Transformation of thioamide compounds to corresponding amides using 12-Tungstosilicic acid

Article abstract of DOI:10.1080/10426500902758964

12-Tungstosilicic acid (H₄SiW₁₂O₄₀) is applied for the conversion of a series of thioamides to their corresponding oxo analogues in excellent yields in acetonitrile. In the case of thioketones, no reaction is observed under these conditions. The reusability of the catalyst also is investigated.

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Transformation of Thioamide Compounds
to Corresponding Amides Using 12-
Tungstosilicic Acid
a
a
Masoud Nasr-Esfahani , Morteza Montazerozohori , Majid
b
b
a
Moghadam , Iraj Mohammadpoor-Baltork & Sareh Moradi
a
Department of Chemistry, Yasouj University, Yasouj, Iran
b
Department of Chemistry, Catalysis Division, University of Isfahan,
Isfahan, Iran
Version of record first published: 03 Feb 2010.
To cite this article: Masoud Nasr-Esfahani , Morteza Montazerozohori , Majid Moghadam , Iraj
Mohammadpoor-Baltork & Sareh Moradi (2010): Transformation of Thioamide Compounds to
Corresponding Amides Using 12-Tungstosilicic Acid, Phosphorus, Sulfur, and Silicon and the Related
Elements, 185:2, 261-266
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Phosphorus, Sulfur, and Silicon, 185:261–266, 2010
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DOI: 10.1080/10426500902758964
TRANSFORMATION OF THIOAMIDE COMPOUNDS
TO CORRESPONDING AMIDES USING
1
2-TUNGSTOSILICIC ACID
1
1
Masoud Nasr-Esfahani, Morteza Montazerozohori,
2
2
Majid Moghadam, Iraj Mohammadpoor-Baltork,
1
and Sareh Moradi
1
Department of Chemistry, Yasouj University, Yasouj, Iran
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan, Iran
2
1
2-Tungstosilicic acid (H4SiW12O40) is applied for the conversion of a series of thioamides
to their corresponding oxo analogues in excellent yields in acetonitrile. In the case of
thioketones, no reaction is observed under these conditions. The reusability of the catalyst
also is investigated.
Keywords Amide; oxidations; thioamides; transformation; 12-tungstosilicic acid
INTRODUCTION
In recent years, catalysis of Keggin-type heteropoly acids (HPAs), typically repre-
5
+
4+
sented by the formula H8-x[XM12O40], where X is the heteroatom (e.g., P or Si ), x is its
6+
6+
oxidation state, and M is the addenda atom (usually W or Mo ), has attracted much in-
terest, especially tungstophosphoric acid (H3PW12O40), tungstosilicic acid (H4SiW12O40),
and molybdatophosphoric acid (H3PMo12O40). These are promising materials that have
1
strong acidity as well as oxidizing ability with greater activity than the conventional cata-
2,3
lysts, such as mineral acids, zeolites, ion-exchange resins, and H3PO4/SiO2 and are used
4
–7
as a catalyst for various kinds of organic transformations.
Heteropoly acids have several advantages as catalysts because of their flexibility
in modifying the acid strength, their environmental compatibility, nontoxicity, and exper-
2
a,8,9
imental simplicity, which make them economically and environmentally attractive.
Heteropolyacids have been extensively studied because of their interesting catalytic prop-
erties for the synthesis of antioxidants, medicinal preparations, vitamins, and biologically
active substances.1
0,11
HPAs have several advantages over liquid acid catalysts, including being noncorrosive
and environmentally benign. In aqueous solution, these compounds such as PW, SiW, and
PMo are strong, fully dissociated acids. HPAs in solution are stronger than the usual
Received 14 December 2008; accepted 19 January 2009.
The partial support of this work by Yasouj University Council of Research is acknowledged.
Address correspondence to Masoud Nasr-Esfahani, Department of Chemistry, Yasouj University, Yasouj
75918–74831, Iran. E-mail: manas@mail.yu.ac.ir
2
61

262
M. NASR-ESFAHANI ET AL.
mineral acids such as H2SO4, HNO3, HCl, and HBr, and even strong acids such as HClO4
and CF3SO3H.2 Among heteropolyacids, polytungstic acids are the most widely used
catalysts owing to their high acidic strength, thermal stability, and low reducibilities.
From a synthetic point of view, the transformation of thioamides to their correspond-
ing amides is an important reaction in organic chemistry. Amides are valuable chemical
intermediates in some organic reactions; they can be dehydrated to nitriles, hydrolyzed to
a
12
carboxylic acids, and degraded to amines in Hofmann rearrangement. For this conver-
1
3
14
sion, various methods and reagents such as t-butyl hypochlorite, dimethyl selenoxide,
15
16
17
18
benzeneseleninic anhydride, thiophosgene, dimethyl sulfoxide/iodine, NOBF4, soft
NO species, trifluoroacetic anhydride, p-nitrobenzaldehyde/TMSOTf, manganese
dioxide, clayfen or clayan/MW, Caro’s acid supported on silica gel, oxone,
n-BuPPh3)2S2O8, (n-BuPPh3)2Cr2O7, 3-carboxypyridinium and 2,2 -bipyridinium
chlorochromates, and tetrabutylammonium periodate have been reported. However,
some of these methods are not suitable for conversion of primary thioamides, and some
also show limitations such as low yields of the products, long reaction times, the use of
expensive reagents, and tedious workup procedures.
+
19
20
21
22
23
24
25
2
6
27
’
(
2
8
29
RESULTS AND DISCUSSION
In continuation of our ongoing research program,30 we wish report a mild and effi-
cient transformation of thioamides into the corresponding amides using tungstosilicic acid.
Various thioamides were reacted with the H4SiW12O40 in acetonitrile at reflux to afford the
corresponding amides in excellent yields (Scheme 1).
S
O
H SiW12O
4
40
R1
R2
R
1
R2
CH CN, reflux
3
R1: alkyl, aryl
R2: alkyl, aryl (thioketones)
or NRR' (thioamides, R,R': H, alkyl, aryl)
Scheme 1 Transformation of thioamides to their corresponding amides.
In choosing the reaction media, different solvents were investigated in the conversion
of N-thiobenzoylaniline to N-benzoylaniline with H4SiW12O40 under reflux conditions.
Among the studied solvents, CH3CN was chosen as suitable solvent because higher amide
derivatives were observed (Table I). By employing 0.5 molar equivalent of the reagent in
CH3CN, the amide was obtained after 90 min in 96% yield. These conditions were applied
for the conversion of different thioamides into their corresponding amides.
As shown in Table II, a variety of primary, secondary, and tertiary thioamides were
treated with tungstosilicic acid in refluxing acetonitrile to afford the corresponding carbonyl
compounds in excellent yields (Table II, entries 1–15). In the case of thioketones such as
thiobenzophenone or 3-thiopentanone, no reaction was observed under these conditions.
Therefore thioamides can be selectively converted to amide analogues in the presence of
thioketones.
Large scale deprotection of some thioamides to their corresponding amides was also
investigated. The results were comparable to those of small scale experiments; therefore, it

TRANSFORMATION OF THIOAMIDE COMPOUNDS
263
Table I Conversion of N-thiobenzoyl aniline to corresponding amide with H4SiW12O40 in different solvents
under reflux conditions
Solvent
H4SiW12O40(mmol)
Time (min)
Yield (%)a
H2O
CH2Cl2
CCl4
CH3CH2OH
CH3OH
CHCl3
CH3COCH3
CH3CN
CH3CN
CH3CN
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1
90
90
90
90
90
90
90
90
40
10
10
7
8
5
0
90
97
25
0.5
0.25
90
150
aIsolated yields.
seems that this method is also applicable for operation on a large scale desulfurization of
thioamides.
The reusability of the catalyst was monitored using multiple sequential conversion
of N-thiobenzoyl aniline as a typical thioamide with tungstosilicic acid. For each of the re-
peated reactions, the catalyst was recovered and dried before being used for fresh thioamide.
The catalyst was consecutively reused four times without a detectable catalyst leaching or
a significant loss of its activity (Table III).
In order to detail the ability of our method with respect to previous reports, some
of our results in comparison with some other methods are summarized in Table IV. As is
shown, the yield/time ratios of our present method are better or comparable with others.
Table II Transformation of thioamide derivatives to their corresponding amides with H4SiW12O40 in
a
acetonitrile
◦
Mp ( C)
b
Reported34
Entry
R1
H2NCS
R2
Time (min)
Yields (%)
Found
3
4b
1
2
3
4
5
6
7
8
9
NH2
90
90
97
96
95
94
90
93
94
97
95
93
90
95
94
93
90
298–299
160–162
152–154
146–147
105–107
150–152
215–217
239–240
159–160
210–212
87–88
>300
3
3
3
3
4a
4c
4c
4c
C6H5
C6H5NH
163
155
148
107
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
C6H5
2-CH3C6H4NH
2-CH3OC6H4NH
C6H5NCH3
C6H5CH2NH
4-NO2C6H4NH
2-CH3C6H4NH
2-ClC6H4NH
C6H5NH
(CH2CH3)2N
1-naphthyl-NH
2-CH3OC6H4NH
4-NO2C6H4NH
(CH3)2NH
100
110
150
120
120
90
90
120
90
3
3
3
4b
4b
4c
152–153
215–216
241–242
CH3
3,5-(NO2)2C6H3
4-NO2C6H4
4-NO2C6H4
3,5-(NO2)2C6H3
4-CH3C6H4
C6H5
34c
160
211
89–91
3
4b
1
1
1
1
1
1
0
1
2
3
4
5
3
4c
34c
90
169–170
59–61
200–202
127–129
173
34a
100
120
100
60
3
4b
4c
C6H5
3,5-(NO2)2C6H3
199–200
128–130
3
a
1
All products were identified by comparison with authentic samples (IR, H NMR, mp).
b
Isolated yields.

264
M. NASR-ESFAHANI ET AL.
Table III Reusability of H4SiW12O40 in conversion of N-thiobenzoyl aniline
Row
Time (min)
Yields (%)
1
2
3
4
90
90
95
96
95
95
93
100
In conclusion, we have developed an efficient procedure for the conversion of
thioamides to their carbonyl compounds using tungstosilicic acid in acetonitrile, as a
simple and inexpensive reagent under reflux conditions. The appropriate reaction times,
high product yields, easy workup, and reusability of the catalyst are the advantages of this
method.
EXPERIMENTAL
All of the products were identified by comparison of their physical and spectral
3
1,32
33
data with those of authentic samples. The starting thioamides
prepared according to described procedures.
and thioketones were
General Procedure for the Conversion of Thiocarbonyls to Carbonyl
Compounds in Acetonitrile Solvent
In a round bottomed flask (25 mL), a solution of thiocarbonyl compound (1 mmol)
in CH3CN (10 mL) was treated with H4SiW12O40 (0.5 mmol), and the reaction mixture
was stirred under reflux for the time indicated in Table II. The progress of the reaction was
monitored by TLC (eluent: CCl4:EtOAc, 10:1). After completion, diethyl ether (2×10 mL)
was added to the reaction mixture and the crude product was extracted. The solvent was
evaporated, and the crude product was purified by column chromatography on silica-gel
and recrystallized from n-hexane to afford the pure product.
Table IV Comparison of some of our results with those reported in the literaturea
Entryb
Ac
B
C
D
E
1
2
3
5
7
97/90
96/90
85/180
—
—
90/180
—
—
84/40
81/80
—
—
—
85/10
90/15
78/25
90/25
95/20
90/30
—
93/30
95/30
93/55
94/10
—
95/100
90/150
94/120
93/120
95/90
1
1
0
2
—
90/30
92/70
95/20
—
aValues refer to yield (%)/time (min) ratios.
b
The entries refer to those in Table II.
c
A: Our method; B: Ag2CO3/Celite, CH3CN, r.t.; C: n-Bu4N IO4 /CH2Cl2, r.t.; D: Oxone/Solid phase;25b
35
+
−
29
27
E: (n-BuPPh3)Cr2O7/CH3CN, reflux.

TRANSFORMATION OF THIOAMIDE COMPOUNDS
265
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