Grinding synthesis of schiff bases combined with infrared irradiation

Article abstract of DOI:10.14233/ajchem.2013.14382

Solid-phase synthesis combined with infrared irradiation promoted the formation of a series of Schiff bases in the condensation reaction between substituted benzaldehydes and anilines, in the solvent free. Benzaldehydes and anilines, containing either electron withdrawing or electron-releasing groups, were evaluated their substituent effect on the formation of the Schiff bases. Moreover, this new procedure is environmentally benign because no solvent was employed in the transformations.

Full text of DOI:10.14233/ajchem.2013.14382

Asian Journal of Chemistry; Vol. 25, No. 10 (2013), 5399-5401
http://dx.doi.org/10.14233/ajchem.2013.14382
Grinding Synthesis of Schiff Bases Combined with Infrared Irradiation
1
1
2,*
JIAN-YING TONG , NA-BO SUN and HONG-KE WU
1College of Biology and Environmental Engineering, Zhejiang Shuren University, Hangzhou 310015, Zhejiang, P.R. China
2College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014, Zhejiang, P.R. China
*Corresponding author: E-mail: wuhk910@gmail.com
(Received: 31 July 2012;
Accepted: 8 April 2013)
AJC-13215
Solid-phase synthesis combined with infrared irradiation promoted the formation of a series of Schiff bases in the condensation reaction
between substituted benzaldehydes and anilines, in the solvent free. Benzaldehydes and anilines, containing either electron withdrawing
or electron-releasing groups, were evaluated their substituent effect on the formation of the Schiff bases. Moreover, this new procedure is
environmentally benign because no solvent was employed in the transformations.
Key Words: Solid phase synthesis, Infrared irradiation, Solvent free, Imine, Biological activity.
on a Bruker Equinox55 spectrophotometer as potassium
bromide tablets. 1H NMR spectra were measured on a Bruker
AC-P500 instrument (300 MHz) using tetramethylsilane as
an internal standard and CDCl3 as solvent. infrared irradiation
using an apparatus similar to that reported by Pool and
Teuben22 during 0-30 min.
INTRODUCTION
Schiff bases (C=N) play an important role because of their
many uses1, such as organic synthesis, biological activity, etc.
Especially, imine is exist many compounds, especially nitro
linked heterocyclic compounds2, displayed diversity bioactive3,
for example, they exhibited herbicidal, fungicidal, insecticidal,
antimicrobial and antiinflammatory activity. In addition, they
are as well as valuable intermediates for the synthesis of biolo-
gically active products such as β-lactams, an important class
of pharmaceutical compounds4.
General procedure: The reactants in the molar ratio
substitute benzaldehydes/substitute anilines = 1:1 were put in
mortar. Then the mixture was exposured to the infrared
irradiation under granding. The compound was irradiated for
0-30 min (Table-1) and the completion of the reaction is moni-
tored by TLC examination.Yields are given in Table-1. Almost
all derived Schiff base are known compounds and their spectral
data, as well as melting points of solids, were in agreement
with those known.
To date, many methods have been described for the prepa-
ration of Schiff base. Synthesis of Schiff base is often generally
by refluxing the mixture of aldehyde (or ketone) and amine in
organic medium5.
The development of simple, cheap and clean processes in
the area of 'green chemistry' is of increasing interest6. Chemists
meet the controversy of synthetic procedures developing and
economic to environment friendship, therefore solvent-free
reactions have played strategic roles in methodologies of
organic syntheses. Some are using microwave irradiation and
ultrasound irradiation. So, we have employed solid phase
synthesis combined infrared irradiation as an alternative energy
source, working under solvent free conditions.
RESULTS AND DISCUSSION
Initially, the condensation of p-hydroxy benzaldehyde
(1a) and aniline (2a) under solventless conditions was carried
out at room temperature during 0.5 h and the corresponding
N-benzylidenaniline (3a) was obtained in moderate conver-
sion (48 %). However, when the reaction mixture was grinded,
then irradiated with an infrared lamp (Guangming, 300 W,
220V), the product was obtained with excellent conversion in
only 10 min (61 %, Table-1). Moreover, the infrared irradiation
efficiency was compared with the results obtained under
thermal conditions.
In this work, we have synthesized the Schiff bases using
green method with a proper yield.
EXPERIMENTAL
In addition, to validate this new method and in order to
identify the substituent effect on the formation of the Schiff
bases under grinded combined with infrared irradiation and
Melting points were determined using a Yanaco MP-241
apparatus and are uncorrected. Infrared spectra were recorded

5400 Tong et al.
Asian J. Chem.
TABLE-1
R2
COMPARISON OF REACTIVITY BETWEEN p-OH
BENZALDEHYDE (1a) AND ANILINE (2a) AT ROOM
TEMPERATURE AND PROMOTED BY GRINDING
N
H
CHO
NH2
Grind
R1
R2
no solvent
R1
N
NH2
1a-1g
2a-2g
H
3b-3g
CHO
Grind
R1
R1
R2
R2
no solvent
HO
2a = H
2b = 4-Cl
3b = 4-N(CH3)2
3c = 2-NO2
3d = 3-OCH3
3e = H
3f = H
3g = H
3h = H
H
H
H
2-NO2
3-NO2
4-NO2
4-CH3
1a = 3-CH3
2b = 2-NO2
3c = 2,4-Cl2
4d = 3,4-(OCH3)2
5e = 4-OH
HO
1a
2a
3a
2c = 4-CH3
2d = 3-OCH3
2e = 2-NO2
2f = 3-NO2
2g = 4-NO2
Conversion (%)
Grind (20 min)/IR
Conversion (%)
Grind
Time (min)
0
13
61
88
91
13
21
44
48
6f = 4-N(CH3)2
6g = H
10
20
30
Scheme-I
to the high reactivity of some benzaldehydes and anilines,
particularly those cases in which the reagent is liquid. Indeed,
these results suggest that the efficiency of this new method
is improved by electron-withdrawing substituents on the
benzaldehyde ring and electron-releasing substituents on the
aniline ring. Therefore, the rate of condensation of substituted
benzaldehydes with anilines promoted by this new method,
resembles the corresponding results obtained under a homo-
geneous phase.
solventless conditions, several reactions using both electron-
poor and electron-rich benzaldehydes and anilines (Scheme-
I) were carried out. When substitute-benzaldehyde (1b),
bearing an electron-releasing group was irradiated in the
presence of 2a, the conversion rate decreased (Table-2),
obtaining 3b in lower yield (70 %). However, when benzal-
dehydes with an electron-withdrawing group were employed,
a more efficient conversion to the corresponding imine
(entries 2 and 3) took place.
Finally, the versatility of this novel option to obtain the
Schiff bases was demonstrated by the preparation of a large
number of target molecules 3i-3p (Table-3). Most yields were
high and the products were readily isolated and purified by
crystallization. However, for some benzylideneanilines (e.g.,
3n and 3o), the yields were rather moderate.
TABLE-2
COMPARISON OF YIELDS FOR IMINES 3b-3h
OBTAINED BY GRINDING (20 min)/IR IRRADIATION
Times Conversion Yield
No Imines
R1
R2
(min)
(%)
31
55
76
77
81
100
100
100
25
65
70
70
31
46
69
68
33
42
72
72
40
55
70
70
56
65
85
82
(%)
0
TABLE-3
YIELD (%) OF SCHIFF BASES UNDER GRINDING/IR
10
20
30
0
1
2
3
4
5
6
7
4-N(CH3)2
H
71
3b
3c
3d
3e
3f
Substrate
R1
R2
Yield
80.4
75.6
84.2
83.1
82.6
74.3
72.6
82.3
p-CH3C6H4
p-NO2C6H4
m-NO2C6H4
o-Cl C6H4
3i
3j
10
20
30
0
p-OCH3C6H4
2,4-Cl2C6H3
p-OHC6H4
2-NO2
H
94
61
62
64
63
79
3k
3l
p-OCH3C6H4
p-OCH3C6H4
o-OCH3C6H3
o-OCH3C6H3
p-CH3C6H4
o-OCH3C6H3
3,4-diCH3C6H3
3,4-diOCH3 C6H3
N(CH3)2C6H4
3m
3n
3o
3p
10
20
30
0
3-OCH3
H
10
20
30
0
H
H
H
H
2-NO2
3-NO2
4-NO2
4-CH3
Conclusion
A new, simple, efficient and environmentally benign
method for the preparation of substituted N-benzylideneaniline
derivatives, via condensation of several benzaldehydes and
anilines, by means of grinding combined with infrared
irradiation under solvent-free conditions, was developed.
Additional advantages of the method were lower cost, ease of
work-up and the fact that activation of the reaction by an acid
catalyst was unnecessary.
10
20
30
0
10
20
30
0
3g
3h
10
20
30
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Vol. 25, No. 10 (2013)
Grinding Synthesis of Schiff Bases Combined with Infrared Irradiation 5401
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