Room Temperature Aerobic Oxidation of Amines
COMMUNICATION
[
a]
we have identified the intermediate H O by an in situ FIA
Table 2. Oxidation of BnNH
2
using thejNPycjcatalyst.
2
2
technique developed by our group previously (Figure 2b
[16,17]
and Figure S14 in the Supporting Information).
Similar-
ly the number of electrons (n) involved in the oxidation and
ꢀ
reduction reactions were calculated as n=4e for both the
[
h]
[i]
Entry Catalyst
1a [mmol] Air/O
2
t/h 1b Yield [%]
S
CN [%]
electrochemical oxidation and reduction reactions using
RDE experiments and Koutecky–Levich (K–L) plot analy-
1
2
3
4
5
6
7
8
9
jNPycj
jNPycj
jNPycj
jNPycj
jNPycj
jNPycj
jNPycj
jNPycj
jNPycj
jNPycj
jNPycj
jNPycj
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.10
0.25
0.50
0.05
0.05
0.05
0.05
Ar
Air
O
2
O2
5.3
5.3
5.3
5.3
5.3
5.3
2
46
17
32
48
75
98
97
98
98
98
98
98
98
97
97
98
98
98
N.D.
[
18]
ses (Figure 2c and d, Figure S15 in the Supporting Infor-
mation). In addition, separate FIA experiments for the
BnNH2 oxidation in the presence/absence of O2 on the
membrane catalyst modified electrode were also done. In
the absence of O , an unstable BnNH oxidation current
was noticed; while the currents were stable in the presence
of O . This observation provides an evidence for the partici-
pation of O in the oxidation reaction (Figure S16 in the
[b]
[
[
[
[
c]
d]
e]
f]
O
O
O
O
O
2
2
2
2
2
5.3 >99
2
2
15
24
24
4.5
3.3
1.3
80
48
29
86
63
25
2
10
O2
1
1
1
1
1
2
3
4
O
O
O
O
2
2
2
2
2
Supporting Information). Meanwhile, in situ attenuated total
jNPycj
[
19,20]
reflection infrared spectroscopy (ATR-IR)
was further
[g]
[j]
jNfj
j
5.3 N.D.
used to probe the BnNH oxidation reaction under O at-
mosphere. Figure 3 shows the ATR-IR spectra for the
2
2
[
a] Reaction conditions: BnNH
2
in acetone (1.0 mL), small pieces of the j
NPycj catalyst, room temperature, by-product is benzaldehyde. [b–e]j
NPycj (0.002 mol%, 0.004 mol%, 0.005 mol%, 0.006 mol% of Ru, re-
spectively). [f] 0.007 mol% Ru and the same amount were used for other
experiments (Entry 1-2 & 8-13). [g] Nafion (0.25 g). [h] Yield. [i] Nitrile
selectivity (SCN) determined by GC and GC-MS. [j] N.D.=Not detected.
ingly, optimal conditions of Ru (0.007 mol%), 1a
(
0.05 mmol) and O atmosphere condition were found essen-
2
tial for highly efficient (>99%) and selective (98%) oxida-
tion of 1a to 1b (Table 2, entry 7). The TOF value was
ꢀ
1
found to be 1.07 h (Table 1, entry 1), which is significantly
higher than other catalysts, such as Ru/hydroxyapatite
Figure 3. In situ ATR-IR responses of a BnNH
at 0.5 and 4.5 h in RT.
2
adsorbed jNPycj catalyst
ꢀ
1
[5a]
ꢀ1 [5e]
(TOF=0.5 h ),
Ru(OH) /CeO (TOF=0.06 h ),
and
x
ꢀ
2
1
[5e]
Ru(OH) /TiO (TOF=0.6 h ), at relatively high temper-
x
2
ature (1008C) and pressure. Moreover, the selectivity (98%)
of 1b was significantly higher than those of classical Ru/
BnNH2 adsorbed ZnSe/jNPycj surface. A new peak ap-
ꢀ
1
[5b]
[5c]
peared at 2230 cm corresponding to the stretching of -Cꢀ
N group was observed. The peak intensities increased with
increase in time during the IR measurements. The adsorbed
organic moieties on the membrane surface were isolated
with acetone and examined by GLC and GC-MS
Al O
and Ru/Fe O
catalysts, where 82% selectivity of
2
3
2
3
1b was observed. Under optimal conditions, a series of
BnNH derivatives were subjected to oxidation reactions at
2
RT. As summarized in Table 3, aromatic amines (p-Me, p-
(
Figure S17). Interestingly, the 1a adsorbed jNPycj
[
a]
Table 3. Oxidation of various amines using jNPycj catalyst.
membrane system showed a pronounced 1b forma-
tion. These observations clearly verify the catalysis
[
b]
[c]
Entry Substrate
Product
t/h Yield [%]
S
ele [%]
1
2
3
4
5
6
7
benzylamine
benzonitrile
5.3 >99
98
98
98
97
98
96
of the jNPycj/O interphase for the selective RT
2
[
4-methoxybenzylamine 4-methoxybenzonitrile 4.5 >99
4-methylbenzylamine 4-methylbenzonitrile 3.8 >99
2-methoxybenzylamine 2-methoxybenzonitrile 4.6 >99
20]
amine oxidation.
As summarized in Table 2,
batch reactions were conducted in acetone under
various working parameters, such as Ar, O , air,
4-chlorobenzylamine
n-octylamine
indoline
4-chlorobenzonitrile
n-octylnitrile
indole
3.2 >99
24 >30
2
substrate and catalyst amounts and run time at RT.
In the presence of Ar, no marked yield of 1b was
observed (Table 2, entry 1); whereas air and O2
gave the yield of 48% and 99%, respectively, indi-
cating the specific role of O2 in this reaction
3
>99
>99
[
a] Substrate (0.05 mmol), jNPycj (250 mg, 0.007 mol% Ru), acetone (1.0 mL), RT in
the presence of O . [b] Yield. [c] Selectivity (Sele) determined by GC and GC-MS.
2
(
Table 2, entries 2 and 7). As can be seen in Table 2 an in-
OMe, o-OMe, p-Cl) were efficiently converted into corre-
sponding nitriles rather than benzylamine, due to their elec-
tron donating groups (Table 3, entries 2–5). Non-activated
amine (such as n-octyl amine) was also examined for oxida-
tion reaction. The reactivity of the n-octyl amine was lower
than those of aromatic primary amines (Table 3, entry 6) in
crease in mole% of Ru active sites lead to an increase of
the 1b yield up to 99% (Table 2, entries 3–7). On the other
hand, an increase of reactant concentration (1a) on a fixed
amount of Ru active sites (0.007 mol%) results in a decrease
in the product yield of 1b (Table 2, entries 8–10). Accord-
Chem. Eur. J. 2012, 18, 6147 – 6151
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6149