PEREZ ET AL.
5
was sonicated in an ultrasonic bath for 8 hr until a vis-
cous yellow liquid is obtained. The resulting liquid was
cooled to room temperature before it was washed thrice
with ethyl acetate to remove any unreacted materials.
The mixture was vacuum-dried for 3–4 hr at 80ꢀC and
lyophilized overnight to obtain the pure IL as a viscous
yellow liquid. Both [HMIM]Br and [OMIM]Br ILs were
characterized via FT-IR, 1H-NMR, and 13C-NMR
spectroscopy.
1a: 1-hexyl-3-methylimidazolium bromide [HMIM]
Br: 90% yield. IR (cm−1, neat): 3,369, 3,071, 2,924, 1,569,
1,454, 1,169, 1,042. 1H-NMR (500 MHz, DMSO-D6):
δ(ppm) = 10.11 (s, 1H), 7.52 (d, J = 80.2 Hz, 2H), 4.26 (t,
J = 7.4 Hz, 2H), 4.06 (s, 3H), 1.90–1.76 (m, 2H), 1.38–1.76
(m, 6H), 0.80 (t, J = 6.7 Hz, 3H). 13C-NMR (500 MHz,
CDCl3): δ(ppm) = 137.08, 123.75, 122.01, 50.05, 36.71,
31.02, 30.20, 25.82, 22.33, 13.9.
1b: 1-octyl-3-methylimidazolium bromide [OMIM]Br:
93% yield. IR (cm−1, neat) νmax = 3,415, 3,066, 2,924,
2,854, 1,570, 1,462, 1,377, 1,336, 1,166. 1H-NMR
(500 MHz, DMSO-D6): δ(ppm) = 9.16 (s, 1H), 7.76 (dd,
J = 19.4, 18.0 Hz, 2H), 4.15 (t, J = 7.2 Hz, 2H), 3.84 (s,
3H), 1.80–1.72 (m, 2H), 1.36–1.13 (m, 10H), 0.84 (t,
J = 6.9 Hz, 3H). 13C-NMR (500 MHz, DMSO-D6):
δ(ppm) = 138.9,124.02, 122.69, 49.2, 36.21, 31.62, 29.84,
28.94, 28.79, 25.94, 22.52, 14.41.
fractions containing the desired product were collected,
subjected to rotary evaporation at 40ꢀC, and further lyophi-
lized for 24 hr to obtain the [RMIM]RCOO IL (2a–2h). All
carboxylate-based ILs were then characterized via FT-IR,
1H-NMR, and 13C-NMR spectroscopy.
2a: 1-hexyl-3-methylimidazolium crotonate [HMIM]
crotonate: 87% yield. IR (cm−1, neat) vmax = 3,334, 3,038,
2,920, 2,847, 1,550, 1,349, 1,164 cm−1
.
1H-NMR
(500 MHz, DMSO-D6): δ(ppm) = 9.820 (s, 1H), 7.840 (m,
2H), 6.212 (m, 1H), 5.639 (dq, J = 15.2, 1.6 Hz, 1H), 4.154
(t, J = 7.3 Hz, 2H), 3.850 (s, 3H), 1.729 (m, 2H), 1.618 (m,
3H), 1.207 (m, 6H), 0.807 (t, J = 6.8 Hz, 3H). 13C-NMR
(500 MHz, DMSO-D6): δ(ppm) = 170.477, 137.883,
134.140, 132.573, 123.955, 122.644, 49.021, 35.963, 31.031,
29.928, 25.608, 22.347, 17.492, 14.245.
2b: 1-octyl-3-methylimidazolium crotonate [OMIM]
crotonate: 92% yield. IR (cm−1, neat) νmax = 3,340, 3,140,
1
3,030, 2,900, 2,850, 1,650, 1,550, 1,350, 1,180 cm−1. H-
NMR (500 MHz, DMSO-D6): δ(ppm) = 9.884 (s, 1H),
7.779 (dt, J = 38.3, 1.6 Hz, 2H), 6.149 (m, 1H), 5.617 (m,
1H), 4.139 (t, J = 7.2 Hz, 2H), 3.834 (s, 3H), 1.731 (m,
2H), 1.611 (dd, J = 6.8, 1.7 Hz, 3H), 1.203 (m, 10H), 0.797
(t, J = 6.9 Hz, 3H). 13C-NMR (500 MHz, DMSO-D6):
δ(ppm) = 170.204, 137.993, 134.807, 131.810, 123.941,
122.642, 49.017, 35.969, 31.628, 29.956, 28.970, 25.968,
22.512, 17.490, 14.362.
2c: 1-hexyl-3-methylimidazolium cinnamate [HMIM]
cinnamate: 92% yield. IR (cm−1, neat) vmax = 3,345,
3.3 | Synthesis and characterization of
1-alkyl-3-methylimidazolium carboxylate
[RMIM]RCOO ILs
3,066, 2,931, 2,853, 1,550, 1,354, 1,181 cm−1 1H-NMR
.
(500 MHz, DMSO-D6): δ(ppm) = 9.717 (s, 1H), 7.780 (dt,
J = 37.1, 1.7 Hz, 2H), 7.413 (dd, J = 8.1, 0.9 Hz, 2H),
7.293 (m, 2H), 7.053 (m, 1H), 7.021 (d, J = 15.9 Hz, 1H),
6.370 (d, J = 15.9 Hz, 1H), 4.150 (t, J = 7.3 Hz, 2H), 3.857
(s, 3H), 1.733 (m, 2H), 1.197 (m, 6H), 0.793 (t, J = 5.0 Hz,
3H). 13C-NMR (500 MHz, DMSO-D6): δ(ppm) = 169.882,
137.742, 137.375, 135.004, 131.628, 128.992, 128.121,
127.193, 123.976, 122.656, 49.076, 36.042, 31.019, 29.892,
25.626, 22.341, 14.272.
A glass column (1-cm diameter) was packed with 5.0 g of
wet anion exchange resin Amberlyst A-26 (OH− form).
The column was then washed with deionized water,
followed by equilibration using increasing concentrations
(25, 50, 75, and 100%) of methanol (eluent). To load the
resin with the carboxylate anion, a 1% carboxylic acid
(crotonic, cinnamic, salicylic, or oxalic acid) in methanol
solution was allowed to pass slowly through the resin
until the pH of the eluate matched the pH of the original
acid solution. Subsequently, the column was washed with
methanol until the pH is constant.
A 0.05 M methanolic solution of [RMIM]Br (1a, 1b)
was then slowly passed through the column and the eluates
were obtained in portions. The fractions were subjected to a
silver nitrate test (3 drops of 1% AgNO3) to detect the pres-
ence of bromide ions. The presence of the desired IL
([RMIM]RCOO) is signified by the formation of a white
precipitate (silver carboxylate salt) while a yellow precipi-
tate (AgBr) indicates the presence of bromide ions. Further
addition of a few drops of 1% HNO3 solution dissolves the
silver carboxylate salts but not the AgBr precipitate. All
2d: 1-octyl-3-methylimidazolium cinnamate [OMIM]
cinnamate: 87% yield. IR (cm−1, neat) νmax = 3,340,
3,140, 3,070, 2,900, 2,850, 1,600, 1,550, 1,300, 1,250, 1,170,
1
1,020 cm−1. H-NMR (500 MHz, DMSO-D6): δ(ppm) =
9.70 (s, 1H), 7.78 (dt, J = 38.7, 1.7 Hz, 2H), 7.41 (m, 2H),
7.289 (dd, J = 10.4, 4.7 Hz, 2H), 7.209 (ddt, J = 12.1, 10.9,
5.5 Hz, 1H), 7.02 (d, J = 15.9 Hz, 1H), 6.369 (d,
J = 15.9 Hz, 1H), 4.149 (t, J = 7.2 Hz, 2H), 3.856 (s, 3H),
1.734 (m, 2H), 1.181 (m, 10H), 0.797 (t, J = 7.0 Hz, 3H).
13C-NMR (500 MHz, DMSO-D6): δ(ppm) = 169.880,
137.763, 137.375, 135.004, 131.615, 128.975, 128.107,
127.187, 123.963, 122.662, 49.085, 36.048, 31.614, 29.945,
28.963, 28.829, 25.982, 22.503, 14.372.
2e: 1-hexyl-3-methylimidazolium salicylate [HMIM]
salicylate: 94% yield. IR (cm−1, neat) vmax = 3,071, 2,953,