Synthesis and properties of ambient temperature molten salts based on the quaternary ammonium ion

The synthesis of 16 tetraalkyl ammonium bis(trifluoromethane sulfonyl) imide salts, (C_nH_2n+1)₄ +N -N (SO₂CF₃)₂ (n = 1, 2, 3, 4),  (C₂H₅)₂(i-C₃H₇)₂ +N -N(SO₂CF₃)₂, (C₂H₅)(CH₃)(i-C₃H₇)₂+N-N(SO₂CF₃)₂, (n-C₇H₁₅)(C₂H₅)i-C₃H₇)₂+N-N(SO₂CF₃)₂ and (C_nH_2n+1)(C_mH_2m+1)₃+N-N(SO₂CF₃)₂ (n = 6,7,8; m = 1, 2, 4) are reported in this paper. Trends in properties of these salts are discussed. The symmetrical tetraalkyl ammonium salts with the bis(trifluoromethyl sulfonyl) imide anion exhibited a lower melting point than that of corresponding ammonium halides. The salts with low symmetry ammonium cations were found to be of generally lower melting point, and many were stable liquids at room temperature. Several of these did not crystallize during cooling below room temperature and exhibited glass transition temperatures in the region of −60 °C∼−80 °C. A comparison of properties between the ammonium imide salts and corresponding trifluoromethane sulfonates is also presented.