Chemical Papers
O
H
H
N
H
NH2
O
O
Hydrogen peroxide-Urea
O
MeO
O
MeO
OMe
+ MeOH
(1)
NH2
Urea,MeOH, CO2
1
HO
2-
NH
O
HO
O
O
O
Na2WO4 .2H2O
W
OH
O
O
N
Scheme 3 Reaction pathway of oxidation of aniline to nitrosobenzene
oxide core and silica shell of nanoparticles and W and Na
peaks are totally related to tungstate-immobilized groups.
The percentage of tungsten element observed in the EDS
table, is equivalent to 0.563 mmol of this element in 1 g of
the fnal nanoparticles; while EDS results are not quantita-
tively reliable, as it is a surface probe, the precise amount of
tungsten element was determined using inductively couple
plasma (ICP) analysis. The results showed the presence of
0.557 mmol of tungsten per gram of nanoparticles.
yields do not largely depend to solvent polarity. However,
the reaction mechanism (Scheme 3). With the optimized sol-
vent in hand, various oxidants were tested in the model reac-
tion (entries 12–14). Using hydrogen peroxide and oxone as
oxidant, lower product yields were obtained; surprisingly
when tert-butyl hydrogen peroxide was applied, no product
was detected (entry 14). The efciency of the oxidation reac-
tion using DMC as solvent and UHP as oxidant in elevated
temperatures were tested (entries 15–16). It was observed
that at higher temperatures formation of nitro compounds
precedes over nitroso formation. In addition, efect of lower
and higher amount of catalyst was studied (entries 17–18).
As it was expected, no product was detected in the absence
of the catalyst (entry 19). Furthermore, reaction did not pro-
ceed when magnetite and silica-coated magnetite nanoparti-
cles were used as catalyst (entries 20–21). Overall, DMC and
UHP at ambient temperature were much more selective for
production of nitroso compound in excellent yields.
Transmission electron micrographs of FS and FSW nan-
oparticles are shown in Fig. 6. Core–shell nature of both
nanoparticles is observable.
After characterization of nanoparticles, their catalytic
nitroso benzene as a model reaction (Scheme 2). The opti-
lined in Table 1. Initially, the efect of solvent was surveyed
applied, was kept constant (entries 1–11). In DMF and
DMSO no product formation was observed (entries 1–2).
Considerably, low product yield was obtained in THF (entry
3). The yield of product was moderate in alkane, chlorinated
solvents, alcohols and acetonitrile (entries 4–9). The reaction
in water was not so selective and 20% of nitro product was
observed (entry 10). The oxidation reaction was efcient and
highly selective for nitroso product in dimethyl carbonate as
solvent (entry 11). It can be suggested that, polar protic sol-
vents, i.e., water and alcohols promote the reaction by easy
dissolution of oxidant (UHP), while non-polar solvents dis-
solve the amine substrate which result in comparable product
yield in spite of low solubility of oxidant. Hence the product
After achieving the best reaction condition, substrate
scope of the reaction was surveyed. For electron donating
substituents like methoxy, hydroxy and amino group mod-
erately good yields of corresponding nitroso compound
was obtained (2e–f, 2i–j); while for electron withdrawing
groups like Cl, Br and nitro product yield was diminished
(2g–h and 2k). Even though for double nitro substituted
amine, no product formation was detected (2l). Where two
amino groups were present in the starting material, the
over or di-oxidated product was observed (2e–f) (Table 2).
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