Res. Chem. Intermed.
, Vol. 33, No. 6, pp. 541–548 (2007)
Also available online - www.brill.nl/rci
New environmentally-friendly solvent-free synthesis of
imines using calcium oxide under microwave irradiation
, P. SURESHKUMAR, V. KANAGARAJAN and
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India
Received 2 July 2006; accepted 22 January 2007
Abstract—Condensation of structurally diverse aldehydes including heterocyclic aldehydes, like
furfural, with various amines in the presence of calcium oxide affording the corresponding imines
in solvent-free conditions in good to excellent yields under microwave irradiation is described.
A comparative study has been done under thermal conditions. The synergy between dry media and
microwave irradiation in this reaction is evaluated by condensing less electrophilic aldehydes with
poorly nucleophilic amines. The main advantages of this environmentally friendly protocol are the
use of the non-toxic and inexpensive reagent calcium oxide and the considerable rate enhancement in
comparison with a thermal reaction.
Keywords: Calcium oxide; imines; solvent-free conditions; microwave irradiation; green chemistry.
Imines [1, 2] have been found to possess a wide spectrum of biological activities
such as lipoxygenase inhibitors, anti-inﬂammatory agents  and anti-cancer
agents . Furthermore, imines are used as diverse as versatile components in the
formation of optically active α-alkyl aldehydes , in the preparation of secondary
amines by hydrogenation , in nucleophilic addition with organometallic reagents
 and in cycloaddition reactions [8, 9]. Consequently, numerous methods
involving Lewis acids [10–12] and molecular sieves in ionic liquids  have been
developed for the preparation of imines. However, all these methods have their
own merits and short comings. Moreover, the efﬁciency of the procedures reported
is limited to the reaction of highly electrophilic carbonyl compounds and strongly
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