Electrolysis, controlled-current

Controlled-Potential Electrolysis and Controlled-Current Electrolysis... 

Fig. 5.32 The circuits for (a) con-trolled-potential electrolysis and (b) controlled-current electrolysis (for the circuits based on operational amplifiers, see Figs 5.43 and 5.44).

Controlled-current electrolysis in flowing solution has been extremely useful for analytical purposes. The prevalent techniques are constant-current coulometry and coulometric titrations, which are discussed in Chapter 25. 

The principle of controlled current electrolysis has been known since the beginning of this century.21 However, the utilization of this form of electrochemistry remained dormant for 50 years until three groups of investigators illustrated its many advantages for analytical and physicochemical measurements.22 24 Several works describe this technique in detail,25"27 and other re-... 

A number of embellishments of controlled-current electrolysis have been proposed for specialized systems, but discussion of these is beyond the scope of this chapter. Those interested in pursuing this material are referred to discussions of programmed-current techniques, 4 single-step and double-step gal-vanostatic methods,35 and chronocoulometiy.36... 

Controlled Current Electrolysis Simulation Exploring the Electrogravimetric Method. 

On controlled current electrolysis (200 mA), 2,6-di(terf-butyl)-p-cresol (69) underwent nucleophilic hydroxylation, methoxylation or acetoxylation depending on the solvent system used (IM H2O, MeOH or 0.2 M NaOAc-AcOH in MeCN) to afford the corresponding cyclohexa-2,5-dienones 70, 71 and 72 in 86, 88 and 91% yields, respectively. In the case of 2,4,6-tri(tert-butyl)phenol (73), 2,6-di(tert-butyl)-p-benzoquinone (74) was produced in 96% yield through cyclohexa-2,5-dienone 75 , as shown in Scheme 13. 

Generally, except for the simpler apparatus involved, controlled-current electrolysis offers no advantages over controlled-potential methods. With the commercial availability of suitable potentiostats, controlled-current methods are being used less frequently in analysis and lab-scale preparative electrolysis. For large-scale electrosynthesis or separations involving very high currents, especially in flow systems where the reactants are... 

From an electrochemical point of view, ES-MS might be viewed as a means to monitor the products of a controlled-current electrolysis on-line with mass spectrometry. Carrying out electrochemistry/mass spectrometry (EC/MS) in this fashion requires only a very small amount of sample and provides the molecular weight, and potentially the structure (e.g., via tandem mass spectrometry experiments), for the ionic products of the reactions. Given an experiment for which controlled-current electrolysis is suitable, " utilizing the inherent electrochemistry of ES would be expected to be much simpler than combining discrete electrochemical cells on-line with ES-MS for the same purpose. ... 

In the case of controlled-current electrolysis the instantaneous current is constant with time and the total quantity of electricity passed is simply expressed by... 

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