Montmorillonite K-10 as highly efficient and mild catalyst for deprotection of ketone dimethylhydrazones using microwaves in a solventless system

Article abstract of DOI:10.1515/znb-2002-0818

N,N-Dimethylhydrazones of ketones were efficiently and rapidly deprotected to the corresponding ketones by Montmorillonite K-10 clay using microwave irradiation under solvent free conditions.

Full text of DOI:10.1515/znb-2002-0818

Notizen
961
Montmorillonite K-10 as Highly
Considering, the usefulness of microwave heat-
ing in activating a wide variety of organic reactions
is now well established [12]. Besides, the impor-
tance of surface active catalysts is becoming more
significant, because of their enhanced selectivity
and the use of milder reaction conditions com-
Efficient and Mild Catalyst for
Deprotection of Ketone Dimethyl-
hydrazones Using Microwaves in a
Solventless System
a
b
Rahmam Hosseinzadeh , Ali Sharifi , Moj- pared to conventional ones [13].
b
b
taba Mirzaei , and Kourosh Tabar Heydar
We wish to report herein a solventless system
for regeneration of ketones from dimethylhydra-
zones using montmorillonite K-10 under micro-
a
Department of Chemistry, Mazandaran Univer-
sity, Babolsar, Iran.
b
Chemistry & Chemical Engineering Research wave irradiation.
Center of Iran, Tehran, Iran
Reprint requests to Dr. R. Hosseinzadeh.
E-mail: rahman@umz.ac.ir
Results and Discussion
Z. Naturforsch. 57b, 961Ð962 (2002); received
Montmorillonite K-10 [14] is non-toxic powder,
which can be filtered easily from the process and
may be reused after activation. The reaction pro-
ceeds efficiently in high yields at ambient pressure
in a short time (two minutes) and without involve-
ment of toxic and expensive material. The results
of the deprotection reactions are summarized in
Table 1. For example, when acetophenone dimeth-
ylhydrazone (1a) was treated with montmorillon-
ite K-10 under microwave irradiation acetophe-
none (2a) was obtained in quantitative yield (entry
1). However, when 1a irradiated in solid state
March 19, 2002
Dimethylhydrazones, Montmorillonite K-10,
Microwave
N,N-Dimethylhydrazones of ketones were effi-
ciently and rapidly deprotected to the corre-
sponding ketones by Montmorillonite K-10 clay
using microwave irradiation under solvent free
conditions.
Introduction
(
mixed with SiO or Al O instead of montmorri-
2 2 3
Hydrazones have been found to be one of the
most useful synthetic precursors of aldehydes and
ketones [1]. In this method, a key point is the
cleavage of the hydrazone moiety to the carbonyl
group. Previously, a variety of such methods have
been reported, including oxidative cleavage by
lonite K-10) in the same condition or in a solvent
H O or DMF) the corresponding ketone 2a was
(
2
obtained in much lower yield (entries 2Ð5). The
cleavage of other acyclic or cyclic ketone dimeth-
ylhydrazones 1bÐh with montmorillonite K-10
proceeded easily with good yields (entries 6Ð12).
In conclusion, the present results demonstrate
that montmorillonite K-10 serves as efficient,
rapid, mild, and inexpensive reagent to regenerate
ketones from corresponding dimethylhyrazones
under microwave irradiation. The superiority of
this method over the existing methods coupled
with the ease of operation, the simplicity of work-
up, and the environmental advantage makes the
process very useful.
ozone [2], singlet oxygen [3], NaIO [4], dimethyl-
4
dioxirane [5], or hydrolytic cleavage by oxalic acid
[
6], salt method [7], BF ·OEt [8] and catalytic
3 2
method using bismuth [9], palladium [10] and cop-
per catalyzed hydrolysis [11] catalysis. Some of
these procedures suffer from one or more draw-
backs: use of a heavy metal, toxic solvent or rea-
gent which not ideal from an environment point
of view, long reaction times, difficulties in isolation
of products, and also expensive or potentially ex-
plosive reagents under condition of excessive heat-
ing. The ozonolysis method provides nearly quan-
titative chemical yield under neutral conditions
and short reaction times, but this method can not
Experimental Section
All the reactions were carried out in a domestic
be used if there are other ozone-sensitive groups microwave oven (Moulinex Microchef, 900 W).
such as alkenes in the molecule. Therefore in this N,N-Dimethylhydrazones were prepared from the
context introduction of new methods with envi- corresponding carbonyl compounds according to
ronmental consciousness using inexpensive rea- the standard method [15]. All the isolated carbonyl
gents for such functional group transformations compounds were identified by GLC, IR and NMR
is desirable.
and gave satisfactory results in comparison with au-
0
932Ð0776/2002/0800Ð0961 $06.00 ” 2002 Verlag der Zeitschrift für Naturforschung, Tübingen · www.znaturforsch.com
D

9
62
Table 1
Regeneration of ketones from N,N-
dimethylhydrazones with montmo-
rillonite K-10 under microwave irra-
diation
Entry Hydrazone 1
Conditions
Yield,
a
R
RЈ
CH
%
b
1
2
1a Ph
1a Ph
3
3
100
50
CH
SiO
montmorillonite K-10
Al instead of
montmorillonite K-10
in H O without K-10
2
instead of
3
1a Ph
CH
3
O
2 3
trace
< 10
4
5
6
7
8
9
0
1
2
1a Ph
CH
CH
3
3
2
1a Ph
bin DMF without K-10 < 10
1b Ph
CH
3
CH
2
95
b
1c 1c 2-naphthyl
CH
CH
CH
3
89
b
1d PhCH
2
CH
2
2
3
3
97
a
b
GLC yields and retention times
1e CH
1f
3
(CH
)
5
90
b
compared with authentic samples;
1
1
1
CH
CH
2
(CH
(CH
2
)
)
4
CH
CH
2
88
b
b
1 mmol of substrate, 1 g of mont-
1g
2
2
5
2
83
b
morillonite K-10, 2 min under
microwave irradiation
1h 1-indanone dimethylhydrazone
72
thentic samples. GC was a Perkin Elmer 8700 with a mortar. The mixture was transferred to a 20 ml
a FID detector under helium as a carrier gas.
beaker and irradiated in a domestic microwave
oven for 2 min. The mixture was irradiated twice,
each time for 1 min with 1 min interval. At the
end, the mixture was extracted with dichlorometh-
Typical procedure
1
mmol of a N,N-dimethylhydrazone was mixed ane. Evaporation of the solvent gave the products.
and ground with 1 g of montmorillonite K-10 in Yields were determined by GC.
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