R.M. El-Shishtawy et al. / Dyes and Pigments 96 (2013) 45e51
47
d
55.35, 114.08, 121.63, 125.87, 131.05, 160.62, 163.31, 172.55,
2H, AreH), 8.66 (d, 1H, J ¼ 7.8 Hz, AreH), 8.75 (s, 1H, CH]C). 13
C
181.41.
NMR (125 MHz, CDCl3)
d
12.80, 45.42, 55.49, 69.77, 113.90, 114.44,
114.78, 123.85, 125.11, 125.80, 126.01, 132.47, 134.36, 135.15, 136.96,
138.06, 139.94, 143.91, 153.39, 160.77, 161.68, 170.58, 183.00, 188.07.
2.6. 2-((4-(diethylamino)phenyl)diazenyl)-4-(4-methoxyphenyl)
thiazole-5-carbaldehyde (6)
IR n
/cmꢁ1 2211, 1746, 1697, 1595, 1519, 1214, 1102, 1065. HRMS calcd
for C33H26N6O2S: 570.68. Found: 570.95.
NaNO2 (516 mg, 7.48 mmol) was added to 95e98% H2SO4
(5.6 ml) and the mixture was heated at 65 ꢂC until complete
dissolution. After being cooled in an ice-bath (0e5 ꢂC), the nitro-
sylsulphuric acid solution was diluted with AcOH (3.2 ml) over
3 min and then left for 10 min. Following cooling to ꢁ5 ꢂC,
compound 5 (1.0 g, 6.15 mmol) was added portion wise and, once
the addition was complete (15 min), the reaction mixture was
stirred for 2 h at 5 ꢂC. The so formed diazonium salt solution was
added gradually (10 min) to a mixture of N,N-diethylaniline (1.0 ml,
6.29 mmol) in water (62 ml) and 95e98% H2SO4 (1.2 ml), at 0 ꢂC
under vigorous stirring, after which the reaction mixture was left at
rt for 1 h. The resulting solid was then collected by filtration,
washed with water and dried. Column chromatography on silica gel
using CHCl3 as the eluent afforded compound 6 as violet crystals.
Yield: 43.3%. Mp 167e169 ꢂC. 1H NMR (600 MHz, CDCl3) 1.28 (t, 6H,
J ¼ 7.2 Hz, N (CH2CH3)2), 3.53 (q, 4H, J ¼ 7.2 Hz, N(CH2CH3)2), 3.91 (s,
3H, OCH3), 6.76 (d, 2H, J ¼ 9.6 Hz, AreH), 7.05 (d, 2H, J ¼ 7.2 Hz,
AreH), 7.8 (d, 2H, J ¼ 7.2 Hz, AreH), 7.98 (d, 2H, J ¼ 9 Hz, AreH),
3. Results and discussion
3.1. Synthesis
Hantzsch thiazole synthesis in which the reaction proceeds
between a-halocarbonyl compounds and thioureas or thioamides
provides a useful method for the synthesis of thiazoles. Likewise
the synthetic procedure reported earlier for the synthesis of other
thiazole derivatives, compound 2 was obtained quantitatively by
the treatment of 1 with thiourea in acetone at room temperature
after being neutralized with dilute ammonia [29]. It is known
that heteroaromatic compounds undergo VilsmeiereHaack for-
mylations at the electron rich positions [30]. Thus, it is expected
that compound 2 can be easily formylated at the fifth position in the
thiazole ring. For this propose, it was necessary to protect the
amino group by the usual acetylation reaction as indicated in
Scheme 1 to furnish compound 3, which underwent formylation to
produce the formyl product 4 in good yield. Acid catalyzed deace-
tylation of 4 affords the thiazole derivative 5 in good yield.
The common practice of diazotization and coupling was used to
prepare azo dye 6 using thiazole derivative 5 as the diazo compo-
nent and N,N-diethylaniline as the coupling component. Thus,
thiazole derivative 5 was diazotized with nitrosyl sulfuric acid and
then coupled with N,N-diethylaniline dissolved in 0.36 M H2SO4 in
an ice bath to get the corresponding azo dye 6 (Scheme 1) as the
aldehyde precursor for the NLO chromophores (aec). The struc-
tures of compounds 2e6 were confirmed by their analytical and
spectral data.
10.01 (s, 1H, CHO). 13C NMR (125 MHz, CDCl3)
d 12.73, 45.26,
55.44, 111.68, 114.17, 125.98, 130.70, 131.44, 134.87, 142.69, 153.09,
161.10, 162.94, 182.16, 184.90.
2.7. General procedure for the synthesis of NLO chromophores aec
A mixture of dye 6 (1.18 g, 3 mmol) and indandione (0.438 g,
3 mmol) or malononitrile (0.198 g, 3 mmol) or 3-dicyanovinylindan-
1-one (0.582 g, 3 mmol) in basic ethanol solution (7 ml) was stirred
at room temperature overnight, filtered off and purified by column
chromatography on silica gel using CHCl3 as the eluent, affording
dyes a or b or c, respectively.
Knoevenagel condensation [31] of aldehyde 6 with 1H-indene-
1,3(2H)-dione, malononitrile and 2-(3-oxo-2,3-dihydro-1H-inden-
2.7.1. Dye a
Yield: 75%. Mp 185e187 ꢂC. 1H NMR (600 MHz, CDCl3) 1.3 (t, 6H,
J ¼ 7.2 Hz, N(CH2CH3)2), 3.55 (q, 4H, J ¼ 7.2 Hz, N(CH2CH3)), 3.92 (s,
3H, OCH3), 6.78(d, 2H, J ¼ 9 Hz, AreH), 7.08(d, 2H, J ¼ 9 Hz, AreH), 7.6
(d, 2H, J ¼ 9 Hz, AreH), 7.79 (m, 2H, AreH), 7.96 (m, 1H, AreH), 7.99
(m, 1H, AreH), 8.03 (d, 2H, J ¼ 9.6 Hz, AreH), 8.09 (s, 1H, CH]C). 13C
NMR (125 MHz, CDCl3)
d 12.77, 45.28, 55.45, 114.20, 122.88, 122.96,
124.96, 125.36, 126.46, 132.17, 134.86, 135.02, 136.03, 140.45, 142.03,
143.50, 152.97, 161.16, 168.24, 181.88, 189.71, 190.26. IR
n
/cmꢁ1 2924,
1678,1600,1564,1514, 1351, 1292,1245,1213,1140,1014, 986. HRMS
calcd for C30H26N4O3S: 522.63. Found: 522.91.
2.7.2. Dye b
Yield: 59.7%. Mp 158e160 ꢂC. 1H NMR (600 MHz, CDCl3) 1.31 (t,
6H, J ¼ 7.2 Hz, N(CH2CH3)2), 3.56 (q, 4H, J ¼ 7.2 Hz, N(CH2CH3)), 3.9
(s, 3H, OCH3), 6.78 (d, 2H, J ¼ 9 Hz, AreH), 7.07 (d, 2H, J ¼ 9 Hz,
AreH), 7.64 (d, 2H, J ¼ 7.2, AreH), 7.86 (s, 1H, CH]C), 8.00 (m, 2H,
AreH). 13C NMR (125 MHz, CDCl3)
d 12.80, 45.51, 55.53, 113.44,
114.49, 114.89, 123.42, 125.43, 131.73, 143.56, 150.61, 153.81, 161.57,
166.44, 182.41. IR
n
/cmꢁ1 2917, 2211, 1598, 1538, 1412, 1335, 1224,
1195, 1099, 1063. HRMS calcd for C24H22N6OS: 442.55. Found:
442.97.
2.7.3. Dye c
Yield: 66.6%. Mp 208e210 ꢂC. 1H NMR (600 MHz, CDCl3) 1.31 (t,
6H, J ¼ 7.2 Hz, N(CH2CH3)2), 3.56 (q, 4H, J ¼ 7.2 Hz, N(CH2CH3)), 3.92
(s, 3H, OCH3), 6.78 (d, 2H, J ¼ 9.6 Hz, AreH), 7.08 (d, 2H, J ¼ 7.2 Hz,
AreH), 7.76 (m, 4H, AreH), 7.93 (d, 1H, J ¼ 7.2 Hz, AreH), 8.03 (m,
Scheme 1. Synthesis of 2-((4-(diethylamino)phenyl)diazenyl)-4-(4-methoxyphenyl)
thiazole-5-carbaldehyde. Reagents and conditions. (i) thiourea, acetone, rt, 5%
ammonia solution; (ii) Ac2O, reflux; (iii) DMF-POCl3, 0e80 ꢂC; (vi) 25% HCl/MeOH,
reflux; (v) H2SO4, NaNO2, AcOH, ꢁ5e5 ꢂC, N,N-diethylaniline, H2SO4, H2O, ꢂC to rt.