Redox systems mechanism

Elving, P. J., Bresnahan, W. T, Moiroux, J., Samec, Z., NAD/NADH as a Model Redox System Mechanism, Mediation, Modification by the Environment , Bioelectrochem. Bioeng. 9 (1982) 365-378. 

Hydrogen peroxide may react directiy or after it has first ionized or dissociated into free radicals. Often, the reaction mechanism is extremely complex and may involve catalysis or be dependent on the environment. Enhancement of the relatively mild oxidizing action of hydrogen peroxide is accompHshed in the presence of certain metal catalysts (4). The redox system Fe(II)—Fe(III) is the most widely used catalyst, which, in combination with hydrogen peroxide, is known as Fenton s reagent (5). 

Organic peroxide-aromatic tertiary amine system is a well-known organic redox system 1]. The typical examples are benzoyl peroxide(BPO)-N,N-dimethylani-line(DMA) and BPO-DMT(N,N-dimethyl-p-toluidine) systems. The binary initiation system has been used in vinyl polymerization in dental acrylic resins and composite resins [2] and in bone cement [3]. Many papers have reported the initiation reaction of these systems for several decades, but the initiation mechanism is still not unified and in controversy [4,5]. Another kind of organic redox system consists of organic hydroperoxide and an aromatic tertiary amine system such as cumene hydroperoxide(CHP)-DMT is used in anaerobic adhesives [6]. Much less attention has been paid to this redox system and its initiation mechanism. A water-soluble peroxide such as persulfate and amine systems have been used in industrial aqueous solution and emulsion polymerization [7-10], yet the initiation mechanism has not been proposed in detail until recently [5]. In order to clarify the structural effect of peroxides and amines including functional monomers containing an amino group, a polymerizable amine, on the redox-initiated polymerization of vinyl monomers and its initiation mechanism, a series of studies have been carried out in our laboratory. 

In conjunction with Ag, CO , and acid, peroxydiphosphate forms an efficient redox system for polymerization of vinyl monomers. H2P208 is assumed to be an active species of peroxydiphosphate. The initiating species are OH and HP04 and the termination is considered to be exclusively by mutual method. The following mechanism has been proposed for the redox reaction [46]. 

Based on the ESR studies and the end group analysis, the initiation mechanism of Ce(IV) ion redox systems is proposed as ... 

For example, when the redox system is perturbed by a following chemical reaction, that is, an EC mechanism,... 

Although sulfonyl chlorides add readily to unactivated olefins, with vinylic monomers telomeric and/or polymeric products were observed. This difficulty has been overcome by carrying out the addition in the presence of catalytic amounts of CuCl2, so as to provide a general and convenient synthesis of /5-chlorosulfones (Asscher-Vofsi reaction)63. For the copper-catalyzed system a redox-transfer mechanism has been suggested in which the... 

The chemical mechanism rests on the effect of intervening redox systems (see Section 13.6). Here intermediate reactants such as species on a cathode surface, species on an anode surface, or reducing and oxidizing agents in the solution layer next to the electrode are first produced electrochemicaUy from solution components. The further interaction of these reactants with the organic substance is purely chemical in character, for example, following a reaction... 

Electrochemistry, organic, structure and mechanism in, 12, 1 Electrode processes, physical parameters for the control of, 10, 155 Electron donor-acceptor complexes, electron transfer in the thermal and photochemical activation of, in organic and organometallic reactions. 29, 185 Electron spin resonance, identification of organic free radicals, 1, 284 Electron spin resonance, studies of short-lived organic radicals, 5, 23 Electron storage and transfer in organic redox systems with multiple electrophores, 28, 1 Electron transfer, 35, 117... 

Redox systems, organic, with multiple electrophores, electron storage and transfer in, 28, 1 Reduction.of C—X and X—X bonds (X = 0, S), kinetics and mechanism of the dissociative, 36, 85... 

Thus there is little doubt that the hydroxyl radical, if generated by an unambiguous method such as pulse radiolysis, can be trapped by PBN or DMPO, even if the former has several deficiencies, among them low trapping efficiency and short half-life of HO-PBN. The problem in hydroxyl radical trapping thus rests with the possible competition from the nucleophilic addition-oxidation mechanism, as exemplified in reaction (69) for DMPO and Ox-Red as a general one-electron redox system, or the inverted spin trapping mechanism (70). The treatment to follow will mostly be limited to DMPO. 

Lest we become too complacent in our assessment of the marked progress that has been made in understanding inorganic reaction mechanisms, we should consider the simple and very important redox systems ... 

It is important to point out that not all redox systems will exhibit electrocatalytic activity when probed on high-density edge CNT electrodes or edge pyrolytic graphite. Such phenomenon depends on the particular mechanism of the redox system ]2]. It is important to recall that among the redox species there are some of them whose... 

To summarize, one can say that the electrochemical performance of CNT electrodes is correlated to the DOS of the CNT electrode with energies close to the redox formal potential of the solution species. The electron transfer and adsorption reactivity of CNT electrodes is remarkably dependent on the density of edge sites/defects that are the more reactive sites for that process, increasing considerably the electron-transfer rate. Additionally, surface oxygen functionalities can exert a big influence on the electrode kinetics. However, not all redox systems respond in the same way to the surface characteristics or can have electrocatalytical activity. This is very dependent on their own redox mechanism. Moreover, the high surface area and the nanometer size are the key factors in the electrochemical performance of the carbon nanotubes. 

The action of one-electron redox systems is readily understandable in the context of inner- and outer-sphere mechanisms, whereas two-electron redox systems require additional considerations. First, if a double one-electron transfer is possible from an organic substrate to the same metal ion, does it mean that the same molecule of an organic donor provides these two electrons, or do two molecules of the substrate act as one-electron donors ... 

Up to the present time, use has been made almost entirely of dimethacrylates which are polymerized by free radical mechanisms to yield crosslinked products (81. Polymerization is initiated by redox systems, such as benzoyl peroxlde/aromatic amine, and by... 

Again it seems not necessary to discuss the considerations of the chemical versus electrochemical reaction mechanism. It is clear from the extremely negative standard potential of silicon, from Eqs. (2) and (6), that the Si electrode is in all aqueous solutions a dual redox system, characterized by its OCP, which is the resultant of an anodic Si dissolution current and a simultaneous reduction of oxidizing species in solution. The oxidation of silicon gives four electrons that are consumed in the reduction reaction. Experimental results show clearly that the steady value of the OCP is narrowly dependent on the redox potential of the solution components. In solutions containing only HF, alternatively alkaline species, the oxidizing component is simply the proton H+ or the H2O molecule respectively. 

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