Overcoming acid–base copolymer neutralization using mesoporous carbon and its catalytic activity in the tandem deacetalization–Knoevenagel condensation reaction

Research on Chemical Intermediates

https://doi.org/10.1007/s11164-020-04153-4

Overcoming acid–base copolymer neutralization using

mesoporous carbon and its catalytic activity in the tandem

deacetalization–Knoevenagel condensation reaction

Roozbeh Javad Kalbasi¹ · Fatemeh Rahmati · Omid Mazaheri

2

3,4

Received: 12 December 2019 / Accepted: 11 April 2020

©

Springer Nature B.V. 2020

Abstract

Acid–base copolymer materials are of considerable interest because of their fun-

damental implications for acid–base bifunctional catalysis applications. However,

quenching the acid and base sites of the copolymer with each other in free radical

polymerizations is still challenging. Herein, we demonstrate that the polymerization

of styrenesulfonic acid-co-4-vinylpyridine into the mesoporous carbon material (i.e.,

CMK-3) can control the chain growth polymerization and result in decreasing the

interaction of the acid–base sites. The results showed that by using CMK-3, 40% of

the acid and base sites of the copolymer remain in their original form while 60% of

acid and base sites convert to the pyridinium and sulfonate forms. Furthermore, it

is demonstrated that this material can be processed as a heterogeneous bifunctional

acid–base catalyst in the tandem one-pot acid–base reaction (i.e., deacetalization–

Knoevenagel condensation reaction) with a high catalytic activity in aqueous media.

Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116

4

-020-04153-4) contains supplementary material, which is available to authorized users.

*

Roozbeh Javad Kalbasi

rkalbasi@khu.ac.ir; rkalbasi@gmail.com

Fatemeh Rahmati

rahmaty_f@yahoo.com

Omid Mazaheri

mazaherio@unimelb.edu.au

1

2

3

Faculty of Chemistry, Kharazmi University, Tehran, Iran

Department of Chemistry, Shahreza Branch, Islamic Azad University, Isfahan 311-86145, Iran

School of Agriculture and Food, Faculty of Veterinary and Agricultural Sciences, The

University of Melbourne, Parkville, VIC 3010, Australia

4

Department of Chemical Engineering, The University of Melbourne, Parkville, VIC 3010,

Australia

Vol.:(012

1

3456789)

3

R. Javad Kalbasi et al.

Graphic abstract

Keywords Acid–base copolymer · Mesoporous carbon CMK-3 · Acid–

base neutralization sites · Styrenesulfonic acid · 4-vinylpyridine · Tandem

deacetalization–Knoevenagel condensation

Introduction

Nowadays, tandem organic reactions are getting attractions in modern chemical

industries due to decreasing the time process and reducing the waste generated

[

1–7]. Typically, the presence of acid–base sites in catalysts, which are known as

bifunctional catalysts, is required to fulꢀll the tandem organic reactions [8–11].

However, the neutralization and deactivation of the acid and base sites of the pol-

ymer when the acid and base sites are adjacent to each other are still challenging

[

12–15].

Over the last two decades, several acid–base catalysts in which basic groups

are amines, pyridine, and imidazole and acidic groups are sulfonic acids, acrylic

acids, and carboxylic acids were synthesized [8, 16–18]. One method to create the

acid–base sites in materials is using the acid- and base-functionalized polymers

[

19–22]. The procedure is included in blending two synthesized polymers (acid and

base polymer, separately) [23]. Here, cationic (–SO H) and anionic (–CH NH ) pol-

3

2

ymers are usually mixed to induce acidic and basic properties. Although this proce-

dure is simple, as the acid and base polymers are blending, the acid and base active

sites have high interactions with each other, and as a corollary of this, the catalyst

is neutralized [21, 24]. To overcome with neutralization of acid and base sites, ben-

zene as a spacer is used in the copolymer structure [25–27]. However, the time-con-

suming procedure, its toxicity, and diꢁculty decline the privilege.

1

3

Overcoming acid–base copolymer neutralization using mesoporous…

Besides, post-grafted and bridging are common methods to utilize organosilanes

(

containing –SH and SO Cl functional groups) on the support materials (usually

2

porous structure materials) [28–32]. Here, the functional groups of the organosi-

lanes are oxidized to convert to the acidic groups (–SO H). Multi-step procedure to

3

graft the organosilanes and the high cost of the organosilanes reduce the attention to

use these methods. Moreover, the unprotected acid and base groups in the organosi-

lanes may be quenched [33]. Another method to decrease the acid–base quenching

is co-condensation [12]. Nevertheless, a substantial obstacle in this method is an

incapacity to completely take away the template by neither solvent nor rising tem-

perature methods. Thus, measuring the content of organic materials by the thermo-

gravimetric analysis in the support material is demanding.

Using porous carbon materials such as nanotubes, CMK-n, and 3DOMs (3D

ordered macroporous) and MOFs (Metal–Organic Frameworks) as the polymer sup-

port has some advantages thanks to having high surface area and good connection

between polymer and carbon porous material [10, 34–38]. By this method, the base

and acid polymers become farther from each other, which leads to a decrease in the

neutralization [39]. As the mesoporous carbons have a high surface area and sev-

eral interconnected pores, the polymers can disperse throughout the pores. Thus, the

porous carbon can prevent the acid and base sites of the copolymer from neutraliza-

tion [35].

In our previous works, synthesis of acid or base polymers in porous materials

(

[

i.e., mesoporous silica and carbon) by utilizing simultaneous method was described

40, 41]. In this method, the monomer cannot grow thoroughly into the pores which

led to the homopolymer formation (not a bulk polymer).

In this study, we prompt to synthesize acid–based copolymer (poly(styrenesulfonic

acid-co-4-vinylpyridine)) (poly(SSA-co-4VP)) with the simultaneous method with-

out using spacers, protecting compounds, or organosilanes functionalization (i.e.,

post-grafted, bridging, and co-condensation) into the mesoporous carbon CMK-3.

To the best of our knowledge, trapping acid–base copolymer into the mesoporous

carbon has rarely been applied to overcome the neutralization of acid–base sites

polymer. After the synthesis of materials, we utilize the material as a catalyst in the

deacetalization–Knoevenagel condensation reaction.

Results and discussion

Catalyst characterization

X‑ray powder difraction (XRD)

Figure 1 shows signiꢀcant diꢂraction peaks at around 2θ=1°–2° in the XRD pat-

terns of CMK-3 and poly(SSA-co-4VP)/CMK-3. The peaks are attributed to (100)

reꢃection of 2D ordered 2D hexagonal structure [42–44]. The diꢂraction peak of

poly(SSA-co-4VP)/CMK-3 has been shifted to 1.3° from 1.15°, which can be

explained by incorporation of the copolymer into the mesoporous carbon CMK-3

and slight decrease in its pore size [45]. Moreover, the intensity of the main peak

1

3

R. Javad Kalbasi et al.

Fig. 1 XRD patterns of CMK-3 and poly(SSA-co-4VP)/CMK-3

in the poly(SSA-co-4VP)/CMK-3 reduces demonstrating the existence of the

copolymer into the mesopores of CMK-3. It also can be related to the dilution of

the CMK-3 by the copolymer. However, the survival of diꢂraction peak at 2θ=1.3°

shows that the CMK-3 structure is retained.

FT‑IR analysis

The FT-IR spectra of CMK-3 and poly(SSA-co-4VP)/CMK-3 are represented in

Fig. 2. No tangible absorption is detected in CMK-3 indicating the formation of gra-

phitic frameworks during the carbonization of sucrose [46]. On the other hand, some

Fig. 2 FT-IR spectra of CMK-3 and poly(SSA-co-4VP)/CMK-3

1

3

Overcoming acid–base copolymer neutralization using mesoporous…

new peaks have appeared in the poly(SSA-co-4VP)/CMK-3, which is attributed

−

1

to the presence of the polymer. In detail, the peaks at 2857, 2933, and 3046 cm

are related to the aliphatic and aromatic stretching vibration of C–H bonds [45].

The broad absorption peak of –OH stretching vibration is observed between 3100

−1

and 3700 cm , which is related to either adsorption of water by the polymer and

mesoporous carbon CMK-3 and/or –OH groups of PVSA (polyvinyl sulfonic acid)

−

1

[

47, 48]. Two stretching vibration peaks at 1568 and 1415 cm can be assigned

to the pyridine rings [25, 49]. Moreover, the pyridinium cation absorption at

−1

1

638 cm is related to the zwitterion state formation [25]. Two sharp peaks at 1185

−1

and 1209 cm are attributed to the S=O groups of the polymer that arises from the

asymmetric stretching vibration [25, 27]. The stretching vibration of the S–O(H) in

−

1

–

SO H groups of the polymer shows an absorption band at 909 cm [25]. The other

3

−1

peaks at 1007, 1040, and 1124 cm can be attributed to both the aromatic rings and

–

SO H groups of the copolymer [50]. From these pieces of evidence, the formation

3

of acid–base copolymer into the CMK-3 pores can be justiꢀed.

N₂adsorption–desorption isotherm

The chemisorption and physisorption of CMK-3 and poly(SSA-co-4VP)/CMK-3

have been investigated and are shown in Fig. 3. As can be seen, both samples dem-

onstrate adsorption isotherms of type IV with H hysteresis loop and the capillary

4

condensation between 0.3 and 0.8 relative pressure [44, 45, 51]. The BET surface

2

−1

area of CMK-3 and poly(SSA-co-4VP)/CMK-3 is 1527 and 395 m g , respectively

(

Table 1). Moreover, the mesoporous volume of poly(SSA-co-4VP)/CMK-3 has

3

−1

been decreased by almost double (from 1.26 to 0.6 m g ) showing the incorpora-

tion of polymer into the porous carbon. The slight decrease in the pore size diam-

eter has been observed when the polymers have been deposited into the mesopores

CMK-3. All the BET surface area, mesoporous volume, and pore size diameter data

Fig. 3 N adsorption–desorption isotherms of CMK-3 and poly(SSA-co-4VP)/CMK-3

2

1

3

R. Javad Kalbasi et al.

Table 1 Physicochemical properties of the mesoporous carbon CMK-3 and poly(SSA-co-4VP)/CMK-3

samples obtained from N adsorption–desorption

2

3

−1 a

D (nm)^b

2

−1 c

Sample

BET surface area V (cm g

)

S_m(m g

)

P

p

2

−1

(

m g

)

Mesoporous carbon CMK-3

Poly(SSA-co-4VP)/CMK-3

1527

395

1.26

0.6

3.3

3.1

473

295

a

Total pore volume determined by the BET method

Mesopore diameter determined by BJH method

The micropore surface area was estimated by MP-plot

b

c

are shown that the copolymer is incorporated into the CMK-3. According to the

2

−1

MP plot data, both samples portray microstructure (473 and 295 m g for CMK-3

and poly(SSA-co-4VP)/CMK-3, respectively) (Table 1) representing that after the

polymerization of monomers, the microchannels have not been blocked. The exist-

ence of microchannels facilitates the transformation of substrates in the catalytic

application by decreasing the mesoporous blocking.

Thermal property

Figure 4 presents the TGA curve of poly(SSA-co-4VP)/CMK-3 under N atmos-

2

phere. The poly(SSA-co-4VP)/CMK-3 thermograph depicts two mass loss steps.

The ꢀrst step occurs behind 160 °C which is corresponded to the desorption of water

from both support (CMK-3) and copolymer with around 7.5% w/w mass loss. The

material is losing mass around 22.5% w/w between 170 and 700 °C which is related

to the decomposition of the copolymer. With a comparison between the weight loss

of copolymer trapped into the mesoporous CMK-3 and the conventional copoly-

mer [24], the traditional poly(SSA-co-4VP) has a major weight loss around 92%,

which begins at 350 °C and ends at 430 °C [24]. Demonstrably, the poly(SSA-co-

4

VP)/CMK-3 nanocomposite displays a slower degradation rate than traditional

poly(SSA-co-4VP) which is related to the higher thermal stability of the composite.

It can be authorized by anchoring the copolymers into the mesopores of CMK-3.

Morphology study (SEM and TEM)

The surface morphology of mesoporous carbon CMK-3 and poly(SSA-co-4VP)/

CMK-3 has been investigated using SEM (Fig. 5a, b). As can be seen, the shape

and morphology of poly(SSA-co-4VP)/CMK-3 are similar to the CMK-3 with a

worm-like structure [52, 53]. No signiꢀcant change is observed in the SEM image

in the second sample (poly(SSA-co-4VP)/CMK-3) (Fig. 5b). It may show that the

polymerization of vinyl sulfonic acid and vinyl pyridine mainly occurred into the

CMK-3 pores. It is correspondent with the lower pore volume, smaller pore diam-

eter, and lower surface area of poly(SSA-co-4VP)/CMK-3 in the BET results. Thus,

the CMK-3 structure can provide appropriate support for lying the copolymer due to

having a large amount of volume and surface area.

1

3

Overcoming acid–base copolymer neutralization using mesoporous…

Fig. 4 TGA curves of poly(SSA-co-4VP)/CMK-3

Fig. 5 SEM images of CMK-3 (a) and poly(SSA-co-4VP)/CMK-3 (b), TEM images of CMK-3 (c) and

poly(SSA-co-4VP)/CMK-3 (d)

1

3

R. Javad Kalbasi et al.

The TEM images of poly(SSA-co-4VP)/CMK-3 are illustrated in Fig. 5c, d.

The mesostructured CMK-3 is observed in both CMK-3 and poly(SSA-co-4VP)/

CMK-3 samples which indicates that after the polymerization, the CMK-3 structure

is retained [52]. However, the presence of copolymer into the mesoporous is not

detected because of almost identical carbon-based composite materials of CMK-3

with polymers using the TEM technique.

Potentiometric titration

To evaluate the neutralization of copolymer, the acid and base sites of poly(SSA-

co-4VP)/CMK-3 have been estimated by potentiometric titration. For measur-

ing acid sites, two equivalence points by consuming NaOH have been observed in

1

4

.9 and 5.7 mL. According to the experiment content of styrene sulfonic acid and

-vinylpyridine monomers in the catalyst (10 mg SSA and 10 mg 4-VP in 50 mg of

the catalyst), 4 mg sulfonic acid and 6 mg pyridinium ion have been formed in the

material. Besides, to measure basic sites, HCl has been used for detecting the ꢀrst

and second equivalence points. The total amount of sulfonated form and pyridine

forms was 6 mg and 4 mg, respectively.

Consequently, almost 40% of copolymer sites remained in their acid and base

forms and 60% are in the pyridinium and sulfonate forms. Remaining 40% acid and

base forms without using a complex technique (i.e., spacer or co-condensation) is

noteworthy as in the most literature, zwitterion form of the acid–base copolymer has

been formed and a few amount of acid and base sites remained even by using spacer

method [25, 27, 54]. Therefore, the CMK-3 mesoporous structure can act as a spacer

in the material and no further chemical spacer (i.e., benzene) acquires to separate

the acid and base sites. It demonstrates that this method is eꢂective to separate the

acid and base sites in the copolymer.

Catalytic activity

Reaction optimization

The synthesized poly(SSA-co-4VP)/CMK-3 is utilized as a bifunctional catalyst in

the deacetalization–Knoevenagel condensation reaction. At ꢀrst, the activity of cata-

lyst has been maximized by optimization of acid and base monomers’ molar ratios,

the content of CMK-3 and the catalyst, solvent types, and temperatures, which is

tabulated in Table 2. Then, the catalytic activity has been investigated using some

dimethyl acetal with ethyl cyanoacetate substitutes. Finally, the reusability and the

heterogeneity of the catalyst have been evaluated.

The optimization of the SSA/4-VP molar ratio can promote the activity of the

catalyst in both steps of the reaction (deacetalization and Knoevenagel steps);

by decreasing the molar ratio of SSA/4-VP from 3:2 to 1:2, the catalytic activ-

ity increases. Indeed, by increasing the number of acid sites (SSA), the tendency

of neutralization with base sites increases (entries 1–3). By changing the content

of CMK-3 in poly(SSA-co-4VP)/CMK-3 from 0.125 to 0.5 g, the reaction time

1

3

Overcoming acid–base copolymer neutralization using mesoporous…

1

3

R. Javad Kalbasi et al.

decreases from 210 to 75 min, and subsequently, the product yield increases up to

9

2% (entries 3–6). From the spatial aspects, the copolymer chains trap in a small

conꢀde space and it prevents the entanglement in the mesopores of CMK-3; thus,

the acid–base sites of the copolymer are protected from neutralization (Scheme 1)

[

36]. Another reason to increase the catalytic activity in the poly(SSA-co-4VP)/

CMK-3 is that the mesoporous carbon CMK-3 provides a high surface area in the

catalyst and it can increase the speed and yield of the reaction by increasing the

chance of interaction between the reactants and the acid–base sites [31, 55, 56].

By raising the temperature from 40 to 60 °C, the reaction time and yield improve

to 75 min and 87%, respectively; however, no tangible improvement is detected by

increasing the temperature to 90 °C (entries 3, 7, 8). The amount of catalyst also has

been optimized in which the reaction time and yield remain constant above 0.1 g

of the catalysis uses (entries 8–11). Accordingly, 0.1 g catalyst with the 1:2 SSA/4-

VP molar ratio at 60 °C in water as a solvent has been elected as the optimized

conditions.

The tandem reactions without the poly(SSA-co-4VP)/CMK-3 and using only the

acidic and/or basic polymer in the solvent-free condition have been surveyed (entries

1

2–14). The reaction cannot progress in the absence of the acid sites. However, by

using the acid polymer (SSA) in the tandem reaction, almost all benzaldehyde dime-

thyl acetal is converted to benzaldehyde. It demonstrates that the reaction needs both

acidic and basic components [57, 58]. Since water is well known as a green solvent

and the reaction has been advanced in an appropriate time, no further investigation

on other solvents has been fulꢀlled. However, the solvent-free condition has been

examined, which produced a lower product yield in higher reaction time (entry 15).

The reaction with the electron-withdrawing group (–Cl, –Br and –NO ) and the

2

electron-donating group (–OCH ) substitutes has been studied in the optimized

3

catalyst conditions and is tabulated in Table 3. As can be seen, the reaction time

reduces when the electron-withdrawing groups are on the benzaldehyde dimethyl

acetal while the slight change is observed in the presence of the electron-donating

Scheme 1 Schematic of SSA-co-4VP polymerization into the mesoporous carbon CMK-3 and its cata-

lytic activity in the tandem deacetalization–Knoevenagel condensation reaction

1

3

Overcoming acid–base copolymer neutralization using mesoporous…

Table 3 Optimization of diꢂerent factors on the catalytic activity of the poly(SSA-co-4VP)/CMK-3 in

deacetalization–Knoevenagel condensation reaction

Entry SSA

4-VP

SSA/4-VP CMK-3

Catalyst

(g)

T (°C) Time

Yield (%)^b

(

mmol)^a

(mmol)

a

ratio

(g)

(min)

1

2

3

4

5

6

7

8

9

1

0.032

0.024

0.019

0

0.018

0.027

0.039

0

3:2

1.5:2

1:2

–

0.5

0

0.12

0.25

0.5

0

0.1

0.01

0.1

0.06

0.08

0.12

0

90

40

60

–

420

300

75

280

210

180

75

70

72

92

55

70

75

47

87

45

70

87

0

75

420

360

75

200

50

70

110

0

1

2

3

4

5

0.019

0

0.019

0

–

1:2

0.5

0.1

0 (97)^c

82

65

d

e

0.039

Reaction conditions: benzaldehyde dimethyl acetal (1.87 mmol), ethyl cyanoacetate (1.87 mmol), H O

2

(

4 mL)

a

Based on experimental adding

Isolated yield of benzylidene ethyl cyanoacetate

Isolated yield of benzaldehyde

Reaction condition: benzaldehyde (1.87 mmol), ethyl cyanoacetate (1.87 mmol), H O (4 mL)

The reaction has been accomplished in solvent-free conditions

b

c

d

e

2

group (–OCH and –OH). Meanwhile, the yield of the products in all cases remained

3

almost constant.

According to the mechanism pathway illustrated in Scheme 2, the reaction path-

way contains two steps [58, 59]. During the ꢀrst stage, the acid sites of the catalyst

facilitate the deacetalization via formation of the carbocation and subsequently ben-

zaldehyde production [60]. Then, the basic sites of the catalyst catalyze the reaction

by taking the H-α of ethyl cyanoacetate as a methylene active compound to react

with benzaldehyde. Regarding the electron-withdrawing groups, the possibility of

the carbanion attack to the carbonyl group is more when compared to that of elec-

tron-donating groups [59]. Because the carbonyl group is more activated, the ethyl

cyanoacetate can easily attack the carbonyl group of benzaldehyde [61].

The heterogeneity and reusability study

The catalyst heterogeneity has been checked by removing the catalyst from

the middle of the reaction. For this purpose, after processing the reaction up

to almost 50% in the Knoevenagel step, the catalyst has been removed while

1

3

R. Javad Kalbasi et al.

Scheme 2 A plausible reaction mechanism for the deacetalization–Knoevenagel condensation reaction

by poly(SSA-co-4VP)/CMK-3

the continuation of the reaction was being monitored. The result showed that

no further C–C coupling reaction occurred, and the heterogeneous nature of the

catalyst has been proved.

The activity of the reused catalyst has been checked based on the previous

reports via simple ꢀltration of the catalyst from the reaction and further washing

with hot water and drying in vacuumed oven at 40 °C overnight [62]. It should

be mentioned that the poly(SSA-co-4VP) has an adhesive feature and makes

it hard to remove from the ꢃask; on the other hand, the incorporation of the

polymer into the mesoporous carbon CMK-3 led to having the powdery forma-

tion and facilitates to reuse and recover the catalyst. The outcomes authenticate

that the catalyst can be recycled over 13 times with almost 10% lessening in

the product yield. Moreover, only 7–10% polymer leaching has been detected

by CHNS and potentiometric titration methods that introduces the heterogene-

ity nature of the catalyst. Besides, the SEM images of the recovered catalyst

(

after the sixth run of the reaction) are displayed in Fig. 6. In the XRD pattern of

reused catalyst (Fig. 7), the main peak is shifted to higher 2 theta value, which

can be explained by deformation of the polymer into the CMK-3 pores and sub-

sequently blocking the mesopores [63]. However, comparing these images with

the fresh catalyst (Fig. 5a, b), the CMK-3 mesostructure in the reused catalyst is

well retained (Fig. 7).

The catalyzed activity of various catalysts in the deacetalization–Knoevenagel

condensation reaction was compared with the synthesized catalyst in this study

and is tabulated in Table 4. As can be seen, mostly the deacetalization–Knoev-

enagel condensation reactions process in organic solvents and/or high reaction

time, which can be related to the lower catalytic activity of the catalysts.

1

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Overcoming acid–base copolymer neutralization using mesoporous…

Fig. 6 SEM images of the reused poly(SSA-co-4VP)/CMK-3 after the sixth run

Fig. 7 XRD pattern of the reused poly(SSA-co-4VP)/CMK-3 after the sixth run

Catalyst chemoselectivity

The chemoselectivity of the catalyst in the tandem reaction has been investigated. To

do this, the equal molar concentration of the ketone (acetophenone dimethyl acetal) and

the aldehyde (benzaldehyde dimethyl acetal) was reacted with ethyl cyanoacetate in the

optimum conditions. As can be seen in Scheme 3, the acid–base bifunctional catalyst

distinguishes between the aldehyde and the ketone with a high chemoselectivity with a

7

5% yield in 85 min. The conꢀde space of mesoporous carbon CMK-3 may avoid the

ketone from entering the mesostructured CMK-3, and subsequently, no further interac-

tion happens between the ketone and acid–base sites of the catalyst [32, 74] (Table 5).

1

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R. Javad Kalbasi et al.

Table 4 Deacetalization–Knoevenagel condensation reaction of aromatic dimethyl acetal with ethyl

cyanoacetate catalyzed by poly(SSA-co-4VP)/CMK-3

Entry

1

Substrate

Product

Yield

Time

(min)

75

b

(

%)

8

7

8

2

50

2

8

7

70

3

4

5

8

6

4

75

55

8

7

2

7

80

6

7

105

a

Reaction conditions: catalyst (0.1 g), aromatic dimethyl acetal (1.87 mmol), ethyl cyanoacetate

(

1.87 mmol), H O (4 mL), 60 °C

2

b

Isolated yield

1

3

Overcoming acid–base copolymer neutralization using mesoporous…

Scheme 3 Chemoselectivity survey in the presence of the benzaldehyde dimethyl acetal and

(

1,1-dimethoxyethyl)benzene

Table 5 Deacetalization–Knoevenagel condensation reaction of aromatic dimethyl acetal with ethyl

cyanoacetate using diꢂerent materials

Entry Catalyst

Solvent

T (°C) Time (h) Con. (%) Yield (%) Ref.

1

2

3

4

5

6

H-mont-NH₂

Heptane

Benzene

Toluene

60

80

90

80

1

99

95

94

96

94

91

[64]

[65]

[23]

[66]

[67]

[68]

SO H-MCM-41-NH₂

0.5

1

3

15

100

–

3

SO H–NH –HMS

3

2

AB-MCM-41-g

MIL-101(Al)-NH₂

LZSM-5-AT-OH

1,4-dioxane

Water/acetoni-

trile

7

8

9

1

ZIF8-A61-SO H

1,4-Dioxane

Toluene

DMSO

DMF

1,4-dioxane

Water

80

50

90

45

4

100

97

–

98

99

97

95

99

90

[69]

[70]

[71]

[72]

[73]

[58]

3

P(DVB-NH -0.2-StSO H)

24

5

1.5

2

3

Yb-BCD-NH₂

MOF-cd

0

1

2

Fe O @Cu-HKUST-1

3

4

Ni-Pd@poly (SSA-NVI)/

KIT-6

13

14

15

16

17

S-HPDVB@PBM-1

MIL-101(Al/Fe)-NH₂

Toluene

Water

80

90

80

0.5

1.5

2

1

1.5

99

100

99

100

99

100

99

98

99

[60]

[57]

[35]

[18]

[20]

MONNs-SO H-NH₂

3

DMAN-SO H-OMS-5-5

3

SO H-MONNs

Toluene

3

NH -MONNs

2

18

19

20

21

Acid–base-nanotube+PTSA

ZSM-5@Mg Si O (OH)

Water

r.t

24

10

1

95

99

–

95

99

87

[22]

[9]

[8]

This report

Toluene

Water

80

60

3

4

9

4

NH -SO H-H-ONTFs

2

3

Poly(SSA-co-4VP)/CMK-3

1.25

1

3

R. Javad Kalbasi et al.

Conclusion

In summary, the mesoporous carbon CMK-3 with a high surface area has been

synthesized. Due to the mesoporous structure of the CMK-3 and its high surface

area, the CMK-3 can be utilized as support to incorporate the acid–base copolymer

(

i.e., poly(SSA-co-4VP). Thanks to the good distribution of the copolymer into the

mesopores of the CMK-3, the quenching of the acid and base sites of the polymers

is minimized. The total amount of separated sites has been determined by almost

4

0% with the potentiometric titration method. The poly(SSA-co-4VP)/CMK-3 was

utilized as the bifunctional acid–base catalyst in the tandem one-pot deprotection of

deacetalization–Knoevenagel condensation reaction in aqueous media and in short

reaction time. A profound comprehension of the conduct of acid and base sites in a

solitary material will open the potentials of these kinds of materials toward tandem

reactions, which is our prospect. Using mesomacroporous structured materials as

support can facilitate a broad range of acid–base copolymerization within a highly

accessible acid and base sites and utilizing them as the catalyst in tandem organic

reactions.

Compliance with ethical standards

Conꢀict oꢁ interest The authors declare that they have no conꢃict of interest.

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Article Doi

Overcoming acid–base copolymer neutralization using mesoporous carbon and its catalytic activity in the tandem deacetalization–Knoevenagel condensation reaction

DOI: 10.1007/s11164-020-04153-4

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Full text of DOI:10.1007/s11164-020-04153-4

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