Synthesis of two novel water-soluble iron phthalocyanines and their application in fast chromogenic identification of phenolic pollutants

Article abstract of DOI:10.1007/s10562-013-1178-0

The novel water-soluble and sterically hindered phthalocyanine complexes, i.e. iron(III) tetra-(4-carboxyphenoxy) phthalocyanine (3) and iron(III) tetra-(8-quinolineoxy-5-sulfonicacid)phthalocyanine (4) were synthesized for fast detection of phenolic poll

Full text of DOI:10.1007/s10562-013-1178-0

Catal Lett (2014) 144:487–497
DOI 10.1007/s10562-013-1178-0
Synthesis of Two Novel Water-Soluble Iron Phthalocyanines
and Their Application in Fast Chromogenic Identification
of Phenolic Pollutants
Jingjing Gong
Liyun Ding Yilin Tong
•
•
Dapeng Li
•
•
Jun Huang
•
•
Kun Li
Cong Zhang
Received: 6 October 2013 / Accepted: 26 November 2013 / Published online: 13 December 2013
Springer Science+Business Media New York 2013
ꢀ
Abstract The novel water-soluble and sterically hindered
phthalocyanine complexes, i.e. iron(III) tetra-(4-carboxy-
phenoxy)phthalocyanine (3) and iron(III) tetra-(8-quinoli-
neoxy-5-sulfonicacid)phthalocyanine (4) were synthesized
for fast detection of phenolic pollutants. These two FePc
complexes exhibited the high catalytic activity in the
chromogenic reactions of phenolic pollutants. Five phe-
nolic substrates, including phenol, 2-chlorophenol,
promising for the application of fast chromogenic identi-
fication of phenolic pollutants.
Keywords Iron phthalocyanines ꢀ Chromogenic
identification ꢀ Phenols ꢀ Catalysis ꢀ Oxidation
1
Introduction
4
-chlorophenol, 2,4-dichlorophenol and 1-naphthol could
Iron phthalocyanine (FePc) complexes are attractive and
versatile catalysts not only for the reproduction of biolog-
ical oxidation performance of natural cytochrome P-450
system [1], but also in the application of selective oxidation
and bleaching treatment [2–7]. Among them, tetrasulfo-
nated iron phthalocyanine (TSFePc) has been intensively
studied and become the important representative for its
wide application, low cost and accessibility at a large scale
be efficiently oxidized by tert-butyl hydroperoxide in the
presence of these selected FePc catalyst. UV–Vis spec-
troscopy and HPLC technique were used to monitor the
catalyzed oxidation of phenolic substrates. Compared with
catalytic methods by other reported phthalocyanines, this
system has the obvious advantages of fast oxidation and
high-yield conversion of phenolic substrates. Under the
optimal conditions, the chromogenic process of 2-chloro-
phenol could be completed just within 10 min with more
than 90 % of conversion. Potentially, this system is
[
8–12]. Essentially, the central iron atom is the active site
of TSFePc catalyst, and phthalocyanine ligand can stabilize
iron atom with different valences from II to IV. More
importantly, the substituent groups on Pc ring, as a par-
ticular composite unit, have a great influence on some
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-013-1178-0) contains supplementary
material, which is available to authorized users.
physical properties (such as SO H for water-solubility) and
3
determine the catalytic activity in most cases. Despite of
the good dissolution of TSFePc in aqueous solution and its
satisfactory catalytic activity in most oxidation reactions,
the aggregation of TSFePc monomers was inevitable and
considered to be main reason of low catalytic efficiency
J. Gong ꢀ J. Huang (&) ꢀ L. Ding ꢀ Y. Tong ꢀ K. Li ꢀ C. Zhang
National Engineering Laboratory for Fiber Optic Sensing
Technology, Key Laboratory of Fiber Optic Sensing Technology
and Information Processing (Ministry of Education), Wuhan
University of Technology, Wuhan 430070, People’s Republic of
China
[
13–16]. Thus acetonitrile was commonly used to increase
the ratio of monomers [17], however, the use of organic
solvent would increase cost on TSFePC catalysis in envi-
ronmental pollutant control. To overcome these problems,
the design and synthesis of highly monodisperse FePc
catalysts have been a promising strategy and become a
challenging goal in phthalocyanine catalysis chemistry.
e-mail: hjun@whut.edu.cn
D. Li
Key Laboratory for Micro-Nano Energy Storage and Conversion
Materials of Henan Province, School of Chemistry and Chemical
Engineering, Institute of Surface Micro and Nano Materials,
Xuchang University, Henan 461000, People’s Republic of China
123

4
88
J. Gong et al.
The introduction of sterically hindered groups onto
obvious chromogenic indication and good applicability in
broad pH range, longer time was needed to achieve the
completion of chromogenic reaction. Therefore, the
improvement for higher catalytic efficiency of catalysts to
shorten the test time of chromogenic assay is necessary.
For this purpose, the FePc complexes with sterically hin-
dered groups on Pc ring should be developed and their
optimal working conditions need to be determined.
phthalocyanine ring has proved to be an efficient method to
decrease the aggregation of phthalocyanine monomers.
Many literatures have described the design and synthesis of
metal phthalocyanine with phenyl, quinolyl and other
groups [18–23]. For example, W o¨ hrle’s group synthesized
the variously unsymmetrical zinc phthalocyanine com-
plexes with p-sulfophenoxy and p-carboxyphenoxy
substituted groups and observed the high ratio of monomer
in DMF solution [24]. Iliev’s group reported the synthesis
of zinc tetrakis (8-quinolineoxy-5-sulfonicacid) phthalo-
cyanine complexes [ZnPc(QnSO H) ] and proposed the
In this paper, two novel water-soluble FePc complexes,
i.e. iron(III) tetra-(4-carboxyphenoxy)phthalocyanine (3)
and iron(III) tetra-(8-quinolineoxy-5-sulfonicacid)phthalo-
cyanine (4), were synthesized for the detection of phenolic
pollutants. These two FePc complexes showed excellent
monodispersion in aqueous solution due to the high
hydrophilicity and space steric hindrance of selected
groups on Pc ring. Five phenolic compounds as model
pollutants could be oxidized rapidly and transformed into
pink dyes in the presence of FePc (3 or 4) and tert-butyl
hydroperoxide (t-BuOOH). To the best of our knowledge,
this is the first report upon the high catalytic effectiveness
of novel water-soluble iron phthalocyanines and their fast
chromogenic response to various phenolic pollutants. The
detail mechanism for the formation of dyes and the trans-
formation of iron–oxygen active species was proposed
based on the results of control experiments and current
theory of MPc catalysis. Moreover, the experimental con-
ditions (such as concentration of t-BuOOH and 4-AAP, pH
and temperature) for FePc catalyzed chromogenic reaction
were optimized for the purpose of fast chromogenic iden-
tification of phenolic pollutants.
3
4
high catalytic effectiveness attributed to the high monomer
concentration of ZnPc(QnSO H) [25]. It was reported that
3
4
the phthalocyanine complexes containing quaternized
pyridyl groups also had excellent water solubility and good
monodispersity [20, 21, 23]. These appropriate substituent
groups not only increased the dispersion of metal phtha-
locyanine in water or organic solvents, but also improved
the catalytic behavior.
Phenols and their derivates (such as chlorophenols and
naphtols) are common environmental pollutants generated
from industrial manufacturing processes of pesticide, fun-
gicide, chemical dye and polymer, and so on. Contamina-
tion by these phenolic chemicals is the most serious
problem for their high toxicity, non-biodegradation, and
heavy diffusibility in water environment [26, 27]. For their
damage to natural environment and potential threat to
human health, they have been listed as the priority control
pollutants by US Environmental Protection Agency [28].
Therefore, the requirement for fast identification of phe-
nolic pollutants and facile transformation of them to less
harmful products has been the great research interest. Since
1
965, the K Fe(CN) -based chromogenic reaction for
3
2 Experimental
6
measurement of phenolic compounds has been proved to
be an efficient approach and become a standard method for
the determination of phenols in water [29, 30]. Except for
this standard method, the chromogenic identification of
phenols based on catalytic oxidation by metal complexs
has been studied [31–33]. However, the investigations on
MPc catalytic chromogenic system have just been paid
enough attention until recent years. In 2006, Rajendiran
2.1 Materials
Phenol, 2-chlorophenol (2-CP), 4-chlorophenol (4-CP),
2,4-dichlorophenol (DCP), 1-naphthol (1-NP), and 4-ami-
noantipyrine were purchased from Sinopharm Chemical
Reagent Co., Ltd. Dimethyl sulfoxide (DMSO) and
n-pentanol were purified by pre-drying over BaO and dis-
[
34] presented that metal tetrasulfophthaloyanines (mainly,
tilled under reduced pressure. K
before use. Column chromatography purifications were
preformed on silica gel. Na HPO –KH PO buffer solution
(0.2 M, pH 5.0), Boric acid–borax buffer solution (0.2 M,
pH 9.0) and Na HPO –NaOH buffer solution (0.2 M, pH
2 3
CO was dried in oven
TSMnPc and TSFePc) could catalyze H O oxidation of
2
2
phenol assited with 4-aminoantipyrine (4-AAP). And our
group reported that tetranitro iron(II)phthalocyanine
2
4
2
4
(
TNFe(II)Pc) could efficiently catalyze oxygen oxidation
2
4
of phenols and chlorophenols into pink dyes of quinone
imide in the presence of 4-AAP in 2011 [35]. Although
these chromogenic reactions catalyzed by FePc complexes,
especially by homogeneous TSFePc catalyst, showed the
11.0) were used as catalytic reaction medium. Deionized
water was used in all the experiments. Methanol and ace-
tonitrile (HPLC grade, Sinopharm Chemical Reagent Co.,
Ltd.) were used as elution solution.
1
23

Synthesis of Two Novel Water-Soluble Iron Phthalocyanines
489
Scheme 1 Synthesis of novel
water-soluble iron
phthalocyanines (3 and 4) and
their precursors (1 and 2)
2
.2 Equipment
2.3.1 Synthesis of Precursors (1 and 2)
IR spectra were recorded on a Thermo Nicolet Nexus FT-
1
IR spectrometer with the standard KBr pellet method. H
Precursors (1 and 2) were prepared by reported methods
[24, 25].
NMR spectra were recorded on a Varian NMR System
1: Yield: 90 %; FT-IR (KBr pellets) 3081(m), 2235(s),
-1 1
1679(s), 1587(s), 1486(s), 1249(s), 852(s) cm ; H NMR
6
00 MHz Spectrometer. Elemental analyses were per-
formed on a Vario ELIII Elemental Analyzer. Catalytic
oxidation reaction was monitored by a UV–Vis spectro-
photometer (Shimadzu UV-2450) and high performance
liquid chromatography (HPLC, Dalian Elite P230 series).
The chromatography instrument was equipped with a C 18
reverse column (200 9 4.6 mm) and connected to a vari-
able wavelength UV–Vis detector (set at k = 220 nm).
The mobile phase consisted of acetonitrile–methanol–
water mixture (4:1:5, v/v) with a flow rate of 1.0 mL/min.
The column temperature was set at 25 ꢁC. The inject vol-
ume of each sample was 20 lL.
(600 MHz, d6-DMSO): d 7.26 (d, 2H, 2,6-H), 7.53 (m, 1H,
6 -H), 7.91 (d, 1H, 2 -H), 8.04 (d, 2H, 3,5-H), 8.15 (d, H,
0
0
0
5 -H), 13.05 (s, 1H, COOH).
2: Yield: 66 %; FT-IR (KBr pellets) 3430(s), 3100(w),
2240(s), 1640(w), 1600(s), 1240(s), 1190(s), 1100(s),
-
1
1
1040(s) cm ; H NMR (600 MHz, d6-DMSO): d 7.37
0
(dd, 1H, 6-H), 7.64 (d, 1H, 6 -H), 7.80 (dd, 1H, 2-H), 7.90
0
0
(d, 1H, 2 -H), 8.05 (d, 1H, 7-H), 8.09 (d, 1H, 5 -H), 8.91 (d,
1H, 1-H), 9.43 (d, 1H, 3-H).
2.3.2 Synthesis of Water-Soluble Iron Phthalocyanines
(
3 and 4)
2
.3 Preparation and Characterization of Water-Soluble
Phthalocyanines
The water-soluble iron phthalocyanine complexes (3 and 4)
were prepared via the route similar to the reported litera-
tures [24, 25] with some modifications. For the synthesis of
3, 2 mmol precursor 1, 0.6 mmol Fe (SO ) ꢀxH O and
There are two steps to synthesize the novel water-soluble
iron phthalocyanine complexes of 3 and 4. Step I: the
preparation of precursor (1) of 4-(3,4-dicyanophen-
oxy)benzoic acid and precursor (2) of 5-(3,4-dicyano-
phenoxy)quinoline-8-sulfonic acid. Step II: the synthesis of
water-soluble iron phthalocyanine complexes of 3 and 4
via an organic reaction in refluxed n-pentanol with
Fe (SO ) and precursor (1 or 2) as reactants and 1,8-
2
4 3
2
1 mL DBU were added into a 50 mL two-necked flask
containing 15 mL dried n-pentanol under magnetic stirring.
The mixture was heated slowly to 140 ꢁC to completely
dissolve all the organic solid under the protection of
nitrogen, and subsequently the temperature was kept to
reflux for 12 h. Thereafter, the mixture was cooled to room
temperature and the dark green product was obtained. The
n-pentonal was evaporated under reduced pressure and the
2
4 3
diazabicyclo[5.4.0]undec-7-ene (DBU) as the catalyst
Scheme 1).
(
123

4
90
J. Gong et al.
residue was washed with the mixed solution of water,
methanol and HCl solution for several times. Finally, the
resulting mixture was precipitated from DMSO and
methanol to give the desired product. Yield: 55 %. IR (KBr
pellet): 3425(m), 2931(m), 1714(m), 1599(s), 1473(w),
investigate the catalytic effectiveness of as prepared cata-
lyst 3 and 4. Fig. 1a, b shows the time-dependent UV–Vis
absorption spectra of oxidation of phenol and 2-CP,
respectively, assisted with 4-AAP and the formation pro-
cess of dyes in the presence of 3 and t-BuOOH. Obviously,
the absorbance peaks at 508 nm were observed for the
formation of conjugated products of antipyriloquinonei-
minium dyes, meanwhile, the color of solution changed
much rapidly from pale green to dark pink (see Video
data). When the catalytic reaction lasted for 10 min, the
absorbance intensity of dyes did not increase any more,
which meant the completion of catalytic oxidation. Dif-
ferent from TSFePc which has the Q bands of dimeric and
monmeric forms, only an intend monomer peak in Q band
of 3 was observed, which illuminated that the bulky phenyl
substituent groups on Pc ring prevent p–p interactions
between macrocycles of FePc complexes. Moreover, it is
notable that the intensity of Q band of 3 at 634 nm dis-
appeared when the absorbance of formed dyes achieved to
maximum. According to Nyokong’s investigation on liquid
phase oxidation of cyclohexane with peroxide catalyzed by
FePc complexes, absorbance peaks of FePc in Q band
could decrease gradually when peroxide was mixed with
FePc [15]. For our catalytic system, the disappearance of Q
band of 3 probably resulted from the decomposition of the
phthalocyanine ring, which was a result of the attack of the
-
1
1
265(w), 1238(s), 1161(m), 852(w), 557(w) cm . UV–Vis
-1
3
-1
(
DMSO), kmax/nm (loge, dm mol cm ): 333 (4.63),
5
6
1
71 (3.97), 629 (4.50). Anal. Calcd. for C H FeN O : C,
60 32 8 12
4.76; H, 2.90; N, 10.07. Found: C, 64.27; H, 2.70; N,
0.27.
The synthesis of 4 was similar to that of 3, except that
the precursor 2 was used instead of 1. The prepared crude
product of 4 was purified by flash column with the solution
of CH OH and CH Cl (v/v, 1:3) as the eluent. Yield:
3
2
2
1
1
6
2 %. IR (KBr pellet): 3431(m), 3093(w), 1722(s),
602(m), 1384(m), 1259(w), 1200(m), 1040(s), 818(w),
-
1
38(m), 596(w) cm . UV–Vis (DMSO), kmax/nm (loge,
3
-1
-1
dm mol cm ): 283 (4.62), 601 (3.94), 654 (4.53).
Anal. Calcd. for C H FeN O S : C, 55.89; H, 2.48; N,
6
8
36
12 16 4
1
1.50. Found: C, 55.51; H, 2.18; N, 11.79.
2
.4 Catalytic Oxidation Experiment
The typical catalytic oxidation of phenolic substrates with
-AAP by water-soluble iron phthalocyanine of 3 or 4 was
carried out in aqueous solution at room temperature using
4
•
tert-butyl hydroperoxide (t-BuOOH) as the oxidant. A
phthalocyanine ring by the BuO radical. It is noted that the
3
0 mL of deionized water, 10 mL of 4-AAP aqueous
homogeneous catalytic oxidation of DCP, 4-CP and 1-NP
could be completed just within 10 min in the presence of 3
and t-BuOOH (full UV–Vis spectra not shown). The cat-
alytic oxidation rate for these five substrates follows the
trend: DCP [ 2-CP [ phenol [ 4-CP [ 1-NP (Fig. 1c).
Interestingly, we found the situation of catalytic oxidation
of same phenolic substrates with t-BuOOH in the presence
of 4 was similar to that of 3 (Fig. 1d, e), except for longer
reaction time. (Fig. 1f) Based on the increase rate in dye
absorbance, we believe that catalyst 3 shows higher cata-
lytic activity than 4 under current conditions. The detailed
reasons for activity difference of catalyst 3 and 4 would be
discussed later.
-
solution (1.0 9 10 mol/L), 5 mL of phenolic solution
3
-
1.0 9 10 mol/L), and 5 mL of water-soluble iron
3
(
-
4
phthalocyanine stock solution (1.0 9 10 mol/L, dis-
solving 3 or 4 completely with the addition of proper
NaOH aqueous solution) were sequentially added into a
5
0 mL glass beaker. The catalytic reaction was initiated by
addition of 5 lL t-BuOOH solution following by contin-
uous magnetic stirring at 25 ꢁC. A portion of reaction
solution was collected at regular intervals and immediately
followed with the detection by a UV–Vis spectrophotom-
eter. HPLC was used to monitor the reaction process and
identify the productions in 2-CP system. The 2-CP and
4
-AAP were determined by spiking using standards via
comparison of retention times in HPLC profile.
3.2 Catalytic Process Monitoring by HPLC
Based on the analysis of UV–Vis absorbance spectra of
chromogenic reactions, we concluded that the production
of dye resulted from a fast oxidative coupling between
phenolic substrate and 4-AAP, and thus HPLC chromato-
gram was a suitable method to observe the transformation
process of these two kinds of substrate to dyes. The cata-
lytic oxidation system of 2-CP was selected for its fast
chromogenic identification. Fig. S1a and b of supplemen-
tary data presents HPLC chromatograms corresponding to
chromogenic reactions catalyzed by 3 and 4, respectively.
3
Results and Discussion
3
.1 Chromogenic Reaction of Five Phenolic Substrates
Catalyzed by 3 and 4
It has been reported that phenol and its various derivatives
could be efficiently oxidized by t-BuOOH in the presence
of water-soluble iron phthalocyanine catalyst [2, 9, 10, 13,
1
4], so we selected five kinds of phenolic substrates to
1
23

Synthesis of Two Novel Water-Soluble Iron Phthalocyanines
491
Fig. 1 The time-dependent
UV–Vis absorption spectra of
dye formation process in the
presence of 3 and t-BuOOH for
a phenol system and b 2-CP
system. c The comparison of
dye formation process for five
phenolic substrates with 3 as the
catalyst. (kabs = 508 nm); The
time-dependent UV–Vis
absorption spectra of dye
formation process in the
presence of 4 and t-BuOOH for
d phenol system and e 2-CP
system. f The comparison of dye
formation process for five
phenolic substrates with 4 as the
catalyst. (kabs = 508 nm)
Reaction conditions: phenolic
-4
substrates (1.0 9 10 M),
4
catalyst 3 and 4 (1.0 9 10 M)
and t-BuOOH (5.0 lL)
-
4
-AAP (2.0 9 10 M),
-
5
Obviously, the chromatographic peaks of 2-CP and 4-AAP
disappeared completely at 10 min, which meant the com-
pletion of their oxidative coupling reaction (see Fig. S1a in
supplementary data). Besides, there was only one strong
peak of dyes along with some very weak peaks (retention
time: 4.23 and 6.94 min) in the chromatographic profile of
yield = conversion 9 selectivity/100, the yield of dyes
could be determined as 93 and 95 % for 3 and 4 catalyzed
2-CP system, respectively. It is notable that 3 (or 4) cata-
lyzed chromogenic reactions could be developed to
become an analytical method for their excellent advantages
of fast reaction and high yield of dyes.
1
0 min. The chemical components corresponding to these
peaks could not be determined through the comparison of
their retention times with that of standards such as
p-benzoquinone and chloro-p-benzoquinones [35]. How-
ever, we could not find the peak of 3, the possible reason
was that the phthalocyanine complex was not eluted from
the chromagraphic column for its low polarity. Moreover,
similar chromatographic results could be obtained for 4
catalyzed 2-CP system just except the longer reaction time
of 30 min was needed. According to the relationship of
3.3 Proposed Mechanism of Catalytic Oxidation
Reaction
It is important to understand the mechanism of catalytic
oxidation reaction and determine the role of active species
in chromogenic process for the practical application of
catalytic technology. Therefore, some control experiments
were designed and performed. Firstly, we found that both
FePc catalyst and t-BuOOH were essential to fast
123

4
92
J. Gong et al.
Fig. 2 Dye formation processes
in 2-CP system catalyzed by 3
(
a) and 4 (b) under different
conditions. (kabs = 508 nm)
a Filled square typical catalytic
reaction; b filled circle in the
dark; c filled triangle N
bubbled; d inverted filled
2
triangle without catalyst; e filled
diamond without t-BuOOH;
f left pointing triangle tert-butyl
-
2
alcohol (1.0 9 10 M)
III
t
formation of dyes for the dyes could hardly be formed
without one of them (curve d and e in Fig. 2). Secondly,
the continuous nitrogen-bubbling operation was carried out
to testify the role of dissolve oxygen for the chromogenic
system exposed to air. Surprisingly, the oxygen was also
beneficial to the formation of dyes, especially in the sec-
ond-half stage of chromogenic reaction (curve a versus
curve c). Though the dyes could not be formed rapidly just
in oxygen saturated solution (curve e), the dioxygen should
play a crucial role of oxidant in the dye formation process.
Thirdly, to testify the effect of t-BuOOH in homogeneous
catalytic oxidation, tert-butyl alcohol (TBA, a scavenger
for hydroxyl radical) was used to testify the generation of
PcFe –OO Bu complex could undergo the homolytic or
heterolytic cleavage to produce iron(IV) or iron(V) oxygen
species, respectively. Since iron(V) oxidation state is less
accessible in phthalocyanine complex, and thus the
IV
•
PcFe =O could be the main active species with t-BuO as
the concomitant product [13]. Otherwise, the formation of
•
t-BuO radical could provoke side reactions for the
decomposition of the phthalocyanine complex during
substrates oxidation process [15]. In the second step, the
coordination of iron(IV) site with the two substrates of
phenol and 4-AAP proceeded. The electrons could be
abstracted from O atom of phenol and N atom of 4-AAP
•
and the corresponding radicals (Antipyrine-NH for 4-AAP
•
OH radicals from the homolytic cleavage of O–O bond of
and p-quinoid for 2-CP) could be generated rapidly. In the
third step, these active radicals could undergo an oxidative
coupling reaction with dioxygen as oxidant and the pink
dyes of quinone imide were produced. Meanwhile, the high
t-BuOOH. Indeed, the introduction of TBA showed no
detectable influence on the formation process of dyes
compared with typical catalysis (curve a versus curve f),
•
-
IV
illuminating that the OH would not be the main active
species participating in the generation of dyes. Moreover,
the typical catalytic reaction could also proceed efficiently
in the dark (curve b), which indicates that the chromogenic
reaction was not dependent on light irradiation and very
beneficial for practical measurement of phenolic pollutants.
For the mechanism of catalytic oxidation by water-sol-
uble iron phthalocyanine complexes combined with per-
oxide, more intensive investigations were focused on the
TSFePc/t-BuOOH and TSFePc/H O systems and the well
active PcFe =O complex would transform into the anionic
III
form of PcFe –O and then PcFe –OH resulted from the
-
III
III
combination of PcFe –O with H .
-
?
For the higher sterically hinder effect of quinolyl group
on Pc ring, it was well understood that the catalytic activity
of 4 was lower than that of 3 for the difficulty in the
IV
approach of substrates to iron atom of PcFe =O (coordi-
nation process) and the consequent disassociation from the
iron site. Therefore, the phenyl substituent group on Pc ring
was sufficient for the purpose of improving the homoge-
neous catalytic activity of FePc complexes.
2
2
known mechanism of active iron–oxygen species was
proposed by Meunier and Sorokin [2, 9, 10, 13–16]. Very
recently, the molecular structure of iron(IV) oxo phthalo-
3.4 Effect of the Concentration of t-BuOOH
and 4-AAP on Dye Formation
t
IV
?
cyanine complex of [(Pc Bu )Fe =O(Cl)] was deter-
4
mined via the low temperature UV–Vis and cryospray MS
technology by Sorokin’s group, which further testified the
reliability of proposed hypothesis of iron–oxygen species
For fast and accurate measurement of various phenolic
pollutants, the production of dyes from the transformation
of phenolic compounds should achieve to their maximum
as much as possible. It is known that the concentration of
oxidant shows great influence on oxidation reaction rate
and yield of products [16, 34]. Therefore, we selected
different concentrations of t-BuOOH to investigate reac-
tion rates and final production of dyes. Figure 3 shows the
[
36]. For the catalytic oxidation of various phenols by 3 (or
) in our system, the catalysis processes could also be
4
explained by their proposed mechanism (Scheme 2). In the
first step, when t-BuOOH was added into the reaction
III
t
solution, the initial product of PcFe –OO Bu peroxo
complex was formed. Alternatively, the O–O bond in
1
23

Synthesis of Two Novel Water-Soluble Iron Phthalocyanines
493
Scheme 2 Proposed
mechanism for the
transformation of chlorophenols
to dyes catalyzed by the system
of 3 (or 4) and t-BuOOH
Fig. 3 Effect of peroxide
oxidant on the absorbance of
dyes formed in the presence of 3
(
Reaction conditions: 2-CP
a) and 4 (b). (kabs = 508 nm)
-
4
1.0 9 10 M), 4-AAP
(
-
2.0 9 10 M), catalyst 3 and
(1.0 9 10 M)
4
(
-5
4
123

4
94
J. Gong et al.
absorbance profiles of dye formation process with
t-BuOOH dosage of 5 and 10 lL, respectively. It could be
seen clearly that the initial rate of dye formation with
2-CP was set as 1, 2 and 3 for 3 or 4 catalyzed chromogenic
system. From the comparison of absorbance-time profiles in
Fig. 4a (catalysis by 3), we found that the dye absorbance
-
4
1
0 lL t-BuOOH was higher than that with 5 lL t-BuOOH,
intensities with the 4-AAP concentration of 2.0 9 10
M
-
were a little greater than that of 3.0 9 10 M, while less
4
while more dyes were formed at the end of catalytic
reaction by 3 with less t-BuOOH (Fig. 3a). Interestingly,
the concentration of t-BuOOH on dye formation process by
production of dyes was formed when the concentration of
-
4
4-AAP is decreased to 1.0 9 10 M. For 4 catalyzed
chromogenic reactions, similar situation was found
(Fig. 4b). Therefore, double 4-AAP versus 2-CP was ben-
eficial for maximum production of dyes under selected
conditions, which could also be verified by HPLC results.
3
was similar to that by 4 (Fig. 3b). These phenomenons
could be interpreted as follows: more active iron–oxygen
species would be formed when double dosage of t-BuOOH
was used, which could accelerate the axial coordination of
substrates with these active species and result in more
formation of dyes at initial reaction stage, but excess
t-BuOOH could also provoke side reactions for slow deg-
radation of quinoneimine dyes [37]. Moreover, when H O
3.5 Effect of pH
Since various phenolic pollutants were water-soluble and
existed in two forms of undissociated molecules and
phenoxide ions, and their proportion between these two
forms could be dominated by pH, therefore, their catalytic
oxidation could be pH-dependent as well. According to
the pKa value (8.48) of 2-CP, three buffer solutions with
different pH were prepared to study the effect of pH on
dye formation process, i.e. Na HPO –NaOH buffer solu-
2
2
was used instead of t-BuOOH, the production of dyes
decreased obviously (Fig. 3). For the electronegativity of
peroxide group (–OOH) of t-BuOOH is higher than that of
H O , t-BuOOH has better combination effect with iron
2
2
center of phthalocyanine complexes.
The concentration ratio of 4-AAP versus phenolic sub-
strates was also an important experimental parameter for the
production of dyes. The concentration ratio of 4-AAP versus
2
4
tion (PBS, pH 11.0), boric acid–borax buffer solution
Fig. 4 Effect of concentration
of 4-AAP on the absorbance of
dyes formed in the presence of 3
(
Reaction conditions: 2-CP
a) and 4 (b). (kabs = 508 nm)
-
1.0 9 10 M), catalyst 3 and
4
(
-
5
4
(1.0 9 10 M), t-BuOOH
(
5 lL). The concentration of
-
-AAP is 1 9 10 M (filled
4
4
circle), 2 9 10 M (filled
triangle) and 3 9 10
(
-4
-4
M
filled triangle), respectively
Fig. 5 Dye formation processes in 2-CP system catalyzed by 3
(
(5 lL). Filled square in Na
2
HPO –NaOH buffer solution, pH 11.0;
4
PO buffer solution, pH 5.0; filled
4
a) and
k
4
abs = 508 nm) Reaction conditions: 2-CP (1.0 9 10 M),
(b) under different pH conditions, respectively.
filled circle in Na HPO –KH
2
4
2
-4
(
triangle in boric acid-borax buffer solution, pH 9.0; inverted triangle
in deionized water
-
-AAP (2.0 9 10 M), catalyst 3 and 4 (1.0 9 10 M), t-BuOOH
4
-5
4
1
23

Synthesis of Two Novel Water-Soluble Iron Phthalocyanines
495
Fig. 6 Effect of temperature on
the absorbance of dyes formed
in the presence of 3 (a) and 4
(
(
b), respectively.
abs = 508 nm) Kinetic plots
k
of dye formation at room
temperature (RT) and 40 ꢁC in
the presence of 3 (c) and 4 (d),
respectively. (The kinetic
parameter Ln S, where
? ? t
S = Abs /(Abs - Abs ) are
calculated from absorbance
versus reaction time). Reaction
conditions: 2-CP
-
4
(
(
4
1.0 9 10 M), 4-AAP
-
2.0 9 10 M), catalyst 3 and
(1.0 9 10 M), t-BuOOH
4
-
5
(
5 lL)
Table 1 The maximum intensity of dye absorption (Q
the time to complete chromogenic reaction (T
correlation coefficients (R ) for 2-CP system under different reaction
temperature
s
) at 508 nm,
), rate constants and
(
(
BBS, pH 9.0) and Na HPO –KH PO buffer solution
2 4 2 4
s
PBS, pH 5.0). Besides, the pure deionized water solution
2
was also used for comparison study. Figure 5a shows the
effect of pH on dye formation catalyzed by 3 in 2-CP
system. It is clear that the fastest formation of dyes along
with the highest final production proceeded in pure
deionized water (variable pH), while both acidic pH 5.0
and alkaline pH 11.0 buffer solutions were not beneficial
to the satisfied chromogenic effect due to the low dye
production. When faintly alkaline BBS with pH 9.0 was
used, the corresponding chromogenic effect was inferior
to that in deionized water (Fig. 5a). For 4 catalyzed 2-CP
system, the similar reaction trend was found just except
that the absorbance intensity of dyes was decreased after
-
2
2
Catalyst Temperature
Q
s
T
s
(min) k 9 10
(
R
-1
min )
3
3
4
4
RT
1.824
1.838
8
6
36.10
0.9869
0.9900
0.9679
0.9726
40 ꢁC
RT
43.325
10.604
27.455
1.816 30
1.729 15
40 ꢁC
low catalytic activity. In a similar way to 2-CP, for the
ionization equilibrium between t-BuOOH molecule and
-
t-BuOO anion, the activity of t-BuOOH would also be
1
0 min at pH 11.0, possibly, due to the dye degradation
(
Fig. 5b). In addition, to make clear the reason of fast
improved at the alkaline aqueous solution.
chromogenic reaction in deionized water, pH changes was
monitored and found the slight increase from 7.2 to 7.6 in
3.6 Effect of Reaction Temperature
3
catalyzed 2-CP system (from 7.4 to 7.9 for 4 catalyzed
-CP system), which illuminated that the significant
2
The influence of temperature on the dye formation process
was investigated in 2-CP system catalyzed by 3 and 4,
respectively. Figure 6a, b presented the time-dependent
absorbance profiles for dyes formed at room temperature
(RT) and 40 ꢁC, respectively. Interestingly, similar to our
previous investigation on TNFe(II)Pc catalyzed chromo-
genic reactions [35], more dyes were produced at RT while
the higher reaction rate of dye formation attributed to
contribution of molecular chlorophenols to their fast
transformation into dyes.
Furthermore, the stability of water-soluble FePcs (3 and
) and activity of t-BuOOH was also influenced by the pH
4
of reaction solution. We found that these two water-soluble
FePcs would be precipitated gradually in PBS of pH 5.0,
and their poor solubility in acidic solution resulted in their
123

4
96
J. Gong et al.
Reference
Table 2 Comparison of chromgenic reactions catalyzed by various iron phthalocyanine complexes
-
2
-1
)
Catalyst
Substrate
Oxidation
k 9 10 (min
Byproduct
-
4
TNFe(II)Pc
2-CP (1 9 10 M)
Dissolved O
2
5.338
36.10
Something unknown
Very few
[35]
-4
3
2-CP (1 9 10 M)
t-BuOOH (5 lL)
t-BuOOH (5 lL)
Current method
Current method
[34]
-4
4
2-CP (1 9 10 M)
10.604
19.62
Very few
-
3
TSFe(III)Pc
Phenol (2 9 10 M)
2
H O
2
(500 lL)
Not given
-
4
3
4
Phenol (1 9 10 M)
t-BuOOH (5 lL)
t-BuOOH (5 lL)
32.822
10.219
Not given
Current method
Current method
-
4
Phenol (1 9 10 M)
Not given
higher temperature of 40 ꢁC. Based on the comparison of
rate constants calculated from pseudo-first-order equation
essential for the recombination of p-quinoid radical and
•
Antipyrine-NH . The chromogenic effect in our catalytic
(
Fig. 6c, d), 4 catalyzed chromogenic system was more
sensitive to temperature than that of 3 for their obvious
system was significantly influenced by the concentration of
t-BuOOH and 4-AAP, pH and temperature, respectively.
Compared with other MPc catalytic chromogenic system,
our system has the obvious characteristics of less side
reaction, fast catalytic oxidation and the chromogenic
reaction was not dependent on light irradiation. In con-
clusion, our investigation has illustrated a potential appli-
cation of fast chromogenic identification and measurement
of phenolic pollutants.
-
1
difference between 10.604 (RT) and 27.455 min (40 ꢁC)
Table 1). Indeed, RT could already meet the requirement
(
of chromogenic assay for the fast identification of phenolic
pollutants.
3
.7 Comparison of Several Chromgenic Systems
We summarized the features of various FePc catalyzed
chromogenic reaction for detail comparison (Table 2). For
the identification of 2-CP pollutant, the pseudo-first-order
model was suitable for illuminating the reaction kinetic of
dye formation. Therefore, the catalytic activity could fol-
low the sequence: 3 [ 4 [ TNFe(II)Pc. Despite of the
lower activity and yield of heterogeneous TNFe(II)Pc, it is
superior to other homogeneous catalysts due to its recy-
clable performance and the utilization of green oxidant of
oxygen. For the identification of phenolic pollutant with
homogeneous catalyst of 3, 4 and TSFePc, the chromo-
genic reaction with catalyst 3 still had fastest reaction rate
in three homogeneous catalyst systems. Besides, it is noted
that only less quantity of oxidant (5 lL t-BuOOH) was
used in 3 and 4 catalyzed reaction and sufficient for fast
and obvious chromogenic effect. From the analytical point
of view, catalyst 3 was promising for the application of
identification and measurement of phenolic pollutants in
the future.
Acknowledgments This work was financially supported by the
National Natural Science Foundation of China (Nos. 61377092 and
51302241), the Fundamental Research Funds for the Central Uni-
versities (WUT: 2013-IV-010), the Science and Technology Key
Project of Education Department of Henan Province (No. 13B430233
and No. 13A150743). We thank professor Yu Cao (College of
Chemistry, Huazhong Normal University) for the help of chemical
characterization and measurement. We thank MSc Shilong Zhao
(
School of Materials Science and Engineering, Wuhan University of
Technology) for the help of purification of two novel water-soluble
iron phthalocyanines.
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