Mild oxidative deprotection of aromatic hydrazones and semicarbazones with KMnO4 in ionic liquid medium

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Mild Oxidative Deprotection of Aromatic
Hydrazones and Semicarbazones with
KMnO in Ionic Liquid Medium
4
a
b
Javad Safaei-Ghomi & Abdol R. Hajipour
a
Faculty of Chemistry , University of Kashan , 51167, Kashan, IR,
Iran
b
Department of Pharmacology , University of Wisconsin, Medical
School , Madison, Wisconsin, USA
Published online: 02 Aug 2011.
To cite this article: Javad Safaei-Ghomi & Abdol R. Hajipour (2011) Mild Oxidative Deprotection of
Aromatic Hydrazones and Semicarbazones with KMnO in Ionic Liquid Medium, Organic Preparations
4
and Procedures International: The New Journal for Organic Synthesis, 43:4, 372-376, DOI:
10.1080/00304948.2011.582013
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Organic Preparations and Procedures International, 43:372–376, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5453 online
DOI: 10.1080/00304948.2011.582013
Mild Oxidative Deprotection of Aromatic
Hydrazones and Semicarbazones with KMnO4
in Ionic Liquid Medium
Javad Safaei-Ghomi and Abdol R. Hajipour2
1
1
Faculty of Chemistry, University of Kashan, 51167 Kashan, IR Iran
Department of Pharmacology, University of Wisconsin, Medical School,
2
Madison, Wisconsin, USA
1
The selective deprotection of carbonyl groups is often required in organic synthesis. Highly
crystalline hydrazones, semicarbazones and oximes are very efficient derivatives for the iso-
2
,3
lation, purification and characterization of aldehydes and ketones. Considerable interest
4
in the use of selective and cleaner oxidation methods such as heterogeneous oxidation and
5–11
oxidation in ionic liquids have received much attention in recent years.
The advantages
of these methods over conventional procedures are that they provide greater selectivity,
12
enhanced reaction rates, cleaner products and manipulative simplicity. Although some of
these conventional methods have convenient protocols with good to high yields, most suffer
from at least one of disadvantages such as use of high temperature and long reaction times,
moisture sensitivity, high cost and toxicity of the reagents. Ionic liquids (ILs), which com-
bine good and tunable solubility properties with a negligible vapor pressure and excellent
thermal stabilities, have rapidly found a place of choice as valuable substitutes for many
volatile solvents.6
,11,13,14
Owing to their unique properties, it soon became apparent that ILs
are more than simple neoteric solvent. Reactions in ILs exhibit thermodynamic and kinetic
1
5,16
behaviors different from those of conventional solvents.
Often this lead to improved
process performance such as better selectivity and/or conversion; furthermore, ionic liquids
9
,10,17,18
3,11
lead to enhanced stability of organometallic reagents
and biocatalysts, allow for
product recovery as well as the possibility of recycling of homogeneous catalysts.
1
9,20
In continuation of our studies on the application of ionic liquid media,
we found
that dialkylimidazolium halides such as butylmethylimidazolium bromide ([Bmim]Br) has
many advantages over conventional solvents.2
1–26
Herein we report an efficient method for
the oxidative cleavage of hydrazones and semicarbazones with potassium permanganate in
the presence of [Bmim]Br (BMIM Br) under mild and solvent-free conditions.
Submitted January 17, 2010.
Address correspondence to Javad Safaei-Ghomi, Faculty of Chemistry, University of Kashan,
1167 Kashan, IR Iran. E-mail: safaei@kashanu.ac.ir
5
372

Mild Oxidative Deprotection of Aromatic Hydrazones
373
4
Similar work was reported by Khurana et al. in oxidative hydrolysis of hydra-
zones, semicarbazones and phenylhydrazones with sodium hypochlorite in CH3CN as a
conventional method with lower yields; in some cases, acids were formed as further oxidized
products.
The results obtained from oxidation of 2,4-dinitrophenylhydrazones and semicar-
bazones are listed in Tables 1 and 2, respectively. The use of BMIM Br as reaction medium
for this procedure led a selective oxidation of these compounds to the corresponding ketones
and aldehydes without further oxidation to the acids. Derivatives of aliphatic aldehydes and
Table 1
a
Oxidative Deprotection of 2,4-Dinitrophenylhydrazones
Cmpd
Yield
(%)
bp. (mp.)
( C)
lit. bp. (mp.)
Time
(min)
◦
◦
27
Ar
R
( C)
C6H5
H
H
H
H
H
H
H
H
H
H
H
H
82
86
85
73
76
69
83
86
81
82
80
84
81
68
71
73
68
42
74
79
176
(105–106)
(55–57)
246
179
106
58
248
232
67–70
47
59–60
71
74
204–205
197
201
47–49
20
20
110–111
243
126
54
96
4
3
4
3
2
4
4
2
2
4
2
3
-O2NC6H4
-O2NC6H4
-MeOC6H4
-MeOC6H4
,4-(MeO)2C6H3
-ClC6H4
186
180
252
138
216
168
102
144
144
138
318
246
228
228
402
200
180
231
69
(45–46)
(57–59)
(70–72)
(72–74)
207
195
199
(47)
(18–19)
(19–21)
(108)
241–242
210–212
102
-BrC6H4
,6-Cl2C6H3
,4-Cl2C6H3
-MeC6H4
-MeC6H4
-MeC6H4
H
C6H5
C6H5
C6H5
CH3
CH3
CH2Br
CH3
CH3
CH3
4-ClC6H4
4-BrC6H4
2-HOC6H4
4-Pyridyl
212
102–104
N-Me-anilino
a
1
Yields refer to isolated products characterized from their spectra (IR, H NMR) and comparison
with authentic samples.

374
Safaei-Ghomi and Hajipour
Table 2
a
Oxidative Deprotection of Semicarbazones
Cmpd
Yield
(%)
bp. (mp.)
( C)
lit. bp. (mp.)
Time
(min)
◦
◦
27
Ar
R
( C)
C6H5
H
H
H
H
H
H
H
H
H
H
H
H
86
93
91
90
90
79
91
95
90
95
91
91
93
89
91
90
93
89
90
70
90
176
(105–106)
(55–57)
246
179
106
58
248
232
67–70
47
59–60
71
74
204–205
197
201
47–49
20
20
110–111
243
212
121–124
102–104
60
39
50
130
155
200
42
37
65
30
80
100
65
51
68
49
34
56
45
40
4
3
4
3
2
4
4
2
2
4
2
3
-O2NC6H
-O2NC6H4
-MeOC6H4
-MeOC6H4
,4-(MeO)2C6H3
-ClC6H4
231
69
(45–46)
(57–59)
(70–72)
(72–74)
207
195
199
(47)
(18–19)
(19–21)
(108)
241–242
210–212
142–144
102
-BrC6H4
,6-Cl2C6H3
,4-Cl2C6H3
-MeC6H4
-MeC6H4
-MeC6H4
H
C6H5
C6H5
C6H5
CH3
CH3
CH2Br
CH3
CH3
CH3
CH3
4
4
2
4
4
-ClC6H4
-BrC6H4
-HOC6H4
-Pyridyl
-HO(CH2)2C6H4
N-Me-anilino
50
a
1
Yields refer to isolated products characterized from their spectra (IR, H NMR) and comparison
with authentic samples.
ketones were recovered unreacted. Although the DNPs and semicarbazones of compounds
with aryl groups bearing hydroxy groups gave yields varying from a low 42% to a high of
89%, compounds with a free NH2 or an NH group gave only dark oily products.
Experimental Section
Yields refer to isolated pure products. The products were characterized by comparison
1
their spectral (IR, H NMR), melting and boiling points with authentic samples. All of the
reactions were carried out in a hood with strong ventilation. IR spectra were recorded on
1
Magna-550 IR spectrophotometer. Spectra of solids were obtained as KBr pellets. H NMR
spectra were determined on Hitachi R-24, B-360 spectrometers at 60 MHz using CDCl3 as
solvent and TMS as internal standard.

Mild Oxidative Deprotection of Aromatic Hydrazones
375
Typical Procedure for Oxidative Cleavage of Hydrazones
A mixture of benzaldehyde 2,4-dinitrophenylhydrazone (1 mmol, 0.286 g), KMnO4
◦
(
0.9 mmol, 0.142 g) in [bmim]Br (0.4 mmol, 0.87 g) was heated at 40 C under solvent-
free conditions. After completion of reaction as indicated by TLC on silica gel (EtOAc:
petroleum ether, 1:9), the reaction mixture was diluted with ether (4 × 5 ml) and filtered
by gravity to remove solids. Ionic liquid phase was separated from the organic layer and
recovered for further uses. The ether was evaporated under reduced pressure and the residue
was purified by thin layer chromatography method (EtOAc: petroleum ether, 1:9) to give
◦
27
◦
benzaldehyde (0.087 g, 82%), bp 176 C, lit. 179 C.
Typical Procedure for Oxidative Cleavage of Semicarbazones
This procedure was the same as above with 1:0.7:0.7 mole ratio for semicarbazone:
IL:KMnO4 respectively at room temperature.
Acknowledgements
The authors gratefully acknowledge the financial support of this work by the Research
Affairs Office of the University of Kashan, Kashan, I. R. Iran.
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