Synthesis and characterization of Salamo-type bisoximes based on 3-ethoxysalicyladehyde and Bis(aminooxy)alkane

Article abstract of DOI:10.14233/ajchem.2015.17557

A series of ethoxy-substituted Salamo-type bisoximes H₂L¹-H₂L₄ have been synthesized from 3-ethoxysalicyladehyde and 1,3-bis(aminooxy)propane, 1,4- bis(aminooxy)butane, 1,5-bis(aminooxy)pentane or 1,6-bis(aminoo

Full text of DOI:10.14233/ajchem.2015.17557

Asian Journal of Chemistry; Vol. 27, No. 5 (2015), 1711-1713
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.17557
Synthesis and Characterization of Salamo-type Bisoximes
Based on 3-Ethoxysalicyladehyde and Bis(aminooxy)alkane
*
GANG LI, JIAN-CHUN MA, ZONG-LI REN , WEI-MIN ZHOU, LI WANG and NA WEN
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P.R. China
*Corresponding author: E-mail: zlren8@163.com
Received: 5 March 2014;
Accepted: 15 May 2014;
Published online: 20 February 2015;
AJC-16876
A series of ethoxy-substituted Salamo-type bisoximes H2L1-H2L4 have been synthesized from 3-ethoxysalicyladehyde and 1,3-
bis(aminooxy)propane, 1,4-bis(aminooxy)butane, 1,5-bis(aminooxy)pentane or 1,6-bis(aminooxy)hexane in hot ethanol medium,
respectively and characterized by elemental analyses, IR, UV-visible spectra and 1H NMR spectroscopy. Salamo-type compounds are
conducive to coordinate experiments and construct supramolecular complexes.
Keywords: Salamo-type bisoxime, 3-Ethoxysalicyladehyde, bis(Aminooxy)alkane.
INTRODUCTION
EXPERIMENTAL
Salen (N,N'-disalicylideneethylenediamine) and its
analogues are most versatile chelate ligands in inorganic
and organicmetallic chemistry1-4. Simultaneously, as
bisoxime (-C=N-OR) ligands, they are usually synthesized
by the condensation of aldehydes or ketones with hydroxyl-
amineis. Bisoxime compounds are a kind of good multiden-
tate N2O2-donating ligands with large π-conjugating system
and often showing a diversity of structure. The chemical
characteristics of the oxime compounds have been well
known, since they have been widely used in insecticide,
anti-virus, especially in medicine, analytical chemistry,
metal corrosion and functional material fields5-10. There
contain two hydroxylamine (-C=N-OR) and more than two
hydroxyl (-OH) among each Salamo-type bisoxime ligand,
which provide coordination site to combine metal atoms
and have advantage to construct supramolecular comp-
lexes11. So the study on Salamo-type bisoxime compounds
has good prospects. Therefore, we have research on synthesis
and characterization of those ethoxy-substituted Salamo-
type bisoxime compounds, e.g., 6,6'-diethoxy-2,2'-
[(propylene-1,3-diyldioxy)-bis(nitrilomethylidyne)]-
diphenol (H2L1), 6,6'-diethoxy-2,2'-[(butylene-1,4-diyl-
dioxy)bis(nitrilomethylidyne)]diphenol (H2L2), 6,6'-
diethoxy-2,2'-[(propane-1,5-diyldioxy)-bis(nitrilo-
methylidyne)]diphenol (H2L3) and 6,6'-diethoxy-2,2'-
[(hexane-1,6-diyldioxy)bis(nitrilomethylidyne)]diphenol
(H2L4), which provided a reference for the further investi-
gation.
3-Ethoxysalicyladehyde (≥ 99 %) was purchased and used
without further purification. The others reagents used are the
same as reported earlier11. 1,3-bis(Aminooxy)propane, 1,4-
bis(aminooxy)butane, 1,5-bis(aminooxy)penpane and 1,6-
bis(aminooxy)hexane were synthesized according to an
analogous method reported earlier12-14
.
Preparation of 6,6'-diethoxy-2.2'-[(propylene-1,3-diyl-
dioxy)bis(nitrilomethylidyne)]diphenol (H2L1): To an
ethanolic solution (2 mL) of 1,3-bis(aminooxy)propane (53.10
mg, 0.50 mmol) was added an ethanol solution (4 mL) of 3-
ethoxy-salicyladehyde (155.2 mg, 1 mmol). The reaction
mixture was stirred at 331 K for 4 h, a white precipitation was
obtained immediately. The formed precipitate was separated
by filtration and washed successively with ethanol and ethanol/
hexane (1:4), respectively. The product was dried under
reduced pressure to obtain white compound H2L1 (Fig. 1).
O
C
O
C
O
C
Br
Br
N OH
N O O N
2
rt, 75 h, DMF, Et3N
C
O
C
O
C
O
O
N
O
CHO
OH
N
2
OEt
Ethanol
NH2NH2·H2O
H2N O O NH2
OH HO
EtO
95% Ethanol, Ar
OEt
H2L1
Fig. 1. Synthetic route to the Salamo-type bisoxime H2L1

1712 Li et al.
Asian J. Chem.
O
C
Preparation of 6,6'-diethoxy-2,2'-[(butylene-1,4-
O
C
O
diyldioxy)bis(nitrilomethylidyne)]diphenol (H2L2): To an
ethanol solution (5 mL) of 1,4-bis(aminooxy)butane (122.8
mg, 1.02 mmol) was added an ethanolic solution (10 mL) of
3-ethoxysalicyladehyde (362.2 mg, 2.18 mmol). After the
solution had been stirred at 328 K for 6 h, a pale-yellow
precipitation was obtained immediately. The formed precipitate
was separated by filtration and washed successively with
ethanol and ethanol/hexane (1:4), respectively. The product
was dried under reduced pressure to obtain pale-yellow com-
pound H2L2 (Fig. 2).
C
Br
O
O
Br
N OH
2
N
N
C
O
rt, 75 h, DMF, Et3N
C
O
C
O
O
N
CHO
OH
O
N
2
NH2NH2·H2O
OEt
Ethanol
O
NH2
H2N
O
OH
HO
95% Ethanol, Ar
EtO
H2L4
Fig. 4. Synthetic route to the Salamo-type bisoxime H2L4
OEt
O
C
O
C
O
C
Br
Br
N OH
N O O N
2
rt, 75 h, DMF, Et3N
hexane (1:4), respectively. The product was dried under
reduced pressure to obtain pale-yellow compound H2L4.
C
O
C
O
C
O
O
N
RESULTS AND DISCUSSION
O
N
CHO
OH
Four ethoxy-substituted Salamo-type bisoximes H2L1,
H2L2, H2L3 and H2L4 have been synthesized with good yields
and the compositions are confirmed by elemental analyses,
IR, UV-visible spectra and 1H NMR spectroscopy.
The colour, yields, melting points and elemental analytical
results of the synthesized Salamo-type bisoximes H2L1, H2L2,
H2L3 and H2L4 are summarized in Table-1.
2
OEt
Ethanol
NH2NH2·H2O
H2N O
OH
O NH2
HO
95% Ethanol, Ar
EtO
H2L2
OEt
Fig. 2. Synthetic route to the Salamo-type bisoxime H2L2
Preparation of 6,6'-diethoxy-2,2'-[(propane-1,5-
The bisoxime compounds H2L1, H2L2, H2L3 and H2L4 are
stable in air and soluble in majority of organic solvents that
conclude to coordinated experiments, not soluble in hexane
that they can be recrystallized from n-hexane. The elemental
analytical data and the compositions of the Salamo-type
bisoximes show that the elemental analytical data of Salamo-
type bisoximes close to the theoretical value which demonstrate
the accuracy of the results.
IR spectra: IR spectral data of the Salamo-type bisoximes
H2L1, H2L2, H2L3 and H2L4 exhibit various bands from 4000 to
400 cm-1. The IR spectral details of the Salamo-type bisoximes
H2L1, H2L2, H2L3 and H2L4 are presented in Table-2.
diyldioxy)bis(nitrilomethylidyne)]diphenol (H2L3): To an
ethanolic solution (5 mL) of 1,5-bis(aminooxy)pentane (133.4
mg, 1 mmol) was added an ethanol solution (8 mL) of 3-ethoxy-
salicyladehyde (359.2 mg, 2.16 mmol), After the solution had
been stirred at 325 K for 3 h, a white precipitation was obtained
immediately. The formed precipitate was separated by filtration
and washed successively with ethanol and ethanol/hexane
(1:4), respectively. The product was dried under reduced
pressure to obtain white compound H2L3 (Fig. 3).
O
C
O
C
O
C
The characteristic C=N stretching bands of the Salamo-
type bisoximes H2L1-H2L4 appear at 1605-1611 cm-1,
respectively15. And the Ar-O stretching bands occur at 1247,
1252, 1261 and 1256 cm-1 for the Salamo-type bisoximes
H2L1-H2L4, respectively indicating that 3-ethoxysalicyladehyde
has been condensated with 1,3-bis(aminooxy)propane, 1,4-
bis(aminooxy)butane, 1,5-bis(aminooxy)pentane and 1,6-
bis(aminooxy)hexane, respectively and formed new Salamo-
type bisoximes16. In the 1479-1446 cm-1 region, the observed
bands were attributed to aromatic C=C vibrations. In addition,
the O-H stretching bands of the Salamo-type bisoximes at 3600
cm-1 region disappear, the strong absorption bands of the Salamo-
type bisoximes appear at 3435-3410 cm-1 region, which are
the evidence for the existence of associating hydroxyl group
in the Salamo-type bisoximes. IR spectral results of the
Salamo-type bisoximes further confirmed the accuracy of the
consequence.
Br
Br
N OH
2
N
O
O
N
rt, 75 h, DMF, Et3N
C
O
C
O
C
O
O
N
O
N
CHO
OH
2
OEt
Ethanol
NH2NH2·H2O
H2N O O NH2
OH
HO
95% Ethanol, Ar
EtO
H2L3
OEt
Fig. 3. Synthetic route to the Salamo-type bisoxime H2L3
Preparation of 6,6'-diethoxy-2,2'-[(hexane-1,6-diyl-
dioxy)bis(nitrilomethylidyne)]diphenol (H2L4): To an
ethanolic solution (5 mL) of 1,6-bis(aminooxy)hexane (151.1
mg, 1.02 mmol) was added an ethanolic solution (10 mL) of
3-ethoxysalicyladehyde (347.8 mg, 2.09 mmol).After the solu-
tion had been stirred at 328 K for 6 h, a pale-yellow precipi-
tation was obtained. The formed precipitate was separated by
filtration and washed successively with ethanol and ethanol/
UV-visible and 1H NMR spectra: The UV-visible spectra
of the Salamo-type bisoximes H2L1, H2L2, H2L3 and H2L4 in 5
× 10-5 mol L-1 dichloromethane solution are given in Table-3.
The Salamo-type bisoximes H2L1, H2L2, H2L3 and H2L4 exhibit

Vol. 27, No. 5 (2015)
Compound
Synthesis of Salamo-type Bisoximes Based on 3-Ethoxysalicyladehyde and Bis(aminooxy)alkane 1713
TABLE-1
COLOUR, YIELDS, MELTING POINTS, ELEMENTARY ANALYTICAL RESULTS
AND COMPOSITIONS OF THE BISOXIMES H2L1, H2L2, H2L3 AND H2L4
Elemental analysis (%) Found (Calcd.)
m.f. (m.w.)
Colour
m.p. (K)
Yield (%)
C
H
N
C21H26N2O6
402.44
C22H28N2O6
416.47
C23H30N2O6
430.49
C24H32N2O6
444.52
62.61
(62.67)
63.47
(63.45)
64.20
(64.17)
64.97
(64.85)
6.40
(6.41)
6.75
(6.78)
7.01
(7.02)
7.05
(7.26)
7.01
(6.95)
6.66
(6.73)
6.48
(6.51)
6.12
(6.30)
H2L1
H2L2
H2L3
H2L4
White
Pale-yellow
White
462.5-463.5
413-414
76.5
85.8
67.7
57.2
355.5-356.5
354.5-355.5
Pale-yellow
TABLE-2
IR SPECTRAL DATA FOR THE BISOXIMES H2L1, H2L2, H2L3 AND H2L4 (cm-1)
Compound
ν(O-H)
ν (CH2)
ν (C=N)
ν (Ar-O)
ν (C-C)benzene ring
H2L1
H2L2
H2L3
H2L4
3410
3427
3441
3435
2970, 2885
2977, 2882
2941, 2880
2975, 2879
1605
1607
1611
1608
1247
1252
1261
1256
1446
1475
1481
1479
TABLE-3
UV-VISIBLE SPECTRA AND 1H NMR DATA FOR THE SYNTHESIZED BISOXIMES H2L1, H2L2, H2L3 AND H2L4
π-π*(nm)
1H NMR (400 MHz, DMSO-d6, δ/ppm)
2.18 (m, J = 6.5 Hz, 2H, CH2), 3.92 (s, 6H, CH3), 4.17 (m, J = 7.2 Hz, 4H, CH2-O), 4.36 (m, J = 6.2, 1.4
Hz, 4H, CH2-O), 6.78 (s, 2H, PhH), 6.85 (m, 2H, PhH), 6.92 (dd, J = 7.6, 2.2 Hz, 2H, PhH), 8.25 (s, 2H,
N=CH), 9.89 (s, 2H, OH).
Compound
H2L1
272, 310
2.22 (m, J = 6.2 Hz, 4H, CH2), 3.90 (s, 6H, CH3), 4.16 (m, J = 7.0 Hz, 4H, CH2-O), 4.37 (m, J = 6.0, 1.4
Hz, 4H, CH2-O), 6.78 (s, 2H, PhH), 6.85 (m, 2H, PhH), 6.92 (dd, J = 7.2, 2.3 Hz, 2H, PhH), 8.23 (s, 2H,
N=CH), 9.87 (s, 2H, OH).
2.19 (m, J = 6.2 Hz, 6H, CH2), 3.91 (s, 6H, CH3), 4.18 (m, J = 7.4 Hz, 4H, CH2-O), 4.35 (m, J = 6.3, 1.4
Hz, 4H, CH2-O), 6.78 (s, 2H, PhH), 6.85 (m, 2H, PhH), 6.92 (dd, J = 7.4, 2.2 Hz, 2H, PhH), 8.26 (s, 2H,
N=CH), 9.88 (s, 2H, OH).
2.20 (m, J = 6.0 Hz, 8H, CH2), 3.93 (s, 6H, CH3), 4.18 (m, J = 7.0 Hz, 4H, CH2-O), 4.35 (m, J = 6.4, 1.4
Hz, 4H, CH2-O), 6.78 (s, 2H, PhH), 6.85 (m, 2H, PhH), 6.92 (dd, J = 7.5, 2.0 Hz, 2H, PhH), 8.21 (s, 2H,
N=CH), 9.86 (s, 2H, OH).
H2L2
H2L3
H2L4
274, 315
272, 312
273, 321
two intense peaks at around 272 and 310 nm. The former
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*
attributed to the intra-ligand π-π transition of the C=N bonds17.
It is of note that there was no absorption around 400 nm, which
is seen in the corresponding Salen derivatives. The absorption
is ascribed to the quinoid form of H2salen17.
The 1H NMR spectra of the Salamo-type bisoximes H2L1,
H2L2, H2L3 and H2L4 in DMSO-d6 are shown in Table-3. The
1H NMR spectra showed a singlet at about 8.21-8.26 ppm
indicating the existence of oxime bonds17,18
.
Conclusion
Four Salamo-type bisoximes H2L1-H2L4 have been designed
and successfully synthesized by the reaction of 2 equivalents
of 3-ethoxysalicyladehyde with 1,3-bis(aminooxy)propane,
1,4-bis(aminooxy)butane, 1,5-bis(aminooxy)pentane or 1,6-
bis(aminooxy)hexane under comfortable conditions, respec-
tively.
ACKNOWLEDGEMENTS
This work was supported by the Science and Technology
support funds of Gansu Province (613028).
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