The reduction of 4-nitrobenzene diazonium electrografted layer: An electrochemical study coupled to in situ sum-frequency generation spectroscopy

Abstract

The reduction of 4nitrobenzene diazonium electrografted layer: An electrochemical study coupled to in situ sum-frequency generation spectroscopy. (2018) Electrochimica Acta, 283.

Kinetic Study of Redox Probes on Glassy Carbon Electrode Functionalized by 4-nitrobenzene Diazonium

“…Figure 1 presents the cyclic voltammograms (CVs) obtained on a carefully polished glassy carbon (GC) electrode dipped in a 0.1 M HCl solution containing 2.5 mM NBD. The shape of the first and second scans was classical and consistent with our previous reports [28,31]. Hence, Peak I observed on the first forward scan actually corresponded to diazonium reduction and subsequent grafting onto GC surface while Peaks II and III were rather related to NO2 reduction in NHOH and NH2 groups (Scheme 1).…”

“…It is worth noting that, on this latter scan, Peak I was no longer observed, in accordance with the self-inhibiting and blocking properties of diazonium layers [24,26]. In recent papers [28,31], we have proved that NBD grafting by constant potential electrolysis at a potential corresponding to Peak I (ca. 0.3 V) left the nitro groups unaffected by the electrochemical process.…”

“…0.3 V) left the nitro groups unaffected by the electrochemical process. We have also demonstrated that reduction of the grafted layer at a potential close to that of Peak II afforded a stratified film bearing successively NH2, NHOH and unaffected NO2 while increasing the distance to the electrode surface, in accordance with a charge transfer-limited mechanism and an electron tunneling process, the efficiency of which decreases throughout the film from the electrode to the solution [31]. Further electrolysis at potential of Peak III finally led to a layer mainly consisting of NH2 groups.…”

“…Indeed, it is well established that NO2 can be reversibly converted into the corresponding radical anion in aprotic conditions [30], whereas in protic media the reduction mechanism is more complex, leading to NH2 groups as final product through an intermediary, reversible redox couple, namely nitroso/hydroxylamine (NO/NHOH) [25,28]. In a recent work [31], we have showed by a coupled electrochemical and spectroscopic approach that reduction at -0.1 V vs. SCE of a NBD-functionalized glassy carbon (GC) electrode in aqueous solution leads to a stratified organic film in which the easier NO2 moieties to be reduced are the closest ones to the electrode surface, and the last to be reduced are the ones located at the interface between the film and the solution. Thus, during the electrolysis, the organic film successively exhibits NH2 groups at the electrode surface, then NHOH in its inner, intermediary part and finally remaining NO2 at its outer interface.…”

Recent Advances in the Nanocatalyst-Assisted NaBH4 Reduction of Nitroaromatics in Water

“…34−38 Moreover, gas chromatography–mass spectrometry is needed for the measurement of accurate conversion percentage and for verifying the ensuing reaction products. 39,40…”