Reduction of Dinitrobenzene Derivatives in Ethaline: Hydrogen‐Bonding Interactions through the Inversion of Potentials in a Deep Eutectic Solvent

Abstract

AbstractThe reduction of dinitro‐benzene derivatives have been examined in Ethaline containing a low amount of water (less than 0.2 %) chosen as a prototypical example of Type III‐DES. Analyses of the voltammograms reveal a situation of potential inversion (i. e. the second electron transfer is easier and occurs at a least negative potential) for the reductions of 1,2‐ and 1,4‐dinitrobenzene contrarily to the reduction of dinitrobenzene in a classical organic solvent. This is ascribed to H‐Bond interactions in Ethaline that are different for a delocalized radical anion and the dianion in a molecule bearing two conjugated redox groups. Indeed, the inversion of potential is not observed for the 1,3‐dinitrobenzene reduction. Reduction potentials in Ethaline are less negative than those in organic solvent (acetonitrile, DMF), that falls in line with the H‐bonding stabilization of the electrogenerated charged species in Ethaline. The potential inversion is not observed in ethylene glycol (with 0.2 mol L−1 Et4N+ Cl−) that is one of the components of Ethaline suggesting that choline chloride plays a major role in the H‐bonding/ion‐pairing stabilization. Interestingly and despite these stabilizations, the charge transfer kinetics remain comparable with those measured in common organic solvents (ks around 0.13 cm s−1).