by filtration, dried (110
C), and calcined (550
C) in a flow of air. Atomic absorption spectroscopy analysis showed that the zeolite contained 6.84 wt% of Cu.
As can be seen from Table 9, N-arylation of imidazole with chloroarenes
containing electron-withdrawing groups such as nitro-, cyano-, and trifluoromethylgave quantitative yields (entries 1–3) in shorter reaction times when compared with
4-chloroacetophenone (entry 4). Bromoarenes containing electron-donating groups
afforded the corresponding N-arylated products in high yields after 36 h (entries
5–8). The reaction with iodoarenes resulted in complete conversion in shorter
reaction times (entries 9–11). Reaction of 1-chloro-4-iodobenzene with imidazole
gave selectively N-(4-chlorophenyl)imidazole (entry 12). The catalyst was used for
four cycles successfully with minimal loss of activity (Table 9, entry 7).
After completion of the reaction, the catalyst was separated by simple filtration
and washed with DMF and then with acetone and dried in an oven. AAS results of
the used Cu(II)-NaY catalyst indicate leaching of 1.8% of copper in the N-arylation
reaction of imidazole with 4-bromotoluene after the first cycle and 6.2% leaching
after the fourth cycle. When a fresh reaction was conducted with the filtrate
obtained at the end of the N-arylation reaction, no product formation was observed.
The application of this catalytic system for the coupling of nitrogen-containing
heterocycles with 4-bromo- and 4-iodotoluene was also explored and the desired
N-arylated products were obtained in excellent yields (Table 10). The reaction of
4-chlorotoluene with nitrogen heterocycles provided the products in only trace
amounts even after 48 h.
11 Nanocrystalline Copper(II) Oxide
Nanocrystalline metal oxides find excellent applications as active adsorbents for
gases, the destruction of hazardous chemicals [37, 38], and catalysts for various
organic transformations [39–43]. Recently, we reported the use of nano-CuO as a
catalyst for C–N bond forming reactions [44]. Nano-CuO samples were obtained
from NanoScale Materials, Inc., having a surface area of 136 m
2 /g and crystallite
size of 7–9 nm.
As illustrated in Table 11, the catalytic system (10 mol% of nano-CuO, K 2 CO 3 ,
DMF at 120
C) proved to be highly efficient with other activated chloroarenes.
When o-, m-, and p-nitrochlorobenzenes were used, the corresponding N-arylated
products were obtained in excellent yields (Table 11, entries 1, 2 and 3). Cyano,
nitro, and aldehyde groups are well tolerated (Table 11, entries 1, 4, and 6).
2-Chloropyridine, 4-chloropyridine, and 2-chloropyrimidine also provided
excellent yields as can be seen from Table 11 (entries 7, 8, and 10). The sterically
bulky 4-chlorobenzophenone was converted to the corresponding N-arylated product (Table 11, entry 9) with excellent yields. This catalytic system is completely
inactive in the case of deactivated chloroarenes such as chlorobenzene (Table 11,
entry 12). The activity of nano-CuO is lower than the Cu(II) fluoroapatite catalyst
134
M.L. Kantam et al.
C), and calcined (550
C) in a flow of air. Atomic absorption spectroscopy analysis showed that the zeolite contained 6.84 wt% of Cu.
As can be seen from Table 9, N-arylation of imidazole with chloroarenes
containing electron-withdrawing groups such as nitro-, cyano-, and trifluoromethylgave quantitative yields (entries 1–3) in shorter reaction times when compared with
4-chloroacetophenone (entry 4). Bromoarenes containing electron-donating groups
afforded the corresponding N-arylated products in high yields after 36 h (entries
5–8). The reaction with iodoarenes resulted in complete conversion in shorter
reaction times (entries 9–11). Reaction of 1-chloro-4-iodobenzene with imidazole
gave selectively N-(4-chlorophenyl)imidazole (entry 12). The catalyst was used for
four cycles successfully with minimal loss of activity (Table 9, entry 7).
After completion of the reaction, the catalyst was separated by simple filtration
and washed with DMF and then with acetone and dried in an oven. AAS results of
the used Cu(II)-NaY catalyst indicate leaching of 1.8% of copper in the N-arylation
reaction of imidazole with 4-bromotoluene after the first cycle and 6.2% leaching
after the fourth cycle. When a fresh reaction was conducted with the filtrate
obtained at the end of the N-arylation reaction, no product formation was observed.
The application of this catalytic system for the coupling of nitrogen-containing
heterocycles with 4-bromo- and 4-iodotoluene was also explored and the desired
N-arylated products were obtained in excellent yields (Table 10). The reaction of
4-chlorotoluene with nitrogen heterocycles provided the products in only trace
amounts even after 48 h.
11 Nanocrystalline Copper(II) Oxide
Nanocrystalline metal oxides find excellent applications as active adsorbents for
gases, the destruction of hazardous chemicals [37, 38], and catalysts for various
organic transformations [39–43]. Recently, we reported the use of nano-CuO as a
catalyst for C–N bond forming reactions [44]. Nano-CuO samples were obtained
from NanoScale Materials, Inc., having a surface area of 136 m
2 /g and crystallite
size of 7–9 nm.
As illustrated in Table 11, the catalytic system (10 mol% of nano-CuO, K 2 CO 3 ,
DMF at 120
C) proved to be highly efficient with other activated chloroarenes.
When o-, m-, and p-nitrochlorobenzenes were used, the corresponding N-arylated
products were obtained in excellent yields (Table 11, entries 1, 2 and 3). Cyano,
nitro, and aldehyde groups are well tolerated (Table 11, entries 1, 4, and 6).
2-Chloropyridine, 4-chloropyridine, and 2-chloropyrimidine also provided
excellent yields as can be seen from Table 11 (entries 7, 8, and 10). The sterically
bulky 4-chlorobenzophenone was converted to the corresponding N-arylated product (Table 11, entry 9) with excellent yields. This catalytic system is completely
inactive in the case of deactivated chloroarenes such as chlorobenzene (Table 11,
entry 12). The activity of nano-CuO is lower than the Cu(II) fluoroapatite catalyst
134
M.L. Kantam et al.