New Guanidinium-based Room-temperature Ionic Liquids. Substituent and Anion Effect on Density and Solubility in Water

In order to examine the influence of the alkyl chain length on some physical properties of guanidinium salts, the synthesis of a homologous series of new N ''-n-alkylsubstituted N,N-diethyl-N',N'-di-n-propyl-N ''-n-hexyl guanidinium ionic liquids (gILs), containing chloride (Cl), tetrafluoroborate (BF(4)), acesulfamate (Ace), saccharinate (Sac), and tosylate (Tos) as anions, is reported. C(n)-gILAce, C(n)-gILSac, and C(n)-gILBF(4) were obtained by ion exchange reaction of the corresponding hexasubstituted guanidinium chlorides (C(n)-gCl, n = 3, 4, 6, 8, 10), which were synthesized by a quaternization reaction of the pentaalkyl-substituted guanidine 3 and the corresponding alkylchloride in DMF. The tosylates gILs C(n)-gTos (n = 1, 2, 4, 6, 8, 10) were synthesized by alkylation of 3 with the corresponding alkyltosylates. Some physical properties, such as solubility in water and organic solvents, refractive index and density, are considered as a function of the length of the n-alkyl substituent R and the nature of the anion.