Ionic liquid characteristics of 1-alkyl-n-cyanopyridinium and 1-alkyl-n-(trifluoromethyl)pyridinium salts

Abstract

1-Alkyl-n-cyanopyridinium and 1-alkyl-n-(trifluoromethyl)pyridinium salts have been synthesised and characterised in order to compare the effects of different electron-withdrawing functional groups on their ability to form ionic liquids. The presence of the electron-withdrawing nitrile or trifluoromethyl substituent on the pyridinium ring leads to salts with higher melting points than with the corresponding 1-alkylpyridinium or 1-alkylpicolinium cations. Solid-state structures were determined by single crystal X-ray crystallography for seven salts; 1-methyl-4-cyanopyridinium methylsulfate, and 1-methyl-3-cyanopyridinium, 1-methyl-4-cyanopyridinium, 1-ethyl-2-cyanopyridinium, 1-ethyl-3-cyanopyridinium, 1-ethyl-4-cyanopyridinium and 1-ethyl-4-(trifluormethyl)pyridinium bis{(trifluoromethyl)sulfonyl}imide, and show the effects of ring-substitution position on hydrogen-bonding in the solid-state and on melting points.