2
I. Ku ꢀz niarska-Biernacka et al. / Journal of Molecular Structure 1206 (2020) 127687
metal oxide nanoparticles with reduced graphene oxide [4] have
been used. The heterogeneous catalysts have played a very
important role in the liquid phase phenol hydroxylation due to
their easy separation and reusability, which makes the entire pro-
cess more environmental friendly. Among the heterogeneous cat-
alysts, various solid catalysts containing iron and/or copper take a
special position. From this group of materials for example: copper
modified titanium silicate [1], ferrocene particles incorporated into
(PhCl), tert-butyl hydroperoxide solution - 5.0e6.0 M in decane
(TBHP), acetonitrile (HPLC grade), dichloromethane and methanol
(UVeVis spectroscopy grade) were from Aldrich. NaY zeolite
(CBV100, Si/Al ¼ 2.83) in the powder form was obtained from
Zeolyst International.
2.2. 2- Preparation of the samples
Zr based MOFs [3], magnetically separable CuFe
phene oxide composites [4], metal containing mesoporous MCM-
1 [9,10], copper containing SBA-15 [11] and many others were
applied as catalysts for phenol hydroxylation. However, the draw-
backs of low catalytic activity and easy deactivation of the catalyst
have limited its wide application.
2 4
O reduced gra-
Synthesis of ligand: 1,2-bis((furan-2-yl)methylene)hydrazine
denoted as L). To a solution of furan-2-carbaldehyde (2.0 mmol) in
0 mL of ethanol, hydrazine hydrate (1.0 mmol) was added and the
reaction mixture was heated under reflux for 5 h. The mixture was
concentrated at reduced pressure, which induced precipitation of a
solid. The solid product formed was separated by filtration, purified
by crystallization from ethanol and then dried under vacuum.
(
1
4
Bearing it, we have prepared metal complexes encapsulated in
NaY zeolite using heterocyclic azine derivatives which have a
widespread range of applications in diverse areas such as optics,
electronics and catalysis [12,13]. Heterocyclic Schiff-base and azine
ligands bearing N, O and S heteroatoms in their structure should
exhibit improved coordination ability as well as different catalytic
activity. Therefore, several azine ligands bearing thiophene, pyrrole
and furan heterocycles have been used as versatile building blocks
for supramolecular chemistry [14e16], due to their capacity to form
dinuclear dimers or mononuclear monomers [14,16]. The presence
of two metal centers in complexes might lead to better catalytic
activities. On the other hand, less attention has been paid to their
study as ligands for metal complexes synthesis having in mind their
further application in catalysis. Tetradentate Schiff base, Salen type
transition metal complexes encapsulated in zeolite were widely
studied in hydroxylation of phenol [17]. However, there are no re-
ports for phenol hydroxylation using furanyl-azine Schiff base
complexes encapsulated in Y zeolite catalysts. On the other hand,
our previous studies showed that when binuclear iron pyrrolyl-
azine complex was entrapped into NaY zeolite, highly selective
catalysts were obtained [16]. Consequently, we decided to syn-
thesize a furanyl-azine derivative to be used as ligand on the
preparation of new heterogeneous catalysts based on the transition
metal complexes in zeolites.
1
,2-bis(Furan-2-ylmethylene)hydrazine (L) was obtained as a
ꢀ
ꢀ
brown solid (0.350 g, 93%). Mp: 121.0e123.0 C (134e136 C [15]).
1
H NMR (400 MHz, CDCl
3
)
d
¼ 6.54e6.55 (m, 2H, 2 ꢁ H-4), 6.90 (dd,
2
H, J ¼ 3.2 and 0.4 Hz, 2 ꢁ H-3), 7.60 (d, J ¼ 1.6 Hz, 2H, 2 ꢁ H-5), 8.53
1
3
(
(
(
s, 2H, 2 ꢁ N]CH) ppm. C NMR (100.6 MHz, CDCl
3
)
d
¼ 112.26
2 ꢁ C4), 116.76 (2 ꢁ C3), 145.79 (2 ꢁ C5), 149.42 (2 ꢁ C2), 150.94
2 ꢁ N]CH) ppm.
Synthesis of Cu(II) and Fe(II) complexes. To a solution of the L
ligand (0.54 mmol, 0.10 g) dissolved in 15 mL of methanol was
added of Cu(II) or Fe(II) chloride with 2:1 metal:ligand molar ratio,
then 5 mL of methanol was added. The resulted solution was stirred
and refluxed for 5 h. Complexes were formed as dark-brown solid.
After cooling, the solid products were separated by filtration and
left for 24 h at room temperature. The complexes obtained are
denoted as [M
Analytical data for the neat copper complex is as follows:
Cu LCl ]; Brown solid (yield 0.2 g, 81%). Anal. Calc. For
Cl Cu : C, 26.28; H, 1.76; N, 6.13, Cu, 27.80. Found: C,
2
LCl
4
], where M ¼ Fe or Cu.
[
C
2
2
4
10
H
8
4
2 2 2
N O
6.04; H, 1.50; N, 6.00; Cu, 28.16.
Analytical data for the neat iron complex is as follows:
[Fe
2
LCl
4
(H
2
O)
4
]; Brown solid (yield 0.2 g, 72%). Anal. Calc. For
C
2
10
H16Cl
4
2 2 2
Fe N O : C, 23.38; H, 3.14; N, 5.45; Fe, 21.70 Found: C,
2.38; H, 2.95; N, 5.52; Fe, 21.35.
Preparation of the heterogeneous catalysts. Two methods of
In the present study, Cu and Fe complexes with furanyl-azine
derivative encapsulated in NaY zeolite were prepared as hetero-
geneous catalysts and used for phenol hydroxylation. All the het-
erogeneous catalysts were characterized via FTIR, XRD, elemental
analysis, HR-CS AAS, SEM and N adsorption to investigate the
2
correlation between the catalyst and its activity. In the case of iron
encapsulation were used to prepare the heterogeneous catalysts
based on NaY zeolite and reported by us elsewhere [18e20].
Method A. A solution of L ligand (22.3 mg, 0.12 mmol) and Cu(II)
or Fe(II) chloride (0.24 mmol) in 50 mL ethanol was added to NaY
ꢀ
zeolite (previously dehydrated at 120 C overnight) suspension
complexes, M o€ ssbauer spectroscopy technique was additionally
(
2
1.5 g in 50 mL methanol). The mixture was further stirred for
applied. In addition, the effects of reaction time, different catalysts,
catalyst amount, metal content, solvent, reaction temperature and
catalyst reusability on phenol hydroxylation were studied.
ꢀ
4 h at 80 C. The solid fraction was filtered and washed with
deionized water, followed by Soxhlet extraction with ethanol. The
new heterogeneous catalysts (M
2
L-Y
A
, where M ¼ Fe or Cu) were
The main disadvantage of the homogeneous catalysts is their
problematic separation after the catalytic cycle and possibility re-
use. On the other hand, the heterogeneous catalysts (encapsu-
lated complexes) should join both advantages: (i) high catalytic
activity, due to the presence of active sites from the complexes; (ii)
easy separation/simple filtration, due to the encapsulation of the
complexes on the insoluble material (zeolite) and (iii) reusability, in
order to make the entire process more environmental friendly
ꢀ
dried in the oven at 120 C overnight under reduced pressure.
Method B. NaY zeolite was first ion-exchanged with an aqueous
solution of Cu(II) nitrate or Fe(II) chloride (0.8 mM, liquid/
ꢂ1
solid ¼ 20 mL g ) at room temperature for 24 h, and dried at
ꢀ
1
20 C overnight under reduced pressure. M ꢂ Y solid (1.2 g) was
suspended in the solution of 40 mg (0.21 mmol) ligand L in 50 mL
ꢀ
methanol and the mixture was stirred for 24 h at 80 C. After
filtration and washing, the solids were Soxhlet extracted with
ethanol and dichloromethane to remove the unreacted ligand. The
[
16,17].
new catalysts (M
at 120 C overnight under reduced pressure and characterized.
2
L-Y
B
, where M ¼ Fe or Cu) were dried in the oven
ꢀ
2
. 2- Experimental
2.1. 1- materials
2.3. 3- Physical measurements
Furan-2-carbaldehyde was from Acros Organics. Hydrazine hy-
drate, cuprizone, KBr (FTIR grade), phenol (PhOH), chlorobenzene
Room temperature Fourier Transform Infrared (FTIR) spectra of
ligand, free complexes and solid samples of diluted 4% in KBr pellets