1-(+)-Dehydroabietylimidazolium Salts as Enantiomer Discriminators for NMR Spectroscopy
H. Q. Nimal Gunaratne, Tiina Laaksonen, Kenneth R. Seddon, Kristiina W�h�l�
2017
Australian journal of chemistry (Print)
7 Nine new (+)-dehydroabietylimidazolium salts were synthesised and studied as chiral solvating agents for a number of different 8 racemic aromatic and nonaromatic carboxylate salts. These cationic chiral solvating agents resolve racemic ionic analytes better 9 than non-ionic ones. Bis(dehydroabietylimidazolium) bis(trifluoromethanesulfonimide) gave the best discrimination for the 10 enantiomers of carboxylate salts. Its resolution behaviour was studied by an NMR titration experiment, which
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... cated 1:1 11 complexation with the racemic analyte. The dehydroabietylimidazolium salts were also useful in enantiomeric excess (ee) 12 determinations, and for the recognition of chirality of racemic aromatic and non-aromatic -substituted carboxylic acids. 13 65 mass spectrometry (Brucker MicroTOF LC) with electrospray ionisation (ESI). 66 Compound characterisation 67 NMR experiments were performed using Varian UNITY INOVA 500 and Varian Mercury Plus 300 instruments at 27 °C. 1 H 68 NMR spectra were recorded with 4-16 transients, 4085-8000 Hz spectral width, and 1.9 s acquisition time at 500 MHz. 13 C NMR 69 spectra were recorded with 576-1500 transients, 20000-31446 Hz spectral width and 1.8 s acquisition time at 125 or 75 MHz. 19 F 70 NMR spectra were recorded with 16-32 transients, 19047 Hz spectral width, 5.0 s relaxation delay and 1.0 s acquisition time at 71 470 MHz. All 2D HSQC spectra (see supporting information) were recorded using the Varian UNITY INOVA 500 instrument 72 with 4 transients, 128-300 increments, 8000-4085 Hz spectral widths in 1 H-dimension, 22955-31446 Hz spectral widths in 13 C-73 dimension, 1.0-2.0 s relaxation delays, and 0.128 s acquisition time. TMS was used as the reference compound in NMR 74 measurements. Chemical shift scale of 19 F was fixed by applying absolute, indirect referencing by calculating the frequency 75 position for 0.0 ppm in 19 F chemical shift scale from the 1 H chemical shift scale. To differentiate the proton and carbon signals of 76 aromatic and imidazolium and 2-imidazolinium structures, subscript Ar (CHAr) is used for aromatic and im (CHim) for 77 imidazolium and 2-imidazolinium. 78 79 Preparations 80 Purification of (+)-dehydroabietylamine Crude 60 % (+)-dehydroabietylamine (42.0 g) was dissolved in toluene (70.0 cm 3 ) and 81 ethanoic acid (9.65 g) in toluene (30.0 cm 3 ) was slowly added. The salt was left to crystallise in the refrigerator. The product was 82
doi:10.1071/ch16545
fatcat:ksgtdf4rp5estb6dd6cncgu7dm