Chemical reactions redox-initiated

I) carrying-out a separate chemical reaction, e.g., in rubber latices, using traditional redox initiator technology. This Is limited to polymers which are manufactured as latices, e.g., emulsion polymers, or,... 

Catalytic regeneration of the reagent. The particular case in which the following chemical reaction is a first-order redox reaction which regenerates the initial species is described by the mechanism ... 

A second electrolysis at —0.3 V restores the initial red solution. The voltammogram (curve (e)) performed immediately after the reductive electrolysis of the redox couple of 7"+ is invariant with time. As all the pentacoordinate copper(I) species formed electrochemically are quantitatively transformed into tetracoordinate copper(I) species during the electrolysis, we can give a lower limit of 10 4 s 1 for the rate constant of the chemical reaction. The residual signal at —0.03 V simply reflects an incomplete electrolysis. 

The production of vinyl chloride monomer is only a part of PVC production. Polymerization of the monomer completes the process. Commercially, it is a batch operation by one of three methods suspension, emulsion, or bulk. In all three methods, the chemical reaction is a free radical-initiated chain reaction. Peroxides or redox systems generally are used to provide the initial free radicals. 

Although the one-electron reduction of nitrobenzene to its radical anion in dipolar aprotic solvents is a classical example of a chemically reversible redox couple, the reductions of many organic compounds are chemically irreversible. The redox behavior of /7-chlorobenzonitrile is typical of those systems in which the initial electrode product undergoes rapid, irreversible chemical reaction to give another reducible species. 

Redox Reactions. Aquatic organisms may alter the particular oxidation state of some elements in natural waters during activity. One of the most significant reactions of this type is sulfate reduction to sulfide in anoxic waters. The sulfide formed from this reaction can initiate several chemical reactions that can radically change the types and amounts of elements in solution. The classical example of this reaction is the reduction of ferric iron by sulfide. The resultant ferrous iron and other transition metals may precipitate with additional sulfide formed from further biochemically reduced sulfate. Iron reduction is often accompanied by a release of precipitated or sorbed phosphate. Gardner and Lee (21) and Lee (36) have shown that Lake Mendota surface sediments contain up to 20,000 p.p.m. of ferrous iron and a few thousand p.p.m. of sulfide. The biochemical formation of sulfide is undoubtedly important in determining the oxidation state and amounts of several elements in natural waters. 

In reaction centers, this energy drives an electron transfer reaction, which in turn initiates a series of slower chemical reactions. Energy is saved as redox energy,29,30 inducing a charge separation in a chlorophyll dimer called the special... 

Depending on the velocity of fluid flow, the thickness varies from 10 to 100 pm, and it may cover from less than 20% to more than 90% of the metal surface. Biofilms or macrofouling in seawater can cause redox reactions that initiate or accelerate corrosion. Biofilms accumulate ions, manganese and iron, in concentrations far above those in the surrounding bulk water. They can also act as a diffusion barrier. Finally, some bacteria are capable of being directly involved in the oxidation or reduction of metal ions, particularly iron and manganese. Such bacteria can shift the chemical equilibrium between Fe, Fe2+, and Fe3+, which often influences the corrosion rate. (Dexter)5... 

It appears from the description of radical ions in Sects. 1 and 3 that redox reactions can significantly change the chemical and physical properties of conjugated 7r-systems. Whether the extended jc-species are treated within molecular orbital theory or within band-structure theory, the inherent assumption in these concepts is that an electron transfer is reversible and does not promote subsequent chemical reactions. While inspection of cyclic voltammetric waves and the spectroscopic characterization of the redox species provide reliable criteria for the reversibility of an electron transfer and the maintenance of an intact (T-frame, it is generally accepted that electron transfer, depending on the nature of the substrate and on the experimental conditions, can also initiate chemical reactions under formation or cleavage of er-bonds [244, 245],... 

Another area of NEMS that is receiving tremendous attention is the mimicry of biological systems, aptly referred to as biomimetics. For instance, in the development of linear molecular muscles that undergo contraction and extension movements. Initial work in this field utilized transition metal complexes containing rotaxanes and catenanes, due to the nondestructive redox processes occurring on the metal centers.Though these complexes were actuated by a chemical reaction, the movement was in a noncoherent manner. In order to better mimic skeletal muscle movement, one has to look at the mode of motion within the most efficient molecular machines - in our human bodies. 

One particularly appealing route for effecting controlled redox reactions involves an array of surface-mediated reactions initiated by ultraviolet irradiation of suspended semiconductor particles [3-13]. Such reactions involve band-gap excitation of the semiconductor, interfacial electron transfer, and secondary dark chemical reactions of singly oxidized and reduced adsorbates. Because the semiconductor surface is restored to its original structure and oxidation level after these transformations, these photoreactions are often called photocatalytic, leaving the light-responsive photocatalyst ready to act as initiator for another cycle. The use of such photocatalysts also obviates the need to acquire expensive electrochemical equipment. 

Parallel with normal (enzymatic) four electron reduction of O2 to H2O by cytochrome oxidase, non-enzymatic one electron reduction of O2 to superoxide (O2 ) takes place in mitochondria. This parasitic chemical reaction appears to be inevitable since the initial and middle steps of the respiratory chain contain very reactive electron carriers of negative redox potential (e.g., chemically component in the one electron reduction of oxygen). 

Redox Reactions. The initial chemical reaction is oxidation of uranium dioxide. In the equimolar sodium-potassium nitrate system the product is sodium diuranate. The following reactions are believed to be the only valid oxidation reactions that are possible. 

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