A versatile method for the conversion of aldoximes to nitriles using silica gel/thionyl chloride

Article abstract of DOI:10.1080/10426500490262586

A simple convenient procedure for dehydration of aldoximes has been developed using silica gel/thionyl chloride in heterogeneous conditions. The method has been found to be effective for a wide range of aromatic oximes.

Full text of DOI:10.1080/10426500490262586

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Phosphorus, Sulfur, and Silicon and the Related
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A VERSATILE METHOD FOR THE CONVERSION OF
ALDOXIMES TO NITRILES USING SILICA GEL/THIONYL
CHLORIDE
Foad Kazemi a , Ali Reza Kiasat a & Elham Fadavipoor a
a Shahid Chamran University, Ahvaz, Iran
Published online: 11 Aug 2010.
To cite this article: Foad Kazemi , Ali Reza Kiasat & Elham Fadavipoor (2004) A VERSATILE METHOD FOR THE CONVERSION
OF ALDOXIMES TO NITRILES USING SILICA GEL/THIONYL CHLORIDE, Phosphorus, Sulfur, and Silicon and the Related Elements,
179:2, 433-436, DOI: 10.1080/10426500490262586
To link to this article: http://dx.doi.org/10.1080/10426500490262586
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Phosphorus, Sulfur, and Silicon, 179:433–436, 2004
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Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490262586
A VERSATILE METHOD FOR THE CONVERSION
OF ALDOXIMES TO NITRILES USING SILICA
GEL/THIONYL CHLORIDE
Foad Kazemi, Ali Reza Kiasat, and Elham Fadavipoor
Shahid Chamran University, Ahvaz, Iran
(Received August 26, 2003)
A simple convenient procedure for dehydration of aldoximes has been
developed using silica gel/thionyl chloride in heterogeneous conditions.
The method has been found to be effective for a wide range of aromatic
oximes.
Keywords: Aldoxime; nitrile; silica gel; thionyl chloride
The development of new methods for the synthesis of nitriles is impor-
tant in organic synthesis because nitriles are useful as intermediates
for the preparation of amines and other functional group moieties.1−3
They usually are prepared by nucleophilic substitution with the cyanide
anion or by regenerating the cyano group via oxidation, rearrangement,
or elimination.2 The most efficient route reported so far is based on the
dehydration of aldoximes into the corresponding nitriles. The classi-
cal methods4−7 of dehydration include trifluoroacetic anhydride, chloro-
sulphonyl isocyanate, diphosphorous tetraiodide, selenium dioxide, 4,6-
diphenyl-2-methylthiopyrylium tetrafluoroborate, copper(II) acetate,
and the triphenylphosphine/CCl4. Unfortunately, most of these meth-
ods are deficient in some respects, such as long reaction times, unsatis-
factory yields, harsh reaction conditions, expensive or not readily avail-
able reagents, inconvenient preparation of reagents, need for addition
of an acid or a base, high reaction temperature, and tedious work-up
procedure. Considering these facts, there is still a need for new reagents
for this conversion.
The application of solid adsorbents such as alumina and silica
gel as solid supports in organic synthesis affords a new procedure
The authors acknowledge the partial support of this work by Shahid Chamran Ahvaz
University Research Council.
Address correspondence to Ali Reza Kiasat, Chemistry Department, College of Sci-
ences, Chamran University, Ahvaz, lran.
433

434
F. Kazemi et al.
for functional group transformation.8,9 Recently it was demonstrated
that heterogeneous reaction systems have many advantages such
as simple experimental procedures, mild reaction conditions, and
minimization of chemical wastes as compared to their liquid phase
counterparts.8
Consequently, we decided to seek a heterogeneous system for the
dehydration of aldoximes. In continuation of our studies on the appli-
cations of modified form of thionyl chloride in organic synthesis,7,10,11
we found that various types of nitriles can be synthesized conveniently
from the corresponding aldoximes under mild nonaqueous reaction con-
ditions by silica gel/thionyl chloride in CH2Cl2.
The heterogeneous reagent was prepared easily by the reaction of
3 mmol of thionyl chloride with 1 g of silica gel at room temperature.
The feasibility of this reagent as dehydrating agent was first exam-
ined using benzaldoxime as a model substrate. Thus, the solution of
benzaldoxime (1 mmol) in anhydrous CH2Cl2 was slowly added to 1.5
equiv. of silica gel/SOCl2 at room temperature. The progress of the
reaction was monitored by TLC. After 5 min dehydration of benzal-
doxime was complete and afforded benzonitrile in almost quantitative
yield.
It is worthy to note that attempts to perform the dehydration with
thionyl chloride alone were not successful due to its very high reactivity
and mixtures of unidentified products were obtained.
The effects of other solvents such as CCl4, n-hexane, ether, and THF
also were studied, but in comparison with CH2Cl2 the reaction times
were longer and the yields were considerably lower. The scope and gen-
erality of this process is illustrated with several examples and the re-
sults are summarized in Table I. The procedure turned out to be general
for a range of structurally diverse aromatic aldoximes. Aromatic al-
doximes with electron-withdrawing or electron-donating groups were
cleanly, easily, and efficiently dehydrated and afforded excellent iso-
lated yields of nitriles within a short reaction time. They were of high
purity as determine by TLC and 1H NMR spectroscopy.
All reactions were performed under mild and heterogeneous con-
dition at room temperature in anhydrous CH2Cl2. As shown in
Table I functional groups such as OCH3 (entry 3), OH (entry 9), NO2
(entry 5), and olefinic groups (entry 6) remain unaltered under this
reaction condition.
Compared to some previously reported reagents with major or minor
drawbacks, several noteworthy features of this reagent are apparent.
These are: the easy work-up procedure, availability of the reagent, op-
erational simplicities, and use of inexpensive reagent.

Nitriles
435
TABLE I Dehydration of Aldoximes to Their Corresponding Nitriles Using
a
Silica Gel/SOCl2
Entry
1
Substrate
Product
Time (min)
5
Yield (%)b,c
98
2
3
4
5
6
7
5
35
5
90
95
92
90
92
95
23
5
23
8
9
15
7
90
98
aMolar ratio of substrate to reagent was 1:1.5.
bYields refer to isolated yields.
cProducts were characterized by comparsion of their physical data, IR, NMR spectra
with known samples.
In conclusion, the present one-pot procedure for dehydration of
aldoximes provides an easy, mild, efficient, versatile, and general
methodology for the preparation of nitriles from different classes of al-
doximes; it may be a suitable addition to methodologies already present
in the literature.
EXPERIMENTAL
General
Aldoximes were purchased from Fluka and Merck or were prepared in
our laboratory from the corresponding aldehydes according to known
procedures.12 Products were characterized by comparison of their phys-
1
ical data, IR, and H NMR spectra with authentic samples.13−15 The
purity determination of the products and reaction monitoring were
accomplished by TLC on silica gel polygram SILG/UV 254 plates.

436
F. Kazemi et al.
General Procedure for the Conversion of Aldoximes
to Nitriles with Silica Gel/SOCl2 in CH2Cl2
Silica gel (0.5 g) was mixed with the freshly distilled thionyl chloride
(1.5 mmol, 0.179 g) in a 25 ml round bottomed flask at room tempera-
ture. To the resulting powder, a solution of aldoxime (1 mmol) in anhy-
drous CH2Cl2 (5 ml) was slowly added and stirred at 0◦C for 5–35 min.
The progress of the reaction was followed by TLC until no starting mate-
rial could be detected. The mixture was shaken with CH2Cl2 (5 ml) and
filtered. The residue was washed with CH2Cl2 and the solvent evap-
1
orated under reduced pressure to afford the TLC and HNMR pure
products in 87–98% isolated yields.
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