Solvent-free Knoevenagel condensation over iridium and platinum hydroxyapatites

Article abstract of DOI:10.1134/S0023158411030153

The Knoevenagel condensation between various aldehydes (benzaldehyde, p-methoxybenzaldehyde and 1-naphthaldehyde) and esters (ethylcyanoacetate, ethylacetoacetate and diethylmalonoester) was carried out under solvent-free condition in the presence of iridium or platinum hydroxyapatites as a catalyst.

Full text of DOI:10.1134/S0023158411030153

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2011, Vol. 52, No. 4, pp. 536–539. © Pleiades Publishing, Ltd., 2011.
SolventꢀFree Knoevenagel Condensation over Iridium
and Platinum Hydroxyapatites1
M. K. Pillai, S. Singh, and S. B. Jonnalagadda*
School of Chemistry, Westville Campus, University of KwaZuluꢀNatal, Durban, South Africa
* eꢀmail: jonnalagaddas@ukzn.ac.za
Received June 17, 2010
Abstract—The Knoevenagel condensation between various aldehydes (benzaldehyde, pꢀmethoxybenzaldeꢀ
hyde and 1ꢀnaphthaldehyde) and esters (ethylcyanoacetate, ethylacetoacetate and diethylmalonoester) was
carried out under solventꢀfree condition in the presence of iridium or platinum hydroxyapatites as a catalyst.
DOI: 10.1134/S0023158411030153
1
The Knoevenagel condensation is an important
EXPERIMENTAL
reaction forming carbonꢀcarbon double bond. Some
important end products or intermediates such as pharꢀ
maceuticals, perfumes, polymers etc. are synthesized
by this reaction [1–3]. The reaction is usually cataꢀ
lyzed by bases such as ammonia, primary and secondꢀ
ary amines [4], quaternary ammonium salts [5], Lewis
acids [6–9], and catalytic acidꢀbase sites [10] etc. and
often carried out under homogeneous condition. Such
condition requires organic solvents and use of these
organic solvents has always been concerned due to
their hazardousness and associated environmental
pollution. For the standpoint of sustainable environꢀ
ment and minimizing pollution, solventꢀfree heteroꢀ
geneous catalysts have been receiving increasing
attention. Since, these heterogeneous catalysts not
only avoid the use of organic solvents but also suppress
side reactions such as self condensation, oligomerisaꢀ
tion etc. resulting in better selectivity and product
yield [11]. In recent years, therefore, the use of heterꢀ
ogeneous catalysts [12–15], their recovery and reusꢀ
ability are very much sought after in industry.
An equimolar quantity (2.0 mmol) of aldehyde and
ester was taken in a roundꢀbottom flask and then
IrHAp or PtHAp catalyst was added. The mixture was
refluxed at 120°C with continuous stirring using a
magnetic stirrer. The products (3a–3i) were extracted
with chloroform, then the catalyst was removed by simple
filtration and the extract was evaporated. The products
were purified by recrystallization and/or chromatograꢀ
phy and identified by NMR 1H spectroscopy.
RESULTS AND DISCUSSION
In the present study, we report the Knoevenagel
condensation between various aldehydes, namely benzalꢀ
dehyde (1a), pꢀmethoxybenzaldehyde (1b) and 1ꢀnaphꢀ
thaldehyde (1c) and esters, namely ethylcyanoacetate
(
(
2a), diethylmalonoester (2b) and ethylacetoacetate
2c) under solventꢀfree condition in the presence of
IrHAp or PtHAp as a catalyst (Scheme).
The Knoevenagel condensation between various aldehydes
and esters and their products
We synthesized and characterized several
hydroxyapatites and used them for various studies,
including their catalytic activities [16]. Recently, we
have also reported the use of nickel hydroxyapatite as
a heterogeneous catalyst for the Knoevenagel condenꢀ
sation of benzaldehyde with malononitrile [17]. The
use of fluorapatite as a heterogeneous catalyst for the
Knoevenagel condensation has earlier been reported
in the literature [18]. Based on these evidences, we
envisioned that iridium and platinum hydroxyapatites
R2
R1
R1
R2
IrHAp or PtHAp
C, reflux; solventꢀfree
+
O
120°
R3
R3
H
H
Knoevenagel
condensation
products
aldehydes
esters
1a: R1 = Ph
1b ꢀMeO–C6H4– 2b: R2 = R3 = COOEt
1c: 1ꢀnaphthy1
2a: R2 = CN; R3 = COOEt 3a–3i
:
p
(IrHAp and PtHAp) which we had synthesized for
2c: R2 = COMe; R3 = COOEt
other studies as mentioned earlier could also be
extended as a heterogeneous catalyst for the Knoeveꢀ
nagel condensation and the results of this study are
communicated herewith.
Scheme.
Each one of the reactions was carried out twice but
by varying the amounts of catalyst as 0.05 and 0.100 g.
For example, the reaction of 1a with 2a was carried out
1
The article is published in the original.
536

SOLVENTꢀFREE KNOEVENAGEL CONDENSATION OVER IRIDIUM
Table 1. Synthesis of various alkenes by Knoevenagel condensation using IrHAp
537
Amount of catalyst, g
Aldehyde
Ester
Product
0.050
Time, min
0.100
Time, min
Yield, %
Yield, %
Benzaldehyde (1a
)
2a
2a
2a
2b
2b
2b
2c
2c
2c
3a
3b
3c
3d
3e
3f
62
42
30
65
53
25
61
48
22
60
90
95
68
42
97
82
34
92
78
38
60
90
p
ꢀMethoxybenzaldehyde (1b
)
)
)
1ꢀNaphthaldehyde (1c
Benzaldehyde (1a
ꢀMethoxybenzaldehyde (1b
1ꢀNaphthaldehyde (1c
Benzaldehyde (1a
ꢀMethoxybenzaldehyde (1b
1ꢀNaphthaldehyde (1c
)
240
30
240
30
)
p
120
240
60
120
240
60
)
)
3g
3h
3i
p
120
240
120
240
)
Table 2. Synthesis of various alkenes by Knoevenagel condensation using PtHAp
Amount of catalyst, g
Aldehyde
Ester
Product
0.005
Time, min
0.100
Yield, %
Yield, %
Time, min
Benzaldehyde (1a
)
2a
2a
2a
2b
2b
2b
2c
2c
2c
3a
3b
3c
3d
3e
3f
65
40
25
55
58
23
56
45
21
60
90
91
65
40
95
70
31
90
70
33
60
90
p
ꢀMethoxybenzaldehyde (1b
)
)
)
1ꢀNaphthaldehyde (1c
Benzaldehyde (1a
ꢀMethoxybenzaldehyde (1b
1ꢀNaphthaldehyde (1c
Benzaldehyde (1a
ꢀMethoxybenzaldehyde (1b
1ꢀNaphthaldehyde (1c
)
240
30
240
30
)
p
120
240
60
120
240
60
)
)
3g
3h
3i
p
120
240
120
240
)
in the presence of 0.05 and 0.100 g of IrHAp as catalyst of 95, 97 and 92% respectively, whereas 0.050 mg of
and respectively 62 and 95% of yields of product 3a IrHAp catalyzed reactions of 1a with 2a
2c gave prodꢀ
3d and 3g with moderate yields of 62, 65 and
61%, respectively. Similarly, 0.100 mg of IrHAp cataꢀ
lyzed reactions of 1b with 2a 2c gave products 3b 3e
–
(Table 1) were obtained. Similarly, the reaction of 1a
with 2a was carried out in the presence of 0.05 and
0.100 g of PtHAp as catalyst and respectively 91 and
65% of yields of product 3a (Table 2) were obtained.
The same reactions were carried out under similar
reaction conditions without IrHAp or PtHAp and it
did not give any product. These results confirm the
necessity of IrHAp or PtHAp as catalyst for the proꢀ
posed condensation reaction. The percentage yields of
ucts 3a
,
–
,
and 3h with moderate to good yields of 68, 82 and 78%
respectively, whereas 0.050 mg of IrHAp catalyzed
reactions of 1b with 2a–2c gave products 3b, 3e and 3h
with moderate yields of 42, 53 and 48% respectively.
Finally, 0.100 mg of IrHAp catalyzed reactions of 1c
with 2a
yields of 42, 34 and 38% respectively, whereas 0.050 mg
of IrHAp catalyzed reactions of 1c with 2a 2c gave
3e and 3h with poorest yields of 30, 25 and
, 3d and 3g with excellent yields 22% respectively.
–2c gave products 3b, 3e and 3h with poor
other condensation products (3b–3i) are given in
Tables 1 and 2.
–
0.100 mg of IrHAp catalyzed reactions of 1a with products 3b
,
2a
–2c gave products 3a
KINETICS AND CATALYSIS Vol. 52
No. 4
2011

538
PILLAI et al.
Table 3. Comparison of IrHAp and PtHAp catalyzed Knoevenagel condensation of 1a with 2a for the yield of product 3a
with other heterogeneous catalysts
Catalyst
IrHAp
Amount of catalyst, g
Time, min
Yield, %
0.100
0.050
0.100
0.050
1.25
60
60
95
62
90
65
14
45
55
72
74
87
70
86
IrHAp
PtHAp
60
PtHAp
60
Flourapatite [18]
Flourapatite [18]
NiHAp [17]
30
1.25
90
0.083
0.100
3.00
1200
360
60
Zeolite (Znβ) [1]
AlPO4/Al2O3 [19]
Resin [20]
0.100
0.106
0.136
300
480
90
Zeolite [21]
ZnCl [22]
2
Similar trend was also observed with PtHAp cataꢀ catalyst (0.100 g, < 0.1 mmol) is required for producꢀ
lyzed reactions of 1a with 2a
with 2a 2c. 0.100 mg of IrHAp catalyzed reactions of
1a with 2a 2c gave products 3a 3d and 3g with excelꢀ
lent yields of 91, 95 and 90% respectively, whereas
0.050 mg of IrHAp catalyzed reactions of 1a with 2a
2c gave products 3a 3d and 3g with moderate yields of
65, 55 and 56% respectively. Similarly, 0.100 mg of
IrHAp catalyzed reactions of 1b with 2a 2c gave prodꢀ
ucts 3b 3e and 3h with moderate to good yields of 65,
70 and 70% respectively, whereas 0.050 mg of IrHAp
catalyzed reactions of 1b with 2a 2c gave products 3b
–
2c
,
1b with 2a
–
2c and 1c ing over 90% yield of the same product, 3a
.
–
We have demonstrated the efficiency of IrHAp and
PtHAp as catalysts for the Knoevenagel condensation
–
,
between various aldehydes (1a
The reactions were carried out by refluxing at 120
–1c) and esters (2a–2c).
–
°C
,
under solventꢀfree conditions. IrHAp and PtHAp can
be a good alternative to the existing homogeneous catꢀ
alyst as well as many other heterogeneous catalysts.
This research has been supported by a grant from
National Research Foundation and the University of
KwaZulu Natal, DurbanꢀWestville Campus. One of
the authors, M.K. Pillai, thanks the National
Research Foundation and the University of KwaZulu
Natal for postdoctoral bursary.
–
,
–
,
3e and 3h with moderate yields of 40, 58 and 45%
respectively. Finally, 0.100 mg of IrHAp catalyzed
reactions of 1c with 2a–2c gave products 3b, 3e and 3h
with poor yields of 40, 31 and 33% respectively,
whereas 0.050 mg of IrHAp catalyzed reactions of 1c
with 2a–2c gave products 3b, 3e and 3h with poorest
REFERENCES
yields of 25, 21 and 23% respectively.
1. Saravanamurugan, S., Palanichamy, M., Hartman, M.,
and Murugesan, V., Appl. Catal., A, 2006, vol. 298, p. 8.
In general, IrHAp catalyzed reactions gave someꢀ
what higher yields than PtHAp catalyzed reactions
(Tables 1 and 2). Overall, both IrHAp and PtHAp catꢀ
alyzed reactions were very efficient towards the reacꢀ
2. Marciniak, G., Delgado, A., Leclerc, G., Velly, J.,
Decker, N., and Schwartz, J., J. Med. Chem., 1989,
vol. 32, p. 1402.
tions of 1a with 2a
,
2b and 2c which gave the products,
3. Enders, D., Muller, E., and Demir, A.S., Tetrahedron
Lett., 1988, vol. 29, p. 6437.
respectively, 3a 3d and 3g with excellent yields.
,
4. Cope, A.C., Organic Reactions, Jones, G., Ed., New
A literature survey was done on the yields reported
for Knoevenagel condensation reaction of 1a with 2a
to give 3a by various heterogeneous catalysts. The
summary of the literature values of yields are given in
Table 3. It was observed that PtHAp or PtHAp catalyst
was found to be better than other heterogeneous cataꢀ
lyst in the sense that it required a meagre quantity to
provide a maximum yield. For example, a large
amount of fluorapatite catalyst (1.25 g, > 1 mmol) was
required to produce 45% yield of product 3a [16].
However, only a small quantity of IrHAp or PtHAp
York: Wiley, 1967, vol. 15, p. 204.
5. Wang, S., Ren, Z., Cao, W., and Tong, W., Synth. Comꢀ
mun., 2001, vol. 31, p. 673.
6. Wang, G.W. and Cheng, B., ARKIVOC, 2004, no. (ix), p. 4.
7. Attanasi, O., Fillippone, P., and Mei, A., Synth. Comꢀ
mun., 1983, vol. 13, p. 1203.
8. Shanthan Rao, P. and Venkatratnam, R.V., Tetrahedron
Lett., 1991, vol. 32, p. 5821.
9. Bao, W., Zhang, Y., and Wang, J., Synth. Commun.
1996, vol. 26, p. 3025.
,
KINETICS AND CATALYSIS Vol. 52
No. 4
2011

SOLVENTꢀFREE KNOEVENAGEL CONDENSATION OVER IRIDIUM
539
10. Reeves, R.L. and Patai, S., The Chemistry of Carbonyl 17. Pullabhotla, V.S.S.R., Rahman, A., and Jonnalaꢀ
Compounds, New York: Interscience, 1996, p. 567.
gadda, S.B., Catal. Commun., 2009, vol. 10, p. 365.
11. Zhnag, X., Lai, E.S.M., MartinꢀAranda, R., and
Yeung, K.L., Appl. Catal., A, 2004, vol. 261, p. 109.
12. Balalaie, S. and Nemati, N., Synth. Commun., 2000,
18. Sebti, S., Nazih, R., Tahir, R., Salhi, L., and Saber, A.,
Appl. Catal., A, 2000, vol. 197, p. L187.
19. Cabello, J.A., Campelo, J.M., Garcia, A., Luna, D.,
and Marinas, J.M., J. Org. Chem., 1984, vol. 49,
p. 5195.
vol. 30, p. 869.
13. Wang, G.W. and Cheng, B., ARKIVOC, 1994, no. (x), p. 4.
14. Mogilaiah, K., Prashanthi, M., Reddy, G.R.,
Reddy, C.S., and Reddy, N.V., Synth. Commun., 2003,
vol. 33, p. 2309.
20. Saito, T., Goto, H., Honda, K., and Fujii, T., Tetraheꢀ
dron Lett., 1992, vol. 33, p. 7535.
21. Reddy, T.I. and Varma, R.S., Tetrahedron Lett., 1997,
15. Reddy, G.V., Maitraie, D., Narsaiah, M.B., Rambabu, Y.,
vol. 38, p. 1721.
and Rao, P.S., Synth. Commun., 2001, vol. 31, p. 2881.
16. Singh, S. and Jonnalagadda, S.B., Catal. Lett., 2008, 22. Rao, P.S. and Venkataraman, R.V., Tetrahedron Lett.
,
vol. 126, p. 200.
1991, vol. 32, p. 5821.
KINETICS AND CATALYSIS Vol. 52
No. 4
2011