Synthesis of Schiff Base Complexes of Mn(II)

Canadian Chemical Transactions
Year 2015 | Volume 3 | Issue 1 | Page 65-71
Ca
Research Article
DOI:10.13179/canchemtrans.2015.03.01.0166
Synthesis of Schiff Base Complexes of Mn(II) and Co(II) and
their Catalytic Oxidation towards Olefins and Alcohols
Imtiyaz Rasool Parrey and Athar adil Hashmi*
Department of chemistry, Jamia Millia Islamia (Central University), New Delhi (INDIA)
*
Corresponding Author: Email: dr.aahashmi@yahoo.co.in Tel:0091-11-26981717 Ext.3269
Received: February 3, 2015
Revised: March 1, 2015 Accepted: March 10, 2015
Published:
March 12, 2015
Abstract: Synthesis of two Schiff base metal complexes of Mn(II) and Co(II). The complexes were
analyzed by different Spectrochemical techniques like Vib. FT-IR spectrum - UV-vis spectrum, EPR
spectrum. The catalytic activity of both the complexes was observed in cyclohexane and benzyl alcohol
using eco-friendly, non-toxic hydrogen peroxide. Both the complexes show better activity towards the
oxidation of substrates (cyclohexane and benzyl alcohol). In both the substrates the complex Co (II)
shows better activity than Mn(II).
Keywords: Schiff base, FT-IR Spectrum, Hydrogen peroxide. Cyclohexane, benzyl alcohol
1. INTRODUCTION
Ligands containing more than one donor sites are extensively used for the preparation of metal
complexes with interesting properties. Among these ligands, Schiff bases containing hetero atoms as
donor atoms are of considerable interest due to their potential application in catalysis, medicine and
material science [1-5]. The Transition metal complexes of these ligands display varying configurations,
structural lability and sensitivity to molecular environments. The central metal ions in these complexes
act as active sites for catalyzing chemical reactions. Based on the versatile applications on these transition
metal complexes in catalytic oxidation reaction number of reports where found some reports were
oxidation is carried out using molecular oxygen at ambient conditions. In a series of communications
Taqui khan et al reported the catalytic oxidations of olefins, saturated hydrocarbons and amines using
Ru(III) EDTA complex and molecular oxygen [6,7,8].Mahesh Dalal et al observed that the rate of
oxidation of benzyl alcohol increased linearly with increase in substrate concentration using polymer
anchored Ru (III) Schiff base complex and polymer anchored Ru (III) salen complexes [9,10].Anthony
Theodore david reported the catalytic oxidation of Schiff base modified chitosan in the oxidation of
cyclohexane [11,12]. HareshG.Manyar et al reported green catalytic oxidation of alcohols in water using
highly efficient mangano silicate molecular sieves. Primary alcohols are selectively oxidized to aldehydes
and secondary alcohols are selectively oxidized to ketones [13,14 ]. I.R Parrey et al study the Catalytic
oxidation of alcohols using polystyrene EDTA Cu(II) metal complex and Catalytic oxidation of phenols
using Schiff base Cu(II) metal complex using L-histadine [15].
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2. MATERIALS AND METHODS
Manganese(II) acetate tetrahydrate (Merck), copper(II) cobalt dihydrate (Merck), The amines,
were purchased from Sigma Aldrich Chemicals Private Limited, Bangalore Orthophenylenediamine
(Lobachemie), D-glucose (SD Fine Chem Limited), sodium sulphate (Merck), sodium metaperiodate
(Merck), glacial acetic acid, hydrazine hydrate (Qualigens), soidum bicarbonate (Sisco Research
Laboratories Limited), bromine (Merck) and sodium pyruvate (Sisco Research Laboratories Limited)
were used in the present investigation. Hydrogen peroxide (Merck),cyclohexane (Qualigens),were used
for
the
catalytic
activity
studies
using
metal
complexes..
All
other
eagentswereofanalyticalreagentgradeandthesolventsemployedwereeitherof99% purity or purified by
known procedure. The EPR spectra of the complexes in DMF were recorded on Varian E-112 X/Q band
spectrophotometer at liquid nitrogen temperature and the standard used was tetracyanoethylene (TCNE)
with a g value of 2.0027. The electronic spectra were recorded in the region 200-1100 nm on a
Thermoelectron Nicolet evolution 300 UV-Vis spectrophotometer.
2.1 Synthesized of Modified aldehyde
The following procedure was adopted to synthesize quinoxaline 2 carboxaldehyde. Refluxing Dglucose (36 g, 0.2 mol) with orthophenylenediamine (21.6 g, 0.2 mol) in the presence of hydrazine
hydrate (5 mL, 0.1 mol) and glacial acetic acid (6 mL) on a boiling water bath under carbon dioxide
atmosphere (provided by the addition of a pinch of sodium bicarbonate) for 5 hours gave the compound,
2(D-arabinotetrahydroxybutyl) quinoxaline. This product was purified by recrystallisation from hot water.
The re crystallized 2(D-arabino tetrahydroxy butyl) quinoxaline (5 g, 0.02 mol) was dissolved in water
(300 mL) containing glacial acetic acid (10 mL) and sodium metaperiodate (13 g, 0.06 mol) and was kept
at room temperature with control stirring for 16 hours. It was then filtered and the filtrate was neutralised
with sodium bicarbonate. The neutral solution was then extracted with ether. The ether extract was dried
with anhydrous sodium sulphate. It was then filtered and evaporated to dryness. The resulting residue was
recrystallized from petroleum ether to give pure quinoxaline- 2-carboxaldehyde(Yield): 60%, M.P 107 °C
2.2 Preparation of Schiff base complexes of manganese and cobalt
Quinoxaldehyde (1.580 g, 0.01mol) in methanol (50 mL) was added to 2-amino 5-methylphenol
(1.550 g, 0.01 mol) in water (30 mL). The solution was then refluxed on a water bath for half an hour.
The colour of the solution turns from pale yellow to dark brown. To this hot solution, cobalt chloride
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(1.700 g, 0.01 mol) or manganese acetate tetra hydrate (2.190 g, 0.01 mol) in methanol (20 mL) was
added. Instantaneous formation of a precipitate was observed, and the refluxing was continued for three
Figure 2. Shows the Uv-vis Spectra of Cobalt Complex
hours to ensure complete precipitation. The precipitate was filtered and washed with methanol containing
water and then with acetoneFig1.
L: Yield 90%, m.p 160-165 °C, yellow colour, anal caldfo C16H15N3O(%): calcd C(72.46), H(4.21),
N(15.64); Found C (72.99), H(4.98), N(15.96); I.R( KBr Pallets, cm-1): 3330 ν(0-H), 1626 ν(CN), 1261
ν(CO )
MnL: Yield 65%, m.p 165-170 °C, Red colour, anal caldfo MnC20H23N3O8(%): calcd C(54.78), H(3.98),
N(10.69)Mn(13.96); Found C (54.83), H(4.35), N(10.66), Mn(13.96);; I.R( KBr Pallets, cm-1): 3300 ν(0H), 1606 ν(CN), 1234 ν(CO ), 465 ν(M-O), 413 ν(M-N)
CoL: Yield 85%, m.p 165-170 °C, violet colour, anal cald for CoC32H30N6O2(%): calcd C(63.73),
H(4.23), N(14.24), Co(9.75); Found C(63.70), H(4.36), N(13.97), Co(9.80);; I.R( KBr Pallets, cm-1): 3390
ν(0-H), 1664ν(CN), 1252 ν(CO ), 567 ν(M-O), 468 ν(M-N)
3 RESULT AND DISCUSSION
3.1 Vibrational spectrum
The IR spectrum of ligand and complexes shows bands at 3386 cm-1is due to the OH stretching
vibrations of Schiff base ligand. The ligand exhibits azomethine C=N stretching at 1600 cm-1and C=N of
quinoxaline ring at 1770 cm-1 [16]. There is a sharp intense band at 1665 cm-1 which shows the presence
of keto group. The majority of the bands due to the free ligand are present in the spectra of complexes. A
new broad band at around 3300 cm–1 is seen for all the complexes which may be due to the presence of
hydrated or coordinated water molecule. The strong band observed at 1633 cm–1 for the cobalt(II)
complex suggests that the Schiff base acts as a monobasic tridentate ligand. Appearance of new bands in
the spectra of all complexes in the regions 500–450 and 420–400 cm-1
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3.2UV-vis spectrum of Schiff base metal complex
Electronic spectra of the Schiff base and its complexes were taken in methanol (~5x10-4 molar)
in the range 50000-10000 cm-1. The absorption maxima of spectra are given in Fig.2. The UV-Vis
spectrum of the Schiff base shows two strong bands at 42500 and 26000 cm-1 due to benzene 𝜋 − 𝜋*,
imino 𝜋 − 𝜋* and quinoxiline transitions of Schiff base ligand transitions . The intense bands in the
complexes are observed above 30000 cm-1 are due to charge transfer and intra ligand transitions. The
electronic spectrum of the manganese (II) complex in methanol contain two intense broad band’s at
29800 and 21500 cm-1 [17]. In the electronic spectrum of Co (II) complex the d–d transitions are almost
masked by the high-intensity charge transfer bands. However, a shoulder is observed around 17000 cm -1.
Which may be assigned to the 4T1g(F) to 4T1g(P) transition and transitions in this region have been
reported for octahedral Co(II) complexes Fig.3
Figure 3.Shows the Uv-vis Spectra of Manganese Complex
3.3EPR spectrum of Schiff base Mn(II) metal complex
The spectrum at 77 K in DMSO exhibits six hyperfine lines. The lines are poorly resolved, which
may be due to the poor glass formation. The spectrum gives a g value of 1.99 with an A value of 0.00929
cm-1 Fig.4.
Figure 4. EPR Spectrum of Mn (II) Complex
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2.4Catalytic oxidation of cyclohexane
It is already known to oxidize aliphatic or cyclo aliphatic compounds in the liquid phase using
oxygen or hydrogen peroxide to corresponding alcohols and/or ketones. The chemical inertness of
hydrocarbon makes the activation of C-H bonds really difficult, usually requiring drastic conditions, such
as high temperature and pressure. The selective oxidation of cyclohexane to cyclohexanone or
cyclohexanol is of great industrial importance [18]. Over one billion tonnes of cyclohexanol and
cyclohexanone are produced each year worldwide, which are mostly used in the manufacture of the
polymers Nylon-6 and Nylon-6,6 [19,20]
2.5 Catalytic oxidation reaction
The reactions were carried out in acetonitrile as solvent, using hydrogen peroxide as the oxidant
[21], and the copper (II), iron(III) or manganese(II) complexes as the catalysts. In a typical reaction, an
aqueous solution of 30% H2O2 (1.06 mL, 10 mmol) and cyclohexane (1.08 mL, 10 mmol) were mixed in
5 mL of acetonitrile and the reaction mixture was heated at 343 K with continuous stirring in an oil. The
complex (0.010mmol) was added to their action mixture and there action was considered to be started at
this time. During the reaction, the products were analyzed using a gas chromatograph after specific
interval of time by withdrawing smalla liquot. Table 1show the effect of Catalyst on the catalytic
oxidation of cyclohexane. When the Co catalyst is used using optimum reaction conditions (10mmol
H2O2, 10mmol cyclohexane, 343K temperature Time 2hr and 0.010mmol Complex) the cyclohexanol
conversion rate is maximum but when the reaction is used for long time the adipic acid conversion
increased. In contest the Mn catalyst gives low conversion rate to cyclohexanol.
Table1. Catalytic oxidation of cyclohexane
Catalyst
%C
% Product
C-nol C-one
A-A
Co catalyst
46.22
35.10
10.60
0.52
Mn Catalyst
22.12
18.66
2.00
1.46
% C: Percentage conversion, C-nol: cyclohexanol, C-one: cyclohexanone, A-A: adipic acid
2.6 Catalytic oxidation of benzyl alcohol:
The oxidation of organic substrates is an important reaction in organic synthesis. Among them
oxidation of benzyl alcohol to benzaldehyde is an industrially important reaction. Chlorine free
benzaldehyde is a versatile chemical intermediate widely used in the manufacture of pharmaceuticals,
perfume and flavouring chemicals [22-23]. Several research groups have developed different catalytic
methods for oxidation of benzyl alcohol to benzaldehyde. Among the various methods, transition metal
Schiff base complex catalyzed oxidation is worth mentioning. Same catalytic procedure is applied to
benzyl alcohol. The results are shown in Table 2.
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Table 2. Catalytic oxidation of benzyl alcohol
Catalyst
Co catalyst
Mn Catalyst
%Product
%C
Bal
B-one
BB
48.22
36.10
11.59
0.53
20.12
18.12
2.00
nd
%C: Percentage conversion, Bal: benzaldehyde, B.one: benzanone, BB: benzyl benzoate
4. CONCLUSION
Two Schiff base complexes were synthesized successfully. Both complexes were analyzed by
spectro chemical methods. UV-vis spectrum suggested the octahedral geometry of Co (II) complexes and
tetrahedral geometry of Mn(II) complex. Both complexes were catalytic active towards the olefin and
alcohol. The percentage conversion and product conversion of both the complexes were recorded. The
complex Co(II) shows better activity than Mn(II).
ACKNOWLEDGEMENT
I am highly thankful to my supervisor, faculty members of JMI and also the UGC New Delhi for
providing me BSR fellowship.
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The authors declare no conflict of interest
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