1
p-Chlorobenzenesulfonate (12) obtained has mp 166-169°C. H NMR spectrum, δ, ppm, J (Hz): 2.97 (3H, s,
SCH3); 7.35 (2H, d, J = 8.0, m-H); 7.51 (1H, d, J = 9.0, 3-H); 7.68 (1H, t, J = 7.5, 6-H), 7.89 (1H, d, J = 7.5,
5-H); 7.90-7.94 (3H, m, 7-H, o-H); 8.39 (1H, d, J = 9.0, 4-H); 8.72 (1H, br. d, J = 8.0, 8-H). Found, %: C 52.23;
H 4.03; Cl 9.61; N 3.74; S 17.00. C16H14ClNO3S2. Calculated, %: C 52.24; H 3.84; Cl 9.64; N 3.81; S 17.43.
The solution obtained by washing the mixture with acetonitrile (see above) was poured into aqueous KI
solution (20%) and the bright yellow precipitate was filtered off to give the 1-alkyl-5-methylthioquinolinium
iodide 11a-c. This was purified chromatographically on an Al2O3 column (eluent CH2Cl2–CH3CN, 4:1) and
reprecipitated from CH2Cl2 using ether. The yields and basic parameters for the salts 11a-c are given in Table 2.
Preparation of the Symmetrical Quinocyanines (1a-c). A [5]. A mixture of quinaldine 2 (5 mmol),
compound 3 (5 mmol), and the sulfo ester 4 (11 mmol) was held for 5 h at 140°C, cooled to 120°C, dry pyridine
added (2 ml), and refluxed for 1.5 h. The reaction mass was cooled, poured into aqueous KI solution (20%),
extracted with CH2Cl2, the extract washed with hydrochloric acid (2%) and then water and dried over CaCl2.
The product was evaporated and the residue analyzed by the 1H NMR spectroscopic method.
Column chromatography of the indicated residue on SiO2 gave fractions 1-4 in sequence.
Fraction 1 (eluent CH2Cl2) was evaporated to give crystals of the sulfone 9 which was identical to a
known sample (mp [12] and 1H NMR spectrum) [9].
After repeated chromatography of fraction 2 on SiO2 (eluent CH2Cl2–MeCN, 4:1) the evaporation of the
eluate and reprecipitation of the residue from CH2Cl2 using ether gave the quinocyanines 1a-c. The yields and
basic parameters for the products 1a-c are given in Table 3.
Fraction 3 (eluent CH2Cl2–MeCN, 1:1) was evaporated to give the quinaldinium iodides 5a-c.
Fraction 4 (eluent MeCN) was evaporated to give the N-alkylpyridinium iodides 6a-c. Salt 6c was
identical to that reported in [13] (mp). The 1H NMR spectra for 6a-c were similar and agreed with the structures
for the N-alkylpyridinium salts (cf. [14]).
B. Equimolar amounts of the salts 5a-c and salts 11a-c respectively (0.15 mmol of each) were refluxed
in dry pyridine (1 ml) for 1.5 h, the reaction mixture was cooled, and worked up as in method A. The residue
obtained after evaporation of CH2Cl2 was analyzed using 1H NMR.
Chromatography of the indicated residue on a silica column using benzene gave the 1-alkylquinoline-
2(1H)-thiones 13a-c, CH2Cl2 gave 1-alkylquinoline-2(1H)-ones 14a-c, and a mixture of CH2Cl2–MeCN (4:1) the
quinocyanines 1a-c. The yields and parameters for compounds 1a-c are given in Table 3 and the parameters for
the thiones 13a-c and quinolones 14a-c in Table 4. Compound 13a is identical in 1H NMR spectrum to a sample
synthesized by oxidation of 1-decylquinolinium iodide [15] using potassium ferricyanide in basic medium to the
quinolone 14a (by a known method [16]) and thionylation of the latter with phosphorus pentasulfide using the
method in [17].
C. DMSO (1 ml, dried over molecule sieves) and a drop of Et3N were added to a mixture of equimolar
amounts of the salts 5a-c and salt 11a-c (0.15 mmol of each) and the obtained product was held at 110-120°C
for 1.5 h. It was then cooled, poured into aqueous KI solution (20%), and the precipitate filtered off or extracted
with CH2Cl2. The separation and purification of product 1 followed that in method A. The yields of compounds
1a-c are given in table 3.
Preparation of the Unsymmetrical Dyes 1d-f (Table 3). A. (see also the preparation of compounds
1a-c). A mixture of salt 5a-c (1 mmol) and compound 15 (1 mmol, synthesized as in method [18]) was refluxed
in dry pyridine (1 ml) for 1.5 h and then poured into aqueous KI solution (20%) and worked up as above.
Chromatography on an SiO2 column with CH2Cl2 eluent gave 1-ethylquinoline-2(1H)-thione 16 which was
identical in mp and 1H NMR spectrum to a sample synthesized by an independent route from
1-ethylquinolinium iodide via 1-ethylquinoline-2(1H)-thione (17) by the method in [16, 17]. The eluent CH2Cl2–
MeCN (4:1) gave the quinocyanines 1d-f.
B. DMSO (1 ml, dried over molecular sieves) and Et3N (1 drop) were added to a mixture of equimolar
amount of salt 5a-c and salt 15 (1 mmol of each). The reaction mixture was held at 110-120°C for 1.5 h, cooled,
and worked up as in method A.
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