Silica sulfuric acid/wet SiO2 as a novel heterogeneous system for cleavage of carbon nitrogen double bonds under mild conditions

Article abstract of DOI:10.1080/714040985

Silica sulfuric acid in the presence of wet SiO₂ was caused to react with oximes, hydrazones, semicarbazones, azines, and Schiff-bases. It was observed that it converts them to their corresponding carbonyl compounds in good to excellent yields under mild and heterogeneous conditions.

Full text of DOI:10.1080/714040985

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Phosphorus, Sulfur, and Silicon and the Related
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Silica Sulfuric Acid/Wet SiO as a Novel Heterogeneous
2
System for Cleavage of Carbon Nitrogen Double Bonds
Under Mild Conditions
a
b
c
Mohammad Ali Zolfigol , Iraj Mohammad Poor-Baltork , Bibi Fatemeh Mirjalili , Farhad
d
a
a
a
Shirini , Sadegh Salehzadeh , Hassan Keypour , Arash Ghorbani-Choghamarani
,
a
d
c
Mohammad Hassan Zebarjadian , Kamal Mohammadi & Azizeh Hazar
a
Bu-Ali Sina University, Hamadan, Iran
b
Isfahan University, Isfahan, Iran
c
Yazd University, Yazd, Iran
d
Guilan University, Rasht, Iran
Published online: 18 Jun 2010.
To cite this article: Mohammad Ali Zolfigol , Iraj Mohammad Poor-Baltork , Bibi Fatemeh Mirjalili , Farhad Shirini , Sadegh
Salehzadeh , Hassan Keypour , Arash Ghorbani-Choghamarani , Mohammad Hassan Zebarjadian , Kamal Mohammadi & Azizeh
Hazar (2003) Silica Sulfuric Acid/Wet SiO as a Novel Heterogeneous System for Cleavage of Carbon Nitrogen Double Bonds
2
Under Mild Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements, 178:12, 2735-2743, DOI: 10.1080/714040985
To link to this article: http://dx.doi.org/10.1080/714040985
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Phosphorus, Sulfur, and Silicon, 178:2735–2743, 2003
Copyright ꢀC Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500390252452
SILICA SULFURIC ACID/WET SiO AS A NOVEL
2
HETEROGENEOUS SYSTEM FOR CLEAVAGE OF
CARBON NITROGEN DOUBLE BONDS UNDER
MILD CONDITIONS
a
b
Mohammad Ali Zolfigol, Iraj Mohammad Poor-Baltork, Bibi
c
d
a
Fatemeh Mirjalili, Farhad Shirini, Sadegh Salehzadeh,
a
a
Hassan Keypour, Arash Ghorbani-Choghamarani,
a
d
Mohammad Hassan Zebarjadian, Kamal Mohammadi,
and Azizeh Hazarc
a
Bu-Ali Sina University, Hamadan, Iran; Isfahan University,
b
c
Isfahan, Iran; Yazd University, Yazd, Iran; and Guilan
University, Rasht, Irand
(
Received June 24, 2003; accepted July 15, 2003)
Silica sulfuric acid in the presence of wet SiO2 was caused to react
with oximes, hydrazones, semicarbazones, azines, and Schiff-bases. It
was observed that it converts them to their corresponding carbonyl
compounds in good to excellent yields under mild and heterogeneous
conditions.
Keywords: Silica sulfuric acid; carbon nitrogen double bond cleavage;
oximes; hydrazones; semicarbazones; azines; Schiff-bases
Acids are catalysts that are used most in industry for producing more
8
1
than 1 × 10 Mt/year of products. Among acid catalysts, the most
commonly used are HF, H2SO4, HClO4, and H3PO4 (in liquid form or
supported on Kieselguhr). Solid acids have many advantages such as
their simplicity in handling, likelihood of decreasing reactor and plant
corrosion problems, and having environmentally safe disposal.1 Also,
wastes and by-products can be minimized or avoided by developing
,2
3
cleaner synthesis routes. On the other hand, reduction in the amount
We gratefully acknowledge financial support for this work by Research Affairs, Bu-
Ali Sina University, Hamadan, Iran, and Isfahan University, Isfahan, Iran (as a common
project).
Address correspondence to Mohammad Ali Zolfigol, Department of Chemistry,
College of Science, Bu-Ali Sina University, Hamadan 65174, PO Box 4135, Iran. E-mail:
zolfi@basu.ac.ir
2
735

2
736
M. A. Zolfigol et al.
of sulfuric acid needed and/or any simplification in handling procedures
is required for risk reduction, economic advantage, and environment
protection. In addition, there is current research and general interest
in heterogeneous systems because of their importance in industry and
developing technologies.4
Heterogeneous organic reactions have proven useful to chemists in
the laboratory as well as in the industrial context. These reactions are
effected by the reagents immobilized on the porous solid supports and
have advantages over the conventional solution phase reactions be-
cause of the good dispersion of active reagent sites, associated selec-
5
tivity, and easier work-up. Recently, we, among many others, have
demonstrated that heterogeneous reagent systems have many advan-
tages such as simple experimental procedures, mild reaction conditions,
and minimization of chemical wastes as compared to the liquid phase
6,7
counterparts. In continuation of our studies on the application of in-
6
organic acidic salts and silica chloride, we found that silica gel reacts
with chlorosulfonic acid to give a white powder namely silica sulfuric
acid (I). It is interesting to note that the reaction is easy and clean
without any work-up procedure because HCl gas is evolved from the
reaction vessel immediately (Scheme 1).
SCHEME 1
We hoped that the silica sulfuric acid (I) would be a superior proton
source compared to all reported solid supported acids or acidic resins,
such as polystyrene sulfonic acid and Nafion-H (Nafion has the handi-
2
cap of low surface area which renders it unrealistic for practical use)
for running reactions under heterogeneous conditions. On developing
7
cleaner organic reactions and also the application of this new solid acid,
we were interested in using this inorganic acidic resin (I) for cleavage
of carbon-nitrogen double bond (C N) when used in conjunction with
wet SiO2 and n-hexane.
Oximes, hydrazones, azines, semicarbazones, and Schiff-bases have
been employed as ketone or aldehyde functional group equivalents in
organic synthesis. The regeneration of carbonyl compounds from their
derivatives provides an attractive method for the synthesis of aldehy-
8−12
des and ketones.
compounds,
Since oximes can be prepared from noncarbonyl
the regeneration of carbonyl compounds from oximes
provides an alternative method for the preparation of aldehydes and
1
3−18

Cleavage of Carbon Nitrogen Double Bonds
2737
ketones. Some of the methods of generating carbonyl compounds from
1
9−21
oximes
involve reagents that are often hazardous or very toxic,
expensive, or not readily available, they need to be freshly prepared
or the reactions require drastic conditions, long reaction times and te-
dious work-up. Thus a milder, selective, nonhazardous, and inexpensive
reagent is still in demand. Although, many methods have been devel-
oped recently, for the oxidative cleavage of oximes, hydrazones, and
2
2−32
semicarbazones to the corresponding carbonyl compounds,
little
attention has been paid to the cleavage of the carbon-nitrogen double
bonds of azines and Schiff-bases. We report a simple, cheap, and het-
erogeneous method for the effective cleavage of carbon-nitrogen double
bond (C N) under mild conditions.
The results of the conversions of various oximes, hydrazones, azines,
semicarbazones, and Schiff-bases to their corresponding carbonyl com-
pounds are presented in Scheme 2, and Table I. The products of the
reaction with silica sulfuric acid (I) in the presence of wet SiO2 were
isolated simply by filtering the mixture and evaporating the solvent
from the filtrate. The method has advantages in terms of yields, its het-
erogeneous nature, cheapness and availability of the reagents, short
reaction times, and easy work-up.
SCHEME 2
The oximes, hydrazones, azines, semicarbazones, and Schiff-bases
were prepared by standard procedures.3
3−35
The purity of the com-
pounds was checked by TLC and by their melting points. A mixture of
the substrate, n-hexane, silica sulfuric acid, and wet SiO2 was stirred at
room temperature for the specified time. (The molar ratio of silica sul-
furic acid (I), and wet SiO2 to the substrate was optimized; see Table I),
The reaction was monitored by TLC. After completion of the reaction the
mixture was filtered and the solid residue was washed with n-hexane.
Evaporation of the solvent followed by column chromatography on sil-
ica gel gave the corresponding carbonyl compounds in good to excellent
yields.
In contrast to the normal Schiff-bases, which are unstable in
the presence of water molecules, we synthesized a good range of
3
5
Schiff-bases with a high degree of stability (Table I). Schiff-bases 3

2
738

2739

2
740

Cleavage of Carbon Nitrogen Double Bonds
2741
are very stable due to intramolecular hydrogen bonding.36−37 Differ-
ent kinds of Schiff-bases were also subjected to carbon-nitrogen double
bond (C N) cleavage in the presence of silica sulfuric acid (I), wet SiO2
(
50% w/w), and n-hexane as a solvent under mild and heterogeneous
conditions. All of the above mentioned reactions proceeded without any
application of oxidizing agents. Therefore, we think that the most inter-
esting feature of our results is the remaining of the oxidable functional
groups in the course of the reactions. While under oxidative cleavage
of carbon-nitrogen double bond oxidable functional groups will be oxi-
dized. This method is also suitable for acid sensitive functional groups
due to its heterogeneous nature. Therefore, original aldehydes were ob-
tained with excellent yields and their oxidation to the corresponding
acids did not occur.
In conclusion silica sulfuric acid in the presence of wet SiO2 can
serve as an efficient system for the cleavage of the carbon-nitrogen
double bond of oximes, hydrazones, azines, semicarbazones, and Schiff-
bases. The yields are good to excellent and the procedure is simple and
convenient. Moreover, the reaction is heterogeneous, which makes it a
3
8
suitable procedure for green chemical manufacturing.
EXPERIMENTAL
General procedure: A mixture of the substrate, silica sulfuric acid and
wet SiO2 (SiO2/H2O: 50% w/w) in n-hexane was stirrered for the time.
(
The molar ratio of silica sulfuric acid (I), and wet SiO2 to the substrate
was optimized; see Table I). The reaction was monitored by TLC or GLC.
After completion of the reaction, the mixture was filtered. Anhydrous
MgSO4 was added to the filtrate and filtered. Evaporation of the sol-
vent, being followed by column chromatography on silica gel [eluent:
acetone/petroleum ether (1:5)], gave the corresponding carbonyl com-
pounds in good to excellent yields.
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