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J.B. Chang et al. / Dyes and Pigments 88 (2011) 366e371
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The 1H NMR spectra were recorded on a Bruker Avance 500
spectrometer using DMSO-d6 and TMS as the solvent and the
internal standard, respectively. The FT-IR spectra were recorded on
a Thermo Scientific Nicolet 6700 using ATR method. Densities of
the dyes were measured using a Micromeritics AccuPyc II 1340.
The absorption spectra were measured on a HP 8452A spectro-
photometer which was equipped with a Glan-Thompson polarizer.
2.3. Synthesis of dichroic dyes (Dye1eDye4)
Dyes 1e4 were synthesized as shown in Scheme 2. A mixture
of 0.285 g (0.002 mol) of 5-amino-2-pyridine (I1), 18 mL of 2 M aq
hydrochloric acid and 0.14 g (0.002 mol) of sodium nitrite in water
(1 mL) was stirred for 1 h at 0e5 ꢀC. To this solution, a small amount
of sulfamic acid was added as a nitrous acid scavenger. The resulting
diazonium salt solution was added to a coupling component solu-
tion of J-J acid (I2) (1.07 g, 0.002 mol) dissolved in 150 mL of water
while the temperature and pH of the mixture were maintained at
0e5 ꢀC and 8e9, respectively, in the course of the addition.
After coupling, the solution was stirred for 2 h and the precipitate
was filtered, washed with brine and dried in a vacuum oven. The
crude product (Dye2) was refluxed in ethanol for 2 h, hot filtered,
washed with hot ethanol and then dried in a vacuum oven. The
other dichroic dyes (Dye1, 3, 4) were prepared in a similar manner.
The yields, 1H NMR and FT-IR data of the dyes are given below.
Dye 1: yield ¼ 90.1%; 1H NMR (DMSO-d6, ppm): 6.55 (s, 2H,
NH2), 6.66 (s, 1H, ArH), 6.69 (d, J ¼ 8.7 Hz,1H, ArH), 7.29 (s.1H, ArH),
7.51 (s. 1H, ArH), 7.80 (s. 1H, ArH), 7.82 (d, J ¼ 8.5 Hz, 2H, ArH), 7.87
(s.1H, ArH), 7.93 (d, J ¼ 8.6 Hz,1H, ArH), 7.98 (d, J ¼ 8.5 Hz, 2H, ArH),
8.24 (d, J ¼ 8.6 Hz, 2H, ArH), 15.7 (s, 1H, OH), 15.9 (s, 1H, OH); FT-IR
(ATR. cmꢁ1): 1049,1219 (eSO3),1605 (C]O), 2973 (OeH, carboxylic
acids), 3347 (NeH).
2.2. Synthesis of dye intermediates
2.2.1. Synthesis of dye intermediate (I1)
Dye intermediates were synthesized as shown in Scheme 1. 5-
amino-2-cyanopyridine (2.0 g, 0.0167 mol) was slowly added to
sulfuric acid (20 mL) with reaction stirring and the mixture was
heated at 90 ꢀC for 2 h in a sealed tube. The solution was diluted
with water (40 mL) and heated at 100 ꢀC for another 2 h. The
reaction mixture was cooled to room temperature and poured into
ice-water (200 mL). The solid separated was filtered, washed with
cold water and dried in a vacuum oven: yield ¼ 95.0%; 1H NMR
(DMSO-d6, ppm): 5.85 (s, 2H, NH2), 7.69 (d, J ¼ 8.5 Hz,1H, ArH), 7.69
(d, J ¼ 8.6 Hz, 1H, ArH), 8,95 (s, 1H, ArH); FT-IR (ATR. cmꢁ1): 3039
(OeH, carboxylic acid), 3347 (NeH).
2.2.2. Synthesis of dye intermediate (I2, J-J acid)
Dye 2: yield ¼ 88.2%; 1H NMR (DMSO-d6, ppm): 6.52 (s, 2H,
NH2), 6.65 (s,1H, ArH), 6.68 (d, J ¼ 8.6 Hz,1H, ArH), 7.28 (s.1H, ArH),
7.52 (s. 1H, ArH), 7.84 (s. 1H, ArH), 7.87 (d, J ¼ 9.0 Hz, 1H, ArH), 7.93
(d, J ¼ 8.6 Hz, 1H, ArH), 8.03 (d, J ¼ 8.4 Hz, 1H, ArH), 8.13
(d, J ¼ 8.5 Hz,1H, ArH), 8.24 (d, J ¼ 8.7 Hz,1H, ArH), 8.89 (s.1H, ArH),
15.7 (s, 1H, OH), 15.9 (s, 1H, OH); FT-IR (ATR. cmꢁ1): 1049, 1218
(eSO3), 1605 (C]O), 2974 (OeH, carboxylic acids), 3340 (NeH).
Dye 3: yield ¼ 88.3%; 1H NMR (DMSO-d6, ppm): 6.55 (s, 2H, NH2),
6.66 (s,1H, ArH), 6.69 (d, J ¼ 8.6 Hz,1H, ArH), 7.29 (s.1H, ArH), 7.52 (s.
1H, ArH), 7.53 (t, J ¼ 7.8 Hz,1H, ArH), 7.77 (d, J ¼ 7.6 Hz, 2H, ArH), 7.86
(s. 1H, ArH), 7.86 (d, J ¼ 7.8 Hz, 1H, ArH), 7.93 (d, J ¼ 8.5 Hz, 1H, ArH),
7.99 (d, J ¼ 8.5 Hz, 1H, ArH), 8.17 (s. 1H, ArH), 8.25 (d, J ¼ 9.0 Hz, 1H,
ArH),15.8 (s,1H, OH),16.2 (s,1H, OH)–; FT-IR (ATR. cmꢁ1): 1049,1219
(eSO3), 1608 (C]O), 3066 (OeH, carboxylic acids), 3347 (NeH).
7-amino-4-hydroxy-2-naphthalenesulfonic acid (5.30 g, 0.02 mol)
was dissolved in 100 mL of water at room temperature and pH of the
solution was adjusted to 7.0 by adding 10% sodium carbonate solution.
The solution was cooled to 0e5 ꢀC and 5 mL of 4 M aq sodium nitrite
solution was added dropwise. The ensuing solution was dropped into
50 mL of 2 M hydrochloric acid and stirred for 1 h, after which time,
a small portion of sulfamic acid was added as a nitrous acid scavenger.
The resulting diazonium salt solution was added to a coupling
component solution of 7-amino-4-hydroxy-2-naphthalenesulfonic
acid (5.30 g, 0.02 mol) dissolved in 150 mL of water, while the
temperature and pH of the mixture were maintained at 0e5 ꢀC and
8e9, respectively, in the course of the addition. The reaction mixture
was stirred for 2 h and the precipitate was filtered, washed with brine
and dried in a vacuum oven. The crude product was heated in ethanol
for 2 h under reflux, hot filtered, washed with hot ethanol and then
dried in a vacuum oven: yield ¼ 93.2%; 1H NMR (DMSO-d6, ppm): 6.37
(s, 2H, NH2), 6.66 (s,1H, ArH), 6.70 (d, J ¼ 8.6 Hz, 1H, ArH), 7.09 (s.
1H, ArH), 7.27 (s. 1H, ArH), 7.57 (s. 1H, ArH), 7.91 (s. 1H, ArH), 7.96
(d, J ¼ 8.5 Hz, 2H, ArH), 8.10 (d, J ¼ 9.1 Hz,1H, ArH),10.2 (s,1H, OH),16.3
(s, 1H, OH); FT-IR (ATR. cmꢁ1): 1041, 1180 (eSO3), 1608 (C]O), 3363
(NeH).
X
NaNO2/HCl/ 0-5oC
Diazotization
I2
Ya
NH2
pH 8-9/0-5oC
Yb
X
HO
HO
Ya
N
N
NH2
conc. H2SO4/H2O
NC
NH2
HOOC
NH2
N
N
N
N
Yb
I1
NaO3S
NaO3S
OH
NaNO2/HCl/ 0-5oC
Diazotization
J-acid
Dye1: X=C, Ya=COOH, Yb=H
Dye2: X=N, Ya=COOH, Yb=H
Dye3: X=C, Ya=H, Yb=COOH
Dye4: X=N, Ya=H, Yb=COOH
pH 8-9/0-5oC
HO3S
NH2
HO
HO
N
NH2
N
NaO3S
NaO3S
I2
Scheme 1. Synthesis of the dye intermediates (I1 and I2).
Scheme 2. Synthesis of the dichroic dyes (Dye 1eDye 4).