Chemistry Reference
In-Depth Information
Table 7.1
(Continued)
Reaction
time(h)
Yield
a,b
(%)
Entry
Substrate
Product
9
2
80
OH
O
10
2
73
d
O
OH
a
Isolated yield.
b
Reaction performed on 1 mmol scale;
c
Reaction performed on 0.1 mol scale;
d
Shvo's catalyst (1 mol%).
Me
N
N
Co
N
O
O
HO
OH
OH
HO
hydroquinone/Co(salophen) hybrid catalyst
10
Figure 7.1 Hybrid hydroquinone-Schiff-base Co catalyst.
Moreover, the aerobic oxidation of cyclohexanol on a 100 mmol scale
provided cyclohexanone in 95% yield when using a substrate-to-catalyst ratio
of 1000 (Table 7.1, entry 7). To date, this is one of the fastest catalytic systems
reported for the oxidation of secondary alcohols.
To facilitate the recovery of the catalyst, a heterogenized encapsulated
zeolite of complex 9 was reported with allylic and benzylic primary alcohols
and also secondary alcohols as substrates.
13
Such a catalyst was easier to
handle and to separate from the reaction mixture and could be reused
several times without any decrease in activity. An alternative improved
hybrid catalyst 10 that incorporate both the ETM hydroquinone and the
oxygen-activating agent Co(salophen) in the same complex, was sub-
sequently found to perform the biomimetic catalytic oxidation of alcohols
(Figure 7.1).
14
Faster electron transfer from the substrate to molecular oxy-
gen became possible owing to the closest proximity of the cobalt center and
Search WWH ::
Custom Search