Oxidation-reduction reactions also

In a complexation reaction, a Lewis base donates a pair of electrons to a Lewis acid. In an oxidation-reduction reaction, also known as a redox reaction, electrons are not shared, but are transferred from one reactant to another. As a result of this electron transfer, some of the elements involved in the reaction undergo a change in oxidation state. Those species experiencing an increase in their oxidation state are oxidized, while those experiencing a decrease in their oxidation state are reduced, for example, in the following redox reaction between fe + and oxalic acid, H2C2O4, iron is reduced since its oxidation state changes from -1-3 to +2. 

Pt2(P205H2) - (d8-d8), and Mo6Clft ( )6. Two- electron oxidations of Re2Cl and Pt2(P205H2)it have been achieved by one-electron acceptor quenching of the excited complexes in the presence of Cl, followed by one-electron oxidation of the Cl -trapped mixed-valence species. Two-electron photochemical oxidation-reduction reactions also could occur by excited-state atom transfer pathways, and some encouraging preliminary observations along those lines are reported. 

In this chapter, you will be introduced to oxidation-reduction reactions, also called redox reactions. You will discover how to identify this type of reaction. You will also find out how to balance equations for a redox reaction. 

Enamines have been recognized in organic chemistry as useful synthetic reagents since the early reports from Stork s laboratory1. At almost the same time similar chemical moieties were being implicated in biochemical systems. Because of their intrinsic instability in water, the biochemical enamines exist primarily as intermediates, although, some well-known coenzymes that participate in oxidation-reduction reactions also incorporate enamine structures in one of their oxidation states. The electronic structure of enamines involves two extreme resonance contributions as shown in equation 1. 

Oxidation-reduction reactions, also known as redox reactions, are chemical processes in which electrons are transferred from one atom, ion, or molecule to another. Explosions, fires, batteries, and even our own bodies are powered by oxidation-reduction reactions. When iron rusts or colored paper bleaches in the sun, oxidation-reduction has taken place. 

Identifying oxidation-reduction reactions and their components Reduction is the gain of an electron by a molecule, atom, or ion, thus decreasing its oxidation number. Oxidation is the loss of an electron, thus increasing the oxidation number of the molecule, atom, or ion. These two processes always occur together in oxidation-reduction reactions, also called redox reactions. Electrons lost by one substance are gained by the other. 

Oxidation-reduction reactions (also called redox reactions) are those in which there is a transfer of electrons from an electron donor (the reducing agent) to an electron acceptor (the oxidizing agent). 

INTRODUCTION AND SECTION 20.1 In this chapter we have focused on electrochemistry, the branch of chemistry that relates electricity and chemical reactions. Electrochemistry involves oxidation-reduction reactions, also called redox reactions. These reactions involve a change in the oxidation state of one or more elements. In every oxidation-reduction reaction one substance is oxidized (its oxidation state, or number, increases) and one substance is reduced (its oxidation state, or number, decreases). The substance that is oxidized is referred to as a reducing agent, or reductant, because it causes the reduction of some other substance. Similarly, the substance that is reduced is referred to as an oxidizing agent, or oxidant, because it causes the oxidation of some other substance. 

Riboflavin (vitamin B2) is involved in energy metabolism from glucose and fatty adds. A component of FAD which is the prosthetic group of several enzymes used in oxidation/reduction reactions. Also a component of FMN which is in complex I of the respiratory chain... 

The oxidation-reduction reactions also proceed in the presence of the alkali metal hydroxides ... 

For the most part, the hydrosphere is a dynamic, moving system, so that it provides, perhaps, the most important variety of pathways for moving hazardous waste species in the environment. Once in the hydrosphere, hazardons waste species can nndergo a number of processes by which they are degraded, retained, and transformed. These include the common chemical processes of precipitation-dissolntion, acid-base reactions, hydrolysis, and oxidation-reduction reactions. Also inclnded is a wide variety of biochemical processes that, in most cases, reduce hazards, but in some cases, snch as the biomethylation of mercnry, they greatly increase the risks posed by hazardons wastes. 

In the case of refractory materials made of oxide ingredients, the reactions are mainly an acid-base ones in materials based on SiC and Si3N4, oxidation-reduction reactions also take place. In general, the intensity and rate of the acid-base reactions is highest when one of the substances involved is acidic and the other basic. The rate decreases when the acidity or basicity of the substances is similar. This is illustrated in the example in Table 2.5, in which shown is the dissolution rate of an acidic refractory material in a molten basic FeO. 

Oxidation-reduction reactions also can occur among organic molecules. Oxidation is often recognizable through a gain of oxygen or a loss of hydrogen. 

In qualitative analysis, we determine what substances are present in a mixture but not their quantities. An analysis that aims at identifying the cations present in a mixture is called qualitative cation analysis. Qualitative cation analysis provides us with many examples of precipitation (and dissolution) equilibria, acid-base equilibria, and oxidation-reduction reactions. Also, in the general chemistry laboratory it offers the challenge of unraveling a mystery—solving a qualitative analysis "unknown."... 

The abihty of iron to exist in two stable oxidation states, ie, the ferrous, Fe ", and ferric, Fe ", states in aqueous solutions, is important to the role of iron as a biocatalyst (79) (see Iron compounds). Although the cytochromes of the electron-transport chain contain porphyrins like hemoglobin and myoglobin, the iron ions therein are involved in oxidation—reduction reactions (78). Catalase is a tetramer containing four atoms of iron peroxidase is a monomer having one atom of iron. The iron in these enzymes also undergoes oxidation and reduction (80). 

Nicotinamide is an essential part of two important coenzymes nicotinamide adenine dinucleotide (NAD ) and nicotinamide adenine dinucleotide phosphate (NADP ) (Figure 18.19). The reduced forms of these coenzymes are NADH and NADPH. The nieotinamide eoenzymes (also known as pyridine nucleotides) are electron carriers. They play vital roles in a variety of enzyme-catalyzed oxidation-reduction reactions. (NAD is an electron acceptor in oxidative (catabolic) pathways and NADPH is an electron donor in reductive (biosynthetic) pathways.) These reactions involve direct transfer of hydride anion either to NAD(P) or from NAD(P)H. The enzymes that facilitate such... 

The formal interrelationship between the various oxoacids of sulfur can also be illustrated in a. scheme which places less emphasis on oxidation-reduction reactions but which is useful in suggesting possible alternative synthetic routes... 

N204 also forms expl mixts with incompletely halogenated hydrocarbons, NGu, carbon disulfide, etc (Ref 33). The effect of spontaneous decompn by oxidation-reduction reactions when N204 is mixed with a number of fuels (hydrazine, gasoline, liq paraffin, etc) has resulted in its extensive use in liq propint rocket engines (Refs 12, 22, 27 35)... 

There are also examples of induced complex formation, an essential step of which is always an oxidation-reduction reaction. Rich and Taube found that the rate of exchange between PtCl and Cl was considerably increased by addition of cerium(rV). In the presence of this oxidizing agent a labile complex of Pt(III) is formed, the chloride of which is easily exchangeable. Exchange of platinum between PtCl and PtClg is similarly rapid via the intermediate labile PtCIs complex formed by cerium(IV). 

When developed, this theory proved to be more general than the theory of Lewis, for it includes all the above acid-base definitions and also includes oxidation-reduction reactions. 

Silicon is generally considered to be a congener of carbon and this is also reflected in the evolution of silicon as a reducing agent for metal oxides. Silicon forms a fairly stable solid oxide silica or silicon dioxide (Si02) and also a stable gaseous oxide silicon monoxide (SiO), both of which can be useful in oxide reduction reactions. 

Apart from reactions involving the oxidative addition of oxygen, the usual oxidation-reduction reactions have also been observed for binuclear technetium clusters with multiple M-M bonds (in this case they must be accompanied by a change in the multiplicity of the Tc-Tc bonds up to their complete dissociation)11 (15,16) [11,80],... 

Since anaerobic azo dye reduction is an oxidation-reduction reaction, a liable electron donor is essential to achieve effective color removal rates. It is known that most of the bond reductions occurred during active bacterial growth [48], Therefore, anaerobic azo dye reduction is extremely depended on the type of primary electron donor. It was reported that ethanol, glucose, H2/CO2, and formate are effective electron donors contrarily, acetate and other volatile fatty acids are normally known as poor electron donors [42, 49, 50]. So far, because of the substrate itself or the microorganisms involved, with some primary substrates better color removal rates have been obtained, but with others no effective decolorization have been observed [31]. Electron donor concentration is also important to achieve... 

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