Nitration of benzene and monosubstituted benzenes in liquid SO, by din
itrogen pentaoxide at -11 degrees C gave the corresponding nitroarenes
with substitution patterns similar to those obtained by nitrations wi
th HNO3-H2SO4. For acetophenone an o/m ratio of 0.94 was obtained. The
yields were dependent on the substituents. With a 1:1 ratio of arene:
N2O5 the yields varied from 73% for toluene to 0.4% for nitrobenzene a
s substrates. From competition experiments and the nitration of bibenz
yl it was concluded that the reaction was faster than the macroscopic
rate of mixing. The qualitative order of reactivity for PhX was X = OC
H3 > CH3 > H > Cl > CH3CO > NO2. Nitration with N2O5 in liquid CO2 gav
e similar results. Nitration of pyrimidine, pyrrole, imidazole and ind
ole with N2O5-SO2 gave no nitrated products. With thiophene, 2- (34%)
and 3-nitrothiophene (5%) together with 2,4-(16%) and 2,5-dinitrothiop
hene (8%) were obtained. With pyridine, mono- and di-methylpyridines,
quinoline, isoquinoline and 4-phenylpyridine nitration of the pyridine
ring was obtained. The yields varied from ca. 70% to 16%, except for
3,5-, 2,5- and 2,6-dimethylpyridine for which only traces of nitro-dim
ethylpyridines were obtained. The reaction with the pyridines appears
to be intramolecular both in the SO2 phase and in the water phase used
for quenching the reaction. The reaction was proposed to proceed by a
complex formed in liquid SO2: PyrH + N2O5 + SO2 --> [PyrH (.) SO2 (.)
N2O5] -->/H2O 3-NO(-)Pyr + HNO3