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.
References
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[
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