Nitration of Alkanes
6489 – 6496
nitrogen dioxide is a key step. The initial formation of nitro-
gen dioxide can take place mainly on polyoxomolybdates,
that is, [PMo12O40]nꢀ, and vanadium species enhance the re-
action. Then, the nitration is proceeded via a chain forma-
tion of nitrogen dioxide and an alkyl radical.
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Experimental Section
Materials: Phosphometalates except for [H3PMo12O40], [H4PVMo11O40],
and [VO(H2O)5]H[PMo12O40] were supplied by Nippon Inorganic Colour
and Chemical Co., Ltd. and used after recrystallization from water.
[H3PMo12O40] (Kanto) was used as received. [H4PVMo11O40][24] and
[VO(H2O)5]H[PMo12O40][25] were synthesized according to the literature
procedures. Solvents and concentrated aqueous nitric acid (69 wt%)
were of analytical grade (Tokyo Kasei) and used without the further puri-
fication. Alkanes used in the nitration reactions were commercially ob-
tained from Tokyo Kasei or Aldrich (reagent grade) and purified prior to
use.[26]
Instrumentation: GC analyses were performed on Shimadzu GC-14B
with a flame ionization detector equipped with a TC-WAX capillary or
SE-30 packed column. Mass spectra were determined on Perkin–Elmer
TurboMass at an ionization voltage of 70 eV. NMR spectra were record-
ed on JEOL JNM-EX-270. 1H and 13C NMR spectra were measured at
270 and 67.5 MHz, respectively, in CDCl3 with TMS as an internal stan-
dard. 31P NMR spectra of polyoxometalates were measured at
109.25 MHz in acetic acid. 85% H3PO4 was used as an external standard.
51V NMR spectra of polyoxometalates were measured at 70.90 MHz in
acetic acid. VOCl3 was used as an external standard. Infrared spectra
were measured on Jasco FT/IR-460 Plus using KBr disks. ESR measure-
ments at 100 K (X-band) were performed with a JEOL JES-RE-1X spec-
trometer. The microwave power, resonance frequency, modulation, and
time constant were 1.0 mW, 9.21 GHz, 0.5 mT, and 0.1 s, respectively. A
reactor directly connected to an ESR tube was used to avoid the expo-
sure of the sample to the air. After a certain catalytic reaction period,
the reaction solution was transferred into the ESR tube and the ESR
tube was sealed by firing. The simulation was carried out according to
the literature,[27] assuming the axial symmetry for vanadium.
[4] a) H. Feuer, T. Nielsen, Nitrocompounds: Recent Advances in Syn-
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2003, 2812, and references therein.
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likan, J. Org. Chem. 1952, 17, 906; b) G. B. Bachman, H. B. Hass,
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Procedure for catalytic nitration: Nitration of alkanes was carried out in
a glass vial containing a magnetic stir bar. A typical procedure was as fol-
lows. Into a glass vial were successively placed adamantane (0.33m),
[H4PVMo11O40] (1.67 mm, 0.5 mol%), acetic acid (3 mL), and nitric acid
(0.67m). The glass reactor was then attached to a vacuum line, cooled to
77 K, and degassed by three freeze-pump-thaw cycles. The vial was al-
lowed to warm to 298 K and 1 atm of argon was introduced to the
system. Then, reaction mixture was heated at 356 K for 24 h. All of the
products were confirmed by GC analysis in combination with mass and
1H and 13C NMR spectroscopy as reported previously.[10,28] The yields
were determined by GC analyses using naphthalene or diphenyl as an in-
ternal standard.
Kinetic study: Nitration of alkanes was performed via the same proce-
dure as those described above. The reaction conditions are given in the
Figure captions (Figures 4–6). The reaction was monitored every 30 min
by GC analyses showing no reaction during the induction period in every
case. Reaction rates (R0) for the kinetic analyses were determined from
the slope of reaction profiles (conversion vs time plots, see Figure 3,
inset) at low conversion (<10%) of the substrate after the induction
period.
[9] a) G. W. Smith, H. D. Williams, J. Org. Chem. 1961, 26, 2 2 07; b) H.
Stetter, Angew. Chem. 1954, 66, 217.
[10] a) Y. Nishiwaki, S. Sakaguchi, Y. Ishii, J. Org. Chem. 2002, 67, 5663;
b) S. Sakaguchi, Y. Nishiwaki, T. Kitamura, Y. Ishii, Angew. Chem.
2001, 113, 2 2 8A; ngew. Chem. Int. Ed. 2001, 40, 222; c) S. Isozaki, Y.
Nishiwaki, S. Sakaguchi, Y. Ishii, Chem. Commun. 2001, 1352.
[11] K. Yamaguchi, S. Shinachi, N. Mizuno, Chem. Commun. 2004, 424.
[12] When the ESR spectrum was measured at 4 K, a signal at g=2.005
was observed in addition to the hyperfine structure of vanadium.
The signal may be assignable to an alkyl radical species.
[13] The formation of V4+ by the treatment of [H4PVMo11O40] with cy-
clohexane and toluene, and the reoxidation with nitric acid to form
nitrogen dioxide were observed.
Acknowledgement
This work was supported in part by the Core Research for Evolutional
Science and Technology (CREST) program of Japan Science and Tech-
nology Agency (JST) and a Grant-in-Aid for Scientific Research from
the Ministry of Education, Culture, Sports, Science, and Technology of
Japan.
[14] A 51V NMR signal appeared at d ꢀ559.0 after addition of nitric acid
to the solution. The signal at d ꢀ559.0 is assigned to monomeric
+
VO2 species since the chemical shift is almost the same as that of
+
VO2 species prepared from V2O5 in acetic acid (d ꢀ559.4).[15]
Chem. Eur. J. 2004, 10, 6489 – 6496
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6495