The electrodimerization mechanism of 2,4,6-trichloro- and tribromoanilines in unbuffered acetonitrile

In Situ Electrochemical ESR and Voltammetric Studies on the Anodic Oxidation of para-Haloanilines in Acetonitrile

“…From this, it was found that significant additional anodic contributions were necessary in order to simulate the peak currents using reasonable values for the substrate diffusion coefficient (using the Wilke−Chang approximation, the diffusion coefficient of para -chloroaniline in acetonitrile is estimated at 2.1 × 10 -5 cm 2 s -1 ). This is consistent with the observations made in previous investigations, where larger measured values of n were attributed to the oxidation of ejected halide anions, − but is inconsistent with the rationalization given above for the discrepancies in the deduced kinetic parameters. This led to the suggestion that the modeled mechanism was not the dominant pathway, as suggested by the low signal intensities measured, but ran parallel with an alternative reaction scheme in which HCl is generated quickly and oxidized at the electrode surface, thus contributing to the anodic current.…”

“…In the mechanism proposed by Bacon and Adams 13 for the anodic oxidation of para -chloroaniline in aqueous solution, a Cl - ion is ejected during the dimerization process. If we consider this mechanism taking place in aprotic solvents, where the electrochemical oxidation of chloride is possible at potentials less positive than the oxidation potential of para -chloroaniline, then this additional process may contribute to some extent to the anodic current, as was discussed by Farsang et al − However, it has been shown that, in acetonitrile, the equilibrium constant for the following reaction: is close to 10 -9 mol dm -3 (and 10 -6 mol dm -3 for HBr), and thus, under the experimental conditions employed in this work, the ejected chloride anion is a very strong base and is likely to leave in a protonated form. On the other hand, one cannot rule out the deprotonation of HCl as a result of the basic aniline environment, so a series of experiments was carried out to probe the following equilibrium: where AH 2 and AH 3 + are the neutral and protonated para -chloroaniline molecules, respectively.…”

“…N , N -Dimethyl- para -bromoaniline. It is evident from the observations discussed above, and those reported previously, − that N-deprotonation of the para -haloaniline radical cations plays a crucial role in the follow-up chemistry, suggesting that a different behavior might be observed for an N-methylated aniline derivative, and thus, this was investigated as an interesting aside. Figure depicts typical cyclic voltammograms for 2 mM N , N -dimethyl- para- bromoaniline on a gold macrodisk at a range of scan rates.…”

“…In a recent collection of papers, Farsang and co-workers − studied the electrochemical oxidation of para -haloanilines in DMF 14 and acetonitrile, − developing earlier work by Adams and Bacon in aqueous media . In all cases, the anodic oxidation was reported to proceed via a single electron transfer to generate the corresponding radical cation, which was found to undergo further chemical reaction to ultimately form an electrogenerated dimer product.…”

Dimers of Nineteen-Electron Sandwich Compounds: An Electrochemical Study of the Kinetics of Their Formation

“…The model of Nicholson and co-workers allows one to estimate rate constants for irreversible dimerization reactions of an active species generated through electrochemical reduction or oxidation from the ratio of forward and reverse currents for the electrochemical reaction. It has been applied to a wide variety of organic systems, including anilines, various nitro compounds, chalcones, pyridinium derivatives, dithienylazines, and a few metal–organic systems …”