Electrochemical methodology

The work described here is concerned with the development of electrochemical methodologies to grow compound semiconductors with nanoscale or atomic layer control. That thin-films of some compounds can be formed electrochemically is clear. The questions are how much control over deposit composition, structure and morphology can be obtained What compounds, and of what quality, can be formed ... 

S. Yamamura, Natural products syntheses by means of electrochemical methodology in Electroorganic Synthesis (Eds. R. D. Little, N. L. Weinberg), Marcel Dekker, New York, 1991, pp. 309-315. 

The membrane system considered here is composed of two aqueous solutions wd and w2, separated by a liquid membrane M, and it involves two aqueous solution/ membrane interfaces WifM (outer interface) and M/w2 (inner interface). If the different ohmic drops (and the potentials caused by mass transfers within w1 M, and w2) can be neglected, the membrane potential, EM, defined as the potential difference between wd and w2, is caused by ion transfers taking place at both L/L interfaces. The current associated with the ion transfer across the L/L interfaces is governed by the same mass transport limitations as redox processes on a metal electrode/solution interface. Provided that the ion transport is fast, it can be considered that it is governed by the same diffusion equations, and the electrochemical methodology can be transposed en bloc [18, 24]. With respect to the experimental cell used for electrochemical studies with these systems, it is necessary to consider three sources of resistance, i.e., both the two aqueous and the nonaqueous solutions, with both ITIES sandwiched between them. Therefore, a potentiostat with two reference electrodes is usually used. 

However, the chemical reduction reaction does not work efficiently for the removal of two Bingel addends, whereas the electrochemical reduction process works very efficiently. One of the most interesting examples that illustrates the difference between the chemical and electrochemical methodologies involves the cyclophane type trans-1 ( -37) conjugate [76], The chemical reductive protocol fails completely with this compound, presumably due to ion complexation by the crown ether group and consequent stabilization. When the electroreductive method was used, a clean retrocyclopropanation reaction was observed (Figure 25). 

Modem electrochemistry has evolved to the extent that it has a diverse set of specialized terms and symbols. The latter are defined in Table 1.1 as used in most contemporary electrochemical literature and in this book. Because of the rapid expansion in specialized electrochemical methodology and its application to chemical problems, a nomenclature has evolved for their categorization. This is outlined in Table 1.2 and provides an overview of the complete realm of electrochemical methodology. Within this table, key references to the major monographs for each specialized type of electrochemistry are included.1-36 These references provide the theory and details of applications to complement the introductory and practical presentation of this book. 

Twenty years ago the main applications of electrochemistry were trace-metal analysis (polarography and anodic stripping voltammetry) and selective-ion assay (pH, pNa, pK via potentiometry). A secondary focus was the use of voltammetry to characterize transition-metal coordination complexes (metal-ligand stoichiometry, stability constants, and oxidation-reduction thermodynamics). With the commercial development of (1) low-cost, reliable poten-tiostats (2) pure, inert glassy-carbon electrodes and (3) ultrapure, dry aptotic solvents, molecular characterization via electrochemical methodologies has become accessible to nonspecialists (analogous to carbon-13 NMR and GC/MS). 

An electrochemical methodology using an in situ prepared difluoride from p-iodoanisol is an alternative approach for indirect anodic gem-difluorination of dithioacetals [52],... 

Mercury and solid s-p metal electrodes show stable electrochemical behavior in nonaqueous media, in particular in dipolar aprotic solvents. This knowledge was important for the advancement of electrochemical methodology, e.g., the special branch of polarography in nonaqueous systems has emerged. When performing electrochemical experiments in nonaqueous media, special attention should be paid to the reasonable choice of reversible reference electrodes. 

The virtually unique suitability of electrochemical methodology for preparing fluorinated compounds warrants the inclusion of a separate treatment on this subject (Chapter 25). 

Electrochemical methodology has now become extremely sophisticated, with a vast range of current/potential/ffequency/time parameters available for manipulation, and with the development of microelectrodes, flowcells, and systems of... 

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