Oxidation of Aromatic Amines to Quinones by Iodic Acid under Microwave Irradiation in the Presence of Montmorillonite K10 and Silica Gel

Article abstract of DOI:10.1007/s00706-003-0035-z

A variety of aromatic amines are oxidized to their corresponding quinones in excellent yields by supported iodic acid under microwave irradiation and solvent free conditions.

Full text of DOI:10.1007/s00706-003-0035-z

Monatshefte f €u r Chemie 134, 1561–1563 (2003)
DOI 10.1007/s00706-003-0035-z
Oxidation of Aromatic Amines
to Quinones by Iodic Acid under
Microwave Irradiation in the Presence
of Montmorillonite K10 and Silica Gel
ꢀ
Mohammed M. Hashemi and Maryam Akhbari
Department of Chemistry, Sharif University of Technology, P.O. Box 11365-9516,
Tehran, Iran
Received December 17, 2002; accepted (revised) March 1, 2003
Published online November 13, 2003 # Springer-Verlag 2003
Summary. A variety of aromatic amines are oxidized to their corresponding quinones in excellent
yields by supported iodic acid under microwave irradiation and solvent free conditions.
Keywords. Aromatic amines; Iodic acid; Quinones; Solvent free oxidation; Microwave (MW)
irradiation.
Introduction
Quinone derivatives are important bioactive materials and important intermediates
in the preparation of medicines, e.g. anthrocycline antibiotics and anthrocyclinones
[
1]. Therefore, the oxidation of aromatic amines to quinones using simple methods
can be very valuable. Solid phase reactions can be useful because of their high
efficiency, environmental safety, and simple work up procedures [2–4].
Recently, microwave induced rate acceleration technology has become a
powerful tool for synthetic purposes because of the enhanced selectivity, easy
reaction conditions, rapid reactions, and increased yields [5]. The oxidation of
aromatic amines to quinones is an important reaction in organic chemistry and a
variety of oxidizing reagents such as potassium dichromate [6], ferric chloride [7],
sodium nitrate [8], silver and lead oxide [9], hydrogen peroxide [10], potassium
nitrosodisulfonate [11], lead tetraacetate [12], and hypochlorite ion [13] have been
used.
Most of the reported reagents have strong oxidative power [6, 10, 11], give low
chemical yields [8, 9], and some require tedious work up.
ꢀ Corresponding author. E-mail: mhashemi@sharif.edu

1
562
M. M. Hashemi and M. Akhbari
Here we report the use of iodic acid on montmorillonite K10 and also silica gel
as an oxidant for converting aromatic amines to the corresponding para-quinones
under MW radiation. Polarity of amine derivatives and iodic acid makes them good
candidates for reactions in a microwave oven.
Although we have not experimentally established the mechanism of formation
of the products, it seems that existence of silica gel and montmorillonite as an
acidic support under microwave irradiation can accelerate this new oxidation by
increasing the reactivity of the amine derivatives and also by supporting the for-
mation of polar intermediates [14].
Results and Discussion
Supported HIO on montmorillonite K10 is an excellent oxidant for aromatic
3
amines to quinones as shown in Scheme 1. Ortho-quinones are not produced by
this reagent except in the case of ortho amino- and hydroxyanilines. Aliphatic
amines are converted to various products.
Table 1 lists a variety of aromatic amines oxidized with supported HIO to the
3
corresponding quinones. All yields refer to isolated products.
The following experiments have been performed to check the efficiency of our
method. When this reaction was done on a water bath yields were much lower than
Scheme 1
Table 1. Oxidation of aromatic amines with supported HIO under microwave irradiation
3
Entry Substrate
Time=s= Temperature= Product
ꢁ
Yield=%
Power=w
C
a
b
1
2
3
4
5
6
7
8
9
aniline
30=750
20=750
60
68
1,4-benzoquinone
1,4-benzoquinone
1,2-benzoquinone
1,2-benzoquinone
1,4-benzoquinone
63
85
76
68
61
51
37
60
59
43
28
45
49
48
4-hydroxyaniline
2-hydroxyaniline
2-aminoaniline
4-aminoaniline
3-bromoaniline
N,N-dimethylaniline
20=1000 67
65
20=1000 65
30=1000 65
60=1000 67
2-bromo-1,4-benzoquinone 53
1,4-benzoquinone
1,4-naphtoquinone
1,4-naphtoquinone
48
88
72
4-hydroxynaphtylamine 20=750
1-aminonaphtalene 20=750
61
58
a. Results from montmorillonite K10; b. Results from silica gel

Oxidation of Amines by Iodic Acid
1563
Table 2. Oxidation of aromatic amines with silica gel supported HIO on a water bath
3
a
Entry
Substrate
Time=h
Product
Yield=%
1
2
3
4
5
aniline
2
1
1
2
3
1,4-benzoquinone
1,4-benzoquinone
1,2-benzoquinon
31
35
23
28
18
4-hydroxyaniline
2-aminoaniline
4-aminoaniline
3-bromoaniline
1,4-benzoquinone
2-bromo-1,4-benzoquinone
a
All yields refer to isolated products
under MW conditions (Table 2). In the absence of supporting surface, HIO alone
3
does not oxidize aromatic amines. When the reaction was done using alumina as
support yields were not acceptable.
Experimental
Chemicals were purchased from Merck, Fluka, and Aldrich chemical companies. Products were
separated and purified by column chromatography technique. All products are known compounds
1
and were identified by their mp, IR and H NMR spectroscopic properties.
General Procedure
2
Iodic acid (3mmol), montmorillonite K10 (2g, surface 200 m =g, Fluka), and aromatic amine
(
1mmol) were crushed together using a mortal and pistol. The mixture was exposed to microwave
ꢁ
irradiation or the vapor of boiling water (80 C) under normal atmospheric conditions for the indicated
time (Table 1). The progress of the reaction was followed by TLC, using ethanol:n-hexane¼ 1:4 as
eluent until the starting material was no longer visible. The mixture was extracted with methanol, the
solvent was evaporated, and the products were purified by column chromatography over silica gel and
1
identified by their mp, IR, and H NMR spectroscopic properties.
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