Fiber-Supported Poly(quaternaryammonium bromide)s as Supported

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Kinetics, Catalysis, and Reaction Engineering

Fiber-Supported Poly(quaternaryammonium bromide)s as Supported-Phase Transfer Catalysts in the Spinning Basket Reactor Xian-Lei Shi, Yongju Chen, Qianqian Hu, Hao Meng, and Peigao Duan Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b01302 • Publication Date (Web): 18 May 2018 Downloaded from http://pubs.acs.org on May 18, 2018

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Industrial & Engineering Chemistry Research

Fiber-Supported Poly(quaternaryammonium bromide)s as Supported-Phase Transfer Catalysts in the Spinning Basket Reactor Xian-Lei Shi,* Yongju Chen, Qianqian Hu, Hao Meng, Peigao Duan* Henan Key Laboratory of Coal Green Conversion, Henan Polytechnic University, Jiaozuo, Henan 454003, China. E-mail: [email protected], [email protected]; Tel./fax: +86-0391-3987823

ABSTRACT: In this paper, a newly developed fiber-supported poly(quaternaryammonium bromide)s served as efficient and recyclable supported phase-transfer catalyst in the spinning basket reactor for a series of nucleophilic substitutions, is reported. The fiber catalysts were designed and synthesized systematically from commercially available polyacrylonitrile fiber, and the properties of fiber samples at different stages were characterized detailedly by sorts of technologies. Moreover, the nucleophilic substitutions mediated with fiber supported phase-transfer catalyst exhibited high efficiency to afford a range of substituted products in excellent yields (91-98%) under mild conditions, and on this basis, a solid-liquid phase-transfer catalysis mechanism was proposed. Markedly, the spinning basket reactor with fiber catalyst in its impellers revealed prominent recyclability at least for 15 cycles, and the concise method of operation also exerted a good perspective application in chemical industry.

KEYWORDS: supported phase-transfer catalyst; fiber catalyst; spinning basket reactor, nucleophilic substitutions; recyclability

1. INTRODUCTION The exploitation of new catalysts for more efficient chemical processes is an issue of great importance to promote the development of green chemistry,1,2 and especially for novel catalysts with the potential to greatly impact fine chemicals industry, which, in turn, could bring significant environmental and economic value.3,4 Actually, there is no lack of new types of catalyst being presented every year, however, the possibility of any of these being put into an industrial manufacture is still low. In the actual production, chemists habitually depend on the few species of ACS Paragon Plus Environment

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frequently-used catalysts, which generally utilized responsibly and effectively. Essentially, the obstruction for adopting novel types of catalyst in an industrial manufacture could be impermeable.5 It is undeniable that there are many barriers existed in actual disparities between the typical academic approach and a commercial production technology, particularly the pressures of order date which will not allow the industrial optimization of reported academic procedures. Therefore, the earlier a new catalyst could be certified with high-efficiency in the feasible practice, the more possibilities and ways to put it into real industrial productions. Phase-transfer catalysis (PTC), a catalytic technology developed from the early 1970s, which has been widespread using in pharmaceuticals, pesticides, spices, papermaking and tanneries, and achieved remarkable economic and social benefits.6,7 However, the traditional PTC such as quaternary ammonium salts, crown ethers or polyethers, have some disadvantages including high price, unstable, toxic, environmental pollution, large consumption and difficult to recycle. And with the development of new catalytic technologies, the innovative and recyclable supported phase-transfer catalysts (SPTC) have provided a good way to solve the above problems, and proven to be more crucial to organic synthesis.8,9 So far, all sorts of materials such as polymers,10-13 silica,14-16 and magnetic nanoparticles,17,18 have been served as catalytic material for SPTC in all kinds of organic reactions, although desirable catalytic effect was frequently acquired, the preindustrial experiments were frequently lacking. In other words, most of the SPTC in literatures are simply offer superiorities in academic research, and the reliable SPTC-mediated systems in potential industrial manufactures are still require for further investigation.5 Hence, the development of new approachs for practical SPTC using low-cost and serviceable supports, which give more possibilities of such techniques to be applied in industrial manufactures would be of great benefits.19 Given the excellent flexibility and good application performance, fiber catalysts not only have being utilized in organic synthesis, but also to a series of fuel converting processes, and are deemed as a promising catalyst type from the standpoint of chemical operation.20,21 Many inorganic fibers including metal-fiber,22 carbon-fiber23 or activated carbon fiber,24 silica-fiber,25 glass-fiber,26 and ceramic-fiber27 have been applied to fiber-supported catalysts and exhibited outstanding activities. However, a number of the reported fiber-mediated systems were normally inadequate to the practical application, and exploiting efficient fiber materials with better application performance for more practical industrial catalysis, which may rapidly transfer from the basic laboratories to ACS Paragon Plus Environment

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chemical production, has attracted more and more interests.28 Polyacrylonitrile fiber (PANF), an artificial synthetic polymer material, has been extensively applied in the textile manufacture. Except for the high intensity, the polymer chain structure of PANF has plenty of cyano groups, which provide the active sites for functionalization,29,30 thus, it is advantageous to utilize PANF as a raw material for supported catalysts. Moreover, we have investigated the performance of PANF-supported acid,31 base,32 and metal33,34 catalysts in different types of reactions, based on these studies and in continuation of our interest in supported catalysts,35,36 herein, PANF was reselected as a serviceable support, to present the PANF-supported poly(quaternaryammonium bromide)s as a new form of SPTC, which was set in the spinning basket reactor and verified in various nucleophilic substitutions.

2. EXPERIMENTAL METHODS Preparation of fiber-supported poly(quaternaryammonium bromide)s (PANFPABuBnBr) Step 1. Polyethylene polyamine (30 g) was mixed with water (30 g) in a three-necked flask, and the mixture was preheated to reflux with stirring. Next, PANF (3.00 g) was added to the mixture and it was refluxed (104-105 °C) with stirring for 22 h. Whereafter, removed the fiber and repetitious rinsed it with water (60-70 °C) until the washing solution with a pH value of 7, and vacuum dried the sample at 60 °C to a constant weight to give polyamine functionalized PANF (PANFPA, 3.95 g, weight gain 32%). Step 2. 1-Bromobutane (10 g) was mixed with acetonitrile (60 mL) in a flask, and the mixture was preheated to reflux with stirring. Next, PANFPA (3.78 g) was added to the mixture and it was refluxed (83 °C) with stirring for 12 h. Afterwards, removed the fiber and rinsed it with acetonitrile (2×50 mL), and vacuum dried the sample at 60 °C to a constant weight to obtain PANF-supported poly(butylammonium bromide)s (PANFPABuBr, 5.32 g, butylammonium bromides content 2.11 mmol g-1). Step 3. PANFPABuBr (4.10 g) was introduced to a 5% (mass percent) sodium carbonate solution (100 mL) in a flask, and the mixture was stirred for 2 h at ambient temperature. Subsequently, removed the fiber and rinsed it with water (2×50 mL), and vacuum dried the sample at 60 °C to a constant weight to acquire poly(tertiary amine) functionalized PANF (PANFPABu, 3.40 g, tertiary amines content 2.54 mmol g-1). ACS Paragon Plus Environment


Step 4. Benzyl bromide (10 g) was mixed with acetonitrile (60 mL) in a flask, and the mixture was preheated to reflux with stirring. Next, PANFPABu (3.20 g) was added to the mixture and it was refluxed (83 °C) with stirring for 12 h. Whereafter, removed the fiber and rinsed it with acetonitrile (2×50 mL), and vacuum dried the sample at 60 °C to a constant weight to get PANF-supported poly(quaternaryammonium bromide)s (PANFPABuBnBr, 4.56 g, quaternary ammonium salts content 1.74 mmol g-1). General procedure for nucleophilic substitutions A mixture of halide (5 mmol), nucleophilic reagent (6.5 mmol) and water (15 mL) was stirred (700 rpm) at 60 °C in the spinning basket reactor (50 mL) with the fiber-supported poly(quaternaryammonium bromide)s (the content of quaternary ammonium salt was 2 mol% based on halide) in its impellers. After the reaction was completed, cooled the reaction mixture to room temperature and let out. Then washed the reactor with ethyl acetate (15 mL) and subsequently with water (15 mL), and the two washing solutions were combined to the reaction mixture. Whereafter, separated the organic layer from the above mixture, and the aqueous layer was extracted with ethyl acetate (3×5 mL), washed the combined organic phase with saturated brine, and then dried with anhydrous sodium sulfate. Afterwards, removed the solvent by rotary evaporation to give the crude product, and the pure nucleophilic substitution product was obtained by silica gel column chromatography (petroleum ether/ethyl acetate). Typical gram-scale procedure for nucleophilic substitutions Benzyl chloride (6.33 g, 50 mmol), sodium p-toluenesulfinate (11.58 g, 65 mmol), and water (150 mL) was mixed into a spinning basket reactor (500 mL, with PANFPABuBnBr in its impellers, the content of quaternary ammonium salt was 2 mol% based on benzyl chloride), and the mixture was stirred (700 rpm) at 60 °C for 0.25 h. After the reaction was finished, discharged the reaction mixture, and washed the reaction vessel with water (100 mL) which was combined to the mixture. Finally, the white solid in the mixture was recrystallized and dried to gain pure product (12.03 g, 98%).

3. RESULTS AND DISCUSSION Preparation of fiber-supported phase transfer catalysts ACS Paragon Plus Environment

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The conception for the design of the fiber-supported phase-transfer catalyst was motivated by the following two concerns. On the one hand, PANF, as an artificial synthetic polymer material, the polymer chains of polyacrylonitrile equipped with plenty of cyano groups which possess good soakage behavior not only in organic solvents but also in aqueous solutions. After the immobilization of phase-transfer catalyst on the fiber surrounding with cyano groups, the amphiphilic cyano groups would enhance the interaction of substrates and phase-transfer active sites

to

improve

the

poly(quaternaryammonium

phase-transfer bromide)s,

catalytic as

the

performance. catalysts

On

rooted

the

in

other

the

fiber,

hand, the

poly(quaternaryammonium bromide)s have long-chains and the long-chains dotted with phase-transfer active sites which are very beneficial to the contact with nucleophilic reagents in water, and further to raise the phase-transfer catalytic activity. Therefore, as shown in Scheme 1, the counterplan for the preparation of the fiber-supported phase transfer catalyst was performed firstly by

multilevel

amination

with

PANF

and

finally

to

obtain

the

fiber-supported

poly(quaternaryammonium bromide)s.

Scheme 1. Preparation of the fiber-supported poly(quaternaryammonium bromide)s. Our previous work could be referred34, the step 1 was used to obtain the polyamine-functionalized fiber (PANFPA) by multilevel amination, and the polyamine groups were successfully immobilized on PANF with a weight gain (Weight gain [%]= [(W2−W1)/W1]× 100, where W1 and W2 are the weight of the fiber sample before and after amination, respectively) of 32%. Then, the poly(tertiary amine)-functionalized fibers were acquired by the following two steps, ACS Paragon Plus Environment


which would be used for final quaternization. Selecting the PANFPABuBnBr for example (due to its higher catalytic efficiency), after salinization with 1-bromobutane in acetonitrile, the PANF-supported poly(butylammonium bromide)s (PANFPABuBr) was gained with butylammonium bromide loading of 2.11 mmol g-1. Next, PANFPABuBr was neutralized in sodium carbonate aqueous solution to acquire poly(tertiary amine)-functionalized PANFs (PANFPABu, with a tertiary amine content of 3.10 mmol g-1). Finally, the fiber-supported poly(quaternaryammonium bromide)s were attained by quaternization reaction in step 4. Depending on the orders of different halides used, three kinds of fiber-supported poly(quaternaryammonium bromide)s were obtained, and the contents of poly(quaternaryammonium bromide)s of PANFPABuBuBr, PANFPABuBnBr, PANFPABnBnBr were 1.89, 1.74, 1.64 mmol g-1, respectively. Characterization of fiber-supported phase transfer catalysts To ensure the reliability of the preparation method for synthesizing fiber-supported poly(quaternaryammonium bromide)s and to examine the stability of fiber catalyst, various technologies was used to characterized the fiber samples. The original PANF, PANFPA, PANFPABuBr, PANFPABu, PANFPABuBnBr, and the recovered catalysts PANFPABuBnBr-1 and PANFPABuBnBr-15 from the first and 15th runs in gram-scale model nucleophilic substitution of benzyl chloride and sodium p-toluenesulfinate, were all checked and characterized by morphology, elemental analysis, mechanical property, FTIR spectroscopy and SEM, respectively. Morphology. Firstly, morphologies of PANF, PANFPA, PANFPABuBr, PANFPABu, PANFPABuBnBr, PANFPABuBnBr-1 and PANFPABuBnBr-15 were exhibited in Figure 1. Obviously, the original fiber of PANF showed a bright white color (Figure 1a). In contrast, after multilevel amination and the own color of polyamine was delivered to the fiber, which caused PANFPA with an appearance of faint yellow (Figure 1b). Moreover, compared with PANFPA, the color of fiber samples of PANFPABuBr, PANFPABu and PANFPABuBnBr got a bit deeper with the subsequent salinization, neutralization and quaternization (Figure 1c to e). In addition, apart from a slight color deepening, PANFPABuBnBr-1 and PANFPABuBnBr-15 (Figure 1f and g) after the catalytic processes once to 15 cycles had no obvious change from fresh PANFPABuBnBr. On the whole, as can be observed from the appearance, there was no significant damage on the fiber morphology, and all the samples held their inherent shape no matter whether it is in synthetic process or usage stage.

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Figure 1. Morphology of (a) PANF, (b) PANFPA, (c) PANFPABuBr, (d) PANFPABu, (e) PANFPABuBnBr, (f) PANFPABuBnBr-1, and (g) PANFPABuBnBr-15. Elemental analysis. Then, the elemental analysis data of PANF, PANFPA, PANFPABuBr, PANFPABu, PANFPABuBnBr, PANFPABuBnBr-1, and PANFPABuBnBr-15 were tested and the results are listed in Table 1. PANF and PANFPA had the similar C, H, N and S contents to the reported results, and the related interpretations had been elucidated in our previous work.31,34 Whereafter, the salinization on PANFPA brought 1-bromobutane in the fiber, and the formed PANFPABuBr had decreased C, H, N and S amounts since the own element contents of 1-bromobutane. However, after neutralization in step 3, the content of C, H, N and S of PANFPABu were all increase (Table 1, entry 4), this is because that the hydrogen bromides of PANFPABuBr were balanced out by sodium carbonate. Nevertheless, after the quaternization of PANFPABu and benzyl bromide to form the poly(quaternaryammonium bromide)s, and owing to the immobilization of benzyl bromide which also without N and S, and lower quantities of C, H than PANFPABu, PANFPABuBnBr got a obvious decrease on the amounts of C, H, N and S (Table 1, entry 5). Moreover, with the subsequent utilization in spinning basket reactor for the nucleophilic substitutions, the elemental analysis data of PANFPABuBnBr-1 and PANFPABuBnBr-15 (Table 1, entries 6 and 7) had no substantial change compared with the fresh fiber-supported phase transfer catalyst, however, it should be noted that the small increase of S content could be because of the sodium p-toluenesulfinate or substitution products absorption on the fiber. Table 1. Element contents of PANF, PANFPA, PANFPABuBr, PANFPABu, PANFPABuBnBr, PANFPABuBnBr-1, and PANFPABuBnBr-15 Entry

Fiber simple

C (%)

H (%)

N (%)

S (%)

1

PANF

67.53

5.86

23.65

0.24

2

PANFPA

56.21

6.72

20.29

0.15

3

PANFPABuBr

50.07

6.66

15.64

0.11

4

PANFPABu

60.24

7.57

19.08

0.14

5

PANFPABuBnBr

57.09

6.59

13.73

0.09

6

PANFPABuBnBr-1

57.36

6.31

13.83

0.16

7

PANFPABuBnBr-15

57.44

5.99

13.95

0.47



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Mechanical property. Next, the mechanical property of fibers was inspected, and the average breaking strengths of samples are summarized in Table 2. PANF has a breaking strength as predicted (Table 2, entry 1). After polyamine functionalization, PANFPA retained 79% of the initial fiber strength (Table 2, entry 2), that is 8.38 cN. With the following salinization by 1-bromobutane, PANFPABuBr got a little reduction on the breaking strength, and 77% of the original PANF mechanical property, was maintained (Table 2, entry 3). Moreover, after subsequent neutralization and quaternization, there were only tiny changes of breaking strength on PANFPABu and PANFPABuBnBr (Table 2, entries 4 and 5). Furthermore, after the first utilization in the spinning basket reactor for the nucleophilic substitution, PANFPABuBnBr-1 was almost no intensity reduction compared to fresh PANFPABuBnBr (7.95 cN, Table 2, entry 6). What is more, compared the breaking strength of PANFPABuBnBr-15 with that of PANF, the recovered catalyst after multiple catalytic cycles still reserved about 74% of the original fiber mechanical property (Table 2, entry 7). From the above results, it could be concluded that PANF holds outstanding mechanical property served the purpose of fiber-supported phase transfer catalysts, and the fiber-supported poly(quaternaryammonium bromide)s equipped sufficient strength in impellers of the spinning basket reactor in the vigorous nucleophilic substitutions. Table 2. Mechanical properties of PANF, PANFPA, PANFPABuBr, PANFPABu, PANFPABuBnBr, PANFPABuBnBr-1, and PANFPABuBnBr-15

a

Entry

Fiber

Breaking strength (cN)

Retention ratea (%)

1

PANF

10.61

100

2

PANFPA

8.38

79

3

PANFPABuBr

8.19

77

4

PANFPABu

8.15

77

5

PANFPABuBnBr

7.97

75

6

PANFPABuBnBr-1

7.95

75

7

PANFPABuBnBr-15

7.86

74

Based on PANF.

FTIR spectroscopy. Whereafter, the FTIR spectroscopy of the fiber samples was also studied, and the spectra of PANF, PANFPA, PANFPABuBr, PANFPABu, PANFPABuBnBr, PANFPABuBnBr-1, and PANFPABuBnBr-15 are exhibited in Figure 2. PANF and PANFPA (Figure 2a and b) were provided the similar spectra with our previous paper.31,34 Even so, after salinization, a new weak absorption around 2890 cm-1 of C−H vibrational modes of methyl, was presented in PANFPABuBr (Figure 2c). After neutralization, there was little variation on characteristic absorptions of PANFPABu and ACS Paragon Plus Environment

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PANFPABuBr (Figure 2d and c). However, after the step of quaternization and the introduction of phenyl on the fiber, the PANFPABuBnBr exhibited two new absorption peaks around 745 and 702 cm-1, which could be assigned to the vibrational modes of benzene ring (Figure 2e), and the results are in accord with the synthetic strategy. In addition, with the utilization in the spinning basket reactor for the nucleophilic substitutions, the FTIR spectrum of the recovered fiber catalyst PANFPABuBnBr-1 and PANFPABuBnBr-15 (Figure 2d and e) are almost the same as to the fresh fiber-supported poly(quaternaryammonium bromide)s, these results revealed the fiber-supported phase transfer catalyst possessed good stability and persistent activity for nucleophilic substitutions.

Figure 2. FTIR spectra of (a) PANF, (b) PANFPA, (c) PANFPABuBr, (d) PANFPABu, (e) PANFPABuBnBr, (f) PANFPABuBnBr-1, and (g) PANFPABuBnBr-15. In addition, Form SEM images of the fiber samples (Figures S1), it can be observed that there was no substantial flaw in the fibers, and the fibrous body was maintained in the vigorous agitation conditions. What is more, thermal property of the fiber catalyst was also inspected by thermogravimetry (TG), and the analysis result displayed that there was no significant degradation occurred before 165 °C (Figures S2). Application of the fiber-supported poly(quaternaryammonium bromide)s for nucleophilic substitutions in spinning basket reactor In general, fiber has a larger specific surface area than resin, and could support more functional groups which would greatly improve the catalytic activity. Moreover, fiber is not easy to be broken in the stirring process due to its high intensity, which is very helpful in all types of catalytic reactors. ACS Paragon Plus Environment


Considering these strengths, we intend to take full advantage of PANF and dispose the fiber-supported phase transfer catalyst in spinning basket reactor (Figure 3) in virtue of its prominent flexibility to demonstrate a more efficient catalytic device.

Figure 3. Schematic diagram of the spinning basket reactor. Optimization of the fiber-supported phase transfer catalysts. According to our research plan, the phase transfer catalytic performance of the fiber-supported poly(quaternaryammonium bromide)s in impellers of the spinning basket reactor was tested on nucleophilic substitutions (Table 3), and the nucleophilic substitution of benzyl chloride and potassium thiocyanate for the synthesis of benzyl thiocyanate was elected as the model reaction. In the initial optimization, potassium thiocyanate with a 1.5 equivalent based on benzyl chloride, and the reaction temperature was set at 80 °C. At first, the blank experiments showed that the nucleophilic substitution without catalyst or using original fiber in the system, only obtained 42% and 44% yields of product after a longer time of 4 h (Table 3, entries 1 and 2), respectively. However, with the three fiber catalysts in the spinning basket reactor for nucleophilic substitution, the reaction could complete in short time no more than 1 h, and all the corresponding product yields over 95% (Table 3, entries 3-5). The good results as expected, due to the designed fiber-supported phase transfer catalysts merited both the selected support material (PANF) and the immobilized multilevel active sites of poly(quaternaryammonium bromide)s, which would enhance the collision frequency of substrates and further to promote the ACS Paragon Plus Environment

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phase-transfer activities.

Even

so, it is important to

note

that the

fiber-supported

poly(quaternaryammonium bromide)s with both butyl and benzyl groups of PANFPABuBnBr showed more efficiency than the other two fiber-supported phase transfer catalysts, and the mediated nucleophilic substitution acquired a higher yield of 97% merely took 0.5 h (Table 3, entry 4). So, the PANFPABuBnBr was used for further condition optimization. Next, the influence of the amounts of catalyst and nucleophilic reagent on the substitution was investigated respectively (Table 3, entries 6-11), and the ultimate outcome displayed that with 2 mol% catalyst amount and 1.3 equivalent of potassium thiocyanate based on benzyl chloride, the nucleophilic substitution could still hold its reactivity with the product yield up to 96% with 0.5 h. In addition, it is worth noting that further to cut down the amounts of catalyst or potassium thiocyanate were unfavorable to the substitution (Table 3, entries 8 and 11). Then, the effect of the reaction temperature on the nucleophilic substitution was inquired concisely (Table 4, entries 12-14). Raising reaction temperature to 100 °C, the reaction could accomplish with 0.25 h (Table 3, entry 12), while lower the reaction temperature to 60 °C, a 95% product yield still could be obtained, but further to decrease the temperature to 40 °C, a less than desirable product yield of 81% was gained with the prolonged reaction time (Table 3, entries 13 and 14). Finally to consider the total results, the optimized conditions of the nucleophilic substitution were set at 60 °C, 1.3 eq potassium thiocyanate was used and a 2 mol% PANFPABuBnBr as the catalyst. What is more, the conventional phase-transfer catalyst tetrabutylammonium bromide (TBAB) was used in the controlled experiment (Table 3, entry 15) under the optimized conditions, the result showed that TBAB was less efficiency than the fiber catalyst, and the mediated nucleophilic substitution via a longer reaction time only obtained a lower product yield of 83%. Table 3. Optimization of the fiber catalysts in the spinning basket reactor for nucleophilic substitutionsa

Entry

Cat.

Cat. amountb (mol%)

KSCN (eq)

Temperature (°C)

Time (h)

Yieldc (%)

1

-

-

1.5

80

4.0

42

2

PANF

-

1.5

80

4.0

44

3

PANFPABuBuBr PANFPABuBnBr PANFPABnBnBr

5

1.5

80

0.75

95

5

1.5

80

0.5

97

5

1.5

80

0.5

95

4 5



6 7

PANFPABuBnBr PANFPABuBnBr

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3

1.5

80

0.5

96

2

1.5

80

0.5

96

1

1.5

80

0.5

89

2

2.0

80

0.5

97

2

1.3

80

0.5

96

2

1.2

80

0.5

88

2

1.3

100

0.25

96

2

1.3

60

0.5

95

2

1.3

40

1.0

81

2

1.3

60

1.0

83

Table continue 8 9 10 11 12 13 14 15 a

PANFPABuBnBr PANFPABuBnBr PANFPABuBnBr PANFPABuBnBr PANFPABuBnBr PANFPABuBnBr PANFPABuBnBr TBABd

Reaction conditions: benzyl chloride (5.0 mmol), KSCN (the equivalent was based on benzyl chloride) and

water (15 mL) stirred at the corresponding temperature. b Based on the content of quaternary ammonium salt. c Isolated yield, d Tetrabutylammonium bromide.

Fiber-supported phase transfer catalyst in the spinning basket reactor for nucleophilic substitutions. To continue our research project, the fiber-supported poly(quaternaryammonium bromide)s in impellers of the spinning basket reactor was inspected in different substrates nucleophilic substitutions under the optimized reaction conditions (Table 4). Different types of halides were selected and substituted with four typical nucleophilic reagents including potassium thiocyanate, sodium azide, sodium acetate and sodium p-toluenesulfinate, to inspect the scope of this spinning basket reactor. It can be observed from the results that the technology has a good universality of substrates, and no matter chloro-hydrocarbons or bromo-hydrocarbon, which including both aromatic halides (Table 4, entries 1-3, 5-7, 9-11 and 13-15) and aliphatic halides (Table 4, entries 4, 8, 12 and 16), reacted with the nucleophilic reagents effectively to acquire a series of substituted products in excellent yields (91-98%). By comprehensive analysis, it is clearly that the halogen species and the electronic effect on the aromatic ring did not exhibit obvious influence on nucleophilic substitutions, however, even more noteworthy is the reactivity of aliphatic halides, which was lower than aromatic halides, and the corresponding aliphatic halides (Table 4, entries 4, 8, 12 and 16) only to gain product yields of 91% to 94% even with longer reaction time. In addition, the results also showed that the reactivity of nucleophilic reagents with the order from high to low was sodium p-toluenesulfinate, potassium thiocyanate, sodium azide and sodium acetate. All in all, the above results indicate the fiber-supported poly(quaternaryammonium bromide)s in spinning basket reactor equipped with high catalytic performance and broad applicability for phase-transfer catalyzed nucleophilic substitutions. ACS Paragon Plus Environment

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Table 4. Fiber-supported phase transfer catalyst in spinning basket reactor for virious nucleophilic substitutionsa

Entry

RX

M+Nu-

Time (h)

Product

Yieldb (%)

1

C6H5CH2Cl

KSCN

0.5

3a

95

2

4-O2NC6H4CH2Cl

KSCN

0.5

3b

96

3

C6H5CH2Br

KSCN

0.5

3a

97

4

n-C8H17Br

KSCN

2.0

3c

93

5

C6H5CH2Cl

NaN3

1.0

3d

94

6

4-O2NC6H4CH2Cl

NaN3

1.0

3e

96

7

C6H5CH2Br

NaN3

1.0

3d

96

8

n-C8H17Br

NaN3

2.0

3f

91

9

C6H5CH2Cl

NaOAc

1.5

3g

95

10

4-O2NC6H4CH2Cl

NaOAc

1.5

3h

95

11

C6H5CH2Br

NaOAc

1.5

3g

97

12

n-C8H17Br

NaOAc

3.0

3i

94

13

C6H5CH2Cl

NaSO2Tol

0.25

3j

97

14

4-O2NC6H4CH2Cl

NaSO2Tol

0.25

3k

98

15

C6H5CH2Br

NaSO2Tol

0.25

3j

97

16

n-C8H17Br

NaSO2Tol

1.0

3l

94

a

Reaction conditions: halide (5 mmol), nucleophilic reagent (6.5 mmol), and PANFPABuBnBr (2 mol%) in water at 60 °C for the corresponding time. b Isolated yield.

Recyclability of the fiber-supported phase transfer catalyst in spinning basket reactor. The recyclability and large-scalability of the fiber-supported poly(quaternaryammonium bromide)s in impellers of the spinning basket reactor was also demonstrated on the nucleophilic substitution of benzyl chloride and sodium p-toluenesulfinate in gram-scale. In the study, the operation procedures were performed on the spinning basket reactor with catalyst in its impellers, and the reaction mixture was discharged out from the spout after the reaction, whereafter, the reactor was applied to the next cycle just by simply rinse with water. The results indicated that the nucleophilic substitution proceeded smoothly with almost no yield decrease of product (Figure 4, from 98% to 96%) and weight change of PANFPABuBnBr (from 0.579 g to 0.575g) over 15 cycles (no test for more runs). Moreover, the phase-transfer active groups had little loss from the fiber and PANFPABuBnBr-15 with a quaternaryammonium bromide content of 1.69 mmol g-1. In addition, the fiber-supported phase transfer catalyst in spinning basket reactor without remarkable geometry destructions in the



Page 14 of 20

catalytic cycles. Nevertheless, it should be noted that the possible structuration of fiber catalyst into pads is complicated, and any change of the intricate geometric structure during the reaction would affect the catalytic activities.20,21 Furthermore, during the research, a certain stability of fiber-supported poly(quaternaryammonium bromide)s was also tested, and PANFPABuBnBr stored on shelves without special protection kept equally catalyst effectiveness at least up to three months.

Figure 4. Recyclability of the fiber catalyst in the spinning basket reactor for nucleophilic substitutions. The proposed phase-transfer catalytic mechanism Finally,

a

possible

phase-transfer

catalytic

mechanism

of

the

fiber-supported

poly(quaternary-ammonium bromide)s-mediated nucleophilic substitutions was proposed (Figure 5). Referred to the relevant literatures37,38 and based on our previous work,33,35 we believe that the functionalization process for immobilizing catalytic active groups is onto the surface layer of the fiber, that is, the supported active components, i.e. quaternaryammonium bromides were in the interior of the fiber, which would interact with the polymer chains to construct a very unique “microenvironment”, and the catalytic reactions were proceeded in the microenvironment (in the red box of Figure 5). On the one hand, the polymer chains of PANF involve plentiful cyano and formyloxy (from the second monomer methyl acrylate) groups, which have favourable soakage behavior for organic reagents, and after the immobilization of phase-transfer active sites on the fiber surrounding with cyano and formyloxy groups in the interior of the fiber, the organic halides would enriched in the microenvironment and its interphase due to their poor solubility in water. On the ACS Paragon Plus Environment

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other hand, the poly(quaternaryammonium bromide)s equipped with long-chains and the long-chains dotted with phase-transfer active sites, which could swing along with solvent to contact with the inorganic salts of nucleophilic reagents dispersed in water, and with the help of the phase-transfer active sites by anion exchange of bromide ion and anionic nucleophile, the anionic nucleophile could be brought into the microenvironment in the interior of the fiber, then the halides would react with anionic nucleophile and accomplished the nucleophilic substitutions.

Figure 5. The schematic diagram of the phase-transfer catalysis mechanism. Moreover, a “hot filtration test” was also investigated to ascertain the catalytic behavior of the fiber catalyst. The hot filtration test of the fiber-supported phase transfer catalytic system was performed on the model nucleophilic substitution. In the course of operation, the fiber-supported poly(quaternaryammonium bromide)s was eliminated timely from the spinning basket reactor after normal reaction for 15 min, afterwards, the remaining mixture was continued and couldn’t proceed smoothly, just acquired 59% of the product yield (Blank control: yield 42% without any catalyst for 4 h, table 3, entry 1). The above results suggested that there was little catalytic behavior was allocated to the homogeneous way.

4. CONCLUSIONS In summary, a new-type fiber-supported phase transfer catalyst with high efficient, prominent recyclability and large-scalability in impellers of the spinning basket reactor has been developed ACS Paragon Plus Environment


and verified in nucleophilic substitutions. The method for the synthesis of fiber-supported poly(quaternaryammonium bromide)s proved the design concept on the new supported-phase transfer catalyst, and the conception was consistent with the proposed phase-transfer catalysis mechanism, because both the support material selected and multilevel active sites immobilized were very beneficial to the contacts of the substrates, which would contribute to phase transfer catalysis. Moreover, the fiber catalyst was characterized detailedly throughout the study, and was capable of long-term storage. Furthermore, the fiber-supported poly(quaternaryammonium bromide)s in impellers of the spinning basket reactor mediated the nucleophilic substitutions under mild conditions and obtained a series of substituted products with excellent yields. In addition, the novel spinning basket reactor without marked catalytic ability loss, and the fiber catalyst could be reused up to 15 cycles in gram-scale. From the results and discussion above, and in virtue of the own superiority of PANF, it is attractive to imitate the spinning basket reactor with fiber catalyst in its impellers for actual productions. The factory trial of the fiber catalyst in the spinning basket reactor is underway.

ASSOCIATED CONTENT Supplementary Information The supporting material contains experimental details, preparation of PANFPABuBuBr, preparation of PANFPABnBnBr, mechanical strength test method, SEM images of fiber samples, TGA of the fiber catalyst, 1H NMR data and copies of 1H NMR spectra of synthesized compounds.

AUTHOR INFORMATION Corresponding Author *Xian-Lei Shi. E-mail: [email protected] *Peigao Duan. E-mail: [email protected] ORCID Xian-Lei Shi: 0000-0003-4703-6601 Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENTS Funding support from the Henan Province Office of Education (17A150012), Science and Technology Research Project of Henan Province (172102210282), Fundamental Research Funds for the Universities of Henan Province (NSFRF170910), Natural Science Foundation of Henan Province (182300410143), Technological Innovation Team in University of Henan Province (18IRTSTHN010) are gratefully acknowledged.

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Fiber-Supported Poly(quaternaryammonium bromide)s as Supported

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