Application of an immobilized ionic liquid for the preparation of hydroxylamine via hydrolysis of cyclohexanone oxime

Article abstract of DOI:10.1002/zaac.202000370

Preparation of hydroxylamine via hydrolysis of cyclohexanone oxime was studied over porous SiO₂ supported acid ionic liquid catalyst. The catalyst [SPIPTES]CF₃SO₃@SiO₂ was prepared through sol-gel method and characterized by elemental analysis, IR and TG, etc. Various parameters such as reaction temperature and time, catalyst amount were investigated systematically. The optimized reaction conditions investigated were catalyst:cyclohexanone oxime (mass ratio) 4 : 1, conducted at 60 °C for 1 h. Since the present hydrolysis reaction is controlled by thermodynamics, the conversion of cyclohexanone oxime could not be very high. However, reasonable result was achieved under the optimized reaction conditions. Cyclohexanone oxime conversion was 38.41 % and NH₂OH yield was 37.65 %. Additionally, combining experiments with density functional theory calculations, a possible catalyst structure and reaction pathway involved protonated cyclohexanone oxime mechanism was proposed for the present hydrolysis in this study.

Full text of DOI:10.1002/zaac.202000370

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.202000370
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
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Application of an immobilized ionic liquid for the
preparation of hydroxylamine via hydrolysis of
cyclohexanone oxime
Shuangyu Wang,[a] Jiaqi Liu,[a] Peng Cheng,[a] Zhihui Li,[a] Dongsheng Zhang,*[a]
Qiusheng Yang,*[a] Xinqiang Zhao,[a] and Yanji Wang[a]
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Preparation of hydroxylamine via hydrolysis of cyclohexanone
oxime was studied over porous SiO2 supported acid ionic liquid
catalyst. The catalyst [SPIPTES]CF3SO3@SiO2 was prepared
through sol-gel method and characterized by elemental analy-
sis, IR and TG, etc. Various parameters such as reaction
temperature and time, catalyst amount were investigated
systematically. The optimized reaction conditions investigated
were catalyst:cyclohexanone oxime (mass ratio) 4:1, conducted
controlled by thermodynamics, the conversion of cyclohexa-
none oxime could not be very high. However, reasonable result
was achieved under the optimized reaction conditions. Cyclo-
hexanone oxime conversion was 38.41% and NH2OH yield was
37.65%. Additionally, combining experiments with density
functional theory calculations, a possible catalyst structure and
reaction pathway involved protonated cyclohexanone oxime
mechanism was proposed for the present hydrolysis in this
study.
°
at 60 C for 1 h. Since the present hydrolysis reaction is
Introduction
hydroxylamine salt and ketones as raw materials in the
industrial process. Thus, it was taken for granted that the
reverse reaction as hydrolysis of oximes to form hydroxylamine
is not practicable. Fortunately, with the development of
titanium silicalite catalyst and its application to direct synthesis
of oximes from ketones,[11] the oximes can be produced easily
without using hydroxylamine salt. From this point of view, the
process of synthesizing NH2OH from the hydrolysis of oximes
(Reaction (1)) is proposed to overcome above-mentioned
drawbacks.[12]
Hydroxylamine (NH2OH) is an important intermediate for the
production of ɛ-caprolactam. It has aroused extensive attention
in virtue of their applications such as pharmaceutical,[1]
pesticide,[2] rubber,[3] dye,[4] military[5] and nuclear industries.[6]
Nowadays much effort has been devoted to preparing NH2OH.
The common way is neutralization method. Inorganic base
reacts with hydroxylamine salt to make hydroxylamine.[7]
Another approach is an alcohol reaction. This process needs
alkali metal oxide reacting with alcohol to form an alkoxide,
and then the alkoxide reacting with the hydroxylamine salt to
give hydroxylamine.[8] However, these methods suffer from
some drawbacks like complicated reaction process, the corro-
sive material handling, producing by-products and using
inorganic bases. Recently, Mantegazza[9] used ammonia, hydro-
gen peroxide as raw materials to synthesize NH2OH directly
over titanium silicalite catalyst. However, the amount of
ammonia employed in this process is much larger than that of
hydrogen peroxide, and the yield of hydroxylamine is too low
(<1%) to apply to industry.
(1)
Up till now, there are several types of catalysts approaching
for the hydrolysis reaction. Firstly, inorganic acids like sulfuric
acid and hydrochloric acid are used as catalyst, although the
hydrolysis reaction rate of oximes in the acidic solution is very
high, the conversion of oximeis still unsatisfied. Thus the
reaction tended to be controlled by thermodynamics rather
than dynamics.[10] However, the process suffers from some
drawbacks, such as corrosion of the equipment and discharge
pollution. Second route involves a subcritical water catalytic
system carried out under severe reaction condition.[13] And the
third approach involves a new catalytic system to hydrolysis of
cyclohexanone oxime, which includes a liquid mixture of ionic
liquids (ILs) 1-butyl-3-methylimidazole and CuCl2, FeCl3 or other
metal chlorides.[14] The homogeneous ionic liquid catalytic
system overcomes the above-mentioned difficulties such as
corrosion and severe condition. But it has several drawbacks in
terms of separation and recycling of ILs.[15]
In addition, hydroxylamine can also be produced from
hydrolysis of oximes (cyclohexanone oxime, 2-butanone oxime,
etc).[10] Actually, synthesis of oximes is conducted using
[a] S. Wang, J. Liu, P. Cheng, Z. Li, Prof. D. Zhang, Prof. Q. Yang,
Prof. X. Zhao, Prof. Y. Wang
Hebei Provincial Key Lab of Green Chemical Technology and High
Efficient Energy Saving
Hebei Province Technology Institute of Green Chemical Industry
School of Chemical Engineering and Technology
Hebei University of Technology
Tianjin (China), 300130
E-mail: zds1301@hebut.edu.cn
yqiusheng@hebut.edu.cn
Z. Anorg. Allg. Chem. 2021, 647, 742–750
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Journal of Inorganic and General Chemistry
ARTICLE
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In recent years, acid ILs have drawn considerable attentions
hexanone oxime over porous SiO2 supported acid ionic liquid
catalyst.
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as an environmentally benign catalyst owing to their unique
characteristics such as low melting point, negligible volatility,
high solubility, high thermal stability and tunable acidity.[16]
However, several drawbacks of the traditional ionic liquids Results and Discussion
including difficulty of product separation and catalyst recovery,
largely restricted their widespread practical applications.[17] For
these reasons, many works have been focused on supported ILs
over different materials, such as silica,[18] polymers,[19] and
magnetic materials.[20] The produced mesoporous silica using
TEOS as silica source possessed the excellent characteristics
such as stable mesoporous structure, high surface area, control-
lable pore size and a large amount of silanol group. These
advantageous characteristics made mesoporous silica an attrac-
tive solid support in the field of catalysis and functional
materials.[21] These excellent characteristics made the mesopo-
rous silica an attractive solid support for the preparation of
immobilized ionic liquid catalyst. Hassan[22] loaded
trifluoromethylsulfonyl ionic liquids onto silicon dioxide by
physical impregnation to prepare the supported catalyst, which
was used for the adsorption of lead ions and obtained good
results (�99%). Seyed[23] reported that methyl imidazole
chloride ionic liquid was loaded onto SiO2 by chemical bond
method, being as catalyst for dehydrogenation of formic acid.
Robabeh[24] studied that SiO2-supported N-methylimidazolium
chloride ILs was used for oxidation of olefins into their
corresponding epoxides. Wang[25] pointed out that 1-methyl-3-
(triethoxylsililyl propyl) imidazole chloride was directly fixed in
silica gel by covalent bond for removing sulfur compounds
from fuel. Han[26] successfully synthesized sulfonated ionic liquid
supported by silica gel, which showed excellent activity in
synthesis of glycerol monolaurate. However, there were few
studies about the preparation of immobilized Brønsted acidi ILs
catalyst using TEOS as silica source, and its application for
hydrolysis of cyclohexanone-oxime.
Reaction optimization
Effect of different supported ILs catalysts
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Since the hydrolysis of cyclohexanone oxime to NH2OH is
controlled by thermodynamics,[10] and the conversion of cyclo-
hexanone oxime could not be very high. The activity of
different supported ILs catalysts prepared by impregnation or
sol-gel method is listed in Table 1. From which it can be found
that, the main products are cyclohexanone and hydroxylamine.
All the supported ILs catalysts have some activity toward the
hydrolysis. The supported ionic liquid 1-butylsulfonate-3-meth-
ylimidazolium trifluoromethanesulfonate catalyst gives 18.67%
cyclohexanone oxime conversion (XCyoÀ O) with 11.19% hydroxyl-
amine yield (YNH2OH). While for [SPIPTES]CF3SO3/SiO2 catalyst, the
conversion of cyclohexanone oxime increases to 37.13% (the
NH2OH yield is 36.69%). So the [SPIPTES]CF3SO3/SiO2 catalyst
seem to be a better choice for the reaction. However, when the
[SPIPTES]CF3SO3/SiO2 was recycled and used for the second
time, the cyclohexanone oxime conversion was decreased to
24.49%. A similar trend was found over the other supported ILs
catalysts prepared by the impregnation method. The catalytic
activity is greatly decreased, and almost half of the activity is
lost on these recycled catalysts (No. 1~6). The reusability of the
prepared catalyst is not satisfactory and the activity loss of the
catalyst is great.
As for [SPIPTES]CF3SO3@SiO2-5 catalyst (No. 8), it was
prepared by sol-gel method. The cyclohexanone oxime con-
version is 38.41% on fresh catalyst. For the recycled catalyst,
the conversion is still relatively high (35.52%). It means that
ionic liquids grafted by chemical bonding (proved by IR, BET
and SEM in supporting information) have better stability than
that of catalysts prepared by impregnation. For this reason, the
[SPIPTES]CF3SO3@SiO2 catalyst was selected for further optimiza-
tion.
Therefore, the objective of this study was to investigate the
possibility of using supported acid ionic liquids as catalyst in
the hydrolysis reaction of cyclohexanone oxime. Various
parameters including different catalyst, catalyst amount, reac-
tion temperature and time, were investigated for optimization
of the hydrolysis process. In the course of this investigation, we
achieved a novel route for synthesis of NH2OH from cyclo-
Table 1. Effect of different supported ILs catalysts on hydrolysis of cyclohexanone oxime.
No.
Catalyst sample
Fresh catalyst
CyoÀ O (%)
Recycled catalyst
Cyo-O (%) NH2OH (%)
X
Y
NH2OH (%)
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Y
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1-butylsulfonate-3-methylimidazolium trifluoromethanesulfonate/SiO2
N-butylsulfonate pyridinium tosylate/SiO2
N-propylsulfonate pyridinium hydrogensulfate/SiO2
1-propylsulfonic-3-methylimidazolium trifluoroacetate/SiO2
1-butyl-3-methyl-imidazolium-tosylate/SiO2
1-propylsulfonate-3-methylimidazolium trifluoromethanesulfonae/SiO2
[SPIPTES]CF3SO3/SiO2
[SPIPTES]CF3SO3@SiO2-5
18.67
23.39
26.89
27.59
34.39
34.87
37.13
38.41
11.19
12.99
17.28
19.88
28.71
29.32
36.69
37.65
14.52
15.91
16.19
17.56
20.63
20.86
24.49
35.52
10.34
10.61
13.83
15.04
18.75
19.34
23.34
34.86
°
Reaction conditions: cyclohexanone oxime=0.5 g, H2O=30 mL, ILs/SiO2 catalyst amount=2 g, temperature=60 C, time=1 h.
Z. Anorg. Allg. Chem. 2021, 742–750
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Journal of Inorganic and General Chemistry
ARTICLE
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Effect of different sol-gel conditions for [SPIPTES]
CF3SO3@SiO2
other catalysts with using templating agent, the activity was
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improved greatly. It indicates that adding templating agent is
beneficial to improve the activity of the catalyst. PEO-PPO-PEO
addition amount also can affect the catalytic activity. With the
increasing of template agent from 1 g to 4.95 g ([SPIPTES]
CF3SO3@SiO2-6), the loss of catalytic activity decreases from
5.32% to 2.62%, when PEO-PPO-PEO amount increased to 6 g,
catalytic activity loss increases slightly. It means that the
addition of template agent is needed to reach a certain amount.
Otherwise, it would hinder the grafting process[27] as well as its
catalytic activity. Based on these results, the [SPIPTES]
CF3SO3@SiO2-6 catalyst was taken as a preferred catalyst and
used for further optimization.
A series of [SPIPTES]CF3SO3@SiO2 catalysts were prepared using
different sol-gel process. The activity of the fresh and recycled
catalysts was measured. The results are shown in Table 2. The
addition of H2O and sol-gel time has important impacts on the
activity of [SPIPTES]CF3SO3@SiO2 catalysts. With the addition of
H2O from 15 mL to 45 mL, cyclohexanone oxime conversion
increases from 31.32% to 36.37% over the fresh catalysts. When
the catalysts were used for second time, the conversion
decreased obviously (see Table 2). As the addition amount of
H2O increases to 55 mL, the conversion of cyclohexanone oxime
decreases slightly to 36.01%. The reason may be that with the
increase of water added, the solution mixture is gradually
uniform and the dispersion of each material becomes better,
which is conducive to the grafting of ionic liquid. However,
excessive water will reduce the concentration of each sub-
stance, leading to the relative dilution of system concentration
and the decrease of solution viscosity, which makes it difficult
to form glue.
The effect of sol-gel time on catalyst activity was also
examined. With the increase of sol-gel time from 1 h to 4 h, the
activity loss (Δ) over these catalysts decreases gradually from
3.32% to 2.62%. With further increasing of sol-gel time to 6 h,
the activity loss increases to 3.62%. Thus 4 h was a better
choice for the present sol-gel process.
Moreover, the loss of catalyst activity was also increased
from 2.62% to 4.06% with the decreasing of prehydrolysis time
from 7 h to 2 h. It maybe that the uniform mixing of reaction
liquid need more time, which is favorable for the bonding
between ionic liquid and silica. A suitable sol-gel time is 7 h.
In addition, when [SPIPTES]CF3SO3@SiO2-16 catalyst was
prepared without adding templating agent (PEO-PPO-PEO). It
gives only 25.31% cyclohexanone oxime conversion. For the
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Effect of reaction temperature
The effect of reaction temperature was explored. The results are
shown in Figure 1. It can be seen that the conversion of
cyclohexanone oxime (XCyoÀ O), as well as the yield of NH2OH
(YNH2OH), increases as the reaction temperature is raised from
°
°
40 C to 60 C. Since the hydrolysis reaction of cyclohexanone
oxime is an endothermic reaction, the increase in temperature
favors the hydrolysis process.[10] However when the temperature
°
exceed 60 C, the conversion tends to be flat (38.26%~39.08%).
Meanwhile, the NH2OH product would be decomposed at high
°
temperature. Hence 60 C was chosen as a suitable reaction
temperature.
Table 2. Effect of different preparation conditions on the hydrolysis reaction.
Catalyst
H2O (mL)
Sol-gel time (h)
Prehydrolysis time (h)
Template agent (g)a
XCyo-O (%)
1stb
2ndc
Δd
[SPIPTES]CF3SO3@SiO2-1
[SPIPTES]CF3SO3@SiO2-2
[SPIPTES]CF3SO3@SiO2-3
[SPIPTES]CF3SO3@SiO2-4
[SPIPTES]CF3SO3@SiO2-5
[SPIPTES]CF3SO3@SiO2-6
[SPIPTES]CF3SO3@SiO2-7
[SPIPTES]CF3SO3@SiO2-8
[SPIPTES]CF3SO3@SiO2-9
[SPIPTES]CF3SO3@SiO2-10
[SPIPTES]CF3SO3@SiO2-11
[SPIPTES]CF3SO3@SiO2-12
[SPIPTES]CF3SO3@SiO2-13
[SPIPTES]CF3SO3@SiO2-14
[SPIPTES]CF3SO3@SiO2-15
[SPIPTES]CF3SO3@SiO2-16
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25
45
55
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45
45
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1
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1
4
6
4
4
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4
4
4
4
4
4
7
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7
7
7
7
7
5
3
2
7
7
7
7
7
7
4.95
4.95
4.95
4.95
4.95
4.95
4.95
4.95
4.95
4.95
6
31.32
33.27
36.37
36.01
33.61
38.41
37.88
35.21
34.68
34.31
33.25
32.56
31.24
30.55
29.34
25.31
26.85
28.02
31.94
30.73
30.29
35.79
34.26
32.23
30.86
30.25
29.85
28.01
26.98
26.92
24.02
19.63
À 4.47
À 5.25
À 4.43
À 5.28
À 3.32
À 2.62
À 3.62
À 2.98
À 3.82
À 4.06
À 3.40
À 4.55
À 4.26
À 4.63
À 5.32
À 5.68
4
3
2
1
0
a Template agent is polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO). b 1st is the conversion of cyclohexanone
c
d
oxime over the fresh catalyst. 2nd is the conversion of cyclohexanone oxime over the recycled catalyst. the activity loss (Δ=2nd-1st)
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Reaction conditions:cyclohexanone oxime=0.5 g, catalyst:
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3
°
cyclohexanone oxime=4, H2O=30 mL, 60 C
Effect of catalyst/cyclohexanone oxime ratio
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The influence of catalyst ([SPIPTES]CF3SO3@SiO2-6)/cyclohexa-
none oxime mass ratio was investigated. The results are shown
in Figure 3. It showed that the ratio has a significant effect on
the hydrolysis. Increasing catalyst:cyclohexanone oxime mass
ratio (1:1~4:1) would gradually increase the conversion of
cyclohexanone oxime from 13.6% to 37.36%. An increase of
catalyst amount leads to acidic sites increase, which is beneficial
to the reaction. However, when the ratio is increased from 4:1
to 5:1, the conversion tends to be gentle. And further
increasing the ratio does not meet economic requirements.
Therefore, a suitable mass ratio of catalyst:cyclohexanone oxime
is 4:1.
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Figure 1. Effect of temperature on the hydrolysis of cyclohexanone-
oxime.
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Reaction conditions: cyclohexanone oxime=0.5 g,catalyst:
cyclohexanone oxime=4, H2O=30 mL, 1 h
Reaction conditions:(c) cyclohexanone oxime=0.5 g,
°
H2O=30 mL, 60 C, 1 h
Effect of reaction time
Reproducibility test of catalyst
The influence of reaction time was also studied. The results are
shown in Figure 2. It can be found that the overall trend of
XCyoÀ O and YNH2OH is increasing gradually with the time
prolonging. When the initial reaction time is 0.5 h, cyclo-
hexanone oxime conversion is low(20.88%). After that, the
conversion generally increases to 37.68% at 1 h and then
remains steady as the time increasing from 1 h to 2.5 h. These
results show that the hydrolysis reaction rate is relatively fast
and the reversible reaction rapidly reached balance during the
reaction period. Although the present reaction rate is relatively
high, cyclohexanone oxime conversion is still not satisfactory.
Thus the reaction tended to be controlled by thermodynamics
rather than dynamics.[10] Therefore, one hour is enough for the
hydrolysis.
After completion of the hydrolysis reaction, the catalyst was
filtered and washed several times with ethanol, and then dried
in vacuum for further use. In the next round of reaction, the
recycled catalyst and new reactant were added to carry out the
reaction. Catalyst activity was evaluated by comparing XCyoÀ O
and YNH2OH. The results are showed in Figure 4. It was found that
the conversion of cyclohexanone oxime and the yield of NH2OH
decrease gradually after using five times. The decrease of the
catalyst activity may be due to the loss of ionic liquid during
the recovery process. The chemical composition of fresh and
reused [SPIPTES]CF3SO3@SiO2-6 catalysts (after five times) was
characterized by elemental analysis. As shown in Table 3, the S
element is 1.74%. So the fresh ionic liquid has a loading of
14.79% (based on the data of S element). After five cycles, the
catalyst loading is 11.43%. According to the results of elemental
Figure 3. Effect of catalyst/cyclohexanone oxime ratio on the
hydrolysis of cyclohexanone-oxime.
Figure 2. Effect of time on the hydrolysis of cyclohexanone-oxime.
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Structure analysis for the [SPIPTES]CF3SO3@SiO2-6 by
computational method
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A model of amorphous silica containing 4 tetrahedral silicon
atoms (T4) was obtained from the crystal structure of the zeolite
H-MOR, with all silicon atoms terminated in oxygen. To create
the dual-site model containing the grafted ILs adjacent to a
silanol group, two terminal SiÀ O fragments are substituted for
Si-OH and Si-IL respectively.
Density functional theory (DFT) calculations were performed
using a M062X hybrid function with the Gaussian 09 program
package. This M062X method with dispersion correction is
preferred to be a general purpose for describing nonbonded
interactions.[28] It has been verified to be appropriate for silica
cluster and ionic liquids system in a number of previous
studies.[29] Molclus program was used to study the possible
structure of cations by conformation search, and then the most
stable five structures were chosen. With placing anions on
different positions around cations, the structure for [SPIPTES]
CF3SO3@SiO2-6 with the lowest energy can be obtained by
optimizing at the level of 6–31+g(d,p) in the gas phase.[30]
Frequency analyses were conducted with the same basis set to
confirm that the optimized structures were ground states
without imaginary frequency. In addition, geometry parameters
and electrostatic potentials were determined, and Natural bond
orbital (NBO) analysis was performed for the optimized
structures of the grafted ionic liquids.
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Figure 4. Catalytic performance of re-used [SPIPTES]CF3SO3@SiO2-6
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Table 3. Elemental analysis of [SPIPTES]CF3SO3@SiO2-6 catalyst.
Catalyst
Element
N%
C%
H%
S%
Fresh [SPIPTES]CF3SO3@SiO2
5th [SPIPTES]CF3SO3@SiO2
0.87
0.86
5.84
5.10
0.84
0.78
1.74
1.46
analysis, it seems a little release of [SPIPTES]CF3SO3. The release
amount of ionic liquid is about 3.36%. This is one of the reasons
for the decrease of catalytic activity.
In addition, the acidic ionic liquid may combine with a small
amount of alkaline hydroxylamine (considering that hydroxyl-
amine is usually existed in the form of inorganic acidic
hydroxylamine salts) during the reaction process. Thus degra-
dated the catalytic activity. To further investigate that the
decrease in catalytic activity of the recovered catalyst is due to
the chemical action between the acidic center and hydroxyl-
amine, acid-base titration was used to determine the acid
amount between fresh and recovered catalyst. The results
showed that acid content of the fresh catalyst was 0.78 mmol/g.
While the recovered one decreased to 0.12 mmol/g. It is verified
that the deactivation of the recovered catalyst is due to the
decrease of the amount of effective acid in the catalyst.
Structure analysis for the [SPIPTES]CF3SO3@SiO2-6 by DFT
calculations
Density functional theory calculations were further carried out
to verify the structure. The typical five structures and the
distance between each atom are depicted in Figure 5 and
Figure 6. The cation part grafted on the surface of silicon cluster
has three active hydrogens, such as H25, H26 and H27. There
are strong interactions between the active hydrogen and
oxygen involved trifluoroalfonic acid and sulfonic acid group.
The two structures (a and b in Figure 6) both have lower energy
than the latter three structures (c, d, e in Figure 6) by more than
3 kcal/mol. The structure a is the most stable structure of the
five, and which energy is only 0.22 kcal/mol lower than that of
structure b.
We further studied the optimal structure a and b on the
structural parameters, NBO charge and stabilization energy of
E(2). According to the van der Waals radius of the H and O
atoms, the shorter the distance between 2.7 Å and 1.0 Å
(between hydrogen to the oxygen atom), the stronger the H
bond. In structures a, there are two strong H bonds in the
structure: O51… H26-O13, O52…H17-O27, the bond length is
1.4470 Å, 1.8008 Å, corresponding to 82.86 kcal/mol and
19.36 kcal/mol respectively for the stabilization energy of E(2),
the former E(2) maybe comes mainly from the electrostatic
interactions. Secondly, there are also three moderate H bonds
between O50, O17 and neighbouring H with the distance of
2.1-2.3 Å, resulting in the total E(2) of more than 19.00 kcal/mol.
Reaction conditions: Cyclohexanone oxime=0.5 g, catalyst
°
amount=2 g, H2O=30 mL, temperature=60 C, time=1 h
Preliminary study on the structure of supported [SPIPTES]
CF3SO3@SiO2-6 catalyst
The catalyst [SPIPTES]CF3SO3@SiO2 was characterized by BET, IR
and TG, etc (see supporting information). The results showed
that ionic liquid has been immobilized on silica-gel by chemical
covalent bond.
To further clarify the structure for [SPIPTES]CF3SO3@SiO2-6,
quantitative calculation methods were used as follows.
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Figure 5. Optimized geometry (distance unit: Å, blue) of the [SPIPTES]CF3SO3@SiO2.
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Figure 6. Optimized geometry (distance unit: Å, blue) of the [SPIPTES]CF3SO3@SiO2.
Figure 7. Catalyst preparation process of [SPIPTES]CF3SO3@SiO2
Thirdly, weak H bonds come into being around O14 within the
cation moiety. Apparently, two strong and two moderate H
bonds take place between CF3SO3 and the cation moiety. These
E(2) originate from the lone pair electron orbital of the O atom,
and which provides electrons to the neighboring antibonding
orbital. In summary, the stability of structure a emerges from
the strong interaction between the CF3SO3 and the cation
moiety.
In structures b, two strong and two moderate H bonds
appear, but the strongest H bond occurs in the cation itself, i.e.
The distance is 1.4813 Å of O13-H26…O17 along with the E(2)
of 64.02 kcal/mol. Additional weak H bonds grow near O50,
O51, O52. Compared with the structure a, the structure b arises
from the stability of the cation moiety. Form the analysis of
NBO charge, the overall NBO charge transferred from the cation
moiety to CF3SO3 is 0.188e for the structure a, while the NBO
charge is 0.120e in the structure b, thus indicating stronger
interaction between two parts for the structure a than the
structure b.
To sum up, two typical structures (structure a and b) both
exist on the surface of silica cluster. The NBO charge of H25,
H26 and H27 on the grafted ionic liquid cations is hold from
0.30 to 0.58, especially more than 0.55 of NBO charge of the
latter two. And thus the acidity is H25<H26�H27. H26 and
H27 with strong acidity play an important role, while H25 with
weak acidity plays a synergistic role during the catalytic
reaction.
The Gibbs free energy value in the parenthesis is the gap to
the structure a (unit: kcal/mol)
Additionally, combining the DFT calculations with experi-
ment results, a possible reaction pathway involved protonated
cyclohexanone oxime mechanism for the present hydrolysis
was proposed as shown in supporting information.
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supported ILs catalyst (ILs/SiO2). Several ILs/SiO2 catalysts were
prepared by impregnation method as shown in Table 1.
Conclusion
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In this work, preparation of NH2OH via hydrolysis of cyclo-
hexanone oxime was studied over porous SiO2 supported acid
ionic liquid catalyst. The catalyst [SPIPTES]CF3SO3@SiO2 was
prepared through sol-gel method and characterized by BET, IR
and TG, etc (shown in supporting information). Various
parameters such as reaction temperature and time, catalyst
amount were investigated systematically.
Preliminary study on the structure of supported ILs was
studies by quantitative computation, and a reaction mechanism
was also proposed. The optimized reaction conditions inves-
tigated were catalyst:cyclohexanone oxime (mass ratio) 4:1,
Method II: several [SPIPTES]CF3SO3@SiO2 catalysts were
prepared by sol-gel method
A series of supported ILs catalysts [SPIPTES]CF3SO3@SiO2 were
prepared by sol-gel method, giving rise to porous silica materials[31]
and ionic liquid gel-type silica where ILs is confined within the silica
particle.
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Firstly, The appropriate amount of imidazole, 0.1 mol of 3-
chloropropyltriethoxysilane and 10 mL of anhydrous toluene were
added into a 100 mL three-necked flask. Then the reaction mixture
was reacted under nitrogen atmosphere and toluene reflux for
24 h. After that, the mixture was distilled under reduced press to
obtain 3-(1-imidazolium) propyl triethoxysilane (IPTES).
°
conducted at 60 C for 1 h. Since the present hydrolysis is
controlled by thermodynamics, cyclohexanone oxime conver-
sion was 38.41% and NH2OH yield was 37.85% under the
Secondly, the obtained IPTES, 10 mL of anhydrous toluene and
0.1 mol of 1,3-propanesultone were added to a 100 mL three-
necked flask, the mixture was reacted under nitrogen atmosphere
and toluene reflux for 24 h as well, which can obtain 3-(3-sulfonic
acid propyl-1-imidazole) propyl triethoxysilane (SPIPTES).
optimizedreaction
conditions.
The
catalyst
[SPIPTES]
CF3SO3@SiO2 still has acceptable results after using five times.
Additionally, combining experiments with density functional
theory(DFT) calculations, a possible catalyst structure and
reaction pathway involved protonated cyclohexanone oxime
mechanism for the present hydrolysis was proposed in this
study (shown in supporting information). Thus, the immobilized
ionic liquid catalyst [SPIPTES]CF3SO3@SiO2 prepared in this study
was proved to be a high efficient heterogeneous catalyst for
the hydrolysis of cyclohexanone.
Thirdly, equimolar CF3SO3H was added dropwise to the prepared
°
SPIPTES. After that, the mixture was reacted at 80 C to obtain ionic
liquid [SPIPTES]CF3SO3, which was washed three times by Diethyl
ether.
Finally, [SPIPTES]CF3SO3 was added in a 100 mL three-necked flask
of ethanol solution of tetraethyl orthosilicate (TEOS:EtOH=1: 0.7),
which to cause hydrolysis and condensation reaction, and then
°
hydrochloric acid was added to form a gel, which was aged at 60 C
°
for 12 h and dried at 100 C for 2.5 h to obtain a porous SiO2
Experimental Section
supported ILs catalyst (denoted as [SPIPTES]CF3SO3@SiO2).
Materials and reagents
Catalytic activity measurements
Cyclohexanoneoxime (�99.0%), imidazole (�99.0%), 1,3-propane-
sultone (�99.0%), trifluoromethanesulfonic acid (�99.0%), anhy-
drous ethanol (�99.7%), tetraethyl orthosilicate (�99.0%) and 3-
chloropropyltriethoxysilane were supplied by Aladdin Company of
Shanghai, China. Toluene (�99.0%) and hydrochloric acid (36 wt%)
were obtained by Haotian Company of Tianjin, China. Ionic liquids
1-butylsulfonate-3-methylimidazolium
(�99.0%),N-propylsulfonate pyridinium hydrogensulfate (�99.0%),
N-propylsulfonate
ylimidazoliumtrifluoroacetate (�99.0%),1-butyl-3-methyl-imidazo-
lium-tosylate (�99.0%),1-propylsulfonate-3-methylimidazolium tri-
fluoromethanesulfonate (�99.0%), were supplied by Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences, China.
All other chemicals were of commercial reagent grade and were
used without further purification.
The hydrolysis reaction was carried out in a 100 mL three-necked
flask. Typically, 0.5 g of cyclohexanone oxime, 2 g of [SPIPTES]
CF3SO3@SiO2 catalyst and 30 mL of deionized water were loaded
°
into the flask. Then the mixture was stirred for about 1 h at 60 C.
After completion of the reaction, extraction with toluene was
conducted at the reaction temperature. Then the solid ILs catalyst
was separated from the reaction solution by centrifugal separation,
cyclohexanone and unreacted cyclohexanone oxime were obtained
from the organic phase, and hydroxylamine was obtained from the
aqueous phase. The separated ILs catalyst was washed three times
trifluoromethanesulfonate
(�99.0%),1-propylsulfonic-3-Meth-
°
with ethanol, and then dried in vacuum (À 0.1 MPa, 80 C) for
further use.
The organic phase was identified by comparison of their retention
time with those of authentic samples, and by a Thermo Trace DSQ
gas chromatography-mass spectrometry. The concentrations of
organic components were analyzed by a 7890B gas chromatog-
raphy. A capillary column of DB-WAX was used for most analyses.
Figure 8 shows a typical gas chromatogram. From which it can be
found that besides the organic product cyclohexanone, no other
Catalyst preparation
Method I: catalysts (ILs/SiO2) were prepared by
impregnation method
byproduct was observed. Cyclohexanone oxime conversion (XCyoÀ O
)
was calculated by the following (Equation (1)). The hydroxylamine
in the aqueous phase was analyzed by oxidation-reduction titration
with potassium permanganate,[30] and the yield of hydroxylamine
(YNH2OH) was calculated by (Equation (2)).
Typically, 2 g of carrier SiO2 was weighed, and then 0.5 g of ILs was
accurately weighed and dissolved in ultra-pure water (9 mL) to
prepare the impregnation solution. Then the prepared impregnat-
ing solution was slowly and evenly dripped onto the carrier silica.
After being impregnated for 36 h at room temperature, it was put
°
into a vacuum drying chamber and dried at 80 C to obtain the
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The TA2000 differential thermal analyzer of DuPont was used for
thermogravimetric (TG) analysis of the samples, and the temper-
1
2
3
4
5
°
ature rose from room temperature to 800 C with a heating rate of
°
10 C/min under nitrogen atmosphere.
Additionally, structure analysis for the [SPIPTES]CF3SO3@SiO2 by
density functional theory (DFT) of quantitative computation calcu-
lations were performed, using M062X hybrid function with the
Gaussian 09 program package.
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Acknowledgements
This work supported by the National Natural Science Founda-
tion of China (21878069, 21646015) and Natural Science
Foundation of Hebei Province (B2016202335).
Figure 8. Gas chromatography of reaction product for the hydrol-
ysis of cyclohexanone oxime: 1.Toluene; 2. Cyclohexanone; 3.
Cyclohexanone oxime.
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Keywords: Acidity
Heterogeneous catalysis · Hydrolysis · Ionic liquids · Supported
catalysts
·
Density functional calculations
·
WCyoÀ O
MCyoÀ O
XCyo À O ¼ ½1 À
� � 100%
(1)
(2)
Wi
Mi
S
YNH2OH ¼
5 � 100%
ðV1 À V2Þ � 10À 3 � C1 � 2
[1] a) V. Nadaraj, S. T. Selvi, J. Chem. Pharm. Res. 2012, 4, 2850–
2853; b) G. Yasaki, Y. Xu, S. B. King, Synth. Commun. 2000, 30,
2041–2047; c) M. Takhi, C. Murugan, M. Munikumar, K.
Bhaskarreddy, G. Singh, K. Sreenivas, M. Sitaramkumar, N.
Selvakumar, J. Med. Chem. Lett. 2006, 16, 2391–2395.
[2] a) J. H. Chang, U.S. Patent.4405357.(September 20, 1983). b) U.
Klein, E. Buschmann, M. Keil, G. Norbert, A. Harreus, U.S. Patent.
5585520. (December 17, 1996)
[3] B. L. Zhang, W. Y. Deng, H. H. Huang, L. Ding, Y. Z. Wang, P. Y.
Wang, Adv. Mater. Res. 2012, 396, 1879–1884.
[4] D. Han, J. Wan, Y. Ma, Y. Wang, M. Huang, Y. Chen, D. Li, Z.
Guan, Y. Li, Chem. Eng. J. 2014, 256, 316–323.
[5] K. F. Mueller, K. L. Wagaman, U.S. Patent,1768. (January
5,1999).
[6] V. Marchenko, K. Dvoeglazov, O. Savilova, V. Volk, Radio-
chemistry 2012, 54, 459–464.
[7] a) M. C. Thomas, U. H. Edwards, E. P. Patent 108294. (May 10,
1984); b) M. L. Levinthal, R. L. Willer, D. J. Park, U.S. Patent.
(November 30, 1993); c) T. Mathew, H. E. Ulmer, E. P. Patent.
0108294. (March 23, 1983)
[8] M. A. Mantegazza, G. Leofanti, G. Petrini, M. Padovan, A.
Zecchina, S. Bordiga, Stud. Surf. Sci. Catal. 1994,82, 541–550.
[9] F. Zhao, K. You, C. Peng, S. Tan, R. Li, Chem. Eng. J. 2015, 272,
102–107.
[10] a) H. Ichihashi, H. Sato, Appl. Catal. 2001, A 221, 359–366; b) R.
Chen, Z. Bu, Z. Li, Z. Zhong, W. Jin, W. Xing, Chem. Eng. J. 2010,
156, 418–422; c) A. C. Yip, X. Hu, Ind. Eng. Chem. Res. 2011, 50,
13703–13710; d) C. Shen, Y. J. Wang, C. Dong, G. S. Luo, Chem.
Eng. J. 2014, 235, 75–82.
[11] a) J. H. Bonfield, S. Sifniades, H. E. Ulmer, European Patent.
0074472. (July 5, 1982); b) J. P. Schirmann, US Patent. 7164042
B2.(January 16, 2007); c) W. Zhang, D. Jiang, Z. Ren, J. Yang, L.
Yang, CN Patent. 101100293 A. (January 9, 2008).
[12] W. Zhang, X. Su, Z. Hao, S. Qin, W. Qing, C. Xia, Ind. Eng. Chem.
Res. 2014, 54, 100–107.
[13] Y. Ikushima, J. Am. Chem. Soc. 2000, 122(9), 1908–1918.
[14] B. Lu, X. Zhang, Q. H. Cai, CN, Patent. 201010179257 (Septem-
ber 22, 2010).
[15] a) J. G. Huddleston, A. E. Visser, W. M. Reichert, H. D. Willauer,
G. A. Broker, R. D. Rogers, Green Chem. 2001,3, 156–164. b)
Yodoya, S. Domi, Y. Usui, H. Sakaguchi, Chem Select, 2019, 4(4),
1375–1378.
nCyo À O
Where:
V1 is the amount of potassium permanganate standard solution,
V2 is the amount of potassium permanganate standard solution in
the blank test,
C1 is the concentration of potassium permanganate standard
solution,
Wi is the weight percentage of i component in the products,
Mi is the molar mass of i component,
WCyoÀ O is the weight percentage of cyclohexanone oxime compo-
nent,
n
CyoÀ O is the molar of cyclohexanone oxime component,
M
CyoÀ O is the molar mass of cyclohexanone oxime component.
Catalyst characterization
Elemental analysis was performed on the Virio EL C/H/N elemental
analyzer produced by elementar element analysis system, Germany.
The sample was 0.02800 mg, the decomposition temperature was
950~1200 C, and 2~3 L He was consumed for each analysis.
Determination range: C (0.0330 mg abs), H (0.033 mg abs), N
(0.0310 mg abs).
°
The surface area, pore volume and pore diameter of ILs catalysts
°
were measured by nitrogen adsorption-desorption at À 196 C using
a Micromeritics ASAP 2020 instrument. The pore volume and pore
diameter were estimated from the desorption branch of the N2 is
other by using the Barrett-Joyner-Halenda (BJH) method, and the
surface area was calculated by Brunauer-Emmett-Teller (BET)
method.
Infrared (IR) spectra of the samples were recorded with a Nicolet
Nexus 470 FT-IR spectrometer using the potassium bromide pellet
technique.
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[16] Ghasemi, E. Kowsari, Res. Chem. Intermed. 2017, 43(7), 3691–
[26] X. Han, G. Zhu, Y. Ding, Y. Miao, K. Wang, H. Zhang, S. B. Liu,
Chem. Eng. J. 2019, 359, 733–745.
[27] P. Han, T. Liu, X. Ji, S. Tang, Chinese Chem Lett. 2018, 29(8),
1
2
3
4
5
6
7
8
9
3709.
[17] a) S. Sahoo, P. Kumar, F. Lefebvre, S. B. Halligudi, Appl. Catal. A
2009, 354, 17–25; b) L. L. Zhu, Y. H. Liu, J. Chen, Ind. Eng. Chem.
Res. 2009, 48, 3261–3267.
[18] H. Xu, H. Zhao, H. Song, Z. Miao, J. Yang, J. Zhao, L. Chou, J.
Mol. Catal. A-Chem. 2015, 410, 235–241.
[19] C. M. Maroneze, A. Rahim, N. Fattori, L. P. da Costa, F. A. Sigoli,
I. O. Mazali, Y. Gushikem, Electrochim. Acta 2014, 123, 435–440.
[20] a) J. N. Li, L. N. Wang, T. Qi, Y. Zhou, C. H. Liu, J. L. Chu,
Microporous Mesoporous Mater. 2008 110, 442–450; b) E. A.
Sujandi, D. S. Prasetyanto, S. C. Han, S. E. Lee, Park, Catal.
Today 2009, 141, 3, 74–377; c) J. N. Li, T. Qi, L. N. Wang, C. H.
Liu, Y. Zhang, Mater. Lett. 2007, 61, 3197–3200.
1305–1309.
[28] a) Y. Zhao, D. G. Truhlar, Thero Chem Acc. 2008, 120(1–3), 215–
241; b) A. Karadağ, H. Akbaş, D. Karakaş, K. C. Tekİn, E.
Korkmazer, Turk. J. Chem. 2019, 43(3), 766–777; c) S. Morpurgo,
J. Comput. Chem. 2015, 36(9), 660–669.
[29] a) Y. Wu, L. L. Yue, Q. Z. Liu, X. Wang, Acta Phys-Chim Sin. 2016,
32(8), 1960–1966; b) P. A. Hunt, I. R. Gould, J. Phys. Chem. A.
2006, 110, 2269–2282.
[30] F. Zhao, K. You, R. Li, S. Tan, P. Liu, J. Wu, H. A. Luo, Ind. Eng.
Chem. Res. 2015, 54(3), 819–823.
[31] F. Zhao, K. You, C. Peng, S. Tan, P. Liu, J. Wu, H. Luo, Chin. J.
Appl. Chem. 2015, 32(11), 1312–1318.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
[21] H. Xu, H. Zhao, H. Song, Z. Miao, J. Yang, J. Zhao, L. Chou, J.
Mol. Catal. A-Chem. 2015, 410, 235–241.
[22] H. M. Al-bishri, T. M. Abdel-Fattah, M. E. Mahmoud, J. Ind. Eng.
Chem. 2012, 18(4), 1252–1257.
[23] S. M. Sadeghzadeh, Micropo Mesopor Mat. 2016, 234, 310–316.
[24] R. Hajian, S. Tangestaninejad, M. Moghadam, V. Mirkhani, A. R.
Khosropour, C. R. Chim. 2012, 15(11–12), 975–979.
[25] F. Wang, Z. Zhang, J. Yang, L. Wang, Y. Lin, Y. Wei, Fuel 2013,
107, 394–399.
Manuscript received: October 8, 2020
Revised manuscript received: January 11, 2021
Accepted manuscript online: January 12, 2021
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