Oxidation of Phenols to Quinones by Oxygen Catalysed by a Mixture of Cobalt and Manganese Salts of p-Aminobenzoic Acid Supported on Silica Gel

Article abstract of DOI:10.1039/a705855a

A mixture of cobalt and manganese salts of p-aminobenzoic acid supported on silica gel catalyses the oxidation of phenols to the corresponding quinones in the presence of oxygen.

Full text of DOI:10.1039/a705855a

View Article Online / Journal Homepage / Table of Contents for this issue
138 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 138±139$
Oxidation of Phenols to Quinones by Oxygen
Catalysed by a Mixture of Cobalt and Manganese
Salts of p-Aminobenzoic Acid Supported on
Silica Gel$
Mohammed M. Hashemi* and Yousef Ahmadi Beni
Department of Chemistry, Sharif University of Technology, P.O. Box 11365-9516, Tehran, Iran
A mixture of cobalt and manganese salts of p-aminobenzoic acid supported on silica gel catalyses the oxidation of
phenols to the corresponding quinones in the presence of oxygen.
It is well known that many quinone derivatives possess
bioactivity e.g. anthrocycline antibiotics1 and the tetracyclic
quinone streptonigrin.2 Some quinones are also useful as
intermediates in the preparation of medicines, e.g. the syn-
thesis of anthracyclinones was accomplished via a Diels±
Alder cycloaddition using quinone rings.3 Since substituted
phenols are usually inexpensive, the oxidation of phenols
constitutes a general method for the synthesis of benzo-
quinones. In this regard many oxidants have been developed
to carry out this conversion. Oxidation of hindered phenols
using an oxygen carrying chelate and molecular oxygen
gives the corresponding quinones.4 The catalytic oxidation
of phenols and naphthols to para-quinones with hydrogen
peroxide and methyltrioxorhenium has been reported.5 The
preparations of ortho-quinones have been of interest to
organic chemists, but not many reagents are available for
this purpose. It has been reported that the oxidation of
phenols by benzeneseleninic anhydride gives ortho-quinones
where as benzeneseleninic acid leads to the formation of
para-quinones.6 Similarly, the oxidation of phenols with
potassium nitrosodisulfonate (Fremy's radical) is a good
method for the preparation of either ortho- or para-
benzoquinones, the presence or absence of substituents on
the aromatic ring, para to the hydroxy group controlling the
formation of the products.7
Recently, a heterogeneous catalytic method for the oxi-
dation of phenols to quinones using chromium silicate and
hydrogen peroxide has been reported.10
Here we report another heterogeneous catalytic method
for the selective oxidation of phenols to para-quinones using
manganese and cobalt salts of p-aminobenzoic acid sup-
ported on silica gel in the presence of oxygen. The catalysts
are easily prepared by the following method: silica gel is
heated in a pyrolysis apparatus at 260 8C in 20 mm Hg until
5.7% water is lost. p-Aminobenzoic acid is then treated with
the activated silica gel. The reaction of the acid bonded to
the silica gel with sodium hydrogen carbonate a€ords the
sodium salt of the acid, which is then converted to
the cobalt or manganese salts using cobalt or manganese
chloride solutions.11 The catalyst is recovered quantitatively
in each experiment and can be reused. The results are
summarized in Table 1.
Experimental
Preparation of Activated Silica Gel.ÐIn a pyrolysis apparatus
silica gel (5 g) was heated at 260 8C under reduced pressure (20
mmHg) using phosphorus pentoxide (5 g) as a desiccant. The silica
gel was reduced by 0.28 g in weight after 10 h (5.7 wt%).
Reaction between Activated Silica Gel and p-Aminobenzoic Acid.Ð
To a mixture of ethyl acetate (70 ml) and p-aminobenzoic acid
(2.13 g, 15 mmol) was added activated silica gel (4.79 g). The reac-
tion mixture was then re¯uxed with magnetic stirring at 80 8C for
16 h and then cooled to room temperature and ®ltered. The solid
mass was washed with ethyl acetate for 10 h (Soxhlet) in order to
remove unreacted p-aminobenzoic acid. The solid was then dried in
an oven at 100 8C to a€ord a pale yellow solid (6.05 g). 1.33 g
(9.7 mmol) of the acid had reacted.
Since polynuclear aromatic hydrocarbons are considered
to be environmental carcinogens the synthesis of polycyclic
quinones from the parent hydrocarbons is desirable and
only a few general reagents have been reported. Ceric
ammonium sulfate in dilute sulfuric acid has been reported
to give good yields of quinones.8,9
Table 1 Oxidation of phenols with oxygen catalysed by Co and Mn salts
Entry
Substrate
Phenol
3-Methylphenol
3,5-Dimethylphenol
2-Chlorophenol
2-Bromophenol
1-Naphthol
Solvent
Benzene
Toluene
Product
Yield (%)
1
2
3
4
5
6
1,4-Benzoquinone
64
53
57
39
36
65
2-Methyl-1,4-benzoquinone
2,6-Dimethyl-1,4-benzoquinone
2-Chloro-1,4-benzoquinone
2-Bromo-1,4-benzoquinone
1,4-Naphthoquinone
Toluene
Ethylbenzene
Ethylbenzene
Benzene
*To receive any correspondence.
Preparation of Sodium, Cobalt and Manganese Salts of the
p-Aminobenzoic Acid Supported on Silica Gel.ÐSodium salt of the
p-aminobenzoic acid ( 5 g) supported on silica gel was prepared via
reaction of the acid and a solution of sodium carbonate to give
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

View Article Online
J. CHEM. RESEARCH (S), 1998 139
(5.25 g, 11 mmol, 4.76 wt% increase) of the sodium salt. This result
was veri®ed by XRF to show a 4.47% wt increase. A mixture of
saturated cobalt chloride (50 ml) and the sodium salt (5 g) of the
p-aminobenzoic acid supported on silica gel was re¯uxed at 100 8C
for 2 h. The mixture was then cooled to room temperature and
®ltered. The solid was washed with distilled water for 10 h (Soxhlet)
and then dried in an oven at 110 8C for 5 h to give the cobalt salt
(5.33 g) of the acid as a pink solid (6.0% wt increase). This result
was veri®ed by XRF to show a 6.10% wt increase.
Received, 11th August 1997; Accepted, 28th November 1997
Paper E/7/05855A
References
1 F. Aromone, G. Franceschi and A. Penco Selva, Tetrahedron
Lett., 1969, 1007.
Similarly, the manganese salt of the acid was prepared using
manganese chloride solution to give 5.39 g of a white solid (6.10%
wt increase, XRF showed 5.97% wt increase).
2 S. J. Gould and C. C. Chang, J. Am. Chem. Soc., 1980, 102,
1702.
3 D. W. J. Hansen, R. Pappo and R. B. Carland, J. Org. Chem.,
1988, 53, 4244.
4 P. A. Ganeshpure, A. Sudalai and S. Sutish, Tetrahedron Lett.,
1989, 30, 5922.
5 W. Adam, W. A. Hermann, J. Lin and C. R. Saha-Moller,
J. Org. Chem., 1994, 59, 8281.
Oxidation of Phenols with Oxygen and Co and Mn Salts of
p-Aminobenzoic Acid Supported on Silica Gel as Catalysts. General
Procedure.ÐTo a stirred solution of phenol (1 mmol) in solvent
(25 ml) was added the supported cobalt salt (46 mg, 0.05 mmol Co)
and manganese salt (45 mg, 0.05 mmol Mn). The reaction mixture
was re¯uxed for 8 h during which time oxygen was bubbled at a
6 D. H. R. Barton, J. P. Finit and M. Thomas, Tetrahedron, 1988,
44, 6397.
1
rate of 15 ml min into the solution. The progress of the reaction
was monitored by TLC. The reaction mixture was cooled to room
temperature and then ®ltered to recover the solid material (Co and
Mn salts). The reaction mixture was diluted with solvent (20 ml)
and washed with 5% NaOH solution to remove any unreacted
phenols. The solvent was then evaporated and the product puri®ed
by column chromatography over silica gel, and identi®ed by its mp,
IR and 1H NMR spectroscopic properties.
7 H. Zimmer, D. Lankin and S. W. Horgan, Chem. Rev. 71, 1971,
229.
8 M. Periasamy and V. Bhatt, Synthesis, 1977, 336.
9 A. Bamani, S. Suresh, M. Sasidharan, A. Sudalai and B. M.
Chanda, J. Chem. Res. (S), 1996, 474.
11 M. M. Hashemi and D. Ghazantari, Iran. J. Chem. Chem. Eng.,
1995, 13, 77.