D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
109
documented oxidation reaction catalyzed by MPcTS. Therefore, the
exploration of novel phthalocyanine metal system with green oxi-
dant for catalytic oxidation of phenolic pollutant remains an active
topic. Furthermore, understanding the details of reaction mecha-
nism is important for the development of phthalocyanine catalysis.
(TNFe(II)Pc) could efficiently catalyze oxidation of phenols and
chlorophenols (2-CP, 4-CP and DCP) assisted with 4-AAP in aqueous
medium. The dissolved molecular oxygen as oxidant was suffi-
cient for the catalytic oxidation reaction. Although TNFe(II)Pc is
not a novel phthalocyanine metal complex [20], we found for the
first time that TNFe(II)Pc was an efficient heterogeneous catalyst
for oxidation of phenolic substrates in aqueous medium. Control
•−
experiments demonstrated that superoxide anion radical (O2
)
was the active species involved in catalytic oxidation process and
the resulting pink dye was considered to be generated from radical
coupling. Moreover, we analyzed the resultant dye and proposed a
catalytic mechanism for the chromogenic reaction.
2. Experimental
2.1. Instrumental
UV–Vis spectra were recorded on a Shimadzu UV-2450 spec-
trophotometer. IR spectra were recorded on a Thermo Nicolet
Nexus FT-IR spectrometer with the standard KBr pellet method.
Elemental analyses were performed on a Elementar Vario EL III Ele-
mental Analyzer. 1H NMR spectra were recorded on a Varian NMR
System 600 MHz Spectrometer. Nitrogen adsorption–desorption
isotherms were collected on a Micromeritics Gemini V2380 sur-
face area and porosity analyzer at 77 K after the sample had
been degassed in the flow of N2 at 200 ◦C. Catalytic reaction was
monitored by high performance liquid chromatography (HPLC,
Dalian Elite P230 series). The reaction products were identified
by HPLC–MS. HPLC analyses were carried out using Agilent 1100
instrument equipped with a SGE C18 column (150 mm × 4.6 mm).
The mobile phase consisted of acetonitrile–methanol–water mix-
ture (4:1:5, v/v) with a flow rate of 1.0 mL/min. The column
temperature was set at 25 ◦C. Mass spectrometry (MS) analyses
were performed using Applied Biosystems API2000 instrument.
Electrospray ionization (ESI) source of MS was set at the positive
ionization mode.
Scheme 1. Synthesis of 4-nitrophthalimide and tetranitro iron (II) phthalocyanine
complex.
2.3.1. 4-Nitrophthalimide
The synthesis of 4-nitrophthalimide was adopted according
to Young’s method [21]. Yield: 66%. FT-IR (KBr pellets) 3328(s),
3077(w), 3043(w), 1791(m), 1705(s), 1622(m), 1546(s), 1349(s),
1307(s), 1110(s), 1075(s), 720(s) cm−1 1H NMR (600 MHz, d6-
;
DMSO): ı 8.07 (d, 1H, J = 2.4 Hz, Ph-H), 8.43 (s, 1H, Ph-H), 8.61 (d,
1H, J = 2.4 Hz, Ph-H), 11.84 (s, 1H, NH).
2.2. Materials and reagents
Phenol, 2-chlorophenol, 4-chlorophenol, 2, 4-dichlorophenol
and 4-aminoantipyrine are of analytical reagent grade and
purchased from Sinopharm Chemical Reagent Co., Ltd. The
raw materials used for the synthesis of tetranitro iron (II)
phthalocyanine are phthalimide, urea, ammonium molybdate (VI)
tetrahydrate, iron (II) sulfate heptahydrate, concentrated H2SO4
and fuming HNO3. All these reagents are analytical pure and
used without further purification. Boric acid–borax buffer solu-
tion (0.2 M, pH 7.4 and 9.0) and Na2HPO4–KH2PO4 buffer solution
(0.2 M, pH 5.5) were used as catalytic reaction medium. Deionized
water was used in all the experiments. Methanol and acetonitrile
(HPLC grade, Sinopharm Chemical Reagent Co., Ltd.) was used as
elution solution for HPLC study.
2.3.2. Tetranitro iron (II) phthalocyanine
TNFe(II)Pc was prepared by a reported method [22], but with
some modifications. 3.84 g 4-Nitrophthalimide, 1.4 g FeSO4·7H2O,
0.05 g ammonium molybdate, and excess 12 g urea were added
into a 100 mL three-necked flask containing 20 mL nitrobenzene
under magnetic stirring. Then the mixture was heated slowly to
130 ◦C to completely dissolve all the organic solid under the protec-
tion of N2, and subsequently the temperature was raised to reflux
for 3 h. Thereafter, the mixture was cooled to room temperature
and dark blue product was obtained. The product solution was
poured into ethanol, stirred and collected by vacuum filtration to
afford the crude product. Then the crude product was added into
400 mL of 1 M HCl solution, boiled for about 30 min and then fil-
tered, washed with deionized water for several times, followed by
the further treatment with 400 mL of 1 M NaOH solution by the sim-
ilar treatment mentioned above. Finally, the TNFe(II)Pc solid was
washed with ethanol by Soxhlet extraction to remove the residual
nitrobenzene, then the dark blue solid was collected and dried at
100 ◦C overnight in vacuum. Yield: 56%. FT-IR (KBr pellets) 733(m),
760(m), 808(w), 852(w), 1097(m), 1142(m), 1254(w), 1335(s),
1517(s), 1614(w) cm−1. UV–Vis (DMSO) ꢀmax = 284, 682 nm. Anal.
2.3. Preparation and characterization of TNFe(II)Pc
the nitration reaction of phthalimide to 4-nitrophthalimide; (II)
the formation of TNFe(II)Pc via the reaction of 4-nitrophthalimide,
urea, FeSO4 and ammonium molybdate. The synthetic procedure
for TNFe(II)Pc is described in Scheme 1.