Propellants, Explosives, Pyrotechnics 26, 109  111 (2001) 109
Review on the Nitration of [60]Fullerene
Nai-Xing Wang*
Institute of Photographic Chemistry, Chinese Academy of Sciences, Beijing 100080, (PR China)
Summary methods, including the thermal decomposition of heavy
metal nitrate, the oxidation of nitric acid, the reaction of
[60]Fullerenes continued to attract the interest of a broad scientific
dinitrogen trioxide with dinitrogen pentoxide, the reaction of
community since the method of macroscopic synthesis of fullerenes
nitric acid with sulfur dioxide, phosphorus pentoxide or
was discovered in 1990. Studies on the nitration of fullerenes have
copper, the reaction of nitrosyl chloride with silver nitrate,
been carried out under different conditions and nitration reagents. The
radical ( NO2) is an excellent reactivity group to make direct multiplet and the reaction of nitrosyl hydrogen sulfate with potassium
additions with [60]fullerene to get polynitrofullerenes. Radical ( NO2)
nitrate(12). The brown colored nitrogen dioxide exists in
can be obtained by many different methods.
equilibrium with its dimer dinitrogen tetroxide N2O4,
which is colorless. At ambient temperature the ratio of
N2O4=NO2 is about 86:16(13). The equilibrium content of
NO2 increases as the temperature rises and reaches 99% of
1. Introduction
an NOx mixture at 135 C(12). Nitrogen dioxide is a reactive
intermediate for nitration reactions of many organic olefins.
Since the discovery of C60 and its large scale prepara-
The reaction is normally initiated by the attack of a nitronium
tion(1,2) a lot of work has been devoted to this research
ion, which is generated by the release of the unpaired electron
field(3 5).
from NO2, to an olefinic double band.
C60 has a good anticompression performance, therefore,
It has been suggested that C60 acts like a closed-cage
C60 can become an excellent solid rocket fuel additive to bear
alkene rather than an aromatic molecule due to its poor
a huge pressure in the propellants. Some energetic groups
electron delocalization(14). For example, C60 undergoes
such as trinitrophenyl were lead into C60 to get a better new
many organic reactions, such as reactions including various
fuel additive(6).
addition reactions. The additions can be categorized into
The nitration of fullerene molecules has been carried out
additions of halogens(15  17), Diels-Alder cycloaddition(18)
under different conditions and nitration reagents, including a
and radical addition(19). The radical addition is the main
mixture of conc. HNO3 and sodium nitrite(7), dinitrogen
chemical reaction of C60 due to its high electron affinity
tetroxide(8), fuming nitric acid(9), and a mixture of aqueous
allowing a direct chemical attack by the radicals. It has
sodium nitrite, FeSO4, and H2SO4 in the presence of air(10).
been proved that the C60 molecule is high reactive towards
However, polynitrofullerenes react slowly with H2O to yield
radical species(20,21) and its reactivity can be much greater
partially hydroxylated products of poly(hydroxynitro)-
than that of a typical olefin towards the same radical.
fullerenes. In the presence of an aqueous alkaline solution a
Therefore, radical NO2 is an excellent reactivity group to
rapid and complete hydrolysis of polynitrofullerenes was
make direct multiplet additions with [60]fullerenes to get
observed to produce fullerenol molecules containing at least
polynitrofullerenes.
16 hydroxy groups per C60 cage(7).
How to get as much as possible of NO2 radical? Recently,
L. Y. Chiang et al.(22) reported nitration experiments and
some methods for the generation of nitrogen dioxide which
2. Nitration Agent
was obtained by the reaction of sodium nitrite with conc.
HNO3 or from the reduction of conc. HNO3 by copper
The nitronium ion (NOþ) as a nitration agent was first
powder. Under their conditions, an instantaneous production
2
reported in the reaction with fullerene molecules forming
of red-brown NO2 gas was observed due to a fast reaction of
reactive polynitrofullerenic carbocation intermediates(11).
Cu with N2O4.
For the synthesis of separable nitrofullerene derivatives,
nitrogen dioxide radical ( NO2) was the commonly used
nitration reagent. It was generated by a number of preparative
3. Development
During the NO2=N2O4 generation NO2 is the only gaseous
product available among several other possible nitrogen
* e-mail: [e-mail] oxide species, such as NOþ, NOþ, NOð23Þ. The progress of
2 2
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110 Nai-Xing Wang Propellants, Explosives, Pyrotechnics 26, 109  111 (2001)
[NO2]4 [NO2]6
Figure 1. Nitration of fullerene.
C60 nitration was monitored by the disappearance of the In 1992, Chiang et al. reported the versatile nitronium
purple color of solution of C60 and the formation of the red chemistry for C60 fullerene functionalization(10) and then in
polynitrated fullerene product. 1996 they reported that the C60 molecule exhibited high
The nitration rate depends on both the temperature and the reactivity towards the addition reaction of nitrogen dioxide
concentration of [ NO2]. The completion of the reaction was radical ( NO2). NO2 was generated by the reaction of sodium
achieved within 1.0 h at 160 C or 8 days at 15  20 C. nitrite with conc. HNO3 and this chemical functionalization
It is known that a chemical equilibrium is built between of C60 resulted in polynitro fullerene C60ðNO2Þð7Þ. Sakar
x
NO2 and N2O4. et al.(9) reported that C60 was nitrated by the multiple
addition of NO2 and the product isomerized partly to the
2 NO2 , N2O4
nitrito form with subsequent hydrolysis by atmospheric
moisture to yield nitrofullerols consisting of 6 8 nitro and
A pressure increase is not advantageous for the generation
7 12 hydroxy groups per C60. In their method(9) NO2 was
of radical [ NO2]. When NO2 was injected into the reaction
passed through a toluene solution of C60, resulting in a color
medium containing C60 molecules, its self-ionization into
change to deep orange within 5 min at ambient conditions.
NOþ and NO 2 is known to be a slow process(24). This allows
2
Addition of an excess of light petroleum (40  60 C) or
to count on the nitrogen dioxide radicals as the main species
in the reaction with C60. An odd-numbered addition of NO2 n-hexane precipitated a yellow-brown solid in high yield
with an average of 6 8 nitro and 7 12 hydroxy groups per
radicals to a C60 molecule may get a net residual radical on
C60 molecule. The IR spectra of the solid showed typical NO2
the C60, polynitrated fullerene products that allow to char-
vibrations at 1560, 1336 and 809 cm71. In 1993 the author
acterize these products unlike C60 containing an even number
used a lot of time for the research on [60]fullerene and some
of nitro groups(22).
of its derivatives(29). He thinks that C60 actually is an active
Fullerene nitro functional groups were found to be some-
carbon cage and it reacts very easily with radical ions. It is not
what thermally unstable in solution or on SiO2 which
difficult for energetic materials chemists to get NO2 radicals.
prohibits the direct purification and separation of polyni-
Experimental conditions were set up under inert atmosphere
trated isomers under prolonged chromatographic conditions.
to obtain a higher yield of polynitrofullerene which is an
Each tetranitro[60]fullerene isomer comprising 56 conju-
excellent research field.
gated olefinic carbons should display at least 28 or 56
aromatic carbon peaks if the compound exhibits either a
twofold or no structural symmetry. However, as the number
4. References
of regioisomers increases the total number of aromatic
carbon peaks increases rapidly, which is an isomers
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