backbone (Liddle and Arnold 2005). The imidazolium salts with SiOMe 3 groups can
also be synthesized with greater yield using direct quaternization. The hydrophilicity
of these imidazolium salts may be controlled on the surfaces of Si/SiO 2 by anion
exchange (Gao et al. 2004).
Less attention was given on the synthesis of pyridinium-based functionalized
ionic liquids rather than imidazolium systems. Pyridinium-based ionic liquids are
successfully functionalized as the nitrile salt, 1,2,4-substitute-triazolium salts, and
phosphazene-based ionic liquids. Other low melting salts have also been formed
using quaternization of pyrazine and pyrimidine with alkyl and polyfluoroalkyl
halides. Functionalized ammonium ionic liquids, also known as ammonium salts,
have been synthesized with ether groups. The ammonium salts show enhancement in
cathodic and anodic stability and provide larger electrochemical window (Zhao
2007).
Table 12.1 Physical properties of ionic liquids at 25
C
Cation
Anion
Abbreviation
Melting
Point
C
Density
g ml
À1
Viscosity
cP
N
N
[BF 4 ]
À
[C 2 mim][BF 4 ]
6
1.248
66
[PF 6 ]
À
[C 2 mim][PF 6 ]
5 8 –62
1.373
450
N
N
[BF 4 ]
À
[C 4 mim][BF 4 ]
À82
1.208
233
[PF 6 ]
À
[C 4 mim][PF 6 ]
10
1.373
400
[CF 3 SO 3 ]
À [C 4 mim][CF 3 SO 3 ] 16
1.290
90
[Tf 2 N]
À
[C 4 mim][Tf 2 N]
À8
1.404
48
N
N
[BF 4 ]
À
[C 6 mim][BF 4 ]
À82
1.075
211
[PF 6 ]
À
[C 6 mim][PF 6 ]
À61
1.304
800
N
N
[BF 4 ]
À
[C 8 mim][BF 4 ]
À79
1.11
440
[cl]
À
[C 8 mim][cl]
0
1.000 16,000
N
[Tf 2 N]
À
[C 1 pyr][Tf 2 N]
0
1.44
39
N
N
[Br]
[C 4 mim][Br]
65–75
1.3
1486.49
[N(CN) 2 ] [C 4 mim][N(CN) 2 ] À6
1.06
334
[CH 3 COO] [C 4 mim][CH 3 COO] À20
1,02
440
N
N
[C 4 SO 3 ]
[C 2 mim][C 4 SO 3 ]
1–7
1.17
180.8
Han and Row (2010)
C ¼ alkyl group; mim ¼ methyl imidazolium; pyr ¼ pyridinium
396
D. S. Patle et al.
also be synthesized with greater yield using direct quaternization. The hydrophilicity
of these imidazolium salts may be controlled on the surfaces of Si/SiO 2 by anion
exchange (Gao et al. 2004).
Less attention was given on the synthesis of pyridinium-based functionalized
ionic liquids rather than imidazolium systems. Pyridinium-based ionic liquids are
successfully functionalized as the nitrile salt, 1,2,4-substitute-triazolium salts, and
phosphazene-based ionic liquids. Other low melting salts have also been formed
using quaternization of pyrazine and pyrimidine with alkyl and polyfluoroalkyl
halides. Functionalized ammonium ionic liquids, also known as ammonium salts,
have been synthesized with ether groups. The ammonium salts show enhancement in
cathodic and anodic stability and provide larger electrochemical window (Zhao
2007).
Table 12.1 Physical properties of ionic liquids at 25
C
Cation
Anion
Abbreviation
Melting
Point
C
Density
g ml
À1
Viscosity
cP
N
N
[BF 4 ]
À
[C 2 mim][BF 4 ]
6
1.248
66
[PF 6 ]
À
[C 2 mim][PF 6 ]
5 8 –62
1.373
450
N
N
[BF 4 ]
À
[C 4 mim][BF 4 ]
À82
1.208
233
[PF 6 ]
À
[C 4 mim][PF 6 ]
10
1.373
400
[CF 3 SO 3 ]
À [C 4 mim][CF 3 SO 3 ] 16
1.290
90
[Tf 2 N]
À
[C 4 mim][Tf 2 N]
À8
1.404
48
N
N
[BF 4 ]
À
[C 6 mim][BF 4 ]
À82
1.075
211
[PF 6 ]
À
[C 6 mim][PF 6 ]
À61
1.304
800
N
N
[BF 4 ]
À
[C 8 mim][BF 4 ]
À79
1.11
440
[cl]
À
[C 8 mim][cl]
0
1.000 16,000
N
[Tf 2 N]
À
[C 1 pyr][Tf 2 N]
0
1.44
39
N
N
[Br]
[C 4 mim][Br]
65–75
1.3
1486.49
[N(CN) 2 ] [C 4 mim][N(CN) 2 ] À6
1.06
334
[CH 3 COO] [C 4 mim][CH 3 COO] À20
1,02
440
N
N
[C 4 SO 3 ]
[C 2 mim][C 4 SO 3 ]
1–7
1.17
180.8
Han and Row (2010)
C ¼ alkyl group; mim ¼ methyl imidazolium; pyr ¼ pyridinium
396
D. S. Patle et al.