Chemistry Reference
In-Depth Information
OH
O
TEMPO, CuCl, Ligand
O
2
, [bmim][PF
6
], 65
o
C
R
1
R
2
R
1
R
2
d
n
4
r
4
n
g
|
0
Ligand :
N
N
N
N
N
N
PF
6
PF
6
Imidazolium ionic liquid-grafted 2,2
0
-bipyridine ligand in Cu-TEMPO
catalyst system.
Figure 2.20
5 mol% Cu(ClO
4
)
2
, 10 mol% DMAP
R
OH
R
O
5 mol% acetamido-TEMPO
[bmpy]PF
6
, O
2
, RT
Figure 2.21 Cu-TEMPO-catalyzed oxidation of alcohols in 1-butyl-4-methylpyridi-
nium hexafluorophosphate ([bmpy]PF
6
.
OH
O
TEMPO-IL (5 mol%), CuCl (5 mol%), Molecular sieves 3Å
R
1
R
2
R
1
R
2
O
2
, [bmim][PF
6
], 80
o
C
R
1
= aryls, alkyls;
R
2
= H, aryls, alkyls
N
O
PF
6
N
O
TEMPO-IL :
N
O
.
Figure 2.22 Molecular sieve-promoted oxidation of alcohols catalyzed by copper
halide and immobilized TEMPO on an ionic liquid.
Jiang and Ragauskas reported a three-component acetamido-TEMPO-Cu
catalytic system to catalyze the oxidation of primary alcohols selectively over
secondary alcohols using DMAP as a base in ionic liquids (Figure 2.21).
79
Kinetic studies with a range of bases provided mechanistic insights into the
catalytic cycle.
80
Catalytic oxidations of alcohols have been carried out with a copper-based
system with TEMPO immobilized on an ionic liquid and a heterogeneous
promoter, molecular sieves 3Å, in an ionic liquid (Figure 2.22). The hetero-
geneous promoter acted as a Brønsted base to increase the reaction rate and
the catalyst could easily be recycled and reused without a decrease in
activity.
81,82
A three component catalytic system comprising CuBr-4-pyrrolidinopyr-
idine-acetamido-TEMPO under solvent-free conditions is capable of che-
mospecific aerobic oxidation of 1-(4-hydroxymethylphenyl)ethanol with high
selectivity.
83
The catalyst can be recycled by an antisolvent precipitation
method. For solid alcohols, PEG-200 is used as solvent. The dimeric
Search WWH ::
Custom Search