Understanding the Effect of Solvent Structure on Organic Reaction Outcomes When Using Ionic Liquid/Acetonitrile Mixtures.

The rate constant for the reaction between hexan-1-amine and 4-methoxybenzaldehyde was determined in ionic liquids containing an imidazolium cation. The effect on the rate constant of increasing the length of the alkyl substituent on the cation was examined in a number of ionic liquid/acetonitrile mixtures. In general it was found that there was no significant effect of changing the alkyl substituent on the rate constant of this process, suggesting that any nanodomains in these mixtures do not have a significant effect on the outcome of this process. A series of small-angle X-ray scattering and wide-angle X-ray scattering experiments were performed on mixtures of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][N(CF3 SO2 )2 ]) and acetonitrile; this work indicated that the main structural changes in the mixtures occur by about a 0.2 mole fraction of ionic liquid in the mixture (χIL ). This region at which the main changes in the solvent structuring occurs corresponds to the region at which the main changes in the rate constant and activation parameters occur for SN 2 and condensation reactions examined previously; this is the first time that such a correlation has been observed. To examine the ordering of the solvent about the nucleophile hexan-1-amine, WAXS experiments were performed on a number of [Bmim][N(CF3 SO2 )2 ]/acetonitrile/hexan-1-amine mixtures, where it was found that some of the patterns featured asymmetric peaks as well as additional peaks not observed in the [Bmim][N(CF3 SO2 )2 ]/acetonitrile mixtures; this suggests that the addition of hexan-1-amine to the mixture affects the bulk structure of the liquid. The SAXS/WAXS patterns of mixtures of 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([Bm2 im][N(CF3 SO2 )2 ]) and acetonitrile were also determined, with the results suggesting that [Bm2 im][N(CF3 SO2 )2 ] is more ordered than [Bmim][N(CF3 SO2 )2 ] due to an enhancement in the short-range interactions.