Preparation, Physicochemical Properties, and Crystal Structures of Trifluoroacetic Acid Aminium Salts

Monoethanolaminium trifluoroacetate (HO‒CH2CH2‒NH $$_{3}^{ + }$$ ‒O(O)C‒CF3), triethanolaminium trifluoroacetate ((HO‒CH2CH2)3NH+ ‒O(O)C‒CF3), tris(hydroxymethyl)methanaminium trifluoroacetate ((HO‒CH2)3C-NH $$_{3}^{ + }$$ ‒O(O)C‒CF3), and 2,2'-(ethylenedioxy)di(ethylaminium) bis(trifluoroacetate) (CF3-C(O)O‒ +H3N-(CH2CH2O)2CH2CH2-NH $$_{3}^{ + }$$ ‒O(O)C‒CF3) were synthesized by the reactions of trifluoroacetic acid with monoethanolamine, triethanolamine, tris(hydroxymethyl)methanamine, and 2,2'-(ethylenedioxy)di(ethylamine), respectively. Ammonium trifluoroacetate (NH $$_{4}^{ + }$$ ‒OC(O)CF3) was prepared by the reaction of trifluoroacetic acid with hexamethyldisilazane and with trimethylsilyl trifluoroacetate CF3C(O)OSi(CH3)3. The synthesized compounds are low-melting crystalline salts, which are transferred into a vapor phase upon heating to 200–220°С. The reaction of CF3C(O)OSi(CH3)3 with monoethanolamine afforded monoethanolaminium trifluoroacetate instead of expected 2,2,2-trifluoro-N-(2-hydroxyethyl)acetamide CF3C(O)-NH-CH2CH2OH. The aminium salts were characterized by IR and NMR spectroscopy, mass spectrometry, high-performance liquid chromatography, and scanning electron microscopy. The thermal behavior and thermal stability of the salts were studied by differential scanning calorimetry and thermogravimetry, respectively. The molecular structures of monoethanolaminium trifluoroacetate, triethanolaminium trifluoroacetate, tris(hydroxymethyl)methanaminium trifluoroacetate, and ammonium trifluoroacetate were determined.