collected in a Buchner funnel and washed with excess distilled
water until the filtrate was neutral to phenolphthalein indica-
tor. These hydrogel beads were directly used in the catalytic
experiments.
Acknowledgements
We wish to thank the CSIR for financial support under the
Task Force Project CMM-0006. K. R. and C. U. M. thank
UGC and CSIR, respectively, for Junior Research Fellow-
ships.
Quantitative GC analysis of free amines in chitosan beads. In
a typical experiment, 20 units of chitosan hydrogel beads were
taken into 2.5 mL of a solution of salicylaldehyde (0.16
mol Lꢁ1) in ethanol to form a Schiff base complex. Accessible
free amines were determined by analysing the remaining
unreacted salicylaldehyde by GC, using nitrobenzene as the
internal standard.11 Accessible free amines in chitosan hydro-
gel beads, commercial chitosan and dried chitosan beads were
55–65, 2.5 and 1.65%, respectively, based on an average of
80% deacetylated units in commercial chitosan.
References
1 (a) A. Berkessel, in Asymmetric Organocatalysis, ed. H. Groger,
Wiley-VCH, Weinheim, 2005, pp. 203; (b) B. List, Tetrahedron,
2002, 58, 5573; (c) P. I. Dalko and L. Moisan, Angew. Chem., Int.
Ed., 2004, 43, 5138.
2 (a) M. Benaglia, A. Puglisi and F. Cozzi, Chem. Rev., 2003, 103,
3401; (b) Y. Wang, H. Jiang, H. Liua and P. Liu, Tetrahedron
Lett., 2005, 46, 3935; (c) C. Ogawa, M. Sugiura and S. Kobayashi,
Chem. Commun., 2003, 192; (d) H. Hagiwara, J. Hamaya, T. Hoshi
and C. Yokoyama, Tetrahedron Lett., 2005, 46, 393; (e) H. S. Kim,
Y. M. Song, J. S. Choi, J. W. Yang and H. Han, Tetrahedron, 2004,
60, 2051.
Catalytic studies
Typical procedure for an aldol reaction catalysed by chitosan
hydrogel beads. Chitosan hydrogel beads (20 units), para-
nitrobenzaldehyde (1 mmol), acetone (1 mL) and DMSO
(4 mL) were placed in a round-bottomed flask and stirred at
room temperature for 18 h. The resulting reaction mixture was
filtered to remove the catalyst, and the filtrate was extracted
with ethyl acetate and washed with water. The organic portion
was separated and evaporated under vacuum to obtain the
crude products.
3 D. L. Kaplan, Biopolymers from Renewable Resources, Springer-
Verlag, Berlin, 1998.
4 (a) H. Sashiwa and S. Aiba, Prog. Polym. Sci., 2004, 29, 887; (b) M.
N. V. Ravi Kumar, React. Funct. Polym., 2000, 46, 1.
5 (a) E. Guibal, Prog. Polym. Sci., 2005, 30, 71; (b) D. J. Macquarrie
and J. J. E. Hardy, Ind. Eng. Chem. Res., 2005, 44, 8499.
6 (a) L. F. Xiao, F. W. Li and C. G. Xia, Appl. Catal., A, 2005, 279,
125; (b) G. Huai-min and C. Xian-su, Polym. Adv. Technol., 2004,
15, 89; (c) F. Quignard, A. Choplin and A. Domard, Langmuir,
2000, 16, 9106; (d) J. J. E. Hardy, S. Hubert, D. J. Macquarrie and
A. J. Wilson, Green Chem., 2004, 6, 53.
7 R. Valentin, K. Molvinger, F. Quignard and D. Brunel, New J.
Chem., 2003, 27, 1690.
8 (a) K. R. Reddy, N. S. Kumar, P. S. Reddy, B. Sreedhar and M.
Lakshmi Kantam, J. Mol. Catal. A: Chem., 2006, 252, 12; (b) K. R.
Reddy, N. S. Kumar, B. Sreedhar and M. Lakshmi Kantam, J.
Mol. Catal. A: Chem., 2006, 252, 136.
9 A. V. Kucherov, N. V. Kramareva, E. D. Finashina, A. E. Koklin
and L. M. Kustov, J. Mol. Catal. A: Chem., 2003, 198, 333.
10 The average dried weight of 20 units of the chitosan hydrogel
beads is 33 mg, which corresponds to 0.2 mmol of the catalyst.
However, based on the active accessible free amine groups, as
reported in the experimental section (55–65%), the active catalyst
for 20 units will be in the range 11–13 mol% with respect to the
aldehyde.
Typical procedure for a Knoevenagel reaction catalysed by
chitosan hydrogel beads. A similar procedure to that described
above for aldol reactions was employed, except that in place of
acetone, an active methylene compound (malononitrile, 1.1
mmol) was added and stirred until the completion of the
reaction, as monitored by thin layer chromatography (TLC).
The filtered catalysts were used directly for further recycling
experiments.
Table 1, entry 1: Isolated yield: 87.2%. 1H NMR (300 MHz,
CDCl3) d 8.20 (d, J = 8.5 Hz, 1 H), 7.55 (d, J = 8.5 Hz, 1 H),
5.25 (m, 1 H), 3.56 (br, 1 H), 2.85 (m, 2 H) and 2.25 (s, 3 H).
Table 2, entry 1: Isolated yield = 96.4%. 1H NMR
(300 MHz, CDCl3) d 8.40 (d, J = 8.7 Hz, 2 H, Ar), 8.09 (d,
J = 8.7 Hz, 2 H, Ar) and 7.88 (s, 1 H).
11 T. G. Waddell, D. E. Leyden and M. T. Debello, J. Am. Chem.
Soc., 1981, 103, 5303.
ꢀc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006
1552 | New J. Chem., 2006, 30, 1549–1552