Synthesis and tautomeric structure of 3,6-bis(arylazo)pyrazolo [1,5-a]pyrimidine-5,7(4H,6H)-diones

Article abstract of DOI:10.3184/030823408X339782

Two series of 3,6-bis(arylazo)pyrazolo[1,5-a]pyrimidine-5,7-diones were prepared, and their acid dissociation constant pK_as were determined and correlated with the Hammett equation. The results of these correlations, together with the spectroscopic data, indicated that the title compounds exist predominantly in the 3-arylazo-6- arylhydrazonopyrazolo[1,5-a]pyrimidine-5,7- dione tautomeric form, both in the solid and solution phases.

Full text of DOI:10.3184/030823408X339782

452 RESEARCH PAPER
AUGUST, 452–456
JOURNAL OF CHEMICAL RESEARCH 2008
Synthesis and tautomeric structure of 3,6-bis(arylazo)pyrazolo
[1,5-a]pyrimidine-5,7(4H,6H)-diones
Ahmad S. Shawali*, Mosselhi A. N. Mosselhi, Thoraya A. Farghaly, Mohamed R. Shehata and
Nagla M. Tawfik
Department of Chemistry, Faculty of Science, University of Cairo, Giza, Egypt
Two series of 3,6-bis(arylazo)pyrazolo[1,5-a]pyrimidine-5,7-diones were prepared, and their acid dissociation
constant pK s were determined and correlated with the Hammett equation. The results of these correlations,
a
together with the spectroscopic data, indicated that the title compounds exist predominantly in the 3-arylazo-6-
arylhydrazonopyrazolo[1,5-a]pyrimidine-5,7-dione tautomeric form, both in the solid and solution phases.
Keywords: azo-hydrazone tautomerism, pyrazoles, fused pyrazoles, pyrimidines, Hammett equation
Ar
A literature search revealed that many arylazoheterocycles
H3C
N
N
N
are evaluated and patented for use in various sectors of
industry, including hair dyeing, thermal transfer printing,
nonlinear optics, disperse dyes, pigments, dyeing and printing
polyesters, and ink-jet inks.1 In the light of these applications,
and as part of our comprehensive programme for the synthesis
and elucidation of the tautomeric structures of bis(arylazo)
heterocycles,2-4 we report here the synthesis of two new series
of bis-azo dyes which have not been reported previously. Our
interest in such azo derivatives is to elucidate their tautomeric
structure prior to exploring their utility. This is because such
dyes can exist in one or other of the seven tautomeric forms
A–G depicted in Fig. 1. The authors of an earlier report5
assigned the tautomeric form E to three such dyes without
providing spectroscopic evidence for their assignment.
A knowledge of the precise tautomeric form(s) of azo dyes
in solution and in the solid phase is an important factor
in the industrial and biological applications of azo dyes.
Furthermore, investigation of azo-hydrazone tautomerism is
of interest from a practical and theoretical point of view.
Ar
H3C
N
N
N
H2C(CO2Et)2
NaOEt
N
NH
NH2
N
H
O
O
1
2
Ar''N2Cl
3, Ar = Ph, Ar' = C6H4X
4, Ar = C6H4X, Ar' = Ph
Ar
H3C
N
N
N
3,4
X
3,4
X
N
NH
a
b
c
d
e
4-OCH3
4-CH3
3-CH3
H
f
3-Cl
3-NO2
4-NO2
g
h
i
O
O
N
4-COCH3
4-CO2Et
NH
Ar'
4-Cl
j
3,4 a–j
Results and discussion
Scheme 1
The synthetic approach to the target azo dyes is outlined in
Scheme 1. The starting 3-arylazo-2-methylpyrazolo[1,5-a]
pyrimidine-5,7(4H,6H)-diones 2 were prepared by reaction of
diethyl malonate with the 5-amino-4-arylazo-3-methylpyrazoles
1 as previously described.5,6 Coupling of 2d with diazotised
anilines in aqueous ethanol in the presence of sodium acetate
yielded the respective bis-arylazo derivatives 3a–j. Similar
coupling of diazotised aniline with each of 2a–i under the same
conditions afforded the bis-arylazo derivatives 4a–j (Scheme 1).
Ar
NH
Ar
Ar
H3C
N
H3C
N
H3C
HN
N
N
N
N
N
N
NH
N
N
N
N
O
O
O
O
O
O
N
N
N
NH
Ar'
NH
NH
A
B
C
Ar'
Ar'
Ar
Ar
Ar
Ar
H3C
N
N
N
H3C
N
N
N
H3C
N
N
N
H3C
N
N
N
N
NH
N
N
N
N
N
NH
HO
HO
O
OH
O
O
OH
OH
N
N
N
N
N
N
N
NH
Ar'
Ar'
Ar'
Ar'
E
G
D
F
Fig. 1 Prototropic tautomerism in the 3-(arylazo)-6-(arylhydrazono)pyrazolo[1,5-a]pyrimidine-5,7-diones.
* Correspondent. E-mail: as_shawali@mail.com

JOURNAL OF CHEMICAL RESEARCH 2008 453
Table 1 Electronic absorption spectra of compounds 3 in dioxan–water and their acid dissociation constantsa
-
Compd
Omax (log H)
pK1
pK2
VX
3a
3b
3c
3d
3e
3f
437 (4.85), 327 (4.39)
436 (4.82), 327 (4.39)
412 (5.02), 387 (5.02)
424 (4.95), 340 (4.54)b
424 (4.37), 330 (4.37)
417 (4.76), 326 (4.56)
407 (4.67), 337 (4.50)
414 (4.75), 320 (4.54)
423 (4.71), 336 (4.52)
412 (4.89), 329 (4.74)
6.63
6.62
6.59
6.57
6.51
6.46
6.36
6.18
6.36
6.32
9.65
9.43
9.20
9.08
8.55
8.18
7.43
6.10
7.43
7.06
-0.27
-0.17
-0.07
0.00
0.23
0.37
0.71
1.28
0.68
0.84
3g
3h
3i
3j
aIn dioxan-water (1:1 v/v) at 25°C, μ = 0.10 and standard deviation s = 0.03-0.05.
bSolvent Omax (log H): acetic acid 429 (4.75), 329 (4.37); ethanol 424 (4.70), 330 (4.22); chloroform 440 (4.70), 340 (4.30); petroleum
ether 425 (4.76), 335 (4.37).
Table 2 Electronic absorption spectra of compounds 4 in dioxan–water and their acid dissociation constantsa
-
Compd
Omax (log H)
pK1
pK2
VX
4a
4b
4d
4e
4f
4g
4h
4i
431 (4.92), 355 (4.64)
424 (4.91), 339 (4.56)
424 (4.95), 340 (4.54)
419 (4.71), 329 (4.44)
424 (4.65), 346 (4.73)
420 (4.77), 377 (4.83)
422 (4.70), 383 (4.65)
444 (4.65), 339 (4.53)
6.91
6.79
6.57
6.28
6.07
5.63
4.92
5.71
9.15
9.12
9.08
9.01
8.97
8.87
8.71
8.88
-0.27
-0.17
0.00
0.23
0.37
0.71
1.28
0.68
aIn dioxan–water (1:1 v/v) at 25°C, μ = 0.10 and standard deviation s = 0.03–0.05.
The structures of the isolated products 3 and 4 were established
by their spectroscopic (IR, 1H NMR and MS) data and
elemental analyses (see Experimental). Each can exist in one
or other of the seven tautomeric structures A-G (Fig. 1). To
ascertain the actual tautomeric structure(s) of such products,
the higher acidity constant K1 was found to be dependent on
the nature of the substituent in the arylazo group, whereas the
lower acidity constant K2 is independent of such substituents.
7KHVHꢀ ¿QGLQJVꢀ VHHPꢀ FRQVLVWHQWꢀ ZLWKꢀ WKHꢀ WDXWRPHULFꢀ VWUXFWXUHꢀ
A and indicate that K1 and K2 correspond to the deprotonation
of the hydrazone NH and amide NH groups, respectively.
This assignment is further supported by correlation of the
1
their IR, H NMR and UV spectra were examined. Their IR
VSHFWUDꢀUHYHDOꢁꢀLQꢀHDFKꢀFDVHꢁꢀWZRꢀ& 2ꢀYLEUDWLRQꢀEDQGVꢀLQꢀWKHꢀ
regions 1725–1710 and 1663–1656 cm-1. In addition, their
spectra showed NH bands in the regions 3317–3216 cm-1
(see Experimental). Such data, while consistent with one
of the three tautomeric forms A–C, exclude the tautomeric
forms D–G. The structure C was discarded on the basis of the
1H NMR spectral data. Thus, their 1H NMR spectra in DMSO
showed, in each case, two characteristic signals assignable to
K\GUD]RQHꢀ DQGꢀ DPLGHꢀ SURWRQVꢀ LQꢀ WKHꢀ UHJLRQVꢀ įꢀ ꢂꢃꢄꢅꢆ±ꢂꢅꢄꢇꢃꢀ
and 12.45–12.00, respectively. Furthermore, their electronic
absorption spectra in dioxan display, in each case, two
absorption bands in the regions 444–407 and 387–302 nm
(Tables 1 and 2). The spectra of the unsubstituted derivative
3d, taken as typical example of the two series prepared, in
different solvents of different polarity, showed little, if any,
change (Table 1, footnote b). Such spectral data collectively
indicate that the products 3 and 4 exist in one tautomeric form,
namely the azo-hydrazone form A.
To provide further evidence for the assignment of the
tautomeric structure A to compounds 3 and 4, their acid
dissociation constants were determined and their correlation
with Hammett substituent constants were examined.3,7-10 The
acid dissociation constants for the two series 3a–j and 4a–i were
determined potentiometrically at 25 0.1°C in 50% dioxan-
water mixture (v/v). In all determinations, the ionic strength was
kept constant at 0.1 M. From the pH-titrant volume data, the acid
dissociation constants of the compounds 3 and 4 were calculated
and the results are summarised in Tables 1 and 2. These results
show that each of the studied dyes behaves as a dibasic acid
(H2A) since each dye has two acidity constants pK1 and pK2.
For series 3, the higher acidity constant K1 was found to be
independent of the nature of the substituent in the arylazo group
at position 3, whereas the lower acidity constant K2 is affected
by such substituents (Table 1). In contrast to this, for series 4,
pK values of each series with the Hammett equation (pK ꢀ ꢀ
a
-
pK0 – U V ).11 Thus, when the pK2 values for the studied
x
compounds 3 are plotted versus Hammett substituent constant
V , a linear correlation was obtained. The equation of the
-
x
regression line obtained is:
pK2 (3ꢈꢀ ꢀꢉꢄꢊꢃꢀ±ꢀꢆꢄꢆꢉꢋꢀı–
x
ZLWKꢀFRUUHODWLRQꢀFRHI¿FLHQWꢀU2ꢀ ꢀꢊꢄꢉꢉꢉꢀDQGꢀVWDQGDUGꢀGHYLDWLRQꢀ
Vꢀ ꢀ“ꢀꢊꢄꢊꢌꢄꢀ7KHꢀS.1 values for the other series 4 gave also
11
a linear correlation ZLWKꢀ+DPPHWWꢀVXEVWLWXHQWꢀFRQVWDQWꢀı–
The equation of the regression line obtained is:
.
x
pK1(4ꢈꢀ ꢀꢇꢄꢃꢋꢀ±ꢀꢂꢄꢆꢍꢉꢀı–
x
ZLWKꢀFRUUHODWLRQꢀFRHI¿FLHQWꢀU2ꢀ ꢀꢊꢄꢉꢉꢉꢀDQGꢀVWDQGDUGꢀGHYLDWLRQꢀ
Vꢀ ꢀ“ꢀꢊꢄꢊꢆꢄ
Such linear correlations and the values of the reaction constant
U provide further evidence that both series of compounds 3 and
4 exist predominantly in the 4H-6-arylhydrazono-3-arylazo
form A and exclude the tautomeric structure B (Fig. 1). This is
because, if the structure B were the predominant form, it would
be expected that both U values for the two series will be similar,
and this is found not to be the case. Furthermore, the value
of U2 (2.297) found for series 3 is similar to that reported for
ionisation of phenols (Uꢀ ꢀꢆꢄꢇꢋꢈꢁꢀDQLOLQLXPꢀLRQVꢀꢎUꢀ ꢀꢆꢄꢋꢋꢈꢀ12-15
and typical arylhydrazones (Uꢀ ꢀꢆꢄꢃꢂꢈ12 in 50% ethanol–water.
Also, the value of U1 (1.289) found for series 4 is similar to that
reported for ionisation of 2-arylazophenols (Uꢀ ꢀꢂꢄꢆꢆꢅꢈꢀLQꢀꢃꢊꢏꢀ
ethanol–water.13,16 The low value (U1ꢀ ꢀꢂꢄꢆꢍꢉꢈꢀVHHPVꢀWRꢀEHꢀGXHꢀ
WRꢀWKHꢀIDFWꢀWKDWꢀWKHꢀWUDQVPLVVLRQꢀIDFWRUꢀIRUꢀWKHꢀEULGJHꢀ±1 1±&ꢎꢍꢈꢀ
&ꢎꢍDꢈꢐꢀLQꢀIRUPꢀA is expected to be 0.32 as the transmission
IDFWRUꢀIRUꢀ±1 1±ꢀDQGꢀ±& &±ꢀEULGJHVꢀZHUHꢀUHSRUWHGꢀWRꢀEHꢀꢊꢄꢇꢉꢀ
and 0.47, respectively.17

454 JOURNAL OF CHEMICAL RESEARCH 2008
Preparation of 3-arylazo-2-methylpyrazolo[1,5-a]pyrimidine-5,7
(4H,6H)-diones (2): general procedure
In conclusion, both the spectral data and the observed linear
correlation of the acid dissociation constants by the Hammett
equation indicate collectively that the 4H-6-arylhydrazono-3-
arylazo form A (Fig. 1) is the predominant tautomeric form
for both compounds 3 and 4 in solid and solution phase.
To a suspension of the appropriate arylazopyrazole derivative 1
(5 mmol) in ethanol (20 ml), diethyl malonate (0.75 ml, 5 mmol)
in ethanolic sodium ethoxide, prepared from sodium metal (0.58 g,
0.1 mole) and absolute ethanol (20 ml), was added. The mixture was
UHÀX[HGꢀIRUꢀꢅꢊ±ꢃꢊꢀKRXUVꢄꢀ7KHꢀVROXWLRQꢀZDVꢀFRROHGꢀDQGꢀGLOXWHGꢀZLWKꢀ
ZDWHUꢁꢀWKHQꢀDFLGL¿HGꢀZLWKꢀFRQFꢄꢀ+&Oꢄꢀ7KHꢀSUHFLSLWDWHꢀWKDWꢀIRUPHGꢀZDVꢀ
¿OWHUHGꢀ RIIꢀ DQGꢀ FU\VWDOOLVHGꢀ IURPꢀ WKHꢀ LQGLFDWHGꢀ VROYHQWꢀ WRꢀ JLYHꢀ WKHꢀ
respective compound 2.
Experimental
Melting points were determined on a Gallenkamp apparatus. IR
spectra were recorded in potassium bromide using Perkin Elmer
FTIR 1650 and Pye-Unicam SP300 infrared spectrometers.
1H NMR spectra were recorded in deuterated chloroform or
deuterated dimethyl sulfoxide using a Varian Gemini 300 NMR
spectrometer. Mass spectra were recorded on GCMS-QP 1000
EX Shimadzu and GCMS 5988-A HP spectrometers. Electronic
absorption spectra were recorded on a Perkin-Elmer Lamda 40
spectrophotometer. Elemental analyses were carried out at the
Microanalytical Laboratory of Cairo University, Giza, Egypt.
3-(4-Methoxyphenylazo)-2-methylpyrazolo[1,5-a]pyrimidine-
5,7(4H,6H)-dione (2a): Orange solid (1.38 g, 92%), m.p. 240°C
(dioxan/MeOH). (lit.5 m.p. 195°&ꢈꢄꢀ,5ꢑꢀȞmax 3120, 1728, 1689 cm-1.
NMR (CDCl3): GH 2.50 (s, 3H, CH3), 3.84 (s, 3H, OCH3), 5.11 (s, 2H,
CH2), 7.05 (d, Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢍꢍꢀꢎGꢁꢀJꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢂꢄꢍꢌꢀ
(s, 1H, NH). MS: m/z (%) 301 (M+ + 2, 3), 300 (M+ + 1, 20), 299
(M+, 100), 203 (27), 192 (31), 188 (23), 164 (18), 122 (45), 107 (46),
92 (34), 77 (45). Anal. Calcd for C14H13N5O3 (299.29): C, 56.19; H,
4.35; N, 23.41. Found: C, 56.20; H, 4.00; N, 23.13%.
2-Arylhydrazono-3-iminobutyronitriles were prepared by
a
2-Methyl-3-(4-methylphenylazo)pyrazolo[1,5-a]pyrimidine-
5,7(4H,6H)-dione (2b): Orange solid (1.26 g, 89%), m.p. 234–235°C
ꢎGLR[DQꢈꢄꢀ,5ꢑꢀȞmax 3246, 1700, 1660 cm-1. NMR (CDCl3): GH 2.37 (s,
3H, CH3), 2.49 (s, 3H, CH3), 5.15 (s, 2H, CH2), 7.30 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ
ArH), 7.76 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢂꢄꢉꢊꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢒꢀ06ꢀm/z (%)
285 (M+ + 2, 4), 284 (M+ + 1, 20), 283 (M+, 100), 268 (14), 192 (52),
187 (20), 164 (27), 124 (15), 106 (21), 104 (13), 91 (67), 77 (30).
Anal. Calcd for C14H13N5O2 (283.29): C, 59.36; H, 4.63; N, 24.72.
Found: C, 59.26; H, 4.34; N, 24.65%.
literature method.18
Preparation of 5-amino-4-arylazo-3-methylpyrazoles (1): General
procedure
A solution of 2-arylhydrazono-3-iminobutyronitrile (0.1 mol) and
hydrazine hydrate (5.0 ml, 0.1 mol) in absolute ethanol (100 ml) was
KHDWHGꢀWRꢀUHÀX[ꢀIRUꢀꢂꢃꢀKꢁꢀDQGꢀWKHQꢀWKHꢀVROYHQWꢀZDVꢀHYDSRUDWHGꢀXQGHUꢀ
reduced pressure. The solid left was collected and recrystallised
from the appropriate solvent to give the respective compound 1.
The physical constants of the compounds 1a–h are given below.
5-Amino-4-(4-methoxyphenylazo)-3-methylpyrazole (1a): Yellow
solid (19.9 g, 86%), m.p. 180–182°C (EtOH) (Lit.19 m.p. 187–
188°&ꢈꢄꢀ ,5ꢑꢀȞmax 3467, 3355 cm-1. NMR (CDCl3) GH 2.35 (s, 3H,
CH3), 3.79 (s, 3H, OCH3), 6.20 (s, 2H, NH2), 6.98 (d, Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ
ArH), 7.64 (d, Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢂꢄꢇꢊꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢄꢀ06ꢀm/z (%)
232 (M+ + 1, 16), 231 (M+, 100), 188 (11), 124 (70), 122 (11), 107
(13), 92 (27), 77 (26). Anal. Calcd. for C11H13N5O (231.26): C, 57.13;
H, 5.67; N, 30.28. Found: C, 56.82; H, 5.43; N, 30.00%.
2-Methyl-3-(phenylazo)pyrazolo[1,5-a]pyrimidine-5,7(4H,6H)-
dione (2d): Yellow solid (1.08 g, 80%), m.p. 220°C (EtOH) (Lit.6
m.p. 222°C).
3-(4-Chlorophenylazo)-2-methylpyrazolo[1,5-a]pyrimidine-5,7
(4H,6H)-dione (2e): Orange solid (1.43 g, 94%), m.p. 240–242°C
ꢎGLR[DQꢈꢄꢀ,5ꢑꢀȞmax 3245, 1661, 1654 cm-1. NMR (CDCl3): GH 2.47
(s, 3H, CH3), 5.15 (s, 2H, CH2), 7.55 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢉꢂꢀꢎGꢁꢀ
Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢊꢄꢆꢇꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢄꢀ06ꢑꢀm/z (%) 306 (M+ + 2,
6), 305 (M+ + 1, 34), 304 (M+, 19), 303 (87), 277 (17), 207 (11), 192
(88), 164 (34), 126 (17), 124 (40), 113 (16), 111 (60), 91 (11), 76
(13). Anal. Calcd for C13H10ClN5O2 (303.71): C, 51.41; H, 3.32; N,
23.06. Found: C, 51.00; H, 3.52; N, 23.52%.
5-Amino-3-methyl-4-(4-methylphenylazo)pyrazole (1b): Yellow
solid (17.4 g, 81%), m.p. 177°C (EtOH) (Lit.20 m.p. 178°C).
5-Amino-3-methyl-4-(phenylazo)pyrazole(1d):Yellowsolid(16.5g,
82%), m.p. 164–166°C (EtOH) (lit.19 m.p. 165–166°C).
3-(3-Chlorophenylazo)-2-methylpyrazolo[1,5-a]pyrimidine-5,7(4H,
6H)-dione (2f): Orange solid (1.23 g, 81%), m.p. 184–186°C (EtOH).
,5ꢑꢀ Ȟmax 3389, 1690, 1653 cm-1. NMR (DMSO-d6): 2.35 (s, 3H,
CH3), 5.20 (s, 2H, CH2), 7.06-7.81 (m, 4H, ArH), 12.42 (s, 1H, NH).
MS: m/z (%) 303 (M+, 3), 253 (44), 200 (30), 124 (100), 113 (29),
111 (87), 99 (17), 90 (19), 75 (83). Anal. Calcd for C13H10ClN5O2
(303.71): C, 51.41; H, 3.32; N, 23.06. Found: C, 51.63; H, 3.00; N,
23.36%.
2-Methyl-3-(3-nitrophenylazo)pyrazolo[1,5-a]pyrimidine-
5,7(4H,6H)-dione (2g): Dark yellow solid (1.32 g, 84%), m.p. 256–
258°&ꢀꢎGLR[DQꢈꢄꢀ,5ꢑꢀȞmax 3199, 1720, 1653 cm-1. NMR (DMSO-d6):
2.38 (s, 3H, CH3), 5.15 (s, 2H, CH2), 7.12–7.84 (m, 4H, ArH), 12.43
(s, 1H, NH). MS: m/z (%) 314 (M+, 8), 313 (7), 288 (52), 246 (32),
245 (10), 166 (51), 138 (28), 124 (100), 111 (16), 92 (23), 77 (17),
76 (37). Anal. Calcd for C13H10N6O4 (314.26): C, 49.69; H, 3.21; N,
26.74. Found: C, 50.02; H, 3.36; N, 26.54%.
2-Methyl-3-(4-nitrophenylazo)pyrazolo[1,5-a]pyrimidine-
5,7(4H,6H)-dione (2h): Dark red solid (1.26 g, 80%), m.p. 310–
312°C (AcOH) (lit.5 m.p. 218°&ꢈꢄꢀ,5ꢑꢀȞmax 3250, 1718, 1638 cm-1.
NMR (DMSO-d6): GH 2.32 (s, 3H, CH3), 5.14 (s, 2H, CH2), 6.97 (d,
Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢃꢋꢀꢎGꢁꢀJꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢂꢄꢆꢃꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢄꢀ
MS: m/z (%) 314 (M+, 11), 246 (16), 138 (63), 124 (23),108 (100),
92 (30), 77 (12), 76 (16). Anal. Calcd for C13H10N6O4 (314.26): C,
49.69; H, 3.21; N, 26.74. Found: C, 49.62; H, 3.41; N, 26.91%.
3-(4-Acetylphenylazo)-2-methylpyrazolo[1,5-a]pyrimidine-
5,7(4H,6H)-dione (2i): Orange solid (1.24 g, 80%), m.p. 240–242°C
ꢎ(W2+ꢈꢄꢀ,5ꢑꢀȞmax 3172, 1708, 1681, 1658 cm-1. NMR (DMSO-d6):
GH 2.42 (s, 3H, CH3), 2.94 (s, 3H, COCH3), 5.18 (s, 2H, CH2), 7.58
(d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢍꢆꢀꢎGꢁꢀJꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢂꢄꢊꢇꢀꢎVꢁꢀꢂ+ꢁꢀ
NH). MS: m/z (%) 313 (M+ + 2, 12), 312 (M+ + 1, 49), 311 (M+, 68),
296 (10), 200 (12), 192 (74), 164 (34), 124 (19), 119 (17), 104 (11),
91 (22), 77 (21), 69 (100). Anal. Calcd for C15H13N5O3 (311.30): C,
57.88; H, 4.21; N, 22.50. Found: C, 58.08, H, 4.00, N, 22.63%.
5-Amino-4-(4-chlorophenylazo)-3-methylpyrazole (1e): Yellow
solid (18.8 g, 80%), m.p. 180–182°&ꢀꢎ(W2+ꢈꢄꢀ,5ꢑꢀȞmax 3410, 3298
cm-1. NMR (CDCl3): GH 2.33 (s, 3H, CH3), 6.35 (s, 2H, NH2), 7.42
(d, Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢇꢅꢀꢎGꢁꢀJꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢊꢄꢍꢍꢀꢎVꢁꢀꢂ+ꢁꢀ
NH). MS: m/z (%) 237 (M+ + 2, 12), 236 (M+ + 1, 5), 235 (M+, 34),
139 (5), 124 (100), 113 (20), 111 (74), 95 (27), 76 (12). Anal. Calcd.
for C10H10ClN5 (235.68): C, 50.96; H, 4.28; N, 29.72. Found: C,
50.74; H, 4.01; N, 29.53%.
5-Amino-4-(3-chlorophenylazo)-3-methylpyrazole (1f): Yellow
solid, (19.5 g, 83%), m.p. 168–170°&ꢀ ꢎ(W2+ꢈꢄꢀ ,5ꢑꢀ Ȟmax 3402,
3294 cm-1. NMR (DMSO-d6): GH 2.32 (s, 3H, CH3), 6.42 (s, 2H,
NH2), 7.30–7.62 (m, 4H, ArH), 10.92 (s, 1H, NH). MS: m/z (%) 237
(M+ + 2, 18), 236 (M+ + 1, 4), 235 (M+, 2), 224 (29), 222 (47), 167
(18), 152 (59), 150 (21), 139 (16), 129 (11), 125 (11), 111 (46), 93
(24), 76 (26). Anal. Calcd. for C10H10ClN5 (235.68): C, 50.96; H,
4.28; N, 29.72. Found: C, 50.84; H, 4.18; N, 29.55%.
5-Amino-3-methyl-4-(3-nitrophenylazo)-pyrazole (1g): Yellow
solid, (20.0 g, 82%), m.p. 210–212°&ꢀꢎ(W2+ꢈꢄꢀ,5ꢑꢀȞmax 3456, 3348
cm-1. NMR (DMSO-d6): GH 2.29 (s, 3H, CH3), 6.50 (s, 2H, NH2),
7.32–8.24 (m, 4H, ArH),11.02 (s, 1H, NH). MS: m/z (%) 247 (M+
+ 1, 4), 246 (M+, 32), 172 (2), 124 (100), 122 (17), 92 (13), 76 (59).
Anal. Calcd. for C10H10N6O2 (246.23): C, 48.78; H, 4.09; N, 34.13.
Found: C, 48.33; H, 3.94; N, 34.05%.
5-Amino-3-methyl-4-(4-nitrophenylazo)-pyrazole (1h): Yellow solid
(19.6 g, 80%), m.p. 150–152°C (EtOH) (Lit20. m.p. 226–227°C). IR:
Ȟmax 3483, 3363 cm-1. NMR (DMSO-d6): GH 2.49 (s, 3H, CH3), 5.80 (s,
2H, NH2), 6.61 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢉꢌꢀꢎGꢁꢀJꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀ
11.0 (s, 1H, NH). MS: m/z (%) 246 (M+, 12), 245 (34), 124 (68), 105
(36), 91 (18), 77 (60). Anal. Calcd. for C10H10 N6O2 (246.23): C, 48.78;
H, 4.09; N, 34.13. Found: C, 48.62; H, 3.91; N, 33.84%.
5-Amino-3-methyl-4-(4-acetylphenylazo)-pyrazole (1i): Yellow
solid (21.2 g, 87%), m.p. 218–220°&ꢀꢎ(W2+ꢈꢄꢀ,5ꢑꢀȞmax 3445, 3260,
1698 cm-1. NMR (DMSO-d6): GH 2.32 (s, 3H, CH3), 2.49 (s, 3H, CH3),
6.55 (s, 2H, NH2), 7.21 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢃꢂꢀꢎGꢁꢀJꢀ ꢀꢍꢀ+]ꢁꢀ
2H, ArH), 11.32 (s, 1H, NH). MS: m/z (%) 245 (M+ + 2, 1), 244 (M+
+ 1, 2), 243 (M+, 7), 216 (12), 188 (12), 146 (3), 118 (13), 92 (45),
85 (14), 77 (19), 43 (100). Anal. Calcd. for C12H13N5O (243.27): C,
59.26; H, 5.35; N, 28.81. Found: C, 59.12; H, 5.40; N, 28.43%.
Preparation of 3-(arylazo)-6-(arylhydrazono)-2-methylpyrazolo[1,
5-a]pyrimidine-5,7(4H,6H)-diones (3 and 4): general procedure
A solution of the phenylazopyrazole 2d (2.5 mmol) and sodium
acetate trihydrate (0.33 g, 2.5 mmol) in ethanol (10 ml) was cooled
to 0–5°C and a cold solution of diazotised aniline or its derivative

JOURNAL OF CHEMICAL RESEARCH 2008 455
(2.5 mmol) added dropwise with stirring over 30 min. The stirring
ZDVꢀ FRQWLQXHGꢀ IRUꢀ ꢅꢀ KUVꢄꢀ 7KHꢀ VROLGꢀ WKDWꢀ IRUPHGꢀ ZDVꢀ ¿OWHUHGꢀ RIIꢁꢀ
washed with water and crystallised from the indicated solvent to give
the compounds 3a–j. The same procedure, taking each of 2a–h in
place of 2d and diazotised aniline, gave the respective 4a–h.
6-(4-Methoxyphenylhydrazono)-2-methyl-3-phenylazopyrazolo
[1,5-a]pyrimidine-5,7(4H,6H)-dione (3a): Dark red solid (0.48 g,
80%), m.p. 218–220°&ꢀꢎGLR[DQꢓ(W2+ꢈꢄꢀ,5ꢑꢀȞmax 3294, 3066, 1712,
1662 cm-1. NMR (CDCl3): GH 2.48 (s, 3H, CH3), 3.78 (s, 3H, OCH3),
7.03 (d, Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢌꢂ±ꢋꢄꢇꢌꢀꢎPꢁꢀꢃ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢉꢂꢀꢎGꢁꢀJꢀ ꢀꢉꢀ+]ꢁꢀ
2H, ArH), 12.20 (s, 1H, NH), 14.81 (s, 1H, NH). MS: m/z (%) 404
(M+ + 1, 4), 403 (M+, 14), 228 (28), 149 (30), 137 (46), 129 (37), 123
(37), 119 (14), 123 (37), 109 (46), 97 (100), 91 (34), 77 (20). Anal.
Calcd for C20H17N7O3 (403.40): C, 59.55; H, 4.25; N, 24.30. Found:
C, 59.50; H, 4.00; N, 24.00%.
2-Methyl-6-(4-methylphenylhydrazono)-3-(phenylazo)pyrazolo
[1,5-a]pyrimidine-5,7(4H,6H)-dione (3b): Orange solid (0.50 g,
86%), m.p. 270–272°&ꢀ ꢎ$F2+ꢈꢄꢀ ,5ꢑꢀ Ȟmax 3426, 3060, 1721, 1659
cm-1. NMR (CDCl3): GH 2.30 (s, 3H, CH3), 2.48 (s, 3H, CH3), 7.26
(d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢅꢉ±ꢋꢄꢃꢇꢀꢎPꢁꢀꢃ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢉꢆꢀꢎGꢁꢀJꢀ ꢀꢍꢀ+]ꢁꢀ
2H, ArH), 12.40 (s, 1H, NH), 14.69 (s, 1H, NH). MS: m/z (%) 389
(M+ + 2, 26), 388 (M+ + 1, 100), 387 (M+, 1), 298 (12), 296 (66),
229 (57), 228 (66), 212 (11), 106 (17), 105 (12), 104 (11), 91 (71),
77 (79). Anal. Calcd for C20H17N7O2 (387.40): C, 62.01; H, 4.42; N,
25.31. Found: C, 62.00; H, 4.40; N, 25.10%.
2-Methyl-6-(3-methylphenylhydrazono)-3-(phenylazo)pyrazolo
[1,5-a]pyrimidine-5,7(4H,6H)-dione (3c): Orange solid (0.49 g,
84%), m.p. 250–252°&ꢀꢎ$F2+ꢈꢄꢀ,5ꢀꢎ.%UꢈꢀȞmax 3249, 3057, 1733,
1699 cm-1. NMR (DMSO-d6): GH 2.38 (s, 3H, CH3), 2.48 (s, 3H,
CH3), 7.01–8.14 (m, 9H, ArH), 12.19 (s, 1H, NH), 13.65 (s, 1H, NH).
MS: m/z (%) 389 (M+ + 2, 1), 388 (M+ + 1, 8), 387 (M+, 37), 386
(39), 295 (30), 228 (26), 227 (43), 105 (17), 104 (18), 103 (15), 91
(86), 77 (100). Anal. Calcd for C20H17N7O2 (387.40): C, 62.01; H,
4.42; N, 25.31. Found: C, 61.98; H, 4.51; N, 25.00%.
2-Methyl-3-(phenylazo)-6-(phenylhydrazono)pyrazolo[1,5-a]
pyrimidine-5,7(4H,6H)-dione (3d): Orange solid (0.47 g, 84%),
m.p. 198–200°C (AcOH) (Lit.5 m.p. >300°&ꢈꢄꢀ,5ꢑꢀȞmax 3380, 3300,
1720, 1651 cm-1. NMR (CDCl3): GH 2.70 (s, 3H, CH3), 7.26–7.86
(m, 10H, ArH), 10.10 (s, 1H, NH), 15.00 (s, 1H, NH). MS: m/z (%)
375 (M+ + 2, 22), 374 (M+ + 1, 88), 373 (M+, 1), 298 (13), 297 (78),
229 (30), 228 (39), 92 (48), 77 (100). Anal. Calcd for C19H15N7O2
(373.38): C, 61.12; H, 4.05; N, 26.26. Found: C, 61.00; H, 3.84; N,
26.20%.
6-(4-Chlorophenylhydrazono)-2-methyl-3-(phenylazo)
pyrazolo[1,5-a]pyrimidine-5,7(4H,6H)-dione (3e): Red solid (0.54 g,
89%), m.p. 288–290°&ꢀꢎ$F2+ꢈꢄꢀ,5ꢑꢀȞmax 3325, 3074, 1720, 1662 cm-1.
NMR (DMSO-d6): GH 1.92 (s, 3H, CH3), 7.45–7.50 and 7.95–7.99
(m, 5H, ArH), 7.53 (d, Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢋꢆꢀꢎGꢁꢀJꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ
ArH), 12.00 (s, 1H, NH), 14.60 (s, 1H, NH). MS: m/z (%) 409 (M+ +
2, 29), 408 (M+ + 1, 91), 407 (M+, 66), 331 (21), 298 (17), 297 (97),
296 (75), 228 (77), 150 (12), 126 (14), 111 (60), 92 (74), 77 (100).
Anal. Calcd for C19H14ClN7O2 (407.82): C, 55.96; H, 3.46; N, 24.04.
Found: C, 55.83; H, 3.25; N, 24.00%.
6-(3-Chlorophenylhydrazono)-2-methyl-3-(phenylazo)
pyrazolo[1,5-a]pyrimidine-5,7(4H,6H)-dione (3f): Dark orange solid
(0.53 g, 86%), m.p. 256–258°&ꢀꢎGLR[DQꢈꢄꢀ,5ꢑꢀȞmax 3163, 3070, 1724,
1651 cm-1. NMR (CDCl3): GH 2.47 (s, 3H, CH3), 7.25–7.93 (m, 9H,
ArH), 12.25 (s, 1H, NH), 14.98 (s, 1H, NH). MS: m/z (%) 409 (M+ +
2, 8), 408 (M+ + 1, 26), 407 (M+, 17), 167 (22), 149 (100), 139 (10),
125 (25),123 (21), 121 (17), 95 (40), 83 (56), 77 (9). Anal. Calcd
for C19H14ClN7O2 (407.82): C, 55.96; H, 3.46; N, 24.04. Found: C,
55.85; H, 3.64; N, 23.93%.
3-Phenylazo-2-methyl-6-(3-nitrophenylhydrazonopyrazolo[1,5-a]
pyrimidine-5,7(4H,6H)-dione (3g): Dark orange solid (0.52 g, 83%),
m.p. 196–198°&ꢀ ꢎGLR[DQꢈꢄꢀ ,5ꢑꢀ Ȟmax 3300, 3058, 1701, 1658 cm-1.
NMR (DMSO-d6): GH 2.48 (s, 3H, CH3), 7.23–8.10 (m, 9H, ArH),
12.45 (s, 1H, NH), 15.10 (s, 1H, NH). MS: m/z (%) 419 (M+ + 1, 16),
418 (M+, 63), 341 (11), 295 (67), 228 (68), 212 (21), 192 (22), 150
(32), 122 (35), 92 (52), 91 (35), 77 (100). Anal. Calcd for C19H14N8O4
(418.37): C, 54.55; H, 3.37; N, 26.78. Found: C, 54.00; H, 3.24; N,
26.93%.
2-Methyl-6-(4-nitrophenylhydrazono)-3-(phenylazo)pyrazolo[1,5-a]
pyrimidine-5,7(4H,6H)-dione (3h): Red solid (0.55 g, 88%), m.p.
296–298°&ꢀꢎ$F2+ꢈꢄꢀ,5ꢑꢀȞmax 3114, 3057, 1716, 1681 cm-1. NMR
(CDCl3): GH 2.49 (s, 3H, CH3), 7.42–7.54 (m, 5H, ArH), 7.86 (d,
Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢉꢅꢀꢎGꢁꢀJꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢆꢄꢌꢃꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢁꢀ
14.41 (s, 1H, NH). MS: m/z (%) 420 (M+ + 2, 17), 419 (M+ + 1, 75),
418 (M+, 23), 342 (16), 296 (85), 229 (44), 228 (56), 212 (19), 150
(15), 122 (21), 92 (72), 77 (100). Anal. Calcd for C19H14N8O4 (418.37):
C, 54.55; H, 3.37; N, 26.78. Found: C, 54.34; H, 3.21; N, 26.67%.
6-(4-Acetylphenylhydrazono)-2-methyl-3-(phenylazo)
pyrazolo[1,5-a]pyrimidine-5,7(4H,6H)-dione (3i): Dark orange solid
(0.54 g, 86%), m.p. 242–244°&ꢀꢎGLR[DQꢓ(W2+ꢈꢄꢀ,5ꢑꢀȞmax 3424, 3058,
1729, 1665, 1650 cm-1. NMR (CDCl3): GH 2.63 (s, 3H, CH3), 2.70
(s, 3H, COCH3), 7.27–8.05 (m, 14H, ArH), 10.10 (s, 1H, NH), 14.70
(s, 1H, NH). MS m/z (%) 416 (M+ + 1, 56), 415 (M+, 60), 361 (52),
294 (100), 268 (64), 229 (64), 224 (72), 206 (60), 158 (80), 139 (52),
111 (72), 100 (56), 91 (48). Anal. Calcd for C21H17N7O3 (415.41): C,
60.72; H, 4.12; N, 23.60. Found: C, 60.54, H, 4.00, N, 23.79%.
6-(4-Ethoxycarbonylphenylhydrazono)-2-methyl-3-
(phenylazo)pyrazolo[1,5-a]pyrimidine-5,7(4H,6H)-dione (3j): Dark
orange solid (0.57 g, 85%), m.p. 268–270°&ꢀꢎ'0)ꢓ(W2+ꢈꢄꢀ,5ꢑꢀȞmax
3325, 3062, 1739, 1712, 1658 cm-1. NMR (DMSO-d6): GH 1.29 (t,
Jꢀ ꢀꢋꢀ+]ꢁꢀꢅ+ꢁꢀ&+3), 2.34 (s, 3H, CH3), 4.25 (q, Jꢀ ꢀꢋꢀ+]ꢁꢀꢆ+ꢁꢀ&+2),
7.31-7.63 and 7.87 –7.96 (m, 5H, ArH), 7.64 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀ
7.80 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢆꢄꢉꢃꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢁꢀꢂꢌꢄꢌꢊꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢄꢀ
MS: m/z (%) 446 (M+ + 1, 3), 445 (M+, 4), 431 (37), 295 (42), 228
(32), 227 (29), 134 (22), 105 (13), 102 (18), 92 (60), 91 (62), 77 (91),
76 (100). Anal. Calcd for C22H19N7O4 (445.44): C, 59.32; H, 4.30; N,
22.01. Found: C, 59.00, H, 4.54, N, 22.00%.
3-(4-Methoxyphenylazo)-2-methyl-6-(phenylhydrazono)pyrazolo
[1,5-a]pyrimidine-5,7(4H,6H)-dione (4a): Dark red solid (0.50 g,
82%), m.p. 156–158°&ꢀꢎGLR[DQꢓ0H2+ꢈꢄꢀ,5ꢑꢀȞmax 3317, 3063, 1720,
1657 cm-1. NMR (DMSO-d6): GH 2.47 (s, 3H, CH3), 3.80 (s, 3H,
OCH3), 7.01 (d, Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢆꢇ±ꢋꢄꢇꢉꢀꢎPꢁꢀꢃ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢉꢊꢀ
(d, Jꢀ ꢀꢉꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢆꢄꢊꢊꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢁꢀꢂꢌꢄꢇꢅꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢄꢀ06ꢑꢀ
m/z (%) 405 (M+ + 2, 2), 404 (M+ + 1, 12), 403 (M+, 44), 325 (26),
258 (16), 257 (22), 121 (34), 106 (27), 91 (35), 77 (100). Anal. Calcd
for C20H17N7O3 (403.40): C, 59.55; H, 4.25; N, 24.30. Found: C,
59.83; H, 4.00; N, 24.15%.
2-Methyl-3-(4-methylphenylazo)-6-(phenylhydrazono)pyrazolo[1,
5-a]pyrimidine-5,7(4H,6H)-dione (4b): Orange solid (0.46 g, 80%),
m.p. 280–281°&ꢀꢎGLR[DQꢓ0H2+ꢈꢄꢀ,5ꢑꢀȞmax 3234, 3061, 1725, 1663
cm-1. NMR (DMSO-d6): GH 2.36 (s, 3H, CH3), 2.49 (s, 3H, CH3),
7.28–7.53 (m, 5H, ArH), 7.66 (d, Jꢀ ꢀ ꢉꢀ +]ꢁꢀ ꢆ+ꢁꢀ $U+ꢈꢁꢀ ꢋꢄꢍꢌꢀ ꢎGꢁꢀ
Jꢀ ꢀꢉꢀ+], 2H, ArH), 12.20 (s, 1H, NH), 14.64 (s, 1H, NH); MS m/z
(%) 389 (M+ + 2, 1), 388 (M+ + 1, 9), 387 (M+, 35), 386 (46), 310
(24), 242 (19), 241 (22), 105 (32), 90 (56), 77 (100). Anal. Calcd for
C20H17N7O2 (387.40): C, 62.01; H, 4.42; N, 25.31. Found: C, 62.00;
H, 4.25; N, 25.14%.
3-(4-Chlorophenylazo)-2-methyl-6-(phenylhydrazono)pyrazolo
[1,5-a]pyrimidine-5,7(4H,6H)-dione (4e): Dark yellow solid (0.53 g,
86%), m.p. 144–146°&ꢀꢎGLR[DQꢓ(W2+ꢈꢄꢀ,5ꢑꢀȞmax 3380, 3063, 1720,
1658 cm-1. NMR (DMSO-d6): GH 2.49 (s, 3H, CH3), 7.28–7.53 (m,
5H, ArH), 7.56 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢉꢍꢀꢎGꢁꢀJꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀ
12.32 (s, 1H, NH), 14.64 (s, 1H, NH). MS: m/z (%) 409 (M+ + 2,
11), 408 (M+ + 1, 14), 407 (M+, 28), 407 (28), 406 (32), 330 (24),
261 (18), 125 (24), 113 (11), 111 (31), 91 (22), 77 (100). Anal. Calcd
for C19H14ClN7O2 (407.82): C, 55.96; H, 3.46; N, 24.04. Found: C,
55.82; H, 3.43; N, 24.35%.
3-(3-Chlorophenylazo)-2-methyl-6-(phenylhydrazono)pyrazolo[1,5-a]
pyrimidine-5,7(4H,6H)-dione (4f): Dark orange solid (0.51 g,
83%), m.p. 238–239°&ꢀꢎGLR[DQꢈꢄꢀ,5ꢑꢀȞmax 3244, 3065, 1705, 1669
cm-1. NMR (CDCl3): GH 2.51 (s, 3H, CH3), 7.34-8.03 (m, 9H, ArH),
12.17 (s, 1H, NH), 13.80 (s, 1H, NH). MS: m/z (%) 409 (M+ + 1,
14), 408 (M+, 15), 407 (37), 332 (48), 330 (54), 262 (50), 200 (34),
192 (50), 127 (46), 125 (32),124 (53), 90 (28), 77 (53). Anal. Calcd
for C19H14ClN7O2 (407.82): C, 55.96; H, 3.46; N, 24.04. Found: C,
55.84; H, 3.43; N, 24.40%.
2-Methyl-3-(3-nitrophenylazo)-6-(phenylhydrazono)pyrazolo[1,5-a]
pyrimidine-5,7(4H,6H)-dione (4g): Dark orange solid (0.51 g, 82%),
m.p. 272–274°&ꢀ ꢎGLR[DQꢈꢄꢀ ,5ꢑꢀ Ȟmax 3216, 3086, 1720, 1656 cm-1.
NMR (CDCl3): GH 2.42 (s, 3H, CH3), 7.25–7.62 (m, 9H, ArH), 12.19
(s, 1H, NH), 14.25 (s, 1H, NH). MS: m/z (%) 418 (M+, 12), 246 (34),
192 (13), 166 (22), 153 (21), 150 (100), 125 (21), 124 (69), 122 (38),
92 (42), 77 (42). Anal. Calcd for C19H14N8O4 (418.37): C, 54.55; H,
3.37; N, 26.78. Found: C, 54.81; H, 3.00; N, 26.74%.
2-Methyl-3-(4-Nitrophenylazo)-6-(phenylhydrazono)pyrazolo[1,5-a]
pyrimidine-5,7(4H,6H)-dione (4h): Dark red solid (0.51 g, 81%),
m.p. 292–294°&ꢀ ꢎGLR[DQꢈꢄꢀ ,5ꢑꢀ Ȟmax 3219, 3100, 1710, 1655 cm-1.
NMR (CDCl3): GH 2.35 (s, 3H, CH3), 7.14–7.54 (m, 5H, ArH), 7.58
(d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢋꢄꢍꢂꢀꢎGꢁꢀJꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢆꢄꢅꢅꢀꢎVꢁꢀꢂ+ꢁꢀ
NH), 15.32 (s, 1H, NH). MS: m/z (%) 419 (M+ + 1, 6), 418 (M+, 11),
272 (74), 246 (21), 242 (12), 150 (100), 138 (23), 124 (18), 122 (28),
108 (25), 93 (31), 77 (33). Anal. Calcd for C19H14N8O4 (418.37): C,
54.55; H, 3.37; N, 26.78. Found: C, 54.35; H, 3.02; N, 26.59%.
3-(4-Acetylphenylazo)-2-methyl-6-(phenylhydrazono)pyrazolo
[1,5-a]pyrimidine-5,7(4H,6H)-dione (4i): Dark red solid (0.50 g,

456 JOURNAL OF CHEMICAL RESEARCH 2008
80%), m.p. 250–252°&ꢀꢎGLR[DQꢓ0H2+ꢈꢄꢀ,5ꢑꢀȞmax 3385, 3061, 1720,
1670, 1656 cm-1. NMR (CDCl3): GH 2.27 (s, 3H, CH3), 2.43 (s, 3H,
COCH3), 7.15–7.61 (m, 5H, ArH), 7.63 (d, Jꢀ ꢀ ꢍꢀ +]ꢁꢀ ꢆ+ꢁꢀ$U+ꢈꢁꢀ
7.81 (d, Jꢀ ꢀꢍꢀ+]ꢁꢀꢆ+ꢁꢀ$U+ꢈꢁꢀꢂꢆꢄꢌꢃꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢁꢀꢂꢌꢄꢇꢌꢀꢎVꢁꢀꢂ+ꢁꢀ1+ꢈꢄꢀ
MS: m/z (%) 416 (M+ + 1, 8), 415 (M+, 21), 414 (25), 390 (21), 270
(15), 221 (29), 119 (27), 106 (20), 105 (16), 91 (63), 77 (100). Anal.
Calcd for C21H17N7O3 (415.41): C, 60.72; H, 4.12; N, 23.60. Found:
C, 60.35, H, 4.36, N, 23.45%.
References
1
2
A.S. Shawali and M.A.N. Mosselhi, J. Heterocyclic Chem., 2003, 40, 725.
A.S. Shawali, M.A. Abdallah and M.E.M. Zayed, J. Chinese Chem. Soc.,
2002, 49, 1035.
3
4
A.S. Shawali, M.H. Abdel Kader and F.M.A. Altalbawy, Tetrahedron,
2002, 58, 2875.
A.S. Shawali, M.A. Abdallah, M.A.N. Mosselhi and Y.F. Mohamed,
Z. Naturforsch., 2002, 57b, 552.
5
6
D.W. Rangnekar and S.S. Puro, Indian J. Fibre Textile Res., 1990, 15, 23.
M.H. Elnagdi, M.M.M. Sallam, H.M. Fahmy, S.A. Ibrahim and
M.A.M. Elias, Helv. Chim. Acta, 1976, 59, 551.
M.N. Mosselhi, M.A. Abdallah, Y.F. Mohamed and A.S. Shawali,
Phosphorus, Sulfur Silicon, 2002, 177, 487.
A.S. Shawali, I.F. Zeid, M.H. Abdelkader and F.M.A. Altalbawy,
J. Chinese Chem. Soc., 2001, 48, 65.
M.N. Mosselhi, M.A. Abdallah, S.M. Riyadh, A.E. Harhash and
A.S. Shawali, J. Prakt. Chem., 1998, 340, 160.
pKa Determination of compounds 3 and 4
The acid dissociation constants of the compounds 3 and 4 were
determined potentiometrically in 50% dioxan–water mixture
at 25 0.1°C and ionic strength (KNO3) of 0.1 M. A Metrohm
686 titroprocessor equipped with 665 Dosimat was employed.
The electrode and the titroprocessor were calibrated with standard
Beckman buffer solutions of pH 4.01 and 7.00. The pH meter reading
B recorded in 50% dioxan–water solution was converted to hydrogen
ion concentration [H+] by means of the widely used relation of van
Uitert and Hass,21 namely:
7
8
9
10 A.S. Shawali, N.M.S. Harb and K.O. Badahdah, J. Heterocycl. Chem.,
1985, 22, 1397.
11 C.D. Johnson, The Hammett Equation, Cambridge University Press,
1973.
12 A.S. Shawali, M.A.N. Mosselhi and T.A. Farghaly, J. Chem. Res.,
2007, 479.
13 A.S. Shawali, M.S. Rizk, A.O. Abdelhamid, M.A. Abdallah, C. Parkanyi
and M.E. Wojciechowska, Heterocycles, 1983, 20, 2211.
14 A.S. Shawali, H.M. Hassaneen and M.A. Hanna, Heterocycles, 1981,
15, 697.
log [H+@ꢀ ꢀ%ꢀꢔꢀORJꢀ8H
where log UH is the correction factor for the solvent composition and
ionic strength used for which B is read. The value of log UH for the
medium in our work was found to be 0.21. A carbonate-free sodium
hydroxide titrant was prepared and standardised against potassium
hydrogen phthalate solution.
The experimental procedure followed in the determination of pKa
values and their calculations, by the method of least squares, from the
titrant volume-pH data using the relation:
15A.E. Elhilaly, A.S. Shawali and M.A. Madkour, Inorg. Chim. Acta, 1979,
36, 179.
16 K.U. Sadek, N.S. Ibrahim and M.H. Elnagdi, Arch. Pharm. (Weinheim),
1988, 321, 141.
17 A.S. Shawali, E.S.S. Darwish and M.A. Farag, Asian J. Spect., 2007,
11, 115.
pKaꢀ ꢀS+i – log V/(V – V)
i
e
i
where pHi is the corrected pH value of the solution when the volume
of the added titrant is Vi and V is the volume of the titrant at the
e
equivalent point as previously described.22 The calculations of the pKa
values were carried out using the computer program MINIQUAD-
75.23 The pKa values obtained were reproducible to within 0.02 pKa
unit. The results are recorded in Tables 1 and 2.
18 V.B. Hirsch, Liebigs Ann. Chem., 1965, 690, 33.
19 M.H. Elnagdi, N.H. Taha, F.A. Abd El All, R.M. Abdel Motaleb and
F.F. Mahmoud, Collect. Czech. Chem. Commun., 1989, 54, 1082.
20 F. Karci and A. Demircali, Dyes Pigments, 2007, 74, 288.
21 L.G. Van Uitert and C.G. Haas, J. Am. Chem. Soc., 1953, 75, 451.
22 A. Albert and E.P. Serjeant, The Determination of Ionisation Constants,
Chapman and Hall, London, 1971.
Received 21 March 2008; accepted 5 June 2008
Paper 08/5172 doi:10.3184/030823408X339782
Published online: 26 August 2008
22 P. Gans, A. Sabatini and A. Vacca, Inorg. Chim. Acta, 1976, 18, 237.