New synthetic strategy for novel 6-arylazo-5-methyl-3-aryl-thiazolo[2,3-c]- [1,2,4]triazoles and study of their solvatochromic properties

Article abstract of DOI:10.3906/kim-1211-36

Two series of 6-arylazothiazol[2,3- c ][1,2,4]triazoles were prepared via oxidative cyclization of the respective aldehyde N-(5-arylazo-4-methylthiazol-2- yl)-hydrazones. The structures of the latter hydrazone precursors and the azo compounds were confirm

Full text of DOI:10.3906/kim-1211-36

Turk J Chem
Turkish Journal of Chemistry
(2013) 37: 413 – 421
¨
http://journals.tubitak.gov.tr/chem/
˙
c
ꢀ TUBITAK
doi:10.3906/kim-1211-36
Research Article
New synthetic strategy for novel
6-arylazo-5-methyl-3-aryl-thiazolo[2,3-c]-[1,2,4]triazoles and study of their
solvatochromic properties
Ahmad Sami SHAWALI,1,∗ Mohie Eldin Moustafa ZAYED2
1Department of Chemistry, Faculty of Science, University of Cairo, Giza, Egypt
2Department of Chemistry, Faculty of Science, King Abdulaziz University, Jedda, Kingdom of Saudi Arabia
Received: 24.11.2012
•
Accepted: 20.03.2013
•
Published Online: 10.06.2013
•
Printed: 08.07.2013
Abstract: Two series of 6-arylazothiazol[2,3-c][1,2,4]triazoles were prepared via oxidative cyclization of the respective
aldehyde N-(5-arylazo-4-methylthiazol-2-yl)-hydrazones. The structures of the latter hydrazone precursors and the azo
compounds were confirmed by spectral and elemental analyses. The solvatochromism of the title azo dyes is evaluated
by means of the Kamlet–Taft equation and discussed.
Key words: Arylazoheterocycles, thiazole, 1,5-electrocyclization, solvatochromism, hydrazonoyl halides
1. Introduction
Many arylazo derivatives of heterocyclic compounds have found various applications in industry including hair
dyeing, disperse dyes, ink-jet inks, and laser materials.1,2 In the light of this and in continuation of our studies on
exploring the utility of hydrazonoyl halides in the synthesis of aryl- and hetaryl-azo derivatives of heterocyclic
compounds,3−10 we wish to report herein a new synthetic strategy for the thiazolo[2,3-c][1,2,4]triazole ring
system and its 6-arylazo derivatives, which have not been reported hitherto (Scheme 1). In addition, it
was thought interesting to study the solvatochromic properties of such dyes via application of Kamlet–Taft
equations11,12 prior to exploring their applications.
2. Experimental
All melting points were determined on a Gallenkamp apparatus and are uncorrected. Solvents were generally
distilled and dried by standard literature procedures prior to use. The IR spectra were measured on a Pye-
Unicam SP300 instrument in potassium bromide disks. The 1 H NMR spectra were recorded on a Varian
Mercury VXR-300 MHz spectrometer and the chemical shifts δ downfield from tetramethylsilane (TMS) as
an internal standard. The mass spectra were recorded on GCMS-Q1000-EX Shimadzu and GCMS 5988-A
HP spectrometers; the ionizing voltage was 70 eV. Elemental analyses were carried out by the Microanalytical
Center of Cairo University, Giza, Egypt. Both the hydrazonoyl chlorides 113 and substituted benzaldehyde
thiosemicarbazones 2 were prepared as previously described.14
∗Correspondence: as shawali@mail.com
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2.1. Synthesis of substituted-benzaldehyde N-(5-arylazo-4-methylthiazol-2-yl)-hydrazones (3)
General procedure: To a mixture of benzaldehyde thiosemicarbazaone 2c (0.01 mol) and the appropriate N-
aryl-2-oxopropanehydrazonoyl chloride 1 (0.01 mol) in absolute ethanol (50 mL) was added triethylamine (1.01
g, 0.01 mol). The reaction mixture was refluxed for 5 h and then cooled to room temperature. The precipitate
formed was filtered off, washed with water and ethanol, and finally crystallized from the appropriate solvent to
give the corresponding benzaldehyde N-(5-arylazo-4-methyl-thiazol-2-yl)hydrazones 3A.
When the above procedure was repeated using 2a–e each with the hydrazonoyl halide 1c, it yielded the
respective substituted-benzaldehyde N-(5-phenylazo-4-methyl-thiazol-2-yl)hydrazones 3B.
The compounds 3Aa–e and 3Ba–e prepared, together with their physical constants, are given below.
Benzaldehyde N-(5-methoxyphenylazo-4-methylthiazol-2-yl)-hydrazone (3Aa): brown solid,
;
yield 2.24 g (64%), mp 215 ◦ C; IR (KBr) ν 3171 (NH), 1240 (CH3 O) cm−1 1 H NMR (DMSO-d6) δ 2.65 (s,
3H, CH3), 3.80 (s, 3H, OCH3), 6.92 (d, 2H, Ar-H), 7.16 (d, 2H, Ar-H), 7.45–7.50 (m, 5H, Ar-H), 7.85 (s, 1H,
N=CH), 8.60 (s, 1H, NH); MS m/z (%) 352 (M++1, 8), 351 (M+ , 34), 247 (5), 216 (6), 178 (4), 163 (2), 134
(13), 122 (72), 107 (35), 92 (24), 89 (41), 77 (100). Anal. Calcd. for C18 H17 N5 OS (Mw 351.43): C, 61.52; H,
4.88; N, 19.93. Found: C, 61.66; H, 4.45; N, 20.20%.
Benzaldehyde N-(5-p-methylphenylazo-4-methylthiazol-2-yl)-hydrazone (3Ab): reddish solid,
;
yield 2.0 g (60%), mp 220–221 ◦ C; IR (KBr) ν 3180 (NH) cm−1 1 H NMR (DMSO-d6) δ 2.35 (s, 3H, CH3),
2.70 (s, 3H, CH3), 7.12 (d, 2H, Ar-H), 7.16 (d, 2H, Ar-H), 7.45–7.50 (m, 5H, ArH), 7.90 (s, 1H, N=CH), 8.63
(s, 1H, NH); MS m/z (%) 336 (M++1, 8), 335 (M+ , 50), 231 (15), 216 (6), 203 (3), 161 (6), 128 (8), 106 (38),
91 (92), 77 (100). Anal. Calcd. for C18 H17 N5 S (Mw 335.43): C, 64.45; H, 5.11; N, 20.88. Found: C, 64.36; H,
5.26; N, 20.67%.
Benzaldehyde N-(5-phenylazo-4-methylthiazol-2-yl)-hydrazone (3Ac): brown solid, yield 2.0 g
;
(62%), mp 195 ◦ C; IR (KBr) ν 3190 (NH) cm−1 1 H NMR (DMSO-d6) δ 2.63 (s, 3H, CH3), 7.0–7.4 (m, 5H,
ArH), 7.90 (s, 1H, N=CH), 8.63 (s, 1H, NH); MS m/z (%) 322 (M++1, 13), 321 (M+ , 89), 288 (5), 217 (30),
170 (7), 148 (13), 118 (7), 103 (19), 90 (40), 77 (100). Anal. Calcd. for C17 H15 N5 S (Mw 321.41): C, 63.53;
H, 4.70; N, 21.79. Found: C, 63.29; H, 5.02; N, 21.56%.
Benzaldehyde N-(5-p-chlorophenylazo-4-methylthiazol-2-yl)-hydrazone (3Ad): red solid, yield
;
2.2 g (64%), mp 218 ◦ C; IR (KBr) ν 3177 (NH) cm−1 1 H NMR (DMSO-d6) δ 2.70 (s, 3H, CH3), 7.45–7.50
(m, 5H, ArH), 7.82 (d, 2H, Ar-H), 7.89 (d, 2H, Ar-H), 7.90 (s, 1H, N=CH), 8.63 (s, 1H, NH); MS m/z (%) 356
(M++1, 2.3), 355 (M+ , 1), 237 (1.2), 216 (2), 128 (4), 126 (15), 111 (37), 104 (7), 100 (4), 99 (13), 89 (28), 77
(18), 63 (23), 50 (100); Anal. Calcd. for C17 H14 ClN5 S (Mw 355.85): C, 57.38; H, 3.97; N, 19.68. Found: C,
56.98; H, 3.81; N, 19.49%.
Benzaldehyde N-(5-p-nitrophenylazo-4-methylthiazol-2-yl)-hydrazone (3Ae): brown solid, yield
;
2.6 g (71%), mp 230–232 ◦ C; IR (KBr) ν 3200 (NH) cm−1 1 H NMR (DMSO-d6) δ 2.70 (s, 3H, CH3), 7.4–7.5
(m, 5H, ArH), 7.89 (d, 2H, Ar-H), 8.26 (d, 2H, Ar-H), 8.3 (s, 1H, N=CH), 8.70 (s, 1H, NH); MS m/z (%) 366
(M+ , 3), 216 (6), 183 (5), 172 (4), 161 (4), 134 (4), 122 (12), 117 (14), 103 (18), 89 (77), 76 (100); Anal. Calcd.
for C17 H14 N6 O2 S (Mw 366.40): C, 55.73; H, 3.85; N, 22.94. Found: C, 55.48; H, 3.74; N, 22.78%.
p-Methoxybenzaldehyde N-(5-phenylazo-4-methylthiazol-2-yl)-hydrazone (3Ba): brown solid,
yield 2.8 g (80%), mp 170–173 ◦ C; IR (KBr) ν 3273 (NH), 1240 (CH3 O) cm−1 1 H NMR (DMSO-d6) δ 2.67
;
(s, 3H, CH3), 3.85 (s, 3H, OCH3), 6.80 (d, 2H, Ar-H), 7.5 (d, 2H, Ar-H), 7.35–7.50 (m, 5H, Ar-H), 7.80 (s, 1H,
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SHAWALI and ZAYED/Turk J Chem
N=CH), 8.60 (s, 1H, NH); MS m/z (%) 352 (M+ , 100), 323 (20), 245 (17), 216 (45), 211 (10), 147 (18), 134
(14), 119 (15), 104 (12), 91 (35), 77 (41). Anal. Calcd. for C18 H17 N5 OS (351.43): C, 61.52; H, 4.88; N, 19.93.
Found: C, 61.40; H, 4.90; N, 20.00%.
p-Methylbenzaldehyde N-(5-phenlazo-4-methylthiazol-2-yl)-hydrazone (3Bb): orange solid,
;
yield 2.84 g (85%), mp 180–182 ◦ C; IR (KBr) ν 3397 (NH) cm−1 1 H NMR (DMSO-d6) δ 2.42 (s, 3H, CH3),
2.68 (s, 3H, CH3), 7.2 (d, 2H, Ar-H), 7.3 (d, 2H, Ar-H), 7.40–7.50 (m, 5H, ArH), 7.8 (s, 1H, N=CH), 8.6 (s,
1H, NH); MS m/z (%) 336 (M++1, 3), 335 (M+ , 70), 302 (8), 244 (4), 217 (17), 197 (8), 148 (8), 118 (19),
103 (26), 91 (73), 77 (100). Anal. Calcd. for C18 H17 N5 S (Mw 335.43): C, 64.45; H, 5.11; N, 20.88. Found: C,
64.18; H, 4.94; N, 20.33%.
p-Chlorobenzaldehyde N-(5-p-chlorophenylazo-4-methylthiazol-2-yl)-hydrazone (3Bd): or-
;
ange solid, yield 2.9 g (81%), mp 205–207 ◦ C; IR (KBr) ν 3417 (NH) cm−1 1 H NMR (DMSO-d6) δ 2.7 (s,
3H, CH3), 7.20 (d, 2H, Ar-H), 7.38 (d, 2H, Ar-H), 7.34–7.50 (m, 5H, ArH), 7.90 (s, 1H, N=CH), 8.63 (s, 1H,
NH); MS m/z (%) 358 (M++2, 3), 357 (M++1, 46), 355 (M+ , 100), 244 (6), 217 (41), 170 (6), 137 (14), 111
(24), 92 (29), 77 (92); Anal. Calcd. for C17 H14 ClN5 S (Mw 355.85): C, 57.38; H, 3.97; N, 19.68. Found: C,
56.98; H, 3.71; N, 19.86%.
p-Nitrobenzaldehyde N-(5-phenylazo-4-methylthiazol-2-yl)-hydrazone (3Be): reddish brown
;
solid, yield 3.1 g (86%), mp 215–217 ◦ C; IR (KBr) ν 3279 (NH) cm−1 1 H NMR (DMSO-d6) δ 2.70 (s, 3H,
CH3), 7.3–7.4 (m, 5H, ArH), 7.5 (s, 1H, N=CH), 8.1 (d, 2H, Ar-H), 8.4 (d, 2H, Ar-H), 8.70 (s, 1H, NH); MS
m/z (%) 367 (M++1, 13), 366 (M+ , 100), 217 (13), 170 (4), 149 (20), 118 (8), 104 (6), 92 (26), 89 (6), 77
(78); Anal. Calcd. for C17 H14 N6 O2 S (Mw 366.40): C, 55.73; H, 3.85; N, 22.94. Found: C, 55.52; H, 3.97; N,
22.58%.
2.2. Synthesis of 3-aryl-5-methyl-6-phenylazo[thiazolo[2,3-c][1,2,4]-triazoles (4)
General procedure: To a solution of the appropriate hydrazone 3 (2.5 mmol) in ethanol (50 mL) was added
a solution of ferric chloride (2 M, 2 mL) and the mixture was refluxed for 45 min and then cooled to room
temperature. The precipitated solid was filtered off, washed with water and then with ethanol, and finally
crystallized from a chloroform–ethanol mixture to give the respective 3-phenyl-5-methyl-6-arylazo[thiazolo[2,3-
c][1,2,4]-triazole 4 as a dark colored solid. The compounds 4A(B)a–e prepared, together with their physical
constants, are given below.
3-Phenyl-5-methyl-6-(p-methoxyphenylazo)-thiazolo[2,3-c][1,2,4]-triazole (4Aa): yield 0.54 g
;
(62%), mp 200 ◦ C; IR (KBr) ν 1243 (CH3 OC) cm−1 1 H NMR (DMSO-d6) δ 2.7 (s, 3H, CH3), 3.90 (s, 3H,
ArOCH3), 7.2 (d, 2H, Ar-H), 7.22–7.50 (m, 5H, Ar-H), 8.9 (d, 2H, Ar-H); MS m/z (%) 349 (M+ , 0.4), 227
(0.4), 216 (0.6), 196 (0.8), 171 (0.7), 150 (1.36), 139 (3), 122 (7), 91 (9), 89 (15), 76 (36), 50 (100). Anal. Calcd.
for C18 H15 N5 OS (Mw 349.42): C, 61.87; H, 4.33; N, 20.04. Found: C, 54.40; H, 4.53; N, 20.07%.
3-Phenyl-5-methyl-6-(p-methylphenylazo)-thiazolo[2,3-c][1,2,4]-triazole (4Ab): yield 0.47 g
(56% yield), mp 205 ◦ C; 1 H NMR (DMSO-d6) δ 2.4 (s, 3H, CH3), 2.70 (s, 3H, CH3), 7.11 (d, 2H, Ar-
H), 7.16 (d, 2H, Ar-H), 7.2–7.5 (m, 5H, ArH); MS m/z (%) 335 (M++2, 23), 333 (M+ , 0.3), 231 (8), 129 (6),
106 (33), 91 (80), 77 (100). Anal. Calcd. for C18 H15 N5 S (Mw 333.42): C, 64.84; H, 4.53; N, 21.00. Found: C,
64.46; H, 4.59; N, 21.08%.
3-Phenyl-5-methyl-6-phenylazo-thiazolo[2,3-c][1,2,4]triazole (4Ac): yield 0.35 g (45%), mp 200
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SHAWALI and ZAYED/Turk J Chem
◦ C; 1 H NMR (DMSO-d6) δ 2.3 (s, 3H, CH3), 7.3–8.0 (m, 10H, ArH); MS m/z (%) 319 (M+ , 1), 205 (1.1),
217 (1.1), 135 (1.4), 108 (2), 90 (3), 77 (13), 65 (13), 50 (100). Anal. Calcd. for C17 H13 N5 S (Mw 319.39): C,
63.93; H, 4.10; N, 21.93. Found: C, 63.72; H, 3.95; N, 21.75%.
3-Phenyl-5-methyl-6-(p-chlorophenylazo)-thiazolo[2,3-c][1,2,4]-triazole (4Ad): yield 0.61 g
(69%), mp 208 ◦ C; 1 H NMR (DMSO-d6) δ 2.6 (s, 3H, CH3), 7.10–7.40 (m, 5H, ArH), 7.52 (d, 2H, Ar-
H), 7.9 (d, 2H, Ar-H); MS m/z (%) 354 (M++1, 0.2), 353 (M+ , 1), 169 (15), 126 (3), 111 (22), 98 (28), 89
(21), 74 (100); Anal. Calcd. for C17 H12 ClN5 S (Mw 353.84): C, 57.71; H, 3.42; N, 19.79. Found: C, 52.50; H,
4.00; N, 19.60%.
3-Phenyl-5-methyl-6-(p-nitrophenylazo)-thiazolo[2,3-c][1,2,4]-triazole (4Ae): yield 0.81 g (90%),
mp 220 ◦ C; 1 H NMR (DMSO-d6) δ 2.60 (s, 3H, CH3), 7.4–7.5 (m, 5H, ArH), 7.9 (d, 2H, Ar-H), 8.3 (d, 2H,
Ar-H); MS m/z (%) 365 (M++1, 1.4), 262 (2), 215 (1.5), 172 (1.5), 149 (1.6), 121 (2.6), 108 (8.7), 92 (3.6), 89
(9), 50 (100); Anal. Calcd. for C17 H12 N6 O2 S (Mw 364.39): C, 56.04; H, 3.32; N, 23.06. Found: C, 55.42; H,
3.34; N, 22.91%.
3-(p-Methoxyphenyl)-5-methyl-6-phenylazo-thiazolo[2,3-c][1,2,4]-triazole (4Ba): yield 0.42 g
;
(48%), mp 208–210 ◦ C; IR (KBr) νmax 1246 (CH3 OC) cm−1 1 H NMR (DMSO-d6) δ 2.3 (s, 3H, CH3), 3.85
(s, 3H, ArOCH3), 7.2 (d, 2H, Ar-H), 7.22–7.50 (m, 5H, Ar-H), 8.9 (d, 2H, Ar-H); MS m/z (%) 351 (M+ , 16),
268 (14), 211 (11), 161 (8), 135 (29), 117 (7), 92 (99), 78 (9), 76 (100). Anal. Calcd. for C18 H15 N5 OS (Mw
349.42): C, 61.87; H, 4.33; N, 20.04. Found: C, 61.66; H, 5.04; N, 19.95%.
3-(p-Methylphenyl)-5-methyl-6-phenylazo-thiazolo[2,3-c][1,2,4]triazole (4Bb): yield 0.25 g (30%),
mp 205 ◦ C; 1 H NMR (DMSO-d6) δ 2.4 (s, 3H, CH3), 2.80 (s, 3H, CH3), 7.00–8.1 (m, 9H, Ar-H); MS m/z
(%) 333 (M+ , 02), 248 (0.3), 182 (1), 165 (1), 135 (5), 115 (18), 103 (28), 91 (30), 76 (53). 50 (100). Anal.
Calcd. for C18 H15 N5 S (Mw 333.42): C, 64.84; H, 4.53; N, 21.00. Found: C, 60.50; H, 3.77; N, 20.83%.
3-(p-Chloropheny)l-5-methyl-6-phenylazo-thiazolo[2,3-c][1,2,4]-triazole (4Bd): yield 0.34 g
(39%), mp 172–175 ◦ C; 1 H NMR (DMSO-d6) δ 2.4 (s, 3H, CH3), 7.0–7.6 (m, 9H, ArH); MS m/z (%) 355
(M++1, 2), 274 (2), 253 (2.2), 217 (2), 170 (2.6), 137 (4), 111 (14), 92 (3), 89 (17), 77 (8), 51 (100); Anal.
Calcd. for C17 H12 ClN5 S (Mw 353.84): C, 57.715 H, 3.42; N, 19.79. Found: C, 57.40; H, 3.56; N, 19.86%.
3-(p-Nitrophenyl)-5-methyl-6-phenylazo-thiazolo[2,3-c][1,2,4]-triazole (4Be): yield 0.58 g (64%),
mp 210–212 ◦ C; 1 H NMR (DMSO-d6) δ 2.70 (s, 3H, CH3), 7.4–7.5 (m, 5H, ArH), 8.05 (d, 2H, Ar-H), 8.35
(d, 2H, Ar-H); MS m/z (%) 365 (M++1, 1.4), 262 (2), 215 (1.5), 172 (1.5), 149 (1.6), 121 (2.6), 108 (8.7), 92
(3.6), 89 (9), 50 (100); Anal. Calcd. for C17 H12 N6 O2 S (Mw 364.39): C, 56.04; H, 3.32; N, 23.06. Found: C,
55.51; H, 3.43; N, 23.01%.
3. Results and discussion
3.1. Synthesis and characterizations
Treatment of benzaldehyde thiosemicarbazone 1c with each of the hydrazonoyl chlorides 2a–e in refluxing
ethanol in the presence of triethylamine afforded the respective arylazothiazole derivatives 3Aa–e (Scheme 1).
Similar treatment of substituted benzaldehyde thiosemicarbazones 1a–e each with the hydrazonoyl chloride 2c
yielded the respective phenylazothiazole derivatives 3Ba–e. Such reactions seem to follow a pathway similar to
that reported for reactions of hydrazonoyl halides with thiourea and thiosemicarbazide, which were reported to
yield 5-arylazo derivatives of 2-amino- and 2-hydrazino-thiazole, respectively.1 The structures of the compounds
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SHAWALI and ZAYED/Turk J Chem
3A(B) were elucidated on the basis of their spectral data (MS, IR, 1 H NMR, and UV) and elemental analyses
(see Experimental). For example, their IR spectra revealed the absence of the C=O absorption bands present
in the spectra of the starting hydrazonoyl chlorides 2. In addition, their 1 H NMR spectra in CDCl3 revealed 3
characteristic singlet signals at δ 2.6–2.7 (thiazole-4-CH3), 7.8–7.9 (CH=N), and 8.6–8.7 (NH). The electronic
absorption spectra of compounds 3A(B) in ethanol (Table 1) showed in each case an intense absorption band
in the region 450–485 nm assignable to the arylazo chromophoric group. The spectra of the product 3Ac,
taken as a representative example of the series prepared, in different solvents of different polarity showed little,
if any, changes. This finding indicates that the studied compounds 3 exist predominantly in one tautomeric
form, namely the indicated azo-hydrazone tautomeric structure 3 (Scheme 1). The other possible tautomeric
hydrazono-azine structure 5 (Scheme 1) was thus excluded. This conclusion is further confirmed by the oxidative
cyclization of compounds 3A(B) described below.
Et3N
CH3COC(Cl)=NNHAr
2
Ar'-CH=NNHCSNH2
+
-HCl; -H2O
1
CH3
CH3
N
N
Ar'
Ar'
N
N
N
N
N
H
N
S
S
N
NH
Ar
Ar
3A(B)
5
Ar / Ar' : A, 4-XC6H4 / Ph; B, Ph / 4-XC6H4
X : a, CH3O; b, CH3; c, H; d, Cl; e, O2N
Scheme 1.
Table 1. Electronic absorption spectral data of compounds 3A(B) in ethanol.
Compd. no.
3Aa
λmax nm (log ε)
Compd. no.
3Ba
λmax nm (log ε)
479 (4.48), 330 (4.07)
482 (4.60), 319 (4.18)
473 (4.36), 314 (3.96)
473 (4.20), 311 (3.89)
655 (4.11), 467 (4.62)
459 (4.31), 321 (4.75)
457 (4.49), 316 (4.23)
473 (4.36), 314 (3.96)
461 (4.49), 318 (4.18)
478 (4.19), 335 (4.28)
3Ab
3Bb
3Bc
3Bd
3Be
3Aca)
3Ad
3Ae
a) Solvent: λmax nm (log ε): n-PrOH: 459 (4.44), 321 (3.99); dioxane: 458 (4.40), 314 (4.08); HCCl3 : 456 (4.33), 314
(4.07); MeOH: 471 (4.44), 313 (3.03); MeCN: 441 (4.17), 313 (4.02).
When each of the aldehyde N-(5-arylazo-4-methylthiazol-2-yl)hydrazones 3A(B) was treated with an
equivalent amount of iron(III) chloride in refluxing ethanol for 30 min, it furnished, in each case, one crystalline
product as evidenced by TLC analysis. The isolated products proved to be the respective 3-aryl-6-arylazo-5-
methyl-thiazolo[2,3-c][1,2,4]triazoles 4A(B) (Scheme 2). Their structures were confirmed by their spectral data
(MS, IR, and 1 H NMR) and elemental analyses. For example, both the elemental analysis and mass spectrum
of each compound revealed that it has 2 hydrogen atoms less than the respective hydrazone 3. Moreover, their
417

SHAWALI and ZAYED/Turk J Chem
1 H NMR spectra showed the absence of the –N=CH- and hydrazone –NH-N=C proton signals present in the
spectra of their precursors 3.
The conversion of 3 into 4 is considered to proceed via 1,5-electrocyclization of the initially formed
nitrilimines (Scheme 2). This suggested pathway is reminiscent of other related oxidative cyclization of aldehyde
N-heteroarylhydrazones with iron(III) chloride, which was reported to proceed via initial generation of the
respective nitrilimines, which undergo in situ 1,5-electrocyclization to give the respective fused heterocycles.15,16
CH3
Ar'
CH3
+
N
Ar'
N
N
FeCl3
N
N
H
S
N
N
N
N
S
Ar
-
N
3A(B)
Ar
Ar'
CH3
N
N
N
N
S
N
Ar
4A(B)
Ar / Ar' : A, XC6H4 / Ph; B, Ph / XC6H4;
X : a, CH3O; b, CH3; c, H; d, Cl; e, O2N
Scheme 2.
3.2. Solvatochromic properties
The electronic absorption spectra of the azo compounds prepared, 4A(B), were recorded at a concentration
of 10−6 M over the range 300–700 nm using a series of 6 solvents of different polarities, namely 1-propanol,
ethanol, dioxane, chloroform, methanol, and acrtonitrile. The results are given in Tables 2 and 3. As shown in
these tables, each of the studied compounds exhibits 2 absorption bands in the ranges 320–420 and 450–640 nm
in all solvents used. The former UV bands for all of the studied compounds 4A(B) suffer small solvent shifts,
behavior that is expected for local electronic transitions corresponding to π –π * transitions. The main visible
band displayed by all compounds in the region 430–650 nm is an intense one and is relatively influenced by
changing the solvent and the substituent present. For example, the visible spectra of the 2 compounds 4A(B)d
(p-Cl) and 4A(B)e (p-NO2) in acetonitrile (Tables 2 and 3) comprise a band appearing at longer wavelengths
[550 (549) and 636 (616) nm], respectively, which exceed by far the usual solvent shift. This behavior seems to
indicate that such dyes may be liable to form a solvated complex.17−19
Next, the effects of solvent polarity/polarizability and hydrogen bonding property on the absorption
spectra of the studied compounds 4A(B) were evaluated by means of the linear solvation energy relationship
(LSER), namely the Kamlet–Taft equation (Eq. (1)):11,12
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SHAWALI and ZAYED/Turk J Chem
Table 2. Electronic absorption spectral data of compounds 4Aa–e in various solvents.
Compd. no. Solvent: λmax nm (log ε)
Compd. no. Solvent: λmax nm (log ε)
4Aa
4Ab
4Ac
n-PrOH: 459 (4.10), 330 (409);
EtOH: 456 (4.09), 325 (4.04);
Dioxane: 430 (3.99), 343 (4.05);
HCCl3: 426 (4.06), 326 (4.00);
MeOH: 430 (4.38), 304 (4.13);
MeCN: 422 (3.99), 330 (4.07).
n-PrOH : 466 (4.24), 325 (4.02);
EtOH: 464 (4.25), 320 (3.92);
Dioxane: 452 (4.21), 316 (3.91);
HCCl3: 449 (4.04), 323 (3.81);
MeOH: 459 (3.98), 308 (3.90);
MeCN: 425 (3.62), 325 (3.83).
n-PrOH: 449 (4.02), 329 (4.11);
EtOH: 452 (3.97), 325 (3.99);
Dioxane: 439 (4.08), 329 (4.09);
HCCl3: 422 (4.01), 325 (4.00);
MeOH: 452 (3.97), 319 (3.98);
MeCN: 423 (4.02), 333 (4.08).
4Ad
n-PrOH: 459 (4.27), 320 (4.18);
EtOH: 458 (4.22), 320 (4.06);
Dioxane: 445 (4.28), 313 (4.10);
HCCl3: 439 (4.32), 321 (4.19);
MeOH: 455 (4.19), 304 (4.11);
MeCN: 550 (3.92), 435 (4.12).
n-PrOH: 453 (4.24), 345 (4.13);
EtOH: 453 (4.24), 310 (4.05);
Dioxane: 442 (4.27), 382 (4.15);
HCCl3: 443 (4.17), 337 (3.95);
MeOH: 448 (4.20), 382 (4.10);
MeCN: 636 (4.08), 434 (4.15).
4Ae
Table 3. Electronic absorption spectral data of compounds 4Ba–e in various solvents.
Compd. no. Solvent: λmax nm (log ε) Compd. no. Solvent: λmax nm (log ε)
4Ba
4Bb
4Bc
n-PrOH: 461 (4.09), 329 (4.16);
EtOH: 460 (4.08), 331 (4.17);
Dioxane: 450 (3.96), 325 (4.03);
HCCl3: 439 (4.07), 328 (4.17);
MeOH: 457 (4.05), 325 (4.15);
MeCN: 430 (3.99), 323 (4.15).
n-PrOH: 460 (4.09), 323 (4.08);
EtOH: 456 (4.09), 323 (4.11);
Dioxane: 447 (4.10), 325 (4.12);
HCCl3: 438 (4.06), 329 (4.06);
MeOH: 454 (4.09), 320 (4.12);
MeCN: 425 (4.02), 383 (4.12).
n-PrOH: 449 (4.02), 329 (4.11);
EtOH: 452 (3.97), 320 (3.99);
Dioxane: 439 (4.08), 329 (4.09);
HCCl3: 422 (4.01), 325 (4.00);
MeOH: 452 (3.97), 319 (3.98);
MeCN: 423 (4.02), 333 (4.08).
4Bd
n-PrOH: 460 (4.11), 324 (4.11);
EtOH: 457 (4.11), 323 (4.12);
Dioxane: 446 (4.16), 325 (4.19);
HCCl3: 439 (4.09), 323 (4.10);
MeOH: 456 (4.11), 325 (4.13);
MeCN: 549 (3.84), 409 (4.03).
n-PrOH: 482 (4.40), 346 (4.19);
EtOH: 478 (4.42), 346 (4.21);
Dioxane: 467 (4.39), 337 (4.22);
HCCl3: 466 (4.37), 338 (4.25);
MeOH: 474 (4.43), 340 (425);
MeCN: 616 (4.24), 330 (4.13).
4Be
υ = υo + sπ ∗ +bβ + aα
(1)
where π * is the measure of solvent dipolarity/polarizabilty, β is the scale of the solvent hydrogen bond acceptor
(HBA) basicities, α is the scale of the solvent hydrogen-bond donor (HBD) acidities, and υo is the regression
value of the solute property in the reference solvent cyclohexane. The values of such solvent parameters are
given in Table 4. The regression coefficients s, b, and a in Eq. (1) measure the relative susceptibilities of the
solvent-dependent solute property (absorption frequencies) to the indicated solvent parameters. The values
419

SHAWALI and ZAYED/Turk J Chem
of these regression coefficients were obtained by means of multiple linear regression analysis. The results are
depicted in Table 5. The values (0.985–0.921) of the correlation coefficients R indicate that the spectroscopic
data are fairly correlated by Eq. (1). The negative sign of a given regression coefficient indicates that the energy
of the electronic transition is decreased by the corresponding solvent property and vice versa.
The percentage contributions of the solvatochromic parameters π *, β, and α for the studied compounds
are given in Table 6. As shown, the changes in the spectra of the studied compounds are more influenced by
dipolarity/polarizability than the H-bonding character of the solvents used. This influence is increased by both
electron-donating and electron-withdrawing substituents.
Table 4. Solvent parameters.12
Solvent
π∗
β
α
1-Propanol 0.47 0.88 0.79
Ethanol
Dioxane
0.54 0.77 0.83
0.55 0.37 0.0
Chloroform 0.58 0.0 0.44
Methanol 0.60 0.62 0.93
Acetonitrile 0.75 0.31 0.19
Table 5. Regression fits to solvatochromic parameters (Eq. (1)).
Compound no. υo (103 cm−1
)
s
b
a
Ra
Sb
4Aa
4Ab
4Ac
4Ad
4Ae
4Ba
4Bb
4Bc
4Bd
4Be
21.29
18.85
22.72
33.186
38.895
20.815
19.341
22.72
4.02
6.27
1.659
–1.38 –0.050 0.932 0.453
–0.043 –0.668 0.976 0.263
–1.518 –0.316 0.921 0.452
–18.321 –3.397 1.216 0.931 0.965
–28.726 –4.072 1.955 0.926 1.610
3.51
5.561
1.659
–0.911 –0.264 0.957 0.294
0.225 –0.691 0.985 0.175
–1.518 –0.316 0.921 0.452
33.029
–18.093 –3.395 1.240 0.933 0.944
–25.357 –4.207 2.379 0.932 1.399
35.622
b)
a)Correlation coefficient; standard error of the estimate
Table 6. Contribution percentages of solvatochromic parameters.
Compound no. ρπ* (%) ρβ (%) ρα (%)
4Aa
4Ab
4Ac
4Ad
4Ae
4Ba
4Bb
4Bc
4Bd
4Be
73.76
89.80
47.50
79.88
82.66
74.92
85.85
47.50
79.61
79.38
25.32
0.006
43.40
14.82
11.71
19.44
3.47
43.40
14.94
13.17
0.01
9.57
9.05
5.30
5.62
5.63
10.67
9.05
5.46
7.45
420

SHAWALI and ZAYED/Turk J Chem
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421

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