Study of aromatic nucleophilic substitution with amines on nitrothiophenes in RTILs: are the different effects on the behavior of para-like and orto-like isomers on going from conventional solvents to RTILs related to solvation effects?.

The kinetics of the nucleophilic aromatic substitution of some 2-L-5-nitrothiophenes (para-like isomers)with three different amines (pyrrolidine, piperidine, and morpholine) were studied in three roomtemperatureionic liquids ([bmim][BF4], [bmim][PF6], and [bm2im][BF4], where bmim ) 1-butyl-3-methylimidazolium and bm2im ) 1-butyl-2,3-dimethylimidazolium). To calculate thermodynamicparameters, a useful instrument to gain information concerning reagent-solvent interactions, the reactionwas carried out over the temperature range 293-313 K. The reaction occurs faster in ionic liquids thanin conventional solvents (methanol, benzene), a dependence of rate constants on amine concentrationsimilar to that observed in methanol, suggesting a parallel behavior. The above reaction also was studiedwith 2-bromo-3-nitrothiophene, an ortho-like derivative able to give peculiar intramolecular interactionsin the transition state, which are strongly affected by the reaction medium.