Chemistry Reference
In-Depth Information
OH
O
5 mol% V
2
O
5
, O
2
toluene, 100
o
C
R
'
R
R'
secondary
alcohol
77~95%
d
n
4
r
4
n
g
|
5
O
5 mol% V
2
O
5
, O
2
toluene, 100
o
C
Ph
OH
Ph
O h
primary
alcohol
97%
Scheme 6.24 Aerobic oxidation of alcohols catalyzed by V
2
O
5
.
O
OH
H
cat. V
2
O
5
, O
2
Ph
OH
Ph
OH
Ph
H
Ph
O
Ph
pH = 6
O
cat. V
2
O
5
, O
2
Ph
O h
Scheme 6.25 Mechanism for production of an ester.
O
5 mol% V
2
O
5
, O
2
K
2
CO
3
, toluene, 100
o
C
R
H
R
H
OH
O
O
5 mol% V
2
O
5
, O
2
K
2
CO
3
, toluene,
100
o
C, 16 h
+( )
5
+( )
5
OH
H
.
trace
87%
Scheme 6.26 Aerobic oxidation of alcohols catalyzed by V
2
O
5
in the presence of
K
2
CO
3
.
aldehydes in moderate to high yields (Scheme 6.26). Interestingly, secondary
alcohols can be chemoselectively converted to ketones in high yields in the
presence of primary hydroxyl groups.
31
Punniyamurthy's group also reported that a polyaniline-supported
vanadium complex eciently catalyzes the oxidation of alcohols to aldehydes
and ketones in high yields under O
2
in toluene at 100 1C (Scheme 6.27).
32
The
catalyst was easily prepared by stirring a 1 : 1 (w/w) mixture of VO(acac)
2
and
polyaniline in CH
2
Cl
2
at room temperature for 48 h.
This catalyst catalyzed the aerobic oxidation of benzyl alcohol in toluene
at 100 1C, producing benzaldehyde in 98% yield. On the other hand, the
aerobic oxidation of benzyl alcohol catalyzed by unsupported VO(acac)
2
was
less selective and provided a 2.5 : 1 : 1 mixture of benzaldehyde, benzoic acid
and benzyl benzoate (Scheme 6.28). The catalyst is effective for the aerobic
oxidation of aliphatic alcohols and can be recycled for three runs without a
decrease in activity.
32
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