Synthesis and characterization of nitro salamo-type Bisoxime compounds

Article abstract of DOI:10.14233/ajchem.2013.15445

A series of nitro salamo-type bisoxime compounds have been synthesized from 2-hydroxy-5-nitrobenzaldehyde and 1,2-bis(aminooxy)- ethane, 1,3-bis(aminooxy)propane, 1,4-bis(aminooxy)butane or 1,5-bis(aminooxy)pentane in ethanol medium, respectively and characterized by elemental analyses as well as IR, UV-visible and ¹H NMR spectroscopy.

Full text of DOI:10.14233/ajchem.2013.15445

Asian Journal of Chemistry; Vol. 25, No. 15 (2013), 8759-8761
http://dx.doi.org/10.14233/ajchem.2013.15445
Synthesis and Characterization of Nitro Salamo-Type Bisoxime Compounds
*
GANG LI , LI WANG, YU-HUA YANG, MENG-MENG ZHAO and YU-JIE ZHANG
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P.R. China
*Corresponding author: E-mail: li_gang78@126.com
(Received: 7 March 2013;
Accepted: 29 August 2013)
AJC-14042
A series of nitro salamo-type bisoxime compounds have been synthesized from 2-hydroxy-5-nitrobenzaldehyde and 1,2-bis(aminooxy)-
ethane, 1,3-bis(aminooxy)propane, 1,4-bis(aminooxy)butane or 1,5-bis(aminooxy)pentane in ethanol medium, respectively and charac-
terized by elemental analyses as well as IR, UV-visible and 1H NMR spectroscopy.
Key Words: Salamo-type bisoxime compound, Synthesis, Characterization.
were measured by the use of a microscopic melting point
apparatus made in Beijing Taike Instrument Limited Company
and the thermometer was uncorrected.
INTRODUCTION
The favourable ligand properties of tetradentate Schiff
bases like salen (N,N'-bis(salicylidene)-1,2-ethylenediamine),
salpr (N,N'-bis(salicylidene)-1,3-propanediamine), salbu
(N,N'-bis(salicylidene)-1,4-butanediamine) and their deriva-
tives have ensured continued interest in their metal complexes
for many years1-5. Comparing the ligand properties of salen
and its oxime-based analogue salamo, the salamo derivatives
are at least 104 times more stable than salen derivatives and
the large electronegativity of oxygen atoms is expected to affect
strongly the electronic properties of N2O2 coordination sphere,
which can lead to different and novel properties and structures
of the resulted complexes6-9. Thus, we have recently studied
some novel salen-type bisoxime chelating compounds on the
basis of O-alkyloxime moiety (-CH=N-O-(CH2)n-O-N=CH-)
instead of the imine (-CH=N-(CH2)n-N=CH-) group10. Here
we report the synthesis and characterization of a series of nitro-
group substituted salamo-type bisoxime compounds.
General procedure: Synthetic route to salamo-type
bisoxime compounds H2L1-H2L4 is shown in Fig. 1. 1,2-Bis-
(aminooxy)ethane, 1,3-bis(aminooxy)propane, 1,4-bis-
(aminooxy)butane and 1,5-bis(aminooxy)pentane were
synthesized according to an analogous method reported
earlier7,10
.
n
O
O
N
CHO
N
OH
n
O
ethanol
2
O2N
OH HO
H2N
O
NH2
NO2
+
O2N
H2L1: n = 1; H2L2: n = 2; H2L3: n = 3; H2L4: n = 4
Fig. 1 Synthetic route to salamo-type bisoxime compounds H2L1-H2L4
Preparation of 4,4'-dinitro-2,2'-[ethylenedioxybis
(nitrilomethylidyne)]diphenol (H2L1): To an ethanolic
solution (5 mL) of 5-nitro-2-hydroxybenzaldehyde (157.1 mg,
1 mmol) was added an ethanol solution (2 mL) of 1,2-
bis(aminooxy)ethane (45.1 mg, 0.50 mmol). After the solution
had been stirred at 58 ºC for 2 h, when cooled to room tempe-
rature, the pale-yellow precipitate was filtered and washed
successively with ethanol and ether, respectively. The product
was dried under reduced pressure and purified with recrysta-
llization from ethanol to obtain white crystalline salamo
compound H2L1.
EXPERIMENTAL
2-Hydroxy-5-nitrobenzaldehyde (≥ 98 %), 1,2-dibromo-
ethane, 1,3-dibromopropane, 1,4-dibromobutane and 1,5-
dibromopentane were purchased from Alfa Aesar and used
without further purification. The other reagents and solvents
were analytical grade reagents from Tianjin Chemical Reagent
Factory. C, H and N analyses were carried out with a GmbH
VariuoELV3.00 automatic elemental analyzer. IR spectra were
recorded on a VERTEX70 FT-IR spectrophotometer using
KBr pellets. UV/visible absorption spectra were recorded on
Preparation of 4,4'-dinitro-2,2'-[(propylene-1,3-
diyldioxy)bis(nitrilomethylidyne)]diphenol (H2L2): To an
ethanolic solution (4 mL) of 5-nitro-2-hydroxybenzaldehyde
1
a Shimadzu UV-2550 spectrometer. H NMR spectra were
recorded on a Mercury-400BB spectrometer. Melting points

8760 Li et al.
Asian J. Chem.
(157.3 mg, 1 mmol) was added an ethanolic solution (2 mL)
of 1,3-bis(aminooxy)propane (53.2 mg, 0.50 mmol). The
solution had been stirred at 58 ºC for 4 h. The formed preci-
pitate was separated by filtration and washed successively
with ethanol and ether, respectively. The product was dried
under reduced pressure to obtain white crystalline compound
H2L2.
The colour, yields, melting points and elemental analytical
results of the synthesized salamo-type bisoxime compounds
H2L1-H2L4 are presented in Table-1. Their compositions agree
with the formulae.All the compounds are pale yellow or white
microcrystalline solid, stable in air and soluble in acetone,
chloroform, dichloromethane, tetrahydrofuran, ethyl acetate,
acetonitrile, DMF and DMSO, insoluble in water, ether and
n-hexane. In addition, H2L1 and H2L2 are soluble in hot ethanol
and methanol, but H2L3 and H2L4 are insoluble in hot ethanol
and methanol.
Preparation of 4,4'-dinitro-2,2'-[(1,4-butylenediyl-
dioxy)bis(nitrilomethylidyne)]diphenol (H2L3): To an
ethanolic solution (4 mL) of 5-nitro-2-hydroxybenzaldehyde
(167.4 mg, 1.00 mmol) was added an ethanolic solution (2 mL)
of 1,4-bis(aminooxy)butane (60.0 mg, 0.50 mmol). After the
solution had been stirred at 65 ºC for 5 h, the mixture was
filtered, washed successively with ethanol and ether, respec-
tively. The product was dried under reduced pressure and
purified with recrystallization from ethanol to obtain white
crystalline compound H2L3.
IR Spectra: IR spectra of the salamo-type bisoxime
compounds H2L1-H2L4 are given in Table-2. In the IR spectra
of the H2L1-H2L4, the bands due to characteristic C=N stretching
absorption bands appear11 at 1614-1609 cm-1. TheAr-O stretching
frequencies appear within 1233-1245 cm-1 as reported for similar
bisoxime compounds12. These provide evidence for the forma-
tion of the title compounds. The O-H stretching frequency of
the bisoxime compound is expected in the 3800-3300 cm-1
region, but this frequency is generally displaced to ca. 3424
cm-1 because of the internal hydrogen bond OH···N=C10 here
a strong band at 3439-3429 cm-1 was observed in the title
compounds H2L1-H2L4 and assigned to phenolic alcohol
stretching absorption bands. In addition, in the 1596-1457 cm-1
region, the observed bands were attributed to aromatic C=C
vibrations.
UV-visible spectra and 1H NMR data: The UV-visible
spectra of H2L1-H2L4 in 5 × 10-5 mol/L chloroform solution
are presented in Table-3. UV-visible spectra of H2L1-H2L4
exhibit two intense peaks at around 275 and 320 nm. The
former absorption peak at about 275 nm can be assigned to
the π-π* transition of the benzene rings, while the latter can be
attributed to the intra-ligand π–π* transition of the C=N bonds13.
Preparation of 4,4'-dinitro-2,2'-[(1,5-propanediyl-
dioxy)bis(nitrilomethylidyne)]diphenol (H2L4): To an
ethanolic solution (4 mL) of 5-nitro-2-hydroxybenzaldehyde
(157.6 mg, 1.00 mmol) was added an ethanolic solution (2 mL)
of 1,5-bis(aminooxy)pentane (68.0 mg, 0.50 mmol). After the
solution had been stirred at 55 ºC for 4 h, the mixture was
filtered, washed successively with ethanol and ether, respec-
tively. The product was dried under reduced pressure and
purified with recrystallization from ethanol to obtain white
crystalline title compound H2L4.
RESULTS AND DISCUSSION
A series of salamo-type bisoxime compounds H2L1-H2L4
have been synthesized with good yields and the composition
are confirmed by elemental analyses, IR, UV-visible spectra
and 1H NMR data.
TABLE-1
COLOUR, YIELDS, MELTING POINTS AND ANALYTICAL DATA OF SYNTHESIZED BISOXIME COMPOUNDS (H2L1-H2L4)
Elemental analysis (%):Found (calcd.)
Compound
Colour
m.p. (ºC)
Yield(%)
m.f.(m.w.)
C
H
N
H2L1
H2L2
H2L3
H2L4
Pale yellow
White
202-203
83.3
81.6
76.6
73.2
C16H14N4O8 (390.3)
C17H16N4O8(404.3)
C18H18N4O8(418.4)
C19H20N4O8(432.4)
49.12(49.24)
50.38(50.50)
51.62(51.68)
52.74(52.78)
3.59(3.62)
3.93(3.99)
4.30(4.34)
4.63(4.66)
14.32(14.35)
13.84(13.86)
13.34(13.39)
12.92(12.96)
184.5-185.5
189.5-190.5
139.5-140.5
White
White
TABLE-2
KEY IR BANDS (cm-1) OF THE SALAMO-TYPE BISOXIME COMPOUNDS (H2L1-H2L4)
Compound
ν(O-H)
ν(Ar-O)
ν(C=N)
ν(C-C)benzene ring
ν(CHarom
)
ν(CH2)
H2L1
H2L2
H2L3
H2L4
3435
3429
3439
3433
1236
1233
1245
1241
1613
1614
1609
1609
1573,1521, 1483
1580,1542, 1471
1592,1548, 1467
1596,1543, 1458
3087
3093
3095
3096
2987,2891
2941,2880
2953,2880
2953,2880
TABLE-3
UV-VIS SPECTRA AND 1H NMR DATA OF THE SALAMO-TYPE BISOXIME COMPOUNDS (H2L1-H2L4)
Compound
H2L1
π- π* (nm)
1H NMR (400 MHz, DMSO-d6, δ/ppm)
275, 318
4.43 (s, 4H), 7.01 (d, J = 9.2 Hz, 2H), 8.10 (dd, J = 9.2, 2.6 Hz, 2H), 8.34 (d, J = 2.6 Hz, 2H), 8.36 (s, 2H),
10.20 (s, 2H)
H2L2
H2L3
H2L4
275, 318
276, 320
276, 320
2.38 (d, J = 8.8 Hz, 2H), 4.40 (s, 4H), 6.98 (d, J = 9.0 Hz, 2H), 8.08 (dd, J = 9.0, 2.8 Hz, 2H), 8.25 (d, J = 2.4
Hz, 2H), 8.30 (s, 2H), 9.98 (s, 2H)
2.43 (s, 4H), 4.38 (s, 4H), 6.97 (d, J = 8.8 Hz, 2H), 7.89 (dd, J = 8.6, 2.4 Hz, 2H), 8.24 (d, J = 2.6 Hz, 2H),
8.29 (s, 2H), 9.95 (s, 2H)
2.40 (d, J = 7.8 Hz, 2H), 2.48 (s, 4H), 4.26 (s, 4H), 6.90 (d, J = 7.6 Hz, 2H), 7.78 (dd, J = 8.0, 2.6 Hz, 2H),
8.20 (d, J = 2.6 Hz, 2H), 8.24 (s, 2H), 9.90 (s, 2H)

Vol. 25, No. 15 (2013)
Synthesis and Characterization of Nitro Salamo-Type Bisoxime Compounds 8761
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8.36 ppm indicating the the existence of oxime bonds15.
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A new series of salamo-type compounds H2L1-H2L4 that
have two oxime bonds instead of imine bonds have been
designed and synthesized by the reaction of 2 equivalents of 2-
hydroxy-5-nitrobenzaldehyde with 1,2-bis(aminooxy)ethane,
1,3-bis(aminooxy)propane, 1,4-bis(aminooxy)butane or 1,5-
bis(aminooxy)pentane under mild conditions, respectively. The
salamo-type compounds may be promising units for the cons-
truction of supramolecular complexes.
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