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S.M. Sarkar et al. / Journal of Catalysis 350 (2017) 103–110
dium complex for catalytic application in Mizoroki-Heck reaction.
The complex showed excellent catalytic activity of aryl/heteroaryl
halides and arenediazonium tetrafluoroborate salts with a variety
of olefins under ambient reaction conditions with regeneration of
the catalyst.
tion was adjusted to pH 11 by addition of NaOH solution and the
ratio of methanol and water was always maintained at 4: 1 (v/v).
The poly(methyl acrylate) grafted cellulose 1 (4.5 g) was placed
into a two-neck round bottom flask fixed with a stirrer, condenser
and thermostat water bath. The prepared hydroxylamine solution
was then added to the flask and the reaction mixture was stirred
at 70 °C for 6 h. The resulting poly(hydroxamic acid) chelating
ligand 2 was separated from the hydroxylamine solution by simple
filtration and it was washed with aqueous methanol. Furthermore,
the ligand 2 was treated with 250 mL of 0.1 M HCl (in methanol)
solution for 10 min to neutralize the reaction mixture. The ligand
was filtered, washed with methanol and dried at 50 °C to obtain
a constant weight [63,64].
2. Experimental section
2.1. General information
Ammonium
tetrachloropalladate(II)
[(NH4)2PdCl4]
was
obtained from Aldrich Chemical Industries, Ltd. The 1H NMR
(500 MHz), 13C NMR (125 MHz) spectra were recorded using
BRUKER-500 spectrometer, University Malaysia Pahang (UMP).
1H NMR chemical shifts were reported relative to tetra-
methylsilane (TMS, 0.00 ppm). The 13C NMR chemical shifts were
reported relative to CDCl3 (77.0 ppm). The ICP-AES analysis was
carried out on Shimadzu ICPS-8100 equipment, UMP. TGA was
analyzed by METTLER TOLEDO, TGADSC1, UMP. The FTIR spectra
were recorded by Perkin Elmer (670) spectrometer, UMP. XPS spec-
tra were measured with a Scanning X-ray Microprobe PHI Quan-
tera II, MIMOS, Kuala Lumpur. FE-SEM was measured with JSM-
7800F, UMP. TEM images were measured with HT-7700, Hi-Tech
Instruments SDN BHD, Puchong. TLC plates were obtained Merck
silica gel 60 F254. Wakogel C-200 silica gel was used for column
chromatography.
2.5. Preparation of Pd(II) complex 3
To a stirred suspension of 2 (1.5 g) in 50 mL water, an aqueous
solution of (NH4)2PdCl4 (270 mg, in 40 mL water) was added. The
resulting mixture was stirred for 3 h at room temperature to give
light brown color poly(hydroxamic acid) Pd(II) complex 3. The Pd
(II) complex 3 was filtered, washed with water and MeOH and
dried at 70 °C for 3 h. The ICP-AES analysis revealed that
0.41 mmol/g of palladium was adsorbed onto the poly(hydroxamic
acid) Pd(II) complex 3.
2.6. General procedure for Mizoroki-Heck reaction
2.2. Materials and methods
In a typical experiment, 0.75 mg (0.03 mol%) of 3 was added
into a mixture of aryl halide (1.0 mmol), olefin (2 mmol), Et3N
(3 mmol) in DMF (2 mL), and the reaction mixture was stirred at
130 °C. The formation of coupling product was monitored by
TLC/GC analyses. After disappeared of the aryl halide (checking
by TLC/GC), the reaction mixture was cold at room temperature
and diluted with water and ethyl acetate and the solid Pd(II) com-
plex 3 was separated by filtration. The cross-coupling product was
extracted from the aqueous layer with ethyl acetate (3 Â 5 mL),
dried over MgSO4 and concentrated under reduced pressure. The
crude product was purified by silica gel column chromatography
(ethyl acetate/hexane) to give the corresponding cross-coupling
product.
The waste corn-cobs were collected from Kuantan market,
Malaysia. To obtain pure corn-cob cellulose, the corn-cobs were
cut into ꢀ2–3 cm sizes and refluxed with 10% NaOH (400 mL) for
3 h and washed with distilled water. The resulting cellulose was
refluxed in glacial acetic acid (400 mL), hydrogen peroxide
(250 mL), and 5% NaOH (250 mL) and washed with distilled water
several times respectively. Methyl acrylate was passed through a
column filled activated alumina to remove the inhibitor. Other
chemicals, including ceric ammonium nitrate (CAN Sigma–Aldrich),
methanol (Merck), acids (Lab Scan), metal salts and other analytical
grade reagents were directly used.
2.3. Synthesis of poly(methyl acrylate) 1
2.7. Preparation of Ozagrel butyl ester 4z [65]
The graft copolymerization reaction was carried out in 1.5 L
three-neck round bottom flask equipped with stirrer and con-
denser in a thermostat water bath. Cellulose slurry was prepared
by stirring 5 g of cellulose in 450 mL distilled water for 12 h. The
mixture was then heated to 60 °C with stirring and 1.3 mL of
diluted sulfuric acid (50%) was added. After being stirring for
5 min, 1.25 g of CAN (10 mL aqueous solution) was added and
the reaction mixture was stirred under nitrogen atmosphere. After
20 min, 10 mL methyl acrylate purified monomer was added into
the reaction flask and stirring was continued for 4 h under nitrogen
atmosphere. The mixture was cold, filtrated on a glass filter and
washed several times with aqueous methanol (MeOH:H2O = 4:1)
to give corn-cob cellulose supported poly(methyl acrylate) 1. The
product was oven dried at 50 °C to get a constant weight [63,64].
A mixture of 4y (1 mmol), carbonyldiimidazole (2 mmol), and
anhydrous NMP (10 mL) was stirred at 160 °C for 3 h. After cooling
to 25 °C, the reaction mixture was diluted with EtOAc (20 mL),
washed with H2O (3 Â 20 mL) and brine (15 mL), dried over
MgSO4, and concentrated under reduced pressure. The residue
was purified by column chromatography over silica gel eluting
with CHCl3/MeOH (30/1) to afford Ozagrel butyl ester 4z in 85%
yield.
2.8. Preparation of Ozagrel 5 [65]
To a 10 mL glass vessel was added ozagrel butyl ester 4z
(200 mg, 0.7 mmol), 0.80 M aqueous NaOH (1.5 mL), MeOH
(1 mL), and the mixture was stirred at room temperature for 3 h.
The mixture was concentrated under reduced pressure, and the
residue was acidified with 1.5 M aqueous HCl (5 mL). The resulting
solution was further concentrated under reduce pressure to
remove HCl completely. The residue was dissolved in ethanol
(2 mL) and resulting NaCl solid was filtered off. The filtrate was
concentrated (1 mL) and 5 mL diethyl ether was added during
which time ozagrel 5 was precipitated out with 88% yield.
2.4. Synthesis of poly(hydroxamic acid) ligand 2
The hydroxylamine solution was prepared by dissolving 12 g of
hydroxylamine hydrochloride (NH2OH.HCl) in 300 mL aqueous
methanol (4:1). An ice-cold NaOH solution (50%) was added into
the hydroxylamine hydrochloride; during that time NaCl was pre-
cipitated out and it was separated by filtration. The pH of the reac-