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In comparison with the nitrite containing ionic liquid derived
from the O-nitrosation of N-methyl-N-hydroxybutylimidazolinium
chloride, IL-ONO [10], this immobilized nitrite ionic liquid similarly
produced high yield of product under the identical reaction
conditions. We studied the optimization of the reaction conditions
with different molar ratios of the aniline, ionic liquid and b-naph-
thol. The best ratio of equivalents was found to be 1:1.25:1. In order
to investigate the scope and limitation of IL/silica gel as reagent for
diazotization and subsequent azo-coupling, different anilines and
phenolic compounds as the reactants were also tested and the
results were summarized (Table 1).
It could be found that IL/silica gel could act as nitrosonium
source for diazotization. Good to excellent yields ranging from 73%
to 92% were obtained in all systems under investigation. The
diazotization of aniline, 4- hydroxyaniline and 4-nitroaniline and
subsequent coupling reaction with 2-naphthol or resorcinol gave
expected mixture of products (3a and 3a0), (3d and 3d0), (3j and 3j0)
and (3K and 3K0) in 89%, 88%, 90% and 92% yields respectively. The
mixture of isomers (3a and 3a0), (3d and 3d0), (3j and 3j0) and (3K
and 3K0) with ratio of (1: 0.11), (1: 0.09), (1: 0.08) and (1: 0.13)
respectively were determined by 1H NMR spectroscopic data. We
also examined the diazotization of anilines using the pure
N-methyl-3-(3-trimethoxysilylpropyl) imidazolium nitrite 8 and
subsequent azo-coupling with active benzenes under the same
conditions.
These results suggest that the immobilized ionic liquid 7, IL-ONO
and pure N-methyl-3-(3-trimethoxysilylpropyl) imidazolium
nitrite 8 can act as nitrosonium source for diazotization of anilines.
As it can be seen from Table 2, the reaction times are shorter in the
presence of immobilized ionic liquid in comparison with other IL’s
as a result of its larger interface area.
4. Conclusion
In conclusion, immobilized nitrite ionic liquid was prepared and
used as an efficient nitrosonium source for the convenient diazo-
tization and subsequent azo-coupling. Azo dyes were synthesized
in good yields in short reaction times under mild heterogeneous
conditions. Using of the ionic liquids, pure N-methyl-3-
(3-trimethoxysilylpropyl) imidazolium nitrite and IL-ONO as
nitrosonium sources in this procedure no significant difference in
the results were observed. The reaction times are slightly shorter
and the yields were slightly higher in the presence of immobilized
ionic liquid in comparison with other IL’s as a result of its larger
interface area. The heterogenisation of nitrite ionic liquid can offer
important advantages in handling and in separation and reuse thus
lowering the risks and hazards of a chemical process, as well as
simplifying the work up procedure.
Acknowledgments
The partial financial assistance from the Research Vice Chan-
cellor of Azarbaijan University of Tarbiat Moallem is gratefully
acknowledged.
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