c
J. Chem. Sci. Vol. 123, No. 3, May 2011, pp. 331–334. ꢀ Indian Academy of Sciences.
Diethylamine functionalized polyethylene glycol as a novel and efficient
catalyst for Knoevenagel condensation
WEN YE, HONG JIANG∗ and XIAN-CAO YANG
College of Science, Huazhong Agricultural University, Wuhan, Hubei 430070, China
e-mail: jianghong0066@126.com
MS received 8 July 2010; revised 20 January 2011; accepted 28 February 2011
Abstract. The Knoevenagel condensation of aromatic aldehydes with active methylene is an efficient reac-
tion for carbon–carbon double bond formation. A rapid, efficient, and ecofriendly protocol for the Knoevenagel
condensation of active methylene compounds with aldehydes has been developed with diethylamine functional-
ized polyethylene glycol-600 (PEG-600) as catalyst with good to excellent yields at room temperature without
solvent.
Keywords. Knoevenagel condensation; modified polyethylene glycol; room temperature; solvent-free.
1. Introduction
2. Experimental
The Knoevenagel condensation between aldehydes and 2.1 Synthesis of the catalyst
active methylenes is an important reactions in organic
2.1a Reactants and reagents: PEG600, toluene,
synthesis in forming carbon–carbon double bond, and
the products have E-isomer dominantly. Knoevenagel
condensation has been receiving considerable attention,
due to its broad spectrum of uses including cosmetic,
perfume, pharmaceutical, agrochemicals, and pharma-
ceuticals applications.1,2 In last ten years, lots of meth-
ods to achieve Knoevenagel condensation are known,
For example, some novel heating methods such as
microwave irradiation,3–6 ultrasonic heating7,8 had been
applied in Knoevenagel condensation; in the mean time,
accumulating efforts have been made to explore novel
catalysts for Knoevenagel reaction.9–21 However some
of these methods suffer from some drawbacks such as
long reaction time, the use of harmful catalyst, lots of
solvent, and energy expenses.
pyridine, thionyl chloride, sodium carbonate, abso-
lute ethanol, diethylamine were purchased from China
Chemical Reagent Company.
2.1b The synthesis of dichloro substituted
PEG600:23,24 PEG600 (15 g, 0.025 mol) and pyridine
(5 mL, 0.0625 mol) was dissolved in toluene (20 mL),
◦
stirred at 87 C, thionyl chloride (5 mL, 0.0625 mol)
was added slowly, and the resultant reaction mixture
◦
was stirred for 15 h at 87 C. Then the resulting solid
was removed by filtration. After removal of the solvent
under reduced pressure a viscous liquid residual was
collected as dichloro substituted PEG600 (13.75 g,
91.6%).
In this report, we use modified PEG with tertiary
amine moiety as catalyst, which is synthesized as in
scheme 1. Base has been extensively investigated in
catalysing Knoevenagel reaction.22 As a kind of base,
diethylamine functionalized Polyethylene glycol (PEG)
makes the Knoevenagel condensation at room temper-
ature with good to excellent yields (scheme 2). The
catalyst can be easily recycled and reused without
noticeably decreasing in productivity.
2.1c The synthesis of diethylamine functionalized
PEG: Drop the dichloro substituted PEG600 (7.5 g,
0.0125 mol) into the mixture of absolute ethanol
(10 mL), diethylamine (3.1 mL, 0.03 mol), sodium car-
◦
bonate (1.6 g, 0.015 mol), which was stirred at 80 C
for 20 h. Then the solid produced was filtered. After
removal of the solvent under reduced pressure, diethy-
lamine functionalized PEG was collected as a brown
viscous liquid (8.50 g, 89.4%, the spectrum is listed
below).
2.1d Catalyst (Et2N-PE-NEt2): brown liquid. 1H NMR
(600 MHz, CDCl3): δ 3.572 (s, 60 H), 2.514–2.478
∗For correspondence
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