N. Sudheesh et al. / Journal of Molecular Catalysis A: Chemical 321 (2010) 77–82
81
Table 4
Reusability of the catalyst.
Entry
Catalyst recycle
% conversion
2 h
% selectivity
Jasminaldehyde
2 h
8 h
2-Pentyl-non-2-enal
2 h
8 h
8 h
1
2
3
4
5
6
Fresh
51
49
48
48
47
45
99
98
98
97
97
95
75
72
72
71
71
68
84
83
83
82
80
80
25
28
28
29
29
32
16
17
17
18
20
20
First recycle
Second recycle
Third recycle
Fourth recycle
Fifth recycle
Reaction conditions: heptanal = 7.9 mmol, benzaldehyde = 39.6 mmol, catalyst = 100 mg, temperature = 140 ◦C.
Table 5
Comparison of the chitosan catalyst with closely related catalyst systems.
Entry
Catalyst
% conversion
Time (h)
Temp (◦C)
% selectivity
Ref.
Jasminaldehyde
2-Pentyl-non-2-enal
1
2
3
4
5
6
7
8
9
Chitosan
H-Beta
HY-100
Al-MCM-41
ALPO
94
8
6
16
10
3
22
8
8
125
125
125
125
125
125
125
125
125
82
21
52
56
86
67
56
80
86
18
43
28
35
14
33
44
20
14
Present work
[13]
[13]
[13]
[13]
[13]
[17]
[17]
[16]
93a
53a
99a
96
Na-ALPO
71
58
99
98
Natural talc
Magnesium organo silicate
Hydrotalcite [Mg–Al (3.5)]b
8
a
Other products are also formed (Ref. [13]).
Hydrotalcite as such.
b
jasminaldehyde were 51% and 75% respectively for 2 h, and 99%
and 84% respectively for 8 h (Entry 1). The fresh catalyst separated
by filtration was washed and dried. The catalyst was reused under
identical conditions. For 2 h recycling there was a decrease in con-
version from 51% to 49% in the first recycle (Entries 1 and 2). The
conversion was remained almost the same up to the fourth recycle.
The selectivity to jasminaldehyde also remained almost constant
up to the fourth recycle. A similar trend was observed for the recy-
cling of the catalyst for 8 h. The catalyst was effectively recycled up
to six cycles without much loss in its activity and selectivity.
conditions, giving the highest selectivity to jasminaldehyde 88%,
with >99% conversion with the catalyst of 100 mg at 160 ◦C under
optimized reaction conditions. The effect of parameters such as the
catalyst amount, temperature, and the 1-heptanal to benzaldehyde
ratio has been investigated; the variation of the catalyst amount and
temperature have significantly influenced the conversion. Selec-
tivity to jasminaldehyde was enhanced by increasing the catalyst
amount and 1-heptanal to benzaldehyde ratio. The catalyst was
elegantly separated and effectively reused up to six times. The per-
formance of chitosan catalyst was comparable with the reported
systems and the green nature of catalyst had the advantage over
those systems.
3.4. Comparison with closely related catalysts for synthesis of
jasminaldehyde
Acknowledgments
It is of interest to have comparative insights into the
performance of chitosan as the catalyst for the synthesis of jas-
minaldehyde with closely related reported catalysts. The present
study compared with other catalyst systems (Table 5) indicated
that chitosan has a promising potential to catalyze the synthesis of
jasminaldehyde. H-Beta and Al-MCM-41 was active with the con-
version level higher but was not selective to jasminaldehyde. ALPO
and HT-based catalysts were found to achieve the maximum in
terms of conversion and selectivity of >96% and 86% respectively.
The ALPO catalyst was active and completed the reaction in 3 h.
The present chitosan catalyst was comparable with the ALPO and
HT-based catalyst, showing 94% conversion and 82% selectivity at
125 ◦C. Moreover the green nature of the catalyst has the advan-
tage over other catalyst systems and further improvements in the
catalyst through green routes are preferable to obtain a green aldol
catalyst.
Authors thank Council of Scientific and Industrial Research
(CSIR), New Delhi, India for financial supports for Network Project
for the Development of Specialty Inorganic Materials for Diverse
Applications. One of the authors, N.S. acknowledges CSIR, New
Delhi, for the award of Senior Research Fellowship.
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The chitosan catalyst has been found to be efficient for the selec-
tive synthesis of jasminaldehyde by the condensation of 1-heptanal
with benzaldehyde. The catalyst is operative under solvent-free