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

Article abstract of DOI:10.1080/10426500307885

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

Full text of DOI:10.1080/10426500307885

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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: 27 Oct 2010.
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,
178:7, 1507-1511, DOI: 10.1080/10426500307885
To link to this article: http://dx.doi.org/10.1080/10426500307885
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Phosphorus, Sulfur, and Silicon, 178:1507–1511, 2003
Copyright �C Taylor & Francis Inc.
ISSN: 1042-6507 print
DOI: 10.1080/10426500390212906
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 June 11, 2001; accepted October 2, 2001)
Silver carbonate supported on celite (Ag CO /Celite) is used as a mild
2
3
heterogeneous reagent for conversion of a 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 consti-
tute 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 natural
�
-amino acids. Several general methods are available for the prepa-
1
ration of amides. Among them, the chemical transformation of
thioamides into their corresponding oxo-derivatives, i.e., amides,
is highly valuable for the preparation of nucleic thiobases and
2
thionucleosides. Reported reagents used for the conversion of thio-
carbonyl into carbonyl compounds include iodate or bromate in
3
4
5,6
alkaline solutions, sodium peroxide, dimethyl sulfoxide-acids,
thiophosgene,7 diaryl telluroxide, dimethyl selenoxide, dimethyl
8
9
1
0
11
12
sulfoxide-iodine, benzeneseleninic acid, singlet oxygen, nitric
acid, selenium dioxide, soft NO species,15 clayfen, mercuric
acetate,17 and trifluroacetic anhydride. Very recently, a convenient
and mild procedure was introduced for conversion of secondary and ter-
tiary thioamides into the corresponding amides using Caro’s acid sup-
13
14
+
16
18
1
9
ported on silica gel. Oxidation of thioamides can take several courses,
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
507

1
508
B. Movassagh et al.
but all involve the sulfur atom; sulfur is removed as sulfate and re-
placed by oxygen when an oxidant (e.g. iodine or hydrogen peroxide) is
2
0
used in basic solution.
RESULTS AND DISCUSSION
Oxidations by Ag2CO3/Celite are heterogeneous reactions which take
place under essentially neutral conditions. This reagent is used for oxi-
2
1
dation of different functionalities. Here we report the use of silver car-
bonate supported on celite, Ag2CO3/celite, as a viable new method for ef-
fecting this transformation. This supported reagent can be used for the
generation of a 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.
SCHEME 1
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-(N,N-dimethylamino)benzamide (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 smoothly
converted 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
(
melting point) with those of authentic samples.10,11,19,22 The starting

1509

1
510
B. Movassagh et al.
thioamides were either prepared from the corresponding amides us-
2
3
ing tetraphosphorous decasulfide (P4S10) or the modified Willgerodt-
2
4 1
Kindler reaction.
H-NMR spectra were recorded at 60 MHz in CCl4
and CDCI3 using tetramethylsilane (TMS) as internal standard.
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 wa-
�
ter 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 wa-
ter (30 ml) was then added slowly to the homogeneous suspension and
stirring was continued for a further 15 min. The yellow-green precipi-
tate 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/CCI4, 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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