Kinetic study of the addition of trihalides to unsaturated compounds in ionic liquids.: Evidence of a remarkable solvent effect in the reaction of ICl2-

The kinetic constants and activation parameters for the reactions of Br-3(-) and ICl2- with some alkenes and alkynes have been determined in the ionic liquids [bmim] [PF6], [emim] [Tf2N], [bmim] [Tf2N], [hmim] [TF2N], [bm(2)im] [Tf2N], and [bpy] [TF2N] (where emim = 1-ethyl-3-methylimidazolium, bmim = 1-butyl-3-methylimidazolium, hmim = 1-hexyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bpy = butylpyridinium, PF6 = hexafluorophosphate, and Tf2N = bis(trifluoromethylsulfonyl)imide) and in 1,2-dichloroethane. The rates of both reactions increase on going from 1,2-dichloroethane to ILs. Evidence suggests that, while the hydrogen bonding ability of the imidazolium cation is probably the main factor able to increase the rate of the addition of ICl2- to double and triple bonds, this property has no effect on the electrophilic addition of Br-3(-) to alkenes and alkynes. Furthermore, in the case of the ICl2- reaction, the hydrogen bonding ability of ILs can be exploited to suppress the unwanted nucleophilic substitution reaction on the products by the Cl- anion.