Metal oxide redox reaction

Catalyst Selection. The low resin viscosity and ambient temperature cure systems developed from peroxides have faciUtated the expansion of polyester resins on a commercial scale, using relatively simple fabrication techniques in open molds at ambient temperatures. The dominant catalyst systems used for ambient fabrication processes are based on metal (redox) promoters used in combination with hydroperoxides and peroxides commonly found in commercial MEKP and related perketones (13). Promoters such as styrene-soluble cobalt octoate undergo controlled reduction—oxidation (redox) reactions with MEKP that generate peroxy free radicals to initiate a controlled cross-linking reaction. 

Joining two heteroatoms to a ring by radical combination is not presently a common route to heterocycles. It might become more important if the art of metal-catalyzed redox reactions keeps advancing at the present pace. Current examples are the conversion of 1,5-dithiols to 1,2-dithiepanes by oxidants such as FeCla, and the oxidation of 1,3-propane-bis-hydrazines to 1,2,3,4-tetrazepines (Sections 5.18.4.1 and 5.18.10.1). 

Seven chemical reactions were identified from the chemistry syllabus. These chemical reactions were selected because they were frequently encountered during the 2-year chemistiy course and based on their importance in understanding concepts associated with three topics, namely, acids, bases and salts, metal reactivity series and inorganic chemistry qualitative analysis. The seven types of chemical reactions were combustion of reactive metals in air, chemical reactions between dilute acids and reactive metals, neutralisation reactions between strong acids and strong alkalis, neutralisation reactions between dilute acids and metal oxides, chemical reactions between dilute acids and metal carbonates, ionic precipitation reactions and metal ion displacement reactions. Although two of the chemical reactions involved oxidation and reduction, it was decided not to include the concept of redox in this study as students had only recently been introduced to ion-electron... 

See other METAL NITRATES, OXIDANTS, REDOX REACTIONS... 

For metal carbonyls, redox reactions (see Redox Properties Processes) have been studied in a smaller number of cases, relative to substitution reactions. The simplicity of binary metal carbonyls and the possibility for these compounds to undergo electron transfers make them excellent substrates for studying redox processes in nonaqueous media. Convenient organometallic one-electron oxidants or reductants (number of valence electrons in parenthesis) are " V(CO)e... 

Figure 2 shows this for oxidation of various substituted phenanthroline Fe(II) complexes by Ce(IV). An average rate constant of 2 x 103 M 1 s -1 was found for the phenanthroline-Fe(II)-FE(III) exchanges by this approach (Dulz and Sutin, 1963) this compares with a value of 4 M i s-1 for the free ions. Many studies have verified the Marcus relationship for metal ion redox reactions, and large deviations are assumed to indicate that the reaction occurs by an inner-sphere mechanism. (Note An outer-sphere mechanism can be inferred if the redox reaction is faster than the rates of ligand exchange for the metal ions.)... 

Figure 19. Transformations of Fe(II, III) at an oxic anoxic boundary in the water or sediment column (modified from Davidson, 1985). Peaks in the concentration of solid Fe(III) (hydr)oxides and of dissolved Fe II) are observed at locations of maximum Fe(III) and Fe(II) production, respectively. The combination of ligands and Fe(ll) produced in underlying anoxic regions are most efficient in dissolving Fe(III) (hydr)oxides. Redox reactions of iron—oxidation accompanied by precipitation, reduction accompanied by dissolution—constitute an important cycle at the oxic-anoxic boundary which is often coupled with transformations (adsorption and desorption) or reactive elements such as heavy metals, metalloids, and phosphates.

The chemical reactions that take place in corrosion processes are reduction-oxidation (redox) reactions. Such reactions require a species of material that is oxidized (the metal), and another that is reduced (the oxidizing agent). Thus the complete reaction can be divided into two partial reactions one, oxidation the other, reduction. In oxidation, the metal loses electrons. The zone in which this happens is known as the anode. In the rednction reaction, the oxidizing agent gains the electrons that have been shed by the metal, and the zone in which this happens is the cathode. 

The first type of catalytic activity is better known and is illustrated by numerous examples, which include reactions in which the metal ion changes valence and reactions in which no change in the oxidation state of the metal takes place. Examples of metal-catalyzed redox reactions are the oxidation of oxalate through the formation of the 1 1 Mn(II) oxalate chelate compound, described by Taube (1), and the oxidation of ascorbic acid 2, 3) by chelation with the Cu(II) ion ... 

Antimony Electrode. The antimony electrode is perhaps the best representative of a whole class of metal/metal-oxide redox electrodes that respond to pH. The potential is probably developed as a result of an oxidation-reduction reaction involving antimony and a skin of antimony(III) oxide which forms on the surface of the metal ... 

Compared to sihca-based networks, nonsiliceous ordered mesoporous materials have attracted less attention, due to the relative difficulty to apply the principles employed to create mesoporous silica to nonsilica compositions. Other framework compositions are much more sensitive than silica to redox reactions, hydrolysis, or phase transformations. The reactivity of the inorganic precursors is much more difficult to control in the case of transition metal oxides, the reaction kinetics being much faster. Also, crystalline nonsiliceous frameworks are less prone to adapt the curvature of micellar aggregates, whereas the amorphous nature of silica allows for certain flexibility. 

The electrochemical behavior of water-soluble yS-pyrrole brominated porphyrins is more complex than that of their water insoluble analogs. The metal-centered redox reactions of (TMPyP)Mn and (TMPyPBrg)Mn are reversible while the majority of porphyrin ring-centered redox reactions of the free-base, Cu, and Mn derivatives of TMPyPBrs are irreversible The metal-centered oxidation of (TMPyPBr8)Mn is anodically shifted by 420 mV compared to 1/2 for the corresponding reaction of (TMPyP)Mn (Table 9.2). The metal-centered... 

Redox Reactions. For many electrochemists the paramount concern of their discipline is the reduction and oxidation (redox) reaction that occurs in electrochemical cells, batteries, and many other devices and applications. Reduction takes place when an element or radical (an ionic group) gains electrons, such as when a double positive copper ion in solution gains two electrons to form metallic copper. Oxidation takes place when an element or radical loses electrons, such as when a zinc electrode loses two electrons to form a doubly positive zinc ion in solution. In electrochemical research and applications the sites of oxidation and reduction are spatially separated. The electrons produced by chemical processes can be forced to flow through a wire, and this... 

A number of metals undergo redox reactions in air. For some metals, like aluminum or tin, the oxide formed is structurally stable and forms a protective layer over the underlying metal, preventing further oxidation. For other metals, most notably iron, the metal oxide formed is crumbly and flakes off to expose new metal to further oxidation. The oxidation of iron can be prevented by using a coating that keeps the iron out of contact with air and moisture or by attaching a more active metal to the iron (14.7). 

Many of the reactions involving transition metals are redox reactions (Chapter 9) involving electron transfer. These can be described by half-equations and by ionic equations formed from the combination of two half-equations (with equal numbers of electrons). Disproportionation is a redox reaction involving the simultaneous increase and decrease in oxidation state of the same element. 

The role of Cu as an essential trace element has focused attention on possible roles for copper chelation of biologically active ligands, with subsequent interference of normal transport and distribution, as well as the role of the metal in redox reactions due to the accessible oxidation states of (I) and (II). Similarly, the physiological response of copper levels in disease conditions [50] and the overall role of trace metals in health and disease [51, 52] are relevant and of considerable importance. The increase in serum copper content in infections, arthritic diseases, and certain neoplasms is well documented and, in fact, the subsequent decrease in level upon treatment has been used successfully as an indicator of cancer remission [50]. Copper complexes may be effective in therapy due in part to their ability to mimic this physiological response of elevated copper [53] and, clearly, the interplay of introduced copper with pre-existent bound copper and effects on copper—protein mediated processes will affect the ultimate biological fate of the complex. Likewise, while the excess accumulation of free Cu, and indeed Fe and Zn, caused by malfunction or absence of normal metabolic pathways is extremely damaging to the body, the controlled release of such metals may be beneficially cytotoxic. The widespread pharmacological effects of copper complexes have been briefly reviewed [54]. 

These reactions lead to the formation (transformation) of surface carboxylate and carbonate-like species and to the two electron reduction of the (electrons that can reduce) transition metal ions located in nearest-neighbor positions. On oxidic surfaces that do not contain transition metal ions, redox reactions accompanied by electron transfer from the surface to the adsorbed molecule (or vice versa) are much less probable. 

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