Synthesis of some novel pyrazolo[1,5-a]pyrimidine derivatives and their application as disperse dyes

Article abstract of DOI:10.3390/molecules16065182

A series of novel monoazo-disperse dyes containing pyrazolo[1,5-a] pyrimidine structures were synthesized starting with the coupling reaction between ethyl cyanoacetate and 4-hydroxybenzenediazonium chloride, followed by treatment of the resulting hydrazo

Full text of DOI:10.3390/molecules16065182

Molecules 2011, 16, 5182-5193; doi:10.3390/molecules16065182
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis of Some Novel Pyrazolo[1,5-a]pyrimidine Derivatives
and Their Application as Disperse Dyes
Alya M. Al-Etaibi 1,*, Nouria A. Al-Awadi 2, Morsy A. El-Apasery 2 and Maher R. Ibrahim 2
1
Natural Science Department, College of Health Science, Public Authority for Applied Education
and Training, Kuwait
2
Chemistry Department, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060,
Kuwait
* Author to whom correspondence should be addressed; E-Mail: alya.aletaibi@yahoo.com.
Received: 1 June 2011; in revised form: 9 June 2011 / Accepted: 15 June 2011 /
Published: 22 June 2011
Abstract: A series of novel monoazo-disperse dyes containing pyrazolo[1,5-a]pyrimidine
structures were synthesized starting with the coupling reaction between ethyl cyanoacetate
and 4-hydroxybenzenediazonium chloride, followed by treatment of the resulting
hydrazone product with hydrazine hydrate. The pyrazolohydrazone 6 is then treated with
either 2,4-pentandione and enaminonitrile or aryl-substituted enaminoketones to give
the target pyrazolo[1,5-a]pyrimidine dyes 7 and 15a-d. Structural assignments to the dyes
were made using NMR spectroscopic methods. A new high temperature method, using
microwave heating, was employed to apply these dyes to polyester fibers. Most of the dyed
fabrics tested displayed moderate light fastness and excellent washing fastness properties.
Keywords: enaminone; pyrazolohydrazone; microwave irradiation; disperse dyes; HMBC
2-D, 2,4-pentandione; enaminonitrile
1. Introduction
Pyrazole derivatives are important intermediates in organic synthesis and possess a range of
interesting biological and antimicrobial properties [1-8]. Their fused pyrimidine derivatives are used
as dyes [9-14]. In the current study, we prepared new azopyrazolopyrimidine dyes, starting with

Molecules 2011, 16
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3-amino-4-(4-hydroxyphenyl)azo-1H-2-pyrazoline-5-ones and 3-(4-hydroxyphenylazo-1H-2-pyrazoline-5-
ones, and applied them to polyester fibers as disperse dyes by using a new high temperature
microwave heating method. Microwave irradiation leads to a large increase in dye uptake and dyeing
rate, along with a performance of dye leveling and color homogeneity than can be achieved by using
conductive heating [15-17].
2. Results and Discussion
2.1. Synthesis and Characteristics
Ethyl 2-arylhydrazonocyanoacetate 4 was formed by addition under mild conditions of ethyl
cyanoacetate (1) to 4-hydroxybenzenediazonium chloride (2) that readily affords the corresponding
hydrazone 3. The existence of this substance in the quininoid form 5 was ruled out based on the results
of NOE difference experiments, which showed that irradiation of the two NH signals at 12.1 and
13.0 ppm caused an enhancement of the intensities of the aryl proton resonances at 6.3 and 6.8 ppm,
while irradiation of the two OH signals at 9.68 and 9.57 ppm also resulted in an increase in the
intensities of the aryl proton peak at 6.8 ppm. Moreover, the 13C-NMR spectrum of 3 shows only two
sets of two sp3 carbon signals at 61.7 and 61.2, and 14.20 and 14.0 corresponding to the ethyl group. In
addition, the data demonstrate that the hydrazone product exists as a 1:2 equilibrium mixture of
syn- (3) and anti-forms (4) (Scheme 1). The major isomer is assumed to have the syn-stereochemistry 4
1
based on the expectation that its NH proton would be deshielded in the H-NMR spectrum as a result
of potential hydrogen bonding with the carbonyl ester moiety (cf. Scheme 1).
Scheme 1. Preparation of hydroxyphenylhydrazonopyrazolone 6.
O
O
CN
_
+
N
NC
HN
NC
CH2
HO
N Cl
OEt
OEt
+
CO2Et
N
NH
N
1
2
OH
3
O
5
OEt
NC
O
N
H
N
H
N
HO
N
NH2
NH2NH2.H2O
N
O
6
N
H
OH
4
Brecknell et al. [18] was able to isolate and characterize both isomers. The predominance of the
anti-form of 2-phenylhydrazonoacetate was attributed to stereoelectronic effects. Recently Al-Awadi et al.

Molecules 2011, 16
5184
have shown that in similar systems stereoelectronic effects are more important than hydrogen bonding
in governing syn-anti ratios [19].
Hydrazone 3 undergoes a smooth reaction with hydrazine hydrate to yield 4-(4-hydroxyphenyl-
hydrazonopyrazolone 6. The structure and the chemistry of such compounds have received
considerable attention [20-22]. We have observed that 6 readily condenses with acetylacetone to yield
the pyrazolo[1,5-a]pyrimidine 7, which has the potential of existing in tautomeric form 8. However,
1
the 2D H-NMR analysis results indicate that it exists in only one form having the nonquinoidal
structure 7 (cf. Scheme 2).
Scheme 2. Synthesis of 3-(4-hydroxyphenylazo)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-2-
one (8) and 7-amino-3-(4-hydroxyphenylazo)-pyrazolo[1,5-a]pyrimidin-2-one (12).
The important features of the HMBC 2-D 1H, and 13C signals are shown in Figure 1. H6 at 7.06 ppm
correlates with C5 and C7 at 161.2 and 146.4 ppm; H13 at 7.63 ppm correlates with C12 and C15 at 141.5
and 158.4 ppm; H14 at 6.88 ppm correlates with C13 and C15 at 121.6 and 158.4 ppm; H16 at 2.51 ppm
correlates with C5 and C7 at 161.2 and 146.4 ppm; and H17 at 2.58 ppm correlates with C6 and C7 at
111.9 and 146.4 ppm.
1H-15N HMBC experiments add further support to the assignment of structure 7, such as the
chemical shifts observed for N7a at 210 ppm, N4 at 260 ppm and N12a at 370 ppm, the cross peak
correlations for coupling of H6 at 7.06 ppm is also observed with N7a at 210 ppm (3J) (H6, N7a), and N4

Molecules 2011, 16
5185
at 260 ppm (3J) (H6, N4). Interestingly, coupling of H16 at 2.51 ppm with only N4 at 260 ppm (3J)
(H16, N4) is observed, coupling of H17 at 2.58 ppm takes place only with N7a at 210 ppm (3J) (H17, N7a)
(Figure 1).
Figure 1. 1H- and 13C-NMR spectroscopy assignments of compound 7.
121.6
141.5
116.0
114.8
H
H
H
144.4
161.2
14
13
12
4
N
16
CH3
9.94
HO
N
N
O
N
CH3
HO
N
N
O
2.51
5
3
3a
15
24.1
158.4
2
6
111.9
N
1
N
H
H
H
H
7.06
7a
N
H
N
H
6.88
7
146.4
7.63
H
H
17
3.43
H
161.5
CH3
CH3
21.1
2.58
Hydroxyphenylhydrazonopyrazolone 6 also reacts with 2-piperidinylacrylonitrile (9) to yield a
product for which structures 10-13 are possible based on the absence of an amino-proton resonance in
their 1H-NMR spectra and a cyano band in the IR spectrum. The assignment of structure 10 was made
by H-C correlations in the HMBC 2-D experiments (Figure 2).
Figure 2. 1H and 13C NMR spectroscopy assignments of compound 10.
119.4
137.9
116.0
118.1
H
H
H
147.1
150.0
14
13
4
N
12
15
9.66
8.10
HO
N N
O
N
H
HO
N N
O
H
H
5
3
3a
156.9
6
2
N
1
N
H
H
H
H
7a
N
H
97.1
N
6.86
7
7.50
H
6.47
H
163.6
NH2
146.0
H
NH2
7.91
The correlations of H5 at 8.10 ppm with C6 and C7 at 97.1 and 146.0 ppm, H13 at 7.51 ppm with C12
and C15 at 137.9 and 156.9 ppm, and H14 at 6.90 with C12, C13 and C15 at 137.9, 119.4 and 156.9 ppm
were observed, further structural information came from the results of 1H-15N HMBC experiments, the
chemical shifts for N7a and N4 are 198.7 and 234.2 ppm, respectively, cross peak correlations for
coupling of the shielded proton H6 at 6.47 ppm takes place with N7a at 198.7 ppm (3J) (H-6, N-7a) and
N4 at 234.2 ppm (3J) (H-6, N-4), coupling of the deshielded proton H5 at 8.10 ppm with only N4 at
234.2 ppm (3J) (H-5, N-4) is also observed.
Compound 6 reacts with enaminones 14a-d to yield the corresponding pyrazolo[1,5-a]pyrimidines
15a-d (cf. Scheme 3) whose identities were established by using 2D NMR experiments (Figure 3).

Molecules 2011, 16
Scheme 3. Synthesis of pyrazolo[1,5-a]pyrimidinone derivatives.
5186
HO
N N
O
N
Ar
NMe2
N
N
H
O
6
+
16a-d
Ar
14a-d
HO
N N
O
N
14 a, Ar = C6H5
b, Ar = C6H4Cl(p)
c, Ar = Fur-2-yl
d, Ar = Thien-2-yl
N
N
H
Ar
15a-d
13
1H and C signal assignments and HMBC 2-D derived H-C correlations for 15a. The important
features of the HMBC correlations are the H5 at 8.7 ppm with C7 at 145.0 ppm, H6 at 7.38 ppm with C7
and C8 at 145.0 and 130.1 ppm, H9 at 8.07 ppm with C11 at 131.3 ppm, H10 at 7.64 ppm with C8 at
130.1 pm, H11 at 7.64 ppm with C9 at 129.7 ppm, H13 at 7.71 ppm with C15 at 158.8 ppm, and H14 at
6.90 ppm with C12 at 143.4 ppm.
Figure 3. 1H- and 13C-NMR of compound 15a.
122.4
143.4
115.9
114.2
H
H
145.9
H
151.7
8.70
14
13
4
N
10.02
15
HO
N
N
O
N
H
12
H
H
HO
N
N
O
5
3
3a
158.8
7.38
H
N
2
6
9
H
H
110.6
129.7
1
N
N
H
H
H
145.0
130.1
6.90
7.71
7a
N
7
H
H
H
H
8
161.1
H
H
8.07
10
7.64
H
11
H
128.6
H
7.64
131.3
The possible formation of regioisomers 16 in reactions of 6 with enaminones 14a-d is ruled out
1
based on H-15N HMBC experimental results. Conclusive data for the structure of 15a include
chemical shifts for N7a at 208.7 ppm and N4 at 270.4 ppm. Cross peak correlations for coupling of the
shielded proton H6 at 7.39 ppm are observed with N7a at 208.7 ppm (3J) (H6, N7a) and N4 at 270.4 ppm
(3J) (H6, N4). Coupling of the deshielded proton H5 at 7.70 ppm with N4 at 270.4 ppm (3J) (H5, N4)
only is also observed. The results demonstrate that the phenyl moiety is located at C7 and not at C5.

Molecules 2011, 16
5187
2.2. Dyeing and Fastness Properties
Arylazopyrazolopyrimidine derivatives 6, 7 and 15a-d were tested as dyes for polyester fibers using
the high temperature dyeing method (HT) by employing microwave heating as an energy source. The
physical and analytical data for the dyed fibers, given in Tables 1 and 2, reflect the efficiency of the
microwave irradiation, leading to a large increase in dye uptake and dyeing rate along with a
performance of dye leveling and color homogeneity.
2.2.1. Color strength
Data in Table 1 reveals that the color strengths (K/S) of dyed polyester fabrics are directly
proportional to the amounts of the dyes applied (% o.m.f.). The hues of the fabrics treated with the azo
dyes were found to vary from yellowish-orange to dark orange, based on the substitution patterns.
Differences in the color strength observed depend on the substitution patterns, ‘auxochromes’, present
in the arylazopyrazolopyrimidine disperse dyes referred to as ‘chromogens’ [14,23,24]. Data in Table 1
clearly shows that the magnitude of color strength obtained using dye 15d is much larger than that for 15c.
Table 1. Color strength of dyed polyester using high temperature dyeing method.
Color strength (K/S) % Dye o.m.f.
Color shade on
polyester
Dye
1
2
3
4
6
7
15a
15b
15c
15d
Yellowish-orange
Pale orange
Dark orange
Dark orange
Orange
1.17
2.19
5.66
5.43
4.40
4.08
2.12
3.79
5.95
5.81
4.64
4.73
2.47
4.09
7.12
7.91
4.85
6.02
2.49
6.96
8.31
10.04
6.01
7.06
Orange
2.2.2. Wash fastness
Fastness data, obtained by measuring color intensity changes in the dyed fabrics, are given in Table
2. It shows that wash fastness varies with the substitution patterns in the dyes, where an increase
occurs when stronger electron-attracting groups are present on the aryl moieties. This might be
attributed to the fact that these disperse dyes are mainly dispersed within the pores in the polyester
fabrics and are held in their places by different forces including Van der Waal forces. Electron-attracting
groups enable stronger Van der Waal forces and also hydrogen bonding with the dyed fabrics that
increases their stability to washing.
2.2.3. Light fastness
The light fastness properties of substituted of fabrics treated with the disperse dyes were determined
(Table 2). The low light fastness properties observed are most likely result the photochemical
reactivity of the arylazopyrazolopyrimidine dyes. Indeed, the results of LCMS monitoring of the
photolysate, obtained by irradiation of 3-(4-hydroxyphenylazo)-7-phenylpyrazolo[1,5-a]pyrimidin-2-one

Molecules 2011, 16
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(14a), under 16 W low pressure mercurey arc-lamp (254 nm) in acetonitrile for 48 h, supported this
finding. Elnagdi et al. [25] observed that 3,4-diarylaminopyrazoles are reactive when treated under
reflux with AcOH-H2SO4 mixture.
Table 2. Fastness properties of azo disperse dyes on polyester fabrics, prepared by using
high temperature dyeing method.
Wash fastness a,b
Dye
Light fastness
Alt
SC
SW
(1% o.m.f. dyeing)
6
7
15a
15b
15c
15d
5
5
5
5
4
5
5
5
5
5
5
5
5
5
5
5
4
5
2-3
2
2-3
3
2-3
2
(2% o.m.f. dyeing)
6
7
15a
15b
15c
15d
5
5
5
5
4
5
5
5
5
5
5
5
5
5
5
5
4
5
2-3
2
2
2-3
2-3
2
(3% o.m.f. dyeing)
6
7
5
5
5
5
5
5
2-3
2
15a
15b
15c
15d
4-5
4-5
4
5
5
5
4-5
4-5
4-5
4
2
2
2-3
2
4-5
4-5
(4% o.m.f. dyeing)
6
7
15a
15b
15c
15d
5
5
5
5
4
5
5
5
5
5
5
5
5
5
5
4
2-3
2
2
2
2
4-5
4-5
2
a ISO CO2/CO41; b Alt = alteration; SC = staining on cotton; SW = staining on wool.
3. Experimental
3.1. General
All melting points were recorded on a Gallenkamp apparatus and are uncorrected. IR spectra were
1
13
recorded in KBr disks on a Perkin Elmer System 2000 FT-IR spectrophotometer. H- and C-NMR
spectra were recorded on a Bruker DPX 400 MHz super-conducting NMR spectrometer. Mass spectra
were measured on a VG Auto-spec-Q instrument (high resolution, high performance, tri-sector

Molecules 2011, 16
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GC/MS/MS) and by LC-MS using an Agilent 1100 series LC/MSD with API-ES/APCI ionization
mode. Microanalyses were performed on a LECO CH NS-932 Elemental Analyzer. The microwave
oven used is a single mode cavity Explorer Microwave (CEM Corporation, Matthews, NC, USA) and
irradiate in heavy-walled Pyrex tube (capacity 10 mL and 80 mL for dyeing). The color strengths (K/S)
of the dyed polyester fabrics and the color fastness to light were evaluated at the Dyeing, Printing and
Textile Auxiliaries Department, Textile Research Division, National Research Centre, Giza, Egypt.
3.2. General Procedure for the Synthesis of azo Disperse Dyes
Ethyl cyano(4-hydroxyphenylhydrazono)acetate (3). p-Aminophenol (10.9 g, 0.1 M) was dissolved in
concentrated HCl (30 m) and water cooled in ice (20 mL) and then NaNO2 (7 g) in water (50 mL) was
added in portions. A mixture of ethyl cyanoacetate (10 g, 0.1 M), NaOAc (20 g), ethanol (15 mL) and
water (50 mL) was prepared separately and cooled in ice. The diazonium salt solution was added
slowly to the second solution, with ice cooling. The cooled mixture was stirred for 0.5 h and filtered to
give brown crystals, which were crystallized from alcohol/water to yield 2.0 g (86%) of 3, m.p.
273–274 °C. MS: m/z = 331 (M+, 100%), 238 (50%), 182 (20%). IR: 3432, 3066, 3003, 1623, 1591,
1
1531, 1461, 1232, 829 cm–1. H-NMR (DMSO-d6) 13.02 (s, 1H, NH, syn), 12.16 (s, 1H, NH, anti),
9.68 (s, 1H, OH, syn), 9.57 (s, 1H, OH, anti), 7.36 (d, 2H, J = 7.4 Hz, syn), 7.31 (d, 2H,
J = 8.0 Hz, anti), 6.81 (d, 4H, J = 8.0 Hz, syn+anti), 4.30 (q, 2H, syn), 4.24 (q, 2H, anti), 1.32 (t, 3H,
13
syn), 1.28 ppm (t, 3H, anti). C-NMR (DMSO-d6) 161.4, 161.3, 155.9, 155.3, 134.2, 133.5, 118.0,
117.9, 116.4, 116.0, 115.9, 112.0, 101.9, 101.4, 61.7, 61.2, 14.2, 14.0 ppm. HRMS = 233.0794,
requires C11H11N3O3 233.0794.
5-Amino-4-[(4-hydroxyphenyl)-hydrazono]-2,4-dihydropyrazol-3-one (6). A mixture of 3 (2.33 g,
10 mmol), hydrazine hydrate (2.5 mL) in ethanol (20 mol) was stirred at reflux for 3-4 h. The solvent
was removed under vacuum and the formed solid was collected and crystallized from ethanol/water to
give 6. Red brown crystals from alcohol, yield 2.6 g (73%), m.p. 263 °C. MS: m/z = 219 (M+, 100%),
1
126 (10%), 108 (60%). IR: 3472, 3361, 3283, 3165, 3130, 1678, 1626, 1268, 820 cm–1. H-NMR
(DMSO-d6) 12.90 (br, 1H, NH), 10.45 (s, 1H, NH), 9.50 (br, 1H, OH), 7.37 (d, 2H, J = 8.0 Hz) 6.78
13
(d, 2H, J = 8.0 Hz) 5.71 ppm (br, 2H, NH2); C-NMR (DMSO-d6) 160.7, 158.8, 151.6, 144.9, 143.4,
131.3, 130.0, 129.6, 128.5, 122.4, 115.9, 114.1, 110.6, 115.7 ppm.
General procedure for the synthesis of pyrazolo[1,5-a]pyrimidines 7, 10 and 15a-d
A mixture containing 6 (0.22 g, 10 mmol), and acetylacetone, 2-piperidinylacrylonitrile or enaminones
5a-d (1 mmol) in acetic acid (5 mmol) was irradiated in a microwave oven at 140 °C for 2 min. The
mixture was then poured into ice water (50 mL). The formed was collected and crystallized from the
appropriate solvent (see below).
3-(4-Hydroxyphenylazo)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-2-one (7). Red crystals from DMF,
yield 2.79 g (73%), m.p. 277-278 °C. MS: m/z = 283 (M+, 100%), 190 (90%), 162 (30%). IR: 3458,
3113, 3013, 1620, 1534, 1423, 1250, 1139, 840 cm–1. 1H-NMR (DMSO-d6) 9.94 (s, 1H, OH), 7.63 (dd,
2H, H13 J = 7.4, 1.8 Hz), 7.06 (s, 1H, H6), 6.88 (dd, 2H, H14, J = 7.4, 1.8 Hz), 3.43 (br, 1H, NH), 2.58

Molecules 2011, 16
5190
(s, 3H), 2.51 ppm (s, 3H). 13C-NMR (DMSO-d6) 161.5, 161.2, 158.4, 146.4, 144.4, 141.5, 121.6,
116.0, 114.8, 111.9, 24.0, 16.5 ppm. Anal. Calcd. for C14H13N5O2 (283.3): C 59.36; H 4.63, N 24.72.
Found: C 59.30; H 4.57; N 24.71.
7-Amino-3-(4-hydroxyphenylazo)pyrazolo[1,5-a]pyrimidin-2-one (10). Red crystals from DMF, yield
2.79 g (73%), m.p. 273 °C. MS: m/z = 270 (M+, 75%), 177 (35%), 150 (100%). IR: 3353, 3146, 2926,
1
1649, 1620, 1543, 1444, 1239, 1176, 823 cm–1. H-NMR (DMSO-d6) 9.66 (s, 1H, OH), 8.10 (d, 1H,
H5, J = 6.0 Hz), 7.91 (br, 2H, NH2), 7.50 (d, 2H, J = 8.0 Hz), 6.86 (d, 2H, J = 8.0 Hz), 6.47 ppm
(d, 1H, H6, J = 6.0 Hz). 13C-NMR (DMSO-d6) δ 163.6, 156.9, 150.0, 147.1, 164.0, 137.9, 119.6,
118.1., 116.0, 97.1 ppm. Anal. Calcd. for C12H9N6O2 (269.2): C 53.53; H 3.37, N 31.21. Found: C
53.47; H 3.27; N 31.05.
3-(4-Hydroxyphenylazo)-7-phenylpyrazolo[1,5-a]pyrimidin-2-one (15a). Red crystals from DMF,
yield 2.6 g (78%), m.p. 273-274 °C. MS: m/z = 331 (M+, 100%), 238 (50%), 182 (20%). IR: 3432,
3066, 3003, 1623, 1591, 1531, 1461, 1232, 829 cm–1. 1H-NMR (DMSO-d6) 10.02 (s, 1H, OH), 8.70 (d,
1H, H5, J = 4.2 Hz), 8.07 (dd, 2H, H9, J = 7.2, 1.8 Hz), 7.71 (dd, 2H, H13, J = 7.2, 1.8 Hz), 7.64 (m,
3H, H10, H11), 7.38 (d, 1H, H6, J = 4.2 Hz), 6.90 (dd, 2H, H14, J = 7.2, 1.8 Hz), 3.36 ppm (br, 1H, NH).
13C-NMR (DMSO-d6) 161.1, 158.8, 151.7, 145.0, 145.9, 143.4, 131.3, 130.1, 129.7, 128.6, 122.4,
115.9, 114.2, 110.6 ppm. Anal. Calcd. for C18H13N5O2 (331.3): C 65.25; H 3.95; N 21.14. Found: C
64.93; H 3.92; N 21.03.
7-(4-Chlorophenyl)-3-(4-hydroxyphenylazo)pyrazolo[1,5-a]pyrimidin-2-one (15b). Red crystals from
DMF, yield 2.7 g (84%), m.p. 285–286 °C. MS: m/z = 365 (M+, 100%), 272 (60%), 149 (25%). IR:
3430, 3227, 3095, 1633, 1596, 1514, 1483, 1445, 1253, 821 cm–1. 1H-NMR (DMSO-d6) 10.02 (s, 1H,
OH), 8.71 (d, 1H, J = 4.8 Hz), 8.13 (dd, 2H, J = 7.2, 1.8 Hz), 7.71 (m, 4H), 7.42 (d, 1H,
J = 4.8 Hz), 6.89 (dd, 2H, J = 7.2, 1.8 Hz), 3.38 ppm (br, 1H, NH). 13C-NMR (DMSO-d6) 161.0,
158.8, 151.6, 144.9, 144.7, 143.3, 136.1, 131.5, 128.8, 128.6, 122.4, 115.9, 114.2, 110 ppm. Anal.
Calcd. for C18H12ClN5O2 (365.8): C 59.11; H 3.31, N 19.15. Found: C 58.78; H 3.32; N 18.90.
7-Furan-2-yl-3-(4-hydroxyphenylazo)pyrazolo[1,5-a]pyrimidin-2-one (15c). Red crystals from DMF,
yield 2.7 g (84%), m.p. 291–292 °C. MS: m/z = 321 (M+, 100%), 228 (45%), 172 (15%). IR: 3429,
1
3109, 3035, 1626, 1594, 1536, 1462, 1238, 1132, 828 cm–1. H NMR (DMSO-d6) 10.01 (s, 1H, OH),
8.67 (d, 1H, J = 4.8 Hz), 8.23 (d, 1H, J = 3.6 Hz), 8.15 (d, 1H, J = 3.6 Hz), 7.69 (d, 2H, J = 8.4 Hz),
13
7.62 (d, 1H, J = 4.8 Hz), 6.95 (m, 1H), 6.89 (d, 2H, J = 8.4 Hz), 3.37 ppm (br, 1H, NH). C-NMR
(DMSO-d6) 162.1, 158.6, 150.5, 147.9, 145.0, 142.6, 141.9, 134.6, 121.9, 120.9, 115.9, 114.7, 113.6,
105.8 ppm. Anal. Calcd. for C16H11N5O3 (321.3): C 59.81; H 3.45, N 21.80. Found: C 59.78; H 3.34;
N 21.81.
3-(4-Hydroxyphenylazo)-7-thiophen-2-yl-pyrazolo[1,5-a]pyrimidin-2-one (15d). Red crystals from
DMF, yield 2.6 g (77%), m.p. 284–285 °C. MS: m/z = 337 (M+, 100%), 244 (50%), 188 (20%). IR:
1
3429, 3104, 3035, 1623, 1592, 1535, 1462, 1238, 1160, 826 cm–1. H-NMR (DMSO-d6) 9.99 (s, 1H,
OH), 8.62 (d, 1H, J = 4.8 Hz), 8.55 (d, 1H, J = 3.6 Hz), 8.19 (d, 1H, J = 4.8 Hz), 7.98 (d, 1H,
J = 4.2 Hz), 7.67 (d, 2H, J = 8.4 Hz), 7.41 (t, 1H, J = 4.2 Hz), 6.89 (d, 2H, J = 8.4 Hz), 3.38 ppm (br,

Molecules 2011, 16
5191
13
1H, NH). C-NMR (DMSO-d6) 162.6, 158.2, 150.1, 145.5, 140.4, 139.1, 136.2, 133.1, 129.4, 127.8,
121.3, 116.0, 115.7, 108.0 ppm. Anal. Calcd. for C16H11N5O2S (337.4): C 56.96; H 3.29, N 20.76 ;
S 9.50. Found: C 56.88; H 3.30; N 20.71 ; S 9.46.
3.3. High Temperature Dyeing Method (HT)
3.3.1. Materials
Scoured and bleached polyester 100% (150 130 g/m2, 70/2 denier) was obtained from El-Shourbagy
Co., Egypt. The fabric was treated before dyeing with a solution containing non-ionic detergent
(Hostapal CV, Clariant-Egypt, 5 g/L) and sodium carbonate (2 g/L) in a ratio of 50:1 at 60 °C for
30 min, then thoroughly washed with water and air dried at room temperature.
3.3.2. Dyeing
Dyeing of polyester fabrics was carried out at 130 °C for 60 min, under pressure in a microwave
oven in a 20:1 liquor ratio and pH 5.5 in the presence of a 1:1 ratio of the dispersing agent sodium
lignin sulphonate and the with a 1–4% shade. After dyeing, the fabrics were thoroughly washed and
then subjected to a surface reduction cleaning [(5 g NaOH + 6 g sodium hydrosulphite)/L]. The
samples were heated in this solution for 10 min. at 60 °C and then thoroughly washed and air-dried.
3.4. Color Measurements and Analyses
3.4.1. Color measurements of the dyed fabrics
The color yields of the dyed samples were determined by using the light reflectance technique
performed on a Perkin-Elmer (Lambda 3B) UV/VIS Spectrophotometer. The color strengths, expressed
as K/S values, were determined by applying the Kubelka-Mink equation as follows:
K/S = [(1–R) 2 / 2R] – [(1–Ro) 2 / 2Ro]
where R = decimal fraction of the reflectance of the dyed fabric; Ro = decimal fraction of the
reflectance of the undyed fabric; K = absorption coefficient; S = scattering coefficient.
3.4.2. Fastness testing
After washing using 2 g/L of the non-ionic detergent Hostapal CV at 80 °C for 15 min, the dyed
fabrics were tested, employing ISO standard methods [26]. Wash fastness tests were carried out in
accordance with ISO 105-C04 (1989), in which 5 g/L soap and 2 g/L soda ash solution were used at
95 °C for 30 min in the presence of 10 steel balls (liquor ratio 50:1) and color fastness to light (carbon
arc), ISO 105-B02 (1988).

Molecules 2011, 16
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4. Conclusions
In summary, a series of novel monoazo disperse pyrazolopyrimidine dyes were synthesized via a
sequence involving initial coupling of ethyl cyanoacetate with 4-hydroxybenzenediazonium chlorides.
Subsequent treatment with hydrazine hydrate gave the corresponding pyrazolohydrazone that was then
treated with either 2,5-pentandione or arylenaminoketones to give the target pyrazolo[1,5-a]pyrimidine
dyes. The dyes produced in this manner were then applied to polyester fibers by using HT dyeing
conditions and microwave heating. The dyed fabrics, which displayed yellow to yellow brown hues on
polyester fibers, have low fastness levels to light and excellent wash fastness.
Acknowledgments
The support of the Public Authority for Applied Education and Training, for finance through project
(HS-08-02) and the facilities of AnaLab (SAF) at Kuwait University are gratefully acknowledged.
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Sample Availability: Samples of the compounds 6, 7, 10 and 15a-d are available from the authors
© 2011 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).