Z. Zhang et al. / Catalysis Communications 87 (2016) 18–22
19
oxidant. In this work, we report that TiO
2
supported Pd catalyzed the
by liquid N
2
, then, 1,3-butadiene was introduced as a liquid, and O
2
was
aerobic allylic C–H acetoxylation of terminal alkenes to selectively give
various linear allylic acetate products. The reaction can be performed
under 1 atm of O , and the catalyst exhibits good recyclability.
2
introduced until the pressure reached 2.5 atm. The reaction was con-
ducted at 50 °C for 24 h. After cooling to room temperature, the reaction
mixture was analyzed by GC.
2
. Experimental
3. Result and discussion
2
.1. Material and measurements
3.1. Characterization
Palladium on activated carbon (Pd/C) and palladium nitrate were
HAADF-STEM observation revealed that Pd nanoparticles (NPs)
supplied by Wako Pure Chemical Industries Co., Ltd.. TiO
2
(ST111), γ-
were highly dispersed on TiO
The mean diameter was calculated to be 4.6 ± 1.5 nm. In addition, the
mean diameters of Pd NPs were 3.6 ± 1.1 nm for Pd/Al and 2.4 ±
1.0 nm for Pd/ZrO , respectively (Figs. S2 and S3). The XRD pattern of
Pd/TiO was compared with those of TiO and PdO/TiO (Fig. S4). The
diffraction peaks of Pd/TiO at 40, 46 and 68° were assigned to (111),
(200) and (220) crystalline planes of the face-centered cubic (fcc) lattice
of Pd (PDF-2 Database, No. 01-087-0645) (Fig. S4b). In contrast, only
weak broad peaks of PdO were observed in the XRD patterns of PdO/
2
(supplementary information, Fig. S1).
Al (AKP-G015) and ZrO (RC-100) were supplied from Titan
2
O
3
2
Kogyo, Sumitomo Chemical Co., Ltd. and Daiichi Kigenso Kagaku
Kogyo Co., Ltd., respectively. All other reagents used were commercial
grade. The authentic samples of allylic acetates were purchased from
Wako Pure Chemical Industries Co., Ltd., Tokyo Chemical Industry Co.,
Ltd. and Sigma-Aldrich, Inc.. High angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) observations were
performed using a JEOL JEM-ARM200F. X-ray powder diffraction
2 3
O
2
2
2
2
2
(
XRD) patterns were obtained on a Rigaku MiniFlex600 with a high-in-
tensity Cu Kα radiation source (λ = 0.154178 nm) at a scanning rate of
0°/min. X-ray absorption fine structure (XAFS) measurements were
performed at BL14B2 beam line of SPring-8 (Hyogo, Japan) with Si
311) double crystal monochromator [24–25]. The XAFS spectra were
TiO
2 2
, probably due to the small size of PdO and overlapping with TiO .
2
3.2. Synthesis of cinnamyl acetate from allylbenzene
(
Initially, several organic solvents mixed with AcOH were investigat-
ed for allylic C–H acetoxylation of allylbenzene (1a) over Pd/C (Table 1)‚
and cinnamyl acetate (2a) was determined as the major product. Higher
yield was obtained when the reaction was performed in AcOH/DMSO
than those obtained in AcOH mixed with 1,4-dioxane or DMA (entries
1–3). The selectivity of 2a was slightly decreased when only AcOH
was used probably due to the homocoupling of allylbenzene (entry 4).
The ratio of AcOH and DMSO was adjusted to 10:1 that gave a better re-
sult than using AcOH/DMSO at 1:1 (entry 5). In entry 6, the product
yield was maintained even when the reaction was performed under
recorded in the transmission mode using ionization chambers. The
spectral analysis was performed using the XAFS analysis software, Athe-
na [26]. XPS of the samples was collected using a Shimadzu AXIS-165
spectrometer equipped with a Al Kα anode. The calibration peak is
C1s at 283.6 eV. Palladium loading of the catalysts was analyzed by mi-
crowave plasma-atomic emission spectrometry (MP-AES) by Agilent,
4
100 MP-AES. To analyze the leaching of Pd during the reaction, the
solid catalyst was filtered from the reaction mixture after reaction and
dried at 70 °C overnight, and then, dissolved in amount of aqua regia
for analysis. Conversions and product yields were analyzed by gas chro-
matography (GC) using Agilent GC 6850 Series II equipped with FID and
a J&W HP-1 column (0.25 μm thickness, 0.25 mm I.D., 30 m). H and
NMR spectra were recorded on a JEOL JNM-ECS400 spectrometer at 400
and 100 MHz, respectively. H assignment abbreviations are the follow-
ing: singlet (s), doublet (d), triplet (t), double of doublet (dd), double of
triplet (dt), and multiplet (m).
2
1 atm of O . Furthermore, the reaction temperature and time were
discussed, and the reaction proceeded well at 90 °C for 28 h (entry 7).
The yield was decreased in the absence of sodium acetate (entry 8),
which was in accordance with Szabó's result that carboxylate salt effi-
ciently promoted the allylic C–H acetoxylation process [6]. In this
work, we confirmed that 1 equivalent of sodium acetate was optimum
(entry 9). Next, several metal oxide supported Pd catalysts were
1
13
C
1
2
screened for this process. Among these catalysts, Pd/ZrO showed a
2
.2. Preparation of catalysts
Table 1
Pd/metal oxide catalysts were prepared by an impregnation (IMP)
Optimization of reaction conditions for synthesis of cinnamyl acetate from allylbenzene.
method. Palladium loading was adjusted to 5 wt%. Palladium nitrate
0.114 g) was dissolved in a small portion of water. Support (1.0 g),
such as TiO , was added to the aqueous solution and stirred at room
temperature for 30 min. After impregnation, H O was removed by vac-
uum-freeze drying or evaporation. The obtained catalyst was calcined at
00 °C for 4 h to obtain PdO/TiO . Then, PdO/TiO was reduced in a flow
of pure H (20 mL/min) at 200 °C for 3 h to obtain Pd/TiO
(
2
2
Entry Catalyst
Solvent
O
2
Temp. Conv. Yield
3
2
2
a
a
(atm)
(°C)
(%)
(%)
2
2
.
1
2
3
4
5
6
7
8
9
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Pd/ZrO
AcOH: 1,4-dioxane (1:1) 2.5
80
80
80
80
80
55
64
73
88
88
82
95
63
91
26
85
97
23
19
24
31
13
42
49
58
34
50
24
69
81
11
AcOH: DMA (1:1)
AcOH: DMSO (1:1)
AcOH
2.5
2.5
2.5
2.5
2
2
.3. Catalytic activity test
.3.1. A typical procedure for catalytic reactions
A glass tube was charged with a stirring bar, allylbenzene (1 mmol),
catalyst (Pd 5 mol%), NaOAc (1 mmol), solvent (total amount of AcOH
and DMSO was 2.0 mL), and sealed with an O balloon. The reaction
AcOH: DMSO (10:1)
AcOH: DMSO (10:1)
AcOH: DMSO (10:1)
AcOH: DMSO (10:1)
AcOH: DMSO (10:1)
AcOH: DMSO (10:1)
AcOH: DMSO (10:1)
AcOH: DMSO (10:1)
AcOH: DMSO (10:1)
Balloon 80
Balloon 90
Balloon 90
Balloon 90
Balloon 90
Balloon 90
Balloon 90
Balloon 90
b
c
d
2
was conducted at 90 °C for 28 h. After cooling to room temperature,
the reaction mixture was filtered, and the filtrate was analyzed by GC
using tridecane as an internal standard.
10
2
1
1
1
1
2
3
Pd/Al
Pd/TiO
PdO/TiO
2 3
O
2
2
a
The conversion and yield were calculated by GC analysis using tridecane as an internal
2
.3.2. A typical procedure for acetoxylation of 1,3-butadiene
The reaction was performed in an autoclave which was charged with
standard.
b
Reacted for 28 h.
Without NaOAc.
Pd/TiO
2
(Pd 5 mmol), AcOH/DMSO (10/1 v/v, total amount was 2.0 mL),
c
d
NaOAc (1 mmol) and a stirring bar. The autoclave was cooled below 0 °C
KOAc was used instead of NaOAc.