RSC Advances
COMMUNICATION
Schiff base supported MCM-41 catalyzed the
Knoevenagel condensation in water3
Xiuzhi Dong, Yonghai Hui,* Shaolei Xie, Peng Zhang, Guangpeng Zhou
and Zhengfeng Xie*
Received 9th January 2013,
Accepted 10th January 2013
DOI: 10.1039/c3ra00138e
By employing a MCM-41/Schiff base as catalyst, high yield
Knoevenagel condensation reactions of malononitrile with aro-
matic aldehydes were realized. The reaction afforded the
corresponding products in excellent yields (up to 99%) in water.
Moreover, the catalyst was also found to exhibit excellent
recyclability (up to 10 times) without loss of efficiency.
catalyst for the Knoevenagel condensation reaction in high yields
(up to 99%) under operationally simple conditions using
environmentally benign water as the solvent. An important feature
of the MCM-41/Schiff base catalyst is that it is convenient to
recover and recycle, and the catalyst was recycled over ten times
without any significant loss in activity.
Results and discussion
Introduction
The prepared catalysts were characterized by FT-IR, XRD, SEM and
TEM. The FT-IR spectrum of the parent MCM-41 (a), as well as the
spectrum of 3-aminopropyltriethoxysilane supported MCM-41 (b),
and the spectrum of the Schiff base supported MCM-41 (c) are
shown in Fig. 1. The spectrum of the unmodified MCM-41 (L1), as
well as the spectra of both the modified MCM-41 materials (L2 and
L3), were dominated by strong bands characteristic of the support
matrix, indicating that the support framework remained
unchanged. The band at about 3446 cm21 was due to the surface
hydroxyl groups, and the bands at about 1084, 803 and 459 cm21
were assigned to the asymmetric and symmetric Si–O–Si stretch-
ing of the support framework. After the 3-aminopropyltriethox-
The Knoevenagel condensation reaction is one of the most
powerful strategies for carbon–carbon bond formation in organic
synthesis, and its products can easily be converted into important
organic synthetic intermediates and versatile biologically active
molecules.1 Many synthetic methods have been developed to
accomplish the Knoevenagel condensation reaction successfully.2
The majority of catalysts used in this reaction are enzymes,3
polyacrylonitrile fibers,4 polysiloxanes,5 chitosan biohydrogel
beads,6 mesoporous molecular sieves7 and others. In recent years,
the use of mesoporous silica materials as catalysts has become the
focus of a great deal of current research in organic synthesis
catalysis because of their high surface areas, low cost and
environmentally friendly nature.8 However, all of the research
into mesoporous molecular sieves has mainly been restricted to
discussion of the synthesis and characterization of the
Knoevenagel condensation reaction, and to the best of our
knowledge, the major hurdle in this reaction lies in a lack of
high reactivity for the mesoporous silica materials.9 We previously
reported the use of a Schiff base as the highly efficient
organocatalyst for the Henry reaction10 and the Friedel–Crafts
reaction.11 In view of the great potential of the MCM-41/Schiff base
catalyst (Scheme 1), we would like to further extend the use of the
catalyst. Herein, we describe the use of the MCM-41/Schiff base
Key Laboratory of Oil & Gas Fine Chemicals, Ministry of Education & Xinjiang
Uyghur Autonomous Region, College of Chemistry and Chemical Engineering,
Xinjiang University, Urumqi 830046, China. E-mail: xiezhf72@yahoo.com.cn;
hyhai97@yahoo.com.cn; Fax: (+86)-991-8581-018
Electronic supplementary information (ESI) available: Experimental details and
3
analytical data (1H,13C and MS) for all new compounds. See DOI: 10.1039/c3ra00138e
Scheme 1 The catalyst used in the Knoevenagel condensation reaction
This journal is ß The Royal Society of Chemistry 2013
3222 | RSC Adv., 2013, 3, 3222–3226