A mild and convenient method for conversion of thioamides to their corresponding amides using acidified wet silica-supported permanganate under solvent-free conditions

Article abstract of DOI:10.1080/10426500802080865

A mild and efficient method for conversion of thioamides to their corresponding amides is reported. A series of thioamides are transformed to their corresponding carbonyl compounds in good to excellent yields by acidified wet silica-supported permanganate under solid phase conditions.

Full text of DOI:10.1080/10426500802080865

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Phosphorus, Sulfur, and Silicon
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A Mild and Convenient Method
for Conversion of Thioamides
to Their Corresponding Amides
Using Acidified Wet Silica-
Supported Permanganate
Under Solvent-Free Conditions
Masoud Nasr-Esfahani a , Majid Moghadam b , Iraj
Mohammadpoor-Baltork b & Mohammad Hasan
Boostanifar a
a Department of Chemistry , Yasouj University ,
Yasouj , Iran
b Department of Chemistry, Catalysis Division ,
University of Isfahan , Isfahan , Iran
Published online: 19 Dec 2008.
To cite this article: Masoud Nasr-Esfahani , Majid Moghadam , Iraj Mohammadpoor-
Baltork & Mohammad Hasan Boostanifar (2008) A Mild and Convenient Method for
Conversion of Thioamides to Their Corresponding Amides Using Acidified Wet Silica-
Supported Permanganate Under Solvent-Free Conditions, Phosphorus, Sulfur, and
Silicon and the Related Elements, 184:1, 141-146, DOI: 10.1080/10426500802080865
To link to this article: http://dx.doi.org/10.1080/10426500802080865
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Phosphorus, Sulfur, and Silicon, 184:141–146, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802080865
A Mild and Convenient Method for Conversion of
Thioamides to Their Corresponding Amides Using
Acidified Wet Silica-Supported Permanganate Under
Solvent-Free Conditions
Masoud Nasr-Esfahani,1 Majid Moghadam,2 Iraj
Mohammadpoor-Baltork,2 and Mohammad Hasan
Boostanifar1
1Department of Chemistry, Yasouj University, Yasouj, Iran
2Department of Chemistry, Catalysis Division, University of Isfahan,
Isfahan, Iran
A mild and efficient method for conversion of thioamides to their corresponding
amides is reported. A series of thioamides are transformed to their corresponding
carbonyl compounds in good to excellent yields by acidified wet silica-supported
permanganate under solid phase conditions.
Keywords Acidified wet silica-supported permanganate; amides; solvent-free;
thioamides
INTRODUCTION
The transformation of thioamides to their corresponding amides is a
significant reaction in synthetic organic chemistry. Amides are valu-
able chemical intermediates in some organic reactions; they can be
dehydrated to nitriles, hydrolyzed to carboxylic acids, and degraded to
amines in Hofmann rearrangement. Since all peptides and proteins are
produced from natural α-amino acids, these compounds are very preva-
lent in nature. One of the available methods for preparation of amides
is the chemical transformation of thioamides into their corresponding
oxo-derivatives, i.e., amides, is highly valuable for the nucleic thiobases
and thionucleosides.1
Received 9 January 2008; accepted 20 February 2008.
The partial support of this work by Yasouj University Council of Research is acknowl-
edged.
Address correspondence to Masoud Nasr-Esfahani, Department of Chemistry, Yasouj
University, Yasouj 75914, Iran. E-mail: manas@mail.yu.ac.ir
141

142
M. Nasr-Esfahani et al.
Thiocarbonyl compounds are specific and beneficial tools for
multistep synthetic routes leading to various natural prod-
ucts or biologically active molecules.2 However, the final step
of a total synthesis may involve transformation of a thiocar-
bonyl group into the corresponding carbonyl group. Various
methods and reagents such as t-butyl hypochlorite,3 diaryl
selenoxide,4 dimethyl selenoxide,5 diaryl telluroxide,6 benzenese-
leninic anhydride,7 singlet-oxygen,8 thiophosgene,9 sodiumperoxide,10
dimethyl sulfoxide/iodine,11 m-chloroperbenzoic acid,12 NOBF4,13
N-nitrosamines,14 soft NO+ species,15 trifluoroacetic anhydride,16
clayfen,17 p-nitrobenzaldehyde/TMSOTf,18 2-nitrobenzenesulfonyl
chloride/potassium superoxide,19 manganese dioxide,20 clayfen or
clayan/MW,21 Caro’s acid supported on silica gel,22 ceric ammo-
nium nitrate,23 oxone,24 (n-BuPPh3)2S2O8,25 (n-BuPPh3)2Cr2O7,26
3-carboxypyridinium and 2,2ꢀ -bipyridinium chlorochromates,27 and
tetrabutylammonium periodate28 have been reported for the deprotec-
tion of thiocarbonyl compounds to their oxygen analogues.
However, some of these methods have certain limitations such
as long reaction times,4−6,19 toxic or expensive reagents,7,9,13−15 low
yields of the products4,5,19 and tedious procedures.7,10,15,18 Further-
more, some of these methods are not suitable for deprotection of pri-
mary thioamides.
The use of solid supports has become popular due to their charac-
teristic properties such as enhanced reactivity and selectivity, straight-
forward work-up procedure, milder reaction conditions, and associated
ease of manipulation.29 One of the most striking examples of such a
change in chemical reactivity that has been reported to date is with
potassium permanganate.30 The heterogeneous reaction of sulfides,
alkenes, unsaturated alcohols, benzylic carbons, and α-sulfinyl oximes
and α-sulfinyl hydrazones with potassium permanganate supported on
copper sulfate, alumina, or silica gel are different than heterogeneous
aqueous reactions.31,32
RESULTS AND DISCUSSION
As shown in Table I, a variety of thioamides (primary, secondary, and
tertiary) were treated with KMnO4/acidified wet SiO2 under solid phase
conditions at room temperature to afford the corresponding carbonyl
compounds in good to excellent yields (Table I, entries 1–15). In the
absence of acid, the conversion of thioamides decreased to 5–10%, and
in the absence of SiO2 the thioamides remained intact.

Mild and Convenient Method for Conversion of Thioamides
143
TABLE I Transformation of Thioamide Derivatives to the
Corresponding Amides with KMnO4/Acidified Wet SiO2
Time
(min)
Yields
(%)
Entry
Thioamides
Amides
Ref.
[35]
1
9
92
93
2
7
[37]
3
4
5
4
96
98
[35]
[36]
5
6
16
9
93
96
[36]
[37]
7
8
8
4
94
95
[35]
[37]
9
5
94
[37]
10
11
6
5
98
90
[35]
[37]
(Continued on next page)

144
M. Nasr-Esfahani et al.
TABLE I Transformation of Thioamide Derivatives to the
Corresponding Amides with KMnO4/Acidified Wet SiO2 (Continued)
Time
(min)
Yields
(%)
Entry
Thioamides
Amides
Ref.
[37]
12
2
97
13
14
3
6
94
92
[37]
[37]
15
9
93
[35]
Large scale deprotection of some thioamides to their corresponding
amides was also investigated in a 20 mmol scale. The results were
comparable to those of small scale experiments; therefore, it seems
that this methodology is also applicable for operation on large scale
desulfurization of thioamides. It was found that in these reactions sul-
fur is converted to sulfate and replaced by oxygen, which is indicated
by addition of a solution of BaCl2.
O
C
S
R2
R3
R2
R3
KMnO4/SiO2-HCl
solvent-free, r.t
C
R1
R1
N
N
CONCLUSION
We have developed a mild and convenient procedure for the conversion
of thioamides to their carbonyl compounds using KMnO4/acidified wet
SiO2 as a nontoxic and inexpensive reagent under solvent-free condi-
tions. The short reaction times, high product yields, and heterogeneous
nature of the reagent are the advantages of this method.

Mild and Convenient Method for Conversion of Thioamides
145
EXPERIMENTAL
All of the products were identified by comparison of their physical and
spectral data with those of authentic samples. The starting thioamides
were prepared according to described procedures.33,34
GENERAL PROCEDURE
Acidified wet silica gel was prepared by shaking silica gel (20 g, 70–
230 mesh) with concentrated HCl (6 mL). The reagent was prepared
by mixing of KMnO4(2 mmol, 3.23 g) with acidified wet-silica gel (3 g)
using a pestle and mortar until a fine, homogeneous, purple powder
was obtained. A mixture of thioamides (1 mmol) and KMnO4/ acidified
wet SiO2 (2 mmol, 3.23 g) was ground with a pestle and mortar until
TLC showed complete disappearance of thioamides, which required 2–
12 min (Table I). Ethylacetate (2 × 10 mL) was added to the reaction
mixture, and after vigorous stirring, was filtered through a sintered
glass funnel. After evaporation of the solvent and purification by col-
umn chromatography on silica gel using ethyl acetate as eluent, the
pure amides were obtained in 92–98%.
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