Electrochemical behaviour of 2-nitrobenzidine in N,N-dimethylformamide

In situ CCD video and voltammetric studies on enhanced cathodic peak observed at a hanging mercury drop electrode during consecutive two one-electron redox reactions in aprotic solutions

“…It has been reported that the solution of higher concentration of the supporting electrolyte can minimize the difference between c n and c b of the HMDE [1,16] (Fig. 1C) and effectively ceases the streaming of the mercury surface [5,11,16] and the CVACO. Thus, the substantial decrease of I c2 p with increasing the concentration of and I c2 p were determined from the CVs according to the definition given in Fig.…”

“…Furthermore, except for the case of O 2 , it appears that the value of I c2 p =I c1 p is larger for the redox couple with a larger value of potential difference ðDE c p Þ between the first ðE c1 p Þ and second ðE c2 p Þ reduction peaks. Previously, an enhanced I c2 p has been observed during the redox reactions of DPA [1], 1,1,4,4-tetraphenylbutatriene [4], 2-nitrobenzidine [5] and 1,9-dimethyldibenzo[b,f]pentalene [2,3] at the HMDE, while a smaller I c2 p than I c1 p at the solid plane (e.g., GC) electrode has been obtained during the redox reactions of BQ [32][33][34], MV 2+ [35], DNB [26,29], O 2 [36] and AB [27,31] in different aprotic solutions. For the smaller value of I c2 p , many causes such as the decrease in diffusion coefficient of anion radical (e.g., BQ À ) compared to that of the parent molecule (e.g., BQ) due to solvation or hydrogen-bonding and dimerization of anion radical, and the complexation between dianion (e.g., BQ 2À ) and parent molecule (e.g., (BQ-BQ) 2À ) have been proposed [9,36,37].…”

“…1C) often appears to be smaller ðI c2 p =I c1 p < 1) and larger ðI c2 p =I c1 p > 1) than unity at the solid plane electrode [3,14] and the HMDE [2][3][4][5], respectively. Such an enhanced I c2 p that may be recognized as an unexpected event concerning the electrode kinetics and electroanalysis at the HMDE has been hitherto claimed to result from the electrochemical processes involving the chemical reaction [1,14,15], adsorption [2,14], multielectron transfer and chemical complications [5] and the streaming phenomena of the HMDE [1][2][3]. It has been also reported that the I c2 p =I c1 p > 1 is not specific for a particular compound [2], whereas the streaming (''upward" and ''downward") of the HMDE is its inherent characteristic [1][2][3][8][9][10][11]16,19,20].…”

“…In the past some decades, a number of peculiarities [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] concerning the cyclic voltammograms (CVs) obtained at a hanging mercury drop electrode (HMDE) in aprotic solutions and ionic liquids [9] (e.g., cyclic voltammetric anodic current oscillation (CVACO) [1][2][3][4][5][6][7][8][9][10][11], inverted peak [3,11,12] and larger current of the second cathodic peak than that of the first one of a stepwise one-electron redox reaction [1][2][3][4][5]14,15]) have been reported. These eccentric phenomena especially the CVACO that has been visualized to originate from a novel circular motion [10] at the HMDE|solution interface due to the familiar polarographic streaming phenomena [1,[6][7][8][9][10][11]16] have been reported to be fundamentally very interesting...…”

“…Thus, as the probable reason for I c2 p =I c1 p > 1, the streaming of the HMDE could be most rational, but, unfortunately, there is no relevant study in this regard. Thus far the mechanisms to explain the fact that I c2 p =I c1 p > 1 remain controversial [1][2][3][4][5]14,15]. The streaming of the HMDE surface has been reported to originate from the unequal surface tension (c) at the neck and bottom of HMDE [1,[6][7][8][9][10][11]16,19,20].…”