Oxidation and/or reduction

The oxidation and/or reduction reactions yield polymeric systems having an extended Jt-electron system along the chain. Doping to the conducting state, in the instance of polyacetylene by exposnre to iodine vapor (p-doping, oxidizing). 

Electrochemical processes are particularly well suited for the manufacture of fine chemicals in view of their high sjjecificity (almost comparable to that offered by enzymes), the smaller number of steps required, adoption of milder conditions, lack of scale-up problems, avoidance of effluents, etc. The ease with which oxidation and/or reduction can be carried out with the practically mass-free clean electrons makes electrochemical processes well suited for such jobs, including paired synthesis in effect, we use electricity as a reagent . Consider a standard chemical oxidant like manganic or chromic sulphate. Here, a stoichiometric amount of the reduced salt will be formed the disposal of which can be a serious problem. If we adopt an electrochemical process, then the reduced salt is converted into the desired oxidized salt. 

The ability of thioether macrocyclic complexes (and especially those of [9]aneS3) to support multi-redox behaviour at the coordinated metal centre is particularly notable. This allows a series of reversible stepwise one-electron oxidation and/or reduction processes, and stabilization of highly unusual transition metal oxidation states e.g. mononuclear [Pd([9]aneS3)2]2+/3+/4+,149 [Au([9]aneS3)2]+/2+/3+,150 [Ni([9]aneS3)2]2+/3+,151 and [Rh([9]aneS3)2]+/2+/3+.152 It appears to be the ability of the crown thioethers to readily adjust their... 

Light generation in ECL processes is realized in electron transfer reactions involving strong oxidant and reductant. Principally, both reactants can be prepared in the common chemical way if reactive intermediates are stable enough,49-51 but usage of the chemically produced oxidants and/or reductants seems to be quite cumbersome, especially in quantitative works. The electrochemical way appears to be much more practical (in the cases of relatively unstable intermediates) and advantageous (due to... 

Benzo[6]thiophenes ran also be prepared indirectly by Friedel-Crafts cyclization of styrylsulfonyl chlorides (59JA2000) or 2-phenylethanesulfonyl chlorides (53JA3359). Since these cyclizations produce either benzothiophene sulfones or dihydrobenzothiophene sul-fones, further oxidative and/or reductive steps are required to obtain benzo[ Jthiophenes. 

In section 3.6 we have described the valence (VB) and conduction (GB) bands of semiconductors. When such an electrode is irradiated with light of energy beyond its bandgap, electrons are promoted from VB to GB and positive holes (h+) are left in the VB. If a molecule in contact with the electrode has an orbital (e.g. tt or 7f) between the energy levels of VB and CB, oxidation and/or reduction can take place by electron transfer to or from the excited electrode (Figure 4.67). 

We can now summarise the factors which determine the stability or otherwise of M"+ in crystals. We are talking about stability with respect to oxidation and/or reduction a stable cation is one which is neither easily reduced nor easily oxidised by other ions in the lattice. M"+ is likely to be... 

Many of the E-M cluster complexes are versatile at undergoing oxidation and/or reduction reactions. As noted in the previous section, protonation of many E-M complexes, especially the anionic ones, may result in oxidation of the compound. A common outcome is simple E-M or M-M bond cleavage. This is illustrated in Eq. (253). It is this process that is responsible for the production of [Bi Co(CO)4 4] upon treatment of Bi[Co(CO)4]3 with Cp2Co as in Eq. (254).64-75 In a few cases, oxidation or reduction proceeds with internal bond breakage or formation as anticipated by the... 

Twenty-seven dimetal compounds, bridged by one dimethylarsenide group but containing no direct metal-metal bond, were found to undergo irreversible oxidation and/or reduction (59), usually giving mononuclear... 

The MLCT excited states of the complexes have strong oxidation and/or reduction power. 

Fast one-electron oxidation and/or reduction of ground-state complexes at suitable potentials. (Out of all the multiple redox steps, it is only the first oxidation and the first reduction which are photochemically relevant.)... 

In the simplest case this may be realized in chemical reactions involving strong oxidants and reductants. Both methods for the preparation of the reactants, the common chemical (e.g., [6]), and electrochemical routes (reviewed in [7-13]), can be used, and the observations from these two methods can be nicely related. Employment of chemical oxidants and/or reductants seems to be more cumbersome, especially in quantitative work. The electrochemical route seems to be much more... 

The absence of silver oxidation and/or reduction peaks is evidence for the electrochemical inactivity of the silver deposited on this carbon (in the form of metallic crystallites). The cyclic voltammogram recorded for the D—Ox carbon (Fig. 50, curve 2) exhibits two anodic peaks (fp., = +0.27 V, p,a = +0.77 V) due to the oxidation of adsorbed silver and surface hydroquinone-like groups, respectively. A single cathodic peak (Ep,) = +0.16 V) is due to the reduction of quinone-like surface groups according to Scheme 19. The large cathodic reduction wave confirms the presence of adsorbed silver cations and their reduction... 

The fact that metal ions in complexes often have the ability to undergo oxidation and/or reduction, with the resultant complexes having distinctly different properties as a result of the change in the metal d-electron set, means that techniques able to probe these processes have developed (Table 7.4). In coordination chemistry, the technique of cyclic voltammetry (sometimes called electrochemical spectroscopy because of its capacity to rapidly probe behaviour in different oxidation states in simple solution experiments) is now commonly employed. Thermodynamic properties, such as reaction enthalpy and complex stability... 

It follows from in situ FTIR and DBMS investigations of species adsorbed on a polycrystalline platinum electrodes " in acid medium that a great variety of strongly adsorbed residues of the original molecules could be anchored to the surface of the electrode. These residues are sensitive to oxidative and/or reductive attacks. 

The template removal step, needed to achieve porous materials, is one of the most critical points. In contrast to silica, other compositions are usually more sensitive to thermal treatments and calcination can result in breakdown of the mesostructures. Hydrolysis, redox reactions, or phase transfonnarions to the thermodynamically preferred denser crystalline phases account for this lower thermal stability. Many of the transition metal-based mesostruetured materials synthesized in the presence of cationic surfactants collapse during thermal treatments. The poor thermal stability observed could be due to the different 0x0 chemistry of the metals compared to silicon. Several oxidation states of the metal centers may be responsible for oxidation and/or reduction during calcination. In addition, incomplete condensation of the framewoik is possible. 

We must also consider the possibility of oxidation and/or reduction of the glass, homogeruzation processes, and defect in the glass. 

After confirming the effectiveness of MO theory in determining the oxidation and/or reduction potential of chemical compounds, a design diagram to choose... 

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