[
E.O. Moradi Rufchahi et al. / Chinese Chemical Letters 24 (2013) 425–428
CH3
NH2
OH
O
CH3
+
O
O
HN
CH3SO3H / P2O5
150 oC, 90 min
MW (320 w)
5 min.
2
EtO
OEt
N
H
O
N
H
O
CH3
CH3
I
II
Scheme 1. Preparation of 8-methyl-4-hydroxyl-2-quinolone (II).
2H, J = 8.1, 7.2 Hz), 7.01 (dd, 2H, J = 7.7, 7.2 Hz), 3.58 (s, 2H, –CH2–),
2.34 (s, 6H).
3. Results and discussion
Hydroxyquinolone (II) was obtained using the experimental
method described in Ref. [14], by heating the N,N0-di-(2-
methylphenyl)malonamide (I) (0.56 g, 2.0 mmol) in 3.5 mL
methanesulfunic acid, which contains 10% phosphorus pentoxide
at 150 8C, for 90 min. The dark viscous solution was allowed to
cool. Water was added, and the resultant gum solidified on
prolonged standing. The solid was filtered and then dissolved in
100 mL 10% sodium hydroxide. The aqueous solution was filtered
to remove insoluble material and slowly acidified to pH < 4 with
10% hydrochloric acid. The resulting crude precipitates were
collected, washed with water and dried to afford 8-methyl-4-
hydroxyquinoline-2-(1H)-one (II) as creamy crystals (0.30 g,
87%), mp: 357–358 8C (reported 360 8C [13]); FT-IR (KBr,
The arylazoquinololin-2-one dyes 1–8 were prepared by
coupling reaction of 8-methyl-4-hydroxyquinolin-2-(1H)-one
with diazotized p-substituted aniline derivatives in basic solution
(Scheme 2). The chemical structures of these dyes were confirmed
by some spectroscopic methods and elemental analysis (see
supplementary data). As shown in Scheme 3, azo dyes 1–8 can exist
as a mixture of four tautomeric forms, namely the azo-enol-keto
(T1), hydrazone-keto (T2), hydrazone-keto (T3) and azo-enol-keto
(T4).
The infrared spectra of all the compounds (in KBr) showed
intense carbonyl bands at 1680–1660 cmꢀ1 and showed broad
hydroxyl and amide (NH–C55O) bands at 3459–3442 cmꢀ1 and
3200–3175 cmꢀ1, respectively. It can be suggested that these
compounds do not exist in the hydrazone-keto form in solid state.
cmꢀ1):
(500 MHz, DMSO-d6):
J = 7.8 Hz), 7.30 (d, 1H, J = 7.2 Hz), 7.01 (dd, 1H, J = 7.8, 7.1 Hz),
5.27 (s, 1H), 2.35 (s, 3H); 13C NMR (125 MHz, DMSO-d6):
160.75
n
3470 (OH), 3100 (NH), 1660 (C55O); 1H NMR
d
11.25 (OH), 10.27 (NH), 7.62 (d, 1H,
The FT-IR spectra also show a weak band at 3120–3060 cmꢀ1
which was assigned to aromatic C–H.
,
d
1H NMR spectra measured in DMSO-d6 at 25 8C are given in the
(C55O), 158.24 (C–OH), 139.14 (C), 134.10 (C–CH3), 130.78 (CH),
126.20 (C–H), 124.90 (CH), 116.17(C), 99.10 (CH), 17.01 (CH3).
Anal. Calcd. for C10H9NO2: C, 68.56; H, 5.18; N, 8.00; Found: C,
68.54; H, 5.12; N, 7.78.
supplementary data. In addition to known aromatic and aliphatic
protons, all the prepared azo dyes showed two broad peaks at
d
16.24–15.51 and 15.37–14.89 assigned to hydrazone proton
d
signals (55N–NH–). Undoubtedly, these signals correspond to the
A cold solution of aryldiazonium salt (2.0 mmol) was prepared
by adding a solution of NaNO2 (2.2 mmol, 0.15 g into 1.0 mL H2O)
to a cold solution of arylamine hydrochloride (2.0 mmol of
arylamine in 1.5 mL conc. HCl). The resulting solution of
aryldiazonium salt was added drop wise to a mixture of 8-
methyl-4-hydroxyquinoline-2-(1H)-one (II) (0.35 g, 2.0 mmol) in
10 mL aqueous NaOH (20 mmol, 0.8 g) at 0–5 8C. The pH of the
reaction mixture was maintained at 9–10 by adding 2.5% sodium
hydroxide solution. The resulting mixture was continually stirred
at 0–5 8C for 2 h. After completion of the reaction the pH was
regulated to 4–5 by simultaneous additions of 10% hydrochloric
acid solution. The resulting solid was then filtered off, washed with
cold ethanol, dried at 50 8C in an oven and then recrystallized from
DMF. The purity of all compounds was evaluated by thin layer
chromatography. The physical and spectral data of the purified
dyes are available in the supplementary data accompanied with
this paper.
hydrazone NH proton resonance related to hydrazone-keto forms
T
2 and T3 [15,16]. These results are supported by the fact that the
hydroxyazo OH proton resonance comes 3–5 higher than NH
proton resonance; hence, the OH proton resonance signal of enol
forms is expected to be in the region 9–12 [17,18]. The possibility
d
d
of tautomers involving ring NH rearrangement can be eliminated
by studying the 1H NMR spectrum of the compounds in DMSO-d6.
The 1H NMR spectrum of all the dyes showed two singlets at
d
10.45–10.32 and
d 10.30–10.16. The presence of these two broad
singlets provides firm evidence for presence of the amide (–NH–
C55O) bonds and is related to amide protons of two types of
[(cShem_)3DT$FI]G
H
Ar
H
Ar
O
N
N
O
N
N
N
H
O
N
H
O
CH3
T1
[(Scheme_2)TD$FIG]
CH3
T2
X
OH
OH
N2+Cl-
O
O
N
1) pH:9-10
2) pH:4-5
N
O
N
N
Ar
Ar
N
H
N
H
+
N
H
O
N
H
O
N
H
N
H
O
CH3
CH3
1-8
X
CH3
CH3
T3
II
1: -OCH3 2: -CH3 3: -I
4: -Br
7: -COCH3 8: -NO2
X=
T4
5: -Cl
6: -F
Scheme 2. Synthetic routes for the preparation of azo dyes 1–8.
Scheme 3. Possible tautomeric forms for the synthesized azo dye.