Electroanalytical Investigations Prior to Preparative Scale Electrolysis

2 Electroanalytical Investigations Prior to Preparative Scale Electrolysis 

Cyclovoltammetry (cv) is a simple method that provides useful information about an electrochemical conversion [8], This is illustrated by the cv of 9,10-diphenyl-anthracene (1) (Fig. 1 and Eq. 1). 

With a potentiostat the potential at the working electrode is linearly increased from 1.0 to 1.6 V and then decreased back to 0 V. In the first interval 1 is oxidized to the radical cation l+ with a peak potential of p.a = 1-38 V. 1 is stable in this solvent and is reduced in the reverse scan back to 1 at p,c = 1-32 V. The ratio of the current for reduction and oxidation ip c-ip.a = 1 indicates the stability of the radical cation. All of 1, that is formed by oxidation of 1 is reduced back to 1. This behavior is termed chemically reversible. Upon addition of 2,6-lutidine, the radical cation 1 reacts with the nucleophile to afford 2 , which is further oxidized to a dication, which yields the dication with 2,6-lutidine. This can be seen in the decrease of /p,c fp,a and an increase of due to the transition from an le to a 2e oxidation. From the variation of the ratio ip.c-ip,n with the scan rate, the reaction rate of the radical cation with the nucleophile can be determined [9]. This can also be aehieved by digital simulation of the cyclovoltammogram, whereby the current-potential dependence is calculated from the diffusion coefficients, the rate constants for electron transfer and chemical reactions of substrate and intermediates at the electrode/electrolyte interface [10]. With fast cyclovoltammetry [11] scan rates of up to 10 Vs- can be achieved and the kinetics of very short-lived intermediates thus resolved. 

---