Synthesis of triazenes of n-heterocycles mediated by resin immobilized diazonium ions

Article abstract of DOI:10.14233/ajchem.2017.20443

Diazonium ions were prepared from aromatic amines and immobilized in cation exchange resin support and used for the synthesis of triazenes of piperidine and morpholine in a solid phase synthesis. Immobilization is an excellent technique for the stabilization of diazonium ions and can be preserved in the solid state. Using resin immobilized diazonium ions, triazene synthesis is carried out in the absence of acids thereby increasing the yield of the product and simplifying work up.

Full text of DOI:10.14233/ajchem.2017.20443

Asian Journal of Chemistry; Vol. 29, No. 5 (2017), 1125-1129
ASIAN JOURNAL OF CHEMISTRY
https://doi.org/10.14233/ajchem.2017.20443
Synthesis of Triazenes of N-Heterocycles Mediated by Resin Immobilized Diazonium Ions
*
PRANAB J. DAS and JESMIN BEGUM
Department of Chemistry, Gauhati University, Guwahati-781 014, India
*Corresponding author: E-mail: pranabjdas52@gmail.com
Received: 12 December 2016;
Accepted: 7 February 2017;
Published online: 10 March 2017;
AJC-18312
Diazonium ions were prepared from aromatic amines and immobilized in cation exchange resin support and used for the synthesis of
triazenes of piperidine and morpholine in a solid phase synthesis. Immobilization is an excellent technique for the stabilization of diazonium
ions and can be preserved in the solid state. Using resin immobilized diazonium ions, triazene synthesis is carried out in the absence of
acids thereby increasing the yield of the product and simplifying work up.
Keywords: Solid phase synthesis, Triazenes, Immobilized diazonium ions, Piperidine, Morpholine.
long reaction time is required for completion of the reaction
[16]. The synthesis of triazenes in both aqueous and non-aqueous
solvents was reported by Lazny et al. [7], through protection
of primary and secondary aliphatic and aromatic amines. The
synthesis of methylene-bis-(1-oxy-3,3-dialkyl-1-triazene-2-
oxide) and their analogues acts as promising exogenous nitric
oxide (NO) donor for living organisms these products were
synthesized by the reaction of the corres-ponding amines with
nitric oxide in presence of sodium methoxide followed by
treatment of the resulting salt with dibromomethane in DMF
[17].
INTRODUCTION
Triazenes are high nitrogen compounds characterized by
the presence of the open chain nitrogen triad. Triazenes are
classified as monosubstituted (R-N=N-NH2), disubstituted
(R-N=N-NHR1) and trisubstituted (R-N=N-NR2).The alkyl as
well as aryl triazenes are of considerable interest because of
their biological as well as non-biological uses [1-3]. They are
often used for in vivo generation of diazonium ions in fabric
printing industry [4]. They can serve as suitable protecting
groups for amines because of their high stability towards bases,
organolithium reagents, oxidants, reductants as well as the
alkylating agents [5-7]. Triazenes can function as linkers in
solid phase organic synthesis of alkyl halides, amides, ureas,
thioureas, alcohols, esters, hydrazines, guanidines, sulfoxi-
mines etc. [8-10]. The Cu(II), Ni(II), Co(II), Zn(II), Fe(II)
complexes of triazenes are active antitumor and anticancer
agents [11,12]. The cytostatic activity discovered for several
substituted triazenes has stimulated intense research efforts
towards the development of triazene-based drugs [13].
Most of the reported methods were found to be unsatisfac-
tory as the product triazene is always accompanied by several
by products, which consequently lower the yield. Further it
has been observed that triazenes are not particularly stable in
acidic medium and decomposes to regenerate the diazonium
ions resulting in low yield. Therefore, isolation of the pure
triazene requires stringent pH and temperature control and
also demands tedious and time-consuming separation and
purification procedures. Therefore synthesis of triazene in
quantitative yield is a challenging topic for investigation.
Quantitative synthesis of triazene may be possible provided
their synthesis is carried out in solid phase under neutral condi-
tion and this can be accomplished by using resin immobilized
diazonium ions in a solid phase synthetic procedure. The solid
phase synthesis reported herein gives the comparatively pure
triazenes in high yield.
The classical synthesis of triazene involves the coupling
of diazonium salts with primary and secondary aliphatic or
aromatic amines in presence of slightly basic aqueous solution
at 0-5 °C. Other reported synthetic methods include reaction
of alkyl azides with an organometallic reagent such as Grignard
reagent or alkyllithium. Further alkylation of the 1,3-dialkyl
triazenes in presence of bases like potassium t-butoxide or
potassium hydride with 18-crown-6 followed by methyl iodide
afforded the 1,3,3-trialkyl triazenes [14,15]. The synthesis of
a novel triazene was developed by the ring opening of N-substi-
tuted tetrazole via unusual Vilsmier-Haak reaction. However,
EXPERIMENTAL
All reagents were purchased from Merck and Loba chieme
(India) and were purified by procedures reported in literature

1126 Das et al.
Asian J. Chem.
[18]. Resin immobilized diazonium ions were prepared. The
products were characterized by comparing their melting points
with authentic samples for solid products and spectroscopic
of diazonium ions in the resin surface after immobilization.
Solid state IR spectra obtained of resin immobilized diazonium
ions of 4-nitrobenzenediazonium ions and 4-acetyl benzene
diazonium ions gave additional band appears in the region of
2390-2340 cm-1 possibly due to the presence of -N≡N-stretching
vibration, this absorption band is absent in the preloadedAmberlite
IR-120 (Na+) [19].
1
methods UV-visible, FT-IR, H NMR, 13C NMR and mass
spectrometry. UV-visible spectra were recorded in UV-1800
Shimadzu UV spectrophotometer, IR spectra were recorded
in KBr pellets in a Perkin Elmer FT-IR 1600 spectrophotometer
and 1H and 13C NMR were recorded in Bruker Bio Spin 300
MHz spectrometer using CDCl3 as solvent and TMS as internal
standard. The cation exchange resin chosen was Amberlite
IR-120 (Na+) macroporous type according to Rohm & Haas
specification with type analysis SO3-, 20-50 mesh, Na+ form,
styrene-DVB (8 %). Aromatic amines, from which the diazo-
nium ions were prepared, were obtained commercially and
purified by procedures as described in literature [18].
Preparation of resin immobilized diazonium ion:15 g
of the cation exchange resinAmberlite IR-120 (Na+) was washed
several times with deionized water, dried and taken in a column.
0.05 mol of the aromatic amine diazotized using NaNO2 conc.
HCl at 0-5 °C. On passing the solution of diazonium ions
through the column of the resin, the diazonium ions are grafted
onto the cation exchange resin by displacement of the Na+
ions. The loaded resin was washed several times with deionized
water till the washing was free of diazonium ions. (alkaline 2-
naphthol test). The resin was then recovered and dried over
P2O5 at 50 °C under reduced pressure (50 mm Hg). Thus a
variety of diazonium ions were prepared by taking different
aromatic amines and immobilized onto the cation exchange
resin.
Synthesis of triazenes by immobilized diazonium ions:
To a solution of secondary amine (piperidine or morpholine,
1 mmol) in cyclohexane (25 mL), 5 g of freshly prepared resin
beads containing the diazonium ions were added and the
reaction mixture was stirred at room temperature. The progress
of the reaction was observed by colour change of the resin
beads. On completion of the reaction, the coloured beads were
recovered by simple filtration, washed 2 to 3 times with deionized
water and then dried at room temperature. The product triazenes
which remained adsorbed onto the surface of the beads were
extracted with ethyl acetate (100 mL) in a soxhlet extraction
apparatus. Evaporation of the solvent under reduced pressure
gave the desired triazene. Complete extraction of the triazenes
from the resin beads could not be achieved due to strong asso-
ciation of the triazene to the surface of the resin nevertheless
yield obtained to the extent of 80-90 %. Most triazenes formed
were found to be coloured viscous liquids except a few as
shown in Table-2. The products were purified by TLC using
silica gel H plates and ethyl acetate as the eluent. A single
spot in TLC indicated the excusive formation of the triazene.
Spectral data of some representative compounds
N-(2-Nitrophenylazo)piperidine (1a): Pale yellow oil, IR
(KBr, νmax, cm-1): 1625.99, 1311.59 (-N=O), 1462.04 (-N=N-),
1154.26 (-N-N=N-), UV-visible (EtOH) λmax (-N=N-): 380.54
nm. 1H NMR (300 MHZ, CDCl3, Me4Si) (δH): 7.844 (1H, d, J
= 7.2 Hz, ArH), 7.635 (2H, t, J = 8.4 Hz, ArH), 7.295 (1H, d,
J = 6.9 Hz, ArH), 3.887 (4H, brs, piper-CH2), 2.174 (6H, brs,
piper-CH2). 13C NMR (75 MHZ, CDCl3, Me4Si) δ: 153.49,
146.47, 134.47, 130.80, 129.60, 129.44, 129.19, 120.57, 52.60,
29.22, 26.44. HRMS (ESI): M+ Calcd: 234.11; found:
235.5629.
Estimation and characterization of the resin immobilized
diazonium ions
Reductometric titration test: The dried resin was analyzed
for diazonium ion content by reductometric titration procedure
using 10 mL of 57 % hydroiodic acid and 5 g of immobilized
diazonium ion. The liberated iodine was titrated with standard
sodium thiosulphate solution using starch as indicator [11,12].
This experiment was done with diazonium ions obtained from
different aromatic amines (Table-1) and the average loading
was found to be 2.26 meqv. of ArN2+ per g of the resin. The
dried resin was stored at room temperature and the diazonium
ion content was found to remain constant over a period of six
months. Immobilization of diazonium ions on cation exchange
resin proves to be an excellent method for their stabilization.
N-(2,4-Dichlorophenylazo)piperidine (1b): Pale yellow
oil, IR (KBr, νmax, cm-1): 1469.76 (-N=N-), 1114.86 (-N=N-N-).
1
UV-visible (EtOH) λmax (-N=N-): 357.84 nm. H NMR (300
MHZ, CDCl3, Me4Si) (δH): 8.56 (1H, d, J = 7.2 Hz (1H, d,
ArH, J = 7.2 Hz), 7.548 (1H, s, ArH), 7.472 (1H, d, J = 6.8
Hz, ArH), 2.241 (4H, brs, piper-CH2), 1.756 (6H, brs, piper-
CH2). 13C NMR (75 MHZ, CDCl3, Me4Si) δ: 153.87, 150.60,
144.67, 125.17, 115.89, 36.15, 28.67, 24.48. HRMS (ESI):
M+ Calcd: 257.05; Found: 258.2125.
TABLE-1
DIAZONIUM ION CONTENT IN THE LOADED RESIN
Average
capacity
(m eqv/g)
Resin immobilized diazonium Diazonium
ions obtained from
Entry
N-(4-Methoxyphenylazo)piperidine (1d): Brown solid,
IR (KBr, νmax, cm-1): 1486.19 (-N=N-), 1146.32 (-N-N=N-).
1
UV-visible (EtOH) λmax (-N=N-): 351.06 nm. H NMR (300
ion content
1
2
3
4
5
6
4-Nitro aniline
4-Methyl aniline
4-Chloro aniline
2,4-Dichloro aniline
4-Methoxy aniline
2-Nitro aniline
2.46
2.32
2.21
2.26
2.38
2.07
MHZ, CDCl3, Me4Si) (δH): 7.788 (2H, d, J = 8.4 Hz, ArH),
7.605 (2H, d, J = 7.8 Hz, ArH), 4.115 (3H, s, OCH3), 3.563
13
(4H, brs, piper-CH2), 2.317 (6H, brs, piper-CH2). C NMR
2.26
(75 MHZ, CDCl3, Me4Si) δ: 158.60, 147.88, 125.60, 118.56,
58.74, 48.15, 27.67, 23.98. HRMS (ESI): M+ Calcd: 219.14;
Found: 220.6748.
FT-IR spectra of cation exchange resin before and after
immobilization were recorded in KBr pellets using Perkin
Elmer FT-IR 1600 spectrophotometer to examine the presence
N-(4-Methylphenylazo)piperidine (1e): Dark red solid,
IR (KBr, νmax, cm-1): 1450.47 (-N=N-), 1251.80 (C-N), 1184.29

Vol. 29, No. 5 (2017)
Synthesis of Triazenes of N-Heterocycles Mediated by Resin Immobilized Diazonium Ions 1127
TABLE-2
PHYSICAL CHARACTERISTICS OF TRIAZENES USING RESIN IMMOBILIZED DIAZONIUM IONS WITH 2° AMINES
m.p. (°C)
S. No.
2° Amine
R
Product
Time (min)
Yielda (%)
Lit
Obs
Oil
1
2
2-NO2
2,4-diCl
3-Br
15
15
10
10
10
10
10
15
15
15
15
15
10
10
15
20
15
20
80
81
83
86
85
87
86
80
81
85
87
82
85
83
80
78
75
82
Oil [Ref. 20]
[Ref. 20]
1a
1b
1c
1d
1e
1f
H
N
–
Oil
3
–
Oil
4
4-OCH3
4-CH3
29-31 [[RReeff.. 2211]]
34-35
42-45
48-50
94-97
Oil
5
43-45 [Ref. 21]
[Ref. 21]
N
6
4-CH3CO
4-NO2
–
N
H
7
96 [Ref. 22]
[Ref. 22]
1h
1i
8
2-CH3
Oil [Ref. 20]
[Ref. 20]
H
9
4-Cl-2-NO2
H
–
Oil
1j
11
12
13
14
15
16
17
18
19
–
Oil
2a
2b
2c
2d
2e
2f
4-OCH3
4-Br
–
67-70
62-65
78-80
Oil
H
N
–
4-NO2
–
4-CH3CO
4-CH3
–
Oil [[RReeff.. 2200]]
Oil
2-Cl
–
–
–
Oil
2g
2h
2i
O
4-Cl-2-NO2
2-CH3
Oil
Oil
aYields refer to the pure isolated products. bMelting point reported for solid products
(-N-N=N-), UV-visible (EtOH) λmax (-N=N-): 330.42 nm. 1H
NMR (300 MHZ, CDCl3, Me4Si) (δH): 7.028 (2H, d, J = 4.8
Hz, ArH), 6.771 (2H, d, J = 8.6 Hz, ArH), 2.471 (4H, brs,
piper-CH2), 2.185 (3H, s, CH3), 1.348 (6H, brs, piper-CH2).
13C NMR (75 MHZ, CDCl3, Me4Si) δ: 153.43, 137.61, 130.90,
121.02, 49.09, 29.64, 22.64, 20.40. HRMS (ESI): M+ Calcd:
203.14; Found: 203.0709.
1157.29 (-N=N-N-). UV-visible EtOH λmax (-N=N-): 389.49
nm. 1H NMR (300 MHZ, CDCl3, Me4Si) (δH ppm): 7.986 (2H,
d, J = 8.7 Hz, ArH), 7.597 (2H, d, J = 9.0 Hz, ArH), 3.122
(4H, brs, morph-CH2), 2.102 (4H, brs, morph-CH2). 13C NMR
(75 MHZ, CDCl3, Me4Si) δ: 152.43, 138.97, 126.25, 121.32,
66.32, 54.0. HRMS (ESI): M+ Calcd: 236.09; Found: 236.1211.
N-(4-Methylphenylazo)morpholine (2f): Red solid. IR
(KBr, νmax, cm-1): 1624.67, 1444.68 (-N=N-), 1155.36 (-N=N-N-).
N-(4-Acetylphenylazo)piperidine (1f): Red solid, IR (KBr,
νmax, cm-1): 1646.35 (Ar-C=O), 1418.04 (-N=N-), 1147.65
(-N=N-N-). UV-visible (EtOH) λmax (-N=N-): 363.37 nm. 1H
NMR (300 MHZ, CDCl3, Me4Si) (δH): 7.932 (2H, d, J = 8.4
Hz,ArH), 7.491 (2H, d, J = 8.1 Hz,ArH), 3.858 (3H, s, OCH3),
2.639 (4H, brs, piper-CH2), 1.575 (6H, brs, piper-CH2). 13C
NMR (75 MHZ, CDCl3, Me4Si) δ: 197.65, 154.62, 133.79,
129.52, 120.21, 60.40, 53.41, 29.63, 24.99, 21.02. HRMS
(ESI): M+ Calcd: 231.14; Found: 232.1445.
1
UV-visible EtOH λmax (-N=N-): 372.84 nm. H NMR (300
MHZ, CDCl3, Me4Si) (δH): 7.385 (2H, d, J = 8.4 Hz, ArH),
7.171 (2H, d, J = 8.1 Hz, ArH), 3.825 (4H, brs, morph-CH2),
3.308 (4H, brs, morph-CH2), 2.344 (3H, s, CH3). 13C NMR
(75 MHZ, CDCl3, Me4Si) δ: 152.43, 138.97, 126.25, 121.32,
66.32, 54.0. HRMS (ESI): M+ Calcd: 205.12; Found: 205.9423.
N-(4-Chloro-2-nitrophenylazo)morpholine (2h): Pale
yellow oil IR (KBr, νmax, cm-1): 1602, 13, 1387.61 (Ar-N=O),
1495.34 (-N=N-), 1138.97 (-N=N-N-). UV-visible EtOH λmax
(-N=N-): 382.44 nm. 1H NMR (300 MHZ, CDCl3, Me4Si) (δH):
8.103 (1H, s, ArH), 7.738 (1H, d, J = 7.2 Hz, ArH), 7.526
(1H, d, J = 8.4 Hz, ArH), 3.739 (4H, brs, morph-CH2), 3.118
(4H, brs, morph-CH2). 13C NMR (75 MHZ, CDCl3, Me4Si) δ:
159.11, 147.65, 135.58, 126.75, 122.71, 118.86, 66.02, 54.85.
HRMS (ESI): M+ Calcd: 300.10; found: 301.1210.
N-(4-Chloro-2-nitrophenylazo)piperidine (1j): Red oil,
IR (KBr, νmax, cm-1): 1586.66, 1385.78 (-N=O), 1483.67
(-N=N-), 1148.55 (-N=N-N-). UV-visible EtOH λmax 393.65
1
nm. H NMR (300 MHZ, CDCl3, Me4Si) (δH): 7.832 (1H, s,
ArH), 7.742 (1H, d, J = 8.4 Hz, ArH), 7.545 (1H, t, J = 7.6
Hz, ArH), 3.684 (4H, brs, piper-CH2), 1.862 (6H, brs, piper-
CH2). 13C NMR (75 MHZ, CDCl3, Me4Si) δ: 154.67, 139.34,
132.45, 131.89, 130.34, 122.56, 43.87, 26.68. HRMS (ESI):
M+ Calcd: 268.07; Found: 269.1637.
N-(4-Bromophenylazo)morpholine (2i): Pale yellow
solid, IR (KBr, νmax, cm-1): 1435.04 (-N=N-), 1153.43 (-N=N-
N-). UV-visible EtOH λmax (-N=N-): 346.16 nm. 1H NMR (300
MHZ, CDCl3, Me4Si) (δH): 7.477 (2H, d, J = 6.9 Hz, ArH),
7.340 (2H, d, J = 6.9 Hz, ArH), 3.787 (4H, brs, morph-CH2),
2.178 (4H, brs, morph-CH2). 13C NMR (75 MHZ, CDCl3,
Me4Si) δ: 154.26, 148.33, 129.81, 124.90, 64.12, 48.66. HRMS
(ESI): M+ Calcd: 299.06; Found: 299.9771.
N-(4-Methoxyphenylazo)morpholine (2b): Pale yellow
oil, IR (KBr, νmax, cm-1): 1494.83 (-N=N-), 1155.36 (-N=N-N-).
1
UV-visible EtOH λmax (-N=N-): 375.51 nm. H NMR (300
MHZ, CDCl3, Me4Si) (δH): 7.445 (2H, d, J = 8.7 Hz, ArH),
6.915 (2H, d, J = 8.7 Hz, ArH), 3.865 (4H, brs, morph-CH2),
3.429 (3H, s, OCH3), 3.170 (4H, brs, morph-CH2). 13C NMR
(75 MHZ, CDCl3, Me4Si) δ: 158.37, 143.75, 127.98, 127.75,
121.80, 66.27, 55.18, 51.33. HRMS (ESI): M+ Calcd: 221.12;
Found: 222.1315.
RESULTS AND DISCUSSION
Herein is reported a method for preparation of resin immo-
bilized diazonium ions which were subsequently used to
synthesize the triazene in neutral organic solvents resulting in
N-(4-Nitrophenylazo)morpholine (2d): Red solid, IR
(KBr, νmax, cm-1):1624.67, 1323.71 (Ar-N=O), 1436.57 (-N=N-),

1128 Das et al.
Asian J. Chem.
high yield of the target molecule. In this study, the heterocyclic
amines namely piperidine and morpholine were chosen as the
starting compounds for the synthesis of the corresponding
triazenes namely the N-(arylazo)piperidines and N-(arylazo)-
morpholines. The resin immobilized diazonium ions were
reacted with the heterocyclic amines at room temperature in
presence of organic solvents (Scheme-I). Several solvents such
as toluene, benzene, chloroform, dichloromethane and aceto-
nitrile were screened for their suitability and cyclohexane was
found to be the solvent of choice primarily because in cyclo-
hexane the product triazenes are insoluble and remains em-
bedded onto the resin support which has inherent advantages
in solid phase synthesis. Resin embeded triazenes not only
prevents its contamination with unreacted substrates but also
offers the advantage of using excess of the reagents to speed
up the reaction. The formation of the triazene can be easily
followed by the instant colour change of the resin beads.
Recovery of products requires simple filtration of the beads
and extraction of the triazenes with ethyl acetate. Reduced
pressure removal of solvent yielded triazene in a pure form
and near quantitative yield. Resin immobilized diazonium ions
with both electron-withdrawing and electron-donating substi-
tuents gave comparable yield of the product indicating that
electronic factors do not play any significant control on the
reaction. To examine the fesibility of the solid phase synthesis
reaction, a representative reaction was carried out by preparing
the resin immobilized diazonium ion with 4-methoxyaniline
and brought into reaction with piperidine. The results obtained
were encouraging and the procedure generalized by using
diazonium ions prepared from several aromatic amines, immo-
bilizing them unto the cation exchange resin and carrying out
the N-coupling reaction with both piperidine and morpholine
as the substrates.
a
b
c
d
e
3.0
2.5
2.0
1.5
1.0
0.5
0
N-(4-methylphenylazo)morpholine (372.84 nm)
N-(4-chloro-2-nitrophenylazo)morpholine (392.83 nm)
N-(4-nitrophenylazo)morpholine (389.49 nm)
N-(4-methoxyphenylazo)morpholine (375.51 nm)
N-(2-chlorophenylazo)morpholine (327.17 nm)
c
d
a
b
e
300
350
400
450
Wavelength (nm)
500
550
600
Fig. 1. UV-visible spectra of some selected N-arylazopiperidines in 95 %
ethanol
used as an effective technique for the identification of the
triazene derivatives. Further, triazenes are unstable in acids
and this characteristic can be utilized as an analytical method
for the detection of trizenes. In the present study, UV-visible
spectra of an alcoholic solution of the triazenes were recorded
before and after acidification with conc. H2SO4 (Figs. 2 and 3)
and the hypsochromic shift observed in the triazene maxima
confirmed the formation of the trizenes (Table-3).
1.50
a
b
N-(4-methylphenylazo)morpholine (330.42 nm)
N-(4-methylphenylazo)morpholine + Conc. H2SO4
1.25
1.00
0.75
0.50
0.25
0
b
a
N
N
N
300
350
400 450
Wavelength (nm)
500
550
N
H
Cyclohexane
Fig. 2. UV-visible spectra of compound 1e in EtOH before and after treat-
ment with conc. H2SO4
10-15 mins, r.t.
R
N-arylazopiperidine
3.50
3.25
3.00
(1a-1j)
+
P
SO3-N2
O
R
N
a
b
1-(4-Methylphenyl)-3,3-(1-oxa-tetra-
methylene)-triazene (372.84 nm)
Resin Immobilized Diazonium Ions
2.75
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
N
N
b
O
1-(4-Methylphenyl)-3,3-(1-oxa-tetra-
methylene)-triazene + conc. H2SO4
N
H
R
Cyclohexane
15-20 mins, r.t.
N-arylazomorpholine
a
(2a-2i)
Scheme-I: Solid phase synthesis of triazene namely the N-arylazopiperidines
and N-arylazomorpholines using resin immobilized diazonium
ions
UV-visible spectra of triazenes: All the substituted
triazenes show the UV-visible absorption maxima at λmax
=
330-390 nm due to the presence of -N=N- chromophore
(Fig. 1).
300
350
400
450
500
550
Presence of different functional groups like OCH3,
COCH3, NO2, Cl, Br etc. shifts the absorption maxima towards
longer wavelength. Thus, the UV-visible spectroscopy can be
Wavelength (nm)
Fig. 3. UV-visible spectra of compound 2f in EtOH before and after treat-
ment with conc. H2SO4

Vol. 29, No. 5 (2017)
Synthesis of Triazenes of N-Heterocycles Mediated by Resin Immobilized Diazonium Ions 1129
4. B.H.Venger, C. Hansch, G.J. Hatheway andY.U.Amrein, J. Med. Chem.,
22, 473 (1979);
TABLE-3
SHIFT IN THE UV-VISIBLE MAXIMA OF TRIAZENES
ON ACIDIFICATION OF EtOH SOLUTION
https://doi.org/10.1021/jm00191a003.
5. M.L. Gross, D.H. Blank andW.M. Welch, J. Org. Chem., 58, 2104 (1993);
https://doi.org/10.1021/jo00060a028.
S.
No.
λmax
λmax
Triazene
(nm)
(nm)
285
305
320
330
345
370
6. R. Lazny, J. Poplawski, J. Kobberling, D. Enders and S. Bräse, Synlett,
1304 (1999);
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1
2
3
4
5
6
N-(4-Methylphenylazo)piperidine
N-(4-Methoxyphenylazo)piperidine
N-(2-Nitrophenylazo)piperidine
N-(4-Methylphenylazo)morpholine
N-(4-Methoxyphenylazo)morpholine
N-(2-Nitrophenylazo)morpholine
330
361
380
372
375
395
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https://doi.org/10.1016/S0040-4020(01)00495-1.
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Tetrahedron Lett., 45, 2839 (2004);
https://doi.org/10.1016/j.tetlet.2004.02.002.
Conclusion
In conclusion, a solid phase technique have been deve-
loped for the synthesis of triazenes namely N-arylazopiperidine
and N-arylazomorpholine in good yield using resin immo-
bilized diazonium ions. Resin immobilized diazonium ions
are stable and can be isolated and stored, further the diazo
coupling reaction can be carried out in organic solvent which
is not possible in the classical synthesis. The absence of acids
results in high yield of the acid labile triazene. Recovery and
isolation of the products are simple.
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ACKNOWLEDGEMENTS
17. G.A. Smirnov, P.B. Gordeev, S.V. Nikitin, G.V. Pokhvisneva, T.V. Ternikova
and O.A. Lukyanov, Russ. Chem. Bull., 64, 1057 (2015);
https://doi.org/10.1007/s11172-015-0976-5.
The authors are grateful to IIT Gauhati, RSIC NEHU,
Shillong, India for recording the spectra and The Head,
Department of Chemistry, Gauhati University, Guwahati, India
for laboratory facilities.
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Practical Organic Chemistry, Pearson Education, edn 5 (2008).
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Hajipour, Dyes Pigments, 101, 295 (2014);
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