Chemistry Reference
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in N
2
) was set to 100 psi higher than the N
2
background pressure (600
psig). Two sequential metering valves connected to the O
2
outlet were
adjusted to obtain the desired gas flow rate. The total gas flow out of the
vapor-outlet valve was maintained at around 5 scf h
1
. The reactor was
then purged with the dilute oxygen gas for 10-15 min (8% O
2
in N
2
; 500
psig). The first syringe pump was charged with a Pd(OAc)
2
stock solution
in toluene (10 mM) and the second with alcohol-pyridine stock solution
in toluene (1.0 M/40 mM, respectively). The feed rates of both pumps were
adjusted to achieve the desired liquid residence time in the reaction zone.
The flow tube between the reaction zone and the vapor-liquid separator
consisted of a jacketed stainless-steel tube and, prior to the start of the
reaction, a flow of ethylene glycol cooling fluid (-10 to -20 1C) was passed
through the outer jacket. Both syringe pumps were started to initiate the
flow of liquid solution with the dilute oxygen gas through the reactor.
After starting the pumps (t
ΒΌ
0), the time when the liquid started to
accumulate in the liquid product tank was recorded as the actual liquid
residence time.
d
n
4
r
4
n
g
|
6
Palladium(
III
) acetate in combination with neocuproine as ligand was also
applied on a fairly large scale (20 mmol).
35
Representative procedure for aerobic alcohol oxidation with Pd-neocuproine
catalyst on a 20 mmol scale.
35
Standard catalytic experiments were
carried out in a closed Hastelloy C autoclave (175 mL). The (neocuproi-
ne)Pd(OAc)
2
catalyst (0.02 mmol, 8.6 mg) and NaOAc
H
2
O (1.0 mmol)
were dissolved in 1 : 1 DMSO-water (50 mL). The autoclave was charged
with the catalyst solution, alcohol (20 mmol) and internal standard
(n-heptane, n-octane or n-dodecane) and was pressurized with 8% O
2
in N
2
and heated to 100 1C (30
60 bar) while stirring at 750 rpm.
After reaction, the autoclave was cooled to room temperature and
depressurized. The product mixture was extracted with Et
2
O and the
organic layer was washed with water and dried over MgSO
4
. For water-
DMSO mixtures above 50
55 vol.% water, virtually no DMSO was
extracted with diethyl ether. Below this value, the organic layer could
be washed with water to remove DMSO. A different external standard
(n-dodecane or n-hexadecane) was added to the organic solutions and the
latter were analyzed by GC-MS. Recoveries were always 98
4% with this
procedure. No blank reaction was observed. Isolated yields were generally
above 90%.
.
A palladium catalyst with improved stability towards oxidative conditions
was developed by Muldoon and co-workers.
36
They investigated the use of
commercially available N,O-ligands
to produce highly active Pd(
II
)
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