2
M.K. Alavijeh and M.M. Amini / Polyhedron 173 (2019) 114142
to be necessary. Therefore, MOF solid acids containing hydrophobic
moieties are targeted herein as heterogeneous catalysts for the
transformation of phthalic anhydride into a related ester.
product was dried at 50 °C overnight. Anal. Calc. (Found) for [Cr3O
(BDC–SO3H)3]nÁ25H2O: C, 20.47 (19.80); H, 4.80 (4.40). The acidity
of MIL-101(Cr)–SO3H was measured according to the earlier report
[49]. In a typical procedure, 0.50 g of MIL-101(Cr)–SO3H was
immersed in a saturated aqueous solution of NaCl and stirred at
room temperature for 12 h. Subsequently, the filtrate was titrated
with a 0.1 M NaOH solution.
In this study, our objective was to introduce a dual-functional-
ized MIL-101(Cr) with –SO3H and hydrophobic moieties, for the
first time as a potent solid acid catalyst to improve yields of ester-
ification reactions by the repulsion of the produced water from the
reaction cage, and also to be able to recover and reuse catalyst.
Concomitantly, the impact of surface hydrophobicity of the cata-
lyst on the esterification yield of phthalic anhydride as a probe
reaction was investigated. In addition, to examine the effect of
alcohol type on the reaction yield in the presence and absence of
hydrophobic moieties, several alcohols were used for esterification,
and also a new ester of phthalic anhydride was introduced.
2.3. Preparation of [Cr3O(BDC–SO3H)3Àx(BDC–SO3NH3Bu)x]n
For the synthesis of [Cr3O(BDC–SO3H)3Àx(BDC–SO3NH3Bu)x]n,
100 mg of MIL-101(Cr)–SO3H was placed in a Schlenk tube and
evacuated for 2 h at ambient temperature. Then, the tube was
flushed with dry nitrogen, and solutions containing 0.03, 0.06,
and 0.09 mmol of butylamine in dry THF were added (Fig. 1). The
mixture was then stirred at ambient temperature under a nitrogen
atmosphere for 24 h. The product was collected by centrifugation
and washed two times with 2 mL of dry THF for 15 min each time,
three-times with 2 mL of dry methanol for 15 min each time, and
one time for 12 h. Finally, the product was washed four times with
2 mL of deionized water for 15 min each time, and one time for
12 h, and then was dried at 50 °C overnight [50]. Anal. Calc.
(Found) for [Cr3O(BDC–SO3H)2.7(BDC–SO3NH3Bu)0.3]n.14H2O (10%
BuNH2): C, 24.57 (25.11); H, 3.95 (3.64); N, 0.34 (0.35); for [Cr3O
(BDC–SO3H)2.4(BDC–SO3NH3Bu)0.6]nÁ11H2O (20% BuNH2): C, 26.43
(26.79); H, 3.83 (3.19); N, 0.70 (0.71); and for [Cr3O(BDC–SO3-
H)2.1(BDC–SO3NH3Bu)0.9]nÁ9H2O (30% BuNH2): C, 27.96 (27.78); H,
3.82 (3.43); N, 1.06 (0.96).
2. Experimental
2.1. Materials and instrumentation
All chemicals and solvents were purchased from Merck Chemi-
cal Company (Darmstadt, Germany), Sigma-Aldrich Chemical Com-
pany (Dorset, UK), TCI Chemicals and used without purification.
Merck precoated silica-gel 60 F254 plates were used to perform
thin-layer chromatography (TLC), and compounds were visualized
with 254 nm ultraviolet light. Column chromatography was car-
ried out on silica gel 60 (0.063–0.200 mm). Infrared spectra were
recorded on a Bomem MB-Series FTIR spectrometer. 1H, 13C, and
19F NMR data were collected on a Bruker AVANCE 300 MHz spec-
trometer utilizing CDCl3 as solvent and tetramethylsilane as inter-
nal standard. Mass spectrometry was performed with an Agilent
5975C VL MSD (ion source: EI, 70 eV). A STOE diffractometer
2.4. General procedure for catalytic reaction
In a typical catalytic test, 4 mmol of phthalic anhydride and
20 mmol of alcohol were loaded to a flask equipped with a con-
denser, and then 60 mg of MIL-101(Cr)–SO3H or [Cr3O(BDC–SO3-
equipped with Cu K
a radiation (k = 0.15418 nm) was used to
record powder X-ray diffraction (XRD) patterns. Thermogravimet-
ric analysis (TGA) was performed using a Bahr STA-503 instrument
at a heating rate of 10 °C minÀ1 under a flow of air. The SEM micro-
graphs were taken using a field emission scanning electron micro-
scope (MIRA3 TESCAN). Surface area and texture properties of the
prepared catalyst were determined by N2 physisorption technique
on a Belsorp-miniII porosimeter. The CHN elemental analysis was
accomplished using a Perkin-Elmer 2400 CHN analyzer.
H)2.4(BDC–SO3NH3Bu)0.6 n (20% BuNH2) was added as the
]
catalyst. The reaction was refluxed for 5 h, and then the mixture
was cooled to room temperature and the catalyst was separated
from the reaction mass by filtration, and 100 mL of 20% aqueous
solution of sodium carbonate was added. The reaction mass was
extracted by CH2Cl2 (50 mL Â 2) and the organic layer dried by
sodium sulfate [34]. The crude product was purified by column
chromatography using ethyl acetate/n-hexane (1:15, v:v) as an
eluent, the desired compound was collected, and the yield was
obtained by the weight of the product.
2.2. Preparation of MIL-101(Cr) and MIL-101(Cr)–SO3H ([Cr3O(BDC–
SO3H)3]n)
To evaluate the recyclability of the catalysts, the heterogeneous
To a well grinded mixture of Cr(NO3)3Á9H2O (2.0 g, 5 mmol) and
1,4-benzenedicarboxylic acid (BDC) (0.83 g, 5 mmol), 20 mL of
water was added, and the resulting mixture was sonicated for sev-
eral minutes. Subsequently, the suspension was transferred to a
Teflon-lined stainless-steel autoclave, and the autoclave was
heated at 220 °C in an oven for 24 h. After cooling the autoclave
to ambient temperature, MOF-101(Cr) was isolated by centrifuga-
tion, washed with methanol and acetone, and then was immersed
in DMF overnight at 70 °C. The product was then rewashed with
methanol and acetone and dried at 75 °C [48]. Synthesis and purity
of MIL-101(Cr) were confirmed by FTIR spectroscopy and powder
X-ray diffraction. MIL-101(Cr)–SO3H, was prepared according to
the reported procedure, with some modifications [49]. For this pur-
pose, a mixture of CrO3 (1.25 g, 12.50 mmol), monosodium 2-sul-
foterephthalic acid (3.35 g, 12.50 mmol), and 12 M hydrochloric
acid (0.91 g, 25 mmol) was dissolved into 50 mL of deionized water
and stirred for a few minutes at ambient temperature. The result-
ing mixture was then transferred to a Teflon-lined stainless-steel
autoclave, and the autoclave was heated in an oven at 180 °C for
six days. After separating the green solid product by centrifugation,
it was washed three times with distilled water and methanol. The
[Cr3O(BDC–SO3H)2.4(BDC–SO3NH3Bu)0.6]n (20% BuNH2) was iso-
lated by centrifugation, washed with CH2Cl2, dried at 50 °C, and
used in a subsequent cycle.
2.5. Characterization
Di-ethyl phthalate: FTIR (KBr, cmÀ1): 3073, 2980, 1721, 1654,
1219. 1H NMR (300 MHz, CDCl3) d (ppm): 1.18 (t, 6H, 2(CH3)),
4.20 (q, 4H, 2(–OCH2)), 7.33 (m, 2H, 2 (Ar–H)), 7.55 (m, 2H, 2
(Ar–H)). Di-trifluoroethyl phthalate: FTIR (KBr, cmÀ1): 3012, 2970,
1721, 1581, 1442, 1365, 1280, 1122, 1070, 910, 740 (Fig. S1, Sup-
plementary Information, SI). Anal. Calc. for C12H8F6O4 (Found): C,
43.63 (43.90); H, 2.44 (2.56). MS (EI): m/z (%) = 330 (4) [M+], 316
(6), 298 (10), 279 (3), 256 (8), 239 (3), 203 (7), 185 (61), 149
(27), 112 (27), 97 (26), 83 (37), 71 (60), 57 (100), 43 (83) (Fig. S2,
SI). 1H NMR (300.00 MHz, CDCl3)
d (ppm): 4.38 (q, 4H, 2
(–OCH2)), 7.54 (m, 2H, 2 (Ar–H)), 7.74 (m, 2H, 2 (Ar–H)) (Fig. S3,
SI). 13C NMR (75.43 MHz, CDCl3): 167.6 (C@O), 132.2, 130.9,
128.8 (Ar), 61.6 (–CF3), 14.1 (–CH2) (Fig. S4, SI). 19F NMR
(282.23 MHz, CDCl3): À73.53 (t, 6F, –CF3) (Fig. S5, SI). Di-1-butyl
phthalate: FTIR (KBr, cmÀ1): 3060, 2952, 2860, 1725, 1634, 1215.