Recent developments on phase-transfer catalytic reactions under ultrasound irradiation

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Review

Recent developments on phase-transfer catalytic reactions under ultrasound irradiation Gandavaram Syam Prasad a,b,∗, Maw-Ling Wang c, Chamarthi Naga Raju d, Gollapalli Nageswara Rao e a

Department of Chemistry, Sree Vidyanikethan Engineering College, Sree Sainath Nagar, Tirupati 517102, India Department of Chemical Sciences, Sree Vidyanikethan Degree College, Sree Sainath Nagar, Tirupati 517102, India Coretech System Co., Ltd, 8F-2, No. 32, Taiyuan St., Chupei, Hsinchu 302, Taiwan, ROC d Department of Chemistry, Sri Venkateswara University, Tirupati 517502, India e School of Chemistry, Andhra University, Visakhapatnam 530003, India b c

a r t i c l e

i n f o

Article history: Received 27 May 2016 Revised 10 October 2016 Accepted 20 October 2016 Available online xxx Keywords: Reaction kinetics Phase-transfer catalysis Ultrasound condition

a b s t r a c t The kinetics for various reaction systems were reviewed under the phase-transfer catalysis assisted by ultrasound irradiation conditions. The different factors on the kinetics of the reaction were reviewed. Advantages of chemical reaction under ultrasound irradiation conditions are highlighted. Chemical conversions under phase-transfer catalytic conditions improved the yields. These reactions avoid longer reaction times, enhance the yields of the products and reduce the organic solvent. Development of this methodology and selectivity of various reactions were presented. © 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

1. Introduction Kinetics using Phase-transfer catalysis (PTC) is an exciting field with many opportunities for research and application development, has been drawing increased attention by scientists all over the world. A few groups are engaged in the research on the study of reaction kinetics comparing with presence and absence of ultrasound conditions and it was rather difficult to comprehend the work published in diverse areas in this field. PTC is a technique for conducting reactions between species present in homogeneous and heterogeneous reaction systems [1–7]. PTC is a versatile, wellestablished synthetic technique, applied with several advantages to a number of organic reactions [8–16]. Phase-transfer catalysts, such as quaternary ammonium and phosphonium salts, crown ethers, polyethylene glycols and cryptands, have been used to carry out reactions between reactants which exist in the same or different phase(s) [1–16]. Presently, PTC has been extensively applied in the synthesis of organic chemicals via condensation, elimination, substitution, redox and polymerization. The advantage of using PTC can be carried out under moderate conditions to obtain a high reaction rate. High selectivity of the main product and high conversion of the reactant are obtained [16–19].

∗

Corresponding author. E-mail address: [email protected] (G.S. Prasad).

The application of ultrasound waves in chemistry is a convenient technique for the facilitation of chemical reactions [20]. The primary purpose in adopting PTC in combination with ultrasound irradiation is to search for effective condition to enhance the reaction [21,22]. Direct interaction was not possible between ultrasound and matter, and so it was an indirect phenomenon, i.e., cavitation must be facilitated to induce a reaction. Hence, the use of ultrasound to enhance chemical reactivity [23–26] is now recognized as a viable environmentally benign alternative technology [24–28]. Although sonication methods have been initially applied to homogeneous reactions in a variety of solvents, this approach has now evolved into a useful technique in heterogeneous reactions [29–32]. This review deals with the kinetics for various reaction systems under the PTC assisted with and without ultrasound irradiation conditions for the past ten years. 2. Dichlorocyclopropanation 2.1. Dichlorocyclopropanation of 1,7-octadiene Wang and Rajendran have been reported [33] the kinetics for dichlorocyclopropanation of 1,7-octadiene (Scheme 1) with an excess of chloroform under PTC and ultrasound irradiation conditions at the frequency of 28 kHz output power of 200 W using aqueous sodium hydroxide as the base and also investigated with different factors.

http://dx.doi.org/10.1016/j.jtice.2016.10.040 1876-1070/© 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Please cite this article as: G.S. Prasad et al., Recent developments on phase-transfer catalytic reactions under ultrasound irradiation, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.040

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Scheme 1. Table 1 Reaction condition: 10 mmol of 1,7-octadiene; 30 mL of chloroform; 0.2 mmol of BTEAC; 15 mL of NaOH solution (50 wt.%); 30 °C; ultrasound condition (28 kHz, 200 W). Agitation speed (rpm)

0

200

400

600

800

100

In the presence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 ) In the absence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 )

1.56

3.48

6.05

7.21

11.56

19.64

0.59 –

2.45 –

3.58 1.91

4.21 4.78

7.51 7.94

13.09 13.31

–

–

1.66

3.03

4.49

6.79

Table 2 Reaction condition: 10 mmol of 1,7-octadiene; 30 mL of chloroform; 0.2 mmol of BTEAC; 15 mL of NaOH solution (50 wt.%); 800 rpm; ultrasound condition (28 kHz, 200 W). Temperature (°C)

20

30

35

40

50

In the presence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 ) In the absence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 )

5.66

11.56

18.80

25.29

50.98

4.49 2.29

7.51 7.94

12.84 11.15

14.93 21.22

25.94 42.22

2.49

4.49

6.91

12.48

21.12

2.1.1. Effect of the agitation speed In this study, the conversion is increased with an increase in the agitation speed from 400 to 10 0 0 rounds per minute (rpm) under optimal reaction conditions. In principle, a large agitation speed provides a larger interfacial area of the two phases to increase the mass transfer rate. For such an interfacial reaction, the rate is strongly dependent on the agitation speed. For comparison, the two apparent rate constants (kapp , 1 and kapp , 2) obtained from the PTC reaction [34] in the presence and absence of ultrasonic irradiation were shown in Table 1. 2.1.2. Effect of the temperature The reactivity of 1,7-octadiene is increased with an increase in the temperature along with the ultrasonic effect under optimal reaction conditions. The reason is that the number of reactant molecules, which possess higher activation energy at a higher temperature and thus the ultrasonic wave easily passes through the reactor. Thus the conversion is increased. The two apparent rate constants (kapp , 1 and kapp , 2) obtained from the PTC reaction [34] in the presence and absence of ultrasonic irradiation were shown in Table 2. 2.1.3. Different phase-transfer catalysts Dichlorocarbene addition to 1,7-octadiene has been chosen to study the comparative reactivities of eight different phasetransfer catalysts, namely, tetraethylammonium chloride (TEAC), tetraethylammonium bromide (TEAB), tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide (TBAB), tetrabutylammonium iodide (TBAI), tetrabutylammonium hydrogen sulfate (TBAHS), benzyltriethylammonium chloride (BTEAC) and benzyltriethylammonium bromide (BTEAB) under optimal reaction conditions. For comparison, the two apparent rate constants obtained from the PTC reaction [34] in the presence and absence of ultrasonic irradiation were given in Table 3. Choosing a small size of the anionic ion in the halide groups of PTCs is favourable for a high reaction rate. That is, a higher re-

activity is obtained for a quaternary ammonium salt of less total carbon number. It is thus concluded that the order of the activities is consistent with the results indicated by Starks et al. [16]. 2.1.4. Effect of varying substrate amount The reaction rate constant is increased with the decrease in the concentration of 1,7-octadiene in the organic phase, because the availability of the catalyst per mole of 1,7-octadiene to catalyse the reaction is low at high 1,7-octadiene concentration. Under optimal reaction conditions the measured kapp , 1 and kapp , 2 values in the presence and absence of ultrasonic irradiation were presented in Table 4. 2.1.5. Effect of the amount of inorganic salt (NaCl) In this study, sodium chloride is produced as a by-product from the reaction. Therefore, the addition of NaCl naturally affects the equilibrium of each component between the two phases. The addition of NaCl enhances the reaction as a result of a salting-out effect in the aqueous phase and also the formed dichlorocarbene is more favourable to stay in the organic phase. For comparison, the two apparent rate constants obtained from the PTC reaction [34] under optimal reaction conditions in the presence and absence of ultrasonic irradiation were also shown in Table 5. 2.1.6. Effect of Ultrasonic Power The reaction rate also compared with 28 and 40 kHz having same output power of 200 W. At 40 min, without ultrasonic irradiation the conversion is only 76%, but in the presence of ultrasound the conversion is 97% and almost 100% for 28 and 40 kHz, respectively, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation. 2.2. Dichlorocyclopropanation of styrene Wang and Prasad [35] have been reported the kinetics for dichlorocyclopropanation of styrene with an excess of chloroform

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Table 3 Reaction condition: 10 mmol of 1,7-octadiene; 30 mL of chloroform; 15 mL of NaOH solution (50 wt.%); 800 rpm; 30 °C; ultrasound condition (28 kHz, 200 W). Catalysts

BTEAB

BTEAC

TBAB

TBAC

TBAI

TEAB

TEAC

TBAHS

In the presence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 ) In the absence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 )

9.54

11.56

5.75

6.91

4.57

15.01

23.12

11.45

4.01 5.97

7.51 7.94

3.65 4.40

4.01 5.81

3.43 3.89

8.94 11.04

14.11 14.28

5.25 6.66

3.61

4.49

2.54

3.47

2.31

7.57

8.86

3.79

Table 4 Reaction condition: 30 mL of chloroform; 0.2 mmol of BTEAC; 15 mL of NaOH solution (50 wt.%); 800 rpm; 30 °C; ultrasound condition (28 kHz, 200 W). 1,7-octadiene (mmol)

3.39

6.67

10.00

13.34

20.00

30.00

In the presence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 ) In the absence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 )

19.97

14.86

11.56

9.74

7.69

5.64

13.34 12.69

9.46 11.50

7.51 7.94

5.43 6.49

4.36 5.13

3.95 3.99

7.15

6.75

4.49

4.13

2.95

2.05

Table 5 Reaction condition: 10 mmol of 1,7-octadiene; 30 mL of chloroform; 0.2 mmol of BTEAC; 15 mL of NaOH solution (50 wt.%); 800 rpm; 30 °C; ultrasound condition (28 kHz, 200 W). NaCl (g)

0

0.117

0.585

1.170

1.755

2.925

In the presence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 ) In the absence of ultrasonic irradiation kapp , 1 × 102 (min−1 ) kapp , 2 × 102 (min−1 )

11.56

13.69

15.68

15.90

16.07

14.66

7.51 7.94

8.14 11.28

10.11 12.13

10.42 14.70

11.01 14.76

9.12 13.91

4.49

7.33

8.02

9.14

10.46

8.92

effects by ultrasound, attributed to intense local conditions generated due to cavitation. 4. Etherification Scheme 2.

were studied under phase-transfer catalysis and ultrasound irradiation conditions using aqueous sodium hydroxide as a base and BTEAB as a PTC (Scheme 2). The reaction rate also compared with energy of 28 and 50 kHz having same output power of 200 W. At 60 min, without ultrasonic irradiation the conversion is only 56%, but in the presence of ultrasound the conversion is 73% and 82% for 28 and 50 kHz, respectively, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation.

3. Epoxidation 3.1. Epoxidation of 1,7-octadiene An ultrasound assisted phase-transfer catalysed epoxidation of 1,7-octadiene is greatly enhanced by using a cocatalyst of phosphotungstic acid in the presence of hydrogen peroxide in an organic solvent / aqueous solution two-phase medium has been reported (Scheme 3) by Wang and Rajendran [36]. In this investigation the reaction rate was compared with 28 kHz and 40 kHz having same output power of 200 W. At 120 min, without ultrasonic irradiation the conversion is only 76%, but in the presence of ultrasound the conversion is 97% and almost 100% for 28 kHz and 40 kHz, respectively under ultrasonic irradiation conditions, due to the chemical

4.1. Ethoxylation of 4-chloronitrobenzene Wang and Rajendran [37] reported the synthesis of ethoxy-4-nitrobenzene (1) (Scheme 4) by the reaction of 4chloronitrobenzene with potassium ethoxide in a homogeneous system using PTC under ultrasound irradiation conditions at the frequency of 28 kHz output power of 200 W and also investigated with different factors. 4.1.1. Effect of varying stirring speeds The effect of varying stirring speed on the rate of aromatic nucleophilic substitution reaction of ethoxide ion with 4chloronitrobenzene was studied in the range of 0–10 0 0 rpm and the ultrasonic frequency of 28 kHz output power of 200 W was used throughout the reaction. In the absence of stirring speed and in the presence of the effect of ultrasonic condition at 28 kHz (200 W) the apparent rate constant is 11.2 × 10−3 min−1 , the kapp value at 600 rpm is 13.6 × 10−3 min−1 . In the presence of both conditions (600 rpm combined with the ultrasonic condition) the kapp value is 24.2 × 10−3 min−1 . From this observation the ultrasonic effect enhances the rate 1.8 times with respect to the conventional method. It may be due to the presence of ultrasound irradiation which increases the collision rate between the reactants. 4.1.2. Effect of the amount of BTEAC The conversion of 4-chloronitrobenzene is low when the reaction is carried out in the absence of BTEAC. However, the reaction

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Scheme 3.

Scheme 4.

Fig. 2. Reaction conditions: 10 g of KOH; in 1 mL H2 O; 0.2 g of biphenyl (internal standard); 9.25 mmol of benzyl alcohol; 0.2 g of MPTC; 6.35 mmol of 4chloronitrobenzene; 30 mL of chlorobenzene; 300 rpm. 60 °C.

Fig. 1. Reaction conditions: 16 g KOH; 2 ml water; 1 g of 4-chloronitrobenzene; 40 mL ethanol; 600 rpm; 50 °C; 0.5 g nonane; 60 min of reaction; ultrasound irradiation (28 kHz, 200 W). Scheme 5.

rate is dramatically enhanced when BTEAC is added to the reaction solution. The rate constants were almost linearly dependent on the amount of catalyst used in each reaction. So, the sonication along with PTC, the kapp value increases which may be due to the change in size, and morphology of phase-transfer catalyst [38]. For comparison, the apparent rate constant obtained from the PTC reaction under optimal reaction conditions in the presence and absence of ultrasonic irradiation were also shown in Fig. 1. 4.1.3. Effect of quaternary ammonium salts Quaternary ammonium salts were generally used as phasetransfer catalysts to promote reaction rate. In addition to BTEAC, five other quaternary ammonium salts, such as BTEAB, THAHS, TBAC, TBAB, TBAI and 18-Crown-6 (18-C-6) were investigated to test their reactivity. Based on the experimental results, the order of the reactivities of these quaternary ammonium salts and 18-C-6 were 18-C-6 > TBAI > TBAB > TBAC > TBAHS > BTEAB > BTEAC. It can be seen that 18-C-6 acts as a good catalyst compared with quaternary ammonium salts. It may be due to its more hydrophilic nature than that of the other quaternary ammonium salts. For comparison, the apparent rate constant obtained from the PTC reaction under optimal reaction conditions in the presence and absence of ultrasonic irradiation were also presented in Table 6. 4.1.4. Effect of Ultrasonic Power The reaction rate also compared with the availability of two frequencies namely 28 kHz and 40 kHz having same output power of 200 W. At 60 min, without ultrasonic irradiation the conversion is

only 58%, but in the presence of ultrasound the conversion is 77% and 89% for 28 kHz and 40 kHz, respectively, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation. Thus, ultrasonic-assisted PTC significantly increased the yields. 4.2. Synthesis of 1-(benzyloxy)−4-nitrobenzene Selvaraj et al. [39] were reported the synthesis of 1(benzyloxy)−4-nitrobenzene (2) from the reaction of 4chloronitrobenzene and benzyl alcohol is carried out successfully using potassium hydroxide and catalysed by a new MPTC, namely, 1,3,5-triethyl-1,3,5-trihexyl-1,3,5-triazinane-1,3,5-triium trichloride (Scheme 4). At 30 min, the reaction rate also compared with the frequencies of 0, 28 and 40 kHz having same output power of 300 W as shown in Fig. 2 under optimal conditions. 4.3. Synthesis of 1-butoxy-4-nitrobenzene Harikumar and Rajendran [40] reported the synthesis of 1-butoxy-4-nitrobenzene which is successfully carried out by 4-nitrophenol with n-butyl bromide (BB) using aqueous potassium carbonate and catalysed by different phase-transfer catalysts, namely, N1 , N4 -diethyl-N1 , N1 , N4 , N4 -tetraisopropylbutane-1,4diammonium dibromide, as an MPTC under ultrasonic conditions (40 kHz, 300 W) assisted by organic solvent (Scheme 5).

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Table 6 Reaction condition: 16 g KOH; 2 mL water; 1 g of 4-chloronitrobenzene; 40 mL ethanol; 600 rpm; 50 °C; 0.5 g nonane; 60 min; ultrasound conditions (28 kHz, 200 W). Quaternary ammonium salts & 18-C-6

BTEAC

BTEAB

TBHAS

TBAC

TBAB

TEAI

18-C-6

In the presence of ultrasonic irradiation kapp × 102 (min−1 ) In the absence of ultrasonic irradiation kapp × 102 (min−1 )

24.21

25.83

26.51

26.75

28.87

31.66

36.23

17.42

18.21

18.35

18.54

19.74

23.84

28.71

Table 7 Reaction condition: 20 g of K2 CO3 ; 15 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.3 g of MPTC; 30 mL of chlorobenzene; 600 rpm; 65 °C; ultrasound conditions (40 kHz, 300 W). Butyl bromide (g)

kapp x 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp x 103 min−1 (Without ultrasound)

0.2 0.4 0.6 0.8 1.0

17.68 21.44 26.72 31.82 36.41

3.08 4.66 5.12 6.02 7.22

4.3.1. Effect of the concentration of n-butyl bromide The influence of BB on the kinetics of synthesis of 1-butoxy4-nitrobenzene under ultrasonic irradiation condition (40 kHz, 300 W). The reaction rate increases with increasing the amount of n-butyl bromide. When the n-butyl bromide concentration increased, the probability of finding the substrate with active-site of the catalyst [37]. It may be due to reduction of surface area between the aqueous and organic phases, and hence more reactants collide to each other. In the presence and absence of ultrasound, results were presented in Table 7. 4.3.2. Effect of the organic solvents The influence of various organic solvents on the rate of nbutylation of 4-nitrophenol is followed under standard reaction conditions. Five organic solvents employed in this study are toluene, anisole, cyclohexane, chlorobenzene and benzene. Chlorobenzene possesses a higher reaction rate among the five organic solvents, due to its higher dielectric constant. In another view the ultrasonic irradiation can enhance the rate in the presence of more polar solvents due to passing higher ultrasonic waves to the reactor and makes fruitful collision between the reactants. The kapp in the presence and absence of ultrasonic irradiation conditions were given in Table 8. 4.3.3. Effect of varying potassium carbonate concentration The rate of n-butylation of 4-nitrophenol strongly depends on the strength of the potassium carbonate. The reaction rate tremendously increased with increasing in basicity of CO3 −2 ion. Kinetic experiments were carried out, employing 10–30 g under optimal reaction conditions, presence and absence of ultrasonic irradiation conditions were shown in Table 9. 4.3.4. Effect of Ultrasonic Power The kapp also compared with the frequencies 0, 28 and 40 kHz having same output power of 300 W was shown in Fig. 3 under optimal conditions. The reaction rate increased with increasing the frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation. 4.4. Synthesis of 1,3-bis(allyloxy)benzene Selvaraj and Rajendran [41] were reported the kinetics of synthesis of 1,3-bis(allyloxy)benzene successfully carried out by Oallylation of resorcinol with allyl bromide (AB) using aqueous

Fig. 3. Reaction conditions: 20 g of K2 CO3 ; 15 mL of H2 O; 0.2 g of internal standard(biphenyl); 0.3 g of MPTC; 0.6 g butyl bromide; 30 mL of chlorobenzene; 600 rpm; 65 °C.

Scheme 6.

potassium hydroxide and catalysed by 1,3,5,7-tetrabenzyl hexamethylenetetraammonium tetrachloride as a new MPTC, chlorobenzene as a solvent assisted by ultrasound condition (40 kHz, 300 W) (Scheme 6). 4.4.1. Effect of varying allyl bromide concentration The influence of AB on the kinetics of synthesis of 1,3bis(allyloxy)benzene under ultrasonic irradiation condition (40 kHz, 300 W), the amount of AB is varied from 11.5 g to 13.5 g. In the presence and absence of ultrasound, results were shown in Table 10. The data clearly indicates that reaction rate increases with increasing amount of allyl bromide [37]. 4.4.2. Effect of different phase-transfer catalysts Kinetic studies for the allylation of resorcinol by AB were carried out using different phase-transfer catalysts, namely, 1,3,5,7-tetrabenzylhexamethylenetetraammoniumtetrachloride as an MPTC, BTEAC, BTEAB, TBAB, TEAB and TEAC. The higher reactivity was obtained for a quaternary ammonium salt of less total carbon number [16]. The reaction is carried out under ultrasonic and standard reaction condition as shown in Table 11. 4.4.3. Effect of organic solvents The influence of various organic solvents on the rate of Oallylation of resorcinol is followed under standard reaction conditions. Five organic solvents employed in this study are toluene, anisole, cyclohexane, chlorobenzene, and benzene. Chlorobenzene possesses a higher reaction rate among the five organic solvents,

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G.S. Prasad et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–18 Table 8 Reaction condition: 0.5 g of 4-nitrophenol; 20 g of K2 CO3 ; 15 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.3 g of MPTC; 0.6 g butyl bromide; 600 rpm; 65 °C; ultrasound conditions (40 kHz, 300 W). Solvent

−1

kapp × 10 min (With ultrasound, 40 KHz, 300 W) kapp × 103 min−1 (Without ultrasound) 3

Cyclohexane

Benzene

Toluene

Anisole

Chlorobenzene

12.72

14.58

18.05

23.62

26.72

2.33

2.91

3.63

4.22

5.12

Table 9 Reaction condition: 0.5 g of 4-nitrophenol; 0.2 g of internal standard (biphenyl); 0.3 g of MPTC; 30 mL of chlorobenzene; 0.6 g butyl bromide; 600 rpm; 65 °C; ultrasound conditions (40 kHz, 300 W). Amount of K2 CO3 (g)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

10 15 20 25 30

16.22 20.91 26.72 30.46 34.33

3.09 4.23 5.12 6.02 6.76

Table 10 Reaction condition: 30 g of KOH; 30 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.5 g of MPTC; 30 mL of chlorobenzene; 600 rpm; 45 °C; ultrasound conditions (40 kHz, 300 W). Allyl bromide (g)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

11.5 12.0 12.5 13.0 13.5

18.9 23.8 25.8 28.4 30.8

8.4 10.8 12.5 13.4 13.9

Table 11 Reaction condition: 0.0454 mol of resorcinol; 30 g of KOH; 30 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.1040 mol of allylbromide; 30 mL of chlorobenzene; 600 rpm; 45 °C; ultrasound conditions (40 kHz, 300 W).

Various PTC

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

MPTC TEAC TEAB BTEAC BTEAB TBAB

25.3 23.7 22.4 20.6 19.5 18.9

12.5 12.3 11.7 9.8 8.8 8.4

due to its higher dielectric constant. The kapp in the presence and absence of ultrasonic irradiation conditions were shown in Table 12. 4.4.4. Effect of varying potassium hydroxide concentrations The rate of O-allylation of resorcinol strongly depends on the strength of the potassium hydroxide. The reaction rate tremendously increased with increasing the basicity of hydroxide ion. It suggests that the hydroxide ions are less solvated by water molecules and there by the activity of the hydroxide ion increases. Kinetic experiments were carried out, employing 20-40 g under optimal reaction conditions in presence and absence of ultrasonic irradiation conditions and the results are given in Table 13. 4.4.5. Effect of Ultrasonic Power The kapp also compared with the frequencies 0, 28 and 40 kHz having same output power of 300 W was shown in Fig. 4 under optimal conditions. The reaction rate increased with increasing the

Fig. 4. Reaction conditions: 0.0454 mol of resorcinol; 30 g of KOH; 30 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.1040 mol of allyl bromide; 0.5 g of MPTC; 30 mL of chlorobenzene; 600 rpm; 45 °C.

frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation. 5. Arylation 5.1. Synthesis of 1-(4-nitrophenyl) imidazole Selvaraj and Rajendran [42] were reported the nitroarylation of imidazole catalysed by a novel dual-site PTC in an alkaline solution / imidazole in chlorobenzene two-phase medium with ultrasonic irradiation (40 kHz, 300 W) (Scheme 7). This new synthesized phase-transfer catalyst, N1 , N6 -diethyl-N1 , N1 , N6 , N6 tetraisopropylhexane-1,6-diaminium dichloride as a MPTC, which possesses two-site activity, is obtained from the reaction of 1,6dichlorohexane and N-ethyl-N-isopropylpropane-2-amine. 5.1.1. Effect of the concentration of 4-chloronitrobenzene The influence of 4-chloronitrobenzene on the kinetics of synthesis of 1-(4-nitrophenyl) imidazole under ultrasonic irradiation condition (40 kHz, 300 W). Reaction rate increased with increasing the concentration of 4-chloronitrobenzene, it may be due to the probability of finding the substrate with active-site of the catalyst. The amount of 4-chloronitrobenzene is varied from 1.5 to 3.5 g. In the presence and absence of ultrasound results were given in Table 14. 5.1.2. Effect of organic solvents The influence of various organic solvents on the rate of nitroarylation of imidazole is followed under optimal reaction conditions. Five organic solvents employed in this study are toluene, anisole, cyclohexane, chlorobenzene and benzene. Chlorobenzene possesses a higher reaction rate among the five organic solvents, due to its higher dielectric constant. The kapp in the presence

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Table 12 Reaction condition: 0.0454 mol of resorcinol; 30 g of KOH; 30 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.1040 mol of allylbromide; 0.5 g of MPTC; 600 rpm; 45 °C; ultrasound conditions (40 kHz, 300 W). Solvent

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W) kapp × 103 min−1 (Without ultrasound)

Cyclohexane

Benzene

Toluene

Anisole

Chlorobenzene

10.8

13.2

18.9

23.6

25.2

5.8

6.9

8.8

11.2

12.5

Scheme 7.

Table 13 Reaction condition: 0.0454 mol of resorcinol; 0.2 g of internal standard (biphenyl); 0.1040 mol of allylbromide; 0.5 g of MPTC; 30 mL of chlorobenzene; 600 rpm; 45 °C; ultrasound conditions (40 kHz, 300 W). Amount of KOH (g)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

20 25 30 35 40

16.2 20.9 25.4 33.8 42.3

7.9 9.8 12.5 16.3 20.8

Table 14 Reaction condition: 20 g of NaOH; 15 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.3 g of MPTC; 30 mL of chlorobenzene; 300 rpm; 60 °C; ultrasound conditions (40 kHz, 300 W). 4-chloronitrobenzene (g)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

1.5 2.0 2.5 3.0 3.5

17.68 21.44 26.72 31.82 36.41

3.08 4.66 4.98 6.02 7.22

and absence of ultrasonic irradiation conditions were shown in Table 15. 5.1.3. Effect of varying sodium hydroxide concentrations The rate of nitroarylation of imidazole strongly depends on the strength of the potassium hydroxide. The reaction rate tremendously increased with increasing the basicity of hydroxide ion. It suggests that the hydroxide ions are less solvated by water molecules and there by the activity of the hydroxide ion increases. Kinetic experiments were carried out, employing 10–30 g under optimal reaction conditions in presence and absence of ultrasonic irradiation conditions and the results were presented in Table 16. 5.1.4. Effect of Ultrasonic Power The kapp also compared with the frequencies 0, 28 and 40 kHz having same output power of 300 W was shown in Fig. 5 under

Fig. 5. Reaction conditions: 20 g of NaOH; 15 mL of H2 O; 0.2 g of internal standard(biphenyl); 0.3 g of MPTC; 2.5 g of 4-chloronitrobenzene; 30 mL of chlorobenzene; 300 rpm; 60 °C.

optimal conditions. The reaction rate increased with increasing the frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation.

5.2. Synthesis of 3,5-dimethyl-1-prop-2-enylpyrazole Brahmayya and Wang [43] reported the synthesis of 3,5dimethyl-1-prop-2-enylpyrazole (3) which was successfully carried out by reacting the 3,5-di-methyl pyrazole with 3-bromoprop-1ene in small amount of KOH and organic solvent under PTC conditions assisted by the ultrasonic irradiation (Scheme 7). The reaction rate was also compared with energy of 28 and 50 kHz having same output power of 200 W. At 80 min, without ultrasonic irritation the conversion was only 50%, but in the presence of ultrasound the conversion was 75% and 90% for 28 and 50 kHz, respectively, which may be due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation.

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G.S. Prasad et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–18 Table 15 Reaction condition: 20 g of NaOH; 15 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.3 g of MPTC; 2.5 g of 4-chloronitrobenzene; 300 rpm; 60 °C; ultrasound conditions (40 kHz, 300 W). Solvent

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W) kapp × 103 min−1 (Without ultrasound)

Cyclohexane

Benzene

Toluene

Anisole

Chlorobenzene

12.72

14.58

18.05

23.62

26.72

2.33

2.91

3.63

4.22

4.98

Table 16 Reaction condition: 15 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.3 g of MPTC; 2.5 g of 4-chloronitrobenzene; 30 mL of chlorobenzene; 300 rpm; 60 °C; ultrasound conditions (40 kHz, 300 W). Amount of NaOH (g)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

10 15 20 25 30

16.22 20.91 26.72 30.46 34.33

3.09 4.23 4.98 6.02 6.76

5.3. Synthesis of 3,5-dimethyl-1-(3-phenylpropyl)−1H-pyrazole Wang et al. [44] reported the kinetic study for the synthesis of 3,5-dimethyl-1-(3-phenylpropyl)−1H-pyrazole (4) by reacting the 3,5-dimethyl pyrazole with 1-bromo-3-phenyl propane under phase transfer catalysis and ultrasonic irradiation conditions using aqueous solution of NaOH, excess amount of bromobenzene and PTC (Scheme 7). 5.3.1. Effect of organic solvents The influence of various organic solvents on the rate of Nalkylation of 3,5-dimethyl pyrazole is followed under optimal reaction conditions. Five organic solvents employed in this study are benzene, toluene, anisole, cyclohexane and bromobenzene. Chlorobenzene showed a higher reaction rate among the five organic solvents, due to its higher dielectric constant. The kapp in the presence and absence of ultrasonic irradiation conditions were shown in Table 17. 5.3.2. Effect of Ultrasonic Power The reaction rate also compared with energy of 28 and 50 kHz having same output power of 300 W. At 80 min, without ultrasonic irritation the conversion was only 53%, but in the presence of ultrasound the conversion was 70% and 80% for 28 and 50 kHz, respectively, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation. 6. Alkylation 6.1. Synthesis of 2-phenylvaleronitrile Vivekanand and Wang [45] were reported the kinetics of synthesis of 2-phenylvaleronitrile successfully carried out by selective C-alkylation of benzyl cyanide with n-bromopropane using aqueous KOH and catalysed by TBAB under ultrasonic assisted organic solvent-free conditions (Scheme 8). In this investigation at 80 min, the reaction rate compared without ultrasonic irradiation the conversion is 8.5 × 10−3 min−1 , but in the presence of ultrasonic irradiation with the frequencies 28, 40, 50, and 120 kHz having same output power of 200 W the conversions were 17.7 × 10−3 min−1 , 20.8 × 10−3 min−1 , 23.6 × 10−3 min−1 and 33.4 × 10−3 min−1 respectively, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation.

Scheme 8.

Scheme 9.

6.2. Propargylation of indene-1,3-dione Selvaraj and Rajendran [46] were reported the kinetics of synthesis of 2,2-di(prop-2-ynyl)−1H-indene-1,3(2H)-dione which was successfully carried out by propargylation of indene-1,3dione with propargyl bromide (PB) using aqueous potassium hydroxide and catalysed by N-benzyl-N-ethyl-N-isopropylpropan-2ammonium bromide as a PTC, under ultrasonic conditions (40 kHz, 300 W) assisted by organic solvent (Scheme 9). 6.2.1. Effect of varying propargyl bromide concentration The influence of PB on the kinetics of synthesis of proparglyation of 1,3-indanedione under ultrasonic irradiation condition (40 kHz, 300 W), the amount of PB is varied from 2.0-4.0 mL. In the presence and absence of ultrasound results are shown in Table 18. The data clearly indicates that the kapp value increases with increasing the amount of propargyl bromide, it may be due to the probability of finding the substrate with active-site of the catalyst. 6.2.2. Effect of the organic solvent The influence of various organic solvents on the rate of propargylation of indene-1,3-dione is followed under optimal reaction conditions. Five organic solvents employed in this study were toluene, anisole, cyclohexane, chlorobenzene and benzene. Chlorobenzene possesses a higher reaction rate among the five organic solvents, due to its higher dielectric constant. The kapp in the presence and absence of ultrasonic irradiation conditions was shown in Table 19. 6.2.3. Effect of varying potassium hydroxide concentrations The rate of propargylation of indene-1,3-dione strongly depends on the strength of the potassium hydroxide. The reaction rate tremendously increased with increasing the basicity of hydroxide ion. It suggests that the hydroxide ions are less solvated by water molecules and there by the activity of the hydroxide ion increases. Kinetic experiments were carried out, employing 2040 g under optimal reaction conditions in presence and absence of ultrasonic irradiation conditions and the results were shown in Table 20.

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Table 17 Reaction condition: 9.6 mmol of 3,5-dimethyl pyrazole; 9 mmol of 1-bromo-3-phenyl bromide; 20 mL of sodium hydroxide (1–8 g, 0.05–0.4 g/mL); 0.3 g of internal standard (naphthalene); 1.5 mol % of THAB; 40 °C; ultrasound conditions (50 kHz, 300 W). Solvent

kapp × 103 min−1 (With ultrasound, 50 KHz, 300 W) kapp × 103 min−1 (Without ultrasound)

Cyclohexane

Benzene

Toluene

Anisole

Bromobenzene

13.1

16.1

18.9

24.4

28.05

2.9

3.5

4.2

4.6

5.1

Table 18 Reaction condition: 30 g of KOH; 40 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.5 g of PTC; 30 mL of chlorobenzene; 600 rpm; 45 °C; ultrasound conditions (40 kHz, 300 W). Propargyl bromide (g)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

2.0 2.5 3.0 3.5 4.0

17.91 22.82 24.82 27.42 29.82

8.01 10.02 12.33 13.14 12.97

Scheme 10.

7. Thioetherification 7.1. Synthesis of thioether Wang and Rajendran have been reported [47] the kinetics for the synthesis of thioether (5) (Scheme 10) under ultrasound assisted PTC conditions and also investigated with different factors. In this investigation the reaction rate compared with 28 kHz and 40 kHz having same output power of 200 W. At 1 h, without ultrasonic irradiation the conversion was only 53%, but in the presence of ultrasonic conditions the conversion was 91% and 97% for 28 kHz and 40 kHz, respectively, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation. 7.2. Synthesis of di-p-tolylsulfane Abimannan et al. [48] were reported the synthesis of di-ptolylsulfane (6) from the reaction of 4-bromo-1-methylbenzene (BMB) with sodium sulfide which was carried out using 1,4dihexyl-1,4-diazoniabicyclo[2.2.2]octanium dibromide as a MPTC under ultrasonic irradiation conditions (Scheme 10).

Fig. 6. Reaction conditions: 30 g of KOH; 40 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.0331 mol of propargyl bromide; 0.5 g of PTC; 30 mL of chlorobenzene; 600 rpm; 45 °C.

6.2.4. Effect of Ultrasonic Power The kapp also compared with the frequencies 0, 28 and 40 kHz having same output power of 300 W was shown in Fig. 6 under optimal conditions. The reaction rate increased with increasing the frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation.

7.2.1. Effect of agitation speed To determine the influence of mass-transfer, the stirring speed was varied from 0 to 800 rpm along with ultrasound irradiation using MPTC. In principle, the homogeneous reaction was independent of the agitation speed but heterogeneous reaction was dependent on the agitation speed. As shown in Fig. 7, the increase in the reaction rate is produced with a raise in the stirring speed from 0 to 400 rpm. If the agitation speed exceeds 400 rpm; the conversion of 4-bromo-1-methylbenzene is not dependent on the agitation speed. This result is different from that of other reaction systems that require a high agitation speed to attain larger interfacial area to increase the mass transfer rate [49]. 7.2.2. Effect of the concentration of 4-bromo-1-methylbenzene The influence of 4-bromo-1-methylbenzene on the kinetics of synthesis of di-p-tolylsulfane under ultrasonic irradiation condi-

Table 19 Reaction condition: 30 g of KOH; 40 mL of H2 O; 0.2 g of internal standard (biphenyl); 0.0331 mol of propargyl bromide; 0.5 g of PTC; 60 0 rpm; 45 °C; ultrasound conditions (40 kHz, 30 0 W). Solvent

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W) kapp × 103 min−1 (Without ultrasound)

Cyclohexane

Benzene

Toluene

Anisole

Chlorobenzene

9.82

12.24

17.92

22.61

24.82

5.84

6.92

8.82

11.21

12.53

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7.2.4. Effect of volume of n-hexane The conversion or the reaction rate is directly proportional to the concentration of the reactants. A dilute concentration of the reactant is obtained using a large amount of organic solvent. The conversion of 4-bromo-1-methylbenzene is decreased with the increase in the volume of n-hexane as shown in Table 23. 7.2.5. Effect of different phase-transfer catalysts Kinetic studies for the arylation of sodium sulfide using different phase-transfer catalysts, namely, 1,4-dihexyl-1,4diazoniabicyclo[2.2.2]octanium dibromide as an MPTC, five other single site quaternary ammonium salts, such as tetraoctylammonium bromide (TOAB), tetrahexylammonium bromide (THAB), TBAI, TBAB, and TBAC. Among these, MPTC shows higher reactivity due to it contains two active sites therefore the conversion is faster as compared with other single site PTCs [36]. The reaction was carried out under ultrasonic and standard reaction condition as shown in Table 24. Fig. 7. Reaction conditions: 5 g of Na2 S; 6 mL H2 O; 0.2 g of biphenyl(internal standard); 11.69 mmol of 4-bromo-1-methylbenzene; 0.2 g of MPTC; 30 mL of n-hexane; 60 °C; ultrasound irradiation (40 kHz, 300 W). Table 20 Reaction condition: 0.2 g of internal standard (biphenyl); 0.0331 mol of propargyl bromide; 0.5 g of PTC; 30 mL of chlorobenzene; 600 rpm; 45 °C; ultrasound conditions (40 kHz, 300 W). Amount of KOH (g)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

20 25 30 35 40

15.22 19.93 24.82 32.84 41.34

7.82 9.71 12.11 16.34 20.44

Table 21 Reaction condition: 5 g of Na2 S; 6 mL H2 O; 0.2 g internal standard (biphenyl); 11.69 mmol of 4-bromo-1-methylbenzene; 0.2 g of MPTC; 30 mL of n-hexane; 600 rpm; 60 °C; ultrasound condition (40 kHz, 300 W).

4-Bromo-1-methylbenzene (mmol)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

5.84 8.76 11.69 14.62 17.54

31.83 33.52 35.26 37.30 39.78

4.83 6.52 8.62 10.30 11.78

7.2.6. Effect of varying sodium hydroxide concentration The rate of arylation of sodium sulfide depends on the strength of the sodium hydroxide. Only sodium hydroxide concentration is varied keeping other standard reaction conditions as shown in Table 25, showed the effect of sodium hydroxide amount in the aqueous phase on the di-p-tolylsulfane production. The kapp value increased from 0.5 g to 2.0 g of sodium hydroxide (NaOH). It may be due to increase in the basicity of aqueous phase [37]. From 2.0 to 5.0 g of sodium hydroxide, the kapp value tremendously decreased. According to Hsiao and Weng [50], adding salt (NaOH or NaBr) to the aqueous solution would inhibit the ionization of sodium sulfide, thus the rate of formation of the product is decreased and the second reason is the amount of phase-transfer catalyst salted out from the aqueous phase and thereby the reaction rate is decreased. 7.2.7. Effect of alkyl and aryl halides The coupling of aryl iodides containing electron-withdrawing groups has been taken for arylation of sodium sulfide under optimal conditions at 60 min. The aryl halides carrying an ortho substituent were also found to readily participate in the reaction (Table 26). Further, the most reactive organic reactant is allyl bromide. The reaction is 100% completed within 10 min for allyl bromide. It may be due to its smaller molecular size and the conjugation of π bond. Among the alkyl bromides sec-propyl bromide is the least reactive one because of steric hindrance in its reaction. From 1-propyl bromide to 1-octyl bromide the kapp value decreases due to increasing the carbon chain of the molecules [51,52].

tion (40 kHz, 300 W), the amount of 4-bromo-1-methylbenzene is varied from 1.5 to 3.5 g. In the presence and absence of ultrasound, results were shown in Table 21. The data clearly indicate that the kapp value increases with increasing the amount of BMB. This observation was due to presence of more number of active sites in the MPTC and higher concentration of substrate BMB had co-operatively influence the reaction and thus enhances the more number of contacts between catalyst and substrate.

7.2.8. Effect of Ultrasonic Power The Rp also compared with the frequencies 0, 28 and 40 kHz having same output power of 300 W was shown in Fig. 8 under optimal conditions. The reaction rate increased with increasing the frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation.

7.2.3. Effect of organic solvent The effect of various organic solvents on the rate of arylation of sodium sulfide is determined using five different solvents such as chlorobenzene, toluene, hexane, cyclohexane and chloroform under optimal conditions. The distribution of phase-transfer catalyst between aqueous and organic medium depends on the polarity of the solvent used. Chlorobenzene possesses a higher kapp value among the five organic solvents used, due to higher polarity. The effect of the organic solvents on rate of arylation of sodium sulfide with and without ultrasound conditions are shown in Table 22.

8.1. Polymerization of glycidyl methacrylate

8. Polymerization

Sankar and Rajendran [53] reported the kinetics of multisite phase-transfer catalysed free radical Polymerization of glycidyl methacrylate (GMA) using potassium peroxy disulphate (PDS) as water soluble initiator and newly synthesized 1,4dihexadecylpyrazine-1,4-diium dibromide as multi-site phasetransfer catalyst (MPTC) has been investigated in ethyl acetate / water two phase system under ultrasound irradiation conditions at the frequency of 28 kHz output power of 300 W.

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Table 22 Reaction condition: 5 g of Na2 S; 6 mL H2 O; 0.2 g internal standard (biphenyl); 11.69 mmol of 4-bromo-1methylbenzene; 0.2 g of MPTC; 600 rpm; 60 °C; ultrasound condition (40 kHz, 300 W). Solvent

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W) kapp × 103 min−1 (Without ultrasound)

Chlorobenzene

Toluene

Hexane

Cyclohexane

Chloroform

39.82

37.34

35.26

36.21

36.10

13.82

10.30

8.62

8.88

15.14

Table 23 Reaction condition: 5 g of Na2 S; 6 mL H2 O; 0.2 g internal standard (biphenyl); 11.69 mmol of 4-bromo-1-methylbenzene; 0.2 g of MPTC; 600 rpm; 60 °C; ultrasound condition (40 kHz, 300 W). Volume of n-hexane (mL) 20 30 40 50 60

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W) 38.54 35.26 32.08 29.42 26.56

Table 26 Reaction condition: 5 g of Na2 S; 6 mL H2 O; 0.2 g internal standard (biphenyl); 4 mol% MPTC; 30 mL of n-hexane; 600 rpm; 60 °C; ultrasound condition (40 kHz, 300 W).

kapp × 103 min−1 (Without ultrasound) 11.01 8.61 6.11 3.45 1.67

Table 24 Reaction condition: 5 g of Na2 S; 6 mL H2 O; 0.2 g internal standard (biphenyl); 11.69 mmol of 4-bromo-1-methylbenzene; 30 mL of n-hexane; 600 rpm; 60 °C; ultrasound condition (40 kHz, 300 W).

Various PTC

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

MPTC TOAB THAB TBAI TBAB TBAC

36.20 32.26 29.08 26.42 24.56 21.22

8.61 5.71 3.11 1.85 1.07 0.43

Table 25 Reaction condition: 5 g of Na2 S; 6 mL H2 O; 0.2 g internal standard (biphenyl); 11.69 mmol of 4-bromo-1-methylbenzene; 0.2 g of MPTC; 30 mL of n-hexane; 600 rpm; 60 °C; ultrasound condition (40 kHz, 300 W). Amount of NaOH (g)

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

0 0.5 1.0 1.5 2.0 2.5 3.0

35.26 39.11 41.31 42.88 34.66 30.51 26.51

8.61 12.34 14.01 15.26 8.06 4.21 0.66

8.1.1. Effect of steady state rate of polymerization The steady state rate of polymerization is ascertained by carrying out the polymerization of the monomer GMA at different time intervals keeping the concentrations of monomer, initiator, PTC, ionic strength and pH constant under ultrasound irradiation. The rate of polymerization (Rp) increased to some extent, and then slightly decreased and there after remains constant. When the same reaction is carried out in the absence of ultrasound, it is observed that Rp is almost decreases 3-fold than with ultrasonic irradiation (Table 27). It is due to the effect of ultrasound irradiation which can promote an intensive mixing of aqueous and organic phases, like homogeneous solution. 8.1.2. Effect of [MPTC] on Rp The dependence of Rp on the concentration of MPTC was examined by varying MPTC in the range 1 × 10−2 to 8 × 10−2 mol dm−3

∗

S. No

Alkyl and aryl halides(11.69 mmol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

4-Iodo-1-methoxylbenzene 4-Iodo-1-methylbenzene 4-Bromo-1-methoxybenzene 4-Bromo-1-methylbenzene 2-Iodo-1-methoxybenzene 2-Iodo-1-methylbenzene Benzyl chloride 4-Iodoacetophenone 4-Bromoacetophenone 4-Iodobenzonitrile 4-Chloro-1-methylbenzene 3-Bromopyridine 1-Propyl bromide 1-Butyl bromide 1-Pentyl bromide 1-Hexyl bromide 1-Heptyl bromide 1-Octyl bromide 2-Propyl bromide Allyl bromide∗

kapp × 103 min−1 (With ultrasound, 40 KHz, 300 W)

kapp × 103 min−1 (Without ultrasound)

41.56 39.78 37.42 35.26 29.72 29.44 27.88 25.12 24.42 14.62 6.72 4.57 48.72 40.41 24.67 17.36 11.86 9.38 6.02

10.42 9.92 9.02 8.62 6.91 6.66 6.24 6.02 5.46 4.65 2.44 1.18 12.64 9.83 6.25 5.14 4.22 3.56 2.47

Reaction completed within 10 min.

Fig. 8. Reaction conditions: 5 g of Na2S; 6 mL H2 O; 0.2 g of biphenyl (internal standard); 11.69 mmol of 4-bromo-1-methylbenzene; 0.2 g of MPTC; 30 mL of n-hexane; 600 rpm; 60 °C.

at fixed concentrations of monomer, PDS, pH and ionic strength and combined with ultrasound wave irradiation. The increase in Rp value due to the collision between intermediates [QS2 O8 ] was increased by increasing MPTC amount. Therefore the opportunity of forming a complex between them was largely increased. Hence, the Rp increased with increase in the amount of MPTC. Choi et al.

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G.S. Prasad et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–18 Table 27 Reaction condition: [GMA], 0.55 mol dm−3 ; [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 65 °C; ultrasound condition (28 kHz, 300 W).

Time (min)

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

5 15 25 35 45 55

7.91 5.84 5.25 5.01 4.65 4.67

2.64 1.95 1.75 1.67 1.55 1.56

Table 29 Reaction condition: [GMA], 0.55 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 65 °C; 45 min; ultrasound condition (28 kHz, 300 W). [PDS] × 10−2 mol dm−3

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

1 2 4 5 6 8

3.14 4.52 6.17 6.46 7.41 8.91

1.03 1.56 2.06 2.13 2.42 2.96

Table 30 Reaction condition: [GMA], 0.55 mol dm−3 ; [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 45 min; ultrasound condition (28 kHz, 300 W).

Temp (K)

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

323 328 333 338 343 348

2.29 2.69 3.55 4.68 5.62 6.76

0.74 0.91 1.18 1.56 1.87 2.25

Table 31 Reaction condition: [GMA], 0.55 mol dm−3 ; [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 65 °C; 45 min; ultrasound condition (28 kHz, 300 W).

Fig. 9. Reaction conditions: [GMA], 0.55 mol dm−3 ; [PDS], 2 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; Temp. 65 °C; Time 45 min; ultrasound irradiation (28 kHz, 300 W). Table 28 Reaction condition: [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 65 °C; 45 min; ultrasound condition (28 kHz, 300 W). [GMA] mol dm−3

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

0.37 0.55 0.73 0.92 1.10 1.28

3.09 4.68 5.89 7.41 9.12 10.72

1.03 1.55 1.94 2.46 3.01 3.54

[54] reported that the polymerization rates levelled off at higher concentrations of crown ether in the bulk polymerization of methyl methacrylate (MMA) catalysed by PDS as the water soluble initiator and 18-crown-6 as the phase-transfer catalyst. For comparison, the Rp obtained from the MPTC reaction under optimal reaction conditions in the presence and absence of ultrasonic irradiation were also shown in Fig. 9. 8.1.3. Effect of momomer concentration on Rp The effect of monomer concentration on Rp was studied by varying the concentration in the range of 0.37–1.28 mol dm−3 at fixed concentrations of PDS, MPTC, pH and at constant ionic strength along with ultrasound conditions and absence of ultrasonic irradiation were given in Table 28. A similar order of unity has been observed by Balakrishnan et al. [55]. 8.1.4. Effect of initiator concentration on Rp The polymerization rate increased with increased concentration of K2 S2 O8 (PDS) in the range of 0.01–0.08 mol dm−3 at a fixed

Vw/Vo

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

0.61 0.67 0.75 0.82 0.92 1

4.17 4.27 4.37 4.47 4.57 4.68

1.39 1.42 1.46 1.49 1.52 1.56

concentration of MPTC, pH, monomer and ionic strength is compared with ultrasound conditions and absence of ultrasonic irradiation were presented in Table 29. A similar dependency of Rp order with respect to [initiator] has been reported in the presence of PTC-assisted free radical polymerization of methyl methacrylate [56]. 8.1.5. Effect of temperature on Rp The effect of variation of temperature in the range of 50–75 °C on the polymerization was studied with and without ultrasonic effect with increase in temperature (Table 30). It is obvious that the reactivity was increased with an increase in the temperature along with ultrasonic effect. The reason is that the number of reactant molecules which possess higher activation energy at higher temperature and thus the ultrasonic wave easily passes through the reactor. The collision of the reactants at higher temperature is also increased. Hence, the Rp is increased at higher temperature. 8.1.6. Effect of volume fraction of aqueous on Rp The effect of variation in the ratio of volume of aqueous phase (Vw) to volume of organic phase (Vo), Vw/Vo, on the Rp was studied in the range of 0.61–1.00 with and without ultrasonic effect with increase in temperature (Table 31) at fixed concentrations of all other parameters. It is observed that there is slight increase in the Rp with an increase in volume fraction of aqueous phase ratio (Vw). Balakrishnan et al. [55] observed the reaction exponents

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Table 32 Reaction condition: [GMA], 0.55 mol dm−3 ; [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 65 °C; 45 min; ultrasound condition (28 kHz, 300 W). Solvent Rp × 104 mol dm−3 s−1 Presence of ultrasonic irradiation Absence of ultrasonic irradiation

Cyclohexanone

Chlorobenzene

Ethyl acetate

Toluene

Benzene

Cyclohexane

10.69

7.23

4.65

3.47

2.65

2.22

3.56

2.41

1.54

1.16

0.88

.074

Scheme 11.

Fig. 10. Reaction conditions: [GMA], 0.55 mol dm−3 ; [PDS], 2 × 10−2 mol dm−3 ; [MPTC], 2 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; Temp. 65 °C; Time 45 min.

with respect to Vw/Vo in the polymerisation of MMA in the range of 0.3–0.4 with K2 S2 O8 initiator with different phase transfer catalysts such as tetramethylammonium bromide (TMAB), TEAB and BTEAC. However, Simionescu and coworkers [57] reported an independent nature of Rp on Vw/Vo in the polymerization of MMA using K2 S2 O8 -Arquad phase-transfer catalyst system. 8.1.7. Effect of solvent on Rp The effect of solvent on Rp was determined by carrying out the polymerization reaction of GMA in six different solvents such as cyclohexane, ethyl acetate, cyclohexanone, toluene, benzene and chlorobenzene under ultrasound condition. The effect of the organic solvents on the Rp values with and without ultrasound conditions were shown in Table 32. It is found that the Rp decreased in the order cyclohexanone > chlorobenzene > ethyl acetate > toluene > benzene > cyclohexane. The main reason is that the effect of the organic solvent involves the solubility of the catalyst, transition state of the reaction, ion transfer, solvation and interfacial phenomena which were difficult to determine to a phasetransfer catalyst system. 8.1.8. Effect of Ultrasonic Power The Rp also compared under optimal conditions with the frequencies 0, 28 and 40 kHz having same output power of 300 W as shown in Fig. 10. The reaction rate increased with increasing the frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation. 8.2. Polymerization of N-vinyl imidazole (7) Loganathan and Rajendran [58] reported the kinetics of phasetransfer catalysed radical polymerization of N-vinyl imidazole (NVI) (Scheme 11) using PDS as water soluble initiator and tetraoctylammonium chloride (TOAC) as PTC in ethyl acetate / water two

Table 33 Reaction condition: [K2 S2 O8 ], 1.0 × 10−2 mol dm−3 ; [TOAC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 60 °C; 50 min; ultrasound condition (28 kHz, 300 W).

[NVI] mol dm−3

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

0.276 0.552 0.828 1.104 1.380 1.656

1.52 3.04 4.57 6.08 7.60 9.12

0.52 1.04 1.56 2.08 2.60 3.12

phase system assisted by ultrasound irradiation at the frequency of 28 kHz output power of 300 W. 8.2.1. Effect of monomer concentration on Rp The effect of monomer concentration Rp was studied by varying the concentration in the range of 0.27–1.65 mol dm−3 at fixed concentrations of PDS, PTC, pH and at constant ionic strength along with ultrasound irradiation compared with absence of ultrasound irradiation (Table 33). 8.2.2. Effect of [TOAC] on Rp The dependence of Rp on the concentration of PTC was examined by varying PTC in the range from 2 × 10−2 to 7 × 10−2 mol dm−3 at fixed concentrations of monomer, PDS, pH and ionic strength and combined with ultrasound irradiation conditions Fig. 11. 8.2.3. Effect of initiator concentration on Rp The polymerization rate increased with increased concentration of PDS in the range from 1 × 10−2 to 7 × 10−2 mol dm−3 at a fixed concentration of PTC, pH, monomer and ionic strength is combined with ultrasound conditions (Table 34). 8.2.4. Effect of temperature on Rp The effect of variation of temperature in the range of 45–70 °C on the polymerization was studied with and without ultrasonic

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G.S. Prasad et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–18 Table 36 Reaction condition: [NVI], 0.552 mol dm−3 ; [K2 S2 O8 ], 1.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 60 °C; 50 min; ultrasound condition (28 kHz, 300 W).

Various PTC

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

TBAI TBAB TBAC THAC TOAC

1.96 2.02 2.06 2.52 3.04

0.59 0.63 0.69 0.82 1.02

Fig. 11. Reaction conditions: [NVI], 0.552 mol dm−3 ; [PDS], 1.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm-3;Temp. 60 °C; Time 50 min; ultrasound irradiation (28 kHz, 300 W). Table 34 Reaction condition: [NVI], 0.552 mol dm−3 ; [TOAC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 60 °C; 50 min; ultrasound condition (28 kHz, 300 W). [PDS] × 10−2 mol dm−3

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

1 2 3 4 5 6 7

3.04 4.60 5.33 6.07 6.35 7.29 8.02

1.04 1.36 1.54 1.86 1.99 2.22 2.68

Table 35 Reaction condition: [NVI], 0.552 mol dm−3 ; [K2 S2 O8 ], 1.0 × 10−2 mol dm−3 ; [TOAC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 50 min; ultrasound condition (28 kHz, 300 W).

Temp (K)

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

318 323 328 333 338 343

1.58 1.78 2.18 3.04 4.17 5.23

0.48 0.60 0.77 1.04 1.42 1.73

effect by keeping other variables constant. The Rp was increased with increasing the temperature as shown in Table 35. 8.2.5. Effect of various catalysts on Rp In addition to ultrasound irradiation condition along with tetraoctylammonium chloride (TOAC) four other single site quaternary ammonium salts, such as terahexylammoniumchloride (THAC), TBAC, TBAB and TBAI, were investigated to test their reactivities. The experimental results were listed in (Table 36). 8.2.6. Effect of solvent on Rp The effect of solvent on Rp was determined by carrying out the polymerization reaction of GMA in six different solvents such as cyclohexane, ethyl acetate, cyclohexanone, toluene, benzene and chlorobenzene under ultrasound condition. The effect of the organic solvents on the Rp values with and without ultrasound conditions were shown in Table 37. It was found that the Rp decreased

Fig. 12. Reaction conditions: [NVI], 0.552 mol dm−3 ; [PDS], 1.0 × 10−2 mol dm−3 ; [TOAC], 2.0 × 10−2 mol dm−3; [H+ ], 0.2 mol dm−3 ; Temp. 60 °C; Time 50 min.

in the order cyclohexanone > chlorobenzene > ethyl acetate > dibutyl ether > toluene > cyclohexane. 8.2.7. Effect of Ultrasonic Power The Rp also compared with the frequencies 0, 28 and 40 kHz having same output power of 300 W was shown in Fig. 12 under optimal conditions. The reaction rate increased with increasing the frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation. 8.3. Polymerization of ethyl methacrylate (8) The kinetics of multi-site phase-transfer catalysed free radical Polymerization of ethyl methacrylate (EMA) using potassium peroxy disulphate (PDS) as a water soluble initiator and newly synthesized 1,4-dihexadecylpyrazine-1,4-diium dibromide as a MPTC under ultrasound irradiation conditions at the frequency of 28 kHz output power of 300 W has been investigated by Sankar and Rajendran [59] (Scheme 11). The ultrasound irradiation conditions at the frequency of 28 kHz output power of 300 W. 8.3.1. Effect of steady state at rate of polymerization The steady state rate of polymerization was ascertained by carrying out the polymerization of the monomer EMA at different time intervals keeping the concentrations of monomer, initiator, MPTC, ionic strength and pH constant under ultrasound irradiation and also the same reaction is carried out in the absence of ultrasound. The results were shown in Table 38. 8.3.2. Effect of temperature on Rp The effect of variation of temperature in the range of 40–65 °C on the polymerization was studied with and without ultrasonic effect and increase in temperature (Table 39).

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Table 37 Reaction condition: [NVI], 0.552 mol dm−3 ; [K2 S2 O8 ], 1.0 × 10−2 mol dm−3 ; [TOAC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 60 °C; 50 min; ultrasound condition (28 kHz, 300 W). Solvent Rp × 104 mol dm−3 s−1 Presence of ultrasonic irradiation Absence of ultrasonic irradiation

Cyclohexanone

Chlorobenzene

Ethyl acetate

Dibutyl ether

Toluene

Cyclohexane

8.62

6.24

3.04

2.87

2.65

2.22

3.26

2.02

1.04

0.92

0.88

0.74

Table 38 Reaction condition: [EMA], 2.01 mol dm−3 ; [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 55 °C; ultrasound condition (28 kHz, 300 W).

Time (min)

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

5 15 25 35 45 55

11.23 8.56 8.47 8.03 7.17 7.17

3.62 2.75 2.79 2.71 2.38 2.36

Table 39 Reaction condition: [EMA], 2.01 mol dm−3 ; [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 45 min; ultrasound condition (28 kHz, 300 W).

Temp (K)

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

313 318 323 328 333 338

3.86 4.53 5.86 7.17 8.51 9.97

1.29 1.52 1.96 2.38 2.84 3.33

Table 40 Reaction condition: [EMA], 2.01 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 55 °C; 45 min; ultrasound condition (28 kHz, 300 W). [PDS] × 10−2 mol dm−3

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

1 2 4 5 6 8

5.31 7.18 10.23 11.43 12.58 14.34

1.79 2.38 3.29 3.82 4.21 4.77

8.3.3. Effect of initiator concentration on Rp The polymerization rate increased with increase in concentration of PDS in the range of 0.01–0.08 mol dm−3 at a fixed concentration of MPTC, pH, monomer and ionic strength was compared with ultrasound conditions and absence of ultrasonic irradiation were shown in Table 40. 8.3.4. Effect of [MPTC] on Rp The dependence of Rp on the concentration of MPTC was examined by varying MPTC in the range of 0.01–0.08 mol dm−3 at fixed concentrations of monomer, PDS, pH and ionic strength and combined with ultrasound wave irradiation. For comparison, the Rp obtained from the MPTC reaction under optimal reaction conditions in the presence and absence of ultrasonic irradiation were also shown in Fig. 13.

Fig. 13. Reaction conditions: [EMA], 2.01 mol dm−3 ; [PDS], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; Temp. 55 °C; Time 45 min; ultrasound irradiation (28 kHz,300 W). Table 41 Reaction condition: [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 45 min; ultrasound condition (28 kHz, 300 W).

[EMA] mol dm−3

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

1.61 1.81 2.01 2.21 2.41 2.61

5.62 6.31 7.17 7.89 8.27 9.09

1.87 2.11 2.38 2.63 2.76 3.05

8.3.5. Effect of momomer concentration on Rp The effect of monomer concentration on Rp was studied by varying the concentration in the range of 1.61–2.61 mol dm−3 at fixed concentrations of PDS, MPTC, pH and at constant ionic strength along with ultrasound conditions and absence of ultrasonic irradiation and the results were shown in Table 41. 8.3.6. Effect of volume fraction of aqueous phase on Rp The effect of variation in the ratio of volume of aqueous phase (Vw) to volume of organic phase (Vo), Vw/Vo, on the Rp was studied in the range of 0.61–1.00 with and without ultrasonic effect with increase in temperature (Table 42) at fixed concentrations of all other parameters. 8.3.7. Effect of solvent on Rp The effect of solvent on Rp is determined by carrying out the polymerization reaction of GMA in six different solvents such as cyclohexane, ethyl acetate, cyclohexanone, toluene, benzene and chlorobenzene under ultrasound irradiation condition. The effect of the organic solvents on the Rp values with and without ultrasound conditions were shown in Table 43. It is found that the

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Table 42 Reaction condition: [EMA], 2.01 mol dm−3 ; [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 55 °C; 45 min; ultrasound condition (28 kHz, 300 W).

Vw/Vo

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

0.61 0.67 0.75 0.82 0.92 1

6.46 6.61 6.76 6.92 7.08 7.17

2.15 2.21 2.26 2.31 2.36 2.38

Fig. 15. Reaction conditions: [AN], 0.552 mol dm−3 ; [PDS], 1.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; Temp. 60 °C; Time 50 min; ultrasound irradiation (40 kHz, 300 W). Table 44 Reaction condition: [K2 S2 O8 ], 1.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 60 °C; 50 min; ultrasound condition (28 kHz, 300 W).

Fig. 14. Reaction conditions: [EMA], 2.01 mol dm−3 ; [PDS], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], Temp. 55 °C; Time 45 min.

Rp decreased in the order cyclohexanone > chlorobenzene > ethyl acetate > toluene > benzene > cyclohexane.

[AN] mol dm−3

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

0.276 0.552 0.828 1.104 1.380 1.656

1.52 3.04 4.57 6.08 7.60 9.12

0.52 1.04 1.56 2.08 2.60 3.12

8.4. Polymerization of acrylonitrile (9)

at fixed concentrations of monomer, PDS, pH and ionic strength and combined with ultrasound wave irradiation (40 kHz, 300 W). The increase in Rp value due to the collision between intermediates [QS2 O8 ] was increased by increasing MPTC amount. Therefore the opportunity of forming a complex between them is largely increased. Hence, the Rp increased with increase in the amount of MPTC. For comparison, the Rp obtained from the MPTC reaction under optimal reaction conditions in the presence and absence of ultrasonic irradiation were also shown in Fig. 15.

Selvaraj and Rajendran [60] reported the kinetics of polymerization of acrylonitrile (AN) which was carried out under heterogeneous condition using a new MPTC, namely, N,N -dihexyl-4,4 bipyridinium dibromide in the presence of water soluble initiator, PDS under chlorobenzene / water two phase system assisted by ultrasound irradiation (Scheme 11).

8.4.2. Effect of monomer concentration on Rp The effect of monomer concentration on Rp was studied by varying the concentration in the range of 0.276–1.656 mol dm−3 at fixed concentrations of PDS, MPTC, pH and at constant ionic strength along with ultrasound conditions and absence of ultrasonic irradiation were shown in Table 44.

8.4.1. Effect of [MPTC] on Rp The dependence of Rp on the concentration of MPTC was examined by varying MPTC in the range 2 × 10−2 to 7 × 10−2 mol dm−3

8.4.3. Effect of initiator concentration on Rp The polymerizationrate increased with increased concentration of K2 S2 O8 (PDS) in the range of 0.01–0.07 mol dm−3 at a fixed

8.3.8. Effect of Ultrasonic Power The Rp also compared with the frequencies 0, 28 and 40 kHz having same output power of 300 W was shown in Fig. 14 under optimal conditions. The reaction rate increased with increasing the frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation.

Table 43 Reaction condition: [EMA], 2.01 mol dm−3 ; [K2 S2 O8 ], 2.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 55 °C; 45 min; ultrasound condition (28 kHz, 300 W). Solvent Rp × 104 mol dm−3 s−1

Cyclohexanone

Chlorobenzene

Ethyl acetate

Toluene

Benzene

Cyclohexane

Presence of ultrasonic irradiation Absence of ultrasonic irradiation

13.69

10.69

7.17

4.47

3.65

3.26

4.52

3.58

2.38

1.47

1.22

1.08

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Table 45 Reaction condition: [AN], 0.552 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 60 °C; 50 min; ultrasound condition (28 kHz, 300 W). [PDS] × 10−2 mol dm−3

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

1 2 3 4 5 6 7

10.01 14.14 17.32 20.01 22.36 24.49 26.45

3.04 4.60 5.33 6.07 6.35 7.29 8.02

Table 46 Reaction condition: [AN], 0.552 mol dm−3 ; [K2 S2 O8 ], 1.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 50 min; ultrasound condition (28 kHz, 300 W).

Temp (K)

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

318 323 328 333 338 343

1.58 1.78 2.18 3.04 4.17 5.23

0.48 0.61 0.77 1.04 1.42 1.73

Fig. 16. Reaction conditions: [AN], 0.552 mol dm−3 ; [PDS], 1.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; Temp. 60 °C; Time 50 min.

tion was carried out under ultrasonic and standard reaction condition as shown in Table 47. 8.4.6. Effect of solvent on Rp The effect of solvent on Rp was determined by carrying out the polymerization of AN in five different solvents such as chlorobenzene, ethylacetate, dibutyl ether, toluene and cyclohexane under ultrasound condition. The effect of the organic solvents on the Rp values with and without ultrasound conditions were shown in Table 48. It was found that the Rp was decreased in the order chlorobenzene > ethylacetate > dibutyl ether > toluene > cyclohexane.

Table 47 Reaction condition: [AN], 0.552 mol dm−3 ; [K2 S2 O8 ], 1.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 60 °C; 50 min; ultrasound condition (28 kHz, 300 W).

Various PTC

Rp × 104 mol dm−3 s−1 (With ultrasonic)

Rp × 104 mol dm−3 s−1 (Without ultrasonic)

NHPB TBAI TBAB TBAC THAC MPTC

1.22 1.96 2.02 2.06 2.52 3.04

0.48 0.59 0.63 0.69 0.82 1.02

8.4.7. Effect of Ultrasonic Power The Rp was also compared with the frequencies 0, 28 and 40 kHz having same output power of 300 W as shown in Fig. 16 under optimal conditions. The reaction rate increased with increasing the frequencies, due to the chemical effects by ultrasound, attributed to intense local conditions generated due to cavitation.

concentration of MPTC, pH, monomer and ionic strength was compared with ultrasound conditions and absence of ultrasonic irradiation were shown in Table 45.

9. Conclusions In conclusion, the reaction rate of product formation catalysed by phase-transfer catalyst combined with ultrasonic irradiation was reviewed. The factors affecting the overall reaction rate, such as the effect of stirring speed, quaternary ammonium salts, amount of catalyst, amount of base / initiator, temperature, ultrasonic frequency and other factors were reviewed to determine the optimal operating conditions. The apparent reaction rates were observed to obey the pseudo-first order kinetics with respect to the reactant. The reaction rate was increased with increasing temperature, stirring speed, amount of base / catalyst / initiator and ultrasonic frequency. Nevertheless, there was an optimum value of the catalyst (initiator) amount to promote the yield or to enhance

8.4.4. Effect of temperature on Rp The effect of variation of temperature in the range of 45–70 °C on the polymerization was studied with and without ultrasonic effect with increase in temperature (Table 46). 8.4.5. Effect of different phase-transfer catalysts Kinetic studies for the polymerization of AN using different phase-transfer catalysts, namely, N,N -dihexyl-4,4 -bipyridinium dibromide as an MPTC, four other single site quaternary ammonium salts, such as N-hexylpyridinium bromide (NHPB), tetrahexylammonium chloride (THAC), BTEAC, TBAC, TBAB, and TBAI. The reac-

Table 48 Reaction condition: [AN], 0.552 mol dm−3 ; [K2 S2 O8 ], 1.0 × 10−2 mol dm−3 ; [MPTC], 2.0 × 10−2 mol dm−3 ; [H+ ], 0.2 mol dm−3 ; 60 °C; 50 min; ultrasound condition (28 kHz, 300 W). Solvent Rp × 104 mol dm−3 s−1

Chlorobenzene

Ethylacetate

Dibutyl ether

Toluene

Cyclohexane

Presence of ultrasonic irradiation Absence of ultrasonic irradiation

6.24

3.04

2.87

2.65

2.22

2.02

1.04

0.92

0.88

0.74

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Please cite this article as: G.S. Prasad et al., Recent developments on phase-transfer catalytic reactions under ultrasound irradiation, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.040