1
Tetrahedron Letters
Green synthesis of ethyl oxalate benzylidinyl hydrazides
a
a,
a,
Zhi Xiang Zhao , Li Ping Cheng and Wan Pang
a
School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 201418, China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Acylhydrazone compounds play an important role in medicine, materials and other fields.
Herein we report the synthesis of ethyl oxalate benzylidinyl hydrazides by the reaction of
benzaldehyde derivatives and ethyl oxalate hydrazide under catalyst-free conditions in
Available online
H O near room temperature. This green synthesis method has the advantages of mild
2
reaction conditions, fast reaction rate, non-catalytic, good yield and easy isolation. These
synthesized ethyl oxalate benzylidinyl hydrazides can be used as Schiff base metal
complexes of small molecule ligands.
Keywords:
Acylhydrazone compounds
green synthesis
Schiff-base
2009 Elsevier Ltd. All rights reserved.
1
4
Schiff-bases were reported with applications in various areas,
the reaction of diethyl oxalate and hydrazine, the yield is 29% .
In this study, 2 equiv diethyl oxalate reacts with 1 equiv
hydrazine hydrate in water under room temperature conditions
stirred for overnight. Then, The aqueous solution was extracted
with ethyl acetate, organic phases containing excessive diethyl
oxalate were discarded and the aqueous of ethyl oxalate
hydrazide were collected. Compound 3 can be stored in aqueous
solution.
1
-3
such as medicine, catalysis and materials . They play important
roles in industrial products of human life. Therefore, synthesis of
Schiff-bases in a green way is very important. The green
chemistry idea is to increase production, reduce environmental
4
pollution and simplify the reaction process . Green chemistry
inspires us to explore a new method to prepare Schiff-bases.
Acylhydrazones are a class of Schiff-base with the special
structure of —CO—NH—N=C—. Due to this construction, they
have quiet a few advantages that ordinary Schiff-bases don’t
We initially envisioned the synthesis of ethyl oxalate 2-
methoxy-benzylidinyl hydrazide 5a. It is delightful that a white
crystal was obtained by treating 2-methoxybenzaldehyde with
ethyl oxalate hydrazide stirred for 7h in aqueous, the yield is
77.8%. Encouraged by this result, several other benzaldehyde
derivatives were subsequently explored for the reaction (Table
1).
5
have . Furthermore, acylhydrazone compounds had widespread
applications in fields of materials, drugs, catalysis, and molecular
6
-10
electronics, etc . Imine synthesis is one of the most useful tools
to build Schiff base molecules. Traditional methods for the
synthesis of acylhydrazones often used organic solvents. For
1
1
example, Maccioni et al. synthesized a few N-arylidenearyl-
hydrazides in 2-propanol. The reaction was carried out under
1
2
reflux with heating. Wang et al. synthesized 4-hydroxy-3-
methoxy-benzaldehyde series of aroyl hydrazones in ethanol and
1
3
heated at 95 °C for 6 h-9 h . These synthesis methods required
not only the presence of organic solvents but also longer reaction
time. The present study developed a simple, green and catalyst-
free method for the synthesis of a series of ethyl oxalate
benzylidinyl hydrazides. They could be easily obtained by the
reaction of benzaldehyde derivatives with ethyl oxalate hydrazide.
Most important of all, all reactions run in water.
Scheme 1. Preparation of the compound monoethyl oxalate
hydrazide 3.
Various benzaldehyde derivatives were added to the aqueous
solution of ethyl oxalate hydrazide 3 and the corresponding
compounds 5a-5p were obtained. The desired compound 5c
could be obtained with the yield 92.3% (Table 1). However,
compounds 5b, 5d, 5e, 5i were obtained in the same method,
which resulted in reduced yields and needed longer reaction time
We began our study with the commercially available diethyl
oxalate 1 and hydrazine hydrate 2 (Scheme 1). According to
previous reports of Braccio et al, compound 3 was prepared by
Corresponding author. Tel.: +86-21-60873250; fax: +86-21-60877231; e-mail: chengliping@sit.edu.cn
Corresponding author. Tel.: +86-21-60873250; fax: +86-21-60877231; e-mail: pangwan@sit.edu.cn