A clean and efficient conversion of aldehydes into the corresponding nitriles using ionic supported triphenylphosphine and CBr4

Article abstract of DOI:10.2174/15701786113109990009

An ionic supported triphenylphosphine and carbon tetrabromide system has been applied to the clean and efficient conversion of various aromatic and aliphatic aldehydes to the corresponding nitriles.

Full text of DOI:10.2174/15701786113109990009

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442
Letters in Organic Chemistry, 2013, 10, 442-444
A Clean and Efficient Conversion of Aldehydes into the Corresponding
Nitriles Using Ionic Supported Triphenylphosphine and CBr4
Congde Huo*, Cheng Wang, Dongcheng Hu and Xiaodong Jia
Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education; College of Chemistry and
Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
Received March 07, 2013: Revised April 20, 2013: Accepted May 03, 2013
Abstract: An ionic supported triphenylphosphine and carbon tetrabromide system has been applied to the clean and effi-
cient conversion of various aromatic and aliphatic aldehydes to the corresponding nitriles.
Keywords: Aldehydes, Nitriles, Ionic Supported, Triphenylphosphine, carbon tetrabromide.
INTRODUCTION
Nitriles are versatile synthetic intermediates for pharma-
ceuticals, agricultural chemicals, dyes and material sciences
[1]. Conventionally, alkyl nitriles can be prepared by the
nucleophilic substitution of alkyl halides with a stoichiomet-
ric amount of inorganic cyanide [2]. Aromatic nitriles can be
Scheme 1.
synthesized by the Sandmeyer reaction and ammoxidation
[3]. Hazardous reagents are usually required in these meth-
ods. So the conversion of easily available aldehydes to the
corresponding nitriles is an important functional group trans-
formation [4]. It’s a convenient 2 step route: aldehydes are
first converted to their aldoximes by condensation with hy-
droxylamine hydrochloride and then dehydrated to the ni-
triles. Many methods have been reported that aldehydes can
be directly converted into nitriles without the isolation of
aldoxime intermediates upon the one-pot treatment with hy-
droxylamine hydrochloride (NH2OH·HCl) in the presence of
various dehydrating reagents [4]. The main disadvantages of
these methods are limited scope of substrates, corrosive,
toxic, expensive, or commercial unavailable reagents, no
reusability of stoichiometric regents, drastic reaction condi-
tions, tedious workup procedures, and unsatisfactory yields.
Therefore, new methods for this transformation are still de-
sirable.
RESULTS AND DISCUSSION
We have earlier developed the use of sodium triphenyl-
phosphine-m-sulfonate (TPPMS) as
a replacement of
triphenylphosphine in the Wittig reaction [5]. And the
TPPMS/CBr4 complex has also been disclosed as a highly
efficient catalyst for the synthesis of acetals from aldehydes
and for the tetrahydropyranylation of alcohols and for
FriedelꢀCrafts alkylation of indoles with carbonyl com-
pounds to produce bis(indolyl)alkane products (BIAs). [6]
The advantage of using TPPMS is that it and its oxidation
product, sodium triphenylphosphine-m-sulfonate oxide
(TPPMSO), can be easily separated and recovered from the
reaction mixture by precipitation with a non-polar solvent,
without the need for tedious chromatography which is usu-
ally required for the removal of triphenylphosphine oxide.
And the recovered TPPMSO can be recycled back to the
TPPMS by our developed method [5].
Herein we report a novel protocol for the one-pot synthe-
sis of nitriles from the corresponding aldehydes by employ-
ing ionic supported triphenylphosphine combined with CBr4
as an easily phase-separable dehydrating system. This newly
developed protocol permits the conversion of various alde-
hydes into nitriles to occur smoothly at room temperature
(Scheme 1).
PPh3/CCl4 system in acetonitrile has been reported as an
dehydration method of 2,6-dichlorobenzonitril and 4-
nitrobenzonitril to the corresponding nitriles [7]. On this
background we considered whether the TPPMS/CCl4 system
could replace the PPh3/CCl4 system in this dehydration reac-
tion as an easily phase-separable reagent. We first investi-
gated the reaction of C6H5CH=NOH under the literature op-
timized reaction condition [PPh3 (4.0 equiv.)/CCl4, (2.0
equiv.) in acetonitrile at room temperature] except using
TPPMS instead of PPh3. Unfortunately, no nitrile product
was detected. And only 10% of C6H5CN was achieved under
the treatment of TPPMS/CBr4 system. We thought the reason
may be due to the poor solubility of TPPMS in MeCN. We
*Address correspondence to this author at the Key Laboratory of
Eco-Environment-Related Polymer Materials Ministry of Education; Col-
lege of Chemistry and Chemical Engineering, Northwest Normal Univer-
sity, Lanzhou, Gansu 730070, China; Tel: +86-0931-7971533;
Fax: +86-0931-7971989; E-mail: huocongde1978@hotmail.com
1875-6255/13 $58.00+.00
© 2013 Bentham Science Publishers

Ionic Supported Conversion of Aldehydes into Nitriles
Letters in Organic Chemistry, 2013, Vol. 10, No. 6 443
Table 1. Reaction Conditions Optimization.
Entry
Substrate
NH2OH HCI
Et3N
1/CBr4
Yielda
1
2
3
4
5
6
7
8
9
4-Br6H4CH=NOH
4-Br6H4CH=NOH
4-Br6H4CH=NOH
4-Br6H4CHO
-
-
TPPMS/CCI4
TPPMS/CBr4
4.0/2.0
<5
10
95
56
72
94
94
75
63
-
-
-
-
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.2 eq
1.0/1.0
4-Br6H4CHO
2.0/1.0
4-Br6H4CHO
4.0/2.0
4-Br6H4CHO
3.0/2.0
4-Br6H4CHO
2.0/2.0
4-Br6H4CHO
3.0/1.0
a Conversion yields based on 1H NMR analysis of the concentrates of the filtrates.
N
20% oleum
[bdmim]Cl
N
Bu
1
Acetone, rt , 24 h
SO3
[bdmim][TPPMS],
Ph2P
Ph2P
SO3Na
TPPMS
Scheme 2. Synthesis of [bdmim][TPPMS].
Table 2. Conversion of Aldehydes into the Corresponding Ni-
triles
then examined the ionic salt 3-butyl-1,2-dimethyl-
imidazolium triphenylphosphine-m-sulfonate ([bdmim]
[TPPMS], 1) to replace TPPMS, prepared from the reaction
of TPPMS with 1,2-dimethyl-3-butylimidazolium bromide
(Scheme 2).[8] To our delight, high conversion was achieved
at room tempertature after overnight. Furthermore, we were
glad to find that [bdmim][TPPMS]/CBr4 system with one
equiv. of Et3N as base was able to convert the aldehyde into
nitrile directly. [bdmim][TPPMS] (3.0 equiv.)/ CBr4 (2.0
equiv.) system gave the best results (Table 1). The reaction
conditions were quite mild, simply stirring of the reaction
mixture at room temperature overnight, high conversion
could be achieved.
Entry
Aldehyde
Yield of Nitrile
1
2
PhCHO
4-MeOC6H4CHO
4-MeC6H4CHO
87
92
86
84
93
92
87
89
87
90
73
85
80
88
91
91
90
75
3
4
4-NO2C6H4CHO
4-CIC6H4CHO
5
6
4-Br C6H4CHO
We then proceeded to investigate its generality and
scope. A variety of aromatic, heterocyclic, and aliphatic al-
dehydes were converted into the corresponding nitriles under
the above optimized reaction conditions (Table 2). Progress
of the reaction was monitored by TLC, and high conversion
could be achieved after overnight. After the reaction, the
excess [bdmim][TPPMS] and its oxidation product
[bdmim][TPPMSO] can be easily and quantitatively re-
moved from the reaction mixture by precipitation with ether
(a nonpolar organic solvent) after completion of the reaction.
The liquid filtrate was evaporated to give the corresponding
nitrile products, usually in good purity. In some cases, fur-
ther purification by simple flash chromatography or crystal-
lization may be required to purify the product from the unre-
acted aldehyde. All nitriles obtained were known compounds
7
3-Br C6H4CHO
8
2-Br C6H4CHO
9
Piperonal
10
11
12
13
14
15
16
17
18
2-Naphthaldehyde
2-Furaldehyde
2-Thiophenecarboxaldehyde
3-Pyridinecarboxaldehyde
Cinnamaldehyde
C5H11CHO
C7H15CHO
1
and identified by H NMR spectral data, comparison with
3-Phenylpropanal
Cyclohexaanecarbaldehyde
those previously reported [4] and authentic samples. It is to
be noted that no traces of phosphorus compound could be
detected in the nitriles by NMR.
a
Isolated yields. Structures were confirmed by comparison of 1H NMR with those of
authentic materials..

444 Letters in Organic Chemistry, 2013, Vol. 10, No. 6
Huo et al.
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CONCLUSION
In summary, these examples demonstrate how ionic sup-
ported reagents can be used in the clean conversion of alde-
hydes to nitriles with a simple work-up and present an effi-
cient and practical methodology for synthetic entry of these
compounds.
CONFLICT OF INTEREST
The authors confirm that this article content has no con-
flicts of interest.
ACKNOWLEDGEMENTS
We thank the National Natural Science Foundation of
China (21002080) and the Specialized Research Fund for the
Doctoral Program of Higher Education of the Education
Ministry (20106203120003) for financially supporting this
work.
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