chapter 5 b. scheme i: aminolytic depolymerization of pet...

©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 91

Chapter 5 B.

Scheme I: Aminolytic depolymerization of PET bottle waste using N-(2-Aminoethyl)

ethanolamine (AEEA)

5 B.1. Discussion

Present work reports the results on aminolytic depolymerization of PET bottle waste

using excess of N-(2-Aminoethyl) ethanolamine (AEEA) under soxhlet by conventional

heating, in the presence of sodium acetate or potassium sulphate as catalysts. The

depolymerization product after purification was found to be bis (-(2-hydroxyethyl amino)

ethyl) terephthalamide (BHAETA). The product was characterized by melting point, IR

spectroscopy, 1H- NMR, 13C-NMR and DSC. It has applications as chain extender in

polyurethane industry (Nortan; 1973; Tadanao and Iyoda; 1990).

O

O O

O CH2

H2C

PET Waste

n

H2N

HN

OH O

NH

HN

HO

O

HN

NH

OHCatalystRef lux

BHAETA

Fig.5.B.1: Aminolysis of PET waste using AEEA

The reaction of esters with N-(2-Aminoethyl) ethanolamine (AEEA) has been studied

extensively. The reaction is not straight forward as it has two amines, one primary and

other secondary, so principally two monoamides may form. The secondary monoamide

results from condensation of primary amine with carboxylic esters whereas tertiary

monoamide results from secondary amine condensation (Gabriel, 1964). Chakrabarti

M P; reported that initially tertiary amide was formed followed by slow, thermally

induced rearrangement to secondary amide as the latter one is thermodynamically more

stable (Chakrabarti M P, 1976).


The probable mechanism of secondary amine such as AEEA attacking ester linkage PET

is shown in Fig.5.B.2

Fig.5.B.2: Probable mechanism of aminolytic depolymerization using AEEA


Optimization of parameters

The amine, AEEA, was studied for the optimization of aminolysis parameters to

get the maximum yield of the product. These results are given in Tables 1-3. Initially, the

reaction mixture is biphasic, a solid phase (PET) and a liquid phase (amine), which

becomes single phase reaction mass after some time under reflux.

Table 5.B.1; gives the effect of time of reaction on the product yield. The

depolymerization with sodium acetate as catalyst gave 72% yield of bis (-(2-

hydroxyethyl amino) ethyl) terephthalamide (BHAETA), whereas using potassium

sulphate 69% yield was obtained for reaction time of 5 h.

Table 5.B.1. Effect of time on aminolysis product of PET

Catalyst concentration: 0.5% (w/w); PET: Amine; 1:4

Table 5.B.2; giving data on the optimization of catalyst concentration indicates that 0.5%

by weight of catalyst (w.r.t. PET) produces maximum yield of the monomer with 1: 4

molar ratio of PET: amine and reaction time of 5 h for both sodium acetate and potassium

sulphate.

Time (h) Yield (%)

Sodium acetate Potassium sulphate

1 15 10

2 32 29

3 50 43

4 67 63

5 72 69

6 70 69


Table 5.B.2. Effect of catalyst concentration on BHAETA yield

Catalyst conc.

(w/w)

Yield (%)


0.3 62 55

0.5 72 69

0.7 73 69

1.0 75 70

PET: amine; 1:4; Time: 5 h

Table 5.B.3 gives data on the optimization of PET: AEEA. The ratio of 1:4 provides

maximum yields with both the catalysts. With increase in the amine ratio further, the

yield decreased due to difficulty in isolation of the product.

Table 5.B.3. Effect of amine concentration on BHAETA yield

Catalyst concentration: 0.5% (w/w); Time: 5 h

In conclusion, aminolysisof PET bottle waste was successfully carried out under

atmospheric pressure in the excess of AEEA. The aminolysis with 1:4 PET: amine ratio,

0.5% w/w sodium acetate catalyst under reflux for 5 h gives pure BHAETA with about

PET: amine

(molar ratio)

Yield (%)


1:2 52 48

1:4 72 69

1:6 65 60

1:8 62 55


72 % yield. The reaction conditions were mild as compared to those reported in the

literature (Table 5.B.4). BHAETA has application as chain extender in polyurethane

industry. It possesses reactive groups, which can be exploited through different chemical

reactions to obtain value added products for use in different fields.

Table 5.B.4: Comparison with literature

PARAMETERS REPORTED PROCESS OUR PROCESS

Reactant Terephthalonitrile PET Waste

Amine Conc. 10 moles 4 moles

Temperature 170 ºC 170 ºC

Time 6 h 4 h

Work up Vacuum distillation Simple Separation

Yield 31 % 67 %


5 B.2. Characterization

Analysis of BHAETA

The FTIR spectrogram for the BHAETA contains the peaks at 1064 cm-1 and

3296 cm-1 due to the presence of primary alcohol, peak at 1625 cm-1 indicates presence of

carbonyl group and the peaks at 1314 cm-1 and 1541 cm-1are due to secondary amide.

The 1H NMR spectrum gave peak at δ 8.5 corresponding to - NHCO groups, the peaks at

δ 2.6 and δ 2.7 corresponding to aliphatic CH2 protons adjacent to secondary amine,

peaks at δ 3.33 and δ 3.44 corresponding to aliphatic –CH2 protons adjacent to hydroxyl

and secondary amide group, respectively. Peak δ 7.91 corresponding to aromatic ring

protons. 13C NMR spectrum of BHAETA shows peak at δ 165.8 due to carbonyl carbon

attached to aromatic ring and the peaks at δ 136.7 and 127.1 corresponding to aromatic

carbons. The peak at δ 60.3 relates to aliphatic carbon attached to the -OH group, peaks at

δ 51.4 and 48.4 corresponding to carbon atoms attached to secondary amine group and

the peak at δ 40.3 is related to –CH2 carbon attached to secondary amide. The DSC scan

shows melting point of the compound 158-162οC. This is in close agreement with melting

point of BHAETA reported by Norton et al., 1973. From all these observations it was

concluded that the structure of purified product is that of BHAETA.


FTIR analysis

Fig.5.B.3: FTIR spectrum of BHAETA


NMR analysis

Fig.5.B.4: NMR spectra of BHAETA

©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India 9

Scheme II: Aminolytic depolymerization of PET bottle waste with 2-amino-2-methyl-1-propanol and 1-amino-2-propanol

5 B.3. Discussion Aminolytic depolymerization of post consumer PET bottle waste with 2-amino-2-

methyl-1-propanol and 1-amino-2-propanol under atmospheric conditions was

investigated in the presence of catalysts zinc acetate or sodium acetate. The virtual

products obtained in pure form were respectively bis (1-hydroxy- 2-methylpropan-2-yl)

terephthalamide (BHMPTA) and bis (2- hydroxypropyl) terephthalamide (BHIPTA)

(Fig.5.B.5).

O

O

O

O

PET Waste

O

NH

OH

O

HN

OH

O

NH

OH

O

HN

HO

BHIPTA BHAMPTA

1-amino-2-propanol 2-amino-2-methyl-1-propanol

n

Fig.5.B.5. Aminoysis of PET waste using 2-amino-2-methyl-1-proanol and

1-amino-2-propanol

©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India 0

Zahn and Pfeifer; 1963 carried out aminolysis of PET with solutions of benzyl amine,

ethylene diamine, hexamethylene diamine, piperidine and aniline and obtained different

reaction products as the diamides of terephthalic acid, which do not possess any potential

for further chemical reactions. During aminolysis of PET with methylamine, methyl

terephthalamide is obtained, which is not enough reactive for its recycling into any useful

product through further reactions (Awoodi et al.; 1987).

Fig.5.B.6. General mechanism of aminolytic depolymerization


Mechanism (Fig.5.B.6) shows that when the salts of Zn, Na or K are used, they are

ionized forming complex with carbonyl group of ester to facilitate the attack of an amine

and subsequently loosing the proton to give corresponding amide (Shukla and Harad;

2005).

Optimization of Parameters

The amine, 2-amino-2-methyl-1-propanol and 1-amino-2-propanol were studied

for the optimization of aminolysis parameters to get the maximum yield of the product.

Initially, the reaction mixture is biphasic, a solid phase (PET) and a liquid phase (amine),

which becomes single phase reaction mass after some time under reflux. The said amine

has two nucleophilic centres, wherein nitrogen is less electronegative than oxygen. The

amine group of 3-amino-1-propanol attacks the ester linkage of PET.

Table 5.B.5. Effect of time on aminolysis product of PET

Catalyst concentration: 0.5% (w/w); PET: Amine ; 1:5

Table 5.B.5 gives the optimization of depolymerization time in the presence of

zinc acetate or sodium acetate as catalyst.

Time

(h)

Yield ( % )

1-amino-2-propanol 2-amino-2-methyl-1-propanol

Zinc acetate Sodium acetate Zinc acetate Sodium acetate

1 52 39 34 18

2 75 52 42 26

3 84 69 60 42

4 83 76 64 55

5 85 82 67 58

6 85 81 63 59


Four hours of depolymerization using 2-amino-2-methyl-1-propanol with zinc

acetate as catalyst gave 64% yield of bis (1-hydroxy-2-methylpropan-2-yl)

terephthalamide (BHMPTA), whereas with sodium acetate, 5 h were needed to get 58%

yield.

The depolymerization using 1-amino-2-propanol with zinc acetate as catalyst,

time of 3 h gave 84% yield of bis-(2-hydroxypropyl) terephthalamide (BHIPTA),

whereas using sodium acetate 82% yield was obtained in 5 h.

2-amino-2-methyl-1-propanol has two methyl groups attached to carbon atom

adjacent to nitrogen which may cause steric hindrance to its attack on carbonyl carbon

atom of PET; while the only methyl group attached to carbon atom adjacent to the

hydroxyl group of the amine can enhance the electron density of nitrogen and therefore

can increase the reaction rate providing better yields (Popoola, 1988).

Since 1-amino-2-propanol has shown better results for depolymerization of PET than 2-

amino-2-methyl-1-propanol, the studies were continued with the former.

Table 5.B.6. Effect of catalyst concentration on BHIPTA yield

Time: 5 h for Sodium acetate and 3h for Zinc acetate

PET: amine; 1:5;Time: 5 h

Catalyst conc.

(w/w)

Yield (%)

Zinc acetate Sodium acetate

0.3 72 60

0.5 84 82

0.7 86 83

1.0 84 79


Table 5.B.6 giving data on the optimization of catalyst concentration, which

indicates that 0.5% by weight of catalyst (w.r.t. PET) produces maximum yield of the

monomer with 1: 5 molar ratio of PET: amine and reaction time of 3 h for zinc acetate

and 5 h for sodium acetate. Zinc acetate has characteristics as a catalyst (Motoyama and

Nishiyama; 2008) and complexation ability (Ozuki and Hobuke; 2003). Our results

indicate that zinc acetate is a slightly better catalyst than sodium acetate in

depolymerization of PET. Kao et al., 1997 have proposed during their studies on

glycolysis of PET that zinc acetate might facilitate the bond scission of polymer chains

and subsequently enhance the depolymerization rate.

Table 5.B.7. Effect of amine concentration on BHIPTA yield

Time: 5 h for Sodium acetate and 3h for Zinc acetate; Catalyst Conc. 0.5% (w/w)

Table 5.B.3 gives data on the optimization of PET: 1-amino-2-propanol ratio. The ratio

of 1:5 provides maximum yields with both the catalysts. With increase in the amine ratio

further, the yield decreased due to difficulty in isolation of the product.

Application of Microwave energy source for aminolytic depolymerization

Microwave (MW) provides an interesting alternative for heating the chemical

reactions. The drastic rate enhancement observed confirms the usefulness of the MW

technique. Solvent-free reactions under MW are promising future. Thus, in order to make

PET: amine

(molar ratio)

Yield (%)


1:3 58 38

1:5 84 82

1:7 72 69

1:9 64 63


the PET depolymerization process more effective, the present work reports the results on

aminolytic depolymerization of PET waste with 1-amino-2-propanol under reflux in a

microwave heated setup.

Microwave heating was studied for aminolytic depolymerization of PET waste

using 1-amino-2-propanol. The same optimized reaction parameters of conventional

heating, viz; 0.5 % w/w zinc acetate and 1: 5 molar ratio of PET: amine were used by

varying time of reaction upto 9 min. The data in Table 5.B.8 indicates that only 5 min are

required to obtain the maximum yield of 87% of BHIPTA for zinc acetate whereas, for

sodium acetate catalyst 9 min were required to get 84% yield. The yields were

comparable to those obtained by conventional heating. Thus, a significant decrease in the

time of aminolytic depolymerization reaction from 3 h to 5 min was achieved on using

microwave irradiation as a heating source for refluxing the reaction mixture.

Table 5.B.8. Effect of time on BHIPTA yield using microwave irradiation

Catalyst concentration: 0.5% (w/w); PET: amine; 1:5

This mayattributed to the fact that microwave effects result from material-wave

interactions and, due to the dipolar polarization phenomenon, the greater the polarity of a

molecule (such as the solvent) the more pronounced is the microwave effect when the

temperature riseis considered (Laurence et al., 2003).

Time (min)

Yield (%)


1 39 29

3 70 42

5 87 62

7 83 78

9 86 84


The microwaves are known to couple directly with the molecules present in a

reaction mixture and lead to rapid but controllable rise in the temperature. Dipole rotation

is an interaction between the polar molecules that try to align themselves with the rapidly

changing electric field of the microwaves, resulting in transfer of energy. Ionic

conduction results if there are free ions or ionic species present in the substance, which

try to orient themselves to the rapidly changing electric field, generating ionic motion

(Hayes, 2002). In terms of reactivity and kinetics, the specific effect has therefore to be

considered in relation to the reaction mechanism, and particularly with regard as to how

the polarity of the system is altered during the progress of the reaction. Similar

mechanism is likely to apply in the present case, wherein the polar solvent is amine

instead of water. Conclusive mechanism can however be determined only if studies are

conducted with microwave frequency changes, which is beyond the scope of present

study.

In conclusion, aminolysis of PET waste using 2-amino-2-methyl-1-propanol and

1-amino-2-propanol was carried out successfully using zinc acetate or sodium acetate as

catalyst. The products BHMPTA and BHIPTA were obtained in pure forms.

Optimization of the parameters for aminolysis gave >84% yield of BHIPTA. Microwave

heating drastically reduced the reaction time from 3 h to 5 min with the same yield and

purity of the reactive monomers. These have the potential of recycling into useful

products with wide applications through further chemical reaction.


Catalyst Study

We have carried out the effect of conventional catalyst with simple catalyst for

depolymerization of PET waste using 1-amino-2-propanol.

Table 5.B.9. Effect of catalysts on BHIPTA yield

Catalyst Time (h) BHIPTA yield (%)

Zinc acetate 3 84

Sodium acetate 5 82

Potassium sulphate 5 78

Catalyst concentration: 0.5% (w/w); PET: amine; 1:5

Conventional catalyst zinc acetate shows little better activity than simple catalyst

such as sodium acetate and potassium sulphate. As explained earliar zinc actetate posses

better complexation ability and Kao et al., 1997 have proposed during their studies on

glycolysis of PET that zinc acetate might facilitate the bond scission of polymer chains

and subsequently enhance the depolymerization rate.

Generally the conventional catalysts used for depolymerization are zinc acetate and lead

acetate. Although they provide better yields than simple catalysts they are harmful in

nature. The toxicity of caused by the heavy metal cations is slow and long lasting. The

heavy metals possess a tendency to accumulate in the living organisms over a period of

time. High exposure levels to lead induce anemia. It also affects the central nervous

system. Although zinc is an essential element in the living organisms at trace levels, its

large doses cause gastrointestinal problems. The permissible limits of Pb and Zn cations

in the effluent discharged to the surface water are 0.1 and 5 ppm, respectively (Saxena,

2002).

So we have carried out other aminolytic studies using simple catalysts such as sodium

acetate and potassium sulphate.


5 B.4. Characterization of BHMPTA & BHIPTA

Analysis of BHMPTA

The FTIR spectrogram for the BHMPTA indicates the peaks at 1053 cm-1and 3333 cm-1

due to the presence of primary alcohol and the peaks at 1319 cm-1 and 1542 cm-1due to

the secondary amide (Fig.5.B.7). The 1H NMR spectrum (Fig.5.B.8) gave the peak at δ

7.7 corresponding to - NHCO groups, at δ 3.5 corresponding to aliphatic CH2 proton, at δ

1.3 corresponding to –CH3 protons, at δ 7.9 corresponding to aromatic ring protons and at

δ 4.9 corresponding to –OH groups. 13C NMR spectrum (Fig.5.B.9) of BHMPTA shows

peak at δ 165.8 due to carbonyl carbon attached to aromatic ring and the peaks at δ 137.5

and 127.1 corresponding to aromatic carbons. The peak at δ 67.2 relates to aliphatic

carbon attached to the -OH group, peak at δ 55.1 is due to carbonattached to amide group

and peak at δ 23.6 is due to –CH3 protons. BHMPTA melts at 230-234 οC. The DSC scan

also shows reasonably sharp endothermic peak at 236 οC.

Analysis of BHIPTA

The FTIR spectrogram for the BHIPTA indicates the peaks at 1061 cm-1 and 3278 cm-1

due to the presence of primary alcohol, peak at 1636 cm-1 indicates presence of carbonyl

group and the peaks at 1323 cm-1 and 1548 cm-1are due to secondary amide (Fig.5.B.7).

The 1H NMR spectrum (Fig.5.B.8) gave peak at δ 8.5 corresponding to - NHCO groups,

at δ 3.2 corresponding to aliphatic CH2 proton, at δ 3.7 corresponding to aliphatic –CH

protons, at δ 1.0 corresponding to –CH3 protons, at δ 7.9 corresponding to aromatic ring

protons and at δ 4.7 corresponding to –OH groups. 13C NMR spectrum (Fig.5.B.9) of

BHIPTA shows peak at δ 165.7 due to carbonyl carbon attached to aromatic ring and the

peaks at δ 136.7 and δ 127.1 corresponding to aromatic carbons. The peak at δ 65.1

relates to aliphatic carbon attached to the -OH group, peak at δ 47.2 is due to

carbonattached to amide group and peak at δ 21.2 is due to –CH3 carbon. Melting point

range observed for BHIPTA is 206-210οC. The DSC scan also shows reasonably sharp

endothermic peak at 208οC.


FTIR analysis

Fig.5.B.7. FTIR spectra of BHAMPTA and BHIPTA


NMR Analysis 1H-NMR

Fig.5.B.8.1H-NMR spectra of BHAMPTA and BHIPTA


13C-NMR

Fig.5.B.9.13C-NMR spectra of BHAMPTA and BHIPTA


Scheme III: Aminolytic depolymerization of PET waste with 3-amino-1-propanol under conventional & microwave irradiation

5 B.5. Discussion

The present work deals with the results on the use of 3-amino-1-propanol for the

aminolytic depolymerization of PET bottle waste in the presence of simple chemicals

such as sodium acetate or potassium sulphate as catalysts under conventional and

microwave source of heating. The depolymerization product after purification was found

to be bis-(3-hydroxy propyl) terephthalamide as characterized by melting point, IR

spectroscopy, NMR and DSC (Fig.5.B.10).

.

O

O

O

O

PET Waste

n

O

NH O

HN

OH

HO

BHPTA

Sodium acetate/potassium sulfate

Fig.5.B.10.Aminoysis of PET waste using 3-amino-1-propanol

The amine, 3-amino-1-propanol, was studied for the optimization of aminolysis

parameters to get the maximum yield of the product. These results are given in Tables

5.B.9-5.B.11


The results on optimization of the reaction parameters, viz., time of reactionunder

conventional heating (Table 5.B.10), catalyst concentration (Table 5.B.11) and PET:

amine ratio (Table 5.B.12) indicate that the maximum yield of the purified product was

obtained with PET: amine ratio as 1:5 and catalyst concentration for both sodium acetate

and potassium sulphate as 0.5% (w/w).

The time required for completion of the aminolysis reaction was 5 h for

conventional heating with 80% yield of purified BHPTA for sodium acetate and 74% for

potassium sulphate catalysts.

Table 5.B.10. Effect of time on BHPTA yield under conventional heating

Catalyst concentration: 0.5% (w/w); PET: amine:: 1:5

Table 5.B.11shows optimization of catalyst concentration. Sodium acetate gave

better yields than potassium sulphate which is well in agreement with literature reported

for aminolysis of PET (Shukla and Harad; 2006). Mechanism shows that when the salts

of Na or K are used they are ionized forming complex with carbonyl group of ester to

facilitate the attack of an amine and subsequently loosing the proton to give

corresponding amide. According to conjugate acid-base theory, acetate ion is stronger

Time (h) Yield %


1 45 37

2 58 49

3 69 55

4 76 69

5 80 74

6 78 73


base than sulphate ion. Therefore, the former may give deprotonation step faster than

latter one.

Table 5.B.11. Effect of catalyst concentration on BHPTA yield

PET: amine; 1:5; Time: 5 h

Table 5.B.12 gives data on the optimization of PET: 3-amino-1-propanol. The ratio of

1:5 provides maximum yields of BHPTA with both the catalysts

Table 5.B.12. Effect of amine concentration on BHPTA yield

Catalyst concentration: 0.5% (w/w); Time: 5 h

.

Catalyst conc.

(w/w)

Yield (%)


0.3 70 66

0.5 80 74

0.7 76 72

1.0 75 72

PET: amine

(molar ratio)

Yield (%)


1:3 58 50

1:5 80 74

1:7 69 68

1:9 71 68


Application of Microwave energy source for aminolytic depolymerization

In continuation, the present work reports the results on aminolytic

depolymerization of PET waste with 3-amino-1-propanol under reflux in a microwave

heated setup.

The same optimized reaction parameters of conventional heating, viz; 0.5 % w/w catalyst

and 1: 5 molar ratio of PET: amine were used by varying time of reaction upto 9 min.

The data in Table 5.B.13 indicates that time required for non-conventional (microwave

irradiation) method was only 7 min with yields comparable to the conventional method.

Thus, a drastic decrease in the time of reaction from 5 h to 7 min was achieved on using

microwave irradiation as a heating source for refluxing the reaction mixture.

Table 5.B.13. Effect of time on BHPTA yield using microwave irradiation

Literature reports the aminolysis of PET using alkyl amines (Zahn & pfiefer, 1963;

Awodi et al; 1987) to get corresponding diamides of terephthalic acid, which do not

possess any potential for further chemical reaction. Alkanol amines such as ethanol

amine (Shukla and Harad, 2006) and diethanol amine (Acar & Orbay, 2011) have

been reported for aminolysis of PET. With diethanol amine, a mixture of amide and ester

with the formation of substantial amounts of piperazine and terephthalic acid as side

Time (min)

Yield (%)


1 45 38

3 62 54

5 76 68

7 82 79

9 78 76


products were obtained. Ethanol amine has been reported to give close to 83 % of pure

bis (2-hydroxy ethylene) terephthalamide from PET bottle waste in presence of sodium

acetate catalyst in 8 h with1:8 PET: amine ratio. These results are comparable to those

reported in the present study using 3-amino-1-propanol. When compared to ethanol

amine, the 3-amino-1-propanol has an extra methylene group which can enhance electron

density on nitrogen and therefore can increase the reaction rate (Popoola, 1988).

In our laboratory the work is carried out on the use of the BHPTA in polymer

chemistry. BHPTA has been successfully reacted with lon chain carboxylic acids to form

various iesters of BHPTA. The said products obtained is currently now tested for the

plasticizing effect on various polymers. Also the work on synthesis of polyurethane from

BHPTA by reacting with diisocyanates is also under progress. So BHPTA obtained from

chemical recycling from PET waste has various applications.

In conclusion, the aminolysis of PET bottle waste using 3-amino-1-propanol

under atmospheric pressure and in the presence of sodium acetate or potassium sulfate as

catalysts gave good yield of the pure product BHPTA under both conventional and non-

conventional microwave heating methods. Heating under microwave reduced the time of

depolymerization from 5 h to 7 min affording great saving in time and energy for the

reaction.


5 B.6. Characterization of BHPTA

The FTIR spectrogram for the BHPTA indicates the peaks at 1054 cm-1 and 3289

cm-1 due to the presence of primary alcohol and the peaks at 1330 cm-1 and 1553 cm-1due

to secondary amide (Fig.5.B.11). Fig. 5.B.12gives 1H NMR for the BHPTA wherein it

may be observed that the peak at δ 8.57 corresponds to -NHCO groups, δ 3.38

corresponds to aliphatic CH2 proton attached to –NH group, δ 3.48 corresponds to CH2

proton attached to –OH group, δ 1.65 corresponds to middle –CH2 group, δ 7.98

corresponds to aromatic ring protons and δ 4.50 corresponds to -OH group. 13C NMR

spectrum (Fig.5.B.12) of BHPTA shows peak at δ 165.8 due to carbonyl carbon attached

to aromatic ring and the peaks at δ 136.8 and δ 127.2 corresponding to aromatic carbons.

The peak at δ 58.7 relates to aliphatic carbon attached to the -OH group, peak at δ 36.8 is

due to carbonattached to amide group and peak at δ 32.4 is due to –CH2 carbon.

Fig.5.B.13 gives DSC scan of BHPTA, which indicates that the range of melting point of

the compound is 206-2100C; which is in close agreement with melting point of BHPTA

reported by Thinius et al (Thinius et al., 1959).

FTIR analysis

Fig.5.B.11: FTIR spectrum of BHPTA


NMR analysis

Fig.5.B.12: NMR spectra of BHPTA


Scheme IV: Synthesis of bis-oxazoline & bis-oxazin from aminolytic depolymerized

products of PET waste

5 B.7. Discussion

Bis-oxazin and bis-oxazoline has wide applications as chain extenders in

polyester and nylon compositions and as cross linking agents in powder paint

compositions.The present work deals with the results on the use of bis (2- hydroxypropyl)

terephthalamide (BHIPTA) and bis (3-hydroxy propyl) terephthalamide (BHPTA) for

synthesis of bis-oxazoline and bis-oxazin, respectively.

Fig.5.B.13.Synthesis of useful products from PET waste

O

O

O

O

n

PET Waste

O

NH

OH

O

HNHO

O

NH

OH

O

HN

OH

BHPTA BHIPTA

HONH2HO NH2

3-amino-1-propanol 1-amino-2-propanol

N

O O

N N

O O

N

PBOXAPBIOXA

SOCl2 SOCl2


A popular approach to prepare oxazolines involves intermolecular cyclization of β–

hydroxy amide through activation of hydroxyl group as leaving group. Thionyl chloride

has often been used as dehydrating agent. In the cold with excess of thionyl chloride,

complex salts are formed which are decomposed by using NaHCO3 to get oxazoline

(Frump, 1971). BHIPTA and BHPTA obtained from aminolysis of PET waste were

subjected to cyclization reaction using thionyl chloride at ambient temperature to get 1,4-

bis (5-methyl-4,5-dihydrooxazol-2-yl) benzene (PBIOXA) and 1,4-bis (5,6-dihydro-4H-

1,3-oxazin-2-yl) benzene (PBOXA), respectively (Fig.5.B.13).

Table 5.B.14. Yield of cyclized products

Sr.

No

Reactant Product Time

(h)

Yield

(%)

1 16 56

2 16 72

Table 5.B.14 shows that PBOXA was obtained with 56% yield from BHPTA, while,

PBIOXA was obtained with 72% yield from BHIPTA. We have investigated the reaction

using TLC analysis which shows that at the end of 16 h, all the reactant is getting

consumed in both the cases. Two/three spots were found which may be consist of

product, alkene compound formed by dehydration reaction between alcohol and adjacent

hydrogen group and chloro compound by direct chlorination of hydroxyl using thionyl

chloride.

Cyclization reaction of BHIPTA to get PBIOXA as a useful product was successful,

which has been reported to be synthesized by reaction of terephthalonitrile with 1-amino-

2-propanol using metal salts at high temperature 190-230οC (Witte & Seeliger, 1973).

O

NH

OH

O

HNHO

O

NH

OH

O

HN

OH

N

O O

N

N

O O

N


Kubelbaeck et al., from Evonik-Degussa in 2010 reported the process for synthesizing

PBOXA from terephthalonitrile obtained using 3-amino-1-propanol in the presence of a

heavy metal catalyst such as zinc-2-ethyl hexanoate at high temperature 140-150°C.

Whereas, we have synthesized PBOXA from BHPTA (obtained PET waste) at ambient

temperature condition.

In conclusion, reactive products obtained from aminolysis of PET waste have the

potential of recycling into useful products with wide applications through further

chemical reactions. BHPTA and BHIPTA obtained from PET waste were successfully

subjected to further chemical reaction to get PBOXA and PBIOXA as a useful product

for polymer and paint industry.


5 B.8. Characterization of PBOXA & PBIOXA

In the FTIR spectrogram for PBOXA, the peak at 1646 cm-1 indicates the

presence of –C=N stretching (Fig.5.B.14) and disappearance of peaks of alcoholic groups

of BHPTA. The 1H NMR for the PBOXA (Fig.5.B.15) shows the peak of δ 1.9

corresponding to middle –CH2 group protons, δ 3.52 corresponding to –CH2 group

attached to oxygen, δ 4.3 corresponds to other –CH2 group protons and δ 7.88

corresponding to aromatic ring protons. The values of δ 8.57 and δ 4.50, which

correspond to –NHCO and -OH group protons respectively in BHPTA were not observed

in PBOXA due to cyclization and dehydration. 13C NMR spectrum (Fig.5.B.16) of

PBOXA shows peak at δ 165.7 due to carbon atom of imine attached to aromatic ring and

the peaks at δ 136.8 and δ 127.2 corresponding to aromatic carbons. The peak at δ 58.2

relates to carbon attached to the oxygen atom, the peak at δ 36.8 is due to carbon attached

to nitrogen other than imine and the peak at δ 32.4 is due to –CH2 carbon. The DSC scan

of PBOXA, which indicates that the melting point of the compound is 219-223 0C. This

is in close agreement with melting point of PBOXA reported by Kubelbaeck et al

(Kubelbaeck et al., 2010).

In the FTIR spectrogram for PBIOXA, the peak at 1637 cm-1 indicates the

presence of –C=N stretching (Fig.5.B.14) and disappearance of peaks of alcoholic groups

of BHIPTA. The 1H NMR for the PBIOXA (Fig.5.B.15) shows the peak of δ 1.3

corresponding to –CH3 group protons, δ 3.5 corresponding to –CH2 group attached to

nitrogen on one side of phenyl group and δ 4.1 corresponding to –CH2 group attached to

nitrogen on the other side of phenyl group. PBIOXA has two asymmetric carbon atoms

therefore the protons show different coupling values owing to different chemical and

magnetic environment. The peak at δ 4.8 corresponds to –CH group protons and δ 7.9

corresponding to aromatic ring protons. The values of δ 8.5 and δ 4.7 which correspond

to –NHCO and -OH group protons respectively in BHIPTA were not observed in

PBIOXA due to cyclization and dehydration. 13C NMR spectrum (Fig.5.B.16) of

PBIOXA shows peak at δ 161.5 due to carbon atom of imine attached to aromatic ring

and the peaks at δ 130.1 and δ 127.8 corresponding to aromatic carbons. The peak at δ

76.1 relates to carbon attached to the methyl group, the peak at δ 61.0 is due to carbon

attached to nitrogen other than imine and the peak at δ 20.0 is due to –CH3 carbon.


Melting point range observed for PBIOXA is 85-89οC. The DSC scan also shows

reasonably sharp endothermic peak at 89οC. This is in close agreement with melting point

of PBIOXA reported by Deiter et al (Deiter et al., 1974).

FTIR Analysis

Fig.5.B.14: FTIR spectra of PBOXA and PBIOXA


1H-NMR Analysis

Fig.5.B.15. 1H-NMR spectra of PBOXA an PBIOXA


13C-NMR Analysis

Fig.5.B.16. 13C-NMR spectra of PBOXA an PBIOXA


Scheme V: Aminolytic depolymerization of PET waste with 4-amino-1-butanol & 2-amino-1-butanol

5 B.9. Discussion

We have carried out initial study on the effect of butanol amines on waste PET

bottle flakes. The amines studied were 4-amino-1-butanol and 2-amino-1-butanol.

Aminolysis of post consumer PET bottle waste with 4-amino-1-butanol and 2-amino-1-

butanol under atmospheric conditions was carried out in the presence of sodium acetate

catalyst. The virtual products obtained in pure form were, respectively, bis (4-

hydroxybutyl) terephthalamide (BHBTA) and bis (1-hydroxybutan-2-yl) terephthalamide

(BHIBTA) (Fig.5.B.17).

Fig.5.B.17.Aminoysis of PET waste using butanolamines


The said butanol amines were used to carry out initial study on waste PET bottle flakes.

The results of product yields shown in Table 5.B.15.

Table 5.B.15. Effect of butanol amines on PET waste

Catalyst concentration (NaOAc): 0.5% (w/w); PET: Amine ; 1:5; Time: 3 h

3 hours of depolymerization using 4-amino-1-butanol gave 72% yield of bis (4-

hydroxybutyl) terephthalamide (BHBTA), whereas with 2-amino-1-butanol in time of 4 h

gave 64% yield of bis (1-hydroxybutan-2-yl) terephthalamide (BHIBTA). The PET:

amine ratio was 1:5 and sodium acetate catalyst concentration 0.5% (w/w) for said

depolymerization.

The products were obtained in good yield from aminolysis of PET waste using butanol

amines. Further studies can be carried out for optimization of parameters such as time,

amine concentration and catalyst concentration. BHBTA and BHIBTA possess free

hydroxyl groups which can be exploited for various reactions to prepare useful

chemicals.


5 B.10. Characterization of BHBTA and BHIBTA

The FTIR spectrogram for the BHBTA indicates the peaks at 1058 cm-1 and 3303 cm-1

due to the presence of primary alcohol and the peaks at 1340 cm-1 and 1541 cm-1due to

secondary amide (Fig.5.B.18). Fig. 5.B.19 gives 1H NMR for the BHBTA wherein it may

be observed that the peak at δ 8.56 corresponds to -NHCO groups, δ 3.23 corresponds to

aliphatic CH2 proton attached to –NH group, δ 3.25 corresponds to CH2 proton attached

to –OH group, δ 1.45 and δ 1.51 corresponds to middle –CH2 group, δ 7.87 corresponds

to aromatic ring protons. 13C NMR spectrum (Fig.5.B.19) of BHBTA shows peak at δ

165.6 due to carbonyl carbon attached to aromatic ring and the peaks at δ 136.9 and δ

127.2 corresponding to aromatic carbons. The peak at δ 60.7 relates to aliphatic carbon

attached to the -OH group, peak at δ 39.6 is due to carbon attached to amide group and

peak at δ 26.1 and δ 30.2 are due to –CH2 carbon. Melting point range observed for

BHBTA is 215-218 οC.

The FTIR spectrogram for the BHIBTA indicates the peaks at 1061 cm-1 and

3278 cm-1 due to the presence of primary alcohol, peak at 1636 cm-1 indicates presence of

carbonyl group and the peaks at 1323 cm-1 and 1548 cm-1are due to secondary amide

(Fig.5.B.18). The 1H NMR spectrum (Fig.5.B.20) gave peak at δ 8.4 corresponding to -

NHCO groups, at δ 1.92 corresponding to -CH2 protons adjacent to –CH3, at δ 4.0

corresponding to aliphatic –CH protons, at δ 0.9 corresponding to –CH3 protons, at δ 7.9

corresponding to aromatic ring protons. 13C NMR spectrum (Fig.5.B.20) of BHIBTA

shows peak at δ 165.8 due to carbonyl carbon attached to aromatic ring and the peaks at δ

136.6 and δ 127.3 corresponding to aromatic carbons. The peak at δ 52.4 relates to

aliphatic carbon attached to the -OH group, peak at δ 47.0 is due to carbon attached to

amide group, peak at δ 10.5 is due to –CH3 carbon and δ 24.5 is corresponding to -CH2

carbon adjacent to –CH3. Melting point range observed for BHIBTA is 238-242 οC.


FTIR Spectra

Fig.5.B.18: FTIR spectra of BHBTA and BHIBTA


NMR spectra

Fig.5.B.19: NMR spectra of BHBTA


Fig.5.B.20: NMR spectra of BHIBTA


Chapter 5 C: Synthesis of 2-oxazolines using novel bronsted acidic IL

5 C.1. Discussion

2-oxazolines are very important class of 5-memberd ring containing nitrogen

atom. They are widely used as crosslinking agent, as chiral catalysts and in the synthesis

of polymers for biomedical uses. They are also used in natural products and

pharmaceutical intermediates.

Various methods have been developed for synthesis of 2-oxazolines comprising

starting materials such as carboxylic acids, nitriles, aldehydes and β-hydroxy amides.

They suffer from various disadvantages such as high temperatures, long reaction time,

modest yields and use of complex reagents.

Novel ionic liquid [SO3H-pBIM][HSO4] was synthesized and characterized by

FTIR, NMR and TGA. It was further used for the synthesis of 2-oxazolines from

corresponding β-hydroxyl amides (Fig.5.C.1). Effect of various parameters such as time,

temperature and substrate studies has been carried out. The products obtained were

characterized by all modern spectroscopic techniques.

Fig.5.C.1.Preparation of 2-oxazolines using novel ionic liquids

IL’s that has lewis acidic character are well precedented and have been studied

thoroughly in various applications but Amanda et al., reported the first ionic liquids that

are designed to be strong Bronted acids (Amanda et al., 2002). In each of the new IL

they synthesized, an alkane sulphonic acid group is covalently connected to the IL cation.

We have synthesized novel bronsted acidic IL by reaction of imidazole

and butyl chloride to get IL 1-butylimidazolium chloride [HBIM]Cl. The IL obtained was

reacted with 1,3-propane sultone to get Bronsted acidic properties containing acid


sulphonic group IL [SO3H-pBIM][Cl] which was subsequently reacted with sulphuric

acid to replace chloride anion with hydrogen sulphate anion [SO3H-pBIM][HSO4]

(Figure.5.C.2).

Fig.5.C.2: Preparation of bronsted acidic IL

The novel Bronsted acidic IL [SO3H-pBIM][HSO4] was characterized by TGA to

analyze the thermal stability. The TGA curve showed that IL is stable upto 200°C. The

synthesized IL was used in the cyclodehydration of N-(2-hydroxyethyl)benzamide to

obtain 2-phenyl oxazoline as a model reaction to determine the optimal reaction

conditions.

Table 5.C.1 gives the effect of time of reaction on the product yield. With 1 ml of

[SO3H-pBIM][HSO4] IL as catalyst and solvent for 2 mmol of N-(2-hydroxyethyl)

benzamide, 95 % yield of 2-phenyl oxazoline was obtained in 3 h.


Table 5.C.1. Effect of time of reaction on the product yield

Time (h) Yield (%)

1 40

2 72

3 95

4 95

Reaction Conditions: All reactions were carried out with [SO3H-pBIM][HSO4] (1 ml)

and N-(2-hydroxyethyl)benzamide (2 mmol), Temperature (90 °C)

Table 5.C.2 gives data on the optimization of reaction temperature parameters. The

reaction gave maximum yield of product at 90 °C. With further increase in temperature,

the yield decreased due to formation of side products.

Table 5.C.2. Effect of temperature on the product yield

Temperature (˚C) Yield (%)

30 -

60 30

90 95

120 80

Reaction Conditions: All reactions were carried out with [SO3H-pBIM][HSO4] (1 ml) and N-(2-hydroxyethyl)benzamide (2 mmol), Time (3 h)

In order to extend the scope of reaction further, a variety of substrates were examined in

the cyclodehydration reaction and the results are listed in Table 5.C.3. It was found that

almost all varieties of β–hydroxy amides were dehydrated smoothly to afford the


corresponding products in good to excellent yields in the presence of [SO3H-

pBIM][HSO4] IL as catalyst an solvent at 90 °C.

Table 5.C.3. Substrate study for synthesis of 2-oxazolines

R NH

O

R N

O[SO3H-pBIM][HSO4]

90 oC, 3h

1a-i, R = Ar' 3a-i, R = Ar'

OH

No. R (1a-i) Product (3a-i) Yield (%)

a. Phenyl N

O

95

b. 2-naphthyl N

O

89

c. 4-ClC6H4

Cl

N

O

92

d. 4-CH3C6H4

H3C

N

O

93

e. 4-CH3OC6H4

OH3C

N

O

84

f. 4-HOC6H4

HO

N

O

75


g. 4-NH2C6H5

H2N

N

O

72

h. 4-NO2C6H4

O2N

N

O

77

i. C6H4C2H2 N

O

78

Reaction Conditions: All reactions were carried out with Amide 1a-i (2 mmol),

[SO3H-pBIM][HSO4] (1ml), Time (3 h), Temp (90˚C).

The cyclodehydration of electron donating substituted β–hydroxy amides such as

N-(2-hydroxyethyl)-4-methylbenzamide gave corresponding product yield as high as 93

%, while the electron withdrawing substituted β–hydroxy amides such as N-(2-

hydroxyethyl)-4-nitrobenzamide under same reaction parameters gave yield of 77 %. The

results showed good to excellent yields of products for both electron donating and

electron withdrawing substituents.

The hydroxyl and amino group substituted β–hydroxy amides gave less product

yield as they were soluble in water. The extractions were carried out 6 times with

addition of salt to get the product yield near 72 %.

The products obtained were characterized by all spectroscopic techniques.

Recyclability of catalyst

The reusability of [SO3H-pBIM][HSO4] IL catalyst was evaluated for

cyclodehydration reaction. As shown in Table 5.C.4 the reused catalyst still showed

good activity upto third cycle. In each and every reaction we lost 1mmol of IL catalyst

for 2mmol of product as it forms salt. So the remaining IL was recycled for further

reactions.


Table 5.C.4. Recyclability study of catalyst

Entry Recycle Product Yield (%)

1 - 95

2 First 93

3 Second 88

4 Third 85

Reaction Conditions: All reactions were carried out with Amide 1a-i (2 mmol),

[SO3H-pBIM][HSO4] (1ml), Time (3 h), Temp (90˚C).

In summary, novel Bronsted acidic IL [SO3H-pBIM][HSO4] was synthesized and

applied in the synthesis of 2-oxazolines. The catalyst showed better thermal stability and

exhibited high catalytic activity in cyclodehydration reaction. The catalyst could be

recovered up to 3 cycles. Thus effective protocol has been developed for the synthesis of

2-oxazolines using [SO3H-pBIM][HSO4] IL as catalyst and solvent.


5 C.2. Application of [SO3H-pBIM][HSO4] IL for synthesis of bis-oxazine and bis-

oxazoline

The synthesized novel IL was used further for synthesis of PBOXA and PBIOXA

from BHPTA and BHIPTA respectively obtained from aminolysis of PET waste.

In chapter 5.B. Scheme IV we have used thionyl chloride as cyclodehyrating

agent for synthesis of PBOXA and PBIOXA. As thionly chloride is hazardous to

environment as after reaction it emits sulphur dioxide and hydrochloric acid. As it is a

need to improve reaction parameters from green chemistry point of view we have tried to

replace thionyl chloride with synthesized IL which is recyclable and less hazardous.

Table 5.C.5. Yield of cyclized products

Sr.

No

Reactant Product Yield

(%)

1 73

2 79

Reaction Conditions: All reactions were carried out with amide (2 mmol),

[SO3H-pBIM][HSO4] (3ml), Time (24 h), Temp (150 ˚C).

The reaction parameters were high as compared to the other derivatives used for

synthesis of oxazoline. The reaction was carried out at higher temperature (150 ̊ C) and

high concentration of IL for 24 h. The main reason may be less solubility of BHPTA and

BHIPTA.

The products PBOXA and PBIOXA were obtained in good yields, 73 % and 79%,

respectively. Thus [SO3H-pBIM][HSO4] IL was successfully used for cyclodehydration

of BHIPTA and BHPTA obtained from aminolysis of PET waste to get useful products

such as PBOXA and PBIOXA.

O

NH

OH

O

HNHO

O

NH

OH

O

HN

OH

N

O O

N

N

O O

N


5 C.3. Characterization of novel IL and oxazolines

Analysis data of IL

N NBuSO3HHSO4

-

FT-IR (neat, cm–1): 3141(C-H), 2968, 2875, 1718(C=C), 1583(C=N), 1450, 1157(S=O sym),

1033(S=O asym), 858, 752; 1H NMR (300 MHz, DMSO, δ ppm): 14.10 (s, 1H), 8.95 (t, 1H), 7.55 (s, 2H), 4.20 (t,), 3.62 (t,

2H), 2.64 (t, 2H), 2.00 (Pent, 2H), 1.65 (Pent, 2H), 1.11 (Sept, 2H), 0.74 (t, 2H) 13C NMR (75 MHz, CDCl3, δ ppm): 21.69, 42.43, 64.91, 126.64, 127.77, 130.05, 133.89, 155.30.

Analaysis data of Derivatives

Table-3 Entry 3a: 2-phenyl-4, 5-dihydrooxazole

FT-IR (neat, cm–1): 2975, 1647, 1450, 1357, 1259, 1062, 1024, 943; 1H NMR (300 MHz,

CDCl3, δ ppm): 4.04 (t, 2H), 4.41 (t, 2H), 7.37-7.49 (m, 3H), 7.93 (d, 2H); 13C NMR (75

MHz, CDCl3, δ ppm): 54.72, 67.46, 127.55, 128.01, 128.21, 131.17, 164,55.

Table-3 Entry 3b: 2-(naphthalen-2-yl)-4,5-dihydrooxazole

FT-IR (neat, cm–1): 3049, 2877, 1639, 1508, 1317, 1242, 1120, 999, 939, 775; 1H NMR

(300 MHz, CDCl3, δ ppm): 4.11 (t, 2H), 4.31 (t, 2H), 7.40-7.49 (m, 2H), 7.57 (t, 1H),

7.79-7.89 (m, 2H), 8.07 (d,1H), 9.14 (d, 1H); 13C NMR (75 MHz, CDCl3, δ ppm): 55.51,

66.29, 124.32, 124.44, 125.87, 126.24, 127.08, 128.24, 128.77, 130.94, 131.66, 133.50,


164.15.

Table-3 Entry 3c: 2-(4-chlorophenyl)-4,5-dihydrooxazole

Cl

N

O

FT-IR (neat, cm–1): 2925, 1643, 1485, 1402, 1259, 1070, 1012, 939, 835, 727; 1H NMR

(300 MHz, CDCl3, δ ppm): 4.03 (t, 2H), 4.41 (t, 2H), 7.37 (d, 2H), 7.86 (d, 2H); 13C

NMR (75 MHz, CDCl3, δ ppm): 54.76, 67.54, 126.03, 128.39, 129.28, 137.18, 163.50.

Table-3 Entry 3d: 2-(p-tolyl)-4,5-dihydrooxazole

FT-IR (neat, cm–1): 2937, 2858, 1737, 1649, 1361, 1240, 1068, 943, 829; 1H NMR (300

MHz, CDCl3, δ ppm): 2.37 (s, 3H), 4.03 (t, 2H), 4.39 (t, 2H), 7.20 (d, 2H), 7.83 (d, 2H); 13C NMR (75 MHz, CDCl3, δ ppm): 21.52, 26.40, 54.85, 67.45, 124.94, 128.07, 129.02,

141.56, 164.66.

Table-3 Entry 3e: 2-(4-methoxyphenyl)-4,5-dihydrooxazole

FT-IR (neat, cm–1): 2970, 2877, 1645, 1606, 1512, 1359, 1253, 1168, 1068, 941, 842; 1H

NMR (300 MHz, CDCl3, δ ppm): 3.83 (s, 3H), 4.02 (t, 2H), 4.39 (t, 2H), 6.88-6.93 (m,

2H), 7.86-7.91 (m, 2H); 13C NMR (75 MHz, CDCl3, δ ppm): 54.70, 55.25, 67.43,

113.60, 120.16, 129.80, 161.95, 164.41.


Table-3 Entry 3f: 4-(4,5-dihydrooxazol-2-yl)phenol

FT-IR (neat, cm–1): 2925, 1585, 1504, 1365, 1257, 1083, 937, 833, 738; 1H NMR (300

MHz, DMSO3, δ ppm): 3.86 (t, 2H), 4.30 (t, 2H), 6.79 (d, 2H), 7.68 (d, 2H), 10.01 (s,

1H); 13C NMR (75 MHz, DMSO, δ ppm): 54.19, 66.95, 115.17, 118.31, 129.51, 160.12,

162.85.

Table-3 Entry 3g: 4-(4,5-dihydrooxazol-2-yl)aniline

FT-IR (neat, cm–1): 3444, 3157, 2923, 1631, 1602, 1357, 1261, 1170, 1080, 943, 837; 1H

NMR (300 MHz, DMSO, δ ppm): 3.83 (t, 2H), 4.27 (t, 2H), 5.67 (s, 2H), 6.54 (d, 2H),

7.52 (d, 2H); 13C NMR (75 MHz, DMSO, δ ppm): 54.08, 66.60, 112.86, 114.25, 129.13,

151.60, 163.31.

Table-3 Entry 3h: 2-(4-nitrophenyl)-4,5-dihydrooxazole

FT-IR (neat, cm–1): 2948, 1726, 1643, 1596, 1502, 1326, 1257, 1064, 935, 850; 1H NMR

(300 MHz, CDCl3, δ ppm): 4.12 (t, 2H), 4.50 (t, 2H), 8.12 (d, 2H), 8.27 (d, 2H); 13C

NMR (75 MHz, CDCl3, δ ppm): 55.20, 68.12, 123.49, 129.14, 133.49, 149.44, 162.84.

Table-3 Entry 3i: 2-styryl-4,5-dihydrooxazole


FT-IR (neat, cm–1): 2925, 1650, 1608, 1448, 1361, 1249, 987, 756; 1H NMR (300 MHz,

CDCl3, δ ppm): 3.98 (t, 2H), 4.33 (t, 2H), 6.64 (d, 1H), 7.27-7.46 (m, 4H), 7.49 (d, 2H); 13C NMR (75 MHz, CDCl3, δ ppm): 54.87, 67.14, 115.13, 127.37, 128.74, 129.32,

135.20, 139.68, 164.27.

FTIR analysis

75090010501350165019502400300036001/cm

30

35

40

45

50

55

60

65

70

75

80

85

90%T

3141

.82

2968

.24

2875

.67

1718

.46

1583

.45

1450

.37

1157

.21

1033

.77

858.

26 752.

19

SIL

Fig.5.C.3: FTIR spectrogram of [SO3H-pBIM][HSO4] IL


NMR Analysis

Fig.5.C.4: NMR spectra of [SO3H-pBIM][HSO4] IL


Fig.5.C.5: NMR spectra of 2-phenyl-4, 5-dihydrooxazole


Fig.5.C.6: NMR spectra of 2-(naphthalen-2-yl)-4,5-dihydrooxazole


Fig.5.C.7: NMR spectra of 2-(4-chlorophenyl)-4,5-dihydrooxazole


Fig.5.C.8: NMR spectra of 2-(p-tolyl)-4,5-dihydrooxazole


Fig.5.C.9: NMR spectra of 2-(4-methoxyphenyl)-4,5-dihydrooxazole


Fig.5.C.10: NMR spectra of 4-(4,5-dihydrooxazol-2-yl)phenol


Fig.5.C.11: NMR spectra of 4-(4,5-dihydrooxazol-2-yl)aniline


Fig.5.C.12: NMR spectra of 2-(4-nitrophenyl)-4,5-dihydrooxazole


Fig.5.C.13: NMR spectra of 2-styryl-4,5-dihydrooxazole


Chapter 5 D: Synthesis of heterocycles from PET waste and evaluation of their antibacterial activity

5 .D.1. Discussion

The present chapter reports on synthesis of heterocyclic compounds such as

triazoles and thiadiazoles from terephthalic dihydrazide (TPHD) an aminolytic product of

PET waste. The said product has been reported to be synthesized by refluxing PET waste

with hydrazine hydrate under conventional heating or microwave irradiation (Fig.5.D.1)

using sodium acetate catalyst (Shukla et al., 2012).

Fig.5.D.1: Aminolysis of PET waste using hydrazine hydrate

Synthesis of bis-thiadiazoles and bis-triazoles

TPHD obtained from PET waste was subjected to condensation reaction with aryl

isothiocyanate in ethanol under reflux condition for 3 h to obtain corresponding

thiosemicarbazide. As TPHD is having hydrazide group on both the sides of benzene

ring, the reaction takes place at both the ends of the compound to produce bis-

thiosemicarbazide (Fig.5.D.2).


The bis-thiosemicarbazide on treatment with sodium hydroxide underwent

cyclization to bis-triazoles, while on treatment with conc. sulphuric acid at RT to produce

bis-thiadiazoles (Fig.5.D.2).

Fig.5.D.2: Synthesis of heterocyclic compounds from TPHD


Table 5.D.1 shows the results for synthesis of bis-thiadiazoles using various

substrates. TPHD was condensed with isothiocyanate to obtain bis-thiosemicarbazide

intermediate with excellent yields upto 90 % for all substrates. The results showed that all

intermediates gave good yields of corresponding bis-thiadiazoles using conc. sulphuric

acid at RT for 3 h.

Table 5.D.1. Substrate study for synthesis of bis-thiadiazoles

No. Ar-NCS Product Yield (%)

2a Phenyl

NN

S S

NN

HN NH

78

2b p-fluoro

NN

S S

NN

HN NH

F F

80

2c p-methoxy

NN

S S

NN

HN NH

OCH3 OCH3

82

2d Naphthyl

NN

S S

NN

HN NH

70

In order to extend the study of intermediate obtained by condensation of TPHD

and aryl isothiocyante it was subjected to cyclization reaction under basic conditions. It

was found that almost all varieties of intermediates were cyclized smoothly to afford the


corresponding bis-triazoles in good yields as shown in Table 5.D.2 under reflux

condition using dil.NaOH solution for 4 h.

Table 5.D.2. Substrate study for synthesis of bis-triazoles

No. Ar-NCS Product Yield (%)

3a Phenyl

68

3b p-fluoro

78

3c p-methoxy

77

3d Naphthyl

70

The bis-thiadiazoles and bis-triazoles obtained were characterized by

spectroscopic techniques and evaluated for their biological activities.

Synthesis of Schiff bases from TPHD

The study was extended to the synthesis of Schiff bases from TPHD obtained

from PET waste. In the present study, the most common and useful procedures for the


preparation of the mercapto and thione-substituted 1,2,4-triazole were applied and their

utility for the synthesis of Schiff bases are discussed.

For the synthesis of 3-thiol-1,2,4-triazole derivatives well known methodology

was applied on the TPHD for which it was reacted with carbon disulphide in alcoholic

KOH solution to form bis-dithiocarbazinate which undergoes ring closure with an excess

of 99% hydrazine hydrate to give the 1,4-phenylene-bis(4- amino-4H-1,2,4-triazole-3-

thiol) (4). This reaction is condensation reaction in which nucleophilic attack of an amine

of dihydrazide takes place on CS2 with formation bisdithiocarbazinate salt which, in the

next step was taken into water and reacted with the hydrazine hydrate for cyclization to

produce bis-triazole (Fig.5.D.3).

Fig.5.D.3: Synthesis of Schiff bases from TPHD

Schiff bases are condensation products of primary amines with carbonyl

compounds.These compounds are also known as anils, imines or azomethines. Because


of the relative ease of preparation, synthetic flexibility, and the special property of C=N

group, Schiff bases are generally excellent chelating agents, especially when a functional

group like –OH or –SH is present close to the azomethine group so as to form a five or

six membered ring with the metal ion.

The bis-4-amino-1,2,4-triazole-3-thiol obtained was reacted with aldehydes under

acidic condition to obtain Schiff bases (Fig.5.D.3). Different aromatic aldehydes were

screened for general applicability of reaction and it was found that moderate to good

yields were obtained (Table 5.D.3). The reaction was carried out using ethanol as solvent

under reflux condition with few drops of conc.HCl as catalyst for 5 h.

Table 5.D.3. Substrate study for synthesis of Schiff bases from TPHD

No. Ar-CHO Product Yield (%)

5a p-Hydoxy

63

5b p-Nitro

74

5c Salicylaldehyde

65

5d o-Vanillin

69


The Schiff bases obtained were characterized by spectroscopic techniques and

tested for biological activities.

Antibacterial activities

The assessment of the antibacterial activities of the synthesized compounds was

determined by the well-diffusion method (Christine & Michael, 1986). The prepared

compounds were tested against the Gram +ve bacteria (Bacillus Cereus) and Gram -ve

bacteria (Escherichia Coli).

The diameter of the inhibition zone that appeared around the holes in each plate was

measured as an indication of antibacterial activity. Activity of each compound was

compared with ciprofloxacin and sulphametoxazol as standards. These results are

summarized in Table 5.D.4.

Table 5.D.4. Biological activites of synthesized compounds

Sample ID Antibacterial Activity in mm ( 1mg/ml)

Escherichia coli Bacillus cereus

2b 6 7

2c 4 6

2d 4 6

3d 3 5

5b 7 7

5d 6 7

Sulphamethoxazol 12 10

Ciprofloxacin 20 18

The compounds showed comparatively moderate activity against Bacillus Cereus and

Escherichia Coli related to standards. The photographic images of the compounds

showing activities are shown in Fig.5.D.4.


In conclusion, TPHD obtained from aminolysis of PET waste have the potential

of recycling into useful products with wide applications through further chemical

reactions. Heterocyclic compounds containing triazole and thiadiazole moieties were

synthesized from TPHD possessing moderate biological activities against commercial

compounds. These compounds can become lead molecules with further chemical

modifications can improve potency and selectivity. The chemical recycling of PET waste

can be used for synthesis of various heterocyclic compounds.


5.D.2. Characterization

Analysis data of derivatives

1.

Solid, Melting point- 196-200 0C; FT-IR (neat, cm–1):3143, 3309, 1668, 1367; 1H NMR

(300 MHz, DMSO, δ ppm): 7.1-8.0 (Ar-H), 9.8 (-NH); 13C NMR (75 MHz, DMSO, δ

ppm): 114.3, 127.8, 135.3, 157.9, 161.1, 165.4, and 181.3

2.

Solid, Melting point- 214-218 0C; FT-IR (neat, cm–1):3101, 3209, 1661, 1346; 1H NMR

(300 MHz, DMSO, δ ppm): 6.8-8.0 (Ar-H), 9.7 (-NH), 3.7 (-OCH3); 13C NMR (75 MHz,

DMSO, δ ppm): 56.3, 113.3, 119.5, 127.7, 131.9, 135.8, 152.2, 156.6 and 165.3

3.

Solid; FT-IR (neat, cm–1):3155, 3285, 1672, 1354; 1H NMR (300 MHz, DMSO, δ ppm):

7.3-8.0 (Ar-H), 9.8 (-NH); 13C NMR (75 MHz, DMSO, δ ppm): 115.0-135.7, 165.6 and

182.7


Solid; Melting point- >3000C; FT-IR (neat, cm–1):3104, 3050, 1610, 1330; 1H NMR (300

MHz, DMSO, δ ppm): 7.2-8.0 (Ar-H), 10.8 (-NH);

5.

Solid; Melting point- >300 0C; FT-IR (neat, cm–1):3108, 3070, 1650, 1330; 1H NMR (300

MHz, DMSO, δ ppm): 6.9-7.2 (Ar-H).

4.

Solid; Melting point- >300 0C; FT-IR (neat, cm–1): 3072, 1512, 1311, 767; 1H NMR (300



5.

NN

S S

NN

HN NH

F F

Solid; Melting point- >300 0C; FT-IR (neat, cm–1):3004, 1622, 1356; 1H NMR (300

MHz, DMSO, δ ppm): 7.2-7.9 (Ar-H), 10.6 (-NH).

6. NN

S S

NN

HN NH

OCH3 OCH3 Solid; Melting point- >300 0C; FT-IR (neat, cm–1): 3045, 1620, 1400; 1H NMR (300

MHz, DMSO, δ ppm): 7.0-7.9 (Ar-H), 10.4 (-NH), 3.7 (-OCH3); 13C NMR (75 MHz,

DMSO, δ ppm): 55.6, 113.7, 128.2, 132.4, 135.8, 157.2, 165.8 and 181.8.

7. NN

S S

NN

HN NH

Solid; Melting point- >300 0C; FT-IR (neat, cm–1): 3004, 1629, 1328; 1H NMR (300



8.

Solid; Melting point- 254-258 0C; FT-IR (neat, cm–1): 3103, 1596, 1512, 1460; 1H NMR

(300 MHz, DMSO, δ ppm): 6.8-8.0 (Ar-H), 3.8 (-OCH3); 13C NMR (75 MHz, DMSO, δ

ppm): 56.0, 115.1-129.0, 147.9, 148.4and 162.7

9.

Solid; Melting point- 288-293 0C; FT-IR (neat, cm–1): 3103, 2767, 1623, 1512, 1353; 1H

NMR (300 MHz, DMSO, δ ppm): 6.8-8.2 (Ar-H), 9.9 (-CH=N), 14.3 (-SH); 13C NMR

(75 MHz, DMSO, δ ppm): 116.6, 118.2, 119.6, 127.2, 128.4, 134.4, 147.9, 158.8 and

163.0

10.


Solid; FT-IR (neat, cm–1): 3112, 1623, 1514, 1307; 1H NMR (300 MHz, DMSO, δ ppm):

6.8-8.1 (Ar-H), 10.0 (-CH=N), 14.2 (-SH); 13C NMR (75 MHz, DMSO, δ ppm): 115.1,

118.2, 119.1, 122.0, 127.8, 128.4,147.8, 147.9, 148.4 and 162.7

11.

Solid; Melting point- 262-2660C; FT-IR (neat, cm–1): 3311, 3099, 2767, 1595, 1517,

1344; 1H NMR (300 MHz, DMSO, δ ppm): 8.0-8.3 (Ar-H), 10.1 (-CH=N), 13.9 (-SH)


NMR Analysis

Fig.5.D.4: NMR Spectra of 1,4-Phenylene bis (4-fluorophenylthiosemicarbazido)


Fig.5.D.5: 1H-NMR Spectra of 5,5-(1,4-Phenylene)bis(4-(4-fluorophenyl)-3-mercapto-

1,2,4-triazole) and 5,5-(1,4-Phenylene)bis(2-(4-fluorophenylamino-1,3,4-thiadiazole)


Fig.5.D.6: NMR Spectra of 1,4-Phenylene bis (4-methoxyphenylthiosemicarbazido)


Fig.5.D.7: NMR Spectra of 5,5-(1,4-Phenylene)bis(2-(4-methoxyphenylamino-1,3,4-

thiadiazole)


Fig.5.D.8: 1H-NMR Spectra of 5,5-(1,4-Phenylene)bis(4-(4-methoxyphenyl)-3-mercapto-

1,2,4-triazole


Fig.5.D.9: NMR Spectra of 1,4-Phenylene bis (naphthylthiosemicarbazido)


Fig.5.D.10: 1H-NMR Spectra of 5,5-(1,4-Phenylene)bis(4-(naphthyl)-3-mercapto-1,2,4-

triazole) and 5,5-(1,4-Phenylene)bis(2-(naphthylamino-1,3,4-thiadiazole)


Fig.5.D.11: NMR Spectra of Schiff base obtained from o-vanillin and bis-4-amino-1,2,4-triazole-3-thiol


Fig.5.D.12: NMR Spectra of Schiff base obtained from salicylaldehyde and bis-4-amino-1,2,4-triazole-3-thiol


Fig.5.D.13: NMR Spectra of Schiff base obtained from p-hydroxybenzaldehyde and bis-4-amino-1,2,4-triazole-3-thiol


Fig.5.D.14: 1H-NMR Spectrum of Schiff base obtained from p-nitrobenzaldehyde and bis-4-amino-1,2,4-triazole-3-thiol


Chapter 5 E: CuO/ EA catalyzed sonogashira coupling reaction

5 E.1. Discussion

The present work reports the studies on copper catalyzed Sonogashira coupling

reaction. It deals with the use of copper(II)oxide to efficiently catalyze the coupling

reaction between aryl acetylene and aryl iodide using ethanolamine as ligand, base and

reaction medium. The reaction generated corresponding cross coupling products in good

to excellent yields in less reaction time under phosphine free conditions.

Fig.5.E.1: Reaction scheme of Sonogashira coupling

Although phosphorous ligand stabilizes many metal complexes and is widely used

for coupling reactions, our main goal was to carry out reaction using inexpensive catalyst

with milder reaction parameters under phosphine free conditions. Sonogashira coupling

reaction was carried out using commercially available copper(II)oxide (CuO) using

ethanolamine (EA) as ligand, base and reaction media.

Thus copper catalysts, such as commercially available copper(II)oxide in EA

were used in the coupling of iodobenzene and phenylacetylene as a model reaction to

determine the optimal reaction conditions.

Table 5.E.1 gives the effect of time of reaction on the product yield. With 15%

(w/w) loading of CuO as a catalyst, 79 % yield of diphenylacetylene was obtained in 5 h.

Yuan et al., had observed poor yield (23 %) of diphenylacetylene using commercial CuO

granules in DMSO with potassium carbonate as a base at 160 °C and 12h (Yuan et al.,

2011), as compared to that with CuO nano-particles (97% yield).


Table 5.E.1. Effect of time of reaction on the product yield

Reaction Conditions: All reactions were carried out with Iodobenzene (1.3 mmol), ethanolamine (2

ml), catalyst (15 % w/w) and phenylacetylene (1 mmol), Temperature (90 °C)

Our experiment indicates that the commercially available CuO coupled with EA provided

good yields (79 %) at 90 °C within 5 h. Thus, EA also played crucial role to carry

forward the coupling reaction along with the catalyst. This may be attributed to the fact

that EA contains both hydroxyl and amine groups within the molecular unit, which bind

with copper to accelerate the rate of reaction.

Table 5.E.2. Effect of temperature on the Sonogashira coupling reaction

Temperature (˚C) Yield (%)

30 18

60 58

90 79

120 68

Reaction Conditions: All reactions were carried out with Iodobenzene (1.3 mmol),

ethanolamine (2 ml), catalyst (15 % w/w) and phenylacetylene (1 mmol), Time (5 h)

Time (h) Yield (%)

1 15

39

54

70

79

78

2

3

4

5

6


Table 5.E.2 gives data on the optimization of temperature parameters. The reaction gave

maximum yield of product at 90 °C. With further increase in temperature, the yield

decreased due to formation of side products such as biphenyl, homocoupled product

obtained from phenyl acetylene, etc.

Table 5.E.3. CuO catalyzed Sonogashira coupling reaction

H Ph+ PhCuO, 15% w/w

5h, 90 °CAr X Ar

X= I, Br

1a-i 2a 3a-iEthanolamine

No Aryl halide (1a-i)

Aryl acetylene Product (3a-i) Yield (%)

a. C6H5I Ph H

79

b. m-CH3C6H4I Ph H

H3C

86

c. p-CH3C6H4I Ph H H3C

88

d. m-OCH3C6H4I Ph H

H3CO

79

e. p-OCH3C6H4I Ph H H3CO

79

f. p-FC6H4I Ph H F

78


g. p-

CH3COC6H4I

Ph H O

H3C

80

h.

SI

Ph H S

76

i. C6H5Br Ph H

10

Reaction Conditions: All reactions were carried out with Aryl halide (1.3 mmol),

ethanolamine (2 ml), catalyst (15 % w/w) and Aryl acetylene (1mmol), Time (5 h), Temp

(90 °C)

In order to extend the scope of reaction further, a variety of substrates were

examined in the coupling reaction and the results are listed in Table 5.E.3. It was found

that almost all varieties of aryl iodides were coupled with alkyne smoothly to afford the

corresponding products in high to excellent yields in the presence of copper(II)oxide as

catalyst and EA at 90 °C. For example, the coupling of electron efficient 1-iodo-3-

methoxy benzene with phenylacetylene gave corresponding product yield as high as 79

%, while the electron deficient 1-iodo-4-acetophenone under same reaction parameters

gave yield of 80 %.

The efficiency of copper catalyst system was lower for phenyl bromide as only 10

% yield of product was obtained under the same reaction conditions. The general

reactivity order of the sp2 species is aryl iodide > aryl bromide > aryl chloride. The low

reactivity of chlorides and bromides is usually attributed to the strength of C-X bond

(bond dissociation energies Ph-X, Cl: 96Kcal/mol-1, Br: 81 Kcal/mol-1, I: 65kcal/mol-1),

which leads to low reactivity of aryl chlorides and aryl bromides to sonogashira coupling

reaction.

In summary, a simple copper catalyzed Sonogashira cross coupling protocol has

been developed. CuO catalyzed coupling reaction between phenyl acetylene and aryl

halide gave good yield of product. The reaction was carried out in ethanolamine as it acts


as base, ligand and solvent at lower temperature of 90 °C. The reaction conditions were

mild and better as compared to those reported in the literature (Table 5.E.4).

Table 5.E.4: Comparison with literature

PARAMETERS REPORTED PROCESS OUR PROCESS

Reactant Aryl Iodide Aryl iodide

Catalyst CuO CuO

Solvent DMSO Ethanol Amine

Temperature 160 ºC 90 ºC

Time 12 h 5 h

Yield (%) 23 % 79 %


5 E.2. Characterization of coupling products

Analysis data of derivatives

Table-3 Entry 3a:1, 2-diphenylethyne

FT-IR (neat, cm–1): 3062, 2921, 2248, 1598, 1490, 1442, 1070, 916, 754; 1H NMR (300

MHz, CDCl3, δ ppm): 7.40 (d, 4H), 7.59-7.63 (m, 6H); 13C NMR (75 MHz, CDCl3, δ

ppm): 89.4, 123.3, 128.3, 128.4, 131.6.

Table-3 Entry 3b:1-methyl-3-(phenylethynyl)benzene

FT-IR (neat, cm–1): 3056, 2921, 2852, 2206, 1600, 1492, 1442, 781, 752, 686; 1H NMR

(300 MHz, CDCl3, δ ppm): 2.39 (s, 3H), 7.17-7.45 (m, 6H), 7.56-7.59(m, 3H); 13C NMR

(75 MHz, CDCl3, δ ppm): 21.2, 89.0, 89.6, 123.1, 123.4, 128.1, 128.2, 128.3, 128.6,

129.1, 131.5, 132.2, 138.0.

Table-3 Entry 3c:1-methyl-4-(phenylethynyl)benzene

FT-IR (neat, cm–1): 3051, 2918, 2216, 1913, 1593, 1508, 1440, 1180, 1070, 1016, 817,

754, 688; 1H NMR (300 MHz, CDCl3, δ ppm): 2.42(s, 3H), 7.21(d, 2H), 7.37-7.42 (m,

3H), 7.50 (d, 2H), 7.60 (dd, 2H); 13C NMR (75 MHz, CDCl3, δ ppm): 21.5, 88.8, 89.6,

120.3, 123.5, 128.1, 128.3, 129.1, 131.5, 131.6, 138.4.


Table-3 Entry 3d:1-methoxy-3-(phenylethynyl)benzene

FT-IR (neat, cm–1): 2939, 2852, 2216, 1853, 1579, 1492, 1321, 1232, 1035, 929, 862,

767, 684; 1H NMR (300 MHz, CDCl3, δ ppm): 3.85(s, 3H), 6.92 (dd, 3H), 7.12-7.41 (m,

6H); 13C NMR (75 MHz, CDCl3, δ ppm): 55.2, 89.2, 89.3, 114.9, 116.4, 123.2, 124.2,

124.3, 128.3, 128.3, 129.4, 131.6, 159.4.

Table-3 Entry 3e:1-methoxy-4-(phenylethynyl)benzene

FT-IR (neat, cm–1): 2923, 2214, 1593, 1508, 1438, 1286, 1245, 1172, 1107, 1024, 914,

835; 1H NMR (300 MHz, CDCl3, δ ppm): 3.84 (s, 3H), 6.90 (d, 2H), 7.35-7.39 (m, 3H),

7.50-7.57 (m, 4H) ;13C NMR (75 MHz, CDCl3, δ ppm): 55.2, 88.1, 89.4, 114.0, 115.4,

123.6, 127.9, 128.3, 131.4, 133.0, 159.6.

Table-3 Entry 3f:1-fluoro-4-(phenylethynyl)benzene

FT-IR (neat, cm–1): 3060, 2923, 2871, 2216, 1890, 1591, 1508, 1442, 1217, 1153, 1097,

1014, 837, 792, 752, 686; 1H NMR (300 MHz, CDCl3, δ ppm): 7.06 (t, 2H), 7.37 (t, 3H),


7.52-7.57 (m, 4H); 13C NMR (75 MHz, CDCl3, δ ppm): 88.3, 89.0, 115.5, 119.4, 123.1,

128.3, 131.5, 133.4, 160.8, 164.1.

Table-3 Entry 3g:1-(4-(phenylethynyl)phenyl)ethanone

FT-IR (neat, cm–1): 3255, 2881, 2217, 1677, 1600, 1402, 1352, 1182, 1068, 837, 759,

692; 1H NMR (300 MHz, CDCl3, δ ppm): 2.60 (s, 3H), 7.34-7.38 (m, 3H), 7.53-7.62 (m,

4H), 7.92 (dd, 2H); 13C NMR (75 MHz, CDCl3, δ ppm): 88.6, 92.7, 122.6, 128.2, 128.2,

128.4, 128.8, 131.6, 131.7, 136.2, 197.3.

Table-3 Entry 3h: 2-(phenylethynyl)thiophene

FT-IR (neat, cm–1): 3099, 2200, 1595, 1485, 1440, 1423, 1213, 1110, 916, 852, 752, 661; 1H NMR (300 MHz, CDCl3, δ ppm): 7.04 (dd, 1H), 7.31-7.39 (m, 4H), 7.54-7.57 (m,

3H); 13C NMR (75 MHz, CDCl3, δ ppm): 82.6, 93.0, 122.9, 123.3, 127.1, 127.2, 128.4,

128.4, 131.4, 132.5.


NMR Analysis

Fig.5.E.2: NMR spectra of 1, 2-diphenylethyne


Fig.5.E.3: NMR spectra of 1-methyl-3-(phenylethynyl)benzene


Fig.5.E.4: NMR spectra of 1-methyl-4-(phenylethynyl)benzene


Fig.5.E.5: NMR spectra of 1-methoxy-3-(phenylethynyl)benzene


Fig.5.E.6: NMR spectra of 1-methoxy-4-(phenylethynyl)benzene


Fig.5.E.7: NMR spectra of 1-fluoro-4-(phenylethynyl)benzene


Fig.5.E.8: NMR spectra of 1-(4-(phenylethynyl)phenyl)ethanone


Fig.5.E.9: NMR spectra of 2-(phenylethynyl)thiophene


SuMMArY


The results of this study indicate the importance of chemical recycling of poly

(ethylene terephthalate) (PET) waste. The recycled products can be source for various

useful materials.

Phase transfer catalyzed alkaline depolymerization of PET, from post-consumer

soft-drink bottles having particle size >6mm, using 1,4-dioxan was revealed to be an

efficient method for the reproduction of TPA. Almost complete depolymerization of PET

with considerably low catalyst concentration, alkali concentration and low temperature

was achieved. The reaction conditions were mild as compared to those reported in the

literature. Tetra butyl ammonium bromide (TBAB) as PTC can also be applied to alkaline

weight reduction process of polyester fibre. The reaction effectively gives 17% of weight

reduction of polyester fibre in just 2 h at 90 °C.

Aminolysisof PET bottle waste was successfully carried out under atmospheric

pressure in the excess of AEEA. The aminolysis with 1:4 PET: amine ratio, 0.5 % w/w

sodium acetate catalyst under reflux for 5 h gives pure BHAETA with about 72 % yield.

The reaction conditions were mild as compared to those reported in the literature.

BHAETA has application as chain extender in polyurethane industry. It possesses

reactive groups, which can be exploited through different chemical reactions to obtain

value added products for use in different fields.

Aminolysis of PET waste using 2-amino-2-methyl-1-propanol, 1-amino-2-

propanol and 3-amino-1-propanol was carried out successfully using sodium acetate as

catalyst. The products BHMPTA, BHIPTA and BHPTA were obtained in pure forms.

Microwave heating drastically reduced the reaction time from 3 h to 5 min with the same

yield and purity of the reactive monomers. These have the potential of recycling into

useful products with wide applications through further chemical reaction. BHPTA and

BHIPTA obtained from PET waste were successfully subjected to further chemical

reaction to get PBOXA and PBIOXA as a useful product for polymer and paint industry.

Novel Bronsted acidic IL [SO3H-pBIM][HSO4] was synthesized and applied in

the synthesis of 2-oxazolines. The catalyst showed better thermal stability and exhibited

high catalytic activity in cyclodehydration reaction. The catalyst could be recovered up to

3 cycles. Thus effective protocol has been developed for the synthesis of 2-oxazolines

using [SO3H-pBIM][HSO4] IL as catalyst and solvent. The synthesized novel IL was


used further for synthesis of PBOXA and PBIOXA from BHPTA and BHIPTA

respectively obtained from aminolysis of PET waste.

TPHD obtained from aminolysis of PET waste have the potential of recycling into

useful products with wide applications through further chemical reactions. Heterocyclic

compounds containing triazole and thiadiazole moieties were synthesized from TPHD

possessing moderate biological activities against commercial compounds. These

compounds can become lead molecules with further chemical modifications can improve

potency and selectivity. The chemical recycling of PET waste can be used for synthesis

of various heterocyclic compounds.

A simple copper catalyzed Sonogashira cross coupling protocol has been

developed. CuO catalyzed coupling reaction between phenyl acetylene and aryl halide

gave good yield of product. The reaction was carried out in ethanolamine as it acts as

base, ligand and solvent at lower temperature of 90 °C. The reaction conditions were mild

and better as compared to those reported in the literature.

In conclusion, we carried out successful chemical recycling of PET waste by first

depolymerizing it into different reactive products and then were subjected to various

chemical reactions to obtain useful chemicals there from.


ScopE

For

FurtHEr WorK


The results of this study indicated the use of novel aminolytic reagents and

improvement in process of chemical recycling of poly (ethylene terephthalate) (PET)

waste. The recycled products can be source for various useful materials.

The process of aminolytic depolymerization of PET waste can be carried out

using heterogeneous, recyclable and environment friendly catalyst such as zeolites, clays

or ionic liquids. So that recycling process can become more efficient.

The recycled products obtained from PET waste possess reactive groups such as

hydroxyl, which can be exploited through different chemical reactions to obtain value

added products for use in different fields. BHPTA and BHIPTA can be reacted with

different isocyanates to produce polyurethanes.

PET waste disposal should be handled carefully by adopting appropriate

technologies.


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