A Kinetic Study of the Reaction between N,N‐Dimethyl‐p‐toluidine and its Electrogenerated Radical Cation in a Room Temperature Ionic Liquid

10.1002/cphc.200500404.absThe reaction between N,N‐dimethyl‐p‐toluidine (DMT) and the radical cation generated through its one‐electron oxidation has been studied electrochemically in the room temperature ionic liquid N‐methyl‐N‐butylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [Py14][NTf2]. Kinetic information obtained as linear sweep and cyclic voltammetry collected at 5 μm, 10 μm and 0.3 mm diameter platinum disk electrodes over a range of initial substrate concentrations and scan rates spanning five orders of magnitude was complemented by chronoamperometric measurements designed to probe the rate of diffusion. At the fastest scan rates the homogeneous reactions following the initial electron transfer were effectively out‐run, facilitating an assessment of the electrode kinetics using DIGISIM®and a validated Nicholson′s method. Through digital simulation the voltammetry was then shown to be consistent with a mechanism established for the same reaction in acetonitrile, involving dimerisation of the DMT radicals following an initial and rate‐determining proton transfer step. After careful consideration of all parameters, a bimolecular rate constant of (3.4±1.1)×102dm3 mol−1s−1was deduced by fitting the data. This was compared to the equivalent value for acetonitrile and, in light of this, the implications on the viability of ionic liquids for use as alternative mainstream solvents briefly assessed. Reaction kinetics in a room temperature ionic liquid are investigated by analysing voltammetry for the anodic dimerisation of N,N‐dimethyl‐p‐toluidine (DMT) in N‐methyl‐N‐butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (see figure). While both diffusion and heterogeneous electron transfer are significantly slowed relative to the same processes in a conventional nonaqueous solvent, the rate of the homogeneous deprotonation step between DMT and its radical cation is found to be largely unchanged.