Silica chloride/wet SiO2 as a novel heterogeneous system for deprotection of oximes, hydrazones, and semicarbazones

Article abstract of DOI:10.1081/SCC-120020193

Oximes, hydrazones, and semicarbazones can be converted to their corresponding carbonyl compounds in good to high yields by a combination of silica chloride and wet SiO₂.

Full text of DOI:10.1081/SCC-120020193

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Silica Chloride/Wet SiO2 as a Novel Heterogeneous
System for Deprotection of Oximes, Hydrazones, and
Semicarbazones
F. Shirini a , M. A. Zolfigol b , M. Khaleghi a & I. Mohammadpour-Baltork c
a Department of Chemistry, College of Science, Guilan University, Rasht, Iran
b Department of Chemistry, College of Science, Bu-Ali Sina University, Hamadan, Iran
c Department of Chemistry, Isfahan University, Isfahan, Iran
Version of record first published: 17 Aug 2006.
To cite this article: F. Shirini, M. A. Zolfigol, M. Khaleghi & I. Mohammadpour-Baltork (2003): Silica Chloride/Wet SiO2 as a
Novel Heterogeneous System for Deprotection of Oximes, Hydrazones, and Semicarbazones, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:11, 1839-1844
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 11, pp. 1839–1844, 2003
Silica Chloride/Wet SiO2 as a Novel
Heterogeneous System for Deprotection of
Oximes, Hydrazones, and Semicarbazones
2
1
F. Shirini,1, M. A. Zolfigol, M. Khaleghi,
*
and I. Mohammadpour-Baltork3
1Department of Chemistry, College of Science,
Guilan University, Rasht, Iran
2Department of Chemistry, College of Science,
Bu-Ali Sina University, Hamadan, Iran
3Department of Chemistry, Isfahan University,
Isfahan, Iran
ABSTRACT
Oximes, hydrazones, and semicarbazones can be converted to their
corresponding carbonyl compounds in good to high yields by a
combination of silica chloride and wet SiO2.
Key Words: Deprotection; Hydrazones; Oximes; Semicarbazones;
Silica chloride.
*Correspondence: F. Shirini, Department of Chemistry, College of Science,
Guilan University, Rasht, Iran; E-mail: shirini@cd.gu.ac.ir.
1839
DOI: 10.1081/SCC-120020193
Copyright & 2003 by Marcel Dekker, Inc.
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1840
Shirini et al.
Regeneration of carbonyl compounds from stable and readily
prepared oximes, hydrazones, and semicarbazones has received attention
[1–7]
recentyears.
Since oximes can be prepared from olefins,[8] esters,[9]
nitriles,[9] nitro compounds,[10,14–16] nitrites,[11] alcohols,[12] and primary
aliphatic amines,[13] the regeneration of carbonyl compounds from
oximes provides an alternative method for the preparation of aldehydes
and ketones. However, many of these methods of generating carbonyl
compounds from oximes involve reagents which are either expensive or
[17–25]
notreadily available.
Little attention has been paid to the cleavage
of carbon–nitrogen double bonds of hydrazones and semicarbazones,
and only a few reports are available dealing with the conversion of the
derivatives into their corresponding carbonyl compounds.[4–7,26,27]
In continuation of our studies on the application of silica chlor-
ide,[28,29] we were interested in using this reagent for regeneration of
carbonyl compounds from oximes, hydrazones, and semicarbazones in
conjunction with wet SiO2 in an organic solvent. In this communication
we wish to report a simple method for the effective cleavage of carbon–
nitrogen double bonds of oximes, hydrazones, and semicarbazones under
mild and heterogeneous conditions (Table 1). Our experiments show that
oximes, hydrazones, and semicarbazones are converted into their corre-
sponding carbonyl compounds from good to high yields. It should be
noted that these deprotection reactions did not proceed using either silica
chloride or wetSiO alone, even after prolonged heating. In order to
2
show the ability of this system we have compared some of the results
with some of those reported in the literature (Table 2).
In summary silica chloride in the presence of wet SiO2 can serve as an
efficient reagent for the cleavage of carbon–nitrogen double bonds of
oximes, hydrazones, and semicarbazones. The yields are almostquanit-
tative and the procedure is simple and convenient. One of the advantages
of this method is the conversion of silica chloride to the silca gel during
the reaction, which can be used for the regeneration of silica chloride for
several times.
EXPERIMENTAL
General Procedure
A mixture of substrate (1 mmol), silica chloride (2 g), and wet
SiO2[(SiO2/H2O: 50% w/w), 1 g] in n-hexane was refluxed for the specified
time (Table 1). The reaction was monitored by TLC or GLC. After
completion of the reaction, the mixture was filtered. Anhydrous

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Silica Chloride/Wet SiO2
1841

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1842
Shirini et al.

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Silica Chloride/Wet SiO2
1843
Table 2. Comparison of some of the results obtained from silica chloride in the
presence of wetSiO (1) with some of those reported with N-bromosuccinimide
2
(2),[30] methylammonium chlorochromate adsorbed on alumina (3),[2] and
carboxypyridinium chlorochromate (4).[31]
Time in hour (Yield %)
Entry
1
Substrate
Product
1
2
3
4
Benzaldehyde-4-
nitrophenylhydrazone
Cyclohexanone
oxime
Benzaldehyde
1 (90)
—
3 (75) 1.5 (71)
2
3
Cyclohexanone 0.08 (92) 4 (80) 3.5 (96)
Acetophenone 0.5 (90)
2 (90)
Acetophenone
semicarbazone
—
—
2.5 (97)
MgSO4 was added to the filtrate and filtered. Evaporation of the solvent,
being followed by column chromatography on silica gel, gave the corre-
sponding carbonyl compounds from good to high yields.
ACKNOWLEDGMENT
Financial support for this work by the research affairs of the Guilan
University is acknowledged.
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Received in the Netherlands August 23, 2002