Cathodic reduction general mechanism

V. CATHODIC REDUCTION OF ORGANOMAGNESIUM COMPOUNDS A. General Mechanism of the Reduction... 

The cathodic reduction of aromatic carboxamides and imides in acid solution at lead or mercury cathodes generally leads to amines and isoindolines, respectively 7,9 These reactions are of great preparative interest but their mechanism have not been examined. Cpe of isonicotinic amide and 2-thiazolecarboxaldehyde in acid solution gives the corresponding aldehydes in good yields 139>141)... 

Anodic methoxylation of aromatic ethers via the EEQCp mechanism has found its widest application in the synthesis of quinone bisketals (LXX) from para-dimethox-ybenzenes (LXIX) [79]. Yields are generally excellent, and the reaction is conveniently carried out at constant current in a single cell [42,80]. The reaction has also been shown to work well for naphthalenes [81] and benzothiophenes [82]. As shown in Table 4, a variety of substituents may be present on the ring. When substituents sensitive to cathodic reduction such as -CHO and -CH CHCO Me are present, a divided cell apparatus may be required to obtain reasonable yields of the corresponding bisketals. 

Anodic oxidation was also shown to be a feasible technique for chlorophenol degradation (55). The mechanisms for this process is not well understood. It is hypothesized that chlorophenol radical cations are first formed and subsequently deprotonated. The product undergoes further oxidation to a benzoquinone derivative and ring-opening to acids, such as muconic, naleic, and oxalic and finally to CO2 (36-38). Just like cathodic reduction, the efficiency of anodic oxidation of chlorophenol depends on the material of the electrodes. Generally, oxide-based anodes perform better than metals as they are less prone to the formation of oligomers, which cause the inactivation of the electrodes (35M39). 

So, any reaction that favors the consumption of Na20 or SO3 will lead to the dissociation of Na2S04 and vice versa. Molten Na2S04 is an ionic conductor the hot corrosion mechanism should generally be electrochemistry [78]. In other words, hot corrosion itself is an electrochemical process that includes anodic oxidation, cathodic reduction and ion diffusioa As for the hot corrosion of Ti3AlC2, the anodic oxidation process mainly consists of the anodic dissolution of Ti and Al ... 

Donahue [37] was one of the first to discuss interactions between partial reactions in electroless systems, specifically electroless Ni with NaH2PC>2 reducing agent, where mention was made of an interaction between H2PO2 ions and the cathodic Ni2+ reduction reaction with a calculated reaction order of 0.7. Donahue also derived some general relationships that may be used as diagnostic criteria in determining if interactions exist between the partial reactions in an electroless solution. Many electroless deposition systems have been reported to not follow the MPT model. However, mention of these solutions may be best left to a discussion of the kinetics and mechanism of electroless deposition, since a study of the latter is usually necessary to understand the adherence or otherwise of an electroless solution to the MPT model. 

The direct reduction of haloalkynes using either mercury or vitreous carbon as the cathode has been examined in considerable detail [80-84] one example is portrayed in Eq (77). The influence of reduction potential, current consumption, proton donor, electrode, and substrate concentration on the course of the process has been examined. Vitreous carbon electrodes are preferred, though mercury has been used in many instances. Unfortunately, these reactions suffer from the formation of diorganomercurials. While both alkyl iodides and bromides can be used, the former is generally preferred. Because of their higher reduction potential, alkyl chlorides react via a different mechanism, one involving isomerization to an allene followed by cyclization [83]. 

The literature reviewed in sections 2—3.6 has shown that oxygen reduction on Pt is quite complex, involving several possible rate-limiting (or co-limit-ing) steps. As we will see in sections 4 and 5, this complexity is a universal feature of all SOFC cathodes, with many of the same themes and issues reappearing for other materials. We therefore highlight below several general observations about the mechanism of Pt that frame the discussion for other solid-state gas-diffusion electrodes involving O2. These observations are as follows. 

Finally, since the anodic and cathodic reactions do not occur at the same potential, the mechanism for oxidation may not be the opposite of reduction. This occurs when there is multiple step electron transfer, possibly with intermediate chemical steps. If this happens then, in general, ara + ac do not add up to unity. 

The relation between the rate of each reaction step and the steric stability of the intermediate species must also be considered to rationalize the stereochemical results. Consider the electrochemical reduction [Eq. (2)] of an alkyl halide (R-X) to the corresponding alkane (R-H) via a radical anion [(R-X) ], radical (R ), and anion (R ) mechanism (ECEC). The order of configurational stability may be R-H > (R-X) > R > R- in general, but the stability of R- is not always lower than that of R when the adsorption of R is weakened by electrostatic repulsion by the cathode. The situation is more compli-... 

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