Conversion of thioamides into their corresponding oxygen analogues using silver carbonate supported on celite

Article abstract of DOI:10.1080/10426500390228620

Silver carbonate supported on celite (Ag₂CO₃/Celite) is used as a mild heterogeneous reagent for conversion of variety of thioamides into their corresponding amides in acetonitrile at room temperature.

Full text of DOI:10.1080/10426500390228620

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Phosphorus, Sulfur, and Silicon and the Related
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Conversion of Thioamides into Their Corresponding
Oxygen Analogues Using Silver Carbonate Supported on
Celite
a
a
a
B. Movassagh , M. M. Lakouraj & A. Gholami
a
Razi University , Kermanshah, Iran
Published online: 23 Aug 2006.
To cite this article: B. Movassagh , M. M. Lakouraj & A. Gholami (2003) Conversion of Thioamides into Their Corresponding
Oxygen Analogues Using Silver Carbonate Supported on Celite, Phosphorus, Sulfur, and Silicon and the Related Elements,
178:9, 1943-1947, DOI: 10.1080/10426500390228620
To link to this article: http://dx.doi.org/10.1080/10426500390228620
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Phosphorus, Sulfur, and Silicon, 178:1943–1947, 2003
Copyright ꢀC Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500390228620
CONVERSION OF THIOAMIDES INTO THEIR
CORRESPONDING OXYGEN ANALOGUES USING
SILVER CARBONATE SUPPORTED ON CELITE
B. Movassagh, M. M. Lakouraj, and A. Gholami
Razi University, Kermanshah, Iran
(
Received August 1, 2001; accepted April 24, 2003)
Silver carbonate supported on celite (Ag CO /Celite) is used as a
2
3
mild heterogeneous reagent for conversion of variety of thioamides into
their corresponding amides in acetonitrile at room temperature.
Keywords: Amides; celite; silver carbonate; thioamides
Amides are important chemical intermediates since they can be hy-
drolyzed to acids, dehydrated to nitriles, and degraded to amines con-
taining one less carbon atom by the Hofmann reaction. They con-
stitute a group of substances of increasing interest and applications
in pharmacology and industry. These compounds are very prevalent
in nature, since all peptides and proteins are polymers of the nat-
ural α-amino acids. Several general methods are available for the
preparation of amides;1 among them, the chemical transformation
of thioamides into their corresponding oxo-derivatives, i.e., amides,
2
is highly valuble for the nucleic thiobases and thionucleosides. Re-
ported reagents used for the conversion of thiocarbonyl into car-
3
bonyl compounds include iodate or bromate in alkaline solutions,
4
5,6
7
sodium peroxide, dimethyl sulfoxide-acids,
thiophosgene, diaryl
8
9
10
telluroxide, dimethyl selenoxide, dimethyl sulfoxide-iodine, ben-
1
1
12
13
14
zeneseleninic acid, singlet oxygen, nitric acid, selenium dioxide,
+
15
16
17
soft NO species, clayfen, mercuric acetate, and trifluroacetic
1
8
anhydride. Very recently, a convenient and mild procedure was in-
troduced for conversion of secondary and tertiary thioamides into the
corresponding amides using Caro’s acid supported on silica gel.19 Oxi-
dation of thioamides can take several courses, but all involve the sulfur
We thank the Razi University Research Council for financial assistance.
Address correspondence to B. Movassagh, Department of Chemistry, Razi University,
Kermanshah 67149, Iran. E-mail: movassagh@hotmail.com
1
943

1
944
B. Movassagh et al.
atom; sulfur is removed as sulfate and replaced by oxygen when an
2
0
oxidant (e.g., iodine or hydrogen peroxide) is used in basic solution.
RESULTS AND DISCUSSION
Oxidations by Ag2CO3/celite are heterogeneous reactions that take
place under essentially neutral conditions. This reagent is used for ox-
idation of different functionalities.21 Here we report the use of silver
carbonate supported on Celite, Ag2CO3/celite, as a viable new method
for effecting this transformation. This supported reagent can be used for
the generation of variety of amides from their corresponding thioamides
in acetonitrile at room temperature under air atmosphere in high to
excellent yields (Table I). Isolation of the product from this oxidation
is remarkably simple and consists merely in filteration to remove the
spent reagent system, followed by evaporation of the solvent.
This procedure is applicable to a variety of thioamides including N,N-
disubstituted-, N-substituted- and unsubstituted thioamides, thioben-
zamides, and thioureas by reaction with one molar equivalent of the
reagent, except for 1,4-dithiobenzoyl piperazine (entry 13, Table I) for
which two molar equivalents of the reagent is used. The highest yield is
obtained with N,N-diethyl-4-nitrobenzamide (98%, entry 12, Table I),
and the lowest with thioacetamide (77%, entry 1, Table I).
From the results above, it can be concluded that, by using silver car-
bonate supported on celite, different types of thioamides are converted
smoothly to amides in high to excellent yields.
EXPERIMENTAL
General
All yields refer to pure isolated products. The amides were character-
1
ized by comparison of their spectral (IR, H-NMR) and physical data
1
0,11,19,22
(
melting point) with those of authentic samples.
The starting
thioamides were either prepared from the corresponding amides us-
23
ing tetraphosphorous decasulfide (P4S10) or the modified Willgerodt-
Kindler reaction.2 H-NMR spectra were recorded at 60 MHz in CCl4
and CDCl3 using tetramethylsilane (TMS) as internal standard.
4 1
Preparation of Silver Carbonate Supported on Celite21
The celite was purified by washing it successively with methanol con-
taining 10% concentrated hydrochloric acid and then with distilled

1945

1
946
B. Movassagh et al.
FIGURE 1
◦
water until neutral; it was dried at 120 C. Purified celite (3 g) was added
to a stirred solution of silver nitrate (3.4 g, 20 mmol) in distilled water
(
20 ml). A solution of sodium carbonate (1.1 g, 10.4 mmol) in distilled
water (30 ml) was then added slowly to the homogeneous suspention
and stirring was continued for a further 15 min. The yellow-green pre-
cipitate, which was formed, was collected by filtration and dried in a
vacuum oven for 3 h. The reagent system thus prepared contained about
0.35 g (1.3 mmol) of Ag2CO3 per gram.
General Procedure for Conversion of Thioamides
Into Amides
A mixture of the thioamide (1 mmol ) and Ag2CO3/celite (1 or 2 mmol) in
acetonitrile (15 ml) was stirred at room temperature for the period in-
dicated (Table I). Progress of the reaction was followed by TLC (eluent:
Et2O/CCl4, 3/1). After completion of the reaction the solids were col-
lected by filtration, washed with excess acetonitrile, and the combined
filtrates evaporated. The crude amide was either recrystallized from
n-heptane, EtOH/H2O, or subjected to column chromatography using
silica gel (n-heptane/Et2O).
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