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J.U. Ahmad et al. / Applied Catalysis A: General 449 (2012) 153–162
a Hewlett Packard 8453 spectrophotometer and a Varian Mercury
200 MHz spectrometer, respectively. Melting points were deter-
mined with an electrothermal melting point apparatus. IR spectra
were recorded on a Perkin Elmer Spectrum One spectrometer. EI-
mass spectra were run with a JEOL JMS-SX 102 mass spectrometer
(ionization voltage 70 eV) from solid samples. Elemental analy-
ses were made using an EA 1110 CHNS-OCE instrument. X-ray
diffractograms were measured in a grazing incidence mode using
PANalytical X’Pert Pro MPD in parallel beam geometry with a con-
stant incident angle of 1◦. The FESEM images were taken with a
Hitachi S-4800 field emission scanning electron microscope. High-
resolution ESI-MS measurements were performed with a micrOTOF
mass spectrometer (Bruker Daltonics, Germany). Theoretical iso-
topic distributions were simulated by Bruker Xmass 6.1.2 software.
was taken into a NMR tube and was dissolved in 0.5 mL of CDCl3.
Beside of the GC method 1H NMR was also used to analyze con-
version by integrating the aldehyde and the corresponding alcohol
peak areas.
Benzaldehyde. Oxidation of benzyl alcohol (324 mg, 3 mmol)
gave benzaldehyde as pale yellow liquid (278 mg, isolated yield
87%, conversion quantitative and selectivity > 99%). Eluent n-
hexane:ethyl acetate = 50:1. 1H NMR (200 MHz, CDCl3, TMS): ıH:
7.47–7.61 (m, 4H, Ar H), 7.86 (d, 1H, J = 6.8 Hz, Ar H), 10.00 (s,
1H, CH O) ppm. 13C NMR (50 MHz, CDCl3): ıC: 128.0, 128.7, 133.4,
135.3, 191.3 ppm. IR (cm−1): 1696 (ꢀC O).
4-Methoxybenzaldehyde. 4-Methoxybenzaldehyde was isolated
as pale yellow liquid (222 mg, isolated yield 56%, conversion 66%
and selectivity > 99%) from oxidation of 4-methoxybenzyl alcohol
(414 mg, 3 mmol). Eluent n-hexane:ethyl acetate = 5:1. 1H NMR
(200 MHz, CDCl3, TMS): ıH: 3.82 (s, 3H, CH3), 6.95 (d, 2H, J = 8.2 Hz,
Ar H), 7.78 (d, 2H, J = 8.4 Hz, Ar H), 9.83 (s, 1H, CH O) ppm.
13C NMR (50 MHz, CDCl3): ıC: 55.4, 114.0, 129.6, 131.7, 164.3,
190.5 ppm. IR (cm−1): 1680 (ꢀC O).
4-Methylbenzaldehyde. Oxidation of 4-methylbenzyl alcohol
(366 mg, 3 mmol) gave 4-methylbenzaldehyde (colorless liquid,
299 mg, isolated yield 83%, conversion 88% and selectivity > 99%).
Eluent n-hexane:ethyl acetate = 20:1. 1H NMR (200 MHz, CDCl3,
TMS): ıH: 2.42 (s, 3H, CH3), 7.31 (d, 2H, J = 7.8 Hz, Ar H), 7.76 (d,
2H, J = 7.6 Hz, Ar H), 9.95 (s, 1H, CH O) ppm. 13C NMR (50 MHz,
CDCl3): ıC: 22.0, 129.7, 129.8, 134.2, 145.5, 191.9 ppm. IR (cm−1):
1686 (ꢀC O).
Excluding bis[N-isopropyl-3,5-di-tert-butylsalicylaldiminato]
copper (L3)2Cu(II) complex, detailed synthesis and analysis of the
ligand precursors and complexes used in this work can be found
elsewhere [29,30].
2.2.1. Synthesis of (L3)2Cu(II)
A solution of Cu(CH3COO)2 (230 mg, 1.267 mmol in 15 mL of
MeOH) was added slowly in a solution of HL3 (697 mg, 2.534 mmol
in 60 mL MeOH) and stirred for 1 h at room temperature. The gray
solid formed was separated with suction filter and recrystallized
from CH2Cl2 and MeOH (1:1) to yield light brown microcrys-
talline solid (670 mg, 86% yield). mp 235–236 ◦C. Anal. Calc. for
4-Nitrobenzaldehyde. 4-Nitrobenzaldehyde was obtained as
white powder (389 mg, isolated yield 86%, conversion 91% and
selectivity > 99%) by oxidizing 4-nitrobenzyl alcohol (459 mg,
3 mmol). Eluent n-hexane:ethyl acetate = 5:1. 1H NMR (200 MHz,
CDCl3, TMS): ıH: 8.10 (d, 2H, J = 8.4 Hz, Ar H), 8.41 (d, 2H,
J = 8.4 Hz, Ar H), 10.18 (s, 1H, CH O) ppm. 13C NMR (50 MHz,
CDCl3): ıC: 124.3, 130.5, 140.0, 151.0, 190.4 ppm. IR (cm−1): 1703
(ꢀC O).
C
36H56CuN2O2 (612.4 g/mol): C, 70.61; H, 9.22; N 4.57%. Found:
C, 70.91; H, 8.91; N, 4.69%. IR (cm−1): 2957–2869 (ꢀC
from
H
tert-butyl groups), 1629 (ꢀC N), 1435 (ꢀC ). UV–vis ꢁmax (nm):
O
284, 327, 382, 359, 629. HRMS (ESI TOF) m/z for C36H56CuN2O2:
Calc. 634.3524 [M+Na]+; found 634.3530; error 0.49 ppm. MS (EI):
+
m/z = 610–616 with appropriate isotopic ratio for C36H56CuN2O2
.
2-Nitrobenzaldehyde. Oxidation of 2-nitrobenzyl alcohol
(459 mg, 3 mmol) resulted in a formation of 2-nitrobenzaldehyde
(white powder, 367 mg, isolated yield 81%, conversion 87% and
selectivity > 99%). Eluent first n-hexane:ethyl acetate = 5:1 and then
changed to 10:1. 1H NMR (200 MHz, CDCl3, TMS): ıH: 7.72–7.85
(m 3H, Ar H), 7.99–8.04 (m, 1H, Ar H), 10.28 (s, 1H, CH O) ppm.
13C NMR (50 MHz, CDCl3): ıC: 124.4, 129.5, 131.1, 133.8, 134.1,
149.3, 188.2 ppm. IR (cm−1): 1693 (ꢀC O).
3-Nitrobenzaldehyde. 3-Nitrobenzyl alcohol (459 mg, 3 mmol)
oxidized to 4-nitrobenzaldehyde (white powder, 403 mg, isolated
yield 95%, conversion quantitative and selectivity > 99%). Eluent n-
hexane:ethyl acetate = 5:1. 1H NMR (200 MHz, CDCl3, TMS): ıH:
7.83 (t, 1H, J = 7.6 Hz, Ar H), 8.29 (d, 1H, J = 7.6 Hz, Ar H), 8.51 (d,
1H, J = 8.0 Hz, Ar H), 8.72 (s, 1H, Ar H), 10.16 (s, 1H, CH O) ppm.
13C NMR (50 MHz, CDCl3): ıC: 124.4, 128.6, 130.5, 134.9, 137.4,
148.7, 190.0 ppm. IR (cm−1): 1690 (ꢀC O).
4-Chlorobenzaldehyde. Oxidation of 4-chlorobenzyl alcohol
(426 mg, 3 mmol) gave 4-chlorobenzaldehyde (white crystals,
378 mg, isolated yield 90%, conversion 91% and selectivity > 99%).
Eluent n-hexane:ethyl acetate = 20:1. 1H NMR (200 MHz, CDCl3,
TMS): ıH: 7.51 (d, 2H, J = 8.4 Hz, Ar H), 7.83 (d, 2H, J = 8.0 Hz, Ar H),
9.99 (s, 1H, CH O) ppm. 13C NMR (50 MHz, CDCl3): ıC: 129.5, 131.0,
134.8, 141.0, 190.9 ppm. IR (cm−1): 1690 (ꢀC O).
Cinnamaldehyde. Cinnamaldehyde was recovered as yellow
liquid (226 mg, isolated yield 57% conversion 63% and selectiv-
ity > 99%) from oxidation reaction of cinnamyl alcohol (402 mg,
3 mmol). Eluent n-hexane:ethyl acetate = 5:1. 1H NMR (200 MHz,
CDCl3, TMS): ıH: 6.61–6.69 (m, 1H, alkenyl H), 7.36–7.43 (m,
6H, Ar H and alkenyl H), 9.64 (d, 1H, J = 7.5 Hz, CH O) ppm. 13C
NMR (75 MHz, CDCl3): ıC: 128.7, 128.8, 129.3, 131.4, 134.2, 152.8,
193.7 ppm. IR (cm−1): 1669 (ꢀC O).
2.3. Open air oxidation of alcohols
An initial set of experiments was performed by placing
CuSO4·5H2O (0.03 mmol from stock solution of 50 mg/mL in H2O)
and salicylaldimine (0.06 mmol) into a 100 mL two-neck round-
bottom flask fitted with a condenser and a magnetic stirring bar.
The reaction mixture was diluted with 5 mL of distilled water and
heated at 80 ◦C for 15 min to ensure the complex formation. After
cooling to room temperature, 0.15 mmol of TEMPO was introduced
into the solution which was heated at desired temperature for
5 min. Benzyl alcohol (3 mmol) was then added into the solution.
The catalysis was carried out for 1.5 h and then the aqueous solution
was extracted with ethyl acetate (3 mL × 3 mL).
For quantitative analysis, 0.5 mL of ethyl acetate extrac-
tion was placed in a sample vial and diluted with 1 mL of
ethyl acetate. 100 L of acetophenone (0.86 mmol) was used
as internal standard. The sample was analyzed by GC (Agi-
lent 6890 chromatograph, Agilent 19091J-413 capillary column
0.32 mm × 30 m × 0.25 m, FID detector). GC–MS method was used
for identification of the products (Agilent 6890 N equipped with
Agilent 5973 mass selective detector, HP 19091 L-102 capillary
columns, 200 mm × 24 m × 0.31 m). All oxidation experiments
were done three times and the reported conversions are average
values of the nearest two.
To determine isolated yield the reaction mixture after ethyl
acetate extraction was dried with anhydrous MgSO4. The solvent
was evaporated after filtration and the resulting residue was puri-
fied by silica gel column chromatography. Isolated product was
identified by 1H, 13C NMR and FT-IR spectroscopy (see below).
Prior to column chromatography, a small portion of the residue