Microwave Assisted Synthesis of Fluorinated Hexahydro 1,3,5-Triazine Derivatives in Aqueous Medium and One Pot Synthesis of 1,2,4-Triazolo(4,3-a)1,3,5-triazines

Article abstract of DOI:10.1081/SCC-120028646

A multi-component condensation of substituted phenylthiourea/urea, aqueous formaldehyde and substituted aromatic/heterocyclic amines lead to 2-thioxohexahydro-1,3,5-triazines (4) in aqueous medium under microwave irradiation in 30-60 sec in quantitative y

Full text of DOI:10.1081/SCC-120028646

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Microwave Assisted Synthesis of Fluorinated
Hexahydro 1,3,5‐Triazine Derivatives in
Aqueous Medium and One Pot Synthesis of
1,2,4‐Triazolo(4,3‐a)1,3,5‐triazines
Anshu Dandia a , Kapil Arya a & Meha Sati a
a Department of Chemistry , University of Rajasthan , Jaipur, 302 0004, India
Published online: 21 Aug 2006.
To cite this article: Anshu Dandia , Kapil Arya & Meha Sati (2004) Microwave Assisted Synthesis of Fluorinated Hexahydro
1,3,5‐Triazine Derivatives in Aqueous Medium and One Pot Synthesis of 1,2,4‐Triazolo(4,3‐a)1,3,5‐triazines, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 34:6, 1141-1155, DOI:
10.1081/SCC-120028646
To link to this article: http://dx.doi.org/10.1081/SCC-120028646
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 6, pp. 1141–1155, 2004
Microwave Assisted Synthesis of
Fluorinated Hexahydro 1,3,5-Triazine
Derivatives in Aqueous Medium
and One Pot Synthesis of
1,2,4-Triazolo(4,3-a)1,3,5-triazines
*
Anshu Dandia, Kapil Arya, and Meha Sati
Department of Chemistry, University of Rajasthan, Jaipur, India
ABSTRACT
A multi-component condensation of substituted phenylthiourea/urea,
aqueous formaldehyde and substituted aromatic/heterocyclic amines lead
to 2-thioxohexahydro-1,3,5-triazines (4) in aqueous medium under
microwave irradiation in 30–60 sec in quantitative yield with reasonable
purity. Further, triazolo[4,3-a]triazines were also prepared by a one-pot
reaction of ‘in situ’ synthesized triazinyl hydrazine (7) with CS2 (9).
Key Words: Fluorinated hexahydro 1,3,5-triazine; Microwave
irradiation; 1,2,4-Triazolo(4,3-a) 1,3,5-triazine.
*
Correspondence: Anshu Dandia, Department of Chemistry, University of Rajasthan,
Jaipur 302 0004, India; E-mail: dranshudandia@eth.net.
1141
DOI: 10.1081/SCC-120028646
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Dandia, Arya, and Sati
1,3,5-Tri-N-substituted hexahydro-2-oxo-1,3,5-triazines (triazones) have
been known for many years in literature.[1–3] Triazones are used for protection
of amino group[4,5] as well as for the synthesis of poly amines,[6a–d] poly
functional amino acids and amino alcohols.[4] Many water soluble triazones
are used as fertilizers,[7] while some have shown potent antitumor,[8] muscle
relaxant properties[9] and are reactive azodyes[10] and substituted triazine
derivatives are patented[11a–f] as herbicides, fungicides and treatment of HIV
infection.
Incorporation of fluorine to different heterocycles is known to affect the
course of the reaction besides, influencing the biological/pharmacological
activity,[12a,b] and more interest has been focused on synthesis of fluorinated
1,3,5-triazines due to wide variety of their uses.[13a–e]
Conventionally, triazones are synthesized (a) by the reaction of phenyl-
isocynate with azomethines in the presence of zinc chloride,[14] (b) by the
reaction of hydrochloride salt of a primary amine with 4-oxo-oxadiazinane,
and (c) by the reaction of primary amines with N,N0-disubstituted ureas and
aqueous formaldehyde with a co-solvent such as toluene/ethanol/ethyl
acetate.[4,5] All these methods suffer from many disadvantages like long
reaction period, low yield, use of strong acids/dehydrating agents or use of
high boiling solvent such as DMF.[3]
Usage of microwave irradiation (MWI) is well known for the synthesis of
variety of compounds[15a,b] along with triazine derivatives[16a,b] wherein
chemical reactions are accelerated because of selective absorption of micro-
waves by polar molecules, but microwave assisted procedures involving the
use of solvents are limited as they give rise to elevated temperatures and
consequently high pressures which can lead to dangerous explosions. In view
of this, more interest has now been focused on dry media synthesis, involving
the coupling of MWI with solid supported reagents. The method provides
unique chemical process with special attribute to enhanced reaction time,
higher yield, greater selectivity and ease of manipulation.[17a–e] But, the above
technique requires an appreciable amount of solvent for adsorption of
reactants and elution of products.
Recently, the use of aqueous media for organic reaction[18] is under
extensive investigation for synthesis and also to exploit hydrophobic
effect.[19a–c] Water has high dielectric constant with a permanent dipole
moment, which allows the coupling between the oscillating electric field and
the molecular tumbling to occur with high efficient heating. Hence, at elevated
temperature it acts as a pseudo-organic solvent and in its use, isolation of
products is also facilitated due to decreased solubility of organic material upon
post reaction cooling.
In continuation to our earlier interest on the environmentally benign
synthesis of biodynamic heterocycles[20a–e] we report herein for the first time

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Synthesis of Fluorinated Hexahydro 1,3,5-Triazine
1143
the facile, one-pot, eco-friendly, multi-component synthesis of a new series of
fluorinated 1,5-diarylhexahydro-2-thioxo-1,3,5-triazines (4); 1,5-diaryl[1,3,5-
triazin]-2-yl hydrazine (7) and 1,5-diaryl[1,3,5-triazin]-2-yl thioaceticacid (8)
in aqueous medium under microwave irradiation (Sch. 1).
In the present studies, under MW irradiation the condensation of
fluorinated/heterocyclic amines (3) with formaldehyde (2) gave imine
formaldehyde co-polymer in the beginning which was reacted with fluorinated
phenyl thioureas to give thioxotriazines (4) in 30–60 sec in 94–98% yield
with reasonable purity, with no need of further crystallization. The process is
general for both the components, e.g. urea/thiourea (aromatic, fluorinated)
and anilines (aromatic, fluorinated, heterocyclic). Thus a number of 1,3,5-
triazines, triazinyl hydrazine/thioaceticacid and 1,2,4, triazolo [4,3-a]-1,3,5-
triazines can be readily obtained by varying the two components.
4 was further reacted with hydrazine hydrate (5) or chloroacetic acid (6)
to give 7 and 8 respectively. When 7 was treated with CS2, a cyclized product
(10) was obtained in quantitative yields. The whole procedure for synthesis of
10 involved a one-pot reaction as the intermediates 4 and 7 were formed in
quantitative yield with reasonable purity (TLC) and were used ‘in situ’ for
further conversion.
For comparative studies some compounds were also synthesized under
thermal conditions (Table 1). Conventional synthesis of 10 require a three step
procedure with prolonged reflux in organic solvents using strong dehydrating
agents/acids, leading to lower yields.
RESULT AND DISCUSSION
1
In the H NMR spectra of triazines (4) the two methylene ring protons
appeared at d 4.32–4.51 ppm (s, 2H, CH2-N-Ph), 4.72–5.20 ppm (s, 2H, CH2-
NH) and multiplet at d 6.57–7.62 ppm for aromatic protons along with a broad
peak at d7.41–7.82 ppm (br, 1H, NH). IR spectra of these compounds revealed
a strong band in the region 1160–1220 cm21 (C55S). The formation of 7 and 8
was confirmed by the IR spectra showing disappearance of C55S band and
appearance of NHNH2 band (3400–3220 cm21) in case of 7, while a sharp
band at 1690–1720 cm21 (.C55O, acidic), and a broad band at 3470–
1
3420 cm21 (OH) in case of 8. The H NMR spectra of 7 showed additional
peaks at d 1.52–1.56 ppm (s, 1H, -NHNH2) and a broad peak at 2.01–
2.06 ppm (br, 2H, 2NHNH2) along with usual signals of CH2-N-Ph, CH2-NH
and Ar-H, while in case of 8, a sharp peak was obtained at d 3.95–3.42 ppm
(s, 2H, 2SCH2) and at 8.45–8.40 ppm (br, 1H, OH). Compounds 10, showed
a characteristic absorption at 3210–3240 cm21 (NH) and 1240–1245
(C55S) cm21 in IR spectra and disappearance of NH2 peak and appearance

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Dandia, Arya, and Sati
Table 1. Comparative study of the synthesis of 4a, 7a, 8a, 10a.
Mode of reaction Temperaturea Time Yieldb
Entry
Medium
D/MW (Power W)
(8C)
(min)
(%)
4a
DMF
D
MW (640)
40
101
720
45 sec.
45 sec.
10
58
96
34
75
58
86
20
60
Aqueous medium
Aqueous medium
Aqueous medium
Aqueous medium
Aqueous medium
Aqueous medium
Ethanol þ Fused
CH3COONa
Neat
D
D
101
101
7a
8a
D
MW (640)
Reflux
102
102
420
1.5
D
D
1.5
420
Reflux
MW (640)
D
D
MW (520)
D
122
122
3
3
85
30
60
85
30
Neat
10a
Anhydrous Pyridine
Neat
Neat
Reflux
122
122
240
3
3
aFinal temperature is measured at the end of microwave irradiation by introducing a
glass thermometer in the reaction mixture in the beaker.
bYield of the isolated products.
1
of a broad peak due to 2NH at d 7.54–7.48 ppm (br, 1H, NH) in HNMR
spectra along with the characteristic signals of CH2-N-Ph, CH2-NH and Ar-H
confirmed the formation of 10. Physical and spectral data of new synthesized
compounds are given in Tables 2 and 3 respectively.
EXPERIMENTAL
Melting points were determined in open glass capillaries and were
uncorrected. IR spectra were recorded on a Perkin-Elmer (Model-577)
infracord spectophotometer using KBr pellets. 1H NMR and 19F NMR spectra
were recorded on Jeol (Model FX-90Q), using CDCl3 as solvent at
1
89.95 MHz. TMS was used as an internal reference for H NMR spectra and
hexafluorobenzene as an external reference for 19F NMR spectra. All
compounds were found homogeneous on TLC in solvent systems like
benzene : ethyl acetate (8 : 2), in case of compound 4, 7, 8 and benzene : ethyl
acetate: Pet ether (7 : 1 : 2) in case of 10. The microwave induced reactions for
the synthesis of 4, 7 and 8 were carried out in unmodified BMO-700T
domestic oven manufactured by BPL multimode Sanyo utilities and

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Synthesis of Fluorinated Hexahydro 1,3,5-Triazine
1145
appliances Ltd. operating at 700 W generating 2450 MHz frequency.
Synthesis of 10 was carried out in a modified microwave oven attached
with reflux condenser and magnetic stirrer fitted at the base of the oven.
1-(2-Trifluoromethylphenyl)-5(2-trifluoromethylphenyl)-2-
thioxo Hexahydro-1,3,5-triazine (4a)
It was prepared by two different methods: (A) Conventional synthesis and
(B) Microwave mediated synthesis.
Conventional Synthesis
An equimolar mixture of 2-trifluromethyl phenyl thiourea 1a (220 mg,
1 mmol), aqueous formaldehyde 2 (2 mL, 5 mmol) and 2-trifluoromethyl
aniline 3a (161 mg, 1 mmol) was stirred at 40–458C (room temperature) for
8 hr in presence of DMF (20 mL). On completion of reaction (TLC), the
reaction mixture was cooled and poured into ice cold water the solid thus
obtained was filtered, washed with water, dried and recrystallized from
ethanol to give the respective product 4a.
Microwave Mediated Synthesis
An equimolar mixture (1 mmol) of 1a and 3a was gently mixed with
excess of 2 (5 mmol). It was then irradiated inside a microwave oven at
640 watts for 30–60 sec to get a white colored solid which was filtered,
washed with water and found to be pure (TLC), with no need of further
crystallization or purification.
1-(2-Trifluoromethylphenyl)-5(2-
trifluoromethylphenyl)[1,3,5-triazin]-2-yl Hydrazine (7a)
Conventional Synthesis
4a (405 mg, 1 mmol) was refluxed with hydrazine hydrate (5) (30–
40 mL) for 6 hr. A crude product appeared on cooling the reaction mixture,
which was filtered, washed with water and recrystallized from ethanol to give
the desired product.

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Dandia, Arya, and Sati

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Synthesis of Fluorinated Hexahydro 1,3,5-Triazine
1147

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1148
Dandia, Arya, and Sati
d
d

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Synthesis of Fluorinated Hexahydro 1,3,5-Triazine
1149

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1150
Dandia, Arya, and Sati
d
d

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Synthesis of Fluorinated Hexahydro 1,3,5-Triazine
1151
Scheme 1.

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1152
Microwave Mediated Synthesis
Dandia, Arya, and Sati
To 4a (synthesized ‘in situ’), hydrazine hydrate (5) (1 mL, 0.005 mole)
was added and irradiated inside microwave oven at 640 watts till the
completion of the reaction (1.5 min). The reaction mixture on cooling gave a
crystalline product 7 with reasonable purity (TLC).
1-(2-Trifluoromethylphenyl)-5(2-
trifluoromethylphenyl)[1,3,5-triazin]-2-yl Thioaceticacid (8a)
Conventional Synthesis
A mixture of 4a (405 mg, 1 mmol), chloroacetic acid (6) (94 mg, 1 mmol)
and fused sodium acetate (1 mmol) in dry ethanol was heated under reflux for
6 hrs. The reaction mixture was cooled to room temperature and the solid thus
separated, was filtered and recrystallized from ethanol to give 8.
Microwave Mediated Synthesis
‘In situ’ synthesized compound 4a was mixed with chloroacetic acid (6)
(94 mg, 0.001 mole) and irradiated inside microwave oven at 640 watts till the
completion of the reaction (3 min). The product was then extracted from
methanol and excess of solvent was evaporated on roto-evaporator to give a
crystalline compound, which was found to be pure (TLC).
The compounds 4b–n, 7b,c and 8b were prepared by following the same
procedure.
1,2,4-Triazolo[4,3-a]-5-thioxo-1(2-trifluoromethylphenyl)-5(2-
trifluoromethylphenyl)-1,3,5-triazine (10a)
Conventional Synthesis
A mixture of 7a (403 mg, 1 mmol) and carbon disulphide 9 (10 mL) in
anhydrous pyridine (30 mL) was refluxed for 4 hr. On cooling the reaction
mixture, crude solid appeared which was filtered, and recrystallized from
DMF to give the desired compound.

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Synthesis of Fluorinated Hexahydro 1,3,5-Triazine
1153
Microwave Mediated Synthesis
In a 100 mL round bottom flask, a neat mixture of 7a (synthesized ‘in
situ’) and carbon disulfide 9 (5 mL) was stirred using rotating magnet and
irradiated with microwaves till the completion of the reaction (3 min) at
520 W. On completion of reaction, white colored needles appeared on cooling
which were filtered and found to be of reasonable purity (TLC) with no need of
further crystallization.
The compounds 10b,c were also prepared on similar lines by following
the same procedure.
ACKNOWLEDGEMENT
Financial assistance from U.G.C. (New Delhi) is gratefully acknowl-
edged. We are also thankful to RSIC, CDRI, Lucknow, for the elemental and
spectral analyses.
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Received in India December 2, 2003

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