Deprotection of semicarbazones using bismuth(III)nitrate pentahydrate supported onto silica gel

Article abstract of DOI:10.1080/10426500307776

Semicarbazones undergo facile and high yielding deprotection in acetone in the presence of Bi(NO₃)₃·5H₂O supported onto silica gel.

Full text of DOI:10.1080/10426500307776

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Deprotection of Semicarbazones Using
Bismuth(III)nitrate Pentahydrate Supported onto Silica
Gel
Shahnaz Khaleghi a , Majid M. Heravi a & Lida Fotouhi a
a Azzahra University , Vanak, Tehran, Iran
Published online: 27 Oct 2010.
To cite this article: Shahnaz Khaleghi , Majid M. Heravi & Lida Fotouhi (2003) Deprotection of Semicarbazones Using
Bismuth(III)nitrate Pentahydrate Supported onto Silica Gel, Phosphorus, Sulfur, and Silicon and the Related Elements, 178:1,
155-158, DOI: 10.1080/10426500307776
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:155–158
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Copyright 2003 Taylor & Francis
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DOI: 10.1080/10426500390170309
DEPROTECTION OF SEMICARBAZONES USING
BISMUTH(III)NITRATE PENTAHYDRATE
SUPPORTED ONTO SILICA GEL
Shahnaz Khaleghi, Majid M. Heravi, and Lida Fotouhi
Azzahra University, Vanak, Tehran, Iran
(Received July 16, 2002)
Semicarbazones undergo facile and high yielding deprotection in ace-
tone in the presence of Bi(NO3 )3 5H2O supported onto silica gel.
Keywords: Bismuth nitrate; carbonyl compounds; desemicarbazona-
tion; nonaqueous condition; supported reagent
INTRODUCTION
Semicarbazones frequently are used to protect, purify, and isolate car-
bonyl compounds1,2 and hence considerable attention has been paid to
develop methods for their deprotection. Regeneration of carbonyl com-
pounds from their semicarbazones has been accomplished by several
reagents such as phthalic anhydride,3 pyruvic acid,4 nitrous acid in
acetic acid, concentrated hydrochloric acid,5 cation exchange resins,6
thallium nitrate,7 titanium chloride,8 chlorotrimethylsilane-sodium
nitrate,9 supported bis (trimethylsilyl) chromate10 supported cerium
ammonium nitrate,11 and hexamethylene tetramine.12 Many of these
regents are strong oxidizing agents, and some of are toxic and produce
waste that persists in the environment. Due to environmental concerns,
there is an increasing need and interest in developing processes that
minimize production of toxic waste; therefore, there is emphasis on the
use and design of environmental friendly solid acid-base catalysis.13
Bismuth compounds are attractive candidates for use in green chem-
istry because bismuth is the less toxic of the heavy metals.14 The
The authors are thankful to the research council of Azzahra University for the partial
financial support. Their gratefulness is expanded to Dr. R. Hekmatshoar and Mrs. M.
Khosroshahi for their kind cooperation.
Address correspondence to Shahnaz Khaleghi, Department of Chemistry, School of
Science, Azzahra University, Vanak, Tehran, Iran. E-mail: khaleghi@azzahra.ac.ir
155

156
S. Khaleghi et al.
biochemistry,15 toxicology,16 and environmental effects17 of bismuth
compounds have been well documented.
Reagents supported by inorganic solids display modified reactivity
and selectivity. Added bonuses are easy work-up and isolation, en-
hanced selectivity, milder reaction conditions, and associated ease of
manipulation.18
RESULTS AND DISCUSSION
Bismuth(III)nitrate recently has been used as an oxidizing agent.19
Bismuth(III)nitrate supported onto montmorillonite K-10 along with
Cu(OAc)2 in a mixture of acetone-water has been reported as a non-
toxic and inexpensive reagent for deprotection of ketoximes.20
Here we wish to report that Bi(NO3)3 5H2O supported onto silica gel
is an efficient reagent for the regeneration of carbonyl compounds from
their semicarbazones.
The supported reagent was prepared by mixing 0.5 mmol of bismuth
nitrate pentahydrate with silica gel (0.1 g) using pestle and mortar.
The use of silica gel gave a better yield of products through desemi-
carbazonation relative to its absence; most probably silica gel acts as
a carrier to increase the surface of heterogeneous reaction. When de-
protection was carried out in the absences of silica gel, in the same
TABLE I Regeneration of Aldehydes and Ketones
from Their Semicarbazonesa
Reaction time
(h)
Yield
(%)
Entry
Aldehyde/ketoned
1
2
3
4
5
6
7
8
9
Benzaldehyde
1/2
1/2
3
1/4
2
3.5
3/4
1.5
1/4
3.5
98b
98c
97b
98c
99b
90b
98c
86b
99b
56b
4-Nitrobenzaldehyde
4-Methylbenzaldehyde
Salicyl aldehyde
Cinnamaldehyde
Crotonaldehyde
2-Butanone
Cyclohexanone
Acetophenone
Camphor
10
aAll semicarbazones have been prepared by a known
literature procedure.21
bRefers to yield determined by GC.
cRefers to yield of isolated product.
dAll products were identified by comparison of their
physical and spectroscopic data with those of authentic
samples.

Deprotection of Semicarbazones
157
condition a considerable amount of semicarbazone was detected un-
changed. However when the supported reagent was heated under re-
flux with semicarbazones in acetone the protection occurred in good to
high yields (Table I). No over-oxidation to carboxylic acid was observed
with this reagent.
When semicarbazone of cinnamaldehyde was examined, only cin-
namaldehyde was obtained and no benzaldehyde was formed showing
the reagent could not cleave carbon-carbon double bond. However, the
semicarbazone of camphor gave a moderate yield of deprotected com-
pound most probably due to steric hindrance.
Deprotection worked very well for a variety of semicarbazones. The
experimental procedure is very simple and involves the heating of semi-
carbazones with the supported reagent in acetone. The isolation of prod-
uct due to the advantage of supported reagent is easy. Acetone was found
to be the best solvent for this deprotection.
In summary, this work demonstrates the use of bismuth(III)nitrate
pentahydrate for the selective deprotection of semicarbazones of alde-
hydes, conjugated aldehydes and ketones. Bismuth(III)nitrate is rela-
tively nontoxic, it is easy to handle, insensitive to air, and inexpensive.
These features coupled with the use of a relatively non-toxic and inex-
pensive solvent (acetone) make this method even more attractive.
EXPERIMENTAL
Deprotection of Semicarbazones Using Bi(NO3)3 5H2O
Supported onto Silica Gel
General Procedure
A solution of an appropriate semicarbazone (1 mmol) was refluxed
with a mixture of Bi(NO3)3 5H2O (0.25 g, 0.5 mmol) and silica gel (0.1 g)
in acetone (2 ml) for the specified time (Table I). The progress of reaction
was monitored by TLC, using petroleum ether/EtOAc, 8:2. The mixture
was filtered and the filtrate was evaporated to dryness to give the cor-
responding carbonyl compound (Table I).
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