Acidified, wet, silica-supported tetrabutylammonium periodate: A convenient and mild reagent for conversion of thioamides to their corresponding amides under solvent-free conditions

Article abstract of DOI:10.1080/10426500802417745

A series of thioamides are transformed to their corresponding oxo analogues in good to excellent yields with acidified, wet, silica-supported tetrabutylammonium periodate under solvent-free conditions.

Full text of DOI:10.1080/10426500802417745

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Phosphorus, Sulfur, and Silicon
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Acidified, Wet,
Silica-Supported
Tetrabutylammonium
Periodate: A Convenient and
Mild Reagent for Conversion
of Thioamides to Their
Corresponding Amides 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: 22 Jul 2009.
To cite this article: Masoud Nasr-Esfahani , Majid Moghadam , Iraj Mohammadpoor-
Baltork & Mohammad Hasan Boostanifar (2009) Acidified, Wet, Silica-Supported
Tetrabutylammonium Periodate: A Convenient and Mild Reagent for Conversion
of Thioamides to Their Corresponding Amides Under Solvent-Free Conditions,
Phosphorus, Sulfur, and Silicon and the Related Elements, 184:8, 2004-2009, DOI:
10.1080/10426500802417745
To link to this article: http://dx.doi.org/10.1080/10426500802417745

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Phosphorus, Sulfur, and Silicon, 184:2004–2009, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802417745
Acidified, Wet, Silica-Supported Tetrabutylammonium
Periodate: A Convenient and Mild Reagent for Conversion
of Thioamides to Their Corresponding Amides 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 series of thioamides are transformed to their corresponding oxo analogues in
good to excellent yields with acidified, wet, silica-supported tetrabutylammonium
periodate under solvent-free conditions.
Keywords Acidified; wet; silica-supported tetrabutylammonium periodate; oxidations;
solid state; solvent-free; thioamides
INTRODUCTION
The production and removal of functional groups is of great importance
in the synthesis of polyfunctional organic molecules. The conversion of
thiocarbonyl compounds to their oxygen analogues has received consid-
erable attention, not only for the development of innovative synthetic
methods but also for their vast potential in medicinal chemistry.1
Over the last years, several new oxidizing reagents such as diaryl
selenoxide,2 dimethyl selenoxide,3 t-butyl hypochlorite,4 benzenese-
leninic anhydride,5 singlet-oxygen,6 diaryl telluroxide,7 thiophosgene,8
sodium peroxide,9 dimethyl sulfoxide/iodine,10 N-nitrosamines,11
soft NO+ species,12 trifluoroacetic anhydride,13 m-chloroperbenzoic
acid,14 NOBF4,15 clayfen,16 p-nitrobenzaldehyde/TMSOTf,17 2-
nitrobenzenesulfonyl chloride/potassium superoxide,18 clayfen or
Received 16 April 2008; accepted 10 August 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
2004

Silica-Supported Tetrabutylammonium Periodate
2005
clayan/MW,19 Caro’s acid supported on silica gel,20 manganese
dioxide,21 ceric ammonium nitrate,22 oxone,23 (n-BuPPh3)2S2O8,24
(n-BuPPh3)2Cr2O7,25 3-carboxypyridinium, and 2,2ꢀ-bipyridinium
chlorochromates26 have been reported for oxidation of thiocarbonyl
compounds to their oxygen analogues. Unfortunately, most of these
reagents suffer from at least one of the following disadvantages: (i)
long reaction time, (ii) no selectivity, (iii) tedious work-up procedure,
(iv) cost of preparation, and (v) low yields of the products.
Recently, much attention has been focused on the use of quater-
nary ammonium salts [such as tetrabutylammonium periodate (n-
Bu4N+IO−4 )] for a variety of functional group transformations in homo-
geneous phase in non-aqueous solvents.27 The solubility of quaternary
ammonium periodate in several solvents provides advantages, such
as low reaction temperatures, high reaction rates, absence of side re-
actions, and higher yields. However, some of them need catalysts for
activation.
The use of solid supports in synthetic organic chemistry has become
more important in recent years due to their characteristic properties
such as the enhanced selectivity and reactivity and the convenient
product isolation they provide.28
Both the Bronsted and Lewis acidic sites of the acidic solid supports
are involved in the generation of active species of periodate,29 which
may be either IO−4 or H5IO6 depending on the site acidity.
RESULT AND DISCUSSION
A variety of thioamides (primary, secondary, and tertiary) were treated
with n-Bu4N+IO4−/acidified, wet SiO2 under solid phase conditions at
room temperature; they afforded the corresponding amides in good to
excellent yields (Entries 1–15, Table I).
As shown in Table II, in the absence of acid, the conversion yields
of thioamide decreased to 5–10%, and without SiO2, no reaction is
observed. The maximum yields were observed when concentrated HCl
was applied for the preparation of catalyst.
For the investigation of the deprotection of larger amounts of the
thioamides, 10 mmol of some thioamides was applied in the reaction.
The results were comparable to those of small scale experiments; there-
fore, this method is also applicable for operation on a molar scale. It
was found that in these reactions, sulfur is converted to sulfate and
replaced by oxygen, which is indicated by the addition of a solution of
BaCl2.

2006
M. Nasr-Esfahani et al.
TABLE I Transformation of Thioamide Derivatives to the
Corresponding Amides with n-Bu4N+IO4−/Acidified, Wet SiO2
Entry
Thioamides
Amides
Time (min) Yields (%)
1
5
93
2
3
2
97
4
94
4
5
5
91
96
11
6
7
8
2
7
2
95
96
96
9
4
2
5
92
94
97
10
11
(Continued on next page)

Silica-Supported Tetrabutylammonium Periodate
2007
TABLE I Transformation of Thioamide Derivatives to the
Corresponding Amides with n-Bu4N+IO4−/Acidified, Wet SiO2
(Continued)
Entry
Thioamides
Amides
Time (min) Yields (%)
12
3
3
91
13
91
14
15
2
8
93
92
In conclusion, we have developed a mild and convenient−procedure
for the conversion of thioamides to amides using n-Bu4N+IO /acidified,
wet SiO2 as a nontoxic and inexpensive reagent under s4olvent-free
conditions.
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.30
TABLE II Solvent-Free Deprotection of N-Thiobenzoylaniline (7)
with n-Bu4N+IO4− Under Different Conditions
Conditiona
Time (min)
Isolated yields (%)
1
2
3
4
5
Absence of SiO2
Dry SiO2
Wet SiO2
Acidified SiO2 with 2M HCl solution
Acidified SiO2 with concentrated HCl
—
7
7
7
7
No reaction
5
10
20
>95
aThe optimized molar ratio of the oxidant/substrate is 1:1.

2008
M. Nasr-Esfahani et al.
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 mix-
ing n-Bu4N+IO−4 (1 mmol, 0.433 g) with acidified, wet silica gel (3.0 g)
using a pestle and mortar until a fine, homogeneous, purple powder was
obtained. A mixture of thioamide (1 mmol) and n-Bu4N+IO4−/acidified,
wet SiO2 (1 mmol, 3.433 g) was ground with a pestle in a mortar until
the TLC showed complete disappearance of the thioamide, which re-
quired 2–11 min (Table I). Ethylacetate (2 × 10 mL) was added to the
reaction mixture, and after vigorous stirring was filtered through a sin-
tered glass funnel and the solvent was then evaporated under vacuum.
The solvent was evaporated, and the crude product was purified by
column chromatography on silica gel using ethyl acetate as an eluent.
The pure products were obtained in 91–97% yields.
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