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Letter to the Editor / Applied Catalysis A: General 481 (2014) 169–172
2.4. Synthesis of the Zn(II) tetrakis[4-(2,4-bis-(1,1-dimethyl-
propyl)-phenoxy)]phthalocyanine
(ZnPc)
A
solution of 4-[2,4-bis-(1,1-dimethyl-propyl)-phenoxy]-
phthalonitrile (300 mg, 0.83 mmol), 1,8-diazabicyclo [5.4.0]
undec-7-ene (DBU) (124 mg g, 0.81 mmol), and Zn(OAc)2 (33 mg,
0.25 mmol) in 5 ml of absolute ethanol (previously distilled from
Mg) was refluxed for 24 h under N2 atmosphere. The organic
layer enabled the separation of a blue-green solid, which was
purified by chromatography (silica, ethyl acetate/hexane 1:9) and
gave a mixture of isomers of the Zn(II)-tetrakis [4-(2,4-bis-(1,1-
dimethyl-propyl)-phenoxy)] phthalocyanine in 50% yields. Their
structure was consistent with the following characterizations:
UV–vis (CHCl3) ꢀmax: 679, 615, 347, 284.5, 248.
2.5. Synthesis of the
phthalocyanine (H2Pc)
Fig. 1. Structure of H2Pc and MPcs.
The (H2Pc) was prepared by following a procedure similar to
that reported in literature [18].
ZnPc (126 mg, 0.08 mmol) was dissolved in 10 ml of Pyridine and
HCl (in molar ratio 4:1). The solution was continuously stirred for
36 h at 120 ◦C and monitored by TLC (thin-layer chromatography).
The reaction mixture was extracted by CH2Cl2 and the crude prod-
uct of the reaction, obtained after evaporation of solvent, purified
by chromatography (silica, ethyl acetate/hexane 0.5:9.5). A dark
green solid (H2Pc) was recovered in 40% yield.
undec-7-ene (DBU) were purchased from Sigma–Aldrich and were
used without further purification.
2.2. Synthesis of the
4-[2,4-bis-(1,1-dimethylpropyl)-phenoxy]-phthalonitrile
4-[2,4-Bis-(1,1-dimethyl-propyl)-phenoxy]-phthalonitrile was
prepared following a procedure reported in literature [15]. 2.75 g
(0.02 mol) of finely ground anhydrous K2CO3 was added gradually
(0.55 g at intervals of 0.5–1 h) under N2 atmosphere and by stir-
ring to a dry DMSO solution (100 ml) containing 3.5 g (0.015 mol)
of 2,4-bis-(1,1-dimethyl-propyl)-phenol and 2.6 g (0.015 mol) of 4-
nitrophthalonitrile. The reaction mixture after 1 day of stirring was
filtered, added to 60 ml of water, extracted with CH2Cl2 and dried
on anhydrous sodium sulfate.
The crude product of the reaction, obtained after evaporation of
the solvent, was purified by column chromatography (silica, CHCl3)
and recovered in 80% yields; mp = 89–90 ◦C. 1H NMR (CDCl3) ı: 7.72
(d, J = 8.6 Hz, 1H), 7.40–7.15 (m, 4H), 6.75 (d, J = 8.4 Hz, 1H), 1.68 (q,
J = 7.5 Hz, 2H), 1.65 (q, J = 7.4, 2H), 1.31 (s, 6H), 0.70 (t, J = 7.4, 3H),
0.64 (t, J = 7.5, 3H) ppm. 13C NMR (CDCl3) ı: 161.9, 149.8, 146.8,
139.0, 135.3, 127.1, 125.2, 121.5, 121.4, 120.7, 117.4, 115.4, 115.0,
108.2, 38.4, 37.8, 36.9, 34.2, 28.4, 28.1, 9.3, 9.0 ppm.
2.6. Preparation of TiO2-H2Pc, TiO2-ZnPc, TiO2-CuPc composites
The composite materials used as photocatalysts for the photore-
activity experiments were prepared by impregnating TiO2 (Tioxide,
anatase phase) with 6.65 mol of sensitizers (CuPc, H2Pc or ZnPc)
per gram of TiO2. Typically, the opportune amount of sensitizers
were dissolved in 5 ml of CH2Cl2 and 500 mg of finely ground TiO2
(previously sonicated for 30 min) was added to this solution. The
mixture was stirred for 6 h and the solvent was removed under
vacuum.
2.7. Photoreactivity experiments
The apparatus used for the photocatalytic experiments (Fig. S1,
SuppoInfo), consisted of a three necked Pyrex batch photoreactor of
cylindrical shape containing 50 ml of aqueous suspension at various
pH. The photoreactor was provided with a jacket for cooling water
circulation and ports in its upper section for the inlet and outlet
of gases, for sampling and for pH and temperature measurements.
A HRC UV-VIS lamp 300 W (Sanolux) and Xe-Halogen lamp 400 W
(Radium) (the emission spectra are reported in Fig. S2 SuppoInfo)
were placed in proximity (5–6 cm) of the reactor. CO2 was bubbled
into the suspensions for approximately 0.5 h before switching on
the lamps to saturate the reaction mixture. The amount of cata-
lyst used for the optimization of the reaction was between 50 and
300 mg. The amount of catalyst used to study of effect of the pH,
the macrocycle, the metal and the quantity of sensitizers on the for-
mation of formic acid was 50 mg. The initial pH, except in the basic
(0.1 M NaOH) and neutral solution, was adjusted to 2.8 by addition
of H3PO4. The temperature inside the reactor was held at approx-
imately 300 K by a continuous circulation of water in the jacket
around the photoreactor. The photoreactivity runs lasted 8.0 h and
formic acid was detected by Ion Chromatography as reported in Fig
S3 (SuppoInfo).
2.3. Synthesis of the Cu(II)
(CuPc)
The preparation of the Cu(II) tetrakis[4-(2,4-bis-(1,1-
dimethylpropyl)phenoxy)] phthalocyanine (CuPc) was previously
reported [15].
A solution of 4-[2,4-bis-(1,1-dimethyl-propyl)-
phenoxy]-phthalonitrile (1.8 g, 0.005 mol), 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU) (0.75 g, 0.0049 mol), and CuCl2 (0.239 g,
0.0014 mol) in 12.5 ml of absolute ethanol was refluxed for 24 h
under N2 atmosphere. The organic layer enabled the separation
of a blue solid which was purified by chromatography (silica,
toluene) and gave a mixture of isomers of the Cu(II)-tetrakis
[4-(2,4-bis-(1,1-dimethyl-propyl)-phenoxy)] phthalocyanine in
60% yields. Their structure was consistent with the following
characterizations: UV–vis (CHCl3) ꢀmax 287, 339, 391, 617, 686 nm.