Convenient syntheses of a family of easily recoverable fluorous primary, secondary, and tertiary aliphatic amines NH3-x[(CH2)(m)(CF2)(7)CF3](x) (m=3-5; x=1-3) - Fine tuning of basicities and fluorous phase affinities
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The alcohols HOCH2(CH2)(m-1)(CF2)7CF3 [m = 3-5; (CF2)7CF3 = R(f8)] are oxidized to aldehydes O=CH(CH2)(m-1)R(f8) (Dess-Martin reagent, 90-96%), which are condensed with NH2CH2C6H5 and Na(AcO)3BH to give benzylamines NH(CH2C6H5)[(CH2)(m)R(f8)] (excess amine, 88-90%) or N(CH2C6H5)[(CH2)mR(f8)]2 (excess aldehyde, 85-91%). Subsequent hydrogenolyses (Pd/C, 1 atm H2) give the title primary amines NH2[(CH2)(m)R(f8)] (10-12; 98-99%) or secondary amines NH[(CH2)(m)R(f8)]2 (13-15; 92-99%). 'The aldehyde condensations are repeated with 13-15 to give tertiary amines N[(CH2)(m)R(f8)]3 (16-18; 86-97%) with very high fluorous phase affinities. These decrease monotonically as the numbers of CH2 groups increase or R(f)8 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 R(f8) group is still detected through five CH2 groups.
author list (cited authors)
Rocaboy, C., Bauer, W., & Gladysz, J. A.