Sulfonic acid-functionalized periodic mesoporous organosilicas in esterification and selective acylation reactions

Article abstract of DOI:10.1039/c5cy00267b

The application of sulfonic acid-functionalized periodic mesoporous organosilicas (PMOs) having either phenyl (1a) or ethyl (1b) bridging groups was investigated in the esterification of a variety of alcohols and fatty acids. It was found that 1b consistently exhibited higher catalytic performance than 1a in the described reaction. In particular, it was proposed that the superior catalytic activity of 1b in esterification of fatty acids with methanol is a result of adequate hydrophobic-hydrophilic surface balance in the ethyl PMO catalyst. In addition, the study of chemoselective acylation of 1,3-butanediol with dodecanoic acid with varied mesoporous silica-supported solid sulfonic acids including both 1a and 1b implies that there is a compromise between the reaction selectivity and the surface physicochemical properties of the employed catalyst. Our results clearly show that the catalyst having high surface hydrophilic nature gives high selectivity toward the formation of mono-acylated products whereas those with relatively high hydrophobic characteristics showed enhanced selectivity toward the formation of di-acylated products.

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Periodic mesoporous organosilica functionalized sulfonic acid in the
esterification and selective acylation reactions
Babak Karimi,*a Hamid M. Mirzaeia, Akbar Mobarakia, and Hojatollah Valib
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
The application of sulfonic acid functionalized periodic mesoporous organosilicas (PMOs) having either
phenylene (1a) or ethyl (1b) bridging groups was investigated in the esterification of a variety of alcohols
and fatty acids. It was found that 1b consistently exhibited higher catalytic performance than the 1a in the
described reaction. In particular, it was proposed that the superior catalytic activity of 1b in esterification
10 of fatty acids with methanol is a result of adequate hydrophobicꢀhydrophilic surface balance in ethyl
PMO catalyst. In addition, the study of chemoselective acylation of 1,3ꢀbutandiol with dodecanoic acid
with varied mesoporous solid acids including both 1a and 1b implies that there is a compromise between
the reaction selectivity and the surface physicochemical properties of the employed catalyst. Our results
clearly show that the catalyst having high surface hydrophilic nature gives high selectivity toward the
15 formation of monoꢀacylated products whereas those with relatively high hydrophobic characteristics
showed enhanced selectivity toward formation of diꢀacylated products.
functionalized mesoporous silicas have been widely explored for
varied important chemical transformations.5 These materials have
gradually become a promising platform for designing new
fascinating catalyst since several investigations showed a clear
50 synergistic effect between the immobilized entities and the
physicochemical nature of mesoporous silica framework. Such
synergy in heterogeneous catalysts consisting hybrid organicꢀ
inorganic mesoporous materials creates features that are
uncommon in most conventional heterogeneous catalysts. One of
55 the most important features is that the surface physicochemical
properties of these materials could be deliberately modified in the
nanospaces of mesoporous materials where the active sites are
actually immobilized with the hope of improving the catalytic
activity and stability and sometimes selectivity.6 Among the
60 hybrid organicꢀinorganic composites, periodic mesoporous
organosilicas (PMO’s)7 which are made from direct condensation
of bridge organosilanes, commonly (R1O)3SiꢀR2ꢀSi(OR1)3, in the
presence of surfactant templates clearly provides a breakthrough
in the field of mesoporous materials. PMOs featured materials
65 with open porous structure and high loading of homogeneous
distribution of organic groups covalently bonded within the
siliceous framework and inside the pore walls. This allows for the
easy tailoring of both the chemical and physical properties while
improving hydrothermal and mechanical stability of the porous
70 framework. Accordingly, sulfonic acid functionalized PMO’s
Introduction
Direct esterification of alcohols and/or acids is one of the
simplest but still challenging reactions from both academic and
20 industrial point of views.1 Although many strong homogeneous
and conventional acid catalysts can normally promote these
transformations toward ester formation, there are several crucial
issues that should be tackled: (1) In most cases the homogeneous
catalysts are either deactivated or decomposed through the
25 solvation with byꢀproduced water, furnishing significant amount
of acidic wastes. (2) These classified protocols require large
quantities of nonꢀrecyclable homogeneous acids. (3) The
selectivity of these systems is often very difficult to control
especially when multiꢀfunctional alcohols or polyols are
30 involved. Although, heterogeneous solid acids have been served
to partly circumvent these issues, to date only a few solid acids
are identified to exhibit acceptable performances in the reactions
that water participates as byꢀproduct.2 Moreover, the high mass
transfer resistance dealing with many commercial solid acid
35 catalysts usually gives rise to their lower catalytic performance as
compared with homogeneous acid catalysts. Therefore, the search
for solid acids with improved water compatibility by emphasizing
the possibility to enhance both catalytic activity and reaction
selectivity has become an emerging area in modern chemistry.
40 Accordingly, the concept of acid sites isolation from water
molecules by controlling the surface wettability of solid acids
proposed and becomes crucial to improve their durability and
catalytic performance in the presence of water.3
were designed and used in
a
variety of reactions like
condensation,10
esterification,8 transesterification,9
etherification,11 rearrangement, and alkylation.12 Sulfonic acid
PMO’s are mainly categorized in two groups: (1) Sulfonic acid
75 groups tethered into organic bridges such as phenylene13 and
ethane.14 (2) Sulfonic acid groups embedded into channel walls of
Since the discovery of ordered mesoporous silicas (OMS),4
45 several types of hybrid organicꢀinorganic catalysts based on
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PMO through an organosilanes precursor such as 3ꢀ
mercaptopropyltrimethoxusilane. Although the first group has
advantages such as higher stability of sulfonic acid sites and
ability of incorporating higher loading of sulfonic acid groups,
the second class benefits from higher local hydrophobicity of
sulfonic acid sites. In this paper, we used route 2 to investigate
the support physicochemical properties in esterification and
acylation reactions. Recently, we found that periodic mesoporous
organosilica functionalized sulfonic acids 1b is an active catalyst
functionalized mesoporous organosilicas were determined by
acidꢀbase titration and pH analysis (Table 1).
55 Results and Discussions
5
To start our investigation, we first examined a set of experiments
to optimize the reaction parameters in benzyl alcohol
esterification with acetic acid (Table 2).
Table 1 Characterization of functionalized PMOs.
10 in biodiesel formation9 and Biginelli reaction (Scheme 1).15
a
b
Entry
PMO
SBET
Vp
Pore Hꢀindexd Acid
sizec
2.4
3.5
3.4
3.0
6.2
5.4
capacitye
0.4
O
O
OH
O
O
OH
1
2
3
4
5
6
1a
404
213
318
305
682
0.27
0.24
0.27
0.27
0.92
0.62
0.4
ꢀ
0.7
ꢀ
0.8
0.2
Si
SO3H
Si
SO3H
CH3
CH3
EtꢀPMOꢀMeꢀPrSH
ꢀ
1b
0.5
1b recycled
SBAꢀ15ꢀPrSO3H
0.4f
1.2
1a
1b
Scheme 1 Sulfonic acid based PMOs having either phenylene 1a or ethyl
1b.
SBAꢀ15ꢀPhꢀPrSO3H 349
0.8
a
b
c
60 BET surface area (m2.gꢀ1). Total pore volume (cm3.gꢀ1) at P/P0=0.99.
d
In these studies we found that the concomitant adjustment of
15 hydrophilicꢀhydrophobic balance and acidic strength in the
interior of mesochannels of these PMO and functionalized
ordered mesoporous materials can indeed facilitate diffusion of
the reactant and products in a set of selected acid catalyzed
reaction,9, 15ꢀ16 thereby enhancing the overall catalyst performance
20 and/or sometimes selectivity. These promising results prompted
us in investigating whether the same approach would enable us to
control the catalyst performance of OMSꢀbased sulfonic acids in
direct esterification of alcohols with carboxylic acids. In this
context, we suspected that the use of a PMO functionalized
25 sulfonic acid having appropriate surface wettability may provide
a means of obtaining highly selective monoꢀacylation of diols
with carboxylic acids. Herein, we wish to disclose our findings
regarding the use of sulfonic acid based PMO having either
phenylene 1a or ethyl 1b as bridge and methylpropylsulfonic acid
30 as functionalized group in esterification of fatty acids, acylation
of alcohols and chemoselective acylation of 1,3ꢀbutanediol.
BJH pore size diameter (nm). Hydrophilicity index (Hꢀindex)= amount
of adsorbed water/amount of N2 adsorbed at (P/P0≈0.92). e determined by
titration after ionꢀexchange (mmolH+.gꢀ1). The N2 sorption and ion
exchange analysis of catalyst recovered from the 10th reaction cycle of
65 esterification of stearic acid with methanol (please Fig. 2)
In this regard, the reaction of benzyl alcohol with acetic acid
with molar ratio of benzyl alcohol to acetic acid (1:10) in the
presence of 5 mol% 1b was proceeded well at even room
temperature after 30 h (Table 2, entry 1). In another experiment,
70 we have used 1a in a similar reaction conditions and it has been
declared that this reaction does not conducted well and only
furnished the corresponding ester in good yield at 60 ºC after 48 h
(Table 2, entry 2). It was also found that the same transformation
º
using 1b went to completion within 6 h at 60 C (Table 2, entry
75 3). To further optimise the reaction conditions, we next decreased
the amount of 1b to as low as 1 mol% under otherwise identical
reaction condition. Whereas a similar quantitative yield of benzyl
acetate was recovered, the reaction time was considerably
increased to 16 h (Table 2, entry 4). In the next stage, the ratio of
80 benzyl alcohol to acetic acid was decreased from 1:10 to 1:5 and
it was found that the reaction still went to completion within 24 h
affording quantitative yields of benzyl acetate (Table 2, entry 5).
Further decreasing the benzyl alcohol/acetic acid ratio led to
inferior benzyl acetate of 94% while higher loading of 1b catalyst
85 (3 mol%) was employed under the same reaction condition
(Table 2, entry 6). In addition, 1a comprising phenylene bridge
functionality was also examined and no yield over 69% was
obtained under the same conditions (Table 2, entry 7). Similarly,
either strong Brønsted mineral acid H2SO4 or SBAꢀ15ꢀPrSO3H
90 displayed a lower activity than 1b catalyst and resulted in the
benzyl acetate yield not exceeding 70% (Table 2, entry 8, 9).
These later two results clearly demonstrated the crucial rule of
surface physicochemical properties of 1b in the close vicinity of
sulfonic acid groups in obtaining high catalytic activity of the
95 material in direct esterification reaction. In particular, the large
differences between 1a and 1b catalytic systems can be also
rationalized by different physicochemical properties of PMO
materials as we explained in our previous publications.9,15 Having
the optimized reaction conditions, we then moved to investigate
100 the generality and activity of 1b catalyst in the esterification
reaction of a variety of alcohols with acetic acid.
Experimental Section
Characterization
Acidꢀfunctionalized mesoporous organosilicas PhꢀPMOꢀMeꢀ
35 PrSO3H (1a) and EtꢀPMOꢀMeꢀPrSO3H (1b) and other ordered
mesoporous silica supported solid acids were synthesized
according to the methods mentioned previously.9 The textural
properties of the functionalized mesoporous materials were
º
determined by nitrogen adsorptionꢀdesorption analysis at ꢀ196 C
º
40 and water sorption at 25 C with a Belsorpꢀmax apparatus (See
ESI). The surface area and pore size distribution were calculated
with the BET and BJH methods, respectively. N2ꢀsorption
isotherms indicate that the distribution of pore diameter of all
samples is in the mesoporous range (Table 1). Also,
45 hydrophilicity indices were measured according to Thommes
method using water and nitrogen sorption analyzes (See ESI for
more information). Organic material present in the solids was
determined by elemental analysis (Pheometric Scientific
analyzer). The organic composition of the modified mesoporous
50 materials was also determined by thermogravimetric analysis
°
(TGA) with heating from room temperature to 800 C under
Argon flow. The ion exchange capacities of the sulfonic acid
2
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Table 2 Esterification of benzyl alcohol with acetic acid in the presence
of and EtꢀPMOꢀMeꢀPrSO3H (1b)a
Entry Catalyst Catalyst
(mol%)
MR
T (ºC)
Time (h) Yield (%)b
1
2
3
4
5
6
7
8
9
1b
1a
1b
1b
1b
1b
1a
H2SO4
SBAꢀ15
PrSO3H
5
5
5
1
1
3
3
3
3
1:10
1:10
1:10
1:10
1:5
1:3
1:3
1:3
1:3
r.t.
60
60
60
60
60
60
60
60
30
48
6
16
24
24
24
24
24
>99
>99
>99
>99
>99
94
69
70
72
a MR is the molar ratio of benzyl alcohol to acetic acid. b Yields are based
on isolated products using column chromatography.
35 Fig. 1 Activity of 1a, 1b and H2SO4 in the esterification of dodecanoic
acid with methanol: dodecanoic acid (1mmol), methanol (10 mmol),
catalyst (3 mol%), 60 °C for 30 h. Products are separated by column
chromatography.
5
As shown in Table 3, our catalyst is also quite effective for
efficient reaction of aromatic alcohols as well as aliphatic
alcohols, giving the corresponding ester products in excellent
isolated yields. In particular, we found that even a long chain
alcohol such as octadecanol gives the corresponding ester product
These initial interesting results stimulated our attention to also
40 investigate the esterification of free fatty acids (FFA) with
methanol, a reaction which is highly desirable in biodiesel
formation (Table 4). For this reason, the esterification of
dodecanoic acid (1 mmol) and methanol (10 mmol) was carried
out over both mesoporous 1a and 1b catalysts, and also sulfuric
45 acid using 3 mol% mesoporous catalysts and equivalent amount
of sulfuric acid (Fig. 1). The reaction mixture was heated at 60 °C
for 30 h and subsequently was filtered and washed with 20 ml
dichloromethane to recover the catalyst. The dichloromethane
and unreacted methanol were evaporated off and the
50 corresponding methyl ester product was isolated by column
chromatography.
10 in quantitative yield without any need for purification through
column chromatography (Table 3, entry 8). In the same way, for
the reaction of secondary alcohols with acetic acid in the presence
of 1b, it was possible to achieve good to excellent yield of the
corresponding acetates by simply increasing the alcohol to acetic
15 acid ratio to 1:10 (Table 3, entries 9ꢀ15). In this way, the present
catalytic system was shown to be even effective for direct
acetylation of relatively hindered secondary alcohols such as (ꢀ)ꢀ
menthol and 2ꢀadamantaol (Table 3, entries 14ꢀ15). However, it
was unfortunately proved that 1b was incapable in catalysing
20 acetylation of tertꢀalcohol like 1ꢀadamantanol even in the
presence of an excess of acetic acid under reflux condition (Table
3, entry 16). From the data embodied in the Table 3, primary fatty
alcohols were particularly found to effectively undergo the direct
acetylation with acetic acid and consequently the corresponding
25 fatty acetates were formed in good to quantitative yields (Table 3,
entries 5ꢀ8).
Table 4 Direct esterification of carboxylic acids with methanol in the
presence of 1b a
Entry
1
Carboxylic acid
Yield (%)b
85
2
3
4
95
95
Table 3 Acylation of a variety of alcohols with acetic acid in the presence
of 1ba
100
Entry
1
2
3
4
5
6
7
8
alcohol
benzyl alcohol
2ꢀphenylethanol
3ꢀphenylpropanꢀ1ꢀol
4ꢀnitrobenzyl alcohol
1ꢀoctanol
MR
1:5
1:5
1:5
1:5
1:5
1:5
1:5
1:5
1:10
1:10
1:10
1:10
1:10
1:10
1:10
ꢀ
Yield (%)b
>99
92
a 1 mmol carboxylic acid, 10 mmol methanol, 3 mol% 1b catalyst at 60 °C
55 for 30 h. b Isolated yield after column chromatography by solvent mixture
(ethyl acetate:nꢀhexane in 1:10 volume ratio).
94
76
89
86
90
>99
78
79
79
90
86
85
95
Figure 1 obviously demonstrated that 1b catalyst has superior
activity compared to 1a and H2SO4. Once again these results
confirmed the high activity of 1b catalyst in esterification of free
60 fatty acids. To examine and screen the ability of 1b catalyst, fatty
acids with varied chain length were used in this reaction. As
summarized in Table 4, 1b catalyst is also quite effective for
efficient reaction of fatty acids and in this way the longest chain
fatty acid gave the highest isolated yield (Table 3, entries 1ꢀ4), a
65 similar behavior which was declared in the esterification of long
chain alcohols (Table 3, entries 5ꢀ8). To provide an initial
assessment on the recyclability of 1b catalyst, a recovery
investigation was conducted in which the esterification of stearic
acid with methanol was studied over 10 cycles under the
70 conditions summarized in Table 4.
1ꢀnonanol
1ꢀdecanol
1ꢀoctadecanol
2ꢀoctanol
9
10
11
12
13
14
15
16c
cyclohexanol
1ꢀcyclohexylethanol
cycloheptanol
cyclooctanol
menthol
2ꢀadamantanol
1ꢀadamantanol
40
a Alcohols (1 mmol) were reacted in the presence of 1 mol% 1b catalyst
30 for 24 h, MR is the molar ratio of alcohol to acetic acid. b Yields are based
on isolated product using column chromatography by a solvent mixture of
ethyl acetate:nꢀhexane (1:10). c Acetic acid (2.5 ml) was used in reflux
condition for 24 h.
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chemoselective acylation of an unsymmetrical diol such as 1,3ꢀ
butanediol with some selected carboxylic acids (Scheme 2).
30
Scheme 2 Chemoselective acylation reaction of 1,3ꢀbutanediol with
carboxylic acids in the presence of 1b catalyst.
For the purpose of comparison, we started our investigation
with comparing esterification of a primary alcohol with a
Fig. 2 Recyclability of 1b catalyst in the esterification of stearic acid with
methanol (1 mmol stearic acid, 10 mmol methanol, 3 mol% catalyst at 60
°C for 30 h.
35 secondary one having similar carbon number in a oneꢀpot
reaction to find whether primary or secondary acetate might be
selectively formed (Scheme 3). In this way, a competitive
acylation reaction between 1ꢀoctanol (1 mmol) and 2ꢀoctanol (1
mmol) with acetic acid (1 mmol) was conducted in the presence
5
In each reaction run, the catalyst 1b was easily separated from
the reaction mixture, washed with dichloromethane and
°
°
subsequently oven dried at 70 C before another reaction was
40 of 1b catalyst at 60 C for 24 h. Subsequently, the corresponding
performed. The recovered material could be added to the fresh
substrate giving almost identical behavior (for at least 6 recycles)
ester products were isolated by column chromatography. The
reaction gave 49% isolated yield and NMR spectroscopy revealed
that there is a mixture of both 1ꢀoctyl acetate and 2ꢀoctyl acetate
in ratio of 5:1 (~83% selectivity for primary alcohol
45 esterification), respectively.
10 and then maintained approximately 85% of the original activity 4
additional cycles, demonstrating its high stability and durability
under the present reaction conditions (Fig. 2). Further evidence
for the stability and robustness of 1b was obtained from TEM and
N2 sorption analysis of catalyst recovered from the final cycle
15 (Fig. 3). As illustrated in Figure 3 the majority of textural as well
as structural characteristics of the recovered 1b were largely
retained. In the last run, titration of ionꢀexchanged catalysts
shows that there is indeed a negligible decrease in the proton
capacity of the recycled catalyst from 0.5 mmol H+ gꢀ1 for fresh
20 catalyst to 0.4 mmol H+ gꢀ1 for the recycled catalyst from the 10th
run (Table 1, entry 4). This result clearly shows the high stability
of our catalyst under the described reaction condition and
recycling experiments.
Scheme 3 Selective acylation reaction of primary and secondary alcohols
Following this result, we next managed to conduct the
esterification reaction of 1,3ꢀbutanediol (1 mmol) with acetic acid
º
50 (1 mmol) at 60 C in the presence of 1b catalyst. After 24 h, the
products were isolated through column chromatography and it
was found in addition to the corresponding mono esters A and B
mixture, diacylated product C were also obtained in 53% and
14% isolated yields, respectively (Table 5, entry 1).
55
Study of selective acylation of 1,3-butanediol
25 To further investigate the utility of 1b in the esterification
reaction, we then chose to evaluate the ability of this catalyst in
Fig. 3 TEM (A) and N2 adsorptionꢀdesorption isotherm (B) of 1b catalyst (the inset is BJH pore size distribution plot) after 10 times recycling from the
esterification reaction of stearic acid with methanol.
4
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Table
5 Chemoselectivity of 1,3ꢀbutanediol in the reaction with
Altogether, these results roughly point to the fact that both
25 hydrophobic and hydrophilic starting materials can similarly
carboxylic acids in the presence of 1ba
penetrate into the nanospaces of 1b, and
a
surface
Entry
1
Carboxylic acid
Yield (%)b
67
Smono (%)c
79
Sdi (%)c
21
O
hydrophilic/hydrophobic balance in 1b might be the major reason
for the observed more or less similar chemoselectivity. To get
insight into whether the surface physicochemical properties in
30 acid catalyst could influence (change) the mode of the described
chemoselectivity, we repeated the esterification of 1,3ꢀbutanediol
with dodecanoic acid in the presence of SBAꢀ15ꢀPrSO3H, SBAꢀ
15ꢀPhꢀPrSO3H, and 1a catalysts under the same reaction
conditions. These catalysts differ from the standpoint of surface
35 polarity as evidenced by their water adsorptionꢀdesorption
isotherm in the gas phase and we suspect that a change in surface
polarity of a catalyst might result in a change in its product
selectivity. As it can be clearly seen in Figure 4, Among the
described solid sulfonic acid catalysts, SBAꢀ15ꢀPrSO3H exhibited
40 the highest water uptake at relative >P/Po ≈ 0.7ꢀ0.8 due to
capillary condensation of water and thus can be considered as the
most hydrophilic catalyst. In contrast, SBAꢀ15ꢀPhꢀPrSO3H
showed the lowest water condensation in the aboveꢀmentioned
relative pressure range, demonstrating that its mesopores are
45 highly hydrophobic in nature. On the other hand, the total
amounts of water uptake in the mesopores of either ethyl or
phenylene PMO supported sulfonic acids are located within these
two limits that is most likely owing to a more or less hydrophilicꢀ
hydrophobic balance in their nanospaces. Having characterized
50 the surface physicochemical properties of the catalyst, the
catalytic activity of these catalysts (3 mol%) was then
individually examined in the esterification of 1,3ꢀbutanediol (1
mmol) with dodecanoic acid (1 mmol) under otherwise optimized
reaction condition demonstrated in Table 5. From the results
55 demonstrated in Table 6, it appeared that while SBAꢀ15ꢀPrSO3H
(most hydrophilic catalyst) exhibited excellent selectivity toward
the formation of monoꢀacylated product A, SBAꢀ15ꢀPhꢀPrSO3H
(most hydrophobic catalyst) resulted in the highest selectivity in
diꢀacylated product C production (Table 6, entries 1, 2). Under
60 similar reaction condition, 1a also exhibited a considerable
selectivity toward diꢀacylated product C but the value is lower
than that of SBAꢀ15ꢀPhꢀPrSO3H whereas it is still higher than
that of 1b (Table 6, entries 2ꢀ4). Taking into consideration the
different surface physicochemical properties of the described
65 catalysts (Fig. 4) and the results in Table 6, it is obviously clear
the catalyst with more hydrophobic character gave more diꢀ
acylated product and the catalyst with hydrophilic character will
result in more monoꢀacylated product. To quantify the
hydrophobicꢀhydrophilic nature of the catalysts, we also used Hꢀ
70 index which shows differences in surface chemistry between
porous materials regardless to their chemical composition.17 To
measure this index, water and nitrogen adsorption analyzes
were performed for all catalysts and the amount of water and
nitrogen gas adsorbed at P/P0~0.92 were converted from gas
75 volume into liquid volume using Gurvich rule assuming that
all pores were filled at this point.
H3C
OH
OH
O
2
3
56
64
72
87
28
13
10
O
OH
16
a 1 mmol carboxylic acid, 1 mmol 1,3ꢀbutanediol, 3 mol% catalyst (0.060
º
g), 60 C, 24 h. b products were isolated by column chromatography and
c
5
reported yield is total isolated yield. Smono and Sdi are selectivity of
monoꢀacylated and diꢀacylated products, respectively.
1
Moreover, HNMR spectroscopy revealed that products A and
B are a mixture with ratio of (2.5:1). Thus, to collect more
10 information about the nature of chemoselectivity in our catalytic
system, other carboxylic acids such as dodecanoic acid and
stearic acid were employed under the same reaction conditions in
the presence of 1b catalyst (Table 5, entries 2ꢀ3). Once again, the
products were isolated and the corresponding A, B, and C product
15 yields were determined using column chromatography and NMR
spectroscopy. Interestingly, these reactions also resulted in the
same ratio of monoꢀacylated products A and B (2.5:1). Moreover,
these experiments demonstrated regardless to the hydrophobic
nature of the employed carboxylic acid a more or less the same
20 reaction selectivity toward monoꢀacylated formation over 1b
catalyst was attained (Table 5, entries 1ꢀ3).
Fig. 4 Water sorption analysis for mesoporous solid acids.
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Table 6 Chemoselectivity of 1,3ꢀbutanediol in the reaction with dodecanoic acid in the presence of various mesoporous sulfonic acidsa
Entry
Catalyst
SBAꢀ15ꢀPrSO3H
SBAꢀ15ꢀPhꢀPrSO3H
1b
Hꢀindex
0.8
0.2
0.7
0.4
MR
1:1
1:1
1:1
1:1
1:2
Yield (%) monoꢀacylated yield (%)b
Smono (%)c diꢀacylated yield (%)b
Sdi (%)c
1
2
3
4
5
59
60
56
41
90
57
25
40
24
29
97
42
72
58
32
2
3
35
16
18
61
58
28
44
68
1a
SBAꢀ15ꢀPhꢀPrSO3H
0.2
º
b
a 1 mmol 1,3ꢀbutanediol, 3 mol% catalyst, 60 C, 24 h. b products were isolated by column chromatography. Smono and Sdi are selectivity of monoꢀ
acylated and diꢀacylated products, respectively.
These indices can be measured according to formula [Hꢀ
index=Vp(water)/Vp(Nitrogen)] where Vp and Vp are,
respectively, the volume of water and nitrogen in liquid form
more hydrophobic as in the case for SBAꢀ15ꢀPhꢀPrSO3H (Hꢀ
index ≈ 0.2), the resulting monoesters A and B would tend to
reside inside the system pore of the catalyst to a greater
extend. This allows monoesters to undergo further
5
(water)
(Nitrogen)
at a P/Po=0.92. In this context, higher Hꢀindex value of a
catalyst is an indication for its higher surface hydrophilicity. 40 esterification at the available catalyst active sites, thus
After calculating this parameter for all catalysts, a diagram
increasing the corresponding diester C products. Based on
this model, it is thereby expected that any increasing the in
the amount of starting dodecanoic acid should improve the
selectivity of the process toward diester formation. In fact,
10 of their individual relative product selectivities either toward
monoꢀ or diꢀacylated products was depicted against the
respected Hꢀindices (Fig. 5). As the Hꢀindex increased from
0.2 to 0.8 the selectivity for monoꢀacylated products 45 we found that by increasing dodecanoic acid:1,3ꢀbutanediol
enhanced markedly. This diagram also highlights the notion
15 that decreasing the Hꢀindex value of the employed catalysts
would gradually result in a selectivity changeover toward the
formation of diꢀacylated product, reaching to a maximum
ratio from 1:1 to 2:1 in the presence of SBAꢀ15ꢀPhꢀPrSO3H,
the selectivity toward the formation of diester was increased
from 58% to 68%, further verifying the validity of this
model. Altogether the results demonstrated in Table 6 offer
value of 58% in the case of SBAꢀ15ꢀPhꢀPrSO3H catalyst 50 the possibility of achieving significant degree of
which has the lowest Hꢀindex ≈ 0.2 (Fig. 5, black dash plot).
20 This diagram accompanied with the data embodied in Table
6 implies that the high surface hydrophobicity of the catalyst
in close vicinity of the active sites is indispensable in
chemoselectivity toward either monoꢀacylated or diꢀacylated
products by adjusting the surface hydrophobicity of the
employed solid acids.
In a similar way, the lower selectivity of either 1a or 1b
attaining high selectivity toward diꢀacylated product. It is 55 compared to SBAꢀbased sulfonic acids might be most likely
clear that the esterification of 1,3ꢀbutanediol with fatty acids
25 like dodecanoic acid would first result in monoester, which
is more hydrophobic than the starting diol. Therefore, it is
reasonable to speculate that high affinity of silica framework
attributed to hydrophilicꢀhydrophobic balance in the system
pores of these PMOꢀbased catalyst, which inevitably allowed
both hydrophobic (monoester and/or dodecanoic acid) and
hydrophilic (1,3ꢀbutanediol) materials to favourably reach at their
in SBAꢀ15ꢀPrSO3H (Hꢀindex ≈ 0.8) for polar 1,3ꢀbutanediol 60 available active site, thus causing significant drop in selective
provides a driving force for rapid departure of monoester
30 form the relatively hydrophilic catalyst surface, thus
suppressing to a great extent the formation of diester C.
formation of either monoꢀ or diacylated products. This
hydrophilicꢀhydrophobic balance inside the nanospaces of 1b
may also account for its enhanced catalytic performance in the
esterification of fatty acids with methanol (Table 4), where a fast
65 mass transfer of both hydrophobic and hydrophilic starting
materials to the active sites located inside the nanospaces of the
catalyst is prerequisite to ensuring the observed high product
yields.
Conclusions
70 Sulfonic acid functionalized Periodic Mesoporous Organosilicas
(PMOs) having ethyl or phenylene bridging groups were
employed in the esterification reaction. It has been shown that
catalyst bearing ethyl bridging group consistently exhibited
higher catalytic performance rather phenylene PMO counterpart.
75 In particular, it was proposed that the superior catalytic activity of
1b in esterification of fatty acids with methanol is a result of
adequate hydrophobicꢀhydrophilic surface balance in ethyl PMO
Fig. 5 Product selectivity dependence for the reaction of 1,3ꢀbutanediol
and dodecanoic acid with Hꢀindex.
35
On the other hand, when the catalyst surface becomes
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DOI: 10.1039/C5CY00267B
Bion, J. Barrault and F. Jérôme, Chem. Commun., 2009, 7000; f) M.
H. Tucker, A. J. Crisci, B. N. Wigington, N. Phadke, R. Alamillo, J.
Zhang, S. L. Scott and J. A. Dumesic, ACS Catal., 2012, 2, 1865.
a) C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S.
Beck, Nature, 1992, 359, 710; b) D. Zhao, J. N. Feng, G. H.
Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 1998, 279,
548.
a) A. P. Wight and M. E. Davis, Chem. Rev., 2002, 102, 3589; b) Z.ꢀ
L. Lu, E. Lindner and H. A. Mayer, Chem. Rev., 2002, 102, 3543; c)
J. A. Melero, R. van Grieken and G. Morales, Chem. Rev., 2006, 106,
3790.
catalyst. In addition, the study of chemoselective acylation of 1,3ꢀ
butandiol with dodecanoic acid with varied mesoporous solid
acids including both 1a and 1b implies that there is a compromise
between the reaction selectivity and the surface physicochemical
properties of the employed catalyst. Our results clearly show that
the catalyst having high surface hydrophilic nature gives high
selectivity toward the formation of monoꢀacylated products
whereas those with relatively high hydrophobic characteristics
showed enhanced selectivity toward formation of diꢀacylated
10 products. We speculate the results of this study would provide
more information in designing novel types of sophisticated hybrid
solid acid catalysts with tuneable selectivity in the described
reaction by just adjusting their surface physicochemical
Properties of the employed catalyst.
45
50
55
60
65
70
75
80
4
5
5
6
7
K. Inumaru, T. Ishihara, Y. Kamiya, T. Okuhara and S. Yamanaka,
Angew. Chem., Int. Ed., 2007, 46, 7625.
a) S. Inagaki, S. Gouan, Y. Fukushima, T. Ohsuna and O. Terasaki, J.
Am. Chem. Soc., 1999, 121, 9611; b) B. J. Melde, B. T. Holland, C.
F. Blanford and A. Stein, Chem. Mater., 1999, 11, 3302; c) C. Ishii,
T. Asefa, N. Coombs, M. J. MacLachlan and G. A. Ozin, Chem.
Commun., 1999, 2539.
a) Q. Yang, M. P. Kapoor and S. Inagaki, J. Am. Chem. Soc., 2002,
124, 9694; b) Q. Yang, M. P. Kapoor, N. Shirokura, M. Ohashi, S.
Inagaki, J. N. Kondo and K. Domen, J. Mater. Chem., 2005, 15, 666;
c) D. Elhamifar, B. Karimi, A. Moradi and J. Rastegar,
ChemPlusChem, 2014, 79, 1147.
8
15 Notes and references
a Prof. Dr. Babak Karimi, Hamid M. Mirzaei, and Akbar Mobaraki
Department of Chemistry, Institute for Advanced Studies in Basic
Sciences (IASBS),Zanjan 45137-6731 (Iran)
9
B. Karimi, H. M. Mirzaei and A. Mobaraki, Catal. Sci. Technol.,
2012, 2, 828.
Fax: (+98)-241-415-3232
20 E-mail:karimi@iasbs.ac.ir
b Prof. Hojatollah Vali
10 V. Dufaud and M. E. Davis, J. Am. Chem. Soc., 2003, 125, 9403.
11 a) J. G. C. Shen, R. G. Herman and K. Klier, J. Phys. Chem. B, 2002,
106, 9975; b) B. Sow, S. Hamoudi, M. H. ZahediꢀNiaki and S.
Kaliaguine, Microporous Mesoporous Mater., 2005, 79, 129.
12 B. Rác, P. Hegyes, P. Forgo and A. Molnár, Applied Catalysis A:
Gen., 2006, 299, 193.
13 a) K. Nakajima, I. Tomita, M. Hara, S. Hayashi, K. Domen and J. N.
Kondo, Adv. Mater., 2005, 17, 1839; b) K. Nakajima, I. Tomita, M.
Hara, S. Hayashi, K. Domen and J. N. Kondo, Catal. Today, 2006,
116, 151; c) D. Esquivel, E. De Canck, C. JimenezꢀSanchidrian, P.
Van Der Voort and F. J. RomeroꢀSalguero, J. Mater. Chem., 2011,
21, 10990.
14 D. Esquivel, O. van den Berg, F. J. RomeroꢀSalguero, F. Du Prez,
and P. Van Der Voort, Chem. Commun., 2013, 49, 2344.
15 B. Karimi, A. Mobaraki, H. M. Mirzaei, D. Zareyee and H. Vali,
ChemCatChem, 2014, 6, 212.
16 a) B. Karimi and D. Zareyee, Org. Lett., 2008, 10, 3989; b) B. Karimi
and D. Zareyee, J. Mater. Chem., 2009, 19, 8665.
Department of Anatomy and Cell Biology and Facility for Electron
Microscopy Research, McGill University, Montreal, Quebec, H3A 2A7
Canada.
25 † Electronic Supplementary Information (ESI) available: [procedures for
catalysts preparation, porosimetry data, TG analysis, TEM, 1HNMR,
13CNMR]. See DOI: 10.1039/b000000x/
1
J. Otera, Esterification: Methods, Reactions and Applications, Wileyꢀ
VCH Verlag GmbH &Co. KGaA, Weinheim, 1st edn, 2003.
a) T. Okuhara, Chem. Rev., 2002, 102, 3641; b) K. Inumaru, T.
Ishihara, Y. Kamiya, T. Okuhara, and S. Yamanaka, Angew.Chem.
Int. Ed. 2007, 46, 7625; c) A. Corma, and M. Renz, Angew. Chem.
Int. Ed. 2007, 46, 298; d) C. Tsai, H. Chen, S. M. Althaus, K. Mao,
T. Kobayashi, M. Pruski, and V. S. –Y, Lin, ACS Catal. 2011, 1, 729;
e) Q. Yang, S. Ma, J. Li, F. Xiao, and H. Xiong, Chem. Commun.
2006, 2495;
30
35
40
2
3
a) I. K. Mbaraka and B. H. Shanks, J. Catal., 2005, 229, 365; b) I. K.
Mbaraka and B. H. Shanks, J. Catal., 2006, 244, 78; c) L. Sherry and
J. A. Sullivan, Catal. Today, 2011, 175, 471; d) P. L. Dhepe, M.
Ohashi, S. Inagaki, M. Ichikawa and A. Fukuoka, Catal. Lett., 2005,
102, 163; e) A. Karam, J. C. Alonso, T. I. Gerganova, P. Ferreira, N.
85 17 M. Thommes, S. Mitchell and J. PérezꢀRamírez, J. Phys. Chem. C,
2012, 116, 18816.
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DOI: 10.1039/C5CY00267B
Graphical Abstract
A simple adjusting of surface physicochemical Properties of the solid acid catalyst would provide
selective formation of the desired product.