Selective oxidation of 2-naphthol to 2-hydroxy-1,4-naphthoquinone with hydrogen peroxide catalyzed by 5,10,15,20-tetrakis(p-sulfonatophenyl)porphinatomanganese(III) chloride in aqueous solution.

Article abstract of DOI:10.1016/j.catcom.2017.03.016

2-Naphthol has been selectively oxidized to 2-hydroxy-1,4-naphthoquinone (HNQ, Lawsone) with hydrogen peroxide in presence of 5,10,15,20-tetrakis-(p-sulfonatophenyl)porphinatomanganese (III) chloride as catalyst in alkaline aqueous solution. The catalytic oxidation afforded 2-hydroxy-1,4-naphthoquinone in high yield (95%). The effect of reaction parameters on the catalytic activity and the yield of HNQ have been investigated. UV–vis spectral analysis during oxidation reaction indicated that oxomanganese intermediate O = Mn(IV)TPPSCl was the active species in the oxidation reaction.

Full text of DOI:10.1016/j.catcom.2017.03.016

Accepted Manuscript
Selective
2-hydroxy-1,4-naphthoquinone with hydrogen peroxide catalyzed
by 5,10,15,20-tetrakis(p-sulfonato-
oxidation
of
2-naphthol
to
phenyl)porphinatomanganese(III) chloride in aqueous solution.
M. Hassanein, S. El-Khalafy, S. Shendy
PII:
DOI:
Reference:
S1566-7367(17)30102-4
doi: 10.1016/j.catcom.2017.03.016
CATCOM 4973
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
11 December 2016
16 March 2017
18 March 2017
Please cite this article as: M. Hassanein, S. El-Khalafy, S. Shendy , Selective oxidation
of 2-naphthol to 2-hydroxy-1,4-naphthoquinone with hydrogen peroxide catalyzed by
5,10,15,20-tetrakis(p-sulfonato-phenyl)porphinatomanganese(III) chloride in aqueous
solution.. The address for the corresponding author was captured as affiliation for all
authors. Please check if appropriate. Catcom(2017), doi: 10.1016/j.catcom.2017.03.016
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ACCEPTED MANUSCRIPT
Selective oxidation of 2-naphthol to 2-hydroxy-1,4-naphthoquinone with
hydrogen peroxide catalyzed by 5,10,15, 20-tetrakis(p- sulfonato-
phenyl)porphinatomanganese(III) chloride in aqueous solution.
M. Hassanein*, S. El-Khalafy, S. Shendy
Tanta University, Faculty of Science, Department of Chemistry, Tanta
31527, Egypt.

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Abstract
2-Naphthol has been selectively oxidized to 2-hydroxy-1,4-naphthoquinone
(HNQ, Lawsone) with hydrogen peroxide in presence of
5, 10, 15, 20-tetrakis-(p-sulfonatophenyl)porphinatomanganese (III) chloride
as catalyst in alkaline aqueous solution. The catalytic oxidation afforded
2-hydroxy-1,4-naphthoquinone in high yield (95 %). The effect of reaction
parameters on the catalytic activity and the yield of HNQ have been
investigated. UV–vis spectral analysis during oxidation reaction indicated
that oxomanganese intermediate O=Mn(IV)TPPSCl was the active species
in the oxidation reaction.
Keywords: Selective catalytic oxidation; 2-Naphthol; Metalloporphyrins;
2-Hydroxy-1,4-naphthoquinone, Hydrogen peroxide.
_____________________________________________________________
* Corresponding author; Tel.: +2 01008591157; fax: +20403350804.
E-mail address: mahmoudtantauniversity2004@yahoo.com
1. Introduction
Selective catalytic oxidation of phenols is of industrial and biological
importance [1]. 2-Hydroxy-1,4-naphthoquinone ( HNQ, Lawsone ) is a
naturally occurring compound [2,3]. 2-Hydroxy-1,4-naphthoquinone and its
derivatives have antitumor activity, [4-7] . It is also used as hair dyestuff [8]
and as an ultraviolet filter in sunscreen formulation [9].
There are only few studies reported in the literature on the selective catalytic
oxidation of naphthol to HNQ [9-12]. The reported methods showed low to

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moderate conversion of 2-naphthol to HNQ. The oxidation of 2-naphthol
with hydrogen peroxide in methanol catalyzed by iron(III) complex of
tetra(4-methoxy)phenyl porphyrin at 0oC gave a yield of 57% HNQ [9].
Zhao and co-workers reported that cobalt porphyrins immobilized on
polymer microspheres as catalysts for the oxidation of 2-naphthol to HNQ
with molecular oxygen in alkaline methanol produced a yield of 28% to 31%
of HNQ [11]. Copper phthalocyanine catalyzed the conversion of 2-naphthol
to 59% of HNQ with hydrogen peroxide in alkaline aqueous solution [12].
The highest conversion previously reported was 62 % for the oxidation of 2-
naphthol to HNQ with molecular oxygen as oxidant and tetra-(4-
methoxyphenyl)porphyrin iron(III) chloride as catalyst in alkaline solution
of 2-propanol at 45C [10].
Therefore it is necessary to investigate an efficient catalytic reaction system
for preparation of HNQ in high yield. A wide variety of oxidation reactions
have been efficiently catalyzed by transition metal complexes of porphyrins
[13-19].
In the present work, we report efficient catalytic system for selective
conversion of 2-naphthol to HNQ in high yield, using water soluble
5,10,15,20-tetrakis-(p-sulfonatophenyl)porphinatomanganese (III) chloride
Mn(III)TPPSCl (Scheme 1) as catalyst and hydrogen peroxide as oxidant in
aqueous solution.
2. Experimental
2.1. Materials and reagents
Hydrogen peroxide 30% aqueous solution (Merck) and 2-naphthol
(Aldrich) were used as received. 5,10,15,20-tetrakis(p-sulfonato-
phenyl)porphinatomanganese(III) chloride was prepared in three steps: a)

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meso-tetraphenylporphyrin (TPP) was prepared and purified as reported
[20]. Elemental microanalysis, found: 79.40% C, 4.90% H, 7,59% N.
b) sulfonation of TPP with fuming sulfuric acid according to the published
method [21] gave 5,10,15,20-tetrakis(p-sulfonatophenyl)porphyrin (TTPS).
Elemental microanalysis of sulphur in TPPS found: 11.5% S. c) Metallation
of TPPS with manganese chloride was performed as described previously
[21] gave Mn(III)TPPSCl. Analysis of Manganese by thermogravimetric
method, found: 4.41%, calculated: 4.6%. UV-Vis: (H2O) λmax, nm (ε, mol-1
L cm-1) 378 (2.87 x 104), 399 (2.94 x104), 468 (5.44 x 104), 565 (0.6 x104),
598 (0.41x104).
All reactions were carried out in double distilled deionized water.
2.2. Instruments
Spectrophotometric measurements were carried out on Schimadzu 3101Pc
Uv-vis Spectrometer. IR spectra were recorded on Perkin-Elmer 1420
1
spectrophotometer using KBr disc technique. H NMR spectra at 300 MHz
was obtained on a Brucker AC spectrometer. Thermogravimetric analysis
(TGA) was performed on thermogravimetric analyzer (Perkin Elmer-
Simultaneous Thermal Analyzer- STA 6000) in the temperature range 30-
995oC at a heating rate 20oc min, using 10-14 mg of powdered complex
under oxygen atmosphere.
2.3 Catalytic Oxidation of 2-Naphthol
Hydrogen peroxide (0.8 ml) was added to a stirred mixture of 2-naphthol
(1.0 mmol), NaOH (100 mmol) and Mn(III)TPPSCl (0.01mmol) dissolved
in 25ml of water at 25oC. Orange color appeared after addition of H2O2. The
reaction mixture was allowed to stand at room temperature for 15 min. The

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resulted mixture was then neutralized with 0.1 M HCl. The precipitate was
filtered off, washed with water, dried in vacuum and was recrystallized in
ethanol. Melting point of the product: 192oC, Lit. m.p.192-194 [11]. IR
(KBr) showed a band at1665 cm-1 assigned to νC=O.
1H NMR (DMSO; Me4Si): δ: 6.2 (s, 1H, Ph-H), 7.75-7.85 (t, 2H, Ph-H),
7.95-8.15(d, 2H, Ph- H), 11.7 (s, 1H, OH).
The effect of reaction parameters on the yield of reaction product was
determined by UV-vis technique. The isolated reaction product was
dissolved in 50 ml of 0.1 N NaOH and was determined quantitatively by
measuring the absorbance at 452 nm characteristic for HNQNa.
3. Results and Discussion
3.1. Catalytic oxidation of 2-naphthol
Oxidation of 2-naphthol (1.0 mmol) with H2O2 (8 mmol) catalyzed by
Mn(III)TPPSCl (0.01 mmol), performed in aqueous alkaline solution of
NaOH( 100 mmol) in 25 ml H2O at 22C gave 95 % yield of HNQ within 15
min. Under the same reaction conditions, only 5 % yield of HNQ was
obtained in absence of catalyst.
Compared to previous reported methods our catalytic reaction gave higher
yield of HNQ and combines the advantages of high activity, high selectivity,
a clean oxidant of H2O2 and water as environmentally clean solvent. Most
previous reported methods were carried out in organic solvents [9-12].
To optimize the catalytic system, the effect of different reaction parameters
on the efficiency of this oxidation has been studied.
The effect of concentration of Mn(III)TPPSCl on the yield of the oxidation
product HNQ was studied by varying its concentration from 0.0025 mmol to
0.03 mmol, while the concentration of 2-naphthol (0.10 mmol) ,NaOH (36

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mmol) and H2O2 (8.0 mmol) in 25 ml of water were kept constant. Data
illustrated in Fig. 1 show that the yield of HNQ increased with increase of
catalyst concentration up to 0.01 mmol and then leveled off at higher
catalyst concentration. The reduced catalytic activity at higher
Mn(III)TPPSCl concentration is possibly due to aggregate formation of the
catalyst [22-25].
To evaluate the effect of sodium hydroxide concentration on the yield of
oxidation product HNQ, the oxidation of 2-naphthol was performed by
varying the amount of sodium hydroxide from 0.20 g (5mmol) to 4.0 g
(100 mmol ). Data illustrated in Figure 2 show that the rate of reaction and
yields of HNQ were enhanced with the increase of the amount of NaOH.
In absence of NaOH no HNQ was observed. The increase of the yield of
HNQ with increasing NaOH concentration could be due to reduce the redox
potentials in the catalytic reaction [9,11].
The effect of hydrogen peroxide concentration on the yield of HNQ was
investigated in the concentration range 2.0 mmol to 20 mmol. The
percentage of product obtained is shown in Fig. 3. The results indicated that
8.0 mmol of H2O2 was the most suitable concentration with the highest
catalytic conversion of 2-naphthol. At higher amount of H2O2, the product
formed probably gets further oxidized and degraded [11,12].
3.2. Mechanism of the catalytic oxidation reaction.
High valent oxomanganese O=MnIV and O=MnV could be the active
intermediate in the oxidation of organic compounds catalyzed by
Mn(III)porphyrins [16, 28-32]. In order to identify the nature of the oxo-
manganese species in the oxidation reaction of 2-naphthol with H2O2
catalyzed by Mn(III)TPPSCl, the oxidation reaction was analyzed by UV–

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vis spectrophotometry at room temperature ( ca. 25oC) . The UV-vis spectra
illustrated in Fig.4 was obtained upon mixing the catalyst in water, H2O2 and
2-naphthol in sodium hydroxide solution consecutively into cuvette (3ml).
In Fig. 4a the absorption peak of Mn(III)TPPSCl appeared at 468 nm (soret
band) [16] . After addition of H2O2 into the solution of porphyrin, a new
absorption peak appeared at 425 nm (Fig. 4b), which is assigned to
O=Mn(IV)TPPSCl , the possibly active catalytic intermediate [16,28-29] .
By addition of the solution of 2-naphthol in NaOH into the reaction mixture;
the absorption peak at 425 nm disappeared and a new broad band was
generated at about 438 nm (Fig.4c), which is probably due to the
simultaneous presence, in solution of both HNQ and O=Mn(IV)TPPSCl.
After ca. 3 min. a new broad peak was observed at 452 nm (Fig. 4d), which
increased with time (Fig. 4e), owing to the formation of HNQ [11,12].
These results indicate that oxomanganese porphyrin complex
O=Mn(IV)TPPSCl is the active species in the oxidation of 2-naphthol with
hydrogen peroxide and Mn(III)TPPSCl.
A suggested mechanism for the oxidation of 2-naphthol by
Mn(III)TPPSCl/H2O2 system in aqueous alkaline medium is shown in
Scheme 2. The high valence oxomanganese porphyrin complex
O=Mn(IV)TPPSCl probably reacts with 2-naphthol to generate 1,2,4-
trihydroxy naphthalene, which is unstable and could be easily oxidized to
HNQ by the oxygen generated from dissociation of hydrogen peroxide as
reported by Yan and co-worker [9].
3.3. Reuse of the catalyst
Re-use of the catalyst has been tested after the 15 min catalytic reaction,
neutralization and isolation of the product. No product was obtained after

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addition of H2O2 to the basic solution 2-naphthol. This could be due to
degradation of Mn(III)TPPSCl. Further studies are in progress for
preparing more stable catalysts.
4. Conclusions
The catalytic oxidation system Mn(III)TPPSCl/ hydrogen peroxide proved
to be an efficient oxidation system for selective conversion of 2-naphthol to
2-hydroxy-1,4-naphthoquinone (HNQ) in 95% yield under mild reaction
conditions. Strong alkaline medium is necessary for the oxidation process.
The yield of HNQ has been found to be affected by variation of the
concentration of catalyst, sodium hydroxide, hydrogen peroxide, and
substrate. UV–vis spectral analysis during oxidation reaction indicated that
oxomanganese intermediate O=Mn(IV)TPPS is the active species in the
oxidation of 2-naphthol with hydrogen peroxide and Mn(III)TPPSCl.
5. References
[1] R.A. Sheldon, J.K. Kochi, Metal Catalyzed Oxidation of Organic
Compounds, Academic Press, New York, 1981, p. 71.
[2] A. Ashnagar, A. Shiri, Int. J. Chem. Tech. Res. 3(4) (2011)1941.
[3] A. Marston, K. Hostettmann, J. Chromatogr. 295(1984) 526–529.
[4] E.M. Hodnett, M. Ernest, C. Wong wiechintana, J. Med. Chem. 26
(1983) 570
[5] P. Dinesh Babu, R.S. Subhasree, Acad. J. Plant. Sci. 2 (2009) 231.
[6] S. Gaikwad, C. Gaikwad, J. Chem. Pharm. Res. 2 (2010) 106.
[7]M. Christian, Fr. Demande FR 2, 543, 434 (Cl. A61K7r13),
05, Oct. 1984, Appl. 83/5, 414, 01 Apr 1983, 16 pp.

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[8] A.C. Watkinson, K.R. Brian, K.A. Walters, J. Hadgraft, Int.
J. Cosmet. Sci. 14 (6) (1992) 265–275.
[9] Y. Yan, F. Xiao, G. Zheng, K. Zhen, C. Fang , J. Mol. Catal. Chem
157(2000) 65–72.
[10] Y. Yan, E. Kang , K. Yang , S. Tong, C. Fang, S. Liu, F. Xiao,
Catal. Commun. 5(2004) 387.
[11] J. Zhao, B. Gao, Y. Gong, Catal. Lett. 141(2011) 1808–1813.
[12] P.A. Pavaskar , A.V. Salker, Curr. Catal. 1(2012) 186-190.
[13] C.M. Che, V.K.Y. Lo, C.Y. Zhou, J.S. Huang, Chem. Soc.
Rev. 40 (2011)1950.
[14] H. J. Lu, X.P. Zhang, Chem. Soc. Rev. 40 (2011) 1899.
[15] L. Que Jr., W. B. Tolman, Nature 455 (2008) 333.
[16] Sahar H. El-Khalafy, M. Hassanein, J. Mol. Catal. A: Chem., 363–
364 (2012) 148.
[17] M. Hassanein, S. Gerges, M. Abdo, S. EL-Khalafy, J. Mol. Catal. A:
Chem., 268 (2007) 24–28.
[18] M. Hassanein, S. Gerges, M. Abdo, S. El-Khalafy, J. Mol. Catal. A:
Chem. 240 (2005) 22-26.
[19] B. Meunier, S.P. de Visser, S.P.S. Shaik, Chem. Rev. 104
(2004) 3947.
[20] A.D. Alder, F.R. Longo, J.D. Finarelli, J. Goldmarcher, J. Assour,
L. Korsakoff, J. Org. Chem. 32 (1967) 476.
[21] H. Turk, W.T. Ford, J. Org. Chem. 56 (1991) 1253.
[22] N.A. Stephenson , A.T. Bell , J. Mol. Catal. A: chemical
272(2007)108.
[23] M.A. Castriciano, M.G. Donato , V. Villari , N. Micali ,A. Romeo ,
L.M. Scolaro J. Phys. Chem. B 113 (2009) 11173.

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[24] M.H. Alkordi , Y. Liu , R.W. Larsen , J.F. Eubank , M . Eddaoudi,
J. Am. Chem. Soc. 130 (2008) 12639.
[25] M.D. Assis, J.R. Lindsay Smith, J Chem. Soc. Perkin Trans. 2
[27] C. Sotirou, W. Lee, R.W. Giese, J. Org. Chem. 55 (1990) 2159.
[28] N.W.J. Kamp, J.R. Lindsay Smith, J. Mol. Catal. A: Chem. 113
(1996) 131.
[29] W. Nam, I. Kim, M.H. Lim, H-J. Choi, J-S. Lee, H.G. Jang, Chem.
Eur. J. 8 (2002) 2067.
[30] Z. Li, C-G Xia, C.-Z. Xu, Tetrahedron Lett. 44 (2003) 9229 and
references therein.
[31] Z. Li, C-G Xia, J. Mol. Catal. A: Chem. 214 ( 2004) 95.
[32] H-J. Zhang, Y. Liu, Y. Lu, X-S. He, X. Wang, X. Ding, J. Mol.
Catal. A: Chem. 787 (2008) 80.

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40
35
30
25
20
15
10
5
0.000
0.005
0.010
0.015
0.020
0.025
0.030
[Mn(III)TPPS] mmol
Fig. 1
100
80
60
40
20
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Wt. NaOH (g)
Fig. 2

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35
30
25
20
15
2
4
6
8
10
12
14
16
18
20
22
[H2O2] mmol
Fig. 3
a
2
d
e
c
b
0
300
400
500
600
700
Wave length (nm)
Fig. 4

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Captions of Figures
Figure 1: Effect of catalyst concentration on percentage yield of HNQ.All
reactions were performed by using of 2-naphthol (1.0 mmol), NaOH (36
mmol), Mn(III)TPPS (0.01 mmol) and H2O2 ( 8 mmol) in water at 22 C.
Total volume of the reaction was 25 ml. The yields of the catalytic reactions
were quantitatively analyzed by UV–vis technique.
Figure 2: Effect of NaOH concentration on percentage yield of HNQ.
Reactions were carried out under experimental conditions reported in Figure
1.
Figure 3: Effect of H2O2 concentration on percentage yield of HNQ.
Reactions were carried out under experimental conditions reported in Figure
1.
Figure 4: UV-visible absorption spectra after mixing of Mn(III)TPPS (1.0 x
10-6 mol/L), H2O2 (1.0 x 10-3 mol/L), NaOH (3.6 x 10-3 mol/L) and 2-
naphthol (1.0 x 10-4 mol/L). a) Mn(III)TPPSCl (λmax 468 nm), b)
O=Mn(IV)TPPSCl (λmax 425 nm), c) λmax 438 nm , which is probably due to
the simultaneous presence, in solution of both HNQ and O=Mn(IV)TPPSCl.
d-e) HNQ (λmax 452 nm).

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SO3Na
N
N
N
MnIII
Cl
SO3Na
NaO3S
N
SO3Na
Scheme 1

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H2O2, OH-
O-
O-
O-
O
+ 2 OH-
+ 2 H2O
+ 2 Mn(III)TPPS
+ 2 Mn (IV)TPPS
O-
O2
O
O
O-
Scheme 2

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Graphical Abstract
O
O
OH
OH
Mn(III)TPPS
H2O2

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Highlights
 Mn(III)TPPSCl showed high activity for oxidation of 2-naphthol to
HNQ by hydrogen peroxide .
 95% yield of HNQ was obtained under mild conditions.
 O=Mn(IV)TPPSCl is the active intermediate in the oxidation reaction.