Using Kamlet-Taft solvent descriptors to explain the reactivity of anionic nucleophiles in ionic liquids.

L. CROWHURST; R. FALCONE; N. L. LANCASTER; V. LLOPIS-MESTRE; T. WELTON

JOURNAL OF ORGANIC CHEMISTRY

American Chemical Society

Lugar: Washington DC, USA; Año: 2006 vol. 71 p. 8847 - 8853

0022-3263

In this paper, we report the effect of ionic liquids on substitution reactions using a variety of anionic nucleophiles. We have combined new studies of the reactivity of polyatomic anions, acetate, trifuoroacetate, cyanide, and thiocyanide, with our previous studies of the halides in [C4C1py][Tf2N], [C4C1py][TfO], and [C4C1im][Tf2N] (where [C4C1im]+ is 1-butyl-3-methylimidazolium and [C4C1py]+ is 1-butyl-1-methylpyrrolidinium) and compared their reactivities, k2, to the same reactions in the molecular solvents dichloromethane, dimethylsulfoxide, and methanol. The Kamlet-Taft solvent descriptors (a, b, ð*) have been used to analyze the rates of the reactions, which were found to have a strong inverse dependency on the a value of the solvent. This result is attributed to the ability of the solvent to hydrogen bond to the nucleophile, so reducing its reactivity. The Eyring activation parameters (ÄH± and ÄS±), while confirming the reaction mechanism, do not offer obvious correlations with the Kamlet-Taft solvent descriptors.