A critical assessment of electrochemistry in a distillable room temperature ionic liquid, DIMCARB

Ionic liquids are frequently advocated as green media for electrochemical Studies. However, they are non-volatile and hence difficult to purify or recover. In this paper the electrochemical behaviour of a 'distillable' room temperature ionic liquid, DIMCARB, has been investigated. This ionic liquid is unusual because it is readily prepared, in large quantities and at low cost, by mixing of gaseous carbon dioxide with dimethylamine and also easily recovered by decomposition back into its gaseous components followed by reassociation. Almost ideal reversible voltammetry is observed for the Cc(+/0) process (Cc = cobalticinium), which therefore is recommended for reference potential calibration. Another IUPAC recommended reference potential process, Fc(+/0) (Fc = ferrocene), is only reversible at fast scan rates and occurs near the positive potential limit available. However, decamethylferrocene (DmFc) is reversibly oxidised and behaves ideally as for the reduction of Cc(+). The small diffusion coefficients of 1.2 x 10(-7) cm(2) s(-1) (Cc(+)) and 5.0 x 10(-8) cm(2) s(-1) (DmFc) at 20 degrees C are attributed to the relatively high viscosity. The potential window of ca. -1.50 V to +0.50 V vs. SHE indicates that DIMCARB is. more suitable for electrochemical studies of reductive rather than oxidative processes. Voltammetric studies in DIMCARB reveal a series of reversible reductive processes for the Keggin [alpha-SiW12O40](4-) polyoxometallate. Comparison of reversible potential data reported in other media indicate that the polarity of DIMCARB is intermediate between that of MeCN and the conventional ionic liquid [BMIM][PF6]. The deposition of metallic Pb also has been studied and reveals that Pb(II) is reduced in a single irreversible 2-electron step to the metallic state via a nucleation/growth mechanism. Overall, these studies show that DIMCARB is highly suitable for electrochemical studies, but that it is a potentially reactive medium.