5,10,15,20-Tetrakis-(4-sulfonatophenyl)porphyrinatocobalt(II) supported on ion exchange resin as reusable and effective catalyst for the oxidative coupling of 2-aminophenol to 2-aminophenoxazine-3-one

Article abstract of DOI:10.1016/j.catcom.2013.06.003

5,10,15,20-Tetrakis-(4-sulfonatophenyl)porphyrinatocobalt(II) supported on Amberlite ion exchange resin showed good catalytic activity as heterogeneous catalyst for the biomimetic oxidative coupling of 2-aminophenol (OAP) to 2-aminophenoxazine-3-one (APX). The reaction rate was found to fit a Michaelis-Menten kinetic model for saturation of catalyst site with increasing OAP concentration. Recycling of the Co(II)TPPS-resin system showed no loss of activity after six successive runs.

Full text of DOI:10.1016/j.catcom.2013.06.003

Catalysis Communications 40 (2013) 125–128
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
5,10,15,20-Tetrakis-(4-sulfonatophenyl)porphyrinatocobalt(II)
supported on ion exchange resin as reusable and effective catalyst for the
oxidative coupling of 2-aminophenol to 2-aminophenoxazine-3-one
⁎
M. Hassanein , S. El-Khalafy, S. Shendy
Tanta University, Faculty of Science, Department of Chemistry, Tanta 31527, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
5,10,15,20-Tetrakis-(4-sulfonatophenyl)porphyrinatocobalt(II) supported on Amberlite ion exchange
resin showed good catalytic activity as heterogeneous catalyst for the biomimetic oxidative coupling of
2-aminophenol (OAP) to 2-aminophenoxazine-3-one (APX). The reaction rate was found to fit a
Michaelis–Menten kinetic model for saturation of catalyst site with increasing OAP concentration.
Recycling of the Co(II)TPPS-resin system showed no loss of activity after six successive runs.
© 2013 Elsevier B.V. All rights reserved.
Received 9 March 2013
Received in revised form 28 May 2013
Accepted 5 June 2013
Available online 14 June 2013
Keywords:
Cobalt(II) tetraphenylporphyrin
Autoxidation
2-Aminophenol
2-Aminophenoxazine-3-one
Anion exchange resin
1. Introduction
complexes immobilized on polymers and mesoporous silica [28,29] as
catalysts.
Oxidation reactions catalyzed by metalloporphyrins have attracted
attention in relevance to the activation of molecular oxygen and oxygen
atom transfer to organic substrates, which are processes dependent on
cytochrome P-450 in biological systems [1,2]. The utility of these
catalysts would be increased significantly if they could be attached to
solid supports, since this should stabilize the catalysts and aid their
recovery and reuse. Moreover, the local environment of the support
can bring higher selectivity and prevent catalyst self-oxidation [3,4].
Synthetic metalloporphyrins have been used to catalyze the transfer
of an oxygen atom from a great variety of oxidizing agents into organic
molecules [1,2,5–18]. Over the past few years, the oxidation of
2-aminophenol to 2-amino-3H-phenoxazine-3-one through catalytic
activation of dioxygen by transition metal salts and complexes has
been intensively studied with the aim to mimic the activity of
phenoxazinone synthase which catalyzes the oxidative coupling of
two molecules of substituted 2-aminophenol to the phenoxazinone
chromophore in the final step at the biosynthesis of actinomycin D
[19–25]. The naturally occurring antineoplastic agent actinomycin D is
used clinically for the treatment of certain types of cancer [26,27]. The
catalytic oxidation of OAP to APX has mostly been studied in homoge-
nous systems [19–25]. However, several studies have been reported
on the heterogeneous oxidation of AOP to APX, using transition metal
In the present investigation, we report 5,10,15,20-tetrakis-(4-
sulfonatophenyl)porphyrinatocobalt(II) [Co(II)TPPS] immobilized
on the resin Amberlite 400 bearing quaternary ammonium groups as
heterogeneous catalyst for the oxidative coupling of 2-aminophenol to
2-amino-3H-phenoxazine-3-one in water.
2. Experimental
2.1. Materials and reagents
2-Aminophenol (Aldrich) was used as received. Meso-
tetraphenylporphyrin was synthesized and purified as reported [30].
The sulfonation of meso-tetraphenylporphyrin was performed with fum-
ing sulfuric acid according to the published method [31]. Metallation of
the sulfonated tetraphenylporphyrin with cobalt chloride was carried
out as previously reported [32]. Elemental microanalysis of sulphur in
Co(II)TPPS found:11.5% S. Resin Amberlite CG-400 (Cl) (Prolabo,
100–200 mesh) was washed with a four-fold (v/v) excess of 5% aqueous
sodium chloride followed by water, methanol and acetone. Elemental
analysis of chlorine indicated 3.4 mmol of Cl/g of resin. Water used in
the reactions was double distilled (deionized water).
2.2. Preparation of Co(II)TPPS supported on Amberlite resin
A solution of Co(II)TPPS (0.015 mmol) in 10 ml of water was added
dropwise to a stirred suspension of resin(0.088 g, 0.3 mmol) in 10 ml of
⁎
Corresponding author. Tel.: +20 1008591157; fax: +20 40 3350804.
E-mail address: mahmoudtantauniversity2004@yahoo.com (M. Hassanein).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.06.003

126
M. Hassanein et al. / Catalysis Communications 40 (2013) 125–128
Table 2
water. The reaction mixture was stirred under nitrogen atmosphere
overnight at room temperature. The resin was then filtered off and
washed with methanol. UV–vis spectra indicated no Co(II)TPPS in the
filtrate.
Effect of [resin] on the rate of autoxidation of OAPa.
b
Amberlite resin
(gm)
kobs
(mol L−1 min−1) × 105
0.022
0.044
0.088
0.176
0.264
0.645
0.949
1.187
0.989
0.791
2.3. Auto-oxidation reactions
Oxidations of 2-aminophenol were performed as previously [25] by
stirring of 100 ml of an aqueous mixture containing 5% volume
methanol in a 250 ml round bottomed flask attached to a gas burette.
The pH was adjusted to 9.0 using borate buffer. All reactions were
carried out at 40 °C and at constant oxygen pressure. Lower partial
pressures of oxygen were obtained by use of oxygen/nitrogen mixture
at 1 atm total pressure. After completion of the reaction the mixture
was extracted by diethyl ether. The extract was analyzed by means
of silica gel thin- layer chromatography using chloroform/methanol
(volume ratio of 20:1). The reaction products were identified by
comparison with authentic samples. All kinetic experiments were
carried in duplicate and reproducible results were obtained.
a
All reactions were carried out under conditions reported in (Table 1)
at pH = 9.0.
b
Initial rate constant calculated from the plot of oxygen consumption
vs. time.
was linear with time, indicating a zero-order dependence on substrate
concentration.
The auto-oxidation of 2-aminophenol was studied in the pH range
of 7.0–11.0, using sodium borate and sodium phosphate buffers. The
initial rate constant kobs of the auto-oxidation reaction reached an
optimum at pH 9.0 and then decreased at higher pH values (Table 1).
The decrease of reaction rate at pH values higher than 9 indicates that
the 2-aminophenoxide anion is not the active species.
To test the effect of mass transfer on the oxidation reaction a
shaker water thermostat (Julabo SW 20 C) was used to shake the
heterogeneous reaction mixture at 120 rpm at fixed temperature of
40
0.1 °C. The reaction was carried out under conditions reported
in Section 2.3.
The effect of concentration of ion exchange resin on the initial rate
constant kobs has been studied by varying the concentration of resin
systematically while the concentration of Co(II)TPPS was kept constant
(0.015 mmol). Data summarized in Table 2 shows that maximum
activity has been attained at 0.3 mmol of the resin (resin/Co(II)TPPS
ratio = 20). The decrease in the rate constant kobs at higher concentra-
tion of resin could be attributed to a decreased concentration of Co(II)
TPPS in the resin phase.
3. Results and discussion
3.1. Auto-oxidation of 2-aminophenol
The activity of Co(II)TPPS supported on ion exchange resin CG-400
was investigated as heterogeneous catalyst for the autoxidation of
OAP to APX. Auto-oxidation of OAP catalyzed by Co(II)TPPS bound
to ion exchange resin CG-400 at pH 9.0 and slightly less than 1 atm
of dioxygen at 40 °C gave within two hour APX in 85% yield and
15% of unreacted OAP. While the oxidation of OAP catalyzed by solu-
ble Co(II)TPPS under the same reaction conditions gave 65% yield of
APX. The higher activity of Co(II)TPPS supported on ion exchange
resin compared to soluble Co(II)TPPS could be attributed to absorption
of the OAP by the resin, which provides a high concentration of the re-
actant at the active site.
Fig. 1 shows the effect of varying the concentration of Co(II)TPPS
supported on fixed amount of resin (0.3 mmol) on the initial rate
constant kobs of the oxidation reaction. The rate constants increased
with increasing the concentration of Co(II)TPPS from 0.38 × 10−5
M
to 1.5 × 10−5 M then decreased at higher Co(II)TPPS concentrations.
Two major causes are believed to be responsible for the decrease
of rate constant kobs at high concentration of cobalt(II) porphyrin
complex: (a) aggregation of Co(II)TPPS and (b) intraparticle diffusion
The rate of 2-aminophenol consumption was determined by
measuring the amount of dioxygen consumed using a gas burette.
After a short induction period, the volume of dioxygen consumed
Table 1
Effect of pH on the rate of autoxidation of OAPa.
pHb
kobs
c
(mol L−1 min−1) × 105
7.0
8.0
9.0
10.0
11.0
0.36
0.98
1.18
1.1
0.76
a
All experiments were carried out at 40 °C and oxygen
pressure of 740 mm Hg with magnetic stirring of 1.5 mmol
of OAP dissolved in 5 ml of methanol dispersed in 100 ml of
distilled water containing 0.015 mmol of Co(II)TPPS support-
ed on 0.3 mmol of resin.
b
The pH was adjusted to 8.0–10.0 using sodium borate
buffers and the pH was adjusted to 7and 11 using phosphate
buffers.
c
Initial rate constant calculated from the plot of oxygen
Fig. 1. Dependence of initial rate constant kobs on Co(II)TPPS concentration. Reactions
consumption vs. time.
were carried out at pH = 9, for conditions, see footnote (a) of Table 1.

M. Hassanein et al. / Catalysis Communications 40 (2013) 125–128
127
limitation. Aggregated Co(II)TPPS is known to be less reactive than the
monomeric form [33].
To test for possible external mass transfer limitation of the overall
reaction rate, the reaction was conducted with vigorous shaking of
the reaction mixture instead of magnetic stirring under standard
reaction conditions of Table 1 at pH 9.0. Magnetic stirring gave a
reaction 1.2 times faster as vigorous shaking. The rate constants are
considered identical within experimental error, since the variation
in the rate constant was typically 10%. This indicates that the rate
of autoxidation of OAP is not limited by mass transfer of dioxygen
or OAP to the active site. The temperature dependence of the rate
constant kobs from 28 °C to 55 °C gave an Arrhenius activation energy
of 10.08 kJ/mol.
The dependence of the initial rate constant kobs of the oxidation
reaction of OAP on the concentration of 2-aminophenol was inves-
tigated in the range of 5 × 10−4 M to 3 × 10−3 M (Fig. 2a). The
initial rate constants kobs increased with increasing the concentration
of 2-aminophenol to 1.5 × 10−3 M and then leveled off. A double
reciprocal Lineweaver–Burk plot (Fig. 2b) showed that the rate fit a
Michaelis–Menten kinetic model for saturation of catalyst site with
increasing concentration of OAP [34].
Fig. 3. a) Dependence of initial rate constant on partial pressure of dioxygen. Reactions
were carried out at pH = 9, for conditions, see footnote (a) of Table 1. b) Lineweaver–
Burk plot of data in Fig. 3a.
The results evaluated from the Lineweaver–Burk plot are Vmax
=
1.32 × 10−5 M min−1, KM = 3.25 × 10−3 M. The data illustrated in
Fig. 3 show that the rate constants kobs of auto-oxidation of OAP
catalyzed by Co(II)TPPS bound to resin depend on the partial
pressure of dioxygen for saturation of catalyst site.
It is well known that o-benzoquinone monoimine (BQMI) is the key
intermediate in the oxidative coupling of OAP to APX [19–25]. The
overall reaction requires several oxidative dehydrogenation steps
involving OAP, molecular oxygen and o-benzoquinone monoimine as
reactants to produce APX [19–25].
On the basis of the results of the observed rate dependence on
2-aminophenol concentration and pressure of dioxygen, the proposed
mechanism for the auto-oxidation of 2-aminophenol catalyzed by
Co(II)TPPS supported on ion exchange resin involves interaction of
the catalyst with a mole of OAP, which reacts with a mole of O2 to
form superoxo derivative (steps 1 and 2 in Scheme 1). Both steps 1
and 2 are assumed to be pre-equilibria involving the catalyst, substrate
(OAP) and O2. The rate determining step involves H-atom abstraction
within the ternary complex forming the reactive amino-phenoxyl
radical (step 3, Scheme 1) which disproportionate leading to the key
intermediate o-benzoquinone monoamine (BQMI) in Scheme 1. The
o-benzoquinone monoimine reacts with OAP in the presence of oxygen
to produce APX [19–25].
Fig. 2. a) Dependence of initial rate constant on OAP concentration. Reactions were car-
ried out at pH = 9, for conditions, see footnote (a) of Table 1. b) Lineweaver–Burk plot
of data in Fig. 2a.

128
M. Hassanein et al. / Catalysis Communications 40 (2013) 125–128
Scheme 1. Proposed mechanism for the oxidation of OAP catalyzed by Co(II)TPPS-resin.
[8] K.A. Jorgensen, Chemical Reviews 89 (1989) 431.
[9] B. Meunier, in: R.A. Sheldon (Ed.), Metalloporphyrins in Catalysis Oxidation,
Marcel Dekker, New York, 1994, p. 133, , (Chapter 5).
3.2. Re-use of catalyst
Reuse of Co(II)TPPS supported on ion exchange resin was tested for
its stability in repeat experiments. The re-use of the catalyst was carried
out under reaction conditions of Table 1 at pH 9.0. The reaction was
followed by dioxygen uptake. After 100% conversion of OAP, the initial
amount of 2-aminophenol was again fed into the reaction mixture
without removal of the reaction products. The recycled Co(II)TPPS/
resin catalyst showed no change in reactivity after six successive runs.
The site isolation of the Co(II)TPPS by supporting it on the ion ex-
change resin prevented porphyrin aggregation and intermolecular
self-oxidation of the cobalt porphyrin catalyst [4].
[10] X.Y. Wang, R.J. Moterkaitis, A.E. Martell, Inorganic Chemistry 23 (1984) 271.
[11] N. Colclough, J.R. Lindsay Smith, Journal of the Chemical Society, Perkin Transac-
tions 2 (1994) 1139.
[12] N.W.J. Kamp, J.R. Lindsay Smith, Journal of Molecular Catalysis A: Chemical 113
(1996) 131.
[13] H. Saleem, L.S. Kerry, Applied Biochemistry and Biotechnology 63–65 (1997) 845.
[14] Y. Yan, E. Kang, K. Yang, S. Tong, C. Fang, S. Liu, F. Xiao, Catalysis Communications
56 (2004) 387–390.
[15] M. Fukushima, K. Tatsumi, Journal of Molecular Catalysis A: Chemical 245 (2006) 178.
[16] H. Zeng, Q. Jian, Y. Zhu, X. Yan, X. Liang, H. Hu, Q. Liu, W. Lin, C. Guo, Journal of Porphy-
rins and Phthalocyanines 10 (2006) 96.
[17] M.T. Hassanein, S.S. Gerges, M.A. Abdo, S.H. El-Khalafy, Journal of Porphyrins and
Phthalocyanines 9 (2005) 621–625.
[18] M. Hassanein, S. Gerges, M. Abdo, S. El-Khalafy, Journal of Molecular Catalysis A:
Chemical 268 (2007) 24–28.
[19] Z. Szeverényi, E.R. Milaeva, L.I. Simándi, Journal of Molecular Catalysis 67 (1991)
252–258.
4. Conclusion
[20] L.I. Simándi, T.M. Simándi, Z. May, G. Besenyei, Coordination Chemistry Reviews
245 (2003) 85–93.
[21] T. Horvath, J. Kaizer, G. Speier, Journal of Molecular Catalysis A: Chemical 215 (2004).
[22] T.M. Simándi, L.I. Simándi, M. Gyor, A. Rockenbauer, A. Gomory, Journal of the
Chemical Society Dalton Transactions (2004) 1056.
[23] I.Cs. Szigyártó, T.M. Simándi, L.I. Simándi, L. Korecz, N. Nagy, Journal of Molecular
Catalysis A: Chemical 251 (2006) 270.
[24] M. Hassanein, M. Abdo, S. Gerges, S. El-Khalafy, Journal of Molecular Catalysis A:
Chemical 287 (2008) 53–56, (and references therein).
Co(II)TPPS bound to resin Amberlite-CG 400 showed good catalytic
activity for the autoxidation of OAP to APX. High conversion of OAP to
2-amino-3H-phenoxazine-3-one has been obtained under mild reac-
tion conditions. The rate of oxidation was found to be affected by the
pH and the concentration of Co(II)TPPS and the resin. Immobilizing.
cobalt(II) porphyrin complex on the ion exchange resin improved its
stability. Recycling of the Co(II)TPPS-resin system showed no loss of
activity after six successive runs.
[25] S.H. El-Khalafy, M. Hassanein, Journal of Molecular Catalysis A: Chemical 363–364
(2012) 148.
[26] E. Frei, Cancer Chemotherapy Reports. Part 1 58 (1974) 49.
[27] U. Holstein, Chemical Reviews 74 (1974) 625.
[28] S.A. El-Safty, J. Evans, M.Y. El-Sheikh, A.B. Zaki, Colloids and Surfaces A 203 (2002)
217.
[29] M.R. Maurya, S. Sikarwar, T. Joseph, S.B. Halligudi, Journal of Molecular Catalysis
A: Chemical 236 (2005) 132.
References
[1] J.T. Groves, T.E. Nemo, R.S. Myers, Journal of the American Chemical Society 101
(1979) 1032.
[2] B. Meunier, Chemical Reviews 92 (1992) 1411.
[3] D.C. Sherrington Pure, Applied Chemistry 60 (1986) 401.
[4] M. Hassanein, S. Gerges, M. Abdo, S. El-Khalafy, Journal of Molecular Catalysis A:
Chemical 240 (2005) 22.
[5] J.R. Lindsay Smith, in: R.A. Sheldon (Ed.), Metalloporphyrins in Catalysis Oxida-
tion, Marcel Decker, New York, 1994, , (Chapter 11).
[6] D. Mansuy, Coordination Chemistry Reviews 125 (1993) 129.
[7] B.A. Arndtsen, R.G. Bergamm, T.A. Mobley, T.H. Petreson, Accounts of Chemical
Research 28 (1995) 154.
[30] A.D. Alder, F.R. Longo, J.D. Finarelli, J. Goldmarcher, J. Assour, L. Korsakoff, Journal
of Organic Chemistry 32 (1967) 476.
[31] E.B. Fleischer, J.M. Palmer, T.S. Srivastava, A. Chatterjee, Journal of the American
Chemical Society 93 (1971) 3162.
[32] H. Turk, W.T. Ford, Journal of Organic Chemistry 56 (1991) 1253.
[33] M.D. Assis, J.R. Lindsay Smith, Journal of the Chemical Society, Perkin Transactions
2 (1998) 2221.
[34] L. Michaelis, M.L. Menten, Biochemische Zeitschrift 49 (1913) 333.