Synthesis and Characterization of Schiff Base Ligands derived from different Aldehydes and Synthetic Diamine

 

Paresh More*, Namrata Ghag, Juhi Suhanda, Zeeshan Barmare, RuchitaMargale,

Rutuja Bhagat, PranaliSalanke, Wahidunnisa Shaikh

Dept. of Chemistry, KET’s, V.G. Vaze College of Arts, Science and Commerce, Mulund (E)-400081, India

*Corresponding Author E-mail: paresh.m34@gmail.com

Three Schiff bases were derived from the condensation of 2-hydroxy-1-naphthaldehyde, 5-nitrosalisaldehyde, salicylaldehyde with the diamine. The diamine was synthesized from p-aminoacetanilide in the presence of glacial acetic acid, boric acid and sodium perboratetetrahydrate. The product obtained was characterized by Elemental analysis, ¹H NMR, and IR. The diamine and Schiff bases were further screened for antibacterial studies.

 

 

1. INTRODUCTION:

The coordination behaviour and synthesis of Schiff bases has received much attention in recent years [1-3].Schiff bases are an important class of ligands having many applications [4]. They possess various biological activities such as fungicidal and insecticidal [5]. Schiff bases offer versatile and flexible ligands capable of binding with metal cation to yield complexes. Some of them have suitable properties for practical applications [6-8]. 4, 4’-diaminoazobenzene is useful as a model compound for studies of the chemistry of colored diamines, specifically for the preparation of colored diisocynates[9].

 

2. MATERIAL AND METHODS:

All chemicals used for the synthesis were of AR grade, 5-nitrosalisaldehyde from Aldrich, 2-hydroxy-1-naphthaldehyde from Fluka, Salicylaldehyde from S.D. Fine and p-aminoacetanilide from Aldrich.

 

Synthesis of diamine[4,4’-diaminoazobenzene]:

The diamine was synthesized according to literature [10] as shown in the scheme 1. (Diamine)

 

Synthesis of Schiff bases:

These Schiff bases were synthesized by adding slowly hot ethanolic solution of diamine to the ethanolic solution of respective aldehyde in 1:2 molar ratios and were refluxed on water bath for 5hrs. The precipitated Schiff bases were filtered, dried, recrystallized using ethanol and dried in vacuum desiccator.

 

Physical measurements:

The melting point of the diamine and all schiff bases were determined by open capillary method. Elemental analyses were carried out in the micro analytical laboratory, University ofMumbai.

 

Infrared spectra of the diamine and the Schiff bases were taken on FTIR-4200 spectrometer supplied by M/S Shimadzu corporation, ¹H NMR. Spectra were received on a Brukner Act 300 (300 mz) spectrophotometer.

 

 

Scheme 1 is represented by the following equation, which represents synthesis of Diamine.

 

 

Scheme 2 represents synthesis of Schiff bases, SB1, SB2 and SB3.

 

Table 1. Physical and Analytical data of the diamine and Schiff bases

Compound	Molecular Formula	Molecular weight	% yield	Melting point	Color	Carbon	Hydrogen	Nitrogen
Diamine	C12H12N4	212	55	238-242	Yellow	68.00(67.92)	6.02 (5.66)	26.41
SB1	C34H24N404	520	60	>300	Orange	79.23(78.46)	5.12 (4.61)	10.76
SB2	C26H18N6O6	510	58	>300	Dark Yellow	61.82(61.11)	4.15 (3.52)	16.47
SB3	C26H20N402	420	72	>300	Light Yellow	66.85 (66.00)	4.85 (4.00)	14.0

 

Table 2:- IR spectral data (cm^-1) of diamine and Schiff bases:

Compound	IR SPECTRAL DATA (cm-1)
	Ν (C=NH)	ν (C-H) Aromatic	ν (C-O) Aliphatic	ν (C-O)	ν (C=N)	ν (C-C)	ν (C-NH2)
Diamine	-	3204	3021	-	1592	548	3377
SB1	1620	-	3198	1482	1581	550	3420
SB2	1619	-	3083	1440	1567	564	3378
SB3	1617	-	3021	1435	1574	548	3376

 

Table 3:- ¹H NMR spectral data of diamine and Schiff bases.

COMPOUND	1H NMR  CHEMICAL SHIFT(δ ppm)
	4H-NH2	AROMATIC PROTON	1H CH=N
Diamine	3.349	6.9-7.9	-
SB1	-	6.6-8.0	12.89
SB2	-	6.2-7.9	12.4
SB3	-	6.4-7.8	13.1

 

 

Table 4:- Antimicrobial activity of the diamine and ligands:

Name of the ligand	Conc. in µg/ml	Zone of inhibition
		E.coli	S. aureus	B. subtilis
Diamine	100	10.2	11.5	12.8
SB1		10.8	11.6	13.5
SB2		11.0	11.4	12.1
SB3		14.5	14.9	13.0
Standard (Norfloxacin)	100	24.0	24.5	26.1

 

3. RESULT AND DISCUSSION:

Schiff bases derived from diamine and substituted aldehyde are coloured. The elemental analysis dataconfirms the structure of Schiff bases and their stoichiometry is 1:2 [1 part of diamine and two parts of aldehyde]. All the Schiff bases are insoluble in most of the solvent such as CHCl₃, CCl₄, methanol, ethanol, however very much soluble in DMF and DMSO. The molar conductance data suggests that these Schiff bases are non-electrolyte in nature [11]. The analytical data is summarized in table 1.

 

IR spectra:

The IR spectra of the diamine and their Schiff bases are recorded in table no.2. The azomethine bands were observed in the range of 1617 to1620 cm^-1 in SB1, SB2 and SB3, whereas such band was absent in the diamine.Fig.1 represents IR of diamine and Fig.2 is representative spectra of Schiff base SB1.

 

¹H NMR spectra:

¹H NMR spectrum of the diamine shows a sharp peak at 3.34 which indicates free NH₂ group. Multiple signals in the range of 7.6 to 7.9 ppm are assigned to aromatic protons [12-13].¹H NMR spectra of the diamine is as shown in the   Fig. 3.

 

¹H NMR spectrum of the Schiff bases SB1, SB2, and SB3 as shown intable no.3 shows absence of band in the range of 3.0 to 4.0 indicates –NH₂- group has participated in the bonding. A new band appears at 12.89 to 13.1 ppm was observed due to azomethine protons confirms formation of Schiff bases. Multiple signals in the region of 7.6 to 7.9 ppm are assigned to aromatic protons [12-13].Representative ¹H NMR spectra of SB1 is as shown in Fig.4.

 

Antimicrobial activity:

Antimicrobial activities for the diamine and all the ligands were carried out by agar diffusion method and the average radius ofzone of inhibition was recovered. The observation were made and compared with the standard Norfloxacin (100µg/ml) as shown in the table 4.

 

All the synthesized ligands and diamine showed activity against gram positive and gram negative bacteria at concentration at 100µg/ml. Best results in case of antimicrobial activity was shown by the ligand SB3 whereas other three showed moderate activities.

 

Fig.1 IR Spectra of Diamine.

 

 

Fig.2 Representative IR Spectra of Schiff base SB1.

 

Fig.3 ¹H NMR of Diamine.

 

 

Fig.4Representative ¹H NMR of Schiff base SB1

 

4. CONCLUSION:

¹H NMR, Elemental Analysis and IR data confirms formation of Schiff bases in 1:2 ratio. From the very dark color we may conclude that they may be dyes. They may play as very valuable colorants for high technological applications. Our future studies will be their characterization as dyes.

 

5. ACKNOWLEDGEMENT:

We are very thankful to the Management, the Principal Dr. B. B Sharma of V.G.Vaze College for their support and the Head of The Chemistry Department Dr. Ms.VandanaPanse for the laboratory facilities.

 

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Received on 16.12.2017         Modified on 28.01.2018

Accepted on 20.02.2018         © AJRC All right reserved