Environmentally safe one-pot solvent-free synthesis of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) catalyzed by NaHSO4-SiO2

Article abstract of DOI:10.1134/S1070428009110220

One-pot condensation of thiourea (urea), diverse aromatic aldehydes, and ammonium acetate in the presence of repeatedly usable heterogeneous catalyst NaHSO₄-SiO₂ in the absence of solvent under the microwave irradiation proceeds fast

Full text of DOI:10.1134/S1070428009110220

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 11, pp. 1707−1713. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © V. Kanagarajan, P. Sureshkumar, J. Thanusu, M. Gopalakrishnan, 2009, published in Zhurnal Organicheskoi Khimii,
2009, Vol. 45, No. 11, pp. 1713−1719.
Environmentally Safe One-Pot Solvent-Free Synthesis
of 6-Aryl-1,2,4,5-tetrazinane-3-thiones(ones) Catalyzed
by NaHSO4-SiO2
V. Kanagarajan, P. Sureshkumar, J. Thanusu, and M. Gopalakrishnan
Synthetic Organic Chemistry Laboratory, Department of Chemistry, Annamalai University
Annamalainagar-608, Tamil Nadu, India
e-mail: profmgk@yahoo.co.in
Received December 14, 2008
Abstract—One-pot condensation of thiourea (urea), diverse aromatic aldehydes, and ammonium acetate in the
presence of repeatedly usable heterogeneous catalyst NaHSO4–SiO2 in the absence of solvent under the microwave
irradiation proceeds faster and with better yields of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) that under common
heating. Compounds synthesized exist as a rule as two isomers distinguished by the position of the phenyl ring:
It is located in the major isomer nearly in the equatorial position, in the minor one, close to axial position.
DOI: 10.1134/S1070428009110220
efficiency in the cancer therapy the 1,2,4,5-tetrazines are
investigated in the National Cancer Institute in USA[11].
These interesting results prompted us to investigate the
reaction described further.
The application of multi-component reactions (MCR)
including domino processes [1] involving at least three
various simple substrates [2] that react in a definite way
to form a single product is a powerful synthetic strategy
[3]. Since the first MCR [4] this well-known concept
[5] widely spread also in the nature has been extensively
employed both in the liquid-phase [3] and in solid-phase
[6] chemistry for quick building of complex heterocyclic
structures important for development of pharmacy [7].
Inasmuch as the formation of an N–N bond is a rela-
tively difficult process the 1,2,4,5-tetrazines are commonly
obtained from hydrazine derivatives or from nitrile imines.
A reaction was described of a number of monohydrazones
of simple aliphatic aldehydes and ketones with thio-
carbohydrazide and 6-alkylhexahydro-1,2,4,5-tetrazine-3-
thiones [12].
Owing to the necessity of the “environmentally safe
technological revolution” [8] a considerable attention is
given to the procedure of microwave irradiation for
ensuring fast synthesis of versatile organic compounds
because of selective absorption of the microwave energy
by polar molecules. The use of heterogeneous catalysts,
in particular, NaHSO4 on SiO2 carrier [9], became
a milestone in various fields of chemistry due to environ-
mental safety combined with good yields and selectivity.
Moreover, NaHSO4–SiO2 is a nontoxic and noncorrosive
substance, and the possibility of repeated use of
NaHSO4–SiO2 in certain processes actually results in
more environmentally friendly synthetic procedures.
In the present study 6-aryl-1,2,4,5-tetrazinane-3-
thiones(ones) Ia–Ih, IIa–IIf were prepared by multi-
component cyclocondensation of 1 mol of thiourea (urea),
1 mol of substituted benzaldehyde, and 2 mol of ammonium
acetate in the presence of hetero-geneous catalyst
NaHSO4–SiO2 in the absence of solvent under the
microwave irradiation or at common heating (Scheme 1).
The reaction was carried out at 80°C and the power
of the microwave radiation of 320 W for 120–180 s or at
heating on an oil bath for 30–70 min at 75°C. On the
completion of the reaction (TLC monitoring) the reaction
mixture was extracted with ethyl acetate, the extract was
concentrated in a vacuum, the residue was purified by
column chromatography using as eluent a mixture
1,2,4,5-Tetrazines are an important class of hetero-
cyclic compounds finding many practically useful
synthetic applications [10]. Nowadays due to their
1707

KANAGARAJAN et al.
Table 1. Comparison of results of synthesis of 6-aryl-1,2,4,5-
1708
Scheme 1.
tetrazinane-3-thiones(ones) Ia–Ih, IIa–IIf under microwave
irradiation (MW, 75–78°C) and at common heating (Δ, 75°C)
X
NH2
X
H2N
O
3
HN2 4NH
.
NH4+
_O
NH4+
HN1 5NH
NaHSO4 SiO2,
MW, 120_180 s
6
_O
+
or Δ,
O
_H2O, _H2
H
O
R
Ià_Ih, IIà_IIf
R
I: X = S, R = H (a), 4-Cl (b), 2-Cl (c), 4-F (d), 4-Me (e),
4-MeO (f), 2-Me (g), 3-PhO (h); II, X = O, R = Ph (a), 4-Cl
(b), 4-F (c), 4-Me (d), 4-MeO (e), 3-NO2 (f).
benzene–ethyl acetate, 2:8. The stoichiometry of the
reaction [the ratio thiourea (urea):NH4OAc:benzaldehyde
1:2:1] also indicated the formation of new 6-aryl-1,2,4,5-
tetrazinane-3-thiones(ones).
In order to detect the possible specific (not only
thermal) effect of the microwave irradiation we also
studied the reaction at an ordinary heating on an oil bath.
Even at a long reaction time under the ordinary heating
the yields were lower than at the microwave activation
(Table 1).
These facts clearly show that the effect of the micro-
wave irradiation is not purely thermal. This behavior is
consistent with the assumed reaction mechanism [13]
shown in Scheme 2. Inasmuch as the reaction proceeds
in a polar environment the specific microwave effects
can be revealed when the transition state is more polar
that the initial state of the reaction. Since the dipole-dipole
electrostatic interactions are more pronounced in the
transition state, its stabilization is higher that that of the
initial state resulting in the decrease in the activation
energy. The polarity of the system in the transition state
increases due to the formation of looser ion pairs that in
the initial state (Scheme 2).
Further we carried out the synthesis of compounds Ia
and IIa varying the power of the microwave radiation
from 80 to 720 W in order to choose the most suitable
power level. The results are shown on the plot in Fig. 1
indicating that the maximum yield is attained at the power
of 320 W.
Fig. 1. Optimization of power level of microwave radiation in
the synthesis of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) Ia
and IIa.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 11 2009

ENVIRONMENTALLY SAFE ONE-POT SOLVENT-FREE SYNTHESIS
1709
Scheme 2.
H
.
NaHSO4 SiO2,
X
X
X
MW
HN
H2N
NH2
NH2
H
H
..
N
O
H
HO
.
CH
NaHSO4 SiO2, MW,
120_180 s,
..
HN
HN
NH3
NH2
OH
_H2
.
NaHSO4 SiO2,
MW
X
HN
HN
NH
NH
H
X
HN
HN
NH
OH
H
X
.
HN
HN
NH
.
H
N
H
..
NH3
X = S, O
We tested the possibility of the repeated application
of NaHSO4–SiO2. The results are shown in Fig. 2. The
catalyst was easily regenerated by washing with ethyl
acetate followed by drying at 110°C for 1 h. Therewith
the catalytic activity was retained in the course of six
runs. However the activity notably decreased after 4 runs
due to the accumulation of organic substances. The
organic substances adsorbed on the solid surface decreas-
ed the number of active sites.Also NaHSO4 was partially
washed out from the SiO2 carrier. The organic substances
can be removed at higher temperature for reactivation
of the catalyst.
(ones) contain characteristic absorption bands of NH
bonds in the region 3400–3100 cm–1, and also bands of
thioamide (C=S) and amide (C=O) bonds at ~1200 and
1680 cm–1.
The composition and structure of 6-aryl-1,2,4,5-
tetrazinane-3-thiones(ones) Ia–Ih, IIa–IIf were proved
by elemental analysis, mass, IR, 1H and 13C NMR spectra
and by 2D NMR spectroscopy with the use of spectra of
homonuclear correlation (HOMOCOR) and hetero-
nuclear single-quantum correlation (HSQC).
Fig. 2. Yield of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) Ia
and IIa at the repeated use of the catalyst NaHSO4–SiO2.
IR spectra of 6-aryl-1,2,4,5-tetrazinane-3-thiones-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 11 2009

KANAGARAJAN et al.
1710
Table 2. Chemical shifts in the 1H and 13C NMR spectra of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) Ia–Ih, IIa–IIfa
a Chemical shifts of the minor isomer are given in parentheses.
major isomer the doublet at 4.96 ppm belongs to the
IR spectra of all compounds lack the band of aldehyde
carbonyl group, and the presence of a weak bands of the
N–N bonds at 1450 cm–1 confirm the formation of 6-
aryl-1,2,4,5-tetrazinane-3-thiones(ones). Besides the
appearance of the phenyl group vibrations, of those
belonging to methine group, and of the overtones
combination also supports the formation of the target
products.
benzyl proton. The triplet signal at 3.90 ppm is due to the
presence of NH protons contiguous to the benzyl atom
C6. The singlet at 8.67 ppm originates from thioimide
protons. The signals of aromatic protons appear in the
region 7.30–7.44 ppm
The spectral pattern of the minor isomer is very similar
to that of the major. This underlies the assignment of
signals of benzyl, amino, and thioimide protons.
1
The H NMR spectrum of 6-phenyl-1,2,4,5-
tetrazinane-3-thione (Ia) (Table 2) shows the presence
of two isomers, major and minor. In the spectrum of the
Besides to prove the assignment of signals of NH
group protons the 1H NMR spectrum was registered after
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 11 2009

ENVIRONMENTALLY SAFE ONE-POT SOLVENT-FREE SYNTHESIS
1711
compounds synthesized the chemical shifts of the carbon
atoms of the phenyl ring are not affected by the conforma-
tion of the tetrazinane ring.
the addition of D2O. The protons with the signals at 3.20,
3.90, 8.46, and 8.67 ppm exchanged with D2O.
In order to confirm the signals assignment we
registered the HOMOCOR spectrum of thione Ia. The
signal at 4.96 ppm gave cross-peaks with the signals at
3.90 and 8.67 ppm. The cross-peak at 3.90 ppm belongs
to two protons.
The signals of the minor isomer are observed at 68.8
and 177.6 ppm. The spectral pattern of this isomer is
nearly identical to that of the major isomer. Therefore
these signals were assigned to the benzyl and thioamide
carbonyl carbon atoms.
The existence of two thione isomers originates from
the difference of their conformations in the solution. In
contrast to carbocyclic six-membered systems the
tetrazines containing four nitrogen atoms evidently do not
exist in the chair conformation due to the interaction
between the four unshared electron pairs. In these
conformations the phenyl group is located in positions
close to axial or equatorial.
The 1H NMR spectrum of 6-phenyl-1,2,4,5-tetrazinan-
3-one (IIa) (Table 2) revealed the presence of two
isomers, major and minor. In the spectrum of the major
isomer the doublet at 5.39 ppm was assigned to the benzyl
proton. The triplet at 2.77 ppm belongs to NH protons
adjacent to the benzyl carbon atom. The singlet at
6.82 ppm was assigned to imide protons, aromatic protons
appeared in the region 7.31–7.58 ppm. The signals of the
minor isomer were observed at 4.99, 3.68, and 7.01 ppm.
The spectral pattern of this isomer is nearly identical to
that of the major isomer. Therefore the observed signals
were assigned to the benzyl, imino, and imido protons.
A spectrum was also registered under the conditions of
exchange with D2O to prove the positions of NH protons
signals. The proton signals at 2.77, 3.68, 6.82, and
7.01 ppm disappeared as a result of the exchange with
D2O.
The quadrupole moment of the nitrogen atom hampers
the calculation of the coupling constants between the
protons linked to the nitrogen. It was only possible to
measure the coupling constant between the protons NH
and H6, therefore we expected to obtain either a triplet
or a doublet of doublets from H6 protons. However in
1
the H NMR spectrum of thione Ia we observed only
two separate doublets at 4.96 and 5.42 ppm with the
spin-spin coupling constants 8.56 and 10.72 Hz
respectively. It clearly indicates that protons H1,5 are
coupled with H6 protons. If the phenyl group is oriented
nearly equatorially then the signal of H5 proton should be
split due to the coupling with H6, but the proton H1 cannot
couple with it since the dihedral angle is close to 90 deg.
In the isomer with the phenyl group in the nearly axial
position the signal of H5 proton is not split by the coupling
with H6, but the proton H1 couples with the latter. The
described analysis of the spectra indicates the presence
of two isomers. In the main isomer the phenyl ring is
oriented nearly equatorially, and the isomer with the phenyl
ring in the position close to axial is the minor one.
The 13C NMR spectrum of 6-phenyl-1,2,4,5-
tetrazinan-3-one (IIa) (Table 2) also indicated the
presence of two isomers, major and minor. In the spectrum
of the major isomer the signals of the benzyl carbon atom
are observed at 68.7 ppm. The signal at 156.2 ppm is due
to the presence of the amide carbonyl carbon atom.
ipso-Carbon gives rise to a signal at 140.4 ppm, the
other aromatic carbon atoms appear in the region 127.4–
128.3 ppm. The signals of the minor isomer were
observed at 64.54 and 155.1 ppm. The spectral pattern
of this isomer is nearly identical to that of the major
isomer. Therefore the observed signals were assigned to
the benzyl and amide carbonyl carbon atoms.
1
In the H NMR spectra of the other 6-aryl-1,2,4,5-
tetrazinane-3-thiones Ib–Ih (Table 2) also two sets of
signals were observed of a high and a low intensity
(except for the aromatic protons).
To prove the validity of the assignment of signals we
registered the HSQC spectrum of compound IIa. The
signals at 5.39 and 4.99 ppm have cross-peaks at 68.7
and 64.5 ppm.
The 13C NMR spectrum of 6-phenyl-1,2,4,5-
tetrazinane-3-thione (Ia) (Table 2) confirms the presence
of two isomers, major and minor. In the spectrum of the
major isomer the signal at 64.9 ppm belongs to the benzyl
carbon atom, at 176.0 ppm, to the carbonyl carbon of the
thioamide group. ipso-Carbon gives rise to a signal at
140.1 ppm, the other aromatic carbon atoms appear in
the region 126.9–128.5 ppm. In the spectra of all
1
Therefore as show the H and 13C NMR spectra of
6-phenyl-1,2,4,5-tetrazinan-3-ones IIa-–IIf here the same
relationships are observed as in thiones Ia–Ih: The
compounds as a rule exist as two isomers distinguished
by the position of the phenyl ring. In the major isomer it
is located close to the equatoirial position, in the minor,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 11 2009

KANAGARAJAN et al.
1712
close to the axial position.
6-Phenyl-1,2,4,5-tetrazinane-3-thione (Ia), mp
187–188°C. IR spectrum, ν, cm–1: 3398, 3211, 3162, 3033,
2896, 1521, 1450, 1178, 700. Found, %: C 49.52; H 5.13;
N 28.86. M+ 195. C8H10N4S. Calculated, %: C 49.48;
H 5.15; N 28.86. M 194.25.
Hence we showed for the first time that NaHSO4–
SiO2 in the absence of solvent can efficiently catalyze
the one-pot condensation of thiourea (urea), substituted
benzaldehyde, and ammonium acetate under the
microwave irradiation and at common heating, leading
under mild conditions to the formation of new 6-aryl-
1,2,4,5-tetrazinane-3-thiones(ones) in an environmentally
safe process. We carry on the study in this direction.
6-(4-Chlorophenyl)-1,2,4,5-tetrazinane-3-thione
(Ib), mp 170–172°C. IR spectrum, ν, cm–1: 3388, 3228,
3180, 3054, 2967, 1593, 1489, 1166, 821. Found, %:
C 42.03; H 3.95; N 24.51. M+ 229. C8H9ClN4S.
Calculated, %: C 42.01; H 3.97; N 24.50. M 228.70.
6-(2-Chlorophenyl)-1,2,4,5-tetrazinane-3-thione
(Ic), mp 158–160°C. IR spectrum, ν, cm–1: 3368, 3240,
3186, 3058, 2968, 1588, 1480, 818. Found: M+ 229.
C8H9ClN4S. Calculated: M 228.70.
EXPERIMENTAL
The reaction progress was monitored and the purity
of compounds was checked by TLC on silica gel plates
Sigma-Aldrich, layer thickness 250 μm, eluent benzene–
EtOAc, 2:8. All melting points were measured in open
capillaries and reported uncorrected. IR spectra have
been recorded on a spectrophotometer Nicolet-Avatar
360 FT-IR from pellets with KBr; only significant
frequency values are reported.
1H and 13C NMR spectra were registered on a
spectrometer Bruker AMX 400 (400 and 100 ΜHz
respectively) in DMSO-d6. The spectrum of homonuclear
correlation (HOMOCOR) and the spectrum of
heteronuclear single-quantum correlation (HSQC) were
measured on a spectrometer Bruker DRX 500 using the
standard parameters. Mass spectra ESI+ve were obtained
on a Bruker Daltonic LC-MS instrument. Satisfactory
microanalyses were obtained on a CHN-analyzed Carlo
Erba 1106. The microwave irradiation was performed
using a domestic microwave oven with a rotating disk
(LG, MG-395 WA, 760 W).
6-(4-Fluorophenyl)-1,2,4,5-tetrazinane-3-thione
(Id), mp 170–172°C. IR spectrum, ν, cm–1: 3380, 3245,
3199, 3067, 2920, 1541, 1450, 1178, 779. Found, %:
C 45.29; H 4.25; N 26.41. M+ 212. C8H9FN4S.
Calculated, %: C 45.27; H 4.27; N 26.40. M 212.24.
6-(4-Tolyl)-1,2,4,5-tetrazinane-3-thione (Ie), mp
146–148°C. IR spectrum, ν, cm–1: 3368, 3198, 3166, 3065,
2920, 1538, 1460, 1175, 768. Found, %: C 51.92; H 5.79;
N 26.92. M+ 209. C9H12N4S. Calculated, %: C 51.90;
H 5.81; N 26.90. M 208.28.
6-(4-Methoxyphenyl)-1,2,4,5-tetrazinane-3-
thione (If), mp 170–174°C. IR spectrum, ν, cm–1: 3316,
3211, 3168, 3071, 2933, 1510, 1463, 1174, 835. Found, %:
C 48.19; H 5.37; N 24.96. M+ 225. C9H12N4OS.
Calculated, %: C 48.20; H 5.39; N 24.96. M 224.28.
6-(2-Tolyl)-1,2,4,5-tetrazinane-3-thione (Ig), mp
160–164°C. IR spectrum, ν, cm–1: 3320, 3216, 3153, 3065,
2920, 1538, 1463, 1175, 760. Found: M+ 209. C9H12N4S.
Calculated: M 208.28.
6-Aryl-1,2,4,5-tetrazinane-3-thiones(ones). a.
A mixture of 10 mmol of thiourea (urea), 10 mmol of
substituted benzaldehyde, 20 mmol of ammonium acetate,
and 100 mg NaHSO4–SiO2 was placed in a bath filled
with alumina, the mixture was thoroughly stirred with
a glass rod for 19 s, then it was subjected to microwave
irradiation at the power 320W for an interval indicated in
Table 1 (TLC monitoring). On the completion of the
reaction the reaction mixture was extracted with ethyl
acetate (3 × 5 ml). The catalyst was filtered off and used
repeatedly. The combined extracts were evaporated in
a vacuum, the residue was purified by column chromato-
graphy, eluent benzene–ethyl acetate, 2:8.
6-(3-Phenoxyphenyl)-1,2,4,5-tetrazinane-3-
thione (Ih), mp 148–150°C. IR spectrum, ν, cm–1: 3407,
3171, 3039, 2902, 1543, 1450, 1248, 783. Found, %:
C 58.70; H 4.92; N 19.55. M+ 287. C14H14N4OS.
Calculated, %: C 58.72; H 4.93; N 19.57. M 286.35.
6-Phenyl-1,2,4,5-tetrazinan-3-one (IIa), mp 192–
194°C. IR spectrum, ν, cm–1: 3398, 3211, 3162, 3033,
2896, 1521, 1450, 1178, 700. Found, %: C 53.95; H 5.60;
N 31.50. M+ 179. C8H10N4O. Calculated, %: C 53.93;
H 5.61; N 31.46. M 178.19.
6-(4-Chlorophenyl)-1,2,4,5-tetrazinan-3-one (IIb),
mp 180–181°C. IR spectrum, ν, cm–1: 3388, 3228, 3180,
3054, 2967, 1593, 1489, 1166, 821. Found, %: C 45.16;
H 4.24; N 16.65. M+ 213. C8H9ClN4O. Calculated, %:
C 45.16; H 4.27; N 16.67. M 212.64.
b. The flask with a mixture of reagents was placed in
an oil bath and heated at 75°C for the time indicated in
Table 1, the workup was performed as described in a.
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ENVIRONMENTALLY SAFE ONE-POT SOLVENT-FREE SYNTHESIS
1713
3. Orru, R.V.A. and de Greef, M., Synthesis, 2003, p. 1471.
6-(4-Fluorophenyl)-1,2,4,5-tetrazinan-3-one
(IIc), mp 150–152°C. IR spectrum, ν, cm–1: 3368, 3240,
3186, 3058, 2968, 1588, 1480, 818. Found: M+ 197.
C8H9FN4O. Calculated: M 196.18.
4. Strecker, A., Lieb. Ann. 1850, vol. 75, p. 27.
5. Posner, G.H., Chem. Rev., 1986, vol. 86, p. 83.
6. Dax, S.L., McNally, J.J., andYoungman, M.A., Curr. Med.
Chem., 1999, vol. 6, p. 255.
6-(4-Tolyl)-1,2,4,5-tetrazinan-3-one (IId), mp 176–
178°C. IR spectrum, ν, cm–1: 3380, 3245, 3199, 3067,
2920, 1541, 1450, 1178, 779. Found, %: C 56.28; H 6.22;
N 29.19. M+ 193. C9H12N4O. Calculated, %: C 56.25;
H 6.25; N 29.16. M 192.22.
7. Nefzi, A., Ostresh, J.M., and Houghten, R.A., Chem. Rev.,
1997, vol. 97, p. 449.
8. Gopalakrishnan, M., Sureshkumar, P., Kanagarajan, V.,
Thanusu, J., and Govindaraju, R. Arkivoc., 2006, vol. 13,
p. 130; Gopalakrishnan, M., Sureshkumar, P., Kanagara-
jan, V., Thanusu, J., Govindaraju, R., and Ezhilarasi, M.R.,
Lett. Org. Chem., 2006, vol. 3, p. 484; Gopalakrishnan, M.,
Sureshkumar, P., Kanagarajan, V., and Thanusu, J., Catal.
Commun., 2005, vol. 6, p. 753; Gopalakrishnan, M.,
Sureshkumar, P., Kanagarajan, V., and Thanusu, J., Lett.
Org. Chem., 2005, vol. 2, p. 444.
6-(4-Methoxy)-1,2,4,5-tetrazinan-3-one (IIe), mp
160–162°C. IR spectrum, ν, cm–1: 3368, 3198, 3166, 3065,
2920, 1538, 1460, 1175, 768. Found, %: C 51.95; H 5.26;
N 26.95. M+ 209. C9H12N4S. Calculated, %: C 51.92;
H 5.28; N 26.92. M 208.22.
9. Gopalakrishnan, M., Sureshkumar, P., Kanagarajan, V.,
Thanusu, J., and Govindaraju, R. J. Chem. Res., 2005,
p. 299; Das, N.B., Ravin-dranath, N., Venkataiah, B., and
Madhusudhan, P., J. Chem. Res., 2000, p. 482; Das, N.B.
and Banerjee, J., Chem. Lett., 2004, vol. 8, p. 960.
10. Neunhoeffer, H., Comp. Heterocycl. Chem., 1984, vol. 3,
p. 531.
6-(3-Nitrophenyl)-1,2,4,5-tetrazinan-3-one (IIf),
mp 188–190°C. IR spectrum, ν, cm–1: 3316, 3211, 3168,
3071, 2933, 1510, 1463, 1174, 835. Found, %: C 43.01;
H 4.04; N 31.35. M+ 224. C8H9N5O3. Calculated, %:
C 43.05; H 4.06; N 31.38. M 223.19.
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