Redox reactions oxidizing metals

Redox reactions of metals with acids are described in Chapter 4. Oxidation of the metal generates hydrogen gas and an aqueous solution of ions. Suppose that 3.50 g of magnesium metal is dropped into 0.150 L of 6.00 M HCl in a 5.00-L cylinder at 25.0 °C whose initial gas pressure is 1.00 atm, and the cylinder is immediately sealed. Find the final partial pressure of hydrogen, the total pressure in the container, and the concentrations of all ions in solution. 

Redox reactions with metal porphyrins (MPs) as photocatalysts. A spectacular example here is the reaction that couples upon illumination with the sunlight, methanol oxidation to formaldehyde with the formation of hydrogen peroxide in be nzene-methanol mixture (90 10)... 

Equilibrium considerations other than those of binding are those of oxidation/reduction potentials to which we drew attention in Section 1.14 considering the elements in the sea. Inside cells certain oxidation/reductions also equilibrate rapidly, especially those of transition metal ions with thiols and -S-S- bonds, while most non-metal oxidation/reduction changes between C/H/N/O compounds are slow and kinetically controlled (see Chapter 2). In the case of fast redox reactions oxidation/reduction potentials are fixed constants. 

Fuhrhop, J.-H. The Oxidation States and Reversible Redox Reactions of Metal-loporphyrins. Vol. 18, pp. 1—67. 

We may predict many redox reactions of metals by using an activity series. An activity series lists reactions showing how various metals and hydrogen oxidize in aqueous solution. Elements at the top of the series are more reactive (active) than elements below. A reaction occurs when an element interacts with a cation of an element lower in the series. The more active elements have a stronger tendency to oxidize than the less active elements. The less active elements tend to reduce instead of oxidize. The reduction reactions are the reverse of the oxidation reactions given in the activity series table, Table 4-1. This is an abbreviated table. Refer to your textbook for a more complete table. 

Since many of the transformations undergone by metabolites involve changes in oxidation state, it is understandable that cofactors have been developed to act as electron acceptors/ donors. One of the most important is that based on NAD/NADP. NAD+ can accept what is essentially two electrons and a proton (a hydride ion) from a substrate such as ethanol in a reaction catalysed by alcohol dehydrogenase, to give the oxidized product, acetaldehyde and the reduced cofactor NADH plus a proton (Figure 5.2). Whereas redox reactions on metal centres usually involve only electron transfers, many oxidation/reduction reactions in intermediary metabolism, as in the case above, involve not only electron transfer but... 

In this section, you learned the half-reaction method for balancing equations for redox reactions. You investigated the redox reactions of metals with acids, and the combustion of two hydrocarbons. After applying the half-reaction method in the following review problems, you will learn a different method in section 10.4. This method will make greater use of oxidation numbers. 

Redox reactions of metal alkoxides Oxidation of organometallic compounds (method 7)... 

In this section, cleavage reactions will be discussed from the point of view of the metal complex. To cleave DNA, an oxidant must be generated. Numerous redox reactions of metal complexes have been used to generate appropriate DNA oxidants (4). The simplest comes from Fenton chemistry, in which peroxide is used to generate hydroxy radicals from Fe2+ (3) ... 

Volumes 26 and 27 are both concerned with reactions occurring at electrodes arising through the passage of current. They provide an introduction to the study of electrode kinetics. The basic ideas and experimental methodology are presented in Volume 26, whilst Volume 27 deals with reactions at particular types of electrode. Thus, Chapter 1 of the present volume deals with redox reactions at metal electrodes, Chapter 2 with semiconducting electrodes and Chapter 3 with reactions at metal oxide electrodes. Both theoretical aspects and experimental results are covered. 

Redox reactions involving metal ions occur by two types of mechanisms inner-sphere and outer-sphere electron transfer. In inner-sphere mechanisms, the oxidant and reductant approach intimately and share a common primary hy-... 

Whereas redox reactions on metal centres usually only involve electron transfers, many oxidation/reduction reactions in intermediary metabolism, as in the case above, involve not only electron transfer, but hydrogen transfer as well — hence the frequently used denomination dehydrogenase . Note that most of these dehydrogenase reactions are reversible. Redox reactions in biosynthetic pathways usually use NADPH as their source of electrons. In addition to NAD and NADP+, which intervene in redox reactions involving oxygen functions, other cofactors like riboflavin (in the form of flavin mononucleotide, FMN, and flavin adenine dinucleotide, FAD) (Figure 5.3) participate in the conversion of [—CH2—CH2— to —CH=CH—], as well as in electron transfer chains. In addition, a number of other redox factors are found, e.g., lipoate in a-ketoacid dehydrogenases, and ubiquinone and its derivatives, in electron transfer chains. 

The existence of hydrogen-oxide bridging in hydroxoaqua ions in the crystalline state, raised the possibility that these hydrogen-oxide bridged species persist in aqueous solution. Primary results obtained by Three Phase Vapor Tensiometry (TPVT), confirm the existence of binuclear hydroxoaqua ions in concentrated solutions. The existence of these ions throws new-light on the mechanism of some substitution and redox reactions of metal ions. 

The ease of the redox reactions of metal cations in the framework suggests that metal cations can be easily substituted into the framework of aluminophosphate molecular sieves. The changes in the coordination of Al ions in the framework by the adsorption of some gases such as H2 have also been reported by some researchers. This has not been observed for aluminosilicate zeolites. Although no investigation has been performed on the influence of the framework environment on the catalytic properties of aluminophosphate molecular sieves, there is a possibility that the restricted redox properties of metal cations in the framework catalyze reactions which proceed over free metal cations, as with oxides or ion-exchanged zeolites. 

Redox reactions. Oxidizing or reducing substances may be determined indirectly by means of the metal ions that can be oxidized or reduced by the... 

This chapter reviews the literature published during the period July 1988 to December 1989. In keeping with previous practice, some selectivity has been exercised. Also, the chapter includes redox reactions between metallic and non-metallic species, regardless of whether or not the nonmetallic component is coordinated to the metal center during electron transfer. The format is such that reactions have been grouped according to their central or reactive nonmetallic element. Some topics have received scant coverage, particularly if they are dealt with elsewhere in this volume. Thus, oxidative addition/reductive elimination reactions are not within the scope of this section. 

Many metals are oxidized by O2, acids, and salts. The redox reactions between metals and acids as well as those between metals and salts are called displacement reactions. The products of these displacement reactions are always an element (H2 or a metal) and a salt Comparing such reactions allows us to rank metals according to their ease of oxidation. A list of metals arranged in order of decreasing ease of oxidation is called an activity series. Any metal on the list can be oxidized by ions of metals (or H ) below it in the series. 

Carbon dioxide may also be activated via direct redox reaction with metals— possibly involving metal-carbon bonds, and necessarily involving low oxidation... 

The nature and properties of metal complexes have been the subject of important research for many years and continue to intrigue some of the world s best chemists. One of the early Nobel prizes was awarded to Alfred Werner in 1913 for developing the basic concepts of coordination chemistry. The 1983 Nobel prize in chemistry was awarded to Henry Taube of Stanford University for his pioneering research on the mechanisms of inorganic oxidation-reduction reactions. He related rates of both substitution and redox reactions of metal complexes to the electronic structures of the metals, and made extensive experimental studies to test and support these relationships. His contributions are the basis for several sections in Chapter 6 and his concept of inner- and outer-sphere electron transfer is used by scientists worldwide. 

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