One-pot synthesis and the fluorescent behavior of 4-acetyl-5-methyl-1,2,3-triazole regioisomers

Article abstract of DOI:10.1016/j.molstruc.2008.05.028

A series of novel 4-acetyl-5-methyl-1,2,3-triazole exclusively with 1,4 regioisomers were synthesized via 1,3-dipolar cycloaddition with high yield from azide and acetyl acetone in the presence of a base, under warm condition in ethanol in a short duration. All the compounds were characterized by using FT-IR and NMR spectroscopic techniques. The isomer purity has been confirmed by means of HPLC. The reaction is affected by the electronic effects; triazole with electron withdrawing substituent reacts faster with maximum yield of 90% compare to the electron donating substituent. All the compounds show fluorescent behavior. Among them, the 1-[4-(cyano)phenyl]-4-acetyl-5-methyl-1,2,3-triazole remarkably shows dual emission in the chloroform solvent.

Full text of DOI:10.1016/j.molstruc.2008.05.028

Journal of Molecular Structure 892 (2008) 210–215
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
One-pot synthesis and the fluorescent behavior of 4-acetyl-5-methyl-1,2,3-triazole
regioisomers
*
V.R. Kamalraj, S. Senthil, P. Kannan
Department of Chemistry, Anna University, Chennai 600 025, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel 4-acetyl-5-methyl-1,2,3-triazole exclusively with 1,4 regioisomers were synthesized via
1,3-dipolar cycloaddition with high yield from azide and acetyl acetone in the presence of a base, under
warm condition in ethanol in a short duration. All the compounds were characterized by using FT-IR and
NMR spectroscopic techniques. The isomer purity has been confirmed by means of HPLC. The reaction is
affected by the electronic effects; triazole with electron withdrawing substituent reacts faster with max-
imum yield of 90% compare to the electron donating substituent. All the compounds show fluorescent
behavior. Among them, the 1-[4-(cyano)phenyl]-4-acetyl-5-methyl-1,2,3-triazole remarkably shows dual
emission in the chloroform solvent.
Received 27 February 2008
Received in revised form 14 May 2008
Accepted 16 May 2008
Available online 24 May 2008
Keywords:
1,3-Cycloaddition
1,2,3-Triazole
Azide
Ó 2008 Elsevier B.V. All rights reserved.
Acetyl acetone
Fluorescence
1. Introduction
comings, attributed to the chelating properties of nitrogen, which
form metal complex with Friedel–Crafts catalyst. Herein, hitherto
The important domain of synthetic organic chemistry is 1,3-
dipolar cycloaddition reaction with organoazide to produce
heterocyclic five membered rings. The 1,2,3-triazole based
derivatives have received much attention due to their wide
coverage of biological properties including antiviral [1], agonist
[2], antibacterial, antimicrobial agent [3], anti-HIV [4,5], anti-
convulsants [6], anti-allergic [7]. In addition, compounds having
1,2,3-triazole group have found industrial application as dyes,
corrosion inhibitors, sensors and photo-stabilizers [8]. Out-
standingly, the 1,2,3-triazole have heat of formation 272 kJ/
mol [9] and triazole based salts are used as energetic materials
[10].
The most popular method for the construction of 1,2,3-triazole
framework is the 1,3-dipolar Huisgen cycloaddition reaction of
azides with alkynes [11–13]. However, the early Huisgen cycload-
dition process required a strong electron withdrawing substituent
either on azide or an alkynes and were often conducted at high
temperature for a prolonged period of time that led to the isolation
of mixture of 1,4 and 1,5 disubstituted regioisomers [14,9] and the
electronic effects of the substituted groups on phenyl ring were not
known clearly. Furthermore, the important method for the prepa-
ration of aryl ketones performed by Friedel–Crafts acylation [15].
Substitution of acyl group on the heterocyclic ring by Friedel–
Crafts acylation is a tedious one with its own demerits and short-
unreported new simple and rapid one-pot synthesis of 4-acetyl-
5-methyl-1,2,3-triazole from organoazide and acetyl acetone in
the presence of a base under warm condition in ethanol is re-
ported. Their synthesis, characterization and fluorescent behavior
are discussed.
2. Experimental section
2.1. Reagents
Substituted anilines were purchased from (Aldrich, USA),
benzyl chloride and bromobutane (Merck, Germany), sodium ni-
trite (Aldrich), sodium azide (Aldrich), potassium carbonate (Al-
drich) were used as supplied. Thin layer chromatography was
performed with TLC sheets coated with silica; spots were de-
tected by UV irradiation. Silica gel (MN Kieselgel 60, 70–230
mesh) was used for column chromatography. Ethanol, chloro-
form, and other solvents were purified by reported procedures
[16].
2.2. Synthesis of substituted azidobenzene
4-Nitroaniline (20 g, 0.144 mol) was dissolved in (91.4 ml)
1:1 ratio of HCl, water and taken in a round bottom flask
equipped with stirrer. The reaction was agitated at 0–5 °C; so-
dium nitrite (10 g, 0.144 mol) was dissolved in 51.30 ml of ice-
cold water and added drop wise, sodium azide (9.36 g
* Corresponding author. Tel.: +91 44 2220 3155; fax: +91 44 2220 0660.
E-mail address: pakannan@annauniv.edu (P. Kannan).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.05.028

V.R. Kamalraj et al. / Journal of Molecular Structure 892 (2008) 210–215
211
0.144 mol) dissolved in 113.40 ml of water and added drop
O
O
wise, then reaction is allowed to continue for 30 min. The resul-
tant precipitate was extracted with chloroform and washed suc-
cessively with water. The organic layer was dried over
anhydrous sodium sulphate, and the solvent stripped out in ro-
tary evaporator to get 4-nitroazidobenzene, yield 93.5% (18.7 g).
The similar procedure was followed for other substituted
anilines.
R
DMSO
N
N
R-X
R-N3
N
K2CO3/Et-OH
NaN3
X
O
R=
X
X= Cl, Br
X
2.3. Synthesis of benzyl azide
O
O
Benzylchloride (6.72 ml; 0.0584 mol) was taken in a round bot-
tom flask with 80 ml of dimethyl sulphoxide equipped with stirrer,
sodium azide (7.6 g; 0.1169 mol) added and stirred overnight. The
reaction mixture was quenched in ice-water and extracted with
diethyl-ether, washed successively with 5% bicarbonate solution
and dried over anhydrous sodium sulphate. The solvent was re-
moved by rotary evaporator to give benzyl azide, yield 71.4%
(4.8 ml), The similar procedure was followed for the preparation
of azidobutane.
NaNO2
N
N
N3
X
H2N
X
N
NaN3
K2CO3/Et-OH
O
X=H, F,Cl, Br, I, NO2, CN, CH3, OCH3
Scheme 1. Scheme of synthesis of triazole.
O
O
2.4. Synthesis of 1-[4-(nitro) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
The 4-nitroazidobenzene (3 g, 0.018 moles), acetyl acetone
(1.8 g, 0.018 moles), potassium carbonate (8 g, 0.057 moles),
absolute ethanol (95%, 45 ml) were taken in a round bottom flask
equipped with stirrer. The reaction mixture was agitated at 75 °C
for 30 min. The progress of the reaction was monitored by TLC.
After the completion of the reaction, the solvent was removed
under vacuum. The residual mass was quenched in the ice-water
mixture and neutralized with 10% HCl solution. The product was
extracted with diethyl ether dried over anhydrous sodium sul-
fate. Evaporation of the solvent yield crude product, which was
purified by column chromatography using chloroform as eluent
and recrystallized from absolute ethanol, yield 79.5% (3.9 g),
m.p. 148 °C. The remaining substituted triazoles were prepared
in the similar manner and their characterization data are as
follows:
Keto-enol
Tautomer
R
N
R
N
OH
O
Dipolarophile
-H2O
OH
O
N
N
N
N
R
N
N
Dipolar
N
H
O
Fig. 1. Mechanism of Triazole formation from azide and acetyl acetone.
2.4.1. 1-[4-(Nitro) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
1H NMR (CDCl3): d 2.68 (s, 3H, CH3), d 2.61(s, 3H, COCH3), d 8.4
(d, 2H, ArAH), d 8.6 (d, 2H, ArAH).13C NMR (CDCl3): d 10.60 (1C,
CH3), 28.23 (1C, COCH3), 194.39 (1C, COCH3) 125.49, 126.10,
137.67, 140.44, 144.38, 148.55. IR (KBr): 1679 cmÀ1 (C@O stretch-
ing), 1600 cmÀ1 (N@N Stretching), 1342 cmÀ1 (ArANO2 stretching),
3084 cmÀ1 (aromatic CAH stretching). MS: M+ = 246. Elemental
anal: C11H10N4O3 calculated: C, 53.6%, H, 4.06%, N, 22.76%, found:
C, 53.45%, H, 4.01%, N, 22.32%. The similar procedure was adopted
for other substituted azides.
2.4.2. 1-[4-(Fluoro) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1685 cmÀ1 (C@O stretching), 1546 cmÀ1 (N@N stretch-
ing), 3099 cmÀ1 (aromatic CAH stretching). 1H NMR (CDCl3): d 2.68
(s, 3H, CH3), d 2.52 (s, 3H, COCH3), d 7.3. (d, 2H, ArAH), d 7.5 (d, 2H,
ArAH). 13C NMR (CDCl3): d 10.21 (1C, CH3), 27.9 (1C, COCH3),
194.36 (1C, COCH3) 124.35, 126.80, 133.05, 134.37, 137.41, 143.85.
MS: M+ = 219. Elemental anal: C11H10N3OF calculated: C,
60.27%, H, 4.5%, N, 19.17%, found: C, 59.32%, H, 4.22%, N, 18.93%.
2.4.3. 1-[4-(Chloro) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1685 cmÀ1 (C@O stretching), 1514 cmÀ1 (N@N
stretching), 3058 cmÀ1 (aromatic CAH Stretching). 1H NMR
(CDCl3): d 2.68 (s, 3H, CH3), d 2.52(s, 3H, COCH3), d 7.3. (d, 2H,
ArAH), d 7.5 (d, 2H, ArAH). 13C NMR (CDCl3): d 10.21 (1C, CH3),
27.9 (1C, COCH3), 194.36 (1C, COCH3) 124.35, 126.80, 133.05,
134.37, 137.41, 143.85. MS: M+ = 235. Elemental anal:
Fig. 2. (a) FT-IR spectrum of 1-[4-(nitro) phenylazide] and (b) FT-IR Spectrum of
1-[4-(nitro) phenyl]-4-acetyl-5-methyl-1,2,3-triazole.

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V.R. Kamalraj et al. / Journal of Molecular Structure 892 (2008) 210–215
Table 1
One-pot synthesis of triazole from azide and acetyl acetone
Entry
1
Azide
Runtime (Min)
30
Yield (%)
83
HPLC (area %)
98.12
MPa (°C)
–
N3
2
3
4
30
40
25
79
80
86
97.32
97.82
98.15
–
N3
108
–
N3
F
N3
5
30
85
99.21
119
Cl
N3
6
30
30
20
20
40
30
85
83
90
89
79
81
99.32
98.34
99.32
98.42
98.25
97.32
120
125
148
160
120
120
Br
N3
7
I
N3
8
No2
NC
H3CO
H3C
N3
9
N3
10
N3
11
N3
a
Melting point.
C11H10N3OCl calculated: C, 56%, H, 4.25%, N, 17.87%, found: C,
55.34%, H, 3.98%, N, 17.12%.
COCH3), d 7.63 (d, 2H, ArAH), d 7.89 (d, 2H, ArAH). 13C NMR
(CDCl3): d 10.3 (1C, CH3), 28.02(1C, COCH3), 194.21 (1C, COCH3)
114.14, 117.46, 125.06, 125.80, 133.81, 137.40, 138.81, 144.09.
MS: M+ = 226. Elemental anal: C12H10N4O calculated: C, 63.71%,
H, 4.42%, N, 24.77%, found: C, 63.34%, H, 3.98%, N, 24.21%.
2.4.4. 1-[4-(Bromo) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1685 cmÀ1 (C@O stretching), 1546 cmÀ1 (N@N stretch-
ing), 3099 cmÀ1 (aromatic CAH stretching). 1H NMR (CDCl3): d 2.75
(s, 3H, CH3), d 2.68(s, 3H, COCH3), d 7.3. (d, 2H, ArAH), d 7.7 (d, 2H,
ArAH). 13C NMR (CDCl3): d 10.21 (1C, CH3), 27.9 (1C, COCH3),
194.36 (1C, COCH3) 124.35, 126.80, 133.05, 134.37, 137.41,
143.85.MS: M+ = 280. Elemental anal: C11H10N3OBr calculated: C,
47%, H, 3.5%, N, 15%, found: C, 46.63%, H, 3.21%, N, 14.45%.
2.4.7. 1-[4-(Methoxy) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1687 cmÀ1 (C@O stretching), 1517 cmÀ1 (N@N stretch-
ing), 3051 cmÀ1 (aromatic CAH stretching) .1H NMR (CDCl3): d 2.47
(s, 3H, CH3), d 2.66(s, 3H, COCH3), d 3.81 (s, 3H, OCH3), d 6.97 (d,
2H,ArAH), d 7.28 (d, 2H, ArAH). 13C NMR (CDCl3): d 10.3 (1C,
CH3), d 21.3 (1C, CH3), 27.89(1C, COCH3), 194.52 (1C, COCH3),
125.16, 130.30, 132.907, 137.49, 140.45, 143.68. MS: M+ = 231. Ele-
mental anal: C12H13N3O calculated: C, 62.3%, H, 5.62%, N, 18.1%,
found: C, 61.89%, H, 5.23%, N, 17.92%.
2.4.5. 1-[4-(Iodo) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1685 cmÀ1 (C@O stretching), 1546 cmÀ1 (N@N stretch-
ing), 3099 cmÀ1 (aromatic CAH stretching). 1H NMR (CDCl3): d 2.75
(s, 3H, CH3), d 2.68(s, 3H, COCH3), d 7.3. (d, 2H, ArAH), d 7.7 (d, 2H,
ArAH). 13C NMR (CDCl3): d 10.21 (1C, CH3), 27.9(1C, COCH3),
194.36 (1C, COCH3)124.35, 126.80, 133.05, 134.37, 137.41,
143.85. MS: M+ = 327. Elemental anal: C11H10N3OI calculated: C,
40.36%, H, 3.05%, N, 12.84%, found: C, 39.83%, H, 2.94%, N, 12.21%.
2.4.8. 1-[4-(Methyl) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1687 cmÀ1 (C@O stretching), 1517 cmÀ1 (N@N stretch-
ing), 3051 cmÀ1 (aromatic CAH stretching) 1H NMR (CDCl3): d 2.04
(s, 3H, CH3), d 2.58 (s, 3H, CH3), d 2.75(s, 3H, COCH3), d 7.28 (d, 2H,
ArAH), d 7.33 (d, 2H, ArAH). 13C NMR (CDCl3): d 10.3 (1C, CH3), d
21.3 (1C, CH3), 27.89(1C, COCH3), 194.52 (1C, COCH3), 125.16,
130.30, 132.907, 137.49, 140.45, 143.68. MS: M+ = 215. Elemental
anal: C12H13N3O calculated: C, 66.97%, H, 6.04%, N, 19.53%, found:
C, 66.34%, H, 5.98%, N, 18.98%.
2.4.6. 1-[4-(Cyano) phenyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1685 cmÀ1 (C@O stretching), 1548 cmÀ1 (N@N stretch-
ing), 3058 cmÀ1 (Aromatic CAH stretching) 2335 cmÀ1 (C„N
stretching).1H NMR (CDCl3): d 2.63 (s, 3H, CH3), d 2.72(s, 3H,

V.R. Kamalraj et al. / Journal of Molecular Structure 892 (2008) 210–215
213
Fig. 3. 1H NMR spectrum of 1-[4-(methoxy) phenyl]-4-acetyl-5-methyl-1,2,3-triazole.
Fig. 4. 13C NMR spectrum of 1-[4-(methoxy) phenyl]-4-acetyl-5-methyl-1,2,3-triazole.

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V.R. Kamalraj et al. / Journal of Molecular Structure 892 (2008) 210–215
0.5
0.45
0.4
0. 2
0.16
0.12
0.08
0.04
0
0.35
0.3
a
0.25
0.2
b
0.15
0.1
0.05
512
562
612
662
712
Wavelength
0
500
550
600
650
700
750
800
Fig. 7. Fluorescence emission of 1-[4-(cyano) phenyl]-4-acetyl-5-methyl-1,2,3-
triazole in methanol.
Wavelength
Fig. 5. Fluorescence emission of (a) 1-[4-(nitro) phenyl]-4-acetyl-5-methyl-1,2,3-
triazole with dark line and (b) 1-[4-(methoxy) phenyl]-4-acetyl-5-methyl-1,2,3-
triazole with thin line.
calculated: C, 59.66%, H, 6.04%, N, 23.2%, found: C, 59.21%, H,
5.98%, N, 22.93%.
2.5. Measurements
0.6
0.5
0.4
0.3
0.2
0.1
0
The 1H NMR spectra were recorded on Brucker 400 MHz spec-
trometers for samples in CDCl3. The signals are expressed as parts
per million down fields from tetramethylsilane, used as an internal
standard (d value). Splitting patterns are indicated as s, singlet; d,
doublet; t, triplet; q, quartet; m, multiplets. IR spectra were mea-
sured using Jasco FT-IR- 300E spectrometer. Mass spectra were ta-
ken with
a Thermo Finnigan mass spectrometer. HPLC was
performed with Kanto Chemical Mightysil RP-18, and chloroform
was used as eluent. The UV–vis absorption and fluorescence spec-
tra were recorded on a shimadzu UV 160 spectrophotometer and a
shimadzu RF 5000U spectrofluorophotometer, respectively.
3. Results and discussion
The simple and rapid one-pot synthesis of 4-acetyl-5-methyl-
1,2,3-triazole from organoazide and acetyl acetone in the presence
of potassium carbonate under warm condition in ethanol was exe-
cuted (Scheme 1). The reaction proceeds via 1,3-dipolar-cycloaddi-
tion, the mechanism is shown in Fig. 1. The experiment was
assayed with 4-nitroazidobenzene and the degree of progress of
the reaction was checked by IR spectra; surprisingly, reaction com-
pleted within 20 min. The azide absorption (2100 cmÀ1) disap-
peared clearly at 20 min after the reaction started as evidenced
in Fig. 2. The product was separated and purified using column
chromatography, the yield of the product was 90% with 99.3% pur-
ity of HPLC. The results revealed that less than 20 min reaction
duration is ideal to get regio-controlled 1, 4 substituted products
exclusively. To know the reactivity, phenyl azides having elec-
tron-withdrawing and electron donating groups in the phenyl
group were applied to this reaction. The results of these reactions
are listed in Table 1. In the case of 4-nitrophenylazide, the reaction
was completed within 20 min, while in 4-methoxyphenylazide de-
manded 40 min. 1H and 13C NMR spectra are shown in Figs. 3 and
4. A similar trend was observed for unsubstituted phenyl azide. On
the other hand, the reaction was carried out for methyl, chloro, flu-
oro, bromo, iodo substituted azides needed the completion of reac-
tion in 30 min. These results indicate that the reaction proceeds
faster in the presence of electron withdrawing group compared
to that of electron donating groups.
510
560
610
660
710
760
Wavelength
Fig. 6. Dual fluorescence emission of 1-[4-(cyano) phenyl]-4-acetyl-5-methyl-
1,2,3-triazole in chloroform.
2.4.9. 1-[Benzyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1685 cmÀ1 (C@O stretching), 1546 cmÀ1 (N@N stretch-
ing), 3099 cmÀ1 (aromatic CAH stretching) 1H NMR (CDCl3): d 2.43
(s, 3H, CH3), d 2.65(s, 3H, COCH3), d 5.47 (s, 2H, CH2), d 6.97 (d, 2H,
ArAH), d 7.28 (d, 2H, ArAH). 13C NMR (CDCl3): d 9.21 (1C, CH3),
27.76(1C, COCH3), 194.47 (1C, COCH3), 54.85, 119.22, 128.37,
129.19, 134.03, 136.98. MS: M+ = 215. Elemental anal: C12H13N3O
calculated: C, 66.97%, H, 6.04%, N, 19.53%, found: C, 66.34%, H,
5.98%, N, 18.98%.
2.4.10. 1-[Butyl]-4-acetyl-5-methyl-1,2,3-triazole
IR (KBr): 1685 cmÀ1 (C@O stretching), 1546 cmÀ1 (N@N stretch-
ing), 3099 cmÀ1 (aromatic CAH stretching). 1H NMR (CDCl3): d 2.44
(s, 3H, CH3), d 2.53(s, 3H, COCH3), d 4.1(t, 2H, CH2), d 0.83 (t, 3H,
CH3), 1.2 (m, 2H, CH3), 3.1(m, 2H, CH3). 13C NMR (CDCl3): d
13.38, 13.50, 19.66, 24.68, 27.49, 30.80, 31.61, 47.35, 77.00,
77.25, 100.38, 202.18. MS: M+ = 181> Elemental anal: C9H15N3O

V.R. Kamalraj et al. / Journal of Molecular Structure 892 (2008) 210–215
215
3.1. Fluorescence emission
laboratory attempt to synthesis new fulgides using these 4-acte-
tyl-5-methyl-1,2,3-triazole through Stobbe Condensation for
molecular switching, which is under progress.
The absorption spectra of nitro substituted triazole shows two
absorption maxima one at 280 nm and other at 480 nm in chloro-
form solvent. There was no fluorescence emission detected when it
excited at 280 nm. Emission was observed when it excited at
480 nm. Fig. 5 shows the fluorescence spectrum of nitro substi-
tuted 4-acetyl-5-methyl-1,2,3-triazole and methoxy substituted
4-acetyl-5-methyl-1,2,3-triazole. The similar type of emission
was observed for all the other substituted triazoles. But, especially
for cyano substituted triazole shows dual emission when excited at
480 nm as shown in Fig. 5. The spectrum has two intensity maxima
one at 535 nm and other at 625 nm. The fluorescence spectrum
was recorded in acetonitrile solvent did not show emission. In
methanol all the compounds shows emission, but the dual emis-
sion of cyano substituted triazole observed in chloroform solvent
(Fig. 6) but failed in methanol solvent, which exhibit only one max-
ima at 538 nm as shown in Fig. 7.
Acknowledgements
This research was supported by grants from Department of Sci-
ence and Technology, New Delhi, Govt. of India (SR/FTP/CS-31/
2005) and Board of Research in Nuclear Sciences, Govt. of India
(2006/37/13/BRNS/205).
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The one-pot synthesis of 4-acetyl-5-methyl-1,2,3-triazole with
1, 4 regioisomer exclusively with very high yield was demon-
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simplicity of reaction procedure and excellent yield which can
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