No. A - 42011/01/2018-Coord. GOVERNMENT OF INDIA/'l-fffif ...
Chapter 5 B. Scheme I: Aminolytic depolymerization of PET...
Transcript of 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).
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 92
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 93
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 94
Table 5.B.2. Effect of catalyst concentration on BHAETA yield
Catalyst conc.
(w/w)
Yield (%)
Sodium acetate Potassium sulphate
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 (%)
Sodium acetate Potassium sulphate
1:2 52 48
1:4 72 69
1:6 65 60
1:8 62 55
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 95
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 %
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 96
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 97
FTIR analysis
Fig.5.B.3: FTIR spectrum of BHAETA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 98
NMR analysis
Fig.5.B.4: NMR spectra of BHAETA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 99
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 Page 100
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 101
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 102
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 103
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 (%)
Zinc acetate Sodium acetate
1:3 58 38
1:5 84 82
1:7 72 69
1:9 64 63
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 104
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 (%)
Zinc acetate Sodium acetate
1 39 29
3 70 42
5 87 62
7 83 78
9 86 84
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 105
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 106
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 107
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 108
FTIR analysis
Fig.5.B.7. FTIR spectra of BHAMPTA and BHIPTA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 109
NMR Analysis 1H-NMR
Fig.5.B.8.1H-NMR spectra of BHAMPTA and BHIPTA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 110
13C-NMR
Fig.5.B.9.13C-NMR spectra of BHAMPTA and BHIPTA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 111
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 112
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 %
Sodium acetate Potassium sulphate
1 45 37
2 58 49
3 69 55
4 76 69
5 80 74
6 78 73
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 113
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 (%)
Sodium acetate Potassium sulphate
0.3 70 66
0.5 80 74
0.7 76 72
1.0 75 72
PET: amine
(molar ratio)
Yield (%)
Sodium acetate Potassium sulphate
1:3 58 50
1:5 80 74
1:7 69 68
1:9 71 68
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 114
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 (%)
Sodium acetate Potassium sulphate
1 45 38
3 62 54
5 76 68
7 82 79
9 78 76
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 115
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 116
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 117
NMR analysis
Fig.5.B.12: NMR spectra of BHPTA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 118
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 119
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 120
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 121
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 122
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 123
1H-NMR Analysis
Fig.5.B.15. 1H-NMR spectra of PBOXA an PBIOXA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 124
13C-NMR Analysis
Fig.5.B.16. 13C-NMR spectra of PBOXA an PBIOXA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 125
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 126
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 127
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 128
FTIR Spectra
Fig.5.B.18: FTIR spectra of BHBTA and BHIBTA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 129
NMR spectra
Fig.5.B.19: NMR spectra of BHBTA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 130
Fig.5.B.20: NMR spectra of BHIBTA
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 131
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 132
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 133
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 134
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 135
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 136
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 137
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 138
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,
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 139
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 140
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 141
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 142
NMR Analysis
Fig.5.C.4: NMR spectra of [SO3H-pBIM][HSO4] IL
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 143
Fig.5.C.5: NMR spectra of 2-phenyl-4, 5-dihydrooxazole
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 144
Fig.5.C.6: NMR spectra of 2-(naphthalen-2-yl)-4,5-dihydrooxazole
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 145
Fig.5.C.7: NMR spectra of 2-(4-chlorophenyl)-4,5-dihydrooxazole
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 146
Fig.5.C.8: NMR spectra of 2-(p-tolyl)-4,5-dihydrooxazole
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 147
Fig.5.C.9: NMR spectra of 2-(4-methoxyphenyl)-4,5-dihydrooxazole
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 148
Fig.5.C.10: NMR spectra of 4-(4,5-dihydrooxazol-2-yl)phenol
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 149
Fig.5.C.11: NMR spectra of 4-(4,5-dihydrooxazol-2-yl)aniline
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 150
Fig.5.C.12: NMR spectra of 2-(4-nitrophenyl)-4,5-dihydrooxazole
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 151
Fig.5.C.13: NMR spectra of 2-styryl-4,5-dihydrooxazole
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 152
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).
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 153
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 154
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 155
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 156
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 157
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 158
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 159
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 160
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 161
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
MHz, DMSO, δ ppm): 7.0-8.0 (Ar-H).
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 162
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
MHz, DMSO, δ ppm): 7.5-8.9 (Ar-H).
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 163
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 164
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)
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 165
NMR Analysis
Fig.5.D.4: NMR Spectra of 1,4-Phenylene bis (4-fluorophenylthiosemicarbazido)
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 166
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)
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 167
Fig.5.D.6: NMR Spectra of 1,4-Phenylene bis (4-methoxyphenylthiosemicarbazido)
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 168
Fig.5.D.7: NMR Spectra of 5,5-(1,4-Phenylene)bis(2-(4-methoxyphenylamino-1,3,4-
thiadiazole)
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 169
Fig.5.D.8: 1H-NMR Spectra of 5,5-(1,4-Phenylene)bis(4-(4-methoxyphenyl)-3-mercapto-
1,2,4-triazole
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 170
Fig.5.D.9: NMR Spectra of 1,4-Phenylene bis (naphthylthiosemicarbazido)
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 171
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)
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 172
Fig.5.D.11: NMR Spectra of Schiff base obtained from o-vanillin and bis-4-amino-1,2,4-triazole-3-thiol
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 173
Fig.5.D.12: NMR Spectra of Schiff base obtained from salicylaldehyde and bis-4-amino-1,2,4-triazole-3-thiol
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 174
Fig.5.D.13: NMR Spectra of Schiff base obtained from p-hydroxybenzaldehyde and bis-4-amino-1,2,4-triazole-3-thiol
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 175
Fig.5.D.14: 1H-NMR Spectrum of Schiff base obtained from p-nitrobenzaldehyde and bis-4-amino-1,2,4-triazole-3-thiol
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 176
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).
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 177
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 178
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 179
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 180
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 %
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 181
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 182
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),
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 183
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 184
NMR Analysis
Fig.5.E.2: NMR spectra of 1, 2-diphenylethyne
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 185
Fig.5.E.3: NMR spectra of 1-methyl-3-(phenylethynyl)benzene
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 186
Fig.5.E.4: NMR spectra of 1-methyl-4-(phenylethynyl)benzene
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 187
Fig.5.E.5: NMR spectra of 1-methoxy-3-(phenylethynyl)benzene
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 188
Fig.5.E.6: NMR spectra of 1-methoxy-4-(phenylethynyl)benzene
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 189
Fig.5.E.7: NMR spectra of 1-fluoro-4-(phenylethynyl)benzene
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 190
Fig.5.E.8: NMR spectra of 1-(4-(phenylethynyl)phenyl)ethanone
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 191
Fig.5.E.9: NMR spectra of 2-(phenylethynyl)thiophene
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 192
SuMMArY
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 193
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
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 194
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 195
ScopE
For
FurtHEr WorK
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 196
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.
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 197
rEFErEncES
©Rikhil Shah, Institute of Chemical Technology (ICT), Mumbai, India Page 198
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