Electrolysis galvanostatic control

In 2006, electrochemically induced synthesis of (3-lactams, by cyclization of haloamides, has been achieved in suitable solvent-supporting electrolyte solutions previously electrolyzed under galvanostatic control [166, 167]. The yields and the stereochemistry of the process were influenced by the nature of the R -R4 substituents, by the solvent-supporting electrolyte solutions, and by the electrolysis conditions (Scheme 69). 

Working under galvanostatic conditions a is constant, and it is possible to identify two different operating regimes at a < 1 the electrolysis is controlled by the applied current, while at a > 1 it is controlled by the mass transport control. 

The simplest of the methods employing controlled current density is electrolysis at constant current density, in which the E-t dependence is measured (the galvanostatic or chronopotentiometric method). The instrumentation for this method is much less involved than for controlled-potential methods. The basic experimental arrangement for galvanostatic measurements is shown in Fig. 5.15, where a recording voltmeter or oscilloscope replaces the potentiometer. The theory of the simplest applications of this method to electrode processes was described in Section 5.4.1 (see Eqs 5.4.16 and 5.4.17). 

In coulometry, the analyte is quantitatively electrolyzed and, from the quantity of electricity (in coulombs) consumed in the electrolysis, the amount of analyte is calculated using Faraday s law, where the Faraday constant is 9.6485309 xlO4 C mol-1. Coulometry is classified into controlled-potential (or potentiostatic) coulometry and controlled-current (or galvanostatic) coulometry, based on the methods of electrolysis [19, 20]. 

The choice of the electrolysis procedure either working at controlled potential (potentiostatic or controlled-potential electrolysis, cpe) or at a fixed current density (galvanostatic)... 

In the galvanostatic electrolysis the potentials of the electrodes adapt automatically. To get an idea of the order of the emerging overpotential, we recorded the cathodic potential in relation to the current flow (Fig. 1) [5]. The declination of the exponential form indicates mixed control regime, i.e., the current is controlled by mass and electron transfer steps. 

Note that the calculated value of n might be a fraction if the current efficiency is less than 100 % or the mechanism followed is complex. Preparative electrolysis can be performed under potentiostatic or galvanostatic conditions. In the former case, the use of a potentiostat ensues that the potential of the working electrode relative to a reference electrode is held at a constant value during the whole electrolysis process independently of the current supplied. Preferentially, the potential should be selected so that the substrate can be electrolyzed without the products or the medium being reduced or oxidized at the same time. It is possible by proper potential adjustment to control the fraction of electrolysis X which is defined according to Eq. 98 as the fraction of the substrate transformed during electrolysis. 

The bulk electrolysis method may be applied in a constant potential (potentiostatic) or constant current (galvanostatic) modes. In a controlled potential electrolysis (CPE) experiment, the working electrode is held at a constant potential until the solution is exhaustively electrolyzed. The... 

A schematic drawing of a possible setup for continuous titration is given in Fig. 4. It contains the electrolysis cell, which can be controlled galvanostatically [15] or potentiometrically [7] by the end point potential of a downstream potentiometric cell. 

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