Microwave assisted facile cleavage of 2,4-dinitrophenylhydrazones to the corresponding carbonyl compounds with N,N′-dibromo-N,N′-1,2- ethanediylbis(p-toluenesulphonamide)

Article abstract of DOI:10.3390/70500465

Deprotections of 2,4-dinitrophenylhydrazones to their corresponding carbonyl compounds have been carried out in good yields by using N,N′-dibromo-N,N′-1,2-ethanediylbis(p-toluenesulphonamide) (BNBTS, 2) under microwave irradiation.

Full text of DOI:10.3390/70500465

Molecules 2002, 7, 465-468
molecules
ISSN 1420-3049
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Microwave Assisted Facile Cleavage of 2,4-Dinitrophenyl-
hydrazones to the Corresponding Carbonyl Compounds with
′
′
N,N -Dibromo-N,N -1,2-ethanediylbis(p-toluenesulphonamide)
*
Ardeshir Khazaei and Ramin Ghorbani Vaghei
Department of Chemistry, Faculty of Science, Bu-Ali Sina University, PIN-65175, Hamadan, Iran
*
Author to whom correspondence should be addressed; Fax: (+98)-811-8272404; e-mail:
khazaei_1326@yahoo.com
Received: 14 October 2001 / Accepted: 25 May 2002 / Published: 31 May 2002
Abstract: Deprotections of 2,4-dinitrophenylhydrazones to their corresponding
′
carbonyl compounds have been carried out in good yields by using N,N -dibromo-
′
N,N -1,2-ethanediylbis(p-toluenesulphonamide) (BNBTS, 2) under microwave
irradiation.
Keywords: Microwave, BNBTS, reagents, synthesis.
Introduction
Carbonyl compound derivatives such as 2,4-dinitrophenylhydrazones and oximes are important
intermediates in organic synthesis because of their use in the characterization and purification [1-3] of
such compounds and the important role they play as protective groups for this functionality [4-7].
Consequently, the regeneration of carbonyl compounds from the corresponding 2,4-dinitrophenyl-
hydrazones under mild conditions is an important process in synthetic organic chemistry. Several such
procedures for regeneration of carbonyl compounds from 2,4-dinitrophenylhydrazones have been
reported, for example: with Dowex-50 cation exchange resin [5], clayfen [6], potassium bromate [7],
etc.
Although some are carried out under mild conditions most of these regenerations are often
hazardous or use very toxic, expensive, or not readily available reagents, or reagents which need to be

Molecules 2002, 7
466
freshly prepared [8-10]. Thus, there is still a need to develop new and facile procedures for the
regeneration of carbonyl compounds from 2,4-dinitrophenylhydrazones.
Result and Discussion
We have previously reported a convenient method for the deoximation of ketone and aldehyde
oximes to their corresponding carbonyl compounds [11] using the new reagent BNBTS (2), prepared
′
from N,N -1,2- ethanediylbis(p-toluenesulphonamide) (1) (Figure 1) [12]. Herein, we wish to report a
mild and convenient method for the clean, fast and economical oxidative deprotection of 2,4-
dinitrophenylhydrazones with this reagent under microwave irradiation.
Figure 1.
CH3
CH3
SO2
N
H
CH )
SO2
CH )
2
N
2
2
2
Br
1
BNBTS (2)
2
,4-Dinitrophenylhydrazones 3 reacted with BNBTS (2) in CH Cl under microwave
2
2
irradiation to afford the corresponding carbonyl compounds 4 without any detectable byproducts
Scheme 1). The products of the reaction with BNBTS were isolated simply by filtering off compound
and evaporating the solvent from the filtrate. The results of the conversion of various 2,4-dinitro-
(
1
phenylhydrazones to their corresponding ketones and aldehydes are presented in Table 1.
Scheme 1.
1
1
R
R
BNBTS
C= O +
C= N NH
1
NO2
, MW
2
CH Cl
2
2
R2
R
NO2
3
4

Molecules 2002, 7
467
Table 1. Cleavage of 2,4-dinitrophenylhydrazones with BNBTS under microwave irradiation
1
2
a
Reaction Times
Entry
R
R
Product
Yield(%)
(
min)
50
60
50
50
60
30
50
40
50
40
50
1
2
3
4
5
6
7
8
9
CH3
CH3
CH3
CH3
C H5
C H5
H
H
H
H
C H5
Acetophenone
p-Chloroacetophenone
p-Methoxyacetophenone
p-Bromoacetophenone
Benzophenone
91
92
94
93
90
92
89
95
92
92
91
6
p-ClC H5
6
p-MeOC H5
p-BrC H5
6
6
C H5
6
6
p-ClC H5
p-Chlorobenzophenone
6
6
C H5
Benzaldehyde
6
p-ClC H5
p-Chlorobenzaldehyde
p-Tolualdehyde
6
p-MeC H5
o-MeOC H5
C H CH(OH)
6
1
1
0
1
o-Methoxybenzaldehyde
Benzoin
6
C H5
6
6
5
a
Products were characterized by their physical constants, IR spectra and comparison with authentic samples.
Conclusions
From the results obtained, we find that the described procedure and the reaction conditions are
simple. The reagent (BNBTS) is stable and the recovered reagent can be reused.
Acknowledgements
The authors are grateful to Bu-Ali Sina University Research Council for partial financial support of
this work.
Experimental
General
IR spectra was recorded using a Shimadzu 435-U-04 spectrophotometer (KBr Pellets). The 2,4-
dinitrophenylhydrazones were prepared by a standard procedure [13]. The purity of compounds was
checked by TLC (silica gel 60 F /CHCl and CCl /UV). A Shivaki Co. microwave (220 v, 700 w, RF
2
54
3
4
output 2450 MHz) was used for the microwave irradiations.
General procedure for facile cleavage of 2,4-dinitrophenylhydrazones with BNBTS under microwave
irradiation.
A mixture of 2,4-dinitrophenylhydrazone (5 mmol), dichloromethane (15 mL) and BNBTS (5
mmol) was introduced in a flask and was refluxed under irradiated in a microwave oven at a power
output of 700 W for the appropriate time as indicated in Table 1. After irradiation, cold water was

Molecules 2002, 7
468
added to hydrolyze the intermediate, and the insoluble sulfonamide 1 was removed by filtration and
washed with cold dichloromethane (10 mL). The organic layer was separated from the aqueous layer,
combined with the washes and dried with MgSO . Dichloromethane was removed under reduced
4
pressure gave the crude product. Solid products were recrystallized from diethyl ether, oily products
were dissolved in ether and the ether solution washed, dried and concentrated.
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6
7
8
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