Synthesis, spectral characterization, crystal structure and thermal behavior of tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate

Article abstract of DOI:10.1007/s10870-012-0363-0

Tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate was prepared from the ethanolic solution of 1-chloro-2,4- dinitrobenzene, tert-butyl 3-oxobutanoate and triethylamine. Acetyl group in tert-butyl 3-oxobutanoate has cleaved off during the formation of the tit

Full text of DOI:10.1007/s10870-012-0363-0

J Chem Crystallogr (2012) 42:1098–1104
DOI 10.1007/s10870-012-0363-0
ORIGINAL PAPER
Synthesis, Spectral Characterization, Crystal Structure
and Thermal Behavior of Tert-butyl 2,2-bis(2,4-
dinitrophenyl)ethanoate
•
D. Kalaivani R. Malarvizhi M. Nethaji
•
Received: 14 November 2011 / Accepted: 20 September 2012 / Published online: 4 October 2012
Ó Springer Science+Business Media New York 2012
Abstract Tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate
was prepared from the ethanolic solution of 1-chloro-2,4-
dinitrobenzene, tert-butyl 3-oxobutanoate and triethyl-
amine. Acetyl group in tert-butyl 3-oxobutanoate has
cleaved off during the formation of the title molecule. UV–
VIS, IR, 1H NMR, 13C NMR, Proton–Proton COSY data
and single crystal XRD results support the proposed
structure. Flammability test, impact sensitivity test and TG/
DTA studies at different heating rates on the synthesized
molecule imply that it is an insensitive high energy density
material.
4-dinitrophenyl)ethanoate (MBDNE) only in 32 % yield by
adopting the same procedure. Carbon-13 NMR study of
EBDNE in liquid ammonia has been made already [2]. An
article has appeared on the crystal structure of EBDNE [3].
This ethyl ester has also been used in colour indication
paper for detecting chlorine containing organic solvents,
alcohols and amines [4]. Ethyl ester has also been employed
in the preparation of photodegradable aqueous inks [5] and
tailor’s chalk [6]. Though the applications of the ethyl ester
(EBDNE) are well documented, only a few reports are
noticed on the methyl ester (MBDNE) [1, 7–9]. No report
has so far appeared on the preparation and applications of
tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate (TBDNE). In
this article we report the synthesis and thermal behavior of
tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate.
Keywords Tert-butyl 2,2-bis(2,4-dinitrophenyl)
ethanoate Á 1-Chloro-2,4-dinitrobenzene Á Triethylamine Á
Tert-butyl 3-oxobutanoate Á Insensitive high energy density
material
Experimental
Introduction
Materials and Methods
Mclvor and Miller have synthesized ethyl 2,2-bis(2,4-dini-
trophenyl)ethanoate (EBDNE) in 32–71 % yield by mixing
equimolar amounts of 1-chloro-2,4-dinitrobenzene (DNCB)
and ethyl 2,4-dinitrophenylacetate in the presence of
tripropylamine in dimethylformamide medium [1]. The
same authors have also prepared methyl 2,2-bis(2,
All reagents and solvents for synthesis and analysis were
commercially available and used as received without fur-
ther purification. The visible data were obtained on a
Perkin-Elmer Lambda 15 UV/VIS spectrometer. The IR
spectra were recorded using Perkin-Elmer RXI infrared
spectrophotometer in KBr pellets. The NMR spectra were
obtained from Bruker DRX-300 spectrometer with
(DMSO) d6 as solvent and TMS as an internal reference.
TGA/DTA data were collected employing Perkin-Elmer
(Pyris Diamond model) at different heating rates under N2
(g) purge using alumina powder as reference.
D. Kalaivani (&) Á R. Malarvizhi
Post Graduate & Research Department of Chemistry,
Seethalakshmi Ramaswami College, Affiliated to Bharathidasan
University, Tiruchirappalli 620 002, Tamil Nadu, India
e-mail: kalaivbalaj@yahoo.co.in
Preparation of tert-butyl 2,2-bis(2,4-dinitrophenyl)ethno-
ate: 1-Chloro-2,4-dinitrobenzene (0.01 mol) in absolute
ethanol was mixed with tert-butyl 3-oxobutanoate (0.01 mol)
M. Nethaji
Department of Inorganic & Physical Chemistry, Indian Institute
of Science, Bangalore 560 012, India
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J Chem Crystallogr (2012) 42:1098–1104
1099
in absolute ethanol. Triethylamine (0.05 mol) was then added
and the mixture was shaken well for 5–6 h. On standing, pale
yellow crystals come out from the solution after 15 days. The
crystals were filtered and washed well with distilled water
and dried. The dried crystals were powdered and washed with
30 ml of ether to remove the unreacted reactants and then
with little absolute alcohol. The crystals obtained after
washing were recrystallized from ethylacetate. Good quality
single crystals of the title compound were obtained from
ethanol at room temperature by slow evaporation (m.p.
427 K, yield 75 %). Micro analysis, calcd.: C, 48.2; H, 3.6;
N, 12.5; found: C, 48.3; H, 3.3; N, 12.2. Solubility: freely
soluble in dimethylsulphoxide and sparingly soluble in water,
Table 2 Selected bond distances
˚
A
Bond distance
C1–C2
1.535(6)
1.522(3)
1.394(5)
1.384(1)
1.365(4)
1.370(1)
1.375(6)
1.196(7)
1.513(4)
1.501(2)
1.514(5)
1.471(2)
1.196(7)
1.204(5)
1.468(9)
1.197(8)
1.188(9)
0.96
C2–C3
C3–C4
C4–C5
C5–C6
C6–C7
C7–C8
C1–O1
C15–C16
C15–C17
C15–C18
C4–N1
ethanol, chloroform, ethylacetate and ether. UV (CHCl3,
1
k
Max): 257 nm. HNMR 300 MHz, (DMSO)d6: d 1.4s, 9H,
C(CH3)3, d 6.3 (s, 1H, CH), d 8.9 (s, 2H, two rings-Ar–H),
d 8.6 (d, J = 14.7 Hz, 2H, two rings-Ar–H), d 7.6 (d, J =
8.7 Hz, 2H, two rings-Ar–H). 13C NMR: d 27, 51, 84, 121,
128, 133, 137, 147, 148, 167. IR (KBr, mmax): 1531, 1351,
N1–O3
N1–O4
C6–N2
N2–O5
N2–O6
C17–H17A
C18–H18A
C2–H2
1723, 2988, 2940, 3114, 1607, 1149, 1063, 837 cm-1
.
Qualitative tests [10] on the synthesized tert-butyl 2,2-bis
(2,4-dinitrophenyl)ethanoate reveal the presence of nitrogen
atom, nitro groups and the absence of chlorine atom.
0.96
0.98
Crystal Structure Determination
CCD diffractometer with graphite monochromated MoKa
˚
radiations (k = 0.71073 A). The data were collected at
A single crystal of the dimension 0.43 9 0.36 9 0.29 was
selected for X-ray diffraction study. Crystallographic
measurements were made employing a Bruker Smart Apex
293(2) K using x scan modes. All hydrogen atoms were
geometrically fixed and allowed to ride with the respective
non hydrogen atoms to which they were covalently bonded.
Table 1 Crystal data
C18H16N4O10
V = 2037.9(10)
Z = 4
Table 3 Selected bond angles
Mr = 448.35
Bond angles
°
Monoclinic, P21/n
˚
a = 12.770 (4) A
MoKa = radiation
l = 0.122 mm-1
T = 293 K
C1–C2–C9
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C7
C6–C7–C8
C7–C8–C3
C5–C6–N2
C6–N2–O6
C6–N2–O5
O5–N2–O6
C4–N1–O3
C4–N1–O4
C2–C1–O2
C2–C1–O1
O1–C1–O2
C17–C15–C18
C16–C15–C18
109.6(7)
123.3(4)
122.7(8)
118.1(2)
121.8(9)
118.5(6)
122.5(6)
118.1(2)
117.8(9)
119.4(5)
122.5(6)
119.6(7)
122.0(1)
109.3(4)
123.4(5)
127.0(1)
111.2(3)
110.7(8)
˚
b = 11.676 (3) A
˚
c = 14.310 (4) A
0.43 9 036 9 0.29
b = 107.277 (6)°
Data collection
Bruker SMART APEX CCD
diffractometer
17,527 measured
reflections
4,831 independent
reflection
Absorption correction : multi-scan
(SADABS; Bruker, 2006)
Tmin = 0.9492,
Tmax = 0.9659
Rint = 0.0479
2,641 reflection with I [ 2r(I)
Refinement
R [F2 [ 2r (F2)] = 0.0618
WR (F2) = 0.2681
292 parameters
H-atom parameters
constrained
4,831 reflections
Goodness of fit
(S) = 1.01
123

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J Chem Crystallogr (2012) 42:1098–1104
Table 4 Hydrogen bond geometry of tert-butyl 2,2bis(2,4-dinitrophenyl)ethanoate
˚
d D–H (A)
˚
˚
d D–A (A)
D–HÁÁÁA (°)
d HÁÁÁA (A)
\DHA (°)
C2–H2ÁÁÁO5(#1)
0.98
0.93
0.93
0.93
0.96
0.96
2.52
2.93
2.81
2.56
2.79
2.93
3.370 (4)
3.712 (4)
3.670 (5)
3.342 (5)
3.708 (6)
3.557 (6)
144
142
154
141
158
124
C5–H5ÁÁÁO2(#2)
C7–H7ÁÁÁO10(#3)
C14–H14ÁÁÁO1(#4)
C17–H17BÁÁÁO10(#5)
C18–H18BÁÁÁO4(#6)
(#1) x - ‘, -y ? ‘, ?z - ‘; (#2) x ? ‘, -y ? ‘, ?z ? ‘; (#3) x ? ‘, -y - ‘, ?z ? ‘; (#4) -x, -y, -z ? 2; (#5) –x - ‘, ?y ? ‘,
-z ? ‘ ? 1; (#6) -x, -y ? 1, -z ? 2
The programs used for the crystal structure determination
are—data collection: APEX2 [11]; cell refinement: SAINT
[11]; data reduction: SAINT [11]; program used to solve
structure: SHELXS97 [12]; program used to refine struc-
ture: SHELXL97 [12]; molecular graphics: ORTEP-III
[13]. Important information concerning crystallographic
data are summarized in Table 1. Selected bond distances
and angles are listed in Tables 2 and 3 respectively. A
number of weak C–HÁÁÁO hydrogen bonds is observed
(Table 4). The ORTEP diagram of title molecule is pre-
sented in Fig. 1.
Results and Discussion
Ketones, beta diketones and beta ketoesters, in the presence
of tertiary amine usually form carbanionic sigma adducts
or bicyclic complexes with electron-deficient nitro aro-
matics [14–20]. In the present investigation, a new ester
containing two dinitrophenyl moieties is formed on adding
excess triethylamine to the ethanolic solution containing
1-chloro-2,4-dinitrobenzene (an electron-deficient nitro
aromatic compound) and tert-butyl 3-oxobutanoate (a
betaketo ester). The same product has been obtained in
Fig. 1 ORTEP view of
tert-butyl 2,2-bis(2,4-
dinitrophenyl)ethanoate
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J Chem Crystallogr (2012) 42:1098–1104
1101
solvents like methanol or 1-propanol and when the bases
such as trimethylamine, tri-n-butylamine, N,N-diethyleth-
anolamine or triethanolamine are used instead of triethyl-
amine. The yield of the product is\60 % with these bases.
The title molecule probably may have formed through the
carbanionic sigma complex 1 [21] as indicated in the
schematic representation (Fig. 2). Acetyl group of tert-
butyl 3-oxobutanoate has cleaved off during the formation
of the title molecule. Similar type of cleavage is reported
by us from ethyl benzoyl acetoacetate in related system
[15]. Spectral and single crystal XRD results are in con-
sistent with the structure of the product (title molecule).
bands at 1,532 and 1,352 cm-1 respectively. The carbonyl
stretching frequency band appears at 1,723 cm-1. The C–O
stretching frequency of ester group appears at 1,150 as a strong
sharp band and the band at 1,063 cm-1 is assigned to C–N
stretching mode. As the methine carbon atom of the title mole-
cule is attached to two electron—with drawing dinitrophenyl
moieties, the methine C–H stretching bond of the isolated mol-
ecule appears in the high frequency region (3,115 cm-1).
1H–1H COSY and 13C NMR Spectra
Methyl protons of tert-butyl group appears as a singlet at d 1.4.
The proton flanked by nitro groups of the aromatic nitro
moiety appears as a singlet at d 8.9. Adjacent ring protons of
nitro moiety resonate at d 8.6 and 7.6 as doublets due to ortho
coupling. Small para coupling is also noticed between the ring
protons. As the methine proton of the molecule is highly de-
shielded due to the attachment of two electron-withdrawing
nitro aromatic moieties, it displays a signal at the low field
region d 6.3. Proton–Proton COSY of the title molecule
exhibits off-diagonal peaks between d 7.4 and 9.0 (Fig. 3).
COSY spectrum substantiates that besides ortho coupling, para
coupling has also occurred between the protons of nitro ring
moiety of the title molecule. As expected, ten signals corre-
sponding to ten different carbon environments are noticed in
the 13C NMR spectrum of the isolated molecule (Fig. 4).
FT-IR Spectra
In the reactant, [1-chloro-2,4-dinitrobenzene (DNCB)], a strong
sharp absorption band characteristic of C–Cl stretching mode has
been observed at 732 cm-1,which is absent in the isolated
product, shows that during the formation of the product chlorine
is remove from DNCB. The asymmetric and symmetric
stretching modes of nitro groups of the title molecule exhibit
Description of the Crystal Structure
The nearly similar bond lengths of various C–C bonds
of dinitroaromatic rings imply that there is charge
Fig. 2 Schematic representation of the formation of tert-butyl
2,2-bis(2,4-dinitrophenyl)ethanoate
Fig. 3 Proton–proton COSY of tert-butyl 2,2-bis(2,4-dinitrophenyl)
ethanoate (d 6.4–9.2)
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J Chem Crystallogr (2012) 42:1098–1104
Fig. 4 13C NMR spectrum
of tert-butyl 2,2-bis(2,4-
dinitrophenyl)ethanoate
delocalization of cyclic p-electron cloud inside the phenyl
ring. As the methine carbon atom is attached to two elec-
tron-withdrawing aromatic moieties, the C(sp3)–H bond
stability, impact insensitivity and explosive performance.
Good thermal stability provides safety in manufacturing,
storage and handling of energetic materials. Emphasis has
also been on cost-effectiveness and eco-friendlyness during
the synthesis of explosives [32–34]. As the title molecule
has four nitro groups, its thermal properties are also
examined. About 5 mg of the title sample was taken in a
nickel spatula and heated over a flame. The substance melts
and moves away from the flame with a hissing sound
producing a dense cloud of black particles characteristics
of secondary explosives. The synthesized molecule was
found to be insensitive towards impact of 2 kg mass
hammer up to the height limit (160 cm) of the instrument.
Many other explosives have also been reported as insen-
sitive towards impact [35, 36]. Activation energies for the
decomposition of the synthesized compound was deter-
mined from the TG/DTA curves (Fig. 5) obtained at three
different heating rates (5, 10, and 20 K/min) applying
Ozawa [37] and Kissinger [38] methods. The decomposi-
tions of tert-butyl 2,2-bis(2,4-dinitrophenyl)-ethanoate has
occurred in four different stages. The temperature ranges of
decomposition processes are summarized in Table 5. The
activation energies of different stages are slightly higher
than the reported insensitive explosives [23, 39–42].
˚
length of it is reduced from the normal value (1.1 A). The
C(sp3)–H bonds of the methyl group are also shortened and
this can be accounted in terms of the delocalization of the
lone pair on the oxygen atom of the ester group over the
adjacent carbonyl group. Thus the hydrogen atoms of
methine and methyl groups are made slightly acidic and are
involved in the formation of a number of weak C–HÁÁÁO
hydrogen bonds which stabilize the structure.
Thermal Behaviour
Many nitro aromatic molecules are high energy materials
to be used as explosives [22]. Primary explosives such as
lead azide, lead styphnate etc., are highly susceptible to
initiation and secondary explosives which include nitro
aromatics and nitramines are more prevalent at military
sites than primary explosives [23]. The interest in devel-
oping better insensitive high energy density materials
(IHEDMS) to be used in explosives, propellants and
pyrotechnics is growing steadily [24–31]. At present there
is a strong requirement for explosives having good thermal
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J Chem Crystallogr (2012) 42:1098–1104
1103
Fig. 5 TG/DTA curve of tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate at the heating rate of 5 K/min
Table 5 Thermal decomposition of tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate (TBDNE)
Compound
Temp. range (°C)
Stage
TG wt loss
(%) found
DTG temp.
peak (°C)
Activation energy kJ/mol (kcal/mol)
Using Ozawa method
Using Kissinger’s method
TBDNE
150–200.5
200.5–230
230–350
1
2
3
4
22.4
10.0
27.0
13.0
191.8(exo)
225.8(exo)
300.0(exo)
413.0(exo)
254(60)
316(75)
93(22)
253(60)
308(73)
89(21)
350–457
320(76)
321(76)
Acknowledgments The authors thank University Grants Commis-
sion for the financial support, SAIF, IIT Madras, Chennai-600 036
and CDRI, Lucknow-226 001 for TG/DTA and spectral data.
Conclusions
The method presented in this article involves ethanol as
solvent which poses less environmental pollution than
other organic solvents. The title molecule is obtained in
good yield with high purity through one-pot synthesis
from low cost materials. Structures of the explosives
have profound effect on activation energy and thermal
stability [23, 31, 43]. The slightly higher activation
energy of the title molecule compared to the reported
secondary explosives may be attributed to the presence
of two phenyl rings.
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