The microwave-assisted synthesis of 5-arylazo-4,6-disubstituted-3-cyano-2-pyridone dyes

Article abstract of DOI:10.1016/j.dyepig.2009.10.006

A novel protocol for the rapid synthesis of pyridone colorants under controlled microwave irradiation in a dedicated reactor is described. Short reaction times, high isolated yields, and versatility for different substrates are the advantages of the reported method.

Full text of DOI:10.1016/j.dyepig.2009.10.006

Dyes and Pigments 85 (2010) 73e78
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The microwave-assisted synthesis of 5-arylazo-4,6-disubstituted-
3-cyano-2-pyridone dyes
a
b
b
b,
*
ꢀ
Dusan Z. Mijin , Mostafa Baghbanzadeh , Claudia Reidlinger , C. Oliver Kappe
a Department of Organic Chemistry, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P.O. Box 3503, 11120 Belgrade, Serbia
b Christian Doppler Laboratory for Microwave Chemistry (CDLMC) and Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstra
b
e 28, A-8010 Graz, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel protocol for the rapid synthesis of pyridone colorants under controlled microwave irradiation in
a dedicated reactor is described. Short reaction times, high isolated yields, and versatility for different
substrates are the advantages of the reported method.
Received 28 July 2009
Received in revised form
30 September 2009
Accepted 5 October 2009
Available online 28 October 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Azo compounds
Cyclocondensation reaction
High-temperature
Microwave chemistry
Nitrile
Pyridone
1. Introduction
followed by condensation with cyanoacetamide (Scheme 1b, R1,
R2 ¼ Me) [17,18]. The arylazo dyes obtained in such manner do not
Azo compounds are the largest group of colorants in terms of
number and production volume of currently marketed dyes and
pigments. The importance of azo compounds as colorants is due to
the simplicity of their synthesis by diazotization and azo coupling,
and to the almost innumerable possibilities presented by variation
on the diazo compounds and coupling components, in conjunction
with their generally high molar extinction coefficient and
moderate/high fastness properties [1]. An important group of
yellow disperse dyes are based on pyridone derivatives as coupling
components, which can easily be obtained from 3-oxobutanoates
and 2-cyanoacetamides. These dyes have largely replaced yellow
disperse dyes based on pyrazolones [1]. Pyridone disperse yellow
dyes, such as C.I. Disperse Yellows 114, 119 and 211, are commonly
used for dyeing polyester fabrics [2,3].
contain unreacted pyridone material and are generally obtained in
higher yields. Long reaction times, the use of a toxic and strong base
for the condensation step, are the other disadvantages of this
method.
This paper concerns an improved method for synthesising
novel, 5-arylazo-4,6-disubstituted-3-cyano-2-pyridone dyes from
b-diketones and various diazonium salts, followed by high speed
microwave-assisted condensation with cyanoacetamide.
2. Experimental
2.1. General
All starting materials were obtained from Aldrich and Fluka, and
were used without further purification. 1,3-Dicarbonyl compounds
2 and 4 were prepared following reported methods [17e19].
Melting points were taken on Stuart SMP3 melting point apparatus.
The 1H and 13C NMR spectra were recorded on a Bruker 300 MHz
instrument. A Biotage Initiator 2.5 EXP was used for the microwave
experiments. Analytical HPLC analysis (Shimadzu LC 20) was
These and other azo dyes have traditionally been prepared from
pyridone as a coupling component and various diazonium salts
(Scheme 1a) [4e16]. Unreacted pyridone and low yields of the
corresponding products are the main disadvantages of this method
[4e16]. Alternatively, arylazo colorants containing pyridone rings
can also be prepared from b-diketones and various diazonium salts,
carried out on
a
C
18 reversed-phase analytical column
ꢁ
(150 ꢀ 4.6 mm, particle size 5 ım) using mobile phases A (water/
* Corresponding author. Tel.: þ43 316 3805352; fax: þ43 316 3809840.
E-mail address: oliver.kappe@uni-graz.at (C. Oliver Kappe).
acetonitrile 90:10 (v/v) þ 0.1% TFA) and B (acetonitrile þ 0.1% TFA)
0143-7208/$ e see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.10.006

74
D.Z. Mijin et al. / Dyes and Pigments 85 (2010) 73e78
Scheme 1. Synthetic methods for the preparation of arylazopyridones.
at a flow rate of 0.5 mL/min. The following gradient was applied:
linear increase from solution 30% B to 100% B in 9 min, hold at 100%
solution B for 5 min. Low-resolution mass spectra were obtained on
an Agilent 1100 LC/MS instrument using atmospheric pressure
chemical ionization (APCI) in positive or negative mode. The
UVevis absorption spectra were taken in the region between 200
and 600 nm using a Shimadzu 1700 UVevis spectrophotometer in
1.00 cm cells at 25 ꢁ 0.1 ꢂC in ethanol at concentration 5 ꢀ 10ꢃ5 mol
NMR (75 MHz, DMSO-d6)
d
(ppm) ¼ 163.9, 157.2, 153.2, 152.9, 140.0,
131.6, 129.5, 117.5, 117.3, 101.8, 100.2, 21.9, 21.2. UVevis (ethanol):
lmax/nm: [(log
(M ¼ 378.0).
3
)]: 384 (4.24). MS (pos. APCI) m/z: 379.0 [M þ Hþ],
2.2.4. 5-((4-Bromophenyl)diazenyl)-4,6-dimethyl-2-oxo-1,2-
dihydropyridine-3-carbonitrile (1d)
Orange powder, Mp >300 ꢂC (Lit. Mp >300 ꢂC [16]). 1H NMR
dmꢃ3
.
(300 MHz, DMSO-d6)
d
(ppm) ¼ 7.64 (d, J ¼ 9 Hz, 2 H, Ar-H), 7.58 (d,
J ¼ 9 Hz, 2 H, Ar-H), 2.55 (s, 3 H, CH3), 2.52 (s, 3 H, CH3). 13C NMR
(75 MHz, DMSO-d6)
d
(ppm) ¼ 170.4, 162.4, 153.0, 149.0, 132.4,
2.2. Synthesis of pyridone colorants
132.3, 123.4, 121.3, 119.9, 96.7, 25.1, 19.8. UVevis (ethanol): lmax
/
nm: [(log
3
)]: 366 (4.26). MS (pos. APCI) m/z: 333.0 [M þ Hþ], MS
A mixture of the dicarbonyl compound 2 or 4 (1 mmol), cya-
noacetamide (2 mmol, 168 mg) and potassium hydroxide
(1.7 mmol, 95 mg) in absolute ethanol (2 mL) was irradiated for
5 min (Table 1). The resulting solid product was collected by
filtration and washed with 2 ꢀ 5 mL of water and 5 mL of ethanol.
All products were identified either by comparison with authentic
samples or in the case of novel structures by 1H/13C NMR spec-
troscopy in addition to MS analysis.
(neg. APCI) m/z: 330.3 [M - Hþ], (M ¼ 331.2).
2.2.5. 5-((4-Bromo-2,6-dimethylphenyl)diazenyl)-4,6-dimethyl-2-
oxo-1,2-dihydropyridine-3-carbonitrile (1e)
Orange powder, Mp >300 ꢂC. 1H NMR (300 MHz, DMSO-d6)
(ppm) ¼ 7.30 (s, 2 H, Ar-H), 2.24 (s, 6H, 2 CH3), 2.45 (s, 3H, CH3),
d
Table 1
2.2.1. 4,6-Dimethyl-2-oxo-5-(phenyldiazenyl)-1,2-dihydropyridine-
3-carbonitrile (1a)
Optimization of different parameters in the reaction of phenylazo acetylacetone (2a)
and cyanoacetamide (3).
Orange powder, Mp >300 ꢂC (Lit. Mp 278e279 ꢂC [7]). 1H NMR
Entrya KOH (equiv.) Amide (equiv.) T (ꢂC) Time (min) Conversion (%)b
(300 MHz, DMSO-d6)
(t, J ¼ 9 Hz, 2 H, Ar-H), 7.33 (t, J ¼ 8 Hz, 1 H, Ar-H), 2.53 (s, 3 H, CH3),
2.51 (s, 3 H, CH3). 13C NMR (75 MHz, DMSO-d6)
(ppm) ¼ 170.6,
162.1, 154.0, 148.4, 132.3, 129.4, 128.6, 121.6, 120.2, 96.2, 25.3, 19.7.
d
(ppm) ¼ 7.65 (d, J ¼ 8.3 Hz, 2 H, Ar-H), 7.46
1
2
3
4
5
6
7
8
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1
1
1
1
1
1
1
1
1
80
90
15
15
15
15
15
15
15
15
15
15
15
15
15
3
13
34
42
50
47
59
46
51
65
70
79
96
99
92
99
99
99
76
95
>99
d
100
110
120
130
140
200
130
130
130
130
130
130
130
130
130
130
130
130
UVevis (ethanol): lmax/nm: [(log
3
)]: 349 (3.96). MS (pos. APCI)
m/z: 253.4 [M þ Hþ], MS (neg. APCI) m/z: 251.4 [M - Hþ], (M ¼ 252.3).
2.2.2. 5-((2,6-Dimethylphenyl)diazenyl)-4,6-dimethyl-2-oxo-1,2-
dihydropyridine-3-carbonitrile (1b)
9
1
10
11
12
13
14
15
16
17
18
19
20
1.3
1.5
1.7
2
2
2
2
2
2
2
Orange powder, Mp >300 ꢂC. 1H NMR (300 MHz, DMSO-d6)
d
(ppm) ¼ 7.11 (brs, 3 H, Ar-H), 2.55 (s, 3 H, CH3), 2.27 (s, 6 H, 2 CH3).
13C NMR (75 MHz, DMSO-d6)
(ppm) ¼ 161.7, 152.7, 147.9, 133.0,
129.7, 129.2, 126.7, 126.4, 120.3, 95.9, 25.4, 19.9, 19.7. UVevis
d
5
(ethanol): lmax/nm: [(log
3)]: 459 (2.85), 351 (4.12). MS (pos. APCI)
10
15
5
5
5
m/z: 281.4 [M þ Hþ], (M ¼ 280.3).
1.5
1.7
2.2.3. 5-((2-Iodophenyl)diazenyl)-4,6-dimethyl-2-oxo-1,2-
dihydropyridine-3-carbonitrile (1c)
2
a
Reaction conditions: A mixture of the phenylazo acetylacetone (2a) (1 mmol),
cyanoacetamide (3) and potassium hydroxide in absolute ethanol (2 mL) was irra-
diated for the appropriate time.
Orange powder, Mp >300 ꢂC. 1H NMR (300 MHz, DMSO-d6)
d
(ppm) ¼ 8.06 (d, J ¼ 8.6 Hz, 1H, Ar-H), 7.15e7.20 (m, 1 H, Ar-H),
7.45e7.51 (m, 2 H, Ar-H), 2.71 (s, 3 H, CH3), 2.65 (s, 3 H, CH3). 13
C
Conversion of phenylazo acetylacetone (2a) measured by HPLC-UV at 369 nm.
b

D.Z. Mijin et al. / Dyes and Pigments 85 (2010) 73e78
75
2.40 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)
162.1, 151.7, 148.2, 132.9, 132.5, 131.5, 120.2, 118.5, 96.2, 25.5, 19.9,
d
(ppm) ¼ 170.3,
2.2.12. 5-((4-Bromo-2,6-dimethylphenyl)diazenyl)-6-hydroxy-4-
methyl-2-oxo-1,2-dihydropyridine-3-carbonitrile (5c)
19.4. UVevis (ethanol): lmax/nm: [(log
3)]: 458 (3.19), 355 (4.22).
Orange powder, Mp >300 ꢂC. 1H NMR (300 MHz, DMSO-d6)
(ppm) ¼ 13.96 (s, 1H, NH), 7.21 (s, 2 H, Ar-H), 2.33 (s, 6 H, 2 CH3),
MS (neg. APCI) m/z: 358.1 [M - Hþ], (M ¼ 359.2).
d
2.22 (s, 3 H, CH3). 13C NMR (75 MHz, DMSO-d6)
d
(ppm) ¼ 196.9,
2.2.6. 4,6-Dimethyl-5-((2-nitrophenyl)diazenyl)-2-oxo-1,2-
dihydropyridine-3-carbonitrile (1f)
164.7, 163.5, 139.9, 132.0, 131.7, 131.1, 129.4, 126.6, 113.9, 27.4, 19.7.
UVevis (ethanol): lmax/nm: [(log 3)]: 432 (3.62), 350 (4.08). MS
Orange powder, Mp >300 ꢂC. 1H NMR (300 MHz, DMSO-d6)
(neg. APCI) m/z: 360.1 [M - Hþ], (M ¼ 361.1).
d
(ppm) ¼ 7.87 (d, J ¼ 13.8 Hz, 1 H, Ar-H), 7.67e7.69 (m, 2 H, Ar-H),
7.43e7.49 (m, 1 H, Ar-H), 2.48 (s, 3 H, CH3), 2.44 (s, 3 H, CH3). 13
NMR (75 MHz, DMSO-d6)
(ppm) ¼ 170.5, 164.1, 149.8, 147.2, 146.1,
C
2.2.13. 5-((4-Bromophenyl)diazenyl)-6-hydroxy-4-methyl-2-oxo-
1,2-dihydropyridine-3-carbonitrile (5d)
d
133.0, 128.1, 123.7, 119.5, 118.4, 97.4, 25.4, 19.8. UVevis (ethanol):
Orange powder, Mp >300 ꢂC. 1H NMR (300 MHz, DMSO-d6)
lmax/nm: [(log
3
)]: 385 (4.19). MS (pos. APCI) m/z: 298.1 [M þ Hþ],
d
(ppm) ¼ 13.74 (s, 1H, NH)/10.26* (s, 1H, NH), 7.57* (d, J ¼ 9 Hz, 2 H,
MS (neg. APCI) m/z: 296.1 [M - Hþ], (M ¼ 297.2).
Ar-H), 7.46* (d, J ¼ 9 Hz, 2 H, Ar-H), 7.44 (d, J ¼ 9 Hz, 2 H, Ar-H), 7.16
(d, J ¼ 9 Hz, 2 H, Ar-H), 2.51* (s, 3 H, CH3)/2.13 (s, 3 H, CH3),
(tautomeric ratio, %: 5d/5d* ¼ 62:38). UVevis (ethanol): lmax/nm:
2.2.7. 5-((2,6-Dimethylphenyl)diazenyl)-2-oxo-4,6-diphenyl-1,2-
dihydropyridine-3-carbonitrile (1g)
[(log
3
)]: 348 (3.69). MS (neg. APCI) m/z: 329.1 [M - Hþ], (M ¼ 333.1).
Red solid, Mp 161e162 ꢂC. 1H NMR (300 MHz, DMSO-d6)
d
(ppm) ¼ 7.42e7.45 (m, 1 H, Ar-H), 7.26e7.36 (m, 8 H, Ar-H),
6.80e6.82 (m, 2 H, Ar-H), 2.48 (s, 3 H, CH3), 1.62 (s, 6 H, 2 CH3). 13
NMR (75 MHz, DMSO-d6)
(ppm) ¼ 170.0, 161.8, 150.4, 149.9, 142.0,
139.1, 132.6, 131.0, 129.8, 129.1, 128.7, 128.2, 127.6, 127.5, 127.4, 127.2,
2.2.14. 6-Hydroxy-2-oxo-4-phenyl-5-(phenyldiazenyl)-1,2-
dihydropyridine-3-carbonitrile (5e)
C
d
Orange powder, Mp >300 ꢂC. 1H NMR (300 MHz, DMSO-d6)
d
(ppm) ¼ 13.96 (s, 1H, NH), 7.82 (d, J ¼ 6.9 Hz, 2 H, Ar-H), 7.57 (t,
119.8, 96.4,19.1. UVevis (ethanol): lmax/nm: [(log
3
)]: 367 (4.13). MS
J ¼ 7.5 Hz,1 H, Ar-H), 7.47 (t, J ¼ 7.5 Hz, 2 H, Ar-H), 7.19e7.24 (m, 2 H,
(pos. APCI) m/z: 405.2 [M þ Hþ], MS (neg. APCI) m/z: 403.2 [M - Hþ],
(M ¼ 404.4).
Ar-H), 6.99 (d, J ¼ 7.5 Hz, 2 H, Ar-H), 6.81 (t, J ¼ 7.5 Hz, 1 H, Ar-H). 13C
NMR (75 MHz, DMSO-d6)
d
(ppm) ¼ 193.4, 165.6, 144.3,140.6, 138.6,
132.5, 129.7, 128.4, 120.7, 113.3. UVevis (ethanol): lmax/nm: [(log
2.2.8. 2-Oxo-4,6-diphenyl-5-(phenyldiazenyl)-1,2-dihydropyridine-
3-carbonitrile (1h)
3
)]: 360 (4.24). MS (pos. APCI) m/z: 318.9 [M þ Hþ], MS (neg. APCI)
m/z: 315.1 [M - Hþ], (M ¼ 316.3).
Yellow powder, Mp 190e192 ꢂC (dec). 1H NMR (300 MHz,
DMSO-d6)
Ar-H), 7.18e7.26 (m, 5 H, Ar-H), 6.89e6.92 (m, 2 H, Ar-H). 13C NMR
(75 MHz, DMSO-d6)
(ppm) ¼ 170.2, 161.8, 152.7, 149.0, 141.3, 138.8,
131.5, 130.5, 129.2, 129.1, 128.9, 128.0, 127.4, 121.4, 119.9, 96.7.
d
(ppm) ¼ 7.47e7.50 (m, 2 H, Ar-H), 7.33e7.35 (m, 6 H,
3. Results and discussion
d
As a starting point for our investigation, we examined the
synthesis of 5-phenylazo-4,6-dimethyl-3-cyano-2-pyridone (1a)
from phenylazo acetylacetone (2a) and cyanoacetamide (3), using
KOH as the base for the reaction (Scheme 2, Table 1) in ethanol as
the solvent. The use of KOH instead of the previously employed
sodium ethoxide [17,18] was found to be more convenient. All
studies were performed applying controlled single-mode micro-
wave heating in sealed vessels [20,21]. Screening of reaction
conditions focused on different amounts of the KOH, amide, and
variations in reaction time and temperature. As can be seen in
Table 1 among different temperatures a better result was obtained
at 130 ꢂC (entries 1e8). The effect of the molar excess of amide 3
was checked and it was found that in the presence of 2 equivalents
of the amide an optimum result was obtained (Table 1, entries
9e13). Running the reaction for different periods of times (Table 1,
entries 13e16), revealed that complete conversions were generally
UVevis (ethanol): lmax/nm: [(log 3)]: 370 (4.01). MS (pos. APCI) m/
z: 377.5 [M þ Hþ], MS (neg. APCI) m/z: 375.6 [M - Hþ], (M ¼ 376.4).
2.2.9. 5-((4-Bromo-2,6-dimethylphenyl)diazenyl)-2-oxo-4,6-
diphenyl-1,2-dihydropyridine-3-carbonitrile (1i)
Dark red solid, Mp 179e180 ꢂC. 1H NMR (300 MHz, DMSO-d6)
d
(ppm) ¼ 7.41e7.44 (m, 2 H, Ar-H), 7.26e7.34 (m, 8 H, Ar-H), 7.03 (s,
2 H, Ar-H), 1.58 (s, 6 H, 2 CH3). 13C NMR (75 MHz, DMSO-d6)
(ppm) ¼ 169.9, 162.2, 150.0, 149.3, 141.9, 139.0, 133.7, 132.5, 131.4,
129.8, 128.7, 128.3, 127.6, 127.6, 127.4, 119.7, 119.6, 96.7, 18.8. UVevis
d
(ethanol): lmax/nm: [(log
3)]: 374 (4.08). MS (neg. APCI) m/z: 482.2
[M - Hþ], (M ¼ 483.4).
2.2.10. 6-Hydroxy-4-methyl-2-oxo-5-(phenyldiazenyl)-1,2-
dihydropyridine-3-carbonitrile (5a)
Orange powder, Mp >300 ꢂC (Lit. Mp 288e289 ꢂC [8]). 1H NMR
(300 MHz, DMSO-d6)
d
(ppm) ¼ 13.74 (s, 1H, NH)/10.17* (s, 1H, NH),
7.54 (d, J ¼ 7.2 Hz, 2H, Ar-H), 7.40 (t, J ¼ 7.5 Hz, 2 H, Ar-H), 7.17*-7.32*
(m, 5 H, Ar-H), 6.91 (t, J ¼ 7.2 Hz, 1 H, Ar-H), 2.51* (s, 3 H, CH3)/2.32
(s, 3 H, CH3) (tautomeric ratio, %: 5a/5a* ¼ 50:50). UVevis
(ethanol): lmax/nm: [(log 3)]: 430 (4.19), 353 (4.19). MS (neg. APCI)
m/z: 253.2 [M - Hþ], (M ¼ 254.2).
2.2.11. 5-((2,6-Dimethylphenyl)diazenyl)-6-hydroxy-4-methyl-2-
oxo-1,2-dihydropyridine-3-carbonitrile (5b)
Orange powder, Mp >300 ꢂC. 1H NMR (300 MHz, DMSO-d6)
d
(ppm) ¼ 14.23 (s, 1 H, NH), 7.02 (d, J ¼ 7.5 Hz, 2 H, Ar-H), 6.85 (t,
J ¼ 7.5 Hz, 1H, Ar-H), 2.34 (s, 6 H, 2 CH3), 2.23 (s, 3 H, CH3). 13C
NMR (75 MHz, DMSO-d6)
138.1, 129.6, 129.1, 128.8, 127.3, 123.0, 27.3, 20.0. UVevis (ethanol):
lmax/nm: [(log
(M ¼ 282.3).
d
(ppm) ¼ 197.2, 165.4, 156.1, 140.2,
3
)]: 412 (4.06). MS (neg. APCI) m/z: 281 [M - Hþ],
Scheme 2.

76
D.Z. Mijin et al. / Dyes and Pigments 85 (2010) 73e78
Table 2
Synthesis of pyridone colorants 1a-i (Scheme 2).
Entry
R1
R2
R3
R4
Product
Yield (%)a
1
Me
H
H
H
99
1a
2
3
4
5
6
Me
Me
Me
Me
Me
Me
Me
H
100
100
92
1b
1c
1d
1e
I
H
H
H
H
Br
Br
H
Me
Me
100
100
NO2
H
1f
7
8
Ph
Ph
Ph
Me
Me
H
83
72
72
1g
1h
H
H
H
9
Me
Me
Br
1i
a
Isolated yield.

D.Z. Mijin et al. / Dyes and Pigments 85 (2010) 73e78
77
Scheme 3.
obtained after 5 min. Along the same lines it was established that
the highest conversions were achieved employing 1.7 equivalents of
KOH base (Table 1, entries 17e20). Evaluation of isolated yields for
the reaction under the optimum conditions represented in Table 1,
entry 20 afforded 99% of the corresponding pyridone product 1a.
Having optimized conditions in hand that allow the preparation
of pyridone 1a within 5 min in high isolated yield (Table 1, entry
20), the synthesis of a variety of different 5-arylazo-4,6-disubsti-
tuted-3-cyano-2-pyridone dyes 1b-i from the condensation of
diketones 2 and cyanoacetamide (3) was investigated (Scheme 2).
The results are summarized in Table 2. As can be seen, products
with methyl substituents at position 4 and 6 on the pyridone ring
were obtained in almost quantitative yield. An important feature of
this work is the preparation of 4,6-disubstituted derivatives in high
yields in a short period of time (Table 2, entries 7e9) which is not
possible under conventional heating. For example, pyridone 1g was
obtained in only 50% isolated yield after 6 h reflux in ethanol. It
worth noting that this is the first report of a high yielding prepa-
ration of 4,6-diphenylsubstituted pyridone dyes. The improvement
in product yield and reaction time clearly shows the advantage of
running reactions at higher temperature as compared to the
conventional oil bath experiment at the boiling point of the solvent
[20,21].
In addition to the results obtained with 1,3-diketone substrates
2 we also evaluated
(Scheme 3). The results are summarized in Table 3. The lower yields
in these cases can be related to the lower reactivity of -ketoesters
4 compared to diketones 2. The UVevis absorption maxima (lmax
b-ketoesters 4 under the optimized condition
b
)
of the electronic transitions involving the free non-bonding elec-
trons of the azo group of the synthesized pyridone dyes and the
Table 3
Synthesis of pyridone colorants.
Entry
R1
R2/R6
R3
R4
R5
Product
Yield (%)a
1
Me
OEt/OH
H
H
H
47
5a
2
Me
Me
OEt/OH
OEt/OH
Me
Me
Me
Me
H
50
80
5b
3
4
Br
5c
Me
OEt/OH
OEt/OH
H
H
H
H
Br
93
78
5d
5e
5
Ph
H
a
Isolated yield.

78
D.Z. Mijin et al. / Dyes and Pigments 85 (2010) 73e78
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Scheme 4. The equilibrium between azo form (I) and hydrazone form (II) of 5-(4-
ꢂ
[5] Cee A, Horakova B, Lyeka A. Structural analysis of substituted 3-arylazo-2-
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methyl-pyridines and their application on polyamide fibre as disperse reactive
dyes. Dyes and Pigments 1988;9:475e80.
[7] Wang PY, Wang IJ. Photofading of azo pyridone dyes in solution. Part II.
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(mono- and di-substituted arylazo)-2-hydroxy-4-methyl-5-cyano-6-pyridone
in N, N-dimethylformamide. Textile Research Journal 1990;60:519e24.
[8] Chen C, Wang I. Synthesis of some pyridone azo dyes from 1-substituted 2-
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[9] Wang I, Hsu Y, Tian J. Synthesis and properties of some pyridone chromium
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[10] Matsui M, Joglekar B, Ishigure Y, Shibata K, Muramatsu H, Murata Y. Synthesis
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molecular extinction coefficients (given as log 3) in ethanol are
given in Experimental section. The spectra were run in spec-
troquality ethanol using concentrations of 5 ꢀ 10e5 mol dmꢃ3. The
obtained data confirm that the positions of the UVevis absorption
maxima depend on the nature of the substituents of the diazo
component as well as on the nature of the substituents of the
pyridone component. Introduction of a substituent into the diazo
component predominantly leads to a bathochromic shift of the
long-wavelength absorption maximum as compared to that of
the unsubstituted dyes [15,16,18]. Change of the substituents in the
pyridone component leads also mainly to bathochromic shifts as
compared to that of the 4,6-dimethyl substituted pyridone dyes. It
should be mentioned that the arylazo pyridone dyes prepared in
this work may exist in two tautomeric forms and that the
tautomerism is influenced mainly by the nature of the substituents
and the polarity of the solvents [16]. This tautomerisation was
observed in the 1H NMR spectra of some of the prepared derivatives
5a and 5d (Scheme 4) (see Experimental Section).
[14] Wang M, Funabiki K, Matsui M. Synthesis and properties of bis(hetaryl)azo
dyes. Dyes and Pigments 2003;57:77e86.
ꢀ
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[15] Usæumliæ G, Mijin D, Valentiæ N, Vajs V, Susiæ B. Substituent and solvent
effects on the UV/Vis absorption spectra of 5-(4-substituted arylazo)-6-hy-
droxy-4-methyl-3-cyano-2-pyridones. Chemical Physics Letters 2004;397:
148e53.
4. Conclusion
ꢀ
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[16] Mijin D, Usæumliæ G, Perisiæ-Janjiæ N, Valentiæ N. Substituent and solvent
effects on the UV/vis absorption spectra of 5-(3- and 4-substituted arylazo)-
4,6-dimethyl-3-cyano-2-pyridones. Chemical Physics Letters 2006;418:223e9.
[17] Elgemeie GEH, El-Zanate AM, Mansour AKE. Reaction of (cyano)thioacetamide
In conclusion a rapid and efficient method for the synthesis of
an important group of azo-based dyes was introduced. Compared
to the traditional method applying conventional heating, the use of
controlled sealed vessel microwave heating allowed the prepara-
tion of a variety of pyridone colorants in very short reaction times
and high yields.
with arylhydrazones of beta-diketones
e novel synthesis of 2(1 H)-pyr-
idinethiones, thieno[2,3-b]pyridines, and pyrazolo[3,4-b]pyridines. Bulletin of
the Chemical Society of Japan 1993;66:555e61.
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[18] Mijin D, Usæumliæ G, Perisiæ-Janjiæ N, Trkulja I, Radetiæ M, Jovaneiæ P.
Synthesis, properties and colour assessment of some new 5-(3- and 4-
substituted phenylazo)-4,6-dimethyl-3-cyano-2-pyridones. Journal of Serbian
Chemical Society 2006;71:435e44.
[19] Bolhofer WA. b-Phenylserine. Journal of American Chemical Society 1952;74:
5459e61.
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synthesis: highlights from the 2004e2008 literature. Molecular Diversity
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[21] Kappe CO. Controlled microwave heating in modern organic synthesis.
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Acknowledgment
ꢀ
D.Z.M. thanks the Austrian Academic Exchange Service for
a scholarship and Prof C.O.Kappe for his support.