Trifluoroacetyl chloride for characterization of organic functional groups by fluorine-19 nuclear magnetic resonance spectrometry

Abstract

The potential utility of trifluoroacetyl chloride as an analytical 19F NMR reagent to characterize alcohols, phenols, thiols, and primary and secondary amines is reported. The 19F chemical shift and yield data for trifluoroacetyl derivatives of approximately 50 model compounds are presented. The importance of an added organic base (2,6-lutidine) in derivative preparation for phenols and primary and secondary amines is discussed.During the past decade several NMR approaches have been suggested to characterize organic functionality (e.g., phenols, alcohols, carboxylic acids, etc.) present in organic compounds and/or mixtures. Nearly all of these approaches rely on the chemical shift parameter to distinguish molecular environment differences for an NMR probe nuclide either present in the functional moiety of interest or by tagging via an appropriate derivative.

The low temperature oxidation of Athabasca oil sand asphaltene observed from 13C, 19F, and pulsed field gradient spin-echo proton n.m.r. spectra

“…Therefore, a majority of detected TFA hydroxyls are attached to benzylic, and 2Њ and 3Њ carbons on long alkyl chains, e.g. 2-octanol (Ϫ8.20 ppm); 3-ethyl-3-heptanol (Ϫ8.40 ppm) [6]. However, the 13 C resonances of methoxy groups attached to 3Њ and 2Њ carbons are unresolved, but may contribute signal to the peaks at ca.…”

99/02454 The low temperature oxidation of Athabasca oil sand asphaltene observed from 13C, 19F, and pulsed field gradient spin-echo proton n.m.r. spectra

“…Most of the high field n.m.r. signal is in the region of TFA benzylic and short-chain alcohols [6]. Trifluoroacetylated secondary and tertiary alcohols have been observed at ca.…”

“…30 s through a solution of asphaltene (0.2 g) or oxidised asphaltene, plus a few drops of 2,6-lutidine (Aldrich) in ca. 2 mL of deuterochloroform (MSD Isotopes) in nitrogen at Ϫ55ЊC in an iso-propanol/dry ice bath [6]. The sample was warmed to room temperature and nitrogen gas was passed through the mixture for ca.…”

“…Ϫ7.85 to Ϫ8.67 ppm, e.g. iso-butanol (Ϫ7.87 ppm); neo-pentanol (Ϫ7.85 ppm); and diethylene glycol (Ϫ7.87 ppm) [6]. Therefore, a majority of detected TFA hydroxyls are attached to benzylic, and 2Њ and 3Њ carbons on long alkyl chains, e.g.…”

“…Therefore, a majority of detected TFA hydroxyls are attached to benzylic, and 2Њ and 3Њ carbons on long alkyl chains, e.g. 2-octanol (Ϫ8.20 ppm); 3-ethyl-3-heptanol (Ϫ8.40 ppm) [6]. However, the 13 C resonances of methoxy groups attached to 3Њ and 2Њ carbons are unresolved, but may contribute signal to the peaks at ca.…”