An environmentally benign system; a simple and effective procedure for dehydration of oximes into nitriles in solvent free conditions

Article abstract of DOI:10.1002/jccs.200800002

In an environmentally benign solvent free system aldoximes are rapidly transformed into nitriles using trimethylsilylchloride under mild conditions.

Full text of DOI:10.1002/jccs.200800002

Journal of the Chinese Chemical Society, 2008, 55, 5-7
5
Communication
An Environmentally Benign System; A Simple and Effective Procedure for
Dehydration of Oximes into Nitriles in Solvent Free Conditions
Rahim Hekmatshoar,* Sodeh Sajadi and Majid M. Heravi
Department of Chemistry, School of Science, Alzahra University, Vanak, Tehran, Iran
In an environmentally benign solvent free system aldoximes are rapidly transformed into nitriles us-
ing trimethylsilylchloride under mild conditions.
Keywords: Nitriles; Oximes; Dehydration; Simple.
Nitrile compounds are organo-cyanides (R-CN) that
occur naturally in plants and as intermediates in microbial
metabolism.1 Nitriles are also products of the petrochemi-
cal industry and are widely used as chemical solvents,
recrystallizing agents, and chiral synthons. The conversion
of aldehydes into the corresponding nitriles is a functional
group transformation of significant practical importance,
especially in the fine chemical industry.
appear.9-13 A few methods are known which involve vari-
ous transformations of other N-substituted azomethine de-
rivatives of aldehydes, such as N,N-dialkylhydrazones,14-15
and imines with 1-amino-4,6-diphenyl-2-pyridone.16 Con-
sequently there is a need for the development of protocols
using readily available and safer reagents which lead to
nitrile compounds. We now wish to report a facile conver-
sion of aldoximes to their corresponding nitriles by tri-
methylsilylchloride in solvent free conditions. The reaction
proceeds efficiently in moderate to high yield under mild
conditions (Scheme I).
The remarkable synthetic properties of the nitrile
group have ensured long standing studies of their utiliza-
tion in organic synthesis.2 Several methods are available to
accomplish the conversion of alkyl or aryl aldehydes to
their corresponding nitriles under a variety of reaction con-
ditions.3 Because of its role in synthetic chemistry, this re-
action continues to receive attention from the chemists in
search for newer methods. There are methods known for
the conversion of aldehydes to nitriles in a one-pot proce-
dure.4
Scheme I
heat
R-CH=N-OH +
ClSi(Me)3
R-C
N
To study the effect of substitution, reactions were per-
formed on different precursors as shown in Table 1, precur-
sors with electron-withdrawing groups showed better yield
in a shorter time. By paying attention to this evidence, the
mechanism shown in (Scheme II) is proposed for the dehy-
dration of oximes. We suggest that the chlorine ion released
during the progress of the reaction acts as a base for separa-
tion of hydrogen at the next stage. Longer reaction times
had no effect on the conversion of oximes.
Unfortunately, many of these one-pot conversions are
limited to aromatic aldehydes which, generally, are trans-
formed more readily to nitriles than the aliphatic alde-
hydes.
Recent methods which have been successfully ap-
plied to both the aliphatic and aromatic compounds include
the use of expensive (2,4-dinitrophenyl hydroxylamine),5
(hydroxylamine o-sulfonic acid),6 hazardous (selenium di-
oxide)7 or corrosive (formic acid)8 reagents and tedious
work-up procedures. The most widely used general method
is based on the dehydration of aldoximes, and although nu-
merous protocols already exist, new variants continue to
In summary, in the present method -apart from the
mild temperatures employed- the transformation has four
important advantages: (i) no organic reagent or solvent is
employed; (ii) the only by-products are relatively harmless;
(iii) less toxic and hazardous chemicals can be used; and
* Corresponding author. E-mail: rhekmatus@yahoo.com

6
J. Chin. Chem. Soc., Vol. 55, No. 1, 2008
Hekmatshoar et al.
Table 1. Conversion of aldoximes into nitriles
Entry
1
Aldoximes
Nitriles
Time (h) Yield/%
NOH
CH
Me
Me
CN
CN
CN
5
5
2
80
85
96
NOH
CH
2
3
MeO
O2N
MeO
O2N
NOH
CH
H
C
CN
NOH
4
5
3
4
73
75
N
N
CH CH CN
CH CH CH NOH
MeO
MeO
NOH
CH
6
7
MeO
MeO
CN
4
69
MeO
MeO
NOH
CH
CN
5
91
CH3(CH2)8CH=NOH
CH3(CH2)6CH=NOH
CH3(CH2)8CN
CH3(CH2)6CN
8
9
5
5
70
75
Scheme II
Si
H
H
R
H
Cl
Cl-
N
O
+
Si
+
N
OH
R
H
N
O
Si
+ HCl
R
Cl-
H
R
C
N
N
O
+
Si
HCl
+
HO Si
+
R
H
(iv) moderate to high yields are obtained (Table 1).
EXPERIMENTAL
°C. Completion of reaction was followed by TLC (n-hex-
ane/ethyl acetate, 2:1). After completion of the reaction,
the mixture was diluted with chloroform and further purifi-
cation was performed by flash chromatography. All com-
pounds were known and their physical and spectroscopic
data were compared with those of authentic samples and
found to be identical. Yields were obtained using GC anal-
Typical Experimental Procedure
A mixture of 1 mmol of aldoximes was added to 108
mg (1 mmol) of trimethylsilyl chloride heated for 5 h at 90

Dehydration of Oximes into Nitriles
J. Chin. Chem. Soc., Vol. 55, No. 1, 2008
7
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Received August 8, 2007.
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