Other Types of Redox Reactions

Several of the reaction type.s that you have already encountered are also redox reactions. 

Combination reactions such as the formation of ammonia from its constituent elements can involve o.vidation and reduction. 

Decomposition can also be a redox reaction, as illustrated by the following examples  

The decomposition of hydrogen peroxide, shown in the preceding equation, is an example of a disproportionation reaction, in which one element undergoes both oxidation and reduction. In the ca.se of H2O2, the oxidation number of O is initially — 1. In the products of the decomposition, O has an oxidation number of —2 in H2O and of 0 in O2. 

2 What species is the reducing agent in the following equation  

1 Determine the oxidation number of sulfur in each of the following species H2S, HSO J, SCI2, and 85. 

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The other type of redox reaction that can occur is the reverse of oxidation, in which an electroactive species receives ( acquires , takes up or gets ) an electron in a reduction reaction ... 

Balancing other types of redox reactions can be more complicated and require more work. Fortunately, there is a set method for solving the complex balancing of redox reactions. These steps must be learned if you are to be successful in balancing a complex redox reaction. We will first consider the reaction As + C1031 —> H3As03 + HC10. 

The viologens are alkyl derivatives of the 4,4 -dipyridylium dication. The one- or two-electron reduction leads to a radical cation or a diamagnetic product, respectively [95]. This type of redox reaction has a good reversibility. In the phthalocyanines (PCs) and other 4-chelates, the nitrogen is also a component of the ring system. Donor-type Li" " insertion compounds of metal-free phthalocyanines were formed reversibly in LiC104/PC with up to six cations [96]. At the anode, copper phthalo-cyanine (CuPC) inserted reversibly y — 0.42 CIO4 anions/mol [97]. For copper tetraphenylporphyrin, y = 0.65 was found [98] (cf. Table 4). Composites of these... 

The nature of the ligand donor atom and the stereochemistry at the metal ion can have a profound effect on the redox potential of redox-active metal ions. What, we may ask, is the redox potential In the sense that they involve group transfer, redox reactions (more correctly oxidation—reduction reactions) are like other types of chemical reactions. Whereas, for example, in hydrolytic reactions a functional group is transferred to water, in oxidation-reduction reactions, electrons are transferred from electron donors (reductants) to electron acceptors (oxidants). Thus, in the reaction... 

On the other hand, fluorination of alkyl- and aryldialkylaminochloro-phosphines, RPC1(NR2), with antimony (or arsenic) trifluoride under similar conditions to reaction (2) affords only the pentavalent fluoro-phosphorane RPFg(NR2) 288, 290) via the same type of redox reaction discussed previously in Section III,A for alkyl- and arylhalophosphines. 

Organic compounds such as aldehydes, alcohols, aliphatic, and aromatic 1,2-diols, nitrocompounds, and sugars have been determined by using two types of redox reactions. The analyte may be reduced with a metal ion in solution and the metal precipitate formed dissolved in nitric acid, and determined by AAS. Alternatively, the unreduced metal may be determined. The other type of method is based on the oxidation of the analyte with periodic acid or potassium permanganate, and addition of metal ion solution. The added metal ion forms, with the oxidized form of the analyte, either an insoluble compound or an uncharged metal complex which can be extracted into the organic phase. The atomic absorption of the metal ion is determined after dissolution of the precipitate or solvent extraction. 

Balancing a redox reaction is often more challenging than balancing other types of reactions, because we must balance both electrons and elements. Perhaps the simplest way to balance a redox reaction is by the half-reaction method, which consists of the following steps. 

Type B (redox) reactions are more complex. Sulfide in this reaction is converted into some other oxidation state of sulfur. For example, sulfides can be converted to a zero oxidation state of elemental sulfur by oxygen ... 

When we mix two solutions the result is often simply a new solution that contains both solutes. However, in some cases the solutes can react with each other. For instance, when we mix a colorless aqueous solution of silver nitrate with a clear yellow aqueous solution of potassium chromate, a red solid forms, indicating that a chemical reaction has occurred (Fig. 1.1). This section and the next two introduce three of the main types of chemical reactions precipitation reactions, acid-base reactions, and redox reactions, all of which are discussed in more depth in later chapters. (The fourth type of reaction discussed in this text, Lewis acid-base reactions, is introduced in Section 10.2.) Because many chemical reactions take place in solution, particularly in water, in this section we begin by considering the nature of aqueous solutions. 

Numerous types of chemical reactions pose potential hazards. Literature and incident data highlight the hazards of common industrial reactions, such as polymerization, decomposition, acid-base, oxidation-reduction (redox), and reactions with water. Polymerization and decomposition can be classified as self-reactions because they often involve just one chemical substance. However, other... 

In both cases, the adopted symbolism only gives a picture of the overall process. In fact, from a mechanistic viewpoint, the redox reactions (as with any other type of reaction) proceed by a series of intermediate steps involving phenomena such as ... 

Roles that are normally associated with metals as Lewis acids and as redox agents [4,5], can be emulated by organic compounds. This review will introduce the reader to the research field of Lewis acid organocatalysts. This field, compared to other types of organocatalysts, which are highlighted in the other chapters of this volume, is still limited. The number of asymmetric catalyzed examples is small, and the obtained enantiomeric excess is sometimes low. Therefore, this review will also cover a number of reactions promoted by achiral catalysts. Nevertheless, due to the broad variety of possible reactions, which are catalyzed by Lewis acids, this research field possesses a large potential. 

The topic of metal- and metalloid-containing polymers can be divided by many means. Here, the topic will be divided according to the type of reaction employed to incorporate the inorganic atom into the polymer chain. While many other types of reactions have been employed to produce metal- and metalloid-containing polymers including redox, coupling,... 

There are, of course, many other types of reaction that can profitably be studied in solvents other than water. Redox reactions will be discussed in Section 9.4, where we will look at analogies between reduction/ oxidation and acid/base processes, and the use of non-aqueous solvents as media suitable for the use of strongly oxidising or reducing agents. 

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