MECHANISM OF HYDROGENATION OF 1,3,5-TRINITROBENZENE
751
Scheme 3.
(X = SMe, OMe, OEt); in the presence of the corre-
sponding trinitro compounds adducts V act as donors
of hydride ion. This scheme is supported by hydride
ion transfer from -adducts VI (X = NH ) [4] and
2
V (X = H) to 1,3,5-trinitrobenzene.
Adducts VIIc VIIl derived from dinitrobenzenes
undergo aromatization to mononitro compounds
molecular hydrogen absorbed by the solvent. The
energy released in reactions outlined in Scheme 3
promotes hydrogen addition at the most activated
VIIIc VIIIl through elimination of HNO molecule
2
and hydride ion. The products are identified via
double bond in the ring of H- -complexes, which
3
1
AA BB patterns in the H NMR spectra. In the series
involves the substituent X and nitro group (Schemes 1
of 1-X-2,4-dinitrobenzenes, hydrogenolysis of the
1
and 2). The double bond at C in -adduct II
1
-substituent was observed for X = SO Me, SOMe,
2
(
X = NH ) is deactivated due to donor effect of the
2
SOC H NO -4, and NHCOC H NO -4; the reaction
6 4 2 6 4 2
amino group; therefore, molecular hydrogen adds at
gave initial m-dinitrobenzene and products of its
further transformations.
The proposed mechanism of hydrogenolysis of
,3,5-trinitrobenzene and 1,3-dinitrobenzene deriva-
4
the double bond at C to form 1-amino-2-aci-nitro-
4
,6-dinitro-5-cyclohexene potassium (or sodium) salt
1
IX. In the H NMR spectra of compounds III (X = H)
and IX the signal of the proton neighboring to the
nitro group appears as a quintet (J 5.5 Hz) in the
region 5.2 5.0 ppm, and signals from nonequivalent
axial and equatorial protons in positions 3 and 5 are
1
tives can be denoted as S Ar(AA E), i.e., nucleophilic
N
2
aromatic substitution via addition addition elimina-
tion. We believe that this mechanism deserves specific
attention, for it also applies to hydrolysis reactions:
for example, it explains formation of 3,5-dinitrophenol
in the initial stage of the reaction of 2,4,6-trinitroben-
zoic acid with NaBH4.
doublets of doublets (J
16 Hz) in the region
ax eq
1
3
3
.7 2.7 ppm. In the C NMR spectra of the same
3
adducts, the signal from the sp -carbon atom attached
2
4
to the nitro group (C and C , respectively) is ob-
served at 78 ppm; in the off-resonance spectrum it
C
REFERENCES
is split into a doublet, indicating that there is a proton
attached thereto.
1. Kaplan, L.A. and Siedle, A.R., J. Chem. Soc., 1971,
vol. 36, no. 7, pp. 937 939.
Adducts IIIb IIIl undergo decomposition by the
action of unreacted trinitro compound, resulting in
2. Machacek, V., Lycka, V., and Nadvornik, M., Collect.
Czech. Chem. Commun., 1985, vol. 50, no. 11,
pp. 2598 2606.
1,2-elimination of HX molecule provided that X is
a readily leaving group. Elimination of HNO was
2
1
observed for X = SMe, OMe, and OEt; in the H
3. Gold, V., Miri, A.Y., and Robinson, S.R., J. Chem.
Soc., Perkin Trans. 2, 1980, no. 2, pp. 243 249.
NMR spectra we observed ABM patterns from the
corresponding dinitro compounds IV (X = SMe,
OMe, OEt). Their precursors are -complexes V
4. Atkins, P.J., Gold, V., and Wassef, W.N., J. Chem.
Soc., Perkin Trans. 2, 1983, no. 8, pp. 1197 1198.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 5 2001