Synthesis and characterization of methoxy-substituted salamo-type bisoximes based on bis(aminooxy)alkane and 3-methoxy-2-hydroxybenzaldehyde

Article abstract of DOI:10.14233/ajchem.2014.17468

Four new methoxy-substituted Salamo-type bisoxime compounds 6,6'-dimethoxy-2,2'-[(propylene-1,3-diyldioxy)bis(nitrilomethylidyne)] diphenol (H₂L¹), 6,6'-dimethoxy-2,2'-[(butylene-1,4-diyldioxy)bis(nitrilomethylidyne)]diphenol (H₂L²), 6,6'-dimethoxy- 2,2'-[(propane-1,5-diyldioxy)bis(nitrilome-thylidyne)]diphenol (H₂L³) and 6,6'-dimethoxy-2,2'-[(hexane-1,6-diyldioxy)bis(nitrilomethylidyne)] diphenol (H₂L⁴) have been synthesized through condensation reactions under hot ethanol medium, respectively and characterized by elemental analyses, IR, UV-visible and ¹H NMR spectra.

Full text of DOI:10.14233/ajchem.2014.17468

Asian Journal of Chemistry; Vol. 26, No. 20 (2014), 6940-6942
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.17468
Synthesis and Characterization of Methoxy-Substituted Salamo-Type
Bisoximes Based on Bis(aminooxy)alkane and 3-Methoxy-2-hydroxybenzaldehyde
1
2
1
1
1,*
ZONG-LI REN , SU-XIA GAO , YANG ZHANG , LI WANG and XIU-YAN DONG
1School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P.R. China
2School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P.R. China
*Corresponding author: E-mail: dxy568@163.com
Received: 25 February 2014;
Accepted: 5 May 2014;
Published online: 25 September 2014;
AJC-16044
Four new methoxy-substituted Salamo-type bisoxime compounds 6,6'-dimethoxy-2,2'-[(propylene-1,3-diyldioxy)bis(nitrilo-
methylidyne)]diphenol (H2L1), 6,6'-dimethoxy-2,2'-[(butylene-1,4-diyldioxy)bis(nitrilomethylidyne)]diphenol (H2L2), 6,6'-dimethoxy-
2,2'-[(propane-1,5-diyldioxy)bis(nitrilome-thylidyne)]diphenol (H2L3) and 6,6'-dimethoxy-2,2'-[(hexane-1,6-diyldioxy)bis(nitrilo-
methylidyne)]diphenol (H2L4) have been synthesized through condensation reactions under hot ethanol medium, respectively and
characterized by elemental analyses, IR, UV-visible and 1H NMR spectra.
Keywords: Synthesis, Salamo-type bisoxime compound, Characterization.
1,6-dibromohexane were purchased fromAlfaAesar and used
without further purification. The other reagents and solvents
were analytical grade reagents from Tianjin Chemical Reagent
Factory. The physico-chemical measurements are the same as
previous literature13.
INTRODUCTION
Salen-type compounds are a kind of linear tetradentate,
N2O2-coordinating ligands which are obtained by condensation
reaction of ketones or aldehydes with diamine. They are used
extensively in the catalysis activity, biological systems, sterili-
zation and antivirus in the last century1-5. Recently, a prefreable
class of Salen-type bisoxime ligands was reported, using an
O-alkyloxime unit [-CH=N-O-(CH2)n-O-N=CH-] instead of
the [-CH=N-(CH2)n-N=CH-] group. The large electronegativity
of oxygen atoms is expected to affect strongly the electronic
properties of the N2O2 coordination sphere, which can lead to
different and novel properties and structures of the resulting
complexes6-9. The new Salen-type compounds and their comp-
lexes play an important role in the development of coordinating
chemistry10-12. In this article, we report the synthesis of four
new Salen-type bisoxime compounds from 3-methoxy-2-
hydroxy-benzaldehyde and several bis(aminooxy)alkane with
different long-chain alkane molecules, 6,6'-dimethoxy-2,2'-
[(propylene-1,3-diyldioxy)bis(nitrilomethylidyne)]diphenol
(H2L1), 6,6'-dimethoxy-2,2'-[(butylene-1,4-diyldioxy)bis-
(nitrilo-methylidyne)]diphenol (H2L2), 6,6'-dimethoxy-2,2'-
[(propane-1,5-diyldioxy)bis(nitrilome-thylidyne)]diphenol
(H2L3) and 6,6'-dimethoxy-2,2'-[(hexane-1,6-diyldioxy)bis-
(nitrilo-methylidyne)]diphenol (H2L4) and their characterizations.
Synthetic route to Salamo-type bisoxime compounds
H2L1-H2L4 are shown in Fig. 1.
1,3-bis(Aminooxy)propane, 1,4-bis(aminooxy)butane,
1,5-bis(aminooxy)pentane and 1,6-bis(aminooxy)hexane were
synthesized according to an analogous method reported
earlier13.
Preparation of 6,6'-dimethoxy-2,2'-[(propylene-1,3-
diyldioxy)bis(nitrilomethylidyne)]diphenol (H2L1): To an
ethanolic solution (5 mL) of 3-methoxy-2-hydroxy-benzal-
dehyde (608.6 mg, 4 mmol) was added an ethanolic solution
(5 mL) of 1,3-bis(aminooxy)propane (212.2 mg, 2 mmol).
After the solution had been stirred at 55 °C for 3 h, then cooled
to room temperature. The formed white precipitate was sepa-
rated by filtration and washed successively with ethanol and
ether. The product was dried under vacuum to yield the com-
pound H2L1, Yield, 87.7 %, m.p. 437-438 K.
Preparation of 6,6'-dimethoxy-2,2'-[(butylene-1,4-
diyldioxy)bis(nitrilomethylidyne)]diphenol (H2L2): To an
ethanolic solution (5 mL) of 3-methoxy-2-hydroxybenzal-
dehyde (608.6 mg, 4 mmol) was added an ethanolic solution
(5 mL) of 1,4-bis(aminooxy)butane (240.3 mg, 2 mmol).After
the solution had been stirred at 55 °C for 3 h, then cooled to
room temperature. The formed white precipitate was separated
by filtration and washed successively with ethanol and ether.
EXPERIMENTAL
3-Methoxy-2-hydroxy-benzaldehyde (≥98 %), 1,3-di-
bromopropane, 1,4-dibromobutane, 1,5-dibromopentane and

Vol. 26, No. 20 (2014)
Synthesis and Characterization of Methoxy-Substituted Salamo-Type Bisoximes 6941
O
n
O
O
n
Br
Br
NH2NH2·H2O
Ethanol, Ar
n
O N
2
N OH
H2N O
O NH2
N O
rt, 75 h, DMF, Et3N
O
O
O
n
O
O
N
CHO
OH
OMe
N
n
Ethanol
55°C stirring
OH
H2N O
O NH2
2
HO
+
OMe
MeO
Fig. 1. Synthetic route to Salamo-type bisoxime compounds H2L1-H2L4 (n = 2-5)
The product was dried under vacuum to yield the compound
H2L2, Yield, 68.8 %, m.p. 387-388 K.
microcrystalline solid.All the compounds are stable in air and
soluble in acetone, methanol, ethanol, chloroform, dichloro-
methane, tetrahydrofuran, ethyl acetate, DMF and DMSO,
insoluble in water, ether, acetonitrile and n-hexane.
Preparation of 6,6'-dimethoxy-2,2'-[(propane-1,5-
diyldioxy)bis(nitrilome-thylidyne)]diphenol (H2L3): To a
ethanolic solution (5 mL) of 3-methoxy-2-hydroxybenzaldehyde
(152.2 mg, 1 mmol) was added an ethanolic solution (2 mL)
of 1,5-bis(aminooxy)pentane (67.1 mg, 0.50 mmol). After the
solution had been stirred at 55 °C for 4 h, then cooled to room
temperature. The light yellow precipitate was filtered and
washed successively with a mixture of ethanol and n-hexane
(v:v = 1:4) and n-hexane, respectively. The product was dried
under vacuum to yield the compound H2L3, Yield, 63.2 %,
m.p. 372-373 K.
IR spectra: The key IR spectral bands for Salamo-type
bisoxime compounds H2L1-H2L4 are given in Table-2.
TABLE-2
KEY IR SPECTRAL BANDS (cm-1) FOR SALAMO-
TYPE BISOXIME COMPOUNDS H2L1-H2L4
Comp.
ν(O-H)
ν(CH2)
ν(C=N)
ν(C=C)
ν(Ar-O)
1255
H2L1
H2L2
H2L3
H2L4
3443 2942, 2887 1606
3438 2936, 2885 1605
3441 2941, 2868 1607
3433 2947, 2885 1605
1586, 1473, 1429
1582, 1474, 1427
1596, 1475, 1425
1593, 1474, 1428
1259
1263
Preparation of 6,6'-dimethoxy-2,2'-[(hexane-1,6-
diyldioxy)bis(nitrilomethylidyne)]diphenol (H2L4): To a hot
ethanolic solution (5 mL) of 3-methoxy-2-hydroxybenzal-
dehyde (152.2 mg, 1 mmol) was added an ethanolic solution
(2 mL) of 1,6-bis(aminooxy)hexane (74.1 mg, 0.50 mmol).
After the solution had been stirred at 55 °C for 4 h, then cooled
to room temperature, the white precipitate was filtered and
washed successively with a mixture of ethanol and n-hexane
(v:v = 1:4) and n-hexane, respectively. The product was dried
under vacuum to yield the compound H2L4, Yield, 82.6 %,
m.p. 359-360 K.
1259
In the IR spectra of Salamo-type bisoxime compounds
H2L1-H2L4, the O-H stretching band of Salamo-type bisoxime
compounds H2L1-H2L4 is expected in the 3800-3300 cm-1
region. However, this frequency is generally displaced to about
3433 cm-1 due to the internal hydrogen bond OH···N=C14. Thus,
each unit of the polymeric ligands behaves as a dibasic tetra-
dentate ONNO donor.As the hydrogen bond becomes stronger,
the band width increases and this band sometimes is not detected.
Electron-donating groups on the phenolic ring increase the
electron density on the hydroxyl oxygen making the H-O bond
stronger, the absorption usually appears as a broad band in
the FT-IR spectrum. Meanwhile, the characteristic C=N stret-
ching bands of Salamo-type bisoxime compounds H2L1-H2L4
appear at 1608-1605 cm-1, respectively, indicating that 3-
methoxy-2-hydroxybenzaldehyde has been condensated with
1,3-bis(aminooxy)propane, 1,4-bis(aminooxy)butane, 1,5-
bis(aminooxy)penpane and 1,6-bis(aminooxy)hexane,
respectively and formed new Salamo-type bisoxime13,14 com-
pounds H2L1-H2L4. In addition, theAr-O stretching bands occur
at 1263-1255 cm-1 as reported for similar bisoxime compounds13.
RESULTS AND DISCUSSION
A series of new Salamo-type bisoxime compounds H2L1-
H2L4 have been synthesized and the composition are confirmed
by elemental analyses, IR, UV-visible and 1H NMR spectra.
Physical and chemistry properties: The colour, yields,
melting points and elemental analytical results of the synthe-
sized Salamo-type bisoxime compounds H2L1-H2L4 are
presented in Table-1.
Their compositions agree with the suggsted molecular
formula. Compounds H2L1-H2L4 are either white or light yellow
TABLE-1
COLOUR, YIELDS, MELTING POINTS AND ANALYTICAL DATA OF SALAMO-TYPE BISOXIME COMPOUNDS H2L1-H2L4
Elemental analysis (%): Found (Calcd.)
Compounds Colour
m.p. (K)
Yield (%)
m.f. (m.w.)
C
H
N
H2L1
H2L2
H2L3
H2L4
White
437~438
387~388
372~373
359~362
87.7
68.8
63.2
82.6
C19H22N2O6 (374.3)
C20H24N2O6 (388.4)
C21H26N2O6 (402.4)
C22H28N2O6(416.5)
60.44 (60.95)
61.74 (61.84)
63.87 (63.99)
64.55 (64.56)
6.07 (5.92)
6.53 (6.23)
7.46 (7.52)
7.67 (7.65)
7.12 (7.48)
7.16 (7.21)
6.48 (6.42)
6.27 (6.26)
White
White
White

6942 Ren et al.
Asian J. Chem.
UV-visible spectra: The UV-visible absorption spectra
Conclusion
of Salamo-type bisoxime compounds H2L1-H2L4 (Table-3) in
diluted dichloromethane solution show that the spectra of
Salamo-type bisoxime compounds H2L1-H2L4 are similar to
each other. Salamo-type bisoxime compounds H2L1-H2L4
exhibit two intense peaks at around 273 and 318 nm. The
former absorption peaks at about 273 nm can be assigned to
the π-π* transition of the benzene rings, while the latter absor-
ption peaks at about 318 nm can be attributed to the intra-
ligand π-π* transition of the C=N bonds15. It is of note that
there was no absorption around 400 nm, which are seen in the
corresponding Salen derivatives. The absorption is ascribed
to the quinoid form of H2 salen16.
In this work, a series of methoxy-substituted Salamo-type
bisoxime compounds H2L1-H2L4 that have two oxime bonds
instead of imine bonds have been designed and synthesized
by the reaction of 2 equivalents of 3-methoxy-2-hydroxybenzal-
dehyde with 1,3-bis(aminooxy)propane, 1,4-bis(aminooxy)-
butane, 1,5-bis(aminooxy)pentane and 1,6-bis(aminooxy)-
hexane under hot ethanolic medium, respectively. It is shown
that a bisoxime moiety is much more useful to assemble
supramolecular systems than a Schiff base moiety. Further
investigation on the synthesis and structures of methoxy-
substituted Salamo-type complexes with transition metal ions,
are now in progress.
ACKNOWLEDGEMENTS
TABLE-3
UV-VISIBLE SPECTRAL DATA FOR THE
SALAMO-TYPE BISOXIME COMPOUNDS H2L1-H2L4
This work was supported by the Fundamental Research
Funds for the Gansu Province Universities (212086) and the
science and technology support funds of Lanzhou Jiaotong
University (ZC2012003), which are gratefully acknowledged.
First band
Second band
C (×10-5 mol L-1)
Comp.
λmax1 (nm)
273
λmax2 (nm)
318
H2L1
H2L2
H2L3
H2L4
5.00
5.00
5.00
5.00
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