Mercuric nitrate-mediated deprotection of oximes, hydrazones, and semicarbazones

Article abstract of DOI:10.1081/SCC-120038512

Mercuric nitrate in wet silica gel is found to be an excellent reagent for the regeneration of carbonyl compounds from oximes, hydrazones, and semicarbazones.

Full text of DOI:10.1081/SCC-120038512

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Mercuric Nitrate‐Mediated Deprotection of Oximes,
Hydrazones, and Semicarbazones
Surya Kanta De a
a Department of Chemistry , University of Washington , Box 351700, Seattle, Washington,
98195, USA
Published online: 17 Aug 2006.
To cite this article: Surya Kanta De (2004) Mercuric Nitrate‐Mediated Deprotection of Oximes, Hydrazones, and
Semicarbazones, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 34:12, 2289-2294, DOI: 10.1081/SCC-120038512
To link to this article: http://dx.doi.org/10.1081/SCC-120038512
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 12, pp. 2289–2294, 2004
Mercuric Nitrate-Mediated Deprotection of
Oximes, Hydrazones, and Semicarbazones
*
Surya Kanta De
Department of Chemistry, University of Washington,
Seattle, Washington, USA
ABSTRACT
Mercuric nitrate in wet silica gel is found to be an excellent reagent for the
regeneration of carbonyl compounds from oximes, hydrazones, and
semicarbazones.
Key Words: Mercuric nitrate; Oximes; Hydrazones; Semicarbazones.
INTRODUCTION
Oximes, hydrazones, and semicarbazones are useful as preferred
derivatives for the identification and characterization of carbonyl com-
pounds.[1] Since oximes can be prepared from non-carbonyl compounds,
*
Correspondence: Surya Kanta De, Department of Chemistry, University of
Washington, Box 351700, Seattle, WA 98195, USA; E-mail: suryakd@hotmail.com
or skd125@yahoo.com.
2289
DOI: 10.1081/SCC-120038512
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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the regeneration of carbonyl compounds from oximes provides an alternative
method for the preparation of aldehydes and ketones.[2] Furthermore, they
play an important role by protecting[3] and selectively a-activating groups[4]
in organic chemistry. Therefore, there has been a continued interest in the
development of procedures for the effective regeneration of carbonyl com-
pounds from the corresponding stable and readily prepared oximes, hydra-
zones, and semicarbazones. As a result, several methods have been
reported for the regeneration of carbonyl compounds from their oximes
such as pyridinium chlorochromate,[5] pyridinium chlorochromate-hydrogen
peroxide,[6] triethyl ammonium-chlorochromate,[7] chromic-anhydride-
chlorotrimethylsilane,[8] dinitrogen tetraoxide,[9] titanium silicate,[10] N-
haloamide,[11] manganese triacetate,[12] Dess-Martin periodane,[13] tetrabutyl-
ammonium peroxydisulfate,[14] clay supported ammonium chlorochro-
mate,[15] and clayfen.[16] Although some of these methods are carried out
under mild reaction conditions, most of them require strong acidic media,
a strong oxidizing agent (which causes over oxidation), and expensive,
and not readily available reagents. Additionally, they can require long reac-
tion times for the regeneration of carbonyl compounds from oximes.
Recently, some microwave techniques have been reported,[17] which are
valuable methods from the synthetic standpoint, but extreme precautions
have to be taken as these reactions were performed under microwave
irradiation or ultrasonic irradiation with an oxidant. Little attention has
been paid to the regeneration of carbonyl compounds from hydrazones
and semicarbazones.[9,13,18,19] Thus, there is still a need to develop a new
and facile procedure for the regeneration of carbonyl compounds from
oximes, hydrazones, and semicarbazones.
2a. R1 ¼ R2 ¼ C6H5; 2b. R1 ¼ C6H5, R2 ¼ Me; 2c. R1 ¼ p-MeOC6H4,
R2 ¼ H; 2d. R1 ¼ p-BrC6H4, R2 ¼ H; 2e. R1 ¼ R2 ¼ –(CH2)5–; 2f. R1 ¼
R2 ¼ –(CH2)4–; 2g. R1 ¼ C6H5, R2 ¼ H; 2h. R1 ¼ p-ClC6H4, R2 ¼ Me; 2i.
R1 ¼p-MeOC6H4, R2 ¼ Me.

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Deprotection of Oximes, Hydrazones, and Semicarbazones
2291
Mercuric nitrate is an inexpensive reagent, which has been used exten-
sively as an oxidizing agent.[20] I believe this is the first report using mercuric
nitrate as the reagent for the deprotection of oximes, hydrazones, and semicar-
bazones. Several oximes were deoximated using mercuric nitrate in silica gel
in the presence of a small amount of water under reflux condition in tetra-
hydrofuran. Semicarbazones and hydrazones were deprotected the same
way (Table 1). The conversions were clean and no undesirable side products
Table 1. Deprotection of oximes, hydrazones, and semicarbazones with mercuric
nitrate in wet silica gel.
Product Time Yield M.p./b.p. (8C)
Entry
Substrate (1)
(2)
(hr)
(%)
Lita/obs
1
2
3
Benzophenone oxime
Acetophenone oxime
4-Methoxybenzaldehyde
oxime
2a
2b
2c
6
8
5
94
91
86
48–49/46–47
202/200–202
248/245–247
4
5
6
4-Bromobenzaldehyde oxime
Cyclohexanone oxime
Cyclopentanone oxime
2d
2e
2f
5
4
5
89
93
88
55–58/55–57
155/150–152
130–131/
128–129
178–179/
179–180
7
Benzaldehyde oxime
2g
5
83
8
9
4-Chloroacetophenone oxime
Benzophenone
semicarbazone
2h
2a
6
8
92
91
232/229–231
10
11
12
13
14
15
16
17
4-Bromobenzaldehyde
semicarbazone
2d
2h
2e
2b
2a
2h
2d
2i
7
8
5
7
8
4
7
5
82
90
88
86
83
89
91
88
4-Chloroacetophenone
semicarbazone
Cyclohexanone
semicarbazone
Acetophenone
semicarbazone
Benzophenone
phenylhydrazone
4-Chloroacetophenone
phenylhydrazone
4-Bromobenzaldehyde
phenylhydrazone
4-Methoxyacetophenone
phenylhydrazone
36–38/34–35
aAvailable from Aldrich Chemical Company.

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De
were observed. A few drops of water and silica gel were found to be essential
for the success of the reaction. Without silica gel support, the reaction is slug-
gish with mercuric nitrate even after prolonged reaction periods.
In conclusion, a facile method has been developed for the regeneration of
carbonyl compounds from their respective oximes, hydrazones, and semicar-
bazones using mercuric nitrate in wet silica gel.
EXPERIMENTAL
All the products are known compounds and were checked by comparison
of their spectral data (IR, 1H NMR) and physical properties with an authentic
sample. The reaction was monitored by thin layer chromatography on silica
gel because overoxidation may occur in some cases after cleavage of protect-
ing groups. All yields refer to isolated products.
General Procedure for the Regeneration of Carbonyl
Compounds from Oximes, Hydrazones, and
Semicarbazones with Mercuric Nitrate
A mixture of substrate (oxime or hydrazone or semicarbazone, 1 mmol),
mercuric nitrate monohydrate (1 mmol), silica gel (1 g), and water (1 mL) in
THF (10 mL) was refluxed for the specified time (Table 1). After completion
of the reaction, the reaction mixture was filtered. Then the filtrate was
extracted with ethyl acetate and washed with sodium bicarbonate and water.
The organic layer was dried over magnesium sulfate then concentrated and
filtered through short silica gel column to afford a pure product in good to
excellent yield.
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Received in the USA March 3, 2004

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