SYNTHESIS OF NICKEL~II) COMPLEXES USING a,~-CONJUGATED SCHIFF BASE COMPOUNDS

Priya AlP Nadarajan

Bachelor of Science with Honours QD (Resource Chemistry)

2015 P961 2015

31.2

['US t • Ii m l Ma UIWU k d ' 01:

UNIVERSrn l'r\ALAYS1A SARAWA I

SYNTHESIS OF NICKEL(II) COMPLEXES USING a,p.CONJUGATED SCHIFF BASE COMPOUNDS

Priya AlP Nadarajan

This report is submitted in partial fulfillment of the requirement for the degree of

Bachelor of Science with Honours (Resource Chemistry)

Supervisor: Dr. Tay Meng Guan

Faculty of Resource Science and Technology

Universiti Malaysia Sarawak

2015

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11 ­Priya AlP Nadarajan (38410)

.' Department of Chemistry

Faculty of Resource Science and Technology

Universiti Malaysia Sarawak

ii

Acknowledgement

My foremost gratitude goes to my project supervisor Dr. Tay Meng Guan and

Nornadia Binti Jasin for their motivation, patience, guidance, innovative ideas, scientific

knowledge and encouragement with which they have inspired me profoundly throughout this

research and writing of this thesis. Besides that, their motivation and guidance helped me to

build my confidence level as well interest towards scientific research.

I would like to express my appreciation and thanks to all lab assistants and technical

staffs for their helps in providing necessary facilities and equipment required for my project. [

would like to thank all master students who have guided me throughout my project. Their

guidance helped me a lot in completing my project. Besides that, I would like to thank my

fellow lab mates and fellow friends for their support and help in order for me to complete my

project successfully.

Last but not least, I would like to express my gratitude towards my family who were

always there for me and give moral support as well as positive encouragement for me to

complete this project.

Thank you.

..

iii

Ill/sat l(hjdmat MakJumal Akaaem ; UNTVERSm MALAYSIA SARAWAK

Table of Content

Declaration ........ ... .................................. ... ... ......................................

Acknowledgement.......... ..... ...... ..... ............................... .. ............. .. .....

Table of Content .. ......................... ....... ................................. ..... ..........

List ofTables .............................................................. . ......................

List of Figure.....................................................................................

Abstract ...... .......... .......................... .. ........................... ... ... .............. .

1.0 Introduction......................... .. ........................................................

1.1 Schiff Base. . . . . ...... . . . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

1.2 Application of Schiff Base .. ...... ...... ........ ............ ...... .......... ........

1.2.1 Biological Activity.......................................................

1.2.2 Corrosive Inhibitor.......................................................

1.2.3 Catalyst ............... ~.............. . .. .. ............ .. ........... ... ......

1.3 a.,~-conjugated Schiff base .......... . ..............................................

1.4 Nickel.................................................................. .. .......... . ..

1.5 Nickel Complex..................................... .. .......... . .......... .... .. .. . .

1.6 Problem Statement............... .... ......................................... ........

1.7 Objective...................................... . .................... ... .................

2.0 Literature Review ....... ... ................. .... . ... '...........................................

2.1 Synthesis of Schiff base related compounds ........................................

2.1.1 Condensation of Aldehyde/Ketone with Amine .. ............. . ......

2.1.2 Microwave irradiation.......................................... .... ........

iv

, ..

11

III

IV

vii

VllI

2

2

3

4

5

5

6

7

7

8

9

10

10

10

10

2.1.3 Green method......... ... ............... . ........................ ............ II

2.1.4 Synthesis and characterization Schiff base complexes .......... . ..... 14

2.2 Complexation of Phenyl pyridine with Transition Metal ............ . ... . ........ 20

2.3 Complexation of a,p-conjugated Schiff base with Transition metal ........ .. .. . 23

3.0 Methodology . ............... . .... . ................ .. ................................... . ... .. ..... 26

3.1 Reagents and Chemicals . . ..... . ....... ... ......... ... .......... .. ...... .. .. ... ......... 26

3.2 Characterisation ...... .. . . .. . ............... ................. .. . . ......... ........ . .... ... 26

3.3 Synthesis of a,p-conjugated Schiff Base with Different R Substituents ....... 27

3.3 .1 a,p-conjugated Schiff Base with R=H (1) . ... .... .... ... .... .. .. . .... ... 27

3.3.2 a,p-conjugated Schiff Base with R=OCH3 (2) ......... ... ........... ,. 28

3.4 Synthesis of nickel(II) complex with a,p-conjugated Schiff Base with

Different R Substituents .. . ...... .... . ..................... . . .. .................... . ... 29

3.4.1 Nickel(II) complex with a,p-conjugated Schiff Base

with R=H (3) ... . . . .. .. ............. .... . . . .... ......... .... .. ... ........ 29

3.4.2 Nickel(II) complex with a,p-conjugated Schiff Base

with R= OCH3 (4) . . .. ... .......... ..... ..... . ............ . . .. . . ..... . . . ... 30

4.0 Results and Discussions ....... . ... .......... ... . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 31

4.1 Physical and Analytical Data of a,p-Conjugated Schiff Bases 1-2

and Their Metal Complexes 3-4 ........ .. . ... ................ ....................... . 31 .. 4.2 Characterisation of a,p-Conjugated Schiff Bases 1-2

and Their Metal Complexes 3-4 .'............ ... ......... .. ....... .. .. . ..... :..... ... 34

4.2.1 UV-Visible Spectroscopy.... . .. . . ....... . ..... .... . ..... ... ..... . . . ..... 34

v

4.2.2 Infrared Spectroscopy.................................................. .... 37

4.2.3 1H NMR spectroscopy ................................... :~.......... ..... 40

5.0 Conclusion...................... .. ........ ........................................................ 44

6.0 Suggestion for Future Research ....... ........ ....... ...... ...................... .. ......... ... 45

7.0 References .. ....... ... .... .. ......... ...... ........ .. ...... ..... .............. .... ................ 46

Appendix.. .......... ..... .......... . .... .. .... ..... .. ......... ... ................. . ..... ..... ......... 50

.>

vi

List of Tables

Table 1: Physical Data of a,~-conjugated Schiff base compounds 1-2 and-their nickel(II)

complexes 3-4

Table 2: Solubility Data of a,~-conjugated Schiff base compounds 1-2 and their nickel(II)

complexes 3-4

Table 3: Electronic absorption data for a,~-conjugated Schiff bases 1-2 and their nickel(lI)

complexes 3-4

Table 4: The IR data of the a,~-conjugated Schiff base compounds (1-2) and their nickel(I1)

complexes (3-4)

Table 5: 'H NMR data for a.~-conjugated Schiff base compounds (1-2) and nickel(II)

complex 4 (ppm)

vii

List of Figures

Figure 1.0: Formation of Schiff base compound

Figure 1.1: Mechanism of Schiff base formation

Figure 1.2: Structure ofN-(Salicylidene)-2-hydroxyaniline

Figure 1.3: Structure of a,p-conjugated Schiff base

Figure 1.4: Structures (a) dinickel bishydrazine ter[( I-H-Tetrazol-3-yl)methan-3yl]-IH­

tetrazole and (b) dinickel tetraazide ter[(I-H-Tetrazol-3-yl)methan-3yl]-IH­

tetrazolate)

Figure l.5: (a) Structure of phenyl pyridine and (b) Structure ofa"p-conjugated Schiff base

Figure l.6: Synthesis of azo Schiff base

Figure 1.7: Preparation of Schiff base using primary amine with highly substituted aromatic

aldehydes

Figure 1.8: Structure indicating ratio of product obtained

Figure 1.9: General Structure of iron(II) and nickel(II) Schiff base complexes

Figure 1.1 0: Structure of the complex proposed by Ummathur et al. (2009)

Figure 1.11: Preparation of Complexes ~.

Figure 1.12: Structure of 2-[( 4-Methylphenylimino )methyl]-6-methoxyphenol

Figure 1.13: Coordination mode of Schiff base ligand with nickel(II) complex

Figure 1.14: Structure of Schiff bases synthesised

viii

)

Figure l.15: General structure of pheny1pyridine !

Figure l.16: Structure of (a) (3-amino, 9-thio [2-N-Ndiethy1aminoethy1]acridine) and (b) (4,5 I

bis [thio(2-N-N-diethy1aminoethyl)], 9methyl 1,8-diazantracene)

Figure 1.17: Formation of iridium(III) complex

Figure l.18: Structure of 2-pheny1pyridine based iridium(III) complexes in combination with

2-[ (diphenylphosphino )methyl]pyridine (dppmp) ligand

Figure 1.19: Synthesis of a,~-conjugated Schiff base by using 4-aminobenzoic acid and

cinnamaldehyde

Figure 1.20: Proposed structure of 4-methoxy-N-(3-pheny1allylidene)ani1ine

Figure l.21 : Electronic spectrum ofa,~-conjugated Schiff base 1, Cl sH13N

Figure l.22: IR spectrum of a,~-conjugated ?chiffbase 1, C1sH13N

Figure l.23: TLC separation using Hexane: DCM in ratio 5:2

Figure 1.24: IH NMR spectrum for compound 2, C17HI702N

Figure 1.25: Square planar geometry of complex 4, Ni(C17H1602N)2

Figure l.26: Electronic spectrum of a,~-conjugated Schiff base 2, C 17H170 2N

.' Figure l.27: Electronic spectrum of complex 3, Ni(C1SH12N)2

Figure 1.28: Electronic spectrum of complex 4, Ni(C17H1602N)2

Figure 1.29: IR spectrum of a,~-conjugated Schiff base 2, C17H170 2N

ix

)

I

Figure 1.30: IR spectrum ofnickel(II) complex 3, Ni(C 1SHI2N)2

Figure 1.31: IR spectrum of Nickel complex 4, Ni(C17HI602Nh

Figure 1.32: IH NMR spectrum for compound 1, C 1sH l3N

Figure 1.33: IH NMR spectrum for complex 4, Ni(C17H1602Nh

Figure 1.34: Elemental data of a,p-conjugated Schiff base compound 1 (ClsH13N) and

Figure 1.35: Elemental data for complex 3, Ni(C 1SHI2N)2

Figure 1.36: Elemental data for complex 4, Ni(C17H I60 2N)2

x

Synthesis of Nickel(lI) Complexes Using a,p-Conjugated Schiff Base Compounds

Priya AlP Nadarajan

Resource Chemistry Faculty of Resource Science and Technology

Universiti Malaysia Sarawak

ABSTRACT

Two types of a,~-conjugated Schiff base compounds with different R substituents were synthesized by the condensation reaction of cinnamaldehyde with aniline (1) and 4­methoxycinnamaldehyde with 4-methoxyaniline (2) in the presence of ethanol. Then, the a,~­conjugated Schiff bases (1-2) were allowed to react with NiCh'6H20 to produce nickel(II) complexes (3-4). The (l,~-conjugated Schiff bases (1-2) and their complexes (3-4) obtained were characterized using Fourier Transform Infrared (FTIR), UV -Vis spectroscopy, CHN analyser and IH Nuclear Magnetic Resonance ('H NMR). Both the (l,p-conjugated Schiff bases (1-2) and complexes (3-4) are polar in nature. Spectral studies suggested that (l,~­

conjugated Schiff base compounds (1-2) acted as a bidentate ligand towards nickel(lI) ion and metal complex 4 was suggested to demonstrate a square planar geometry.

Key words: a,p-conjugated Schiff base compounds, Ni(II) complex, spectroscopic studies.

ABSTRAK

Dua jenis a,~-conjugated bes Schiff dengan R gantian yang berbeza disintesis oleh tindak balas kondensasi antara cinnamaldehyde dengan aniline (1) dan 4-methoxycinnamaldehyde dengan 4-methoxyaniline (2) dalam etanol. Kemudian, a, ~-conjugated bes Schiff (1-2) yang dihasilkan bertindak balas dengan NiCho6H20 untuk menghasilkan nikel(U) kompleks (3-4). a, p-conjugated bes Schiff (1-2) dan kompleksnya (3-4) dicirikan menggunakan Fourier Transform Infrared (FTIR), UV-Vis spektroskopi, CHN analyzer dan 'H Magnetic Resonance Nuklear ('H NMR). Kedua-dua a,~-conjugated bes Schiff (1-2) dan kompleksnya (3-4) adalah polar secara semula jadi. Kajian spektrum mencadangkan bahawa a, ~-conjugated bes Schiff (1-2) bertindak sebagai bidentat ligan ke arah nikel(II) dan komplek 4 telah menunjukkan geometri segi empat planar.

Kata kunci: (l,~-conjugated bes Schiff, Ni (II) kompleks, kajian spektroskopi

1

1.0 INTRODUCTION

1.1 Schiff base

Schiff base compound was first discovered and named by Hugo Schiff in 1864 where the

compound contains the functional group of C=N in the structure (Qin et al., 2013). Schiff

bases can be synthesised using various methods such as microwave irradiation method (Yang

& Sun, 2006), green or envirorunental friendly method and nonnal conventional method

(Zarei & Jarrahpour, 2011). Schiff base or known as imine is a compound that is formed by

condensation reaction of an aldehyde or ketone with a primary amine as shown below in

Figure 1.0, whereby R, RI, and R2 can be an aryl or an alkyl group.

0 R1

\ + C .. C=N-R2 + H2O

R("/ ""R2'" R/

Primary amine Aldehyde/ketone Schiff Base

Figure 1.0: Formation of Schiff base compound

Schiff Base with the aryl R group is more stable and can be easily synthesized compared to

Schiff base with the alkyl R substituent. The nitrogen atom of the Schiff base contains a lone

pair electron with sp2 hybridised orbital that contributes to various biological and chemical

properties, which is very important for research. Besides that, many researches have been done

on Schiff base because it possess many special property of C=N bond (Mishra et al., 2013).

Mechanism of the formation of Schiff base is as skown in Figure 1.1.

2

H- X

X­+

Figure 1.1: Mechanism of Schiff base fonnation

The mechanism begins with the attack of primary amine which acts as a nuc1eophile on the

carbonyl carbon of an aldehyde or ketone. This reaction lead to the fonnation of dipolar

intennediate and followed by addition of proton removed from nitrogen to oxygen fonning

neutral carbinolamine. An acid catalyst (H-X) is used to make OH a better leaving group and

removal of water occur with a fonnation of Schiff base compound (Mcmury & Begley, 2005).

Availability of lone pair electron at the nitrogen atom enables Schiff bases to act as an electron

donor (Rehman et at., 2013). This is the reason for the Schiff base to be so special and has its

own class in coordination chemistry.

1.2 Application of Schiff base

Development in the field of Schiff base synthesis ~nd fonnation of metal complex using Schiff

base as ligand is due to the various interesting facts about their application in the biological,

visual pigments, antitumor agent, and chemical analysis as well as a new technology such as in

optical computers to measure and control the intensity of the radiation (Brodowska & Lodyga­

3

Chruscinska, 2014). These characteristics are due to the presence of C=N linkage in the Schiff

base compound.

1.2.1 Biological activity

Several studies conducted shows that Schiff bases are compound that aids in various biological

activities such as antibacterial, antifungal, anticancer, antiviral and antimalarial properties.

Schiff bases are also an important intennediate in various enzymatic and catalytic reactions as

well as model for some biological systems. One of the example of Schiff base that act as

antibacterial agent is N-(Salicylidene )-2-hydroxyaniline which react actively against

Mycobacterium Tuberculosis (Brodowska & Lodyga-Chruscinska, 2014). Structure of N­

(Salicylidene)-2-hydroxyaniline is shown in Figure 1.2.

n ~N~ ~I'"\U OH

OH

Figure 1.2: Structure ofN-(Salicylidene)-2-hydroxyaniline

Other than that, Chohan et al. (2001) synthesised some substituted pyridine Schiff bases and

studied tl1eir ability to inhibit the growth of Escherichia coli, Staphylococcus aureus and

Pseudomonas aeruginosa. Based on their antibacterial activity analysis done, it has been .

deduced that inhibitory activity of Schiff base compound becomes more significant when the

Schiff base is coordinated to metal to fonn complexes. This is due to the delocalization of 1t

electrons throughout the chelated complex that will increase the lipophilic properties of metal

chelate and eventually allows the penneation through lipoid layers of bacterial membranes to

4

Pusat Khirlm<lt M klumatAkad('n; ;' I YSlA SARAW

enable the chelate to act as a bactericidal. In addition, fungus infection and its related diseases

are increasing at an alarming rate nowadays. Through numbers of researches, chemist

discovered that Schiff base has the potential to act as antifungal agent. According to

Brodowska & Lodyga-Chruscinska (2014), Schiff bases as well as its complexes formed

between furylglycoxal with various amines able to perform antifungal activity against

Helminthosporium gramineum. Certain Schiff base compounds exhibit antitumor properties

that enable it to act as antitumor agent (Mohamed et al., 2006). For an example, some Schiff

bases with metal complexes using Cu, Ni, Zn and Co also exhibit antitumor property with

order of reactivity Ni>Cu>Zn>Co (Kumar et al., 2009). Apart from that, amino Schiff bases

derived with aromatic as well as heterocylic amine possess high antitumor response towards

human tumor cells.

1.2.2 Corrosive Inhibitor

Other than that, one of the special applications of Schiff base is as an effective corrosion

inhibitor because Schiff bases have the ability to spontaneously form a monolayer on the

surface to be protected (Bader, 2010). Chemisorption is the principle that cause Schiff base to

act as an effective corrosive inhibitor (Mishra et al., 2013). Chemisorption results in strong

binding between inhibitor and surface of metal to be protected. This prevents the metal to get

corroded as the inhibitor is tightly bind to metal surfaces avoiding air and water contact on the

metal (Ahmad, 2006 )._.

1.2.3 Catalyst

Schiff bases or more precisely aromatic Schiff bases and their complexes catalyse reactions

such as oxygenation, hydrolysis, electro-reduction and decomposition (Kumar et al., 2009).

5

Besides that, binucleating complex of Ni with Schiff Bases neytralbis(iminopyridyl)benzene

and monoanionicbis(iminopyridyl)phenolate serve as catalysts in the oligomerisation of

ethylene (Mishra et ai., 2013).

1.3 a,p-conjugated Schiff base

Studies related to Schiff base compounds have been done due to its good contribution in

coordination chemistry (Rehman et aI. , 2013). Schiff bases act as an electron donor and

transition metal that involve in the fonnation of Schiff base complex act as an electron

acceptor in coordination chemistry. According to Hing (2014), Schiff base compound possess

all the characteristic that are needed for complexation process and sufficient attention has been

given to the synthesis, characterisation and complexation of Schiff base. Development in the

field of Schiff base synthesis lead to the interest of chemist to study about a ,p-conjugated

Schiff base because electron in a,p-conjugated Schiff base compound has the tendency to

delocalize the electron throughout the structure along the C=C-C=N moiety. The first olefin

carbon counting from C=N is named as a-carbon, whereas the second carbon is named as the

~-carbon as shown in Figure 1.3. Thus, compound with C=C-C=N moiety is named as a,p­

conjugated Schiff base. Conjugated system is a chemistry tenn in which the electrons are

delocalised along the conjugated systems in the molecule. Apart from that, conjugated

compounds refers to compound that has alternating double bond in their structure (Zumdahl &

DeCoste, 20 ~3) . Delocalisation of electron within a structure may lead to a stable compound

especially compounds derived from aromatic aldehyde due to its conjugation properties

(Mohamed et aI., 2013). Although many researches have been done on Schiff bases due to its

ability to act as a ligand and possess interesting characteristics but very few researches has

been conducted on a,p-conjugated Schiff base compound.

6

I '

a.

j 13

Figure 1.3 : Structure of a,p-conjugated Schiff base

1.4 Nickel

Nickel is a metal that can be categorised as a transition metal. It is a silvery-white metal that is

located in Group X and period 4 of periodic table. It has an atomic number and atomic mass of

8 and 58.71 g/morI,respectively, with the electron configuration of [Ar] 4s2 3d8• Nickel is a

fairly good heat and electricity conductor as well as can be easily magnetized. Even though

nickel is relatively unreactive, but it becomes more active at high temperatures. Other than

that, nickel reacts with steam to give nickel oxide and hydrogen gas. Nickel has its own

application in our daily life, for an example nickel is widely used in the making of alloy,

electroplating and to make heavy machinery (Sparrow, 2005). Since nickel has many unique

characteristics, it is chosen to form complex using a,p-conjugated Schiff base compound.

1.S Nickel Complex

Nowadays, chemists widely use transition metals to form complexes because transition metal

possess various unique characteristics such as ability to form colour, possess various oxidation

state and widely used as catalysts (Tang et at., 2011). Nickel complexes present in many

different coordination numbers and geometry. For an example, Ni atoms in

other complex, Ni exist as tetracoordinated complex. In most cases, nickel(II) complex is

coordinated as square planar in complexes. Studies has been conducted to investigate the

7

)

computational study of coordinated Ni(II) complex with high nitrogen content ligands namely

dinickel bishydrazine ter[(l-H-Tetrazol-3-yl)methan-3yl]-IH-tetrazole and dinickel tetraazide

ter[(1 -H-Tetrazol-3-yl)methan-3yl]-IH-tetrazolate) complex as shown in Figure 1.4.

(a) (b)

Figure 1.4: Structures (a) dinickel bishydrazine ter[(l-H-Tetrazol-3-yl)methan-3yl]-lH tetrazole and (b) dinickel tetraazide ter[(I-H-Tetrazol-3-yl)methan-3yl]-IH­

tetrazolate)

1.6 Problem Statement

The structure of a,~-conjugated Schiff base as shown in Figure 1.5 (b) is similar to the basic

structure of phenyl pyridine as shown in Figure 1.5 (a).

N

(a) (b)

Figure 1.5: (a) Structure ofphenylpyridine and (b) Structure of a,~-conjugated Schiff base

8

Phenylpyridine has been widely used as ligand for organometallic complexes because the

complex shows remarkable photophysical properties after the metal bonds ., to phenylpyridine .

However, the a,~-conjugated Schiff base is still lack of attention from inorganic chemists even

though it has similar basic structure of phenylpyridine. Thus, this project was designed to

synthesize different type of a,~-conjugated Schiff base compound using different R­

substituent, and react with nickel(II) ion to study the coordination mode of the complex.

1.7 Objective

The main objectives of this research are:

1. To synthesize two a,~-conjugated Schiff bases, namely Phenyl-(3-phenyl-allylidene)­

amine (1) and (4-methoxy-phenyl)- [3-( 4-methoxy-phenyl)-allylidene ]-amine (2), and

their nickel(lD complexes (3-4) .

2. To characterise the a,~-conjugated Schiff bases (1-2) and their Ni(II) complexes (3-4)

by UV-visible, FTIR, CHN analyser and NMR spectra analysis.

3. To study the coordination mode of the a,~-conjugated Schiff base to nickel complex.

9

2.0 Literature review

2.1 Synthesis of Schiff base related compounds.

2.1.1 Condensation of AldehydelKetone with Amine

A Schiff base is similar to an aldehyde or ketone but the only difference is the C=O is replaced

with C=N-R group. Schiff bases are usually formed by condensation of an aldehyde or ketone

with a primary amine (Ibrahim et al., 2014). In addition, preparation of Schiff bases is done

under acid or base catalysis or in the presence of heat. However, there are some problems that

may arise due to this environment such as formation of insoluble salts with strong acids. They

can be changed back to amine and carbonyl compounds by hydrolysing with aqueous acid.

2.1.2 Microwave irradiation

Another method that can be used to produce Schiff base is by microwave irradiation. Synthesis

of Schiff base via this method enables the process to be done in a shorter period of time

compared to the traditional refluxing method. Rawal et al., (2009) reported that the mixture of

reactants needed only 5 minutes to be irradiated together with zeolite, NaY which acts as a

catalyst in the reaction. Then, the catalyst was removed using ethanol by stirring for about 15

minutes and followed by collection of product from ethanol using filtration and evaporation.

After the filtration process is done, the precipitate obtained is subjected to recrystallization to

produce a pure cQmpound. Even though there are a number of advantages using this method to

produce Schiff base compounds, this method requires the use of solvents and acids which are

more toxic and expansive than the water suspension medium. Yang and Sun (2006), have done

a research to compare three different ways to synthesize a simple Schiff base known as (E)-4­

methyl-N-(3,4,5-trimethoxybenzylidene)benzenamine. The first condition used was using

microwave irradiation, second was under reflux and the last method of synthesizing the Schiff

10

base involves stirring. Based on the result obtained, it has been concluded that the synthesizing

of (E)-4-methyl-N-(3,4,5-trimethoxybenzylidene)benzenamine under microwave irradiation

condition is more efficient compared to reflux and stirring condition. This is because the

highest amount of (E)-4-methyl-N-(3,4,5-trimethoxybenzylidene)benzenamine was obtained

from microwave irradiation method which was 85% yield within 4 minutes compared to the

other two methods. They also mentioned that the yield obtained from reflux and stirring

condition was only 72% and 75% respectively. In addition, they have also reported that the

rate of reaction to synthesis Schiff base increases in the order of microwave irradiation >

stirring> reflux. Besides that, Venugopal and Jayashree (2008) have also reported a research

on microwave-induced synthesis of Schiff bases of aminothiazolyl bromocoumarins as

antibacterial and they have deduced that microwave-induced synthesis of Schiff base is fast

and more efficient method compared to normal conventional method. Based on the results

obtained from research done by Yang and Sun (2006) as well as Venugopal and Jayashree

(2008), it can be concluded that the microwave irradiation condition is very useful in industrial

manufacture compared to normal conventional method as it consumes the least time to

produce the highest percentage of yield.

2.1.3 Green method

There are also many other researches done on the method of synthesis of Schiff bases. Zarei

and Jarrahpour (2011), conducted a research to compare the time and yield of Schiff bases ..

synthesized using green method and classical method. They synthesized azo-Schiff bases by

reacting azoaldehyde with amines in small amount of water in room temperature as shown in

Figure 1.6.

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