Synthesis of novel tri-arm star shaped 1,3,5-triazine hydrazones from 2,4,6-tris(4-acetylphenoxy)-1,3,5-triazine Core

Article abstract of DOI:10.2174/157017812799304051

A series of novel symmetric triazine hydrazones [N₃C ₃(-OC₆H₄-p-C(CH₃)=N-NH-C(O)-C ₆H₄-p-X)₃] (X = H, Br, Cl, F, OH, OCH ₃, CH₃, NO₂, NH₂) were prepared in excellent yields by a three-fold condensation reaction of 2,4,6-tris(4- acetylphenoxy)-1,3,5-triazine with p-substituted benzoic acid hydrazides [NH₂-NH-C(O)-C₆H₄-p-X]. The structures were confirmed by FT-IR, ¹H, ¹³C, 2D-HMQC NMR and mass spectrometry (MALDI-TOF).

Full text of DOI:10.2174/157017812799304051

Letters in Organic Chemistry, 2012, 9, 29-34
29
Synthesis of Novel Tri-Arm Star Shaped 1,3,5-triazine Hydrazones from
2,4,6-tris(4-acetylphenoxy)-1,3,5-triazine Core
Shrinath S. Machakanura, Basavaraj R. Patila, Dayananda S. Badigera, Aishakhanam H. Pathana,
Kalagouda B. Gudasi*,a and Sim W.A. Blighb
aDepartment of Chemistry, Karnatak University, Pavate Nagar, Dharwad, Karnataka 580003, India
bInstitute for Health Research and Policy, London Metropolitan University, Holloway Road, London N7 8DB, UK
Received July 05, 2011: Revised November 04, 2011: Accepted November 04, 2011
Abstract: A series of novel symmetric triazine hydrazones [N3C3(-OC6H4-p-C(CH3)=N-NH-C(O)-C6H4-p-X)3] (X = H,
Br, Cl, F, OH, OCH3, CH3, NO2, NH2) were prepared in excellent yields by a three-fold condensation reaction of 2,4,6-
tris(4-acetylphenoxy)-1,3,5-triazine with p-substituted benzoic acid hydrazides [NH2-NH-C(O)-C6H4-p-X]. The structures
were confirmed by FT-IR, 1H, 13C, 2D-HMQC NMR and mass spectrometry (MALDI-TOF).
Keywords: Cyanuric chloride, hydrazone, triazine, 2,4,6-tris(4-acetylphenoxy)-1,3,5-triazine.
INTRODUCTION
s-triazine AB2 type monomer structural units are utilized in
the synthesis of hyperbranched polymers [10, 11].
1,3,5-Triazine derivatives have been known for a long
period of time and still continue to be the object of
considerable interest. One unique aspect of triazine
chemistry is the ability to control the degree of substitution
on the triazine ring [1]. The most efficient route for selective
substitution of the s-triazine ring utilizes temperature
Though the synthesis of 2,4,6-tris(4-acetylphenoxy)-
1,3,5-triazine (TAPT) is reported [12], the reactivity of its
peripheral functional groups is not explored. We are
interested in the studies of three reactive ketone groups of
2,4,6-tris(4-acetylphenoxy)-1,3,5-triazine (TAPT) for the
formation of schiff bases and hydrazones which can later be
used for biological applications.
controlled nucleophilic aromatic substitution of
a
trihalotriazine. In the synthesis of numerous compounds
bearing the s-triazine core, 2,4,6-trichloro-1,3,5-triazine
(cyanuric chloride) has been largely used as the starting
material. The ease of displacement of chlorine atoms in
cyanuric chloride by various nucleophiles enhances the
utility of this low cost, readily available reagent for the
preparation of mono, di and trisubstituted 1,3,5-triazines
under controlled temperature [2, 3].
Hydrazones are of wide interest because of their diverse
therapeutic and clinical applications. The biological activity
associated with these compounds was attributed to the
presence of the (–CONHN=CH–) moiety [13, 14].
Hydrazones are versatile ligands and their metal complexes
have gained importance due to their biological activities and
application in materials research [15, 16]. Acid-sensitive
hydrazone linkers are used in the controlled release of drugs
from drug-conjugates [17]. Here we present the synthesis
The s-triazine scaffold provides the basis for the design
of biologically relevant molecules with widespread
application as therapeutics and herbicides [4]. Numerous
1,3,5-triazine containing compounds are recognized to be
powerful chelating agents and have been used for the
preparation of metal complexes [5] and liquid crystals [6]. s-
Triazine derivatives have been employed in combinatorial
and supramolecular chemistry [7]. s-Triazine derivatives
have been successfully utilized as reagents in the conversion
of functional groups [8]. More recently, triazine derivatives
are involved in new developments in the field of dendrimers
[9].
and characterization of
a
series of s-1,3,5-triazine
hydrazones, by the three-fold condensation of TAPT with p-
substituted benzoic acid hydrazides.
RESULTS AND DISCUSSION
The reaction of cyanuric chloride and three equivalent of
4-hydroxyacetophenone in the presence of K2CO3 in acetone
yielded TAPT in first step. The reaction of TAPT with 3
equivalents of benzoic hydrazides (2a–i) in THF for 18-24 h
at refluxing temperature yielded the corresponding tri-
functionalized symmetric 1,3,5-triazine hydrazones 3a-i. The
duration of the reaction for the synthesis of 3e and 3h is
comparatively more, perhaps due to the limited solubility of
4-hydroxybenzoic hydrazide and 4-nitrobenzoic hydrazide in
THF. All products were obtained in high yields. The
formation and structures of 3a-i compounds were confirmed
The reactivity of functional groups on the substituents
attached to the 1,3,5-triazine ring system also have drawn
considerable interest. Recently, the reactivity of peripheral
functional groups on the aryl substituents appended on
*Address correspondence to this author at the Department of Chemistry,
Karnatak University, Pavate Nagar, Dharwad, Karnataka 580003, India; Tel:
+91-836-2215286 (Extn-28); Fax: +91-836-2771275;
1
by FT-IR, H, 13C and 2D-HMQC NMR spectroscopy and
MALDI-TOF mass spectrometry.
E-mail: kbgudasi@gmail.com
1875-6255/12 $58.00+.00
© 2012 Bentham Science Publishers

30 Letters in Organic Chemistry, 2012, Vol. 9, No. 1
Machakanur et al.
CH3
O
O
O
O
N
Cl
HO
H3C
N
N
CH3
N
N
O
O
Cl
N
Cl
(TAPT) 1
O
CH3
X
X
CH3
NH2
HN
H
O
N
N
O
HN
O
N
O
N
H3C
N
N
O
O
X
2a-i
N
CH3
O
NH
2, 3
g
a
c
d
e
i
b
f
h
x
OCH3 CH3
H
Cl
F
OH
NO2 NH2
Br
X
3a-i
Scheme 1.
The appearance of C=N stretching frequencies in the
1580-1607 cm-1 region and disappearance of ketone carbonyl
stretching frequency at 1686 cm-1 observed in the IR spectra
of the core (1) confirms the formation of hydrazones. The N-
H stretching frequency of the amide (-NH-C=O) moiety
gives a broad band at 3226-3258 cm-1. A strong band at
1647-1673 cm-1 is assigned to the amide carbonyl stretching
frequency. The C–O-Ar absorption is observed as a distinct
band at 1363-1374 cm-1 which confirms the involvement of
carbon atom of triazine ring in ether linkage. Furthermore,
C=N stretching of s-triazine ring show another important
band in the region 1560 and 1573 cm-1. Thus, the IR spectral
data provide strong evidences for the formation of the s-
triazine hydrazones.
appearance of a broad singlet accounting for three hydrazide
(-CO-NH-N=C) protons in the downfield region 10.53-11.83
ppm confirms the formation of hydrazones 3a-i. For the
description of NMR spectra, we used the arbitrary
numbering of atoms as in Fig. (1). The resonances due to
twenty four aromatic (H2, H3, H9 and H10) protons appear in
the range 7.30 to 7.97 ppm as four doublets for the new
compounds except for 3a which exhibited one triplet and
three doublets accounting for twenty seven (H2, H3, H9, H10
and H11) protons. The three p-hydroxy (-OH) protons of 3e
resonate as a singlet in the downfield region 10.08 ppm. In
case of 3f and 3g a singlet at 3.84 ppm and 2.38 ppm
accounts for nine protons of p-methoxy (-OCH3) and p-
1
methyl (-CH3) groups respectively. As a representative, H
NMR spectrum of 3b is shown in Fig. (1).
The formation of symmetric s-triazine hydrazones (3a-i),
in solution was confirmed by their NMR spectral data. H
The 13C NMR analysis agreed with the 1H NMR analysis
in demonstrating the architecture of the star shaped
hydrazones. In the 13C NMR spectrum of compound 1, the
ketone group carbonyl carbon atoms are observed at 196.75
ppm and the triazine ring carbon at 172.72 ppm . None of the
13C NMR spectra of compounds 3a-i exhibited any signal
1
NMR spectrum of 1 showed a singlet at 2.56 ppm integrating
for nine protons of ketone methyl groups in addition to the
two doublet peaks at 7.36 and 7.98 ppm for the twelve
aromatic protons. The upfield shift of the ketonic methyl
proton resonance to 2.35-2.40 ppm along with the

Synthesis of Novel Tri-Arm Star Shaped 1,3,5-triazine Hydrazones
Letters in Organic Chemistry, 2012, Vol. 9, No. 1
31
Fig. (1). 1H and 13C NMR spectrum of 3b.
that could be attributed to unreacted carbonyl carbon of
ketone functions. 13C NMR spectra of hydrazones showed
resonances in the range 153.49-154.92 and 14.23-15.38 ppm
due to the carbons (C5) of the azomethine (C=N-N) functions
and methyl group (C6) respectively. The signals in the region
161.92–165.86 ppm are assigned to amide carbonyl (C7).
The triazine ring carbon atoms observed in the range 171.77-
173.02 ppm. As a representative, 13C NMR spectrum of 3b is
shown in Fig. (1).
from C1 carbons are shifted upfield compared to the
corresponding signal at 156.07 ppm in 1. The signals of C2
and C3 were observed in the range 121.25-121.71 and
127.55-131.19 ppm respectively. The p-substituents on the
peripheral phenyl group of the hydrazone arm are
presumably too far to influence resonances of these inner
aromatic ring carbons hence there is not much variation in
their chemical shift values. A representative 2D-HMQC
NMR spectrum of compound 3b is shown in Fig. (2).
The 13C NMR peaks of 3a-i at ꢀ values 152.05-152.45
and 132.61-135.93 ppm did not show any contour in 2D
HMQC NMR spectrum confirming that they are not having
any directly attached hydrogen atoms and the peaks were
assigned to C1 and C4 respectively. The resonances arising
The C8 and C11 are not having any directly bonded
hydrogens. So they do not exhibit contours in 2D-HMQC
NMR spectrum and the chemical shifts of these carbons are
influenced by the substituent at C11 carbon. Resonances in
the range 125.47–129.88 ppm are attributed to C10 carbons.

32 Letters in Organic Chemistry, 2012, Vol. 9, No. 1
Machakanur et al.
Fig. (2). 2D HMQC NMR spectrum of 3b (expanded aromatic region is shown in the box inset).
The C11 carbons show large variation in their resonances
depending upon the inductive and mesomeric effect of the
substituent attached. In case of 3a, carbons (C11) bonded to
hydrogen show resonance at 132.64 while in 3g they are
attached to methyl group and resonates at 141.59 ppm. The
signals due to the C11 attached to bromine (3b), chlorine (3c)
and fluorine (3d) show downfield shift with increasing
electro negativity of halogen substitutions and were observed
at 125.10, 135.76 and 164.91 ppm respectively. The
resonances arising from C11 attached to the methoxy (3g),
nitro (3h), hydroxy (3e) and amino (3i) groups are observed
at 161.85, 148.97, 160.44 and 151.94 ppm respectively.
on
a Gallenkamp melting point apparatus and are
uncorrected.
Solvents were purified by standard methods [18].
Cyanuric chloride (Aldrich) and all other chemicals (sd fine
chemicals, India) were used as received. All compounds
were routinely checked by thin-layer chromatography (TLC)
on aluminum-backed silica gel plates.
General Procedure for the Synthesis of p-Substituted
Benzoic Acid Hydrazides (2a-i)
Methyl benzoates were synthesized from their respective
p-substituted benzoic acids, using excess dry methanol in the
presence of H2SO4. p-Substituted benzoic hydrazides (2a-i)
were prepared by reaction of the corresponding methyl
benzoates (10 mmol) with hydrazine hydrate 99% (50 mmol)
in methanol under reflux for 4-6 h. The excess solvent was
removed under vacuo and the residue was filtered under
suction, washed with water, and dried. The spectral and
analytical data of benzoic hydrazide (2a) [19], 4-
bromobenzoic hydrazide (2b) [20], 4-chlorobenzoic
hydrazide (2c) [21], 4-fluorobenzoic hydrazide (2d) [19], 4-
hydroxybenzoic hydrazide (2e) [22], 4-methoxybenzoic
hydrazide (2f) [23], 4-methylbenzoic hydrazide (2g) [21], 4-
nitrobenzoic hydrazide (2h) [21] and 4-aminobenzoic
hydrazide (2i) [21] are in good agreement with literature
values.
The single molecular nature of the hydrazones 3a-i was
also checked by MALDI-TOF mass spectrometry, which
confirmed the expected chemical structures with m/z values
corresponding to (M+Na)+ ion. MALDI-TOF mass
spectrograph of 3b is given as a representative in Fig. (3).
EXPERIMENTAL
Materials and Measurements
The 1H and 13C NMR spectra were recorded in DMSO-d6
solvent on BRUKER-500 MHz High Resolution
Multinuclear FT-NMR Spectrometer at room temperature.
1
The H and 13C NMR chemical shifts were measured using
SiMe4 as an internal standard at ꢀ=0 ppm. IR spectra were
recorded in KBr matrix using an Impact-410 Nicolet (USA)
FT-IR spectrometer in 4000–400 cm–1 range. The MALDI-
TOF mass spectrum was measured with a Voyager-DE STR
spectrometer with ꢁ-cyano-4-hydroxycinnamic acid as the
matrix. Melting points were determined in an open capillary
Synthesis of Tris(4-acetylphenoxy)triazine (TAPT) (1)
A
mixture of 2,4,6-trichloro-1,3,5-triazine (0.018g,
0.1mmol), 4-hydroxyacetophenone (0.042g, 0.31mmol) and
K2CO3 (0.042g, 0.31mmol) in acetone was stirred under

Synthesis of Novel Tri-Arm Star Shaped 1,3,5-triazine Hydrazones
Letters in Organic Chemistry, 2012, Vol. 9, No. 1
33
Fig. (3). MALDI-TOF Mass spectrum of 3b.
reflux for 18 h. The solvent was removed by evaporation
under reduced pressure. The residue was dissolved in ethyl
acetate and washed with 5% NaOH. Solid product was
obtained after the removal of solvent under vacuo.
Remaining compounds experimental data is given as a
supplementary material.
CONCLUSION
Yield: 94%; IR (KBr): 3064 (C-HAr), 1686 (C=O), 1569
(C=NTriazine), 1380 (C-O-Ar) cm-1; 1H NMR (500 MHz,
CDCl3): ꢀ = 2.56 (s, 9H, CH3), 7.36 (d, 6H, C2H). 7.98 (d,
6H, C3H) ppm; 13C NMR (DMSO-d6): ꢀ = 26.66 (C6),
121.68 (C2), 129.87 (C3), 134.62 (C4), 154.70 (C1), 172.72
(CT), 196.75 (C=O) ppm.
Recently we have published the synthesis of hexa-arm
star shaped hydrazones [24]. Using the similar strategy the
preparation of tri-arm star shaped molecules bearing
hydrazone functions is reported in this work. The starting
material 2,4,6-Tris(4-acetylphenoxy)-1,3,5-triazine (TAPT)
was prepared by the reaction of cyanuric chloride and three
equivalents of 4-hydroxyacetophenone. The reactive
terminal ketone groups on the side substituents of TAPT (1)
could be readily elaborated to the trifunctionalized
hydrazones by condensation with the benzoic hydrazides.
The structures of the new tri-arm star shaped s-triazine
hydrazones were identified by FT-IR, 1H, 13C and 2D-
General Procedure for the Synthesis of Triazine
Hydrazone
[N3C3(-OC6H4-p-C(CH3)=N-NH-C(O)-C6H4-p-X)3]
[X=H (3a); Br (3b); Cl (3c); F (3d); OH (3e); OCH3 (3f);
CH3 (3g); NO2 (3h); NH2 (3i)].
HMQC
NMR
spectroscopy.
MALDI-TOF
mass
spectrometry also confirmed the expected chemical
structures.
TAPT (1) (0.115 g, 0.24 mmol) was added to a solution
of benzoic hydrazide (0.108 g, 0.8 mmol) in tetrahydrofuran
(75 mL) and the reaction mixture was stirred under reflux for
18-24 h. The solvent was removed by evaporation under
reduced pressure. The residue was filtered under suction and
washed several times with hot tetrahydrofuran. The resulting
solid (3a) was dried in vacuo at 40°C for 4 h. The same
general procedure was followed for the compounds 3b-i.
These new symmetric triazines hydrazones serve as
synthetic and structural models for the reactions and
molecular structure of the analogous dendrimeric triazines.
Efforts on the synthesis and characterization of higher
generation 1,3,5-triazine hydrazones are in progress and will
be reported in future communications.
Representative Experimental Data of 3b Compound
ACKNOWLEDGEMENTS
2,4,6-tris[4-{(E)-[2'(4-bromophenylcarbonyl)hydrazinyli-
dene]1-methylmethyl}phenoxy]-1,3,5-triazine (3b)
The authors thank the NMR Research Center, Indian
Institute of Science, Bangalore, for NMR facility. Fellowship
for S. S. Machakanur and B. R. Patil by the University
Grants Commission under Research Fellowship in Sciences
for Meritorious Students (UGC-RFSMS) is gratefully
acknowledged. K. B. Gudasi is thankful to the Association of
Commonwealth Universities, for Commonwealth fellowship.
Yield: 94% ; M.p: 265-269 °C; IR (KBr): 3236 (N-H),
1650 (C=O), 1580 (C=N), 1551 (C=NTriazine), 1371 (C-O-Ar)
cm-1; 1H NMR (500 MHz, DMSO-d6): ꢀ = 2.37 (s, 9H, CH3),
7.32 (d, 6H, J = 7.6 Hz, C2H), 7.71 (d, 6H, J = 7.6 Hz, C3H),
7.83 (d, 6H, J = 8.0 Hz, C10H), 7.90 (d, 6H, J = 8.0 Hz, C9H),
10.86 (s, 3H, NH) ppm; 13C NMR (DMSO-d6): ꢀ = 14.55
(C6), 121.33 (C2), 125.10 (C11), 127.63 (C9), 129.90 (C10),
131.19 (C3), 133.00 (C4), 135.73 (C8), 152.17 (C1), 154.92
(C5), 162.89 (C7), 172.89 (CTriazine) ppm; MS (MALDI-TOF)
m/z: 1098.2519 (M+Na)+.
SUPPLEMENTARY MATERIAL
Supplementary material is available on the publishers
Web site along with the published article.

34 Letters in Organic Chemistry, 2012, Vol. 9, No. 1
Machakanur et al.
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