Catalytic regeneration of the reagent

Catalytic regeneration of the reagent following a reversible electron transfer. A particular case of following chemical reaction is constituted by that in which the product of the electrode reaction undergoes a homogeneous, irreversible, first-order (or pseudo-first-order)... 

Figure 21 Typical cyclic voltammograms recorded at increasing scan rates (a < b < c) for a reversible electron transfer (having E° = 0.0 V) coupled to catalytic regeneration of the reagent...

Figure 22 Working curve for the catalytic regeneration of the reagent following a reversible (a) or irreversible (b) electron transfer...

Catalytic regeneration of the reagent following an irreversible electron transfer. When the catalytic reaction follows an irreversible electron transfer, the process can be represented as follows ... 

Catalytic regeneration of the reagent. The particular case in which the following chemical reaction is a first-order redox reaction which regenerates the initial species is described by the mechanism ... 

As far as the use of ferrocene molecules as amperometric sensors is concerned, they have found wide use as redox mediators in the so-called enzymatic electrodes, or biosensors. These are systems able to determine, in a simple and rapid way, the concentration of substances of clinical and physiological interest. The methodology exploits the fact that, in the presence of enzyme-catalysed reactions, the electrode currents are considerably amplified.61 Essentially it is an application of the mechanism of catalytic regeneration of the reagent following a reversible charge transfer , examined in detail in Chapter 2, Section 1.4.2.5 ... 

The presence of the enzyme produces a catalytic oxidation of the ferrocenyl molecule giving rise to an S-like curve with fairly high currents, which is typical of catalytic regeneration of the reagent . It is noted that an extremely slow scan rate is employed (1 mV s-1) in order to allow the catalytic reaction following the electron transfer to run to completion. 

Operationally, the relevant reagents are easy to prepare, safe, and economical. The by-product. Phi, is easy to separate and, in principle, could be reoxidized. Furthermore, most of the reactions described are potentially scalable to multikilogram levels. A next step in this methodology would be catalytic regeneration of the I(III) reagent, that is. 

Reaction of the nucleophilic Collman s reagent (Na2Fe[CO]4) with two alkyl halides affords ketones via successive oxidative additions (Scheme 1.2) [7]. However, no catalytic cycle is achieved because the reaction conditions applied do not lead to regeneration of the reagent. 

The methods available for synthesis have advanced dramatically in the past half-century. Improvements have been made in selectivity of conditions, versatility of transformations, stereochemical control, and the efficiency of synthetic processes. The range of available reagents has expanded. Many reactions involve compounds of boron, silicon, sulfur, selenium, phosphorus, and tin. Catalysis, particularly by transition metal complexes, has also become a key part of organic synthesis. The mechanisms of catalytic reactions are characterized by catalytic cycles and require an understanding not only of the ultimate bond-forming and bond-breaking steps, but also of the mechanism for regeneration of the active catalytic species and the effect of products, by-products, and other reaction components in the catalytic cycle. 

To improve the utility of Nugent s and RajanBabu s conditions even further, catalytic conditions for cyclizations have been developed. They address the issue of reagent control of the cyclization and the mode of its termination. The formation of an alkyl titanocene species after reductive trapping allows two distinctive pathways for the regeneration of the catalyst. 

Since in the described reactions tellurium is regenerated and sodium hydrogen tellnride is prepared from the element and sodium borohydride, a catalytic procedure is also effective, in which only catalytic amounts of preformed reagent are employed. ... 

Finally, it should be mentioned that all the oxidative substitution reactions of aromatics discussed above are stoichiometric processes. Rather expensive reagents are employed, and the processes would not generally be suitable for syntheses on the industrial scale. They do, however, provide simple, attractive routes for bench-scale syntheses for a wide variety of substituted arenes283 284 that are difficult to prepare by other methods. Moreover, electrochemical regeneration of the oxidant could provide for the use of catalytic amounts of expensive metal oxidants. 

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