J. Huang et al. / Journal of Molecular Catalysis A: Chemical 416 (2016) 147–153
149
(the molar ratio of diamine to bromine element in ZnPS–BrPPS
is 5:1). After the mixture was kept at 80 ◦C for 24 h under N2
atmosphere, the resin-like product was filtered and washed
with deionized water. 1a, yield: 76.5%; Found: C, 10.69; H, 1.29;
N, 2.77. Calc. for C9H13O11P3N2Na2Zn3: C, 16.39; H, 1.97; N,
4.25%. 1b, yield: 72.4%; Found: C, 12.13; H, 2.36; N, 3.15. Calc. for
C9H21O11P3N2Na2Zn3: C, 16.19; H, 3.15; N, 4.20%.
in the catalysts 2a–b and is in accordance with the results from
chemical analysis (AAS).
3.1.4. Powder X-ray diffraction
The powder XRD patterns of the parent support ZnPS–BrPPAS
and the heterogeneous catalysts 2a–b (in Fig. 1) display layered
crystalline structure. Meanwhile, XRD patterns of ZnPS–BrPPAS
manifest a broad 001 peak, accompanied with other peaks at
higher-order 00n peaks such as at 35.56◦. This also happens to
the catalyst 2a–b. Moreover, the part of inorganic phosphate in
ZnPS–BrPPAS contributes to the similar patterns at the vicinity of
24.9◦ to that of Zn3(PO4)2, whose lattice parameters is in accord
with the standard data of PDF nos. 29–1390. And the other patterns
of ZnPS–BrPPAS such as at 20.8◦ and 38.2◦ originate in the section
of zinc phosphonate in ZnPS–BrPPAS. Consequently, ZnPS–BrPPAS
is not a mixture of zinc phosphonate and zinc inorganic phosphate
but hybrid material.
On account of XRD patterns in Fig. 1, the interlayer distances (via
the Bragg equation, nꢀ = 2d sin ꢁ) of ZnPS–BrPPAS and 2a–b are all
about 13.3 Å. At the same time, the reflections also display similar
peaks, which verifies that the mesoporous structure of the parent
support ZnPS–BrPPAS remains intact upon the modification with
aryldiamine or alkyldiamine. In addition, the intensities of diffrac-
tion peaks are completely different, which may be ascribed to the
different linkers. According to the catalyst 2a, the intensities of
diffraction peaks are significantly lower than that of ZnPS–BrPPAS
due to the rigid linker p-phenylenediamine; while for the catalyst
2b, the higher intensities of diffraction peaks are owing to the flex-
ible linker 1,6-hexamethylene-diamine. Obviously, the catalyst 2a
indicates different crystalline structure to the catalyst 2b. Above all,
the special structure of ZnPS–BrPPAS, the isolation effect of linkage
on the configuration of the catalyst, and may further contribute to
the catalytic performance.
2.2.3. Synthesis of heterogeneous Mn(III) salen catalysts (2a–b)
A
solution of chiral salen Mn(III) (2.73 g, 4.30 mmol), 1a
(0.50 mmol) and an adequate amount of Et3N in THF was vigor-
ously stirred for 24 h under reflux, followed by cooling down and
neutralizing as well as evaporating. The product 2a was collected by
filtration and washed thoroughly with CH2Cl2 and deionized water
as well as dried under vacuum. The sample 2b was gained accord-
ing to the similar procedure. 2a, yield: 87.6%; Found: C, 36.51; H,
4.33; N, 3.79. Calc. for C45H64O13P3N4Na2Zn3Mn: C, 42.96; H, 5.09;
N, 4.46%. 2b, yield: 83.5%; Found: C, 33.25; H, 4.43; N, 3.44. Calc. for
C45H72O13P3N4Na2Zn3Mn: C, 42.69; H, 5.69; N, 4.42%.
3. Results and discussion
3.1. Characterizations of the supports and the heterogeneous
catalysts
3.1.1. Na and Br content of ZnPS–BrPPAS
The Na content of the support ZnPS–BrPPAS is 5.5%, which is 0.3%
lower than that of theoretical values, could probably be ascribed to
pH leading to the ratio of PO4Na to PO4H.
The chemical equations according to the Br content of are shown
below:
Na2O2+RBr+NaHCO3 → NaBr+CO2 ↑ +H2O
NaBr+AgNO3 → AgBr ↓ +NaNO3
R = aliphatic hydrocarbon
3.1.5. Nitrogen adsorption–desorption isotherms
The Br content of the support ZnPS–BrPPAS is 12.6%, which
is approximate to the theoretical values. On account of this, the
empirical formulate of ZnPS–BrPPAS could be denoted as:
As can be seen in Fig. 2, according to ZnPS–BrPPAS and 2a as well
as 2b, the nitrogen adsorption–desorption isotherms are character-
istic type V, with a sharp increase in N2 adsorption at higher P/P0
values (∼0.9) and a distinct hysteresis loop (type H1). And BJH anal-
ysis gives a broad and non-uniform distribution of pore size. Some
are distributed below 2 nm and some are in the scope of 2–50 nm
as well as the others are over 50 nm. On account of the BET treat-
ment of the isotherms, ZnPS–BrPPAS indicates low specific surfaces
areas (9.2 m2 g−1) and pore volume (4.3 × 10−2 cm3 g−1) as well as
Zn3(PO4Na)1.5(PO4H)0.5[O3PCH2CH2CH2Br]
3.1.2. Br content of catalysts 2a and 2b
The Br content of the catalysts 2a and 2b is 1.9% and 2.8% respec-
tively. Allowing for the Br content of ZnPS–BrPPAS, it could be
deduced that the reactions between ZnPS–BrPPAS and diamine are
not complete. Therefore, there are still some residuary Br element
in the catalysts 2a and 2b, which are unreacted with diamine.
3.1.3. FT-IR spectra
The FT-IR spectra of the parent support ZnPS–BrPPAS and the
heterogeneous catalysts 2a–b are shown in Fig. S1. The strong band
at 3400 cm−1 is ascribed to the OH, which verifies the presence of
surface-bound or intercalated water. The characteristic bands of the
chiral Mn(III) salen complexes could be observed in the spectra of
heterogeneous catalysts. The bands at 3100, 2300, 1650, 850 cm−1
are due to C H vibration of propyl groups and the band assigned to
C
N stretching vibrations of chiral Mn(III) salen is seen at around
1630 cm−1. The absorption band at 1670 cm−1 is attributed to N
H
plane bending vibration of aromatic amine, which is differentiated
to that of the aliphatic amine compound in this region of the spec-
trum. The strong adsorptions at 1400 and 1077 cm−1 are due to the
phosphonate and phosphate stretching vibrations. In addition, after
the immobilization of chiral salen Mn(III) onto diamine-modified
ZnPS–BrPPAS, the C Br peak at 550 cm−1 in the ZnPS–BrPPAS is
still could be identified, which confirms the presence of Br element
Fig. 1. XRD of the heterogeneous catalyst 2b (A), ZnPS–BrPPAS (B) and the hetero-
geneous catalyst 2a (C).