Convenient Syntheses of a Family of Easily Recoverable Fluorous Primary, Secondary, and Tertiary Aliphatic Amines NH3x[(CH2)m(CF2)7CF3]x(m = 3−5; x = 1−3) − Fine Tuning of Basicities and Fluorous Phase Affinities

Abstract

The alcohols HOCH2(CH2)m−1(CF2)7CF3 [m = 3−5; (CF2)7CF3 = Rf8] are oxidized to aldehydes O=CH(CH2)m−1Rf8 (Dess−Martin reagent, 90−96%), which are condensed with NH2CH2C6H5 and Na(AcO)3BH to give benzylamines NH(CH2C6H5)[(CH2)mRf8] (excess amine, 88−90%) or N(CH2C6H5)[(CH2)mRf8]2 (excess aldehyde, 85−91%). Subsequent hydrogenolyses (Pd/C, 1 atm H2) give the title primary amines NH2[(CH2)mRf8] (10−12; 98−99%) or secondary amines NH[(CH2)mRf8]2 (13−15; 92−99%). The aldehyde condensations are repeated with 13−15 to give tertiary amines N[(CH2)mRf8]3 (16−18; 86−97%) with very high fluorous phase affinities. These decrease monotonically as the numbers of CH2 groups increase or Rf8 groups decrease (CF3C6F11/toluene, 24 °C, 16/17/18/13/14/15/10/11/12: >99.7:<0.3, >99.7:<0.3, 99.5:0.5, 96.5:3.5, 95.1:4.9, 93.0:7.0, 70.0:30.0, 63.2:36.8, 56.9:43.1). The relative basicities towards CF3CO2H are probed by NMR in CDCl3. Competitions between N(CH2CH3)3 or N[(CH2)11CH3]3 and 16−18 show 100% or >95%, >95% or 85−90%, and 85−90 or 65−70% protonation of the former. Competitions between 16/17, 17/18, and 16/18 show 60%, 85−90%, and >95% protonation of the latter. Thus, an inductive effect of the Rf8 group is still detected through five CH2 groups.