Synthesis and characterization of two formyl 2-tetrazenes

Article abstract of DOI:10.1002/asia.201100769

The synthesis of two formyl 2-tetrazenes, namely, (E)-1-formyl-1,4,4- trimethyl-2-tetrazene (2) and (E)-1,4-diformyl-1,4-dimethyl-2-tetrazene (3), by oxidation of (E)-1,1,4,4-tetramethyl-2-tetrazene (1) using potassium permanganate in acetone solution is presented. Compound 3 was also synthesized in an improved yield from the oxidation of 1-formyl-1-methylhydrazine (4 a) using potassium permanganate in acetone. Both compounds 2 and 3 were characterized by analytical (elemental analysis, GC-MS) and spectroscopic methods (¹H, ¹³C, and ¹⁵N NMR spectroscopy, and IR and Raman spectroscopy). In addition, the solid-state structures of the compounds were confirmed by low-temperature X-ray analysis. (Compound 2: triclinic; space group P-1; a=5.997(1) A, b=8.714(1) A, c=13.830(2) A; α=107.35(1)°, β=90.53(1)°, γ=103.33(1)°; V_UC=668.9(2) A³; Z=4; ρ_calc=1.292 cm^-3. Compound 3: monoclinic; space group P2₁/c; a=5.840(2) A, b=7.414(3) A, c=8.061(2) A; β=100.75(3) °; V_UC=342(2) A³; Z=2; ρ_calc=1. 396 g cm^-3.) The vibrational frequencies of compounds 2 and 3 were calculated using the B3LYP method with a 6-311+G(d,p) basis set. We also computed the natural bond orbital (NBO) charges using the rMP2/aug-cc-pVDZ method and the heats of formation were determined on the basis of their electronic energies. Furthermore, the thermal stabilities of these compounds, as well as their sensitivity towards classical stimuli, were also assessed by differential scanning calorimetry and standard BAM tests, respectively. Lastly, the attempted synthesis of (E)-1,2,3,4-tetraformyl-2-tetrazene (6) is also discussed.

Full text of DOI:10.1002/asia.201100769

DOI: 10.1002/asia.201100769
Synthesis and Characterization of Two Formyl 2-Tetrazenes
Henri Delalu and Carlos Mirꢀ Sabatꢁ*[a]
Abstract: The synthesis of two formyl
state structures of the compounds were
confirmed by low-temperature X-ray
analysis. (Compound 2: triclinic; space
1calc =1.396 gcmꢀ3.) The vibrational fre-
quencies of compounds 2 and 3 were
calculated using the B3LYP method
with a 6-311+GACTHNGUTERN(UNG d,p) basis set. We also
2-tetrazenes, namely, (E)-1-formyl-
1,4,4-trimethyl-2-tetrazene (2) and (E)-
1,4-diformyl-1,4-dimethyl-2-tetrazene
(3), by oxidation of (E)-1,1,4,4-tetra-
methyl-2-tetrazene (1) using potassium
permanganate in acetone solution is
presented. Compound 3 was also syn-
thesized in an improved yield from the
oxidation of 1-formyl-1-methylhydra-
zine (4a) using potassium permanga-
nate in acetone. Both compounds 2
and 3 were characterized by analytical
(elemental analysis, GC-MS) and spec-
troscopic methods (1H, 13C, and 15N
NMR spectroscopy, and IR and Raman
spectroscopy). In addition, the solid-
group
8.714(1) ꢀ,
P-1;
a=5.997(1) ꢀ,
c=13.830(2) ꢀ;
b=
a=
computed the natural bond orbital
(NBO) charges using the rMP2/aug-cc-
pVDZ method and the heats of forma-
tion were determined on the basis of
their electronic energies. Furthermore,
the thermal stabilities of these com-
pounds, as well as their sensitivity to-
wards classical stimuli, were also as-
sessed by differential scanning calorim-
etry and standard BAM tests, respec-
tively. Lastly, the attempted synthesis
of (E)-1,2,3,4-tetraformyl-2-tetrazene
(6) is also discussed.
107.35(1)8, b=90.53(1)8, g=103.33(1)8;
1calc =
V
UC =668.9(2) ꢀ3;
Z=4;
1.292 cmꢀ3. Compound 3: monoclinic;
space group P21/c; a=5.840(2) ꢀ, b=
7.414(3) ꢀ,
100.75(3)8;
c=8.061(2) ꢀ;
b=
V
UC =342(2) ꢀ3; Z=2;
Keywords: 2-tetrazenes
·
hydra-
zines NMR spectroscopy
·
·
quantum chemistry · X-ray diffrac-
tion
Introduction
In addition to cyclic energetic materials, open-chain com-
pounds containing catenated nitrogen atoms have also been
reported to have interesting energetic properties. For exam-
ple, Shreeve and co-workers,[5] and later ourselves,[6] report-
ed salts based on the 2,2-dimethyltriazanium cation. The
Klapçtke group recently reported the synthesis of function-
alized 2-tetrazenes.[7–9] These latter compounds have high
thermal stabilities and low temperatures of explosion, along
with respectable detonation parameters. These interesting
energetic properties attracted our attention and prompted
us to consider 2-tetrazenes as attractive candidates for ener-
getic applications.
The study of compounds containing nitrogen-catenated and
highly energetic materials for possible energetic application
has been the main focus of our research over the last few
years.[1–2] Compounds containing catenated N N bonds are
ꢀ
very attractive for use in energetic applications. This attrac-
tion is due to the high average two-electron bond energy as-
sociated with the N N triple bond, which is a unique feature
of these compounds and accounts for their high energy con-
tent.
At present, a lot of attention is focused on azole chemis-
try. In particular, triazole- and tetrazole-based energetic ma-
terials have been the center of attention.[1–4] This focus is
due to the unique properties of these types of compounds.
On one side, they are highly energetic (owing to the nitro-
gen catenation) and, on the other, they are relatively chemi-
cally and thermally stable (owing to their aromaticity).
ꢁ
2-Tetrazenes can be generated by oxidation of the corre-
sponding hydrazine (Scheme 1a)[10] and X-ray crystallo-
graphic analysis should allow to unequivocally identify the
geometry of the double bond. The simplest 2-tetrazene is
ꢀ
ꢀ
H2N N=N NH2, which was synthesized by Wiberg et al.
ꢀ
ꢀ
from the trimethylsilyl derivative (Me3Si)2N N=N N-
(SiMe3)2 by reaction with trifluoroacetic acid at ꢀ788C. The
overall synthesis started with the silylation of hydrazine to
ꢀ
form (Me3Si)2N NH
G
[a] Dr. H. Delalu, Dr. C. M. Sabatꢁ
Laboratoire Hydrazines et Composꢁs ðnergꢁtiques
Polyazotꢁs,
ꢀ
ꢀ
Me3Si N=N SiMe3; final dimerization using SiF4 afforded
(Me3Si)2N N=N NACTHNUTRGNEUNG
(SiMe3)2 (Scheme 1b).[11] Unfortunately,
ꢀ
ꢀ
Universitꢁ Claude Bernard Lyon 1,
Bꢂt. Berthollet, 22 Av. Gaston Berger, F-69622 Villeurbanne,
(France)
Fax : (+33)472431291
E-mail: carlos.miro-sabate@univ-lyon1.fr
ꢀ
ꢀ
H2N N=N NH2 is thermally labile and decomposes explo-
sively even when stored at 08C. Small alkyl chains are
known to stabilize thermally labile materials;[12] however,
the dimethyl derivative MeHN N=N NHMe still remains
an elusive species.[13] On the other hand, the tetramethyl de-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100769.
Chem. Asian J. 2012, 7, 715 – 724
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
715

FULL PAPERS
of potassium permanganate gave (after many attempts)
compound 2 as the major product and only a small amount
of (E)-1,4-diformyl-1,4-dimethyl-2-tetrazene (3) was isolat-
ed. Furthermore, if compound 2 was isolated and treated
with a large excess of potassium permanganate, only a low
yield of compound 3 was obtained. Therefore, an alternative
procedure for the synthesis of compound 3 was sought and
1-formyl-1-methylhydrazine (4a) was synthesized from the
formylation of monomethylhydrazine (MMH) with ethyl
formate in refluxing ethanol. Subsequently, compound 4a
was oxidized with potassium permanganate to give an im-
proved yield of compound 3, following a procedure analo-
gous to that reported by Ronco and Erlenmeyer.[20] Hinman
and Fulton previously studied the reactions of carboxylic
acid esters with methylhydrazine and found that the sym-
metrical isomer was the predominant product;[21] this work
concluded that the yield of the unsymmetrical isomer de-
creases with increasing size of the acyl group. According to
Pedersen,[22] the unsymmetrical isomer should be more fa-
vored in the reactions of esters of formic acid owing to both
steric and inductive effects. However, regardless of using
ethyl formate as the formylating agent, a relatively high
yield of the “symmetrical isomer”, 1-formyl-2-methylhydra-
zine (4b), was formed (see the Experimental Section).
During our investigation, we did not observe further oxi-
dation of compound 3 to form either the triformyl- (5) or
tetraformyl derivatives (6). Asymmetrically substituted 2-
tetrazenes are significantly more-challenging to prepare
than their symmetrical analogues. Because compound 3 did
not readily oxidize into either compounds 5 or 6, we decided
to attempt the synthesis of the more-readily available tetra-
formyl derivative (6); for this synthesis, we envisaged that
1,1-diformyl hydrazine (7) would be a suitable precursor.
Unfortunately, following the procedure of Liu et al.[23] for
the synthesis of compound 7 by the formylation of aqueous
hydrazine with ethyl formate (see Scheme 3) only afforded
monoformylhydrazine (8) and 1,2-diformylhydrazine (9) as
the isolated products.
Scheme 1. a) A general procedure for the synthesis of (Z)- and (E)-2-tet-
razenes, and b) the procedure reported by Wiberg et al. for the synthesis
of (E)-2-tetrazene.
ꢀ
ꢀ
rivative Me2N N=N NMe2 has been reported to be signifi-
cantly more stable.[14–18]
Herein, we report the synthesis, analytical and spectro-
scopic characterization, and solid-state crystal structures of
ꢀ
ꢀ
two formyl derivatives of Me2N N=N NMe2: (E)-1-formyl-
1,4,4-trimethyl-2-tetrazene (2) and (E)-1,4-diformyl-1,4-di-
methyl-2-tetrazene (3), as well as the attempted synthesis of
(E)-1,2,3,4-tetraformyl-2-tetrazene (6).
Results and Discussion
Synthesis
Oxidation of 1,1-dimethylhydrazine (UDMH) with yellow
mercury(II) oxide gave (E)-1,1,4,4-tetramethyl-2-tetrazene
(1)[16] as a pale-yellow liquid (Scheme 2). Although Thun
and McBride reported the preparation of compounds 2 and
3,[19a] these results were difficult to reproduce in our hands
and no physical properties or structural characterization of
the materials was given. The reaction of compound 1 with
one equivalent of potassium permanganate in acetone yield-
ed (E)-1-formyl-1,4,4-trimethyl-2-tetrazene (2). On the
other hand, the reaction of compound 1 with a large excess
Spectroscopic Discussion
Frequency calculations for compounds 2 and 3 are summar-
ized in the Supporting Infor-
mation, Tables 1 and 2, togeth-
er with the experimental IR
and Raman spectroscopic data
and tentative assignments of
the vibration modes. The
Gaussian program predicted 51
vibrations for compound 2 and
48 for compound 3 (only se-
lected frequencies are included
in the Supporting Informa-
tion). As might be expected
from the structural similarities
Scheme 2. Synthesis of formyl 2-tetrazenes 2 and 3: i) HgO (yellow, 6 equiv), 08C, Et2O; ii) KMnO4/CaSO4
(4 equiv), ꢀ708C to RT, acetone; iii) KMnO4 (4 equiv), ꢀ708C to RT, acetone; iv) HCO2Et (1 equiv), reflux,
EtOH; v) KMnO4 (4 equiv), 08C to RT, acetone.
between both compounds, the
vibration modes were also very
716
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ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 715 – 724

Synthesis and Characterization of Two Formyl 2-Tetrazenes
163.23 ppm. The 1H and
13C NMR shifts observed for
the diformyl derivative 3 were
very similar to those recorded
for the N
compound 2: d=3.32 (N-
(CHO)Me) and 8.94 ppm
(CHO) in the 1H NMR spec-
trum and d=27.11 (N-
(CHO)Me) and 163.37 ppm
ACHTUNGTREN(NUNG CHO)Me part of
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(CHO) in the 13C NMR spec-
trum. Figure 1 shows the
15N NMR spectra of com-
pounds 2 and 3. The differen-
ces between the two com-
pounds were slightly more sub-
stantial than in the 1H and
13C NMR spectra. Whereas the
Scheme 3. Attempted synthesis of (E)-1,2,3,4-tetraformyl-2-tetrazene (6): a) formylation (e.g., HCO2Et
(2 equiv), reflux, EtOH); b) oxidation (e.g., KMnO4 (4/6 equiv), 08C to RT, acetone).
similar. Therefore, a joint discussion of the vibration modes
for both compounds is useful. In both materials, the two
most-important vibrations are the C=O and N=N double-
bond stretches. For compound 2, these stretches were exper-
imentally observed at 1663 cmꢀ1 (C=O; by both IR and
Raman spectroscopy) and at 1472/1474 and 1443/1429 cmꢀ1
(N=N; IR/Raman); for compound 3, these stretches were
observed at 1665/1711 cmꢀ1 (C=O; IR/Raman) and 1467/
1502 cmꢀ1 (N=N; IR/Raman). These wavenumbers were in
keeping with the vibrational spectrum of semicarbazidium
5,5’-azobistetrazolate[24] and with the shorter C=O and N=N
distances found experimentally for compound 3 than com-
ꢀ
pound 2 (see discussion on the X-ray data). The C H
stretches appeared in the range 2800–3040 cmꢀ1 for both
ꢀ
materials, with the C4 H stretch having the highest energy.
ꢀ
ꢀ
The C N and N N stretching modes were at higher ener-
gies for compound 3 (1230–1445 cmꢀ1) than compound 2
(1130–1300 cmꢀ1); this observation was in agreement with a
higher degree of delocalization in compound 3, which places
more electron density on these bonds. However, the in-
plane bending modes of the CH3 groups appeared experi-
mentally at lower frequencies for compound 3 (1020–
1030 cmꢀ1) than compound 2 (1025–1100 cmꢀ1). The same
trend applies for the out-of-plane bending modes (2: 580–
740, 3: 570–680 cmꢀ1). Below these wavenumbers, torsion
and in-plane rocking mode dominated the Raman spectra of
the compounds.[25]
Figure 1. 15N NMR spectra of (E)-1-formyl-1,4,4-trimethyl-2-tetrazene (2,
top) and (E)-1,4-diformyl-1,4-dimethyl-2-tetrazene (3, bottom) in CDCl3
(NH3 used as an external reference).
monoformyl derivative (2) showed four different resonances
for the nitrogen atoms of the azo bridge (dN3 =413.0 and
dN2 =358.8 ppm), the NMe2 group (dN4 =125.8 ppm) and the
The 1H and 13C NMR spectra of compound 2 showed
three resonances in each spectra, whereas the symmetry in
derivative 3 accounted for only two signals being observed.
NACTHUNTRGNE(UGN CHO)Me moiety (dN1 =186.2 ppm); in comparison, com-
1
In CDCl3, the H NMR resonances of the hydrogen atoms
pound 3 showed low-field shifts for the resonances of the ni-
trogen atoms of the azo bridge (dN2 =391.7 ppm) and of the
of the methyl groups in compound 2 were very similar: d=
3.05 (NMe2) and 3.19 ppm (N
G
NACHTUNGTRENNUNG
dehyde hydrogen atom appeared at lower field (8.78 ppm).
In the 13C NMR spectrum of compound 2 in CDCl3, the res-
onances of the carbon atoms of the methyl groups were sig-
GC-MS analysis. Compound 2 had a retention time of
22.23 minutes in acetone using method A (17.19 min using
method B),[26] whereas compound 3 had a retention time of
23.52 minutes in the same solvent using method C. In the
nificantly different: d=27.09 (N
ACHTUNGTREN(NUNG CHO)Me) and 40.19 ppm
(NMe2), and the aldehyde signal was observed at d=
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ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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717

H. Delalu and C. M. Sabatꢁ
FULL PAPERS
mass spectrum, the most-intense peak for compound 2 was
ing electron density away from the nitrogen atoms. In keep-
ing with the electron-withdrawing character of the CHO
group, the carbon atom of this latter group (C4) holds a sig-
nificantly less-positive charge (+1.273e) than that of the
carbon atom of the methyl group (C3=+2.034e). Lastly, the
oxygen atoms of both compounds 2 and 3 (O5) have similar
highly negative charges (2: ꢀ0.779e, 3: ꢀ0.750e). It is pre-
cisely these oxygen atoms that are involved in the formation
of nonclassical C···O hydrogen-bonding interactions (see X-
ray analysis below).
at m/z=130.1 (100) followed by the mass of the [HN
ACHTUNGRTEN(NUNG CH3)
A
ACHTUNGTRENNUNG
and 43.2 (48), respectively. Other signals with lower intensi-
+
ties included the loss of molecular nitrogen and a [CH3]
group at m/z=28.2 (28) and 15.2 (12), respectively, and the
+
loss of [N
N
(3), respectively. As expected, compound 3 showed similar
mass fragments: 43.2 (100) [CH2=N
(CH3)], 144.1 (97) [M]+,
59.2 (31) [HN(CH3)(CHO)], 48.2 (28) [N2], 15.2 (21, [CH3]),
and 86.1 (7) [MꢀN
(CH3)2]+.
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
T
The gas-phase geometries of compounds 2 and 3 were cal-
culated using the B3LYP hybrid density functional with the
6-311++GACTHNUTRGNEUNG
(d,p) basis set.[27] The optimized geometries of
X-ray Crystal Structures
the gas-phase structures (B3LYP and MP2) are in very good
agreement with the solid-state X-ray diffraction data, as ex-
pected for compounds that only present weak interactions
in the solid state.
X-ray studies clearly confirmed the trans geometry of
compounds 2 and 3 (Table 1). Figure 4 shows the two crys-
tallographically independent molecules of compound 2 in
the asymmetric unit. The azo-bridge N=N bond distances
(1.260(5) and 1.258(5) ꢀ) in compound 2 were slightly
For the optimized structures of formyl 2-tetrazenes 2 and 3,
we performed a natural bond orbital (NBO) analysis (Gaus-
sian 03W, see the Supporting Information for a description
of the method used). Figures 2 and 3 show the structure of
compounds 2 and 3 with their corresponding computed
NBO charges. In compound 2, the nitrogen atoms of the azo
bridge (N1=ꢀ0.993e and N6=ꢀ0.345e) and the nitrogen
atom of the NMe2 moiety (N7=ꢀ0.390e) all have negative
charges, whereas the nitrogen atom that is closest to the
CHO group holds a positive charge (N2=+0.252e). Similar-
ly, whereas the carbon atoms of the CH3 groups have similar
positive charges (+1.952–+2.006e), the carbon atom of the
CHO fragment is less-positively charged (C4=+1.183e). An
analogous situation is found for the diformyl derivative (3),
where the calculated charges on both sides of the azo bridge
are identical by symmetry. In compound 3, the azo bridge
atoms (N1) bear a highly negative charge (ꢀ0.829e) whereas
Table 1. Crystal structure solution and refinement of formyl 2-tetrazenes
2 and 3 and of formyl hydrazine 8.
2
3
8
CCDC No.[29]
Formula
Mr
824059
C4H10N4O
130.15
824058
C4H8N4O2
144.14
279587
CH4N2O
60.05
T [K]
293(2)
293(2)
293(2)
description
color
plate
colorless
block
colorless
needle
colorless
the nitrogen atoms of the NACTHNURGTNE(UNG CHO)Me moiety (N2) are posi-
crystal size [mm]
crystal system
space group
a [ꢀ]
b [ꢀ]
c [ꢀ]
0.56ꢀ0.21ꢀ0.10 0.21ꢀ0.15ꢀ0.14 0.10ꢀ0.03ꢀ0.02
tively charged (+0.336e), owing to the CHO fragment pull-
Triclinic
P-1
Monoclinic
P21/c
Monoclinic
P21/n
5.997(1)
8.714(1)
13.830(2)
107.35(1)
90.53(1)
103.33(1)
668.9(2)
4
5.840(2)
7.414(3)
8.061(2)
90
100.75(3)
90
3.737(1)
10.609(1)
6.574(1)
90
95.11(1)
90
a [8]
b [8]
g [8]
V [ꢀ3]
342(2)
2
259.60(8)
4
Z
1calc [gcmꢀ3
]
1.292
1.396
1.537
m
G
]
0.815
0.110
1.144
Figure 2. Optimized geometry and charge distribution for (E)-1-formyl-
1,4,4-trimethyl-2-tetrazene (2), as determined by NBO analysis (rMP2/
aug-cc-pVDZ).
F
G
280
152
128
3.35–66.59
ꢀ7ꢂhꢂ7
ꢀ10ꢂkꢂ10
ꢀ16ꢂlꢂ15
4909
3.60–29.20
ꢀ7ꢂhꢂ7
ꢀ9ꢂkꢂ9
ꢀ10ꢂlꢂ10
4763
7.95–65.88
ꢀ4ꢂhꢂ4
ꢀ12ꢂkꢂ11
ꢀ6ꢂlꢂ7
842
index ranges
total reflns
unique reflns
Rint
2315
0.056
853
0.021
454
0.044
data/restraints/pa-
rameters
2315/0/164
853/0/46
454/0/38
R(F)/wR(F2) (all re- 0.0979/0.1887
0.0377/0.0413
0.0606/0.1786
flns)[a]
GOF on F2[a]
1.014
1.050
1.042
D1fin (max/min)
ꢀ0.41/0.58
ꢀ0.15/0.20
ꢀ0.38/0.28
[eꢀꢀ3
]
Figure 3. Optimized geometry and charge distribution for (E)-1,4-diform-
yl-1,4-dimethyl-2-tetrazene (3), as determined by NBO analysis (rMP2/
aug-cc-pVDZ).
2
[a] R1 =Sj jFo jꢀjFc j j/SjFo j ;
Rw =[S
(Fo ꢀFc2)/Sw(Fo)2]1/2
;
w=
2
2
[sc ACHTGNUTRENNUNG
718
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ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 715 – 724

Synthesis and Characterization of Two Formyl 2-Tetrazenes
Figure 6. Molecular structure of compound 3 (ellipsoids set at 50% prob-
ability).
N1i =1.247(2) ꢀ), which had clear double-bond character
Figure 4. View of the asymmetric unit of compound 2 (ellipsoids set at
ꢀ
60% probability).
(N=N double bond=1.245 ꢀ) and one elongated N N bond
ꢀ
(N1 N2=1.377(1) ꢀ), which was shorter than the average
[30]
ꢀ
N N single-bond distance (1.454 ꢀ) and was indicative of
conjugation. This last result was supported by two observa-
longer than the analogous distances in compound 3; these
ꢀ
ꢀ
values fitted well with the expected double-bond character
tions: 1) the shorter N C bond distance of the N C(O)H
ꢀ
ꢀ
ꢀ
of this bond. However, the remaining two N N distances
fragment (N2 C4=1.358(1) ꢀ) compared to the N CH3
ꢀ
ꢀ
ꢀ
were shorter (N6 N7=1.355(5) ꢀ and N15 N16=
fragment (N2 C3=1.452(1) ꢀ), and 2) the planarity of the
ꢀ
1.353(5) ꢀ) and significantly longer (N1 N2=1.416(5) ꢀ
and N10-N11=1.409(4) ꢀ) than the corresponding distance
in compound 3 (1.377(1) ꢀ). The elongation of these latter
molecule.
Compound 3 was involved in two very directional interac-
tions (C-H-O=169.0(1)8 and 175.2(1)8), between the
oxygen atoms of one molecule of compound 3 and the hy-
drogen atoms of a second molecule. The two nonclassical
hydrogen bonds (C4···O5i =3.474(2) ꢀ and C3···O5ii =
3.590(2) ꢀ; symmetry codes: (i) x, 0.5ꢀy, 0.5+z, (ii) 1+x, y,
z) were similar in strength to those found in energetic pic-
rate salts[31] and described different graph-set patterns,[28,29]
such as chain motifs of the type C1,1(X) (X=3, 5, 8),
C1,2(X) (X=6, 9), C2,2(X) (X=8, 11, 13, 16), and one
R2,2(16) ring motif (Figure 7).
ꢀ
N N bonds might be attributed to conjugation with the
formyl group, which, in the case of compound 3, are mutual-
ly cancelled out owing to the symmetry of the molecule.
ꢀ
ꢀ
Note that the N2 C4/N11 C13 distances (1.341(5)/
1.334(5) ꢀ) for compound 2 were shortened with respect to
ꢀ
those of compound 3 (1.358(1) ꢀ), whereas the C4 O5/
ꢀ
C13 O14 distances (1.232(5)/1.222(5) ꢀ) in compound 2
were elongated with respect to compound 3 (1.215(1) ꢀ).
In the unit cell, compound 2 formed planar layers that in-
ꢀ
teracted through weak nonclassical hydrogen bonds (C8
As mentioned above, formylation of hydrazine hydrate re-
sulted in the formation of compounds 8 and 9. The unit cell
for compound 9 matches that previously reported.[32] On the
other hand, the structure of compound 8 has not been de-
scribed previously. Compound 8 crystallized in a monoclinic
O5ii =3.791(6) ꢀ, symmetry code: (i) ꢀx, ꢀy, 1ꢀz), which
(using graph-set nomenclature)[28,29] gave R2,4(12) ring net-
works. The other two nonclassical hydrogen bonds
(C9···O5i =3.477(6) ꢀ and C18···O14i =3.478(6) ꢀ, symme-
try code: (ii) 1+x, 1+y, z) connected molecules of compound
2 together to form C1,1(8) infinite chains (Figure 5). Lastly,
ring graph-sets of the type R2,2(16) and R4,4(32) were also
formed.
cell in the space group P21/n.[33] The C1 O1 bond distance
ꢀ
(1.238(3) ꢀ) was longer than for a typical C=O double bond
ꢀ
and the C1 N1 distance (1.316(3) ꢀ) was shorter than that
In compound 3 (Figure 6), half of the molecule was gener-
ated by symmetry (symmetry code: (i) 1ꢀx, ꢀy, 1ꢀz). The
ꢀ
ꢀ
solid-state structure contained one short N N bond (N1
Figure 5. Extended crystal structure of compound 2, showing intermolec-
ular hydrogen-bonding interactions (dotted lines; C12···O18i =3.478(6) ꢀ;
symmetry code: (i) 1+x, 1+y, z) and the C1,1(8) chain networks.
Figure 7. Close packing in the crystal structure of compound 3, showing
hydrogen-bonding interactions (dotted lines) and the formation of a
R2,2(16) ring pattern.
Chem. Asian J. 2012, 7, 715 – 724
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
719

H. Delalu and C. M. Sabatꢁ
FULL PAPERS
ꢀ
Table 3. Selected bond distances [ꢀ] and angles [8] in the crystal structures of com-
pounds 2 and 3, and comparison with the optimized calculated parameters.[a]
of a typical C N single bond, thereby indicating
the amide character of the C(=O)N moiety. On
2 (A)
2 (B)
B3LYP[b] MP2[c]
3
B3LYP[b] MP2[c]
ꢀ
the other hand, the N1 N2 distance of the hydra-
zine moiety (1.413(3) ꢀ) was shorter than that of
H2N NH2 (1.449 ꢀ) and slightly elongated com-
ꢀ
N1 N2
1.416(5) 1.409(4) 1.380
1.260(5) 1.258(5) 1.252
1.447(5) 1.463(5) 1.456
1.341(5) 1.334(5) 1.375
1.353(5) 1.355(5) 1.354
1.443(5) 1.446(5) 1.456
1.449(5) 1.463(5) 1.457
1.232(5) 1.222(5) 1.213
121.6(3) 121.9(3) 122.5
114.5(3) 114.7(3) 115.0
1.365
1.282
1.458
1.457
1.378
1.453
1.378
1.230
–
1.377(1) 1.366
1.247(1) 1.248
1.452(1) 1.458
1.358(1) 1.385
1.367
1.279
1.454
1.385
–
[d]
[34]
ꢀ
N1 N6
ꢀ
ꢀ
N2 C3
pared to the analogous distance in salts based on
the 3,4,5-triamino-1,2,4-triazolium cation (ca.
1.400 ꢀ).[35] The three hydrogen bonds in the mole-
cule participate in the formation of four medium-
to-strong hydrogen bonds (see Table 2). The hy-
drogen bond between the N1 atom of one mole-
cule and the O1 atom of another (N1···O1iii =
2.860(3) ꢀ; symmetry code: (iii) ꢀ0.5+x, 0.5ꢀy,
0.5+z) represents the shortest non-covalent inter-
action in this compound and results in the forma-
tion of infinite chains along a direction parallel to
the c axis.
ꢀ
N2 C4
ꢀ
N6 N7
–
–
–
–
–
–
ꢀ
N7 C8
–
–
ꢀ
N7 C9
ꢀ
C4 O5
1.215(1) 1.209
122.5(1) 122.7
114.4(1) 114.8
112.0(1) 113.2
1.226
122.6
114.4
111.5
–
123.9
123.0
–
N1-N2-C3
N1-N2-C4
–
N2-N1-N6[d] 110.2(3) 109.9(3) 112.7
111.1
112.9
124.3
122.9
118.0
110.3
115.7
N7-N6-N1
N2-C4-O5
C3-N2-C4
N6-N7-C8
N6-N7-C9
C8-N7-C9
113.2(3) 113.6(3) 114.6
124.2(4) 125.0(4) 124.6
123.9(4) 123.4(3) 122.4
119.3(3) 119.5(3) 119.6
113.7(3) 113.1(3) 112.6
119.2(3) 118.6(3) 117.8
–
–
123.8(1) 124.1
122.8(1) 122.5
–
–
–
–
–
–
–
–
Compound 8 crystallizes to form layers that are
hydrogen-bonded to one another (N2···O1i =
3.114(3) ꢀ; symmetry code: (i) 0.5ꢀx, 0.5+y,
0.5ꢀz). The hydrogen-bonding networks found in
[a] For assignment, see Figures 2 and 3; [b] B3LYP/6-31+G
AHCTUNGTRENNUNG
ACHTUNGERTN(NUNG d,p); [c] MP2/6-31++G-
the solid state can be better understood by graph-set analy-
sis.[28,29] The Supporting Information, Table 3, contains a
summary of the graph-set analysis results. At the primary
level, infinite chains of different sizes with the descriptor
C1,1(X) (X=3–5) are formed. At the secondary level, in ad-
dition to infinite chain motifs of the type C1,2(5) and
C2,2(X) (X=6–9), several R2,1(5), R2,4(X) (X=8, 10), and
R4,4(X) (X=12, 16, 18, 20) ring networks are also formed
(Figure 8). For example, the interaction between the NH
Figure 8. View along the c axis in the crystal structure of compound 8,
showing hydrogen-bonding interactions (dotted lines). Selected bond dis-
tances (ꢀ) and angles (8): C1–O1 1.238(3), C1–N1 1.316(3), N1–N2
1.413(3); O1-C1-N1 127.3(2), C1-N1-N2 120.8(2).
and CHO groups of two molecules of compound
8
(N1···O1iii =2.860(3) ꢀ and N1···N2iii =3.187(3) ꢀ; symmetry
code: (iii) ꢀ0.5+x, 0.5ꢀy, 0.5+z) form R2,1(5) graph-sets
and hydrogen bonding of four molecules of compound 8
lead to the formation of R2,4(10) and R4,4(12) motifs.
Lastly, a view of a supercell of the compound along the a-
axis (Figure 9) gives a feeling for the extensive hydrogen
bonding present in the structure of the compound, which in
combination with a layered structure accounts for the rela-
tively high density of the material (1calc =1.537 gcmꢀ3).
Table 2. Geometries of selected hydrogen bonds in the crystal structures
of compounds 2, 3, and 8.
[a]
ꢀ
ꢀ
ꢀ
D H···A
D H [ꢀ]
H···A [ꢀ]
D···A [ꢀ]
D H···A [8]
(E)-1-formyl-1,4,4-trimethyl-2-tetrazene (2)
i
ꢀ
C9 H91···O5
0.950(1)
0.950(1)
2.580(2)
2.570(2)
3.477(4)
3.478(5)
157.2(1)
160.4(1)
i
ꢀ
C18 H181···O14
Figure 9. Hydrogen-bonding interactions (dotted lines) in the 2*2*2
[ꢀ1ꢀ+1] supercell of compound 8 (viewed along the a axis).
(E)-1,4-diformyl-1,4-dimethyl-2-tetrazene (3)
i
ꢀ
C4 H41···O5
0.930(1)
2.550(2)
3.473(2)
169.4(1)
monoformylhydrazine (8)
i
Physical and Chemical Properties
ꢀ
N2 H21···O1
ꢀ
0.865(1)
2.263(2)
2.438(2)
2.098(2)
2.540(3)
3.114(3)
3.175(3)
2.860(3)
3.187(3)
167.5(1)
142.1(1)
151.3(1)
135.0(1)
ii
N2 H22···O1
0.876(2)
0.836(1)
0.836(1)
The thermodynamic data of 2-tetrazenes 2 and 3 (in both
the cis- and trans- forms) were calculated by quantum chem-
ical methods using the computer program Gaussian G03W-
B.03. A full explanation of the method used here can be
found in the Supporting Information.
iii
ꢀ
N1 H11···O1
iii
ꢀ
N1 H12···N2
[a] Symmetry codes for 2: (i) 1+x, 1+y, z. 3: (i) x, 0.5ꢀy, 0.5+z and 8:
(i) 0.5ꢀx, 0.5+y, 0.5ꢀz; (ii) 0.5+x, 0.5ꢀy, 0.5+z; (iii) ꢀ0.5+x, 0.5ꢀy,
0.5+z.
720
www.chemasianj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 715 – 724

Synthesis and Characterization of Two Formyl 2-Tetrazenes
Table 4. Enthalpies (DfH8) and energies of formation (DfU8) of compounds 2 and 3 in the
solid state.
was observed for compound 3 (i=35 J) whereas
compound 2 remained unmodified at i>40 J. By
comparison, these values are significantly lower
than those of commonly used TNT or RDX.[41]
DfH8(g)
[kcalmolꢀ1
DfH8(s)
[kcalmolꢀ1
DfH8(s)
[kJmolꢀ1
Dn[a] DfU8(s)
[kcalmolꢀ1
m
DfU8(s)
[kJkgꢀ1
]
]
]
]
]
[gmolꢀ1
]
trans-2
trans-3
cis-2
+25.6
ꢀ10.2
+40.6
+9.0
+10.9
ꢀ29.9
+26.0
ꢀ10.5
+45.8
ꢀ125.1
+108.7
ꢀ44.2
ꢀ7.5 +15.4
ꢀ7 ꢀ25.7
ꢀ7.5 +30.4
ꢀ7 ꢀ6.4
130.15
144.13
130.15
144.13
+495.0
ꢀ747.7
+978.5
ꢀ186.8
Conclusions
cis-3
[a] Dn=change in the number of moles of gaseous components during the formation of com-
pounds 2 and 3.
Oxidation of 1,1-dimethylhydrazine with yellow
mercury(II) oxide gives (E)-1,1,4,4-tetramethyl-2-
tetrazene (1), which can be further oxidized with
As shown in Table 4, compound 2 is formed endothermi-
cally (DfH8 DfH8(cis-2)=
(trans-2)=++45.8 kJmolꢀ1,
+108.7 kJmolꢀ1) whereas the diformyl derivative (3) is
formed exothermically (DfH8
DfH8
Table 5 contains a summary of some physical and chemi-
cal properties of interest for 2-tetrazenes 2 and 3. The melt-
ing points and thermal stabilities (i.e., decomposition
points) of both materials were assessed by differential scan-
ning calorimetry (DSC). Both compounds 2 and 3 show dis-
potassium permanganate to form (E)-1-formyl-1,4,4-trimeth-
yl-2-tetrazene (2) and (E)-1,4-diformyl-1,4-dimethyl-2-tetra-
zene (3) as highly crystalline solids. No further oxidation to
form the triformyl- (5) or the tetraformyl (6) derivatives was
observed. Direct oxidation of compound 1 to form com-
pound 3 resulted only in low yields and compound 3 was
best synthesized by oxidation of 1-formyl-1-methylhydrazine
(4a) with potassium permanganate. Hydrazine 4a was syn-
thesized by formylation of monomethylhydrazine with ethyl
formate. Formylation of aqueous hydrazine resulted in the
formation of either monoformylhydrazine (8) or 1,2-difor-
mylhydrazine (9). All compounds in this work were charac-
terized by analytical and spectroscopic methods and the
solid-state structures of 2-tetrazenes 2 and 3 and that of
formyl hydrazine 8 were determined by low-temperature X-
ray crystallography. DSC analysis revealed high chemical
and thermal stabilities for compounds 2 and 3 above 1808C
and standard BAM tests showed decreased sensitivities to-
wards impact and friction. The 2-tetrazene derivatives, com-
pounds 2 and 3, may be potentially useful building blocks
for the synthesis of energetic compounds. Preliminary toxici-
ty tests of solid 2-tetrazene derivatives showed lower vapor
pressures in comparison to neutral (liquid) hydrazine (e.g.,
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
Table 5. Physical and chemical properties of 2-tetrazenes 2 and 3.
trans-2
trans-3
formula
Mr
C4H10N4O
130.15
54.0
182.5
43.05
C4H8N4O2
144.13
164.0
201.4
38.87
m.p. [8C][a]
Td [8C][b]
N [%][c]
N+O [%][d]
W [%][e]
55.33
61.07
ꢀ147.5
ꢀ111.0
1 [gcm3][f]
DfU8 [kJkgꢀ1
1.292
1.396
[g]
[h]
]
]
+495
+352
ꢀ747
DfH8 [kJkgꢀ1
ꢀ867
[a] Chemical melting point and [b] decomposition point (DSC onsets)
from measurement with b=58C minꢀ1; [c] Nitrogen percentage; [d] Com-
bined oxygen and nitrogen content; [e] Oxygen balance; [f] Calculated
density (from X-ray measurements); [g] Predicted energy of formation;
[h] Predicted enthalpy of formation.
ꢀ
ꢀ
ꢀ
Me2N NH2) or 2-tetrazene derivatives (e.g., Me2N N=N
NMe2), which suggests the potential of compounds 2 and 3
for the synthesis of energetic compounds with lower toxici-
ties.
tinctive melting points at about 548C and about 1648C for
compounds 2 and 3, respectively (see the Supporting Infor-
mation, Figures 1 and 2). Note, tetramethyl-2-tetrazene 1 is
a pale-yellow liquid with a pungent tetrazene odor that boils
at about 1308C. Both compounds 2 and 3 were obtained as
colorless crystalline solids. Compound 2 is thermally stable
up to about 1828C and can easily be purified by sublima-
tion. On the other hand, the higher-melting diformyl deriva-
tive (3) boils without decomposition at about 1958C. In the
“flame test” (i.e., response to thermal shock) both com-
pounds 2 and 3 burned normally and free of residue.
Experimental Section
Safety Note
2-Tetrazenes and their derivatives are potentially explosive compounds.
Although preliminary testing showed low sensitivity of the compounds
reported herein towards impact and friction, great care must be taken
when operating with 2-tetrazenes, in particular when working on a larger
scale. In any case it is recommended that the synthesis of this type of ma-
terial is to be carried out only by experienced personnel with the best
safety practices and whilst wearing protective equipment such as Kevlar
gloves, earthed shoes, leather coat, face shield, ear plugs, etc. and using
nonconductive equipment.
In addition to DSC analysis, we used standard BAM pro-
cedures[36–40] to assess the sensitivity of compounds 2 and 3
towards impact and friction. Crystalline samples of both
compounds 2 and 3 showed decreased sensitivities towards
impact and friction. Compounds 2 and 3 decomposed non-
explosively in the friction tester at 360 N and 324 N, respec-
tively, and in the drop-hammer, nonexplosive decomposition
Synthesis of (E)-1,1,4,4-Tetramethyl-2-tetrazene (1)
Compound 1 was synthesized according to a literature procedure:[16]
98% 1,1-dimethylhydrazine (89 mL, 1.15 mol) was reacted with yellow
mercury oxide (252.20 g, 1.16 mmol) in Et2O (400 mL) in an ice bath.
Sodium carbonate (ca. 20 g) was added in one portion and the reaction
mixture was stirred for 1 h in the ice bath and then for 4 h at RT. Next,
the insoluble compounds were removed by filtration through Celite and
Chem. Asian J. 2012, 7, 715 – 724
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
721

H. Delalu and C. M. Sabatꢁ
FULL PAPERS
the filtrate was dried with sodium sulfate. The solvent was then removed
under reduced pressure and the bright-yellow crude product was vacuum
distilled to give a pale-yellow liquid (90.57 g, 68%). This compound was
used in the subsequent oxidation reactions. 1H NMR (CDCl3,
400.18 MHz, TMS): d=2.73 ppm (12H, s; CH3).
lized out of the yellow solution upon cooling to room temperature. The
yield was increased by storing the mother liquor in the fridge overnight
(5.68 g, 51% based on compound 4a).
1H NMR (CDCl3, 400.18 MHz, TMS): d=3.32 (6H, s; CH3), 8.94 ppm
(2H, s; CHO); 13C{1H} NMR (CDCl3, 100.52 MHz, TMS): d=27.11 (1C;
N CH3), 163.37 ppm (1C; CHO); 15N NMR (CDCl3, 40.51 MHz, NH3):
ꢀ
d=+391.7 (1N, s; N2), +193.2 ppm (1N, s, N1); DSC (58C minꢀ1): two
endothermic peaks (peak 1: sharp, onset: 164.08C, maximum: 166.08C,
peak 2: broad, onset: 194.88C, maximum: 197.28C), one exothermic peak
(sharp, onset: 201.48C, maximum: 204.28C); GC: 23.52 min (acetone,
method C[26]); GC-MS (ESI): m/z (%): 145.1 (5) [M+H]+, 144.1 (97)
Synthesis of (E)-1-Formyl-1,4,4-trimethyl-2-tetrazene (2)
Compound 2 was synthesized according to a modified literature proce-
dure[19a] as follows: compound 1 (1.16 g, 20.0 mmol) was dissolved in ace-
tone (200 mL) and potassium permanganate (2.12 g, 26.83 mmol) was
added portionwise to form a dark-purple solution. Then, calcium sulfate
(ca. 3 g) was added in one portion. The dark suspension warmed instantly
and manganese(IV) oxide started to precipitate. The reaction mixture
was then stirred at room temperature until the solution turned colorless
(ca. 1 h) and then more potassium permanganate (2.12 g, 26.83 mmol)
was added. The resulting suspension was stirred again until the superna-
tant liquid became colorless (ca. 1 h) and the solution was then filtered
through a plug of Celite. The Celite was then washed with acetone and
the combined acetone filtrates were evaporated to dryness (458C,
200 mbar), leaving behind a pale-yellow liquid. Slow cooling of the liquid
to room temperature resulted in the formation of crystalline compound
3, which was dried for a short time under high vacuum (0.581 g, 45%).
No further purification was necessary. Needlelike single crystals of the
compound were grown by letting the concentrated mother liquor stand at
room temperature for about 3 days. 1H NMR (CDCl3, 400.18 MHz,
TMS): d=3.05 (6H, s; CH3), 3.19 (3H, s; CH3), 8.78 ppm (1H, s; CHO);
[M]+, 87.1 (3) [M+HꢀN
N
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
1418(1), 1395(12), 1377(5), 1348(1), 1229(12), 1128(1), 1064(3), 1026(1),
904(4), 791(1), 418(9), 370(1), 321(3), 291 cmꢀ1 (5); IR (golden gate, rel.
int.): n˜ =3035(w), 2996(w), 2955(w), 2918(w), 1756(w), 1665(m), 1647(m),
1467(m), 1445(w), 1410(w), 1400(w), 1390(w), 1338(s), 1272(w), 1226(m),
1128(w), 1087(w), 1031(s), 1021(s), 851(m), 668(m), 604(w), 573 cmꢀ1 (s);
elemental analysis calcd (%) for C4H8N4O2 (144.13): C 33.33, H 5.59,
N 38.87; found: C 33.21, H 5.69, N 38.67.
Synthesis of 1-Formyl-1-methylhydrazine (4a)
The synthesis of 4a was carried out according to a modified literature
procedure:[23] 98% 1-methylhydrazine (10.5 mL, 9.187 g, 195.44 mmol)
was dissolved in EtOH (15 mL) in a 100 mL round-bottomed flask. To
this solution, 97% ethyl formate (16.0 mL, 14.672 g, 192.11 mmol) was
added portionwise. A highly exothermic reaction took place and the re-
action flask was immersed in an oil bath and heated to reflux for 6 h.
After 6 h, the initial colorless solution had turned bright yellow and the
solvent was removed under reduced pressure (508C). The yellow residue
left in the flask was distilled using a 10 cm length cylinder-filled column
under vacuum (10.692 g, 75%). 1H NMR ([D6]DMSO, 400.18 MHz,
TMS): d=2.86 (3H, s; CH3), 4.11 (2H, br s; NH2), 7.98 ppm (1H, s;
CHO); 13C NMR ([D6]DMSO, 100.52 MHz, TMS): d=36.85 (1C, s;
CH3), 164.32 ppm (1C, s; CHO); DSC (58C minꢀ1):>1708C (dec.), 199–
200 (b.p.); GC: 20.08 min (EtOH, method C[26]); GC-MS (ESI): m/z (%):
75.2 (1) [M+H]+, 74.2 (25) [M]+, 59.2 (3) [MꢀCH3]+, 46.2 (86), 45.2 (100)
[MꢀCHO]+, 44.2 (12), 43.2 (17), 31.2 (24), 30.2 (30) [MꢀCH3ꢀCHO]+,
29.2 (28) [CHO]+, 28.2 (50) [N2], 18.1 (22) [H2O], 17.1 (4), 16.2 (2)
[NH2]+, 15.2 (5) [CH3]+; Raman (rel. int.): n˜ =3216(51), 3004(34), 2924-
13
1
ꢀ
C{ H} NMR (CDCl3, 100.52 MHz, TMS): d=27.09 (1C; N CH3), 40.19
(2C, N CH3), 163.23 ppm (1C; CHO); 15N NMR (CDCl3, 40.51 MHz,
NH3): d=+413.0 (1N, s; N3), +358.8 (1N, s; N2), +186.2 (1N, s; N1),
+125.8 ppm (1N, s; N4); DSC (58C minꢀ1): two endothermic peaks
(peak 1: sharp, onset: 54.08C, maximum: 56.88C; peak 2: broad, onset:
196.28C, maximum: 213.68C), one exothermic peak (sharp, onset:
182.58C, maximum: 186.38C); GC: 22.25 (acetone, method A[26]),
17.19 min (acetone, method B[26]); GC-MS (ESI): m/z (%): 131.1 (7)
[M+H]+, 130.1 (100) [M]+, 101.2 (3) [MꢀCHO]+, 87.1 (15) [M+HꢀN-
ꢀ
G
G
ACHTUGNTRENN(UNG CH3)2], 59.2 (61)
A
R
ACHTUNGTRENNUNG
[CH3]+; MS (ESI-ToF, CHCl3/MeOH): m/z (%): 283.2 (39) [2M+Na]+,
261.2 (41) [2M+H]+, 153.1 (22, [M+Na]+, 131.1 (100) [M+H]+, 130.1 (1)
[M]+; Raman (rel. int.): n˜ =3014(47), 2972(23), 2927(26), 2898(27),
2875(18), 2804(10), 1692(4), 1663(73), 1474ACTHNUTRGNE(UNG 100), 1459(27), 1429(94),
1408(14), 1399(12), 1380(15), 1369(30), 1301(11), 1204(43), 1138(12),
1097(3), 1051(2), 1025(25), 904(18), 850(1), 738(2), 584(25), 506(2),
417(10), 386(21), 342(9), 309 cmꢀ1 (23); IR (golden gate, rel. int.): n˜ =
3032(w), 2972(w), 2944(w), 2893(w), 2890(w), 2801(w), 1749(w), 1663(s),
1472(m), 1443(m), 1409(m), 1400(m), 1385(m), 1368(m), 1298(m),
1227(m) 1204(m), 1140(w), 1093(w), 1052(w), 1027(s), 904(w), 847(m),
738(m), 669(w), 583 cmꢀ1 (m); elemental analysis calcd (%) for
C4H10N4O (130.15): C 36.91, H 7.74, N 43.05; found: C 36.73, H 7.63,
N 42.83.
AHCTUNGTERG(NNUN 100), 2792(14), 2553(3), 2393(2), 1675(24), 1416(62), 1312(15), 1236(11),
1082(14), 1013(8), 873(21), 849(61), 662(54), 607(3), 445(16), 421(15),
316 cmꢀ1 (18); IR (golden gate, rel. int.): n˜ =3446(w), 3315(w), 3213(w),
2924(w), 2882(w), 1652(s), 1484(w), 1418(w), 1398(w), 1359(m), 1234(m),
1081(m), 984(m), 871(m), 849(m), 662(m), 573(w), 563 cmꢀ1 (w); elemen-
tal analysis calcd (%) for C2H6N2O (74.08): C 32.43, H 8.16, N 37.81;
found: C 32.25, H 8.15, N 37.73.
Compound 4 was identified as the desired isomer, 1-formyl-1-methylhy-
drazine (4a), and not 1-formyl-2-methylhydrazine (4b), by formation of
the corresponding acetone hydrazone by dissolving in dry acetone. GC:
20.78 (acetone, method A[26]), 16.06 min (acetone, method C[26]); GC-MS
(ESI): m/z (%): 115.1 (2) [M+H]+, 114.1 (23) [M]+, 99.1 (100)
[MꢀCH3]+, 85.2 (14) [MꢀCHO]+, 71.2 (11), 56.1 (21) [MꢀN-
Synthesis of (E)-1,4-Diformyl-1,4-dimethyl-2-tetrazene (3)
Method 1: Compound 3 was synthesized by the method described above
for (E)-1-formyl-1,4,4-trimethyl-2-tetrazene (2) and using the following
amounts of reagents: compound 1 (2.32 g, 20.0 mmol), acetone (200 mL),
potassium permanganate (8.48 g, 53.66 mmol). No calcium sulfate was
added and the reaction time was about 19 h. Prism-shaped single crystals
of the title compound crystallized out of the concentrated mother liquor
on standing for about 10 days at room temperature (0.451 g, 16%).
AHCTUNGTRENNUNG
(CHO)CH3]+, 42.2 (26) [(CH3)2C]+, 30.2 (14) [HC(=O)H], 29.1 (10)
[CHO]+, 28.2 (6) [N2], 15.2 (3) [CH3]+.
Synthesis of 1-Formyl-2-methylhydrazine (4b)
Method 2: Compound 4a (see synthesis below) was oxidized using the
method reported by Ronco and Erlenmeyer:[20] compound 4a (10.00 g,
134.90 mmol) was dissolved in acetone (150 mL) and cooled to 08C.
Solid potassium permanganate (14.47 g, 91.56 mmol) was then added
slowly. A brown suspension was formed and the reaction mixture was al-
lowed to warm to room temperature and stirred for 6 h. The insoluble
manganese(IV) oxide was then removed by filtration through Celite and
the volatile compounds of the resulting filtrate were removed under re-
duced pressure (508C). Crystals of the title compound separated crystal-
Compound 4b, which was formed as a side-product during the synthesis
of isomer 4a (see above), was characterized by GC-MS and NMR spec-
troscopy from the reaction mixture without isolation. 1H NMR
([D6]DMSO, 400.18 MHz, TMS): d=2.90 (3H, s; CH3), 4.81 (2H, br s;
NH), 7.73 ppm (1H, s; CHO); 13C NMR ([D6]DMSO, 100.52 MHz,
TMS): d=35.20 (1C, s; CH3), 159.18 ppm (1C, s; CHO); GC: 18.17 min
(MeOH, method C[40]); GC-MS (ESI): m/z (%): 75.2 (4) [M+H]+, 74.2
(100) [M]+, 59.2 (2) [MꢀCH3]+, 46.2 (41), 45.2 (62) [MꢀCHO]+, 44.2 (8),
722
www.chemasianj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 715 – 724

Synthesis and Characterization of Two Formyl 2-Tetrazenes
43.2 (11), 31.2 (20), 30.2 (9) [MꢀCH3ꢀCHO]+, 29.2 (25) [CHO]+, 28.2
Acknowledgements
(39) [N2], 18.1 (21) [H2O], 17.1 (3), 16.2 (2) [NH2]+, 15.2 (6) [CH3]+.
Financial support by the Centre National de la Recherche Scientifique
(CNRS), the Centre National d’ꢄtudes Spatiales (CNES), SAFRAN-
SME and the University Claude Bernard of Lyon is gratefully acknowl-
edged. The authors are also indebted to and would like to thank Dr. B.
Fenet and Mr. S. Alamercery for performing the 15N NMR and Raman
spectroscopic measurements, respectively, and Dr. E. Jeanneau for per-
forming the X-ray experiments and crystal-structure solution.
Synthesis of Monoformylhydrazine (8)
Hydrazine monohydrate (5.00 mL, 102.78 mmol) was dissolved in MeOH
(30 mL) in a 100 mL round-bottomed flask before a solution of 97%
ethyl formate (17.12 mL, 205.55 mmol) in MeOH (40 mL) was added
dropwise, whilst the round-bottomed flask was cooled in a water bath.
After the addition was finished, the water bath was warmed to 708C and
the temperature was maintained for about 2 h. Then, the solvent was re-
moved under reduced pressure to yield a white powder, which was dried
under high vacuum and sublimed twice under high vacuum (508C) to
give the pure title compound as colorless single crystals suitable for X-
ray diffraction (4.906 g, 79%). 1H NMR ([D6]DMSO, 400.18 MHz,
TMS): d=4.39 (2H, s; NH2), 7.90 (1H, s; CHO), 9.07 ppm (1H, s; NH);
13C NMR ([D6]DMSO, 100.52 MHz, TMS): d=160.23 ppm (1C,;CHO);
[1] a) T. M. Klapçtke, C. Mirꢅ Sabatꢁ, A. Penger, M. Rusan, J. M.
Welch, Eur. J. Inorg. Chem. 2009, 880–896; Sabatꢁ, M. Rasp, J.
Mater. Chem. 2009, 19, 2240–2252; Sabatꢁ, Z. Anorg. Allg. Chem.
2007, 633, 2671–2677; b) T. M. Klapçtke, C. Mirꢅ Sabatꢁ, J. M.
Welch, Z. Anorg. Allg. Chem. 2008, 634, 857–866; c) T. M. Kla-
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2009, 15, 1164–1176; b) M. Eberspꢆcher, T. M. Klapçtke, C. Mirꢅ
Sabatꢁ, Helv. Chim. Acta 2009, 92, 977–996; c) T. M. Klapçtke, C.
Mirꢅ Sabatꢁ, M. Rasp, J. Mater. Chem. 2009, 19, 2240–2252;
d) T. M. Klapçtke, C. Mirꢅ Sabatꢁ, Z. Anorg. Allg. Chem. 2010, 636,
163–175; e) H. Delalu, K. Karaghiosoff, T. M. Klapçtke, C. Mirꢅ Sa-
batꢁ, Cent. Eur. J. Energ. Mater. 2010, 7, 115–129.
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1006–1017; b) G. Geisberger, T. M. Klapçtke, J. Stierstorfer, Eur. J.
Inorg. Chem. 2007, 4743–4750; c) T. M. Klapçtke, J. Stierstorfer,
Helv. Chim. Acta 2007, 90, 2132–2150; d) J. Stierstorfer, T. M. Kla-
pçtke, A. Hammerl, R. D. Chapman, Z. Anorg. Allg. Chem. 2008,
634, 1051–1057; e) J. Stierstorfer, K. Tarantik, T. M. Klapçtke,
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Eur. J. Org. Chem. 2010, 1169–1175; g) T. M. Klapçtke, B. Krumm,
R. Moll, Eur. J. Inorg. Chem. 2011, 422–428.
15N NMR ([D6]DMSO, 40.51 MHz, NH3): d=+137.5 (1N, s; NH
ACTHNUTRGNEU(GN CHO)),
+52.0 ppm (1N, s; NH2); DSC (58C minꢀ1): two endothermic peaks
(peak 1: sharp, onset: 57.28C, maximum: 65.08C; peak 2: broad, onset:
ca. 1508C, maximum: ca. 2008C), one exothermic peak (broad, onset: ca.
2208C, maximum: ca. 2508C); GC: 22.20 min (MeOH, method C[26]);
GC-MS (ESI): m/z (%): 61.1 (2) [M+H]+, 60.1 (48) [M]+, 45.1 (1)
[MꢀNH]+, 44.1 (3) [MꢀNH2]+, 43.1 (8) [MꢀNH3]+, 32.2 (100)
[N2H3+H]+, 31.2 (82) [N2H3]+, 30.2 (12) [CHO+H]+, 29.2 (53) [CHO]+,
28.2 (10) [CO]+, 17.1 (3) [NH2+H]+, 16.1 (5) [NH2]+, 15.1 (2) [NH]+;
Raman (rel. int.): n˜ =3317(41), 3234(34), 3167(58), 3090(12), 2994(14),
2911(97), 2882(11), 2750(2), 1659(7), 1637(12), 1613(7), 1574(11),
1511(13), 1377ACHTUNGTRENNUNG(100), 1256(38), 1237(20), 1071(9), 1022(16), 982(37),
855(4), 803(9), 399(15), 353(12), 286(6), 202 cmꢀ1 (49); IR (golden gate,
rel. int.): n˜ =3318(w), 3159(m), 2990(w), 2906(w), 2749(w), 2035(w),
1666(m), 1626(m), 1506(m), 1378(w), 1254(m), 1195(w), 1039(m),
1022(m), 976(w), 787 cmꢀ1 (s); elemental analysis calcd (%) for CH4N2O
(60.05): C 20.00, H 6.71, N 46.65; found: C 19.87, H 6.59, N 46.42.
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Synthesis of 1,2-Diformylhydrazine (9)
Hydrazine monohydrate (2.50 mL, 2.572 g, 51.39 mmol) was reacted with
two equivalents of formamide (4.09 mL, 4.629 g, 102.78 mmol) in
a
25 mL round-bottomed flask. The resulting solution was heated in a
water bath (908C) for 2.5 h. The initial colorless solution turned pink
and, by the end of the reaction, a pink solid had precipitated. Addition
of EtOH (10 mL) resulted in the separation of a colorless powder, which
was filtered, washed with EtOH and Et2O and dried in air (2.690 g).
Leaving the combined washings to stand overnight afforded the forma-
tion of single crystals of the compound (0.258 g). No further purification
was necessary and both batches were combined (2.948 g, 65%). Similar
results were obtained when ethyl formate or formic acid (according to
the method reported by Liu et al.[23]) were used as the formylating agent:
hydrazine monohydrate (2.00 mL, 2.058 g, 41.13 mmol) and 97% formic
acid (3.52 mL, 4.292 g, 90.48 mmol) were reacted carefully in an ice bath
and the resulting solution was heated to reflux for 5 h at 1208C. After
slow cooling to room temperature, single crystals of the title compound
precipitated out of the solution, which were filtered, washed with cold
water, acetone, and Et2O (3.24 g, 89%). 1H NMR ([D6]DMSO,
400.18 MHz, TMS): d=9.96 (2H, br s; NH), 8.01 ppm (2H, s; CHO);
13C NMR ([D6]DMSO, 100.52 MHz, TMS): d=159.05 ppm (2C; CHO);
15N NMR ([D6]DMSO, 50.68 MHz, NH3): d=+130.5 ppm (2N, dd, 1J-
ꢀ
A
N
157.98C (m.p.); MS (ꢀc ESI, H2O): m/z (%): 59.0 (5) [MꢀHCO]ꢀ, 87.1
(100) [MꢀH]ꢀ, 99.0 (10), 122.9 (11) [M+Cl]ꢀ; MS (+c ESI, H2O): m/z
(%): 89.0 (9) [M+H]+, 111.0 (42) [M+Na]+, 116.9 (52), 127.0 (15), 152.1
(100), 199.0 (35), 215 (43), 250.8 (28); Raman (rel. int.): n˜ =3069(3),
2994(5), 2923(12), 2882(6), 1685(2), 1612(4), 1581(27), 1556(28),
1385(41), 1248ACHTUNGTRENNUNG(100), 1061(11), 1007(3), 863(7), 841(5), 460(16), 335(14),
296(17), 169 cmꢀ1 (65); IR (golden gate, rel. int.): n˜ =3107(m), 2898(m),
2795(m), 2705(m), 2522(w), 2467(w), 2068(w), 1994(w), 1613(m),
1455(m), 1393(w), 1362(m), 1223(m), 993(w), 921(w), 826(w), 732(s),
720(s), 586(w), 578(w), 562 cmꢀ1 (w); elemental analysis calcd(%) for
C2H4N2O2 (88.06): C 27.28, H 4.58, N 31.81; found: C 27.12, H 4.48,
N 31.56.
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723

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Received: September 12, 2011
Published online: January 20, 2012
724
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ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 715 – 724