K. Ghosh, I. Saha / Journal of Molecular Structure 1042 (2013) 57–65
59
2.5. 3-(2-Chloroacetamido)-N-propylbenzamide (7)
1.08 mmol) was added and the reaction mixture was refluxed for
36 h under nitrogen atmosphere. On cooling the reaction mixture
precipitate appeared and it was filtered off. The precipitate was
washed with CH3CN for several times to give pure chloride salt
11 (0.340 g, yield 77%). The almost pure chloride salt 11 (0.200 g,
0.35 mmol) was next dissolved in 2 mL hot MeOH and NH4PF6
(0.069 g, 0.43 mmol) was added in one portion. After stirring the
reaction mixture for 30 min, water was added. The precipitate
was filtered, washed with water and dried to give 2 (0.210, yield
88%), mp 157 °C. 1H NMR (400 MHz, DMSO-d6) d 10.60 (1H, s),
8.94 (1H, s), 8.93 (1H, s), 8.44 (2H, d, J = 8 Hz), 8.36 (2H, d,
J = 8 Hz), 8.27 (2H, d, J = 8 Hz), 8.05 (1H, d, J = 8 Hz), 7.94 (1H, s),
7.85 (1H, t, J = 8 Hz), 7.77 (1H, t, J = 8 Hz), 7.69 – 7.59 (m, 4H),
7.53 (1H, d, J = 8 Hz), 7.35 (1H, t, J = 8 Hz), 6.80 (2H, s), 5.30 (2H,
s), 4.70 (1H, t, J = 8 Hz), 3.49–3.43 (2H, m) [signal for –OH group
was not found due to broadening]; 13C NMR in CD3CN (100 MHz)
d 166.5, 162.4, 141.1, 137.5, 135.2, 132.0, 131.3, 131.2, 130.9,
130.7, 129.3, 128.8, 127.8, 127.3, 127.0, 125.4, 122.5, 122.3,
121.9, 120.4, 118.2, 113.6, 113.3, 60.3, 48.7, 43.6, 42.0; FTIR (KBr,
cmꢂ1) 3389, 2924, 2852, 1702, 1643, 1591, 1560; Mass (LCMS,
To a stirred solution of 3-amino-N-propylbenzamide 5 (0.70 g,
3.93 mmol) in dry CH2Cl2 (30 mL) chloroacetyl chloride (0.577 g,
5.11 mmol) was added followed by addition of Et3N (0.517 g,
5.11 mmol). After the reaction mixture was stirred for 2 h at room
temperature solvent was evaporated under reduced pressure. The
reaction mixture was then neutralized with NaHCO3 solution and
extracted with CHCl3 (30 mL ꢁ 3). The combined organic layer
was dried over anhydrous Na2SO4 and concentrated on a rotary
evaporator. Purification by silica gel column chromatography using
70% ethyl acetate in petroleum ether yielded the compound 7
(0.750 g, yield 75%), mp. 148 °C, 1H NMR (400 MHz, CDCl3): d 8.45
(1H, s), 7.96 (1H, s) 7.78 (1H, d, J = 8 Hz), 7.57 (1H, d, J = 8 Hz),
7.44 (1H, t, J = 8 Hz), 6.23 (1H, br s), 4.23 (2H, s) 3.47–3.42 (2H,
m), 1.74–1.62 (2H, m), 1.03 (3H, t, J = 3.20 Hz); FTIR (KBr, cmꢂ1
3286, 3107, 2960, 2873, 16773, 1638, 1621, 1597, 1542.
)
2.6. 3-(2-Chloroacetamido)-N-(2-hydroxyethyl)benzamide (8)
To a stirred solution of compound 6 (0.700 g, 3.88 mmol) in dry
CH2Cl2 (30 mL), chloroacetyl chloride (0.658 g, 5.83 mmol) in dry
CH2Cl2 was added dropwise followed by addition of Et3N
(0.590 g, 5.83 mmol). After stirring the reaction mixture for 2 h at
room temperature, solvent was evaporated off under reduced pres-
sure. The crude reaction mixture was neutralized with NaHCO3
solution and the aqueous layer was extracted with CHCl3
(30 mL ꢁ 3). The combined organic layer was dried over anhydrous
Na2SO4 and concentrated on rotary evaporator. The crude mass
was purified by silica gel column chromatography using 2% CH3OH
in CHCl3 to give compound 8 (0.650 g, yield 65%), mp 150 °C. 1H
NMR (400 MHz, DMSO-d6) d 10.44 (1H, s), 8.42 (1H, s), 8.02 (1H,
s), 7.75 (1H, d, J = 8 Hz), 7.56 (1H, d, J = 8 Hz), 7.40 (1H, t,
J = 8 Hz), 4.71 (1H, br, s), 4.26 (s, 2H), 3.67–3.48 (2H, m), 3.33–
3.16 (2H, m); FTIR (KBr, cmꢂ1) 3275, 3108, 2943, 2875, 1673,
1646, 1622, 1598, 1546.
ES+) C33H29N4O3.PFꢂ requires 529.2 for (M–PFꢂ6 ), found 529.1.
6
2.9. General procedure of fluorescence titration
Stock solutions of the hosts and guests were prepared in CHCl3
maintaining the amount of CH3CN and 2.5 ml of the individual host
solution was taken in the cuvette. The solution was irradiated at
the excitation wavelength maintaining the excitation and emission
slits. Upon addition of guest anions, the change in fluorescence
emission of the host was noticed. The corresponding emission val-
ues during titration were noted and used for the determination of
binding constant values. The change of fluorescence emission in
the presence of different amounts of guest anions was used to have
the Stern–Volmer plot.
2.10. General procedure of UV–vis titration
2.7. Receptor 1
The receptors were dissolved in dry UV grade in CHCl3 main-
taining the amount of CH3CN and 2.5 ml of the individual host
solution was taken in the cuvette. Then, anions, dissolved in dry
CH3CN were individually added in different amounts to the recep-
tor solution. The corresponding absorbance values during titration
were noted and used for the determination of binding constant
values.
To a solution of 7 (0.200 g, 0.78 mmol) in dry CH3CN (20 mL), 1-
(9-anthracenylmethyl) benzimidazole 9 [15] (0.251 g, 1.08 mmol)
was added and the reaction mixture was stirred under refluxing
condition for 36 h under nitrogen atmosphere. The reaction mix-
ture was cooled to room temperature and the precipitate was fil-
tered off. The precipitate was washed with CH3CN for several
times to give pure chloride salt 10 (0.350 g, yield 79%). The pure
chloride salt 10 (0.200 g, 0.36 mmol) was dissolved in 2 mL hot
MeOH and NH4PF6 (0.069 g, 0.43 mmol) was added in one portion.
After stirring the solution for 30 min. water was added and the pre-
cipitate was filtered, washed with water and dried to give com-
pound 1 (0.220, 92%), mp 120 °C. 1H NMR (400 MHz, CDCl3
containing 2% DMSO-d6) d 9.84 (1H, s, –NH–), 8.77 (1H, s), 8.64
(1H, s), 81.2–8.06 (4H, m), 7.76–7.70 (3H, m), 7.61–7.44 (8H, m),
7.23 (1H, t, J = 8 Hz), 6.49 (1H, br, t, –NH–), 6.48 (2H, s), 5.20 (2H,
s), 3.25 (2H, q, J = 8 Hz), 1.53–1.50 (2H, m), 0.87 (3H, t, J = 8 Hz);
13C NMR (100 MHz, DMSO-d6) d 166.4, 164.0, 142.7, 138.6, 136.0,
132.6, 131.6, 131.4, 131.0, 129.9, 129.3, 128.4, 127.6, 127.2, 126.1,
123.7, 122.6, 122.0, 118.9, 114.4, 114.3, 49.5, 43.8, 41.4, 22.7, 11.8
(two carbons in aromatic region are not resolved); FTIR (KBr,
cmꢂ1): 3390, 2965, 2934, 1703, 1644, 1591, 1561; Mass (LCMS,
ES+) C34H31N4O2.PF6 requires 527.2 for (M-PF6), found 527.2.
2.11. Method for Job plot [24]
The stoichiometry was determined by the continuous variation
method. In this method, solutions of host and guests of equal con-
centrations were prepared in dry in CHCl3 maintaining the amount
of CH3CN. Then host and guest solutions were mixed in different
proportions maintaining a total volume of 3 mL of the mixture.
The related compositions for host:guest (v/v) were 3:0, 2.8:0.2;
2.5:0.5, 2.2:0.8, 2:1, 1.8:1.2, 1.5:1.5, 1:2, 0.8:2.2, 0.5:2.5, 0.2:2.8.
All the prepared solutions were kept for 1 h with occasional shak-
ing at room temperature. Then emission and absorbance of the
solutions of different compositions was recorded. The concentra-
tion of the complex i.e., [HG] was calculated using the equation
[HG] =
D
I/I0 ꢁ [H] or [HG] =
D
A/A0 ꢁ [H] where
DI/I0 and DA/A0
indicate the relative emission and absorbance intensities. [H] de-
notes the concentration of pure host. Mole fraction of the host
(XH) was plotted against concentration of the complex [HG]. In
the plot, the mole fraction of the host at which the concentration
of the host–guest complex concentration [HG] is maximum, gives
the stoichiometry of the complex.
2.8. Receptor 2
To a stirred solution of 8 (0.200 g, 0.78 mmol) in dry CH3CN
(20 mL), 1-(9-anthracenylmethyl) benzimidazole 9 [15] (0.251 g,