Behavior of Electrogenerated Bases in Room-Temperature Ionic Liquids

Abstract

The reductive electrochemistry of substituted benzophenones in the aprotic room-temperature ionic liquid (RTIL) 1-butyl-1-methylpyrrolidinium bistriflimide occurs via two consecutive one-electron processes leading to the radical anion and dianion, respectively. The radical anion exhibited electrochemical reversibility at all time-scales whereas the dianion exhibited reversibility at potential sweep rates of >or=10 V s(-1), collectively indicating the absence of strong ion-paring with the RTIL cation. In contrast, reduction in 1-butyl-3-methylimidazolium bistriflimide is complicated by proton-transfer from the [Bmim] cation. At low potential sweep rates, reduction involves a single two-electron process characteristic of either an electrochemical, chemical, electrochemical (ECE) or disproportion-type (DISP1) mechanism. The rate of radical anion protonation in [Bmim] is governed by basicity and conforms to the Hammett free-energy relation. At higher potential sweep rates in [Bmim][NTf2], reduction occurs via two consecutive one-electron processes, giving rise to the partially reversible generation of the radical anion and the irreversible generation of the dianion, respectively. Also, the redox potentials for the reversible parent/radical anion couples were found to be a linear function of Hammett substituent constants in both RTIL media and exhibited effectively equivalent solvent-dependent reaction constants, which are similar to those for reduction in polar molecular solvents such as acetonitrile or alcohols.

Surface ECE mechanism in protein film voltammetry—a theoretical study under conditions of square-wave voltammetry

“…This situation is commonly observed for electroactive molecules that can exist as more than one isomer; for example, cis and trans isomers of transition metal complexes, but it is also frequently met by some proteins and other important biomolecules [7,[13][14][15][16][17][18][19]. The features of the SW voltammetric responses in such scenario will significantly depend on the value of the chemical kinetic parameter l, but they will be also affected by the values of the electron transfer kinetic parameters K 1 and K 2 of the two reduction steps.…”

“…If we consider a surface electron transferchemical reaction (EC) mechanism for example, and if the product of the first electron step can be converted chemically to another electroactive specie, then we assign these reactions to follow the surface electron transfer-chemical reactionelectron transfer (ECE) mechanistic pathway. Although this reaction mechanism is quite complex, it is a widespread pathway of many proteins [7] and other important compounds in organic electrochemistry [1,7,[13][14][15][16][17][18][19]. For example, the product of the first electron transfer step can undergo protonation, elimination, substitution, or reorganization reaction to give second electroactive specie [1,[13][14][15][16][17][18][19].…”

“…Although this reaction mechanism is quite complex, it is a widespread pathway of many proteins [7] and other important compounds in organic electrochemistry [1,7,[13][14][15][16][17][18][19]. For example, the product of the first electron transfer step can undergo protonation, elimination, substitution, or reorganization reaction to give second electroactive specie [1,[13][14][15][16][17][18][19]. As the most familiar among the voltammetric techniques, the cyclic voltammetry is commonly used for characterization of electrochemically active systems following the ECE pathway [7, 13-16, 18, 19].…”

The electrochemical reduction of the purines guanine and adenine at platinum electrodes in several room temperature ionic liquids

“…Ionic liquids (ILs) [11][12][13][14] have emerged as a novel non-aqueous, polar class of solvents that hold great promise in investigations of electrochemical mechanisms [15][16][17][18][19]. The wide electrochemical windows [16,20], intrinsic ion conductivity, high viscosity and hydrophobicity have shown that RTILs are suitable media for supporting reductive processes occurring at very negative potentials allowing stabilization of intermediates in some cases, and improving solubility in others.…”

Electrochemical Reaction of Organic Compounds in Ionic Liquids

“…At fast scan rates, the initial reduction (radical anion generation) is partially reversible, whereas the second reduction process (dianion generation) is irreversible and shifted anodically, which is a consequence of the protonation of the electrogenerated dianion. However, at low scan rates ( 0.1 V s À1 ), reduction occurs via a two-electron process with the characteristic of an ECE-or DISP1-type mechanism, where the protonation of the radical anion is the rate-determining step via a slow proton-transfer reaction from the [C 4 mim] cation [44]. (Fig.…”