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 roomtemperature ionic liquids ([bmim][BF4], [bmim][PF6], and [bm2im][BF4], where bmim ) 1-butyl-3- methylimidazolium and bm2im ) 1-butyl-2,3-dimethylimidazolium). To calculate thermodynamic parameters, a useful instrument to gain information concerning reagent-solvent interactions, the reaction was carried out over the temperature range 293-313 K. The reaction occurs faster in ionic liquids than in conventional solvents (methanol, benzene), a dependence of rate constants on amine concentration similar to that observed in methanol, suggesting a parallel behavior. The above reaction also was studied with 2-bromo-3-nitrothiophene, an ortho-like derivative able to give peculiar intramolecular interactions in the transition state, which are strongly affected by the reaction medium

Analysis of substituent effects in the reactions of some2-L-3-nitro-5-X-thiophenes with aniline in benzene. A new interpretation ofthe`element effect`

The kinetic constants for the title reactions have been measured in benzene, at 25 \ub0C, at various aniline concentrations. In spite of the low kB/k0 ratios, the reactions are inferred to be genuinely base-catalyzed. The susceptibility constants estimated for the various steps of the reaction mechanism(s) have allowed to make clear the limits of the so-called "element effect" criterion

Acid- and Base-Catalysis in the Mononuclear Rearrangement of Some (Z)-Arylhydrazones of 5-Amino-3-benzoyl-1,2,4-oxadiazole in Toluene: Effect of Substituents on the Course of Reaction

The reaction rates for the rearrangement of eleven(Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole 3a-kinto the relevant (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas4a-k in the presence of trichloroacetic acid or of piperidinehave been determined in toluene at 313.1 K. The results havebeen related to the effect of the aryl substituent by usingHammett and/or Ingold-Yukawa-Tsuno correlations andhave been compared with those previously collected in a proticpolar solvent (dioxane/water) as well as with those on theanalogous rearrangement of the corresponding (Z)-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole 1a-k in benzene. Some light can thus be shed on the general differences of chemical reactivity between protic polar (or dipolar aprotic) and apolar solvents