Quaternary ammonium ionic liquids containing fluorous ponytails: Competitive alkylation and elimination reactions of I(CH2)nRf (n = 2, 3) with tertiary amines

Abstract

The formation of quaternary ammonium iodides possessing a fluorine-containing chain has been investigated. Reactions of tertiary amines, such as i-PrMe2N and n-BuMe2N with I(CH2)n(CF2)m(CF3), (n=2, m=5 and 7) do not cleanly yield the anticipated quaternary ammonium halide salt, instead elimination occurs and [RMe2NH]I (R=i-Pr, n-Bu) and CH2CH(CF2)m(CF3) are formed. This is confirmed by the crystallographic characterisation of [n-BuMe2NH]I which is found to adopt a micellar-type arrangement in the solid state. Increasing the spacer chain-length to n=3 does result in the desired quaternary ammonium halide salts, [RMe2N(CH2)3(CF2)m(CF3)]I, (m=3, 7). Quaternisation of MeBuN((CH2)3C8F17) with 1-iodooctane gave the asymmetric quaternary ammonium salt possessing a fluorinated alkyl chain, [n-BuMeOctN((CH2)3C8F17)]I. Unlike in previously studied perprotio systems, low symmetry ammonium systems possessing long fluorinated chains do not result in room temperature ionic liquids.