of p-semiquinonediimines respective silver starts immediately, whereas without clusters present at the beginning of the reaction the maximum reaction rate is attained only after a certain induction period.The length of this induction period depends on the pH and the concentration of p-phenylenediamine, but not on the silver ion concentration.It is not the number of the clusters that influences the induction period, but their size.The rate of the main reaction, however, is proportional to the number of the clusters formed.In dilute solutions the main reaction is of first order concerning both of the two reactants, in concentrated solution, however, it is of smaller order. - Keywords: Oxidation / Cluster / p-Phenylenediamines / Silver / Photographic development
1- und 2-Elektronenschritte bei der Oxidation substituierter Paraphenylendiamine mit verschiedenen Oxidationsmitteln. II. Reaktionen mit Hexacyanoferrat
Nickel, Ulrich,Jaenicke, Walther
, p. 695 - 701 (2007/10/02)
The oxidation kinetics of several N- and ring-alkylated p-phenylenediamines with hexacyanoferrate(III) (F3) was studied in the pH-range 2,5-9 by means of a multimixing stopped flow technique which is described in detail.The p-phenylene diamine-derivatives (R) are oxidized via reversible one-electron steps to the semiquinone diimine radical S (rate constants k1, k-1) and the quinone diimine T (rate constants k2, k-2). - k1 and k-1 could be measured directly for all compounds, k2 and k-2 for two derivatives. - Only the unprotonated species of R, S, T, F3 are reactive.The reduction is possible by the unprotonated Fe(CN)64- (F2) and by its protonated form F2H.The complexes of F2 with alkali ions are inactive.In this way the respective association constants could be calculated.The kinetics of the reaction was compared with the thermodynamics, represented by potential-pH-diagrams. - The activation parameters of the reaction of p-phenylene diamine-derivatives with F3, F2 and also with iodine were measured.The activation energies of the second step (k2, k-2) are negligible. - Both oxidants attack the alkylated aminogroup of the p-phenylene diamine derivatives.The radical cation is deprotonated before it is oxidized.
Activation parameters and mechanism of the deamination of N-substituted quinone monoimines and di-imines
Nickel, Ulrich,Jaenicke, Walther
, p. 1601 - 1605 (2007/10/02)
The deamination rates of six N-substituted quinone monoimines in aqueous solution were measured by a stopped-flow method at temperatures between 278 and 323 K in the pH range between 1 and 9 using u.v. spectra. The observed rate constants are given by k = k′[H2O] + k″[OH-]; k′ and k″ differ by 12 orders of magnitude. The enthalpies of activation of k′ and k″ are nearly equal; the entropies of activation are strongly negative for k′ and strongly positive for k″. The activation parameters of the acid and alkaline deamination of N-substituted quinone di-imines were also measured. With regard to the activation entropies similar results were found as for the quinone monoimines. For all deaminations a common mechanism with a preceding solvation equilibrium is proposed.
