55

CHAPTER – III SYNTHESIS, SPECTRAL DATA AND SPECTROPHOTOMETRIC

STUDIES ON o-VANILLIDINE-2-AMINOBENZOTHIAZOLE, o-VANILLIDINE-2-AMINO-4-METHYL BENZOTHIAZOLE,

o-VANILLIDINE-2-AMINO-6-CHLORO BENZOTHIAZOLE AND o-VANILLIDINE-2-AMINO-6-BROMO BENZOTHIAZOLE FOR THE

DETERMINATION OF COPPER

3.1 INTRODUCTION Organic reagents have many applications in chemical analysis. They are

useful in gravimetric, volumetric, spectrophotometric and other instrumental

analysis. Unquestionably scientists constantly look for new, better, simpler,

sensitive and selective reagents. An effort towards developing simpler and more

selective organic reagents was made by preparing several Schiff’s bases by the

condensation reaction between 2-amino benzothiazole and its 4-methyl, 6-chloro,

6-bromo derivatives with o-Vanillin.

The present work was aimed to develop a sensitive and efficient

spectrophotometric method for the determination of Copper, based on

formation of coloured complexes, which are formed by the reaction of the Copper

ion with o-Vanillidine-2-amino-benzothiazole (VBT), o-Vanillidine-2-amino-4-

methyl benzothiazole (VMBT), o-Vanillidine-2-amino-6-chloro benzothiazole

(VCBT) and o-Vanillidine-2-amino-6-bromo benzothiazole (VBBT).

3.2 MATERIALS AND METHODS 3.2.1 Instruments used Infrared Spectra were recorded on KBr disc on a Perkin Elmer FT-IR. 1H NMR spectra were recorded on a Bruker Advanced 600 MHz spectrometer in

CDCl3 and thermo DFS double focusing mass spectrophotometer for mass

spectral measurements. The pH was determined with a model 7007 Digisun

electronic pH meter with combined glass calomel electrode. Graphite furnace

Atomic Absorption Spectrometer was used for the analysis of cations in water

56

samples. Shimadzu UV double beam spectrophotometer was used for

spectrophotometric measurements. 3.2.2 Reagents required All the reagents were of analytical grade and the solutions were prepared

with doubly distilled water. Schiff’s base solutions (0.05% (w/v) were prepared by

dissolving appropriate amounts of VBT, VMBT, VCBT and VBBT in methanol.

o-Vanillin was purchased from Sigma Aldrich (Germany), 0.2 M acetic acid and

0.2 M sodium acetates were used for pH adjustments. Acetone and ethanol were

dried over anhydrous calcium sulphate and calcium oxide respectively and

distilled for getting pure solvents. 2-amino benzothiazole and its 4-methyl,

6-chloro, 6-bromo derivatives were synthesized starting from respective

α-phenylthiourea.

3.3 EXPERIMENTAL PROCEDURES

3.3.1 Synthesis of α-phenylthiourea

In a 500 mL three necked flask fitted with a reflux condenser, a

mechanical stirrer and 100 mL dropping funnel were placed 17 g (0.22 mol) of

ammonium thiocyanate and 100 mL of dry acetone through the dropping funnel

along with stirring, 28.2 g (0.2 mol) of benzoyl chloride. After the complete

addition, the mixture was refluxed for 5 minutes and then a solution of 18.6 g

(0.2 mol) of aniline in 50 mL dry acetone was added at such a rate that, reaction

mixture starts refluxing gently. The mixture was poured carefully with stirring into

1.5 L of water. The yellow precipitate (α- benzoyl-β-phenyl thiourea) obtained

was separated by filtration. The precipitate was dissolved in NaOH (30 g of

NaOH in 270 mL of water) and heated for 5 minutes. After the removal of a small

amount of insoluble material by filtration, the solution was acidified with

Conc. HCl and then made slightly basic with ammonium hydroxide. On allowing

the solution to stand for some time, the crystalline product of α-phenylthiourea

obtained was filtered off. The yield of oven-dried material (m.p 153°C) was 25.8 g

57

(85%). Recrystallization from ethanol yielded 23.2 g of white crystalline solid,

melting at 152-153°C. [Snyder H.R., 1948]

NH4SCN+ NH4Cl

NaOH

Ammonium thiocyanate

+

N

S

H2N

CO N

CS

H

HN

O

NCSbenzoyl isothiocyanate

O

ClBenzoyl chloride

NH2

Aniline

Hα-phenylthiourea

C6H5COOH +Benzoic acid

3.3.2 Synthesis of 2-amino benzothiazole

In a 250 mL R.B flask, 27.6 g (0.2 mol) of α-phenylthiourea was added

with stirring to 72 mL of thionyl chloride (0.56 mol). Refluxed the reaction mixture

for 2-4 hours at 50-55°C. After 4 hours, the reaction mixture, which was viscous,

poured into 2 L of water and stirred for 30 minutes at 60-80°C and filtered.

The filtrate was adjusted to pH 8 with 25% ammonia and the crystals of

2-aminobenzothiazole precipitated out was filtered by suction, washed with water

and dried (m.p 127-128°C). Recrystallization from hot water yielded 16 g of white

flakes melting at 130°C [Papenfuhs Von Theodor, 1982].

(i) SOCl2 50-550C(ii) Hydrolysis

S

N

NH2

2-aminobenzothiazole

NH

S

NH2

α-phenylthiourea

58

3.3.3 Synthesis of 1-(2-methylphenyl) thiourea Similar procedure was adopted as described earlier for the synthesis of

α-phenylthiourea except that, instead of 18.6 g (0.2 mol) of aniline in 50 mL dry

acetone, solution of 21.5 mL (0.2 mol) o-toluidine in 50 mL dry acetone was

used. The crystalline product of 1-(2-methylphenyl) thiourea obtained was filtered

and dried. The yield of oven-dried material was 18.5 g. Recrystallization from

ethanol yielded 15.3 g of white crystalline solid, melting at 150°C [Snyder H.R.,

1948].

NH4SCN + NH4Cl

NaOH

Ammonium thiocyanate

+

CO N

CS

H

HN

O

NCSbenzoyl isothiocyanate

O

ClBenzoyl chloride

NH2

CH3

o-toluidine

H3C

HNS

NH2

H3C

1-(2-methylphenyl) thiourea

C6H5COOH +

Benzoic acid

3.3.4 Synthesis of 2-amino-4-methylbenzothiazole In a 250 mL R.B flask, 29.0 g (0.2 mol) of 1-(2-methyl phenyl) thiourea

was added with stirring to 72 mL of thionyl chloride (0.56 mol). Refluxed the

reaction mixture for 2-4 hours at 50-55°C. After 4 hours, the reaction mixture,

which was usually viscous was poured into 2 L of water and stirred for

30 minutes at 60-80°C and filtered. The filtrate was adjusted to pH 8 with 25%

ammonia; 2-amino-4-methyl benzothiazole precipitated out was filtered by

59

suction, washed with water and dried (m.p 132°C). Recrystallization from hot

water yielded 14 g of white flakes melting at 137°C [Papenfuhs Von Theodor,

1982].

1-(2-methylphenyl) thiourea

HNS

NH2

H3C

(i) SOCl2 50-550C

(ii) HydrolysisS

N

NH2

2-amino-4-methylbenzothiazole

CH3

3.3.5 Synthesis of 1-(4-chloro phenyl) thiourea

1-(4-chloro phenyl) thiourea was prepared similarly as described earlier for

the synthesis of α-phenylthiourea except that, instead of 18.6 g (0.2 mol) of

aniline in 50 mL dry acetone, a solution of 26.0 g (0.2 mol) of p-chloro aniline in

50 mL dry acetone was used. The crystalline product of 1-(4-chloro phenyl)

thiourea obtained was filtered and dried. The yield of oven-dried material was

12.5 g. Recrystallization from ethanol yielded 11.0 g of white crystalline solid,

melting at 152-153°C [Snyder H.R., 1948].

C6H5COOH +

Benzoic acid

NH4SCN + NH4Cl

NaOH

+

NH

S

H2N

Cl CO N

CS

Cl

H

HN

O

NCSbenzoyl isothiocyanate

O

ClBenzoyl chloride

NH2

Cl

p-chloroaniline

1-(4-chlorophenyl)thiourea

Ammoniumthiocyanate

60

3.3.6 Synthesis of 2-amino-6-chloro benzothiazole

10 g of 4-chloro phenyl thiourea was dissolved at 20°C in 15 mL of H2SO4

(98%). In the course of 3 hour durations, 1 mL of HBr solution (48% strength)

was added with 30 minutes intervals. The temperature of 45-50°C was

maintained for 1.5 hours, then 65 to 70°C for 6 hours. The solution was cooled to

20°C and 25 mL of methanol was added. The temperature rose to approximately

70°C. The mixture was then cooled to 20°C and filtered using suction. The

filtered residue was washed three times with 15 mL acetone and dried in air.

9 g of 2-amino-6-chloro-benzothiazole sulphate obtained was placed in a solution

of sodium hydroxide (10 g of NaOH in 15 mL of water) and was stirred for

one hour at 70°C. The mixture was then filtered off using suction and the residue

was washed with water and dried. White solid of 2-amino 6-chlorobenzothiazole

melting at 199-201°C was obtained [Steffen Dapperheld, 1994].

NH

S

H2N

Cl

1-(4-chloro phenyl)thiourea.

S

N

NH2

2-amino-6-chloro benzothiazole

Cl(i)Conc.H2SO4 (ii) HBr

(iii)NaOH

3.3.7 Synthesis of 1-(4-bromo phenyl) thiourea

1-(4-bromophenyl) thiourea was also prepared by the similar procedure

described earlier for synthesis of α-phenylthiourea except that, instead of

18.6 g (0.2 mol) of aniline in 50 mL dry acetone, a solution of 26 g (0.2 mol) of

p-chloro aniline in 50 mL acetone was used. The crystalline product of 1-(4-

bromo phenyl) thiourea obtained was filtered and dried. The yield of oven-dried

material was 12 g. Recrystallization from ethanol yielded 11.5 g of white

crystalline solid, melting at 183-184°C [Snyder H.R., 1948].

61

C6H5COOH +

Benzoic acid

NH4SCN + NH4Cl

NaOH

Ammonium thiocyanate

+

NH

S

H2N

Br CO N

CS

Br

H

HN

O

NCSbenzoyl isothiocyanate

O

ClBenzoyl chloride

NH2

Br

p-bromo aniline

1-(4-bromo phenyl)thiourea 3.3.8 Synthesis of 2-amino-6-bromo benzothiazole

4-bromo phenyl thiourea (10 g) was dissolved at 20°C in 15 mL of H2SO4

(98%). In the course of 3 hours duration, 1 mL of HBr solution (48% strength)

was added each time at 30 minutes intervals. The temperature was maintained

at 45°C to 50°C for 1.5 hours and then 65 to 70° C for 6 hours at. The solution

was cooled to 20°C and 25 mL of methanol was added. The temperature rose to

approximately 70°C. The mixture was then cooled to 20°C and filtered using

suction. The filtered residue was washed thrice with 15 mL acetone and dried in

air. 2-amino-6-bromo benzothiazole sulphate (9 g) obtained was placed in a

solution of sodium hydroxide (10 g of NaOH in 15 mL of water) and was stirred

for one hour at 70°C. The mixture was then filtered off using suction and the

residue was washed with water and dried. The white solid crystalls of 2-amino-6-

bromo benzothiazole with melting point of 213-217°C was obtained [Steffen

Dapperheld 1994].

NH

S

H2N

Br

1-(4-bromo phenyl)thiourea

S

N

NH2

2-amino-6-bromo benzothiazole

Br

(i)Conc.H2SO4 (ii) HBr(iii)NaOH

62

3.3.9 Synthesis of o-Vanillidine-2-amino benzothiazole Schiff’s Base (VBT) 2-amino benzothiazole (1.5 g), was dissolved in absolute ethanol (15 mL)

and then o-Vanillin (1.10 g) was added to the above solution along with a drop of

piperidine. The mixture was refluxed for 3 hours with stirring and kept aside for

eight hours. The yellowish orange solid obtained was filtered and washed several

times with cold ethanol, dried and recrystallized from carbon tetrachloride to yield

yellow crystalline solid.

Analysis of VBT C15H12N2O2S requires 63.36% C, 4.25% H and 9.85% N; found 63.36% C,

4.24% H and 9.84% N; yellow crystalline solid, m.p 164oC. IR (KBr, cm-1): 3432

(O-H), 1593(C=N), 1255 (C-O). 1H NMR (CDCl3, TMS,δ): 3.9 (s, -OCH3), 6.9

to8.0 (m, aromatic protons), 9.3 (s,-CH=N), 12.49(s,-OH). Mass spectrum M+ ion peak 284.

S

N

NHO OCH3

o-Vanillidine-2-amino benzothiazole (VBT)

3.3.10 Synthesis of Copper Complex of VBT Schiff’s Base Methanolic solution of VBT Schiff’s base (10 m mol) was mixed with

Copper acetate (5 m mol) in methanol (10 mL) solution keeping metal ligand ratio

1:2 with continuous stirring. The mixture was then refluxed for 2 hrs, and then

heated on a water bath till the volume of the solution was reduced to 10 mL. The

brown coloured VBT Copper complex precipitated was filtered and washed with

methanol and acetone. Recrystallized from chloroform and then dried in vacuum.

Analysis of VBT Copper Complex C30H22CuN4O4S2 requires 57.18% C, 3.52% H, 10.08% Cu and 8.89% N;

found 57.1% C, 3.5% H, 10.05% Cu and 8.89% N; brown solid, m.p above

260oC, ε.max: 2.87x103 L mol-1 cm-1 (methanol) at 450 nm. IR (KBr, cm-1): 1532

(C=N), 1339 (C-O). 1H NMR (CDCl3, TMS,δ): the signal at 12.49 for –OH is

63

absent in Copper complex and other signals are same as that of the Schiff’s

base(VBT). 3.3.11 Synthesis of o-Vanillidine-2-amino-4-methyl benzothiazole (VMBT) 2-amino-4-methyl benzothiazole (1.66 g) was dissolved in absolute

ethanol (15 mL) and then o-Vanillin (1.10 g) was added to the above solution

along with a drop of piperidine. The mixture was refluxed for 3 hours and kept for

eight hours. The yellowish orange solid obtained was filtered and washed several

times with cold ethanol, dried and recrystallized from carbon tetrachloride to yield

yellow crystalline solid.

Analysis of VMBT C16H14N2O2S requires 64.41%C, 4.73% and 9.39%N; found

64.48% C, 4.7% H and 9.36% N; yellow crystalline solid, m.p 176oC. IR (KBr,

cm-1): 3434 (O-H), 1596 (C=N), 1258 (C-O). 1H NMR (CDCl3, TMS,δ ): 2.76 (s,-

CH3), 3.96 (s,-OCH3), 6.8-7.4 (m, aromatic protons), 9.3 (s,-CH=N), 12.53 (s,-

OH). The –OH signal at 12.53 ppm disappeared upon the addition of D2O to the

solution, indicating that it is an acidic proton. Mass spectrum M+ ion

peak 298.

S

N

NHO OCH3

CH3

o-Vanillidine-2-amino-4-methyl benzothiazole (VMBT)

3.3.12 Synthesis of Copper Complex of VMBT Schiff’s Base Methanolic solution of VMBT Schiff’s base (10 mmol) was mixed with

Copper acetate (5 mmol) in methanol (10 mL) solution keeping metal ligand ratio

1:2 with continuous stirring. The mixture was then refluxed for 2 hrs, and then

heated on a water bath till the volume of the solution got reduced to 10 mL. The

brown coloured VMBT Copper complex precipitated was filtered and washed with

methanol and acetone. Recrystallized from chloroform and then dried in vacuum.

64

Analysis of VMBT Copper Complex C32H26CuN4O4S2 requires 58.39% C, 3.98% H, 9.65% Cu and 8.51% N;

found 58.30% C, 3.94% H, 9.6% Cu and 8.6% N; brown solid, m.p above 260oC, ε.max: 2.94 x103 L mol-1 cm-1 (methanol) at 450 nm. IR (KBr, cm-1): 1542 (C=N),

1375 (C-O). 1H NMR (CDCl3, TMS,δ): The signal at 12.53 for –OH was absent in

Copper complex and other signals were same as that of the Schiff’s base

(VMBT). Mass spectrum M+ ion peak 657. 3.3.13 Synthesis of o-Vanillidine-2-amino-6-chlorobenzothiazole Schiff’s

Base (VCBT) 2-amino-6-chloro benzothiazole (1.84 g, 10 mmol) was dissolved in

absolute ethanol (15 mL) and then o-Vanillin (1.10 g) was added to the above

solution along with a drop of piperidine. The mixture was refluxed for 3 hours with

stirring and kept aside for eight hours. The yellow solid obtained was filtered,

washed several times with cold ethanol, dried and recrystallized from carbon

tetrachloride to yield yellow crystalline solid.

Analysis of VCBT C15H11ClN2O2S requires 56.52% C, 3.48% H and 8.79% N; found 56.50%

C, 3.49% H and 8.79% N; yellow crystalline solid, m.p 224oC. IR (KBr, cm-1):

3440(O-H), 1596(C=N), 1247 (C-O). 1H NMR (CDCl3, TMS,δ): 3.9 (s,-OCH3), 6.9

to 8.0 (m, aromatic protons), 9.3 (s,-CH=N), 12.38 (s-OH). Mass spectrum M+

ion peak 318.

S

N

NHO OCH3

Cl

o-Vanillidine-2-amino-6-chlorobenzothiazole, (VCBT).

3.3.14 Synthesis of Copper Complex of VCBT Schiff’s Base Methanolic solution of VCBT Schiff’s base (10 mmol) was mixed with

Copper acetate (5 mmol) in methanol (10 mL) solution keeping metal ligand ratio

1:2 with continuous stirring. The mixture was then refluxed for 2 hrs, and then

65

heated on a water bath till the volume of the solution got reduced to 10 mL. The

brown coloured VCBT Copper complex precipitated was filtered and washed with

methanol and acetone. Recrystallized from chloroform and then dried in vacuum.

Analysis of VCBT Copper Complex C30H20 ClCu N4O4S2 requires 51.54% C, 2.88% H, 9.09% Cu and 8.01%

N; found 51.52% C, 2.86% H, 9.0% Cu and 8.0% N; brown solid, m.p above

260oC, ε.max: 2.2x103 L mol-1 cm-1 (methanol) at 450 nm. IR (KBr, cm-1):

1573 (C=N), 1304 (C-O). 1H NMR (CDCl3, TMS,δ): The signal at 12.38 for

–OH was absent in Copper complex and other signals were same as that of the

Schiff’s base

3.3.15 Synthesis of o-Vanillidine-2-amino-6-bromo benzothiazole Schiff’s

Base (VBBT) 2-amino-6-bromo benzothiazole (2.20 g) was dissolved in absolute

ethanol (15 mL) and then o-Vanillin (1.10 g) was added to the above solution

along with a drop of piperidine. The mixture was refluxed for 3 hours with stirring

and kept aside for eight hours. The yellow solid obtained was filtered, washed

several times with cold ethanol, dried and recrystallized from carbon tetrachloride

to yield yellow crystalline solid.

Analysis of VBBT C15H11BrN2O2S requires 49.60% C, 3.05% H and 7.71% N; found

49.58% C, 3.02% H and 7.74% N; yellow crystalline solid, m.p 234oC.

IR (KBr, cm-1): 3432(O-H) 1592 (C=N), 1259 (C-O). 1H NMR (CDCl3, TMS,

δ): 3.15(s,-OCH3), 6.8 to 8.0 (m, aromatic protons), 9.3(s,-CH=N), 12.38

(s,-OH). Mass spectrum M+ ion peak 364.

S

N

NHO OCH3

Br

o-Vanillidine-2-amino-6-bromo benzothiazole (VBBT)

66

3.3.16 Synthesis of Copper Complex of VBBT Schiff’s Base Methanolic solution of VBBT Schiff’s base (10 mmol) was mixed with

Copper acetate (5 mmol) in methanol (10 mL) solution keeping metal ligand ratio

1:2 with continuous stirring. The mixture was then refluxed for 2 hrs, and then

heated on a water bath till the volume of the solution got reduced to 10 mL. The

brown coloured VBBT Copper complex precipitated was filtered and washed with

methanol and acetone. Recrystallized from chloroform and then dried in vacuum.

Analysis of VBBT Copper Complex C30H20BrCuN4O4S2 requires 45.73% C, 2.56% H, 8.06% Cu and

22.91% N; found 45.71% C, 2.55% H, 8.01% Cu and 22.89% N; brown solid,

m.p above 260oC, ε.max: 1.53x103 L mol-1 cm-1 (methanol) at 450 nm.

IR (KBr, cm-1): 1538 (C=N), 1304 (C-O). 1H NMR (CDCl3, TMS,δ): The signal at

12.38 for –OH was absent in Copper complex and other signals were same as

that of the Schiff’s base.

3.4 SPECTROPHOTOMETRIC DETERMINATION OF COPPER 3.4.1 Preparation of Copper (II) standard solution Copper (II) solution (1000 mg L-1) was prepared by dissolving a known

amount of Copper (II) sulphate penta hydrate in distilled water, adjusting the pH

of the solution to 1.0 with dilute sulphuric acid and diluting the solution to a liter

with distilled water. The concentration was determined by titrating with EDTA

using 1-(2-Pyridyl azo)-2-naphthol (PAN) as indicator. Working solutions of the

concentrations of 10-5M were prepared by appropriate dilution of standard

solution.

3.4.2 General procedure for the determination of Copper ions using VBT Schiff’s Base

Standard solutions of VBT Schiff’s base of concentration 10-4M were

prepared in A.R methanol. Absorption measurements were made at 450 nm

against the reagent blank from a solution, prepared by 1mL of the VBT Schiff’s

67

base of the concentration 10-4M, 1mL of 0.075 µg mL-1 to 0.9 µg mL-1 of Copper

solution, 2 mL of 5.89 buffer solution and made up to 25 mL with methanol.

3.4.3 General procedure for the determination of Copper ions using VMBT, VCBT and VBBT Schiff’s Bases

Above procedure was repeated with 1mL of the VMBT, VCBT and VBBT

Schiff’s bases.

3.4.4 Determination Copper from the Industrial Effluents The effluent samples were collected from four different industries around

Mysore. Treated effluent solutions were completely evaporated, they were

digested with 10 mL of Conc. HNO3, until all the brown fumes of nitric acid

subside [APHA and AWWA-WPCF, 1995]. The residues obtained were extracted

with dilute acetic acid and made up to 25 mL with redistilled water in a volumetric

flask. The estimations of Copper ions were carried out as described under

general procedure using VBT, VMBT, VCBT and VBBT as analytical reagents

and absorption measurements were made at 450 nm against the reagent blank

and the results are presented in the Table 3.1. The results obtained by the

proposed method agreed with the certified values.

Table 3.1: Results obtained for the determination of Copper from industrial effluents

Industrial effluents

VBT as analytical reagent

(µg mL-1)

VMBT as analytical reagent

(µg mL-1)

VCBT as analytical reagent

(µg mL-1)

VBBT as analytical reagent

(µg mL-1)

AAS method

(µg mL-1 )

Glowtronics 0.026 0.024 0.024 0.022 0.02

Marc batteries 0.024 0.022 0.025 0.0223 0.02

Allcoats 0.031 0.036 0.033 0.0321 0.03

Tritan Valves 0.38 0.356 0.362 0.0359 0.35

68

3.5 RESULTS AND DISCUSSION

3.5.1 General Chemical Reactions

S

N

NH2

R

R1

OHC

HO OCH3

S

N

N

HO OCH3

R

R1

S

N

N

Cu O

N

N

SO

R

R1

R

R1OCH3

H3CO

+

Schiff's base Copper complexes

o-Vanillidine 2-amino benzothiazole Schiff's bases

2-aminobenzothiazoleso-Vanilline

[R=H, R1=H] [R=CH3, R1=H] [R= H, R1= Cl] [R=H, R1=Br]

Cu(II) solution

69

3.5.2 IR Spectra of Synthesized Schiff’s Bases and their Copper Complexes IR spectra of the complexes were compared with those of the free ligands

(Table 3.2). The C=N stretching frequencies in the free ligands were observed

around 1562-1573 cm-1. The shift of this band towards a lower frequency

(1538-1542 cm-1) in all Copper complexes suggests that coordination has

taken place through the nitrogen of the azomethine group. The C-O stretching

modes of the phenolimine form of the free Schiff’s bases were found between

1178 and 1259 cm-1. The shift of the phenolic C-O stretch towards higher

frequencies in all Copper complexes suggests Cu-O bond formation. Therefore, it

is believed that chelation of the Copper ions in their Schiff’s base complexes

occurs through Nitrogen and Oxygen. All the IR data of the Schiff’s bases and

their Copper complexes imply that the Schiff’s bases behave as bidentate ligand

and bonded to Copper ion through phenolic oxygen and imino nitrogen of

azomethine [Neelakantan M.A. et al., 2008].

Table 3.2: IR Spectra for VBT, VMBT, VCBT, VBBT and their respective Copper complexes

Compound (O-H) cm-1

(C=N) azomethine

cm-1 (C-O) cm-1

(C=N) thiazole ring

cm-1

(C-S-C) cm-1

VBT 3432 1567 1256 1594 762

VBT-Cu 3445 1541 1441 1609 752

VMBT 3434 1572 1178 1596 747

VMBT-Cu 3436 1542 1236 1596 747

VCBT 3648 1573 1247 1699 724

VCBT-Cu 3647 1539 1257 1699 723

VBBT 3438 1566 1259 1592 735

VBBT-Cu 3564 1538 1304 1649 723

70

3.5.3 1H NMR Spectra of Synthesized Schiff’s Bases and their Copper Complexes

1H NMR Spectra of the Schiff’s bases exhibit a multiplet around 6.9 to

7.69 δ for the protons of the aromatic ring. A signal at 2.7δ due to hydrogen of

–CH3 was observed only in VMBT Schiff’s base. The azomethine hydrogen

(-CH=N-) leads to a singlet of integration intensity equivalent to one of the

hydrogen around 9.3 δ. The signal around 3.9 δ was due to the hydrogen of the

–OCH3. Schiff’s bases show a singlet equivalent to a hydrogen around 12.5 δ

corresponding to free –OH. Disappearance of the signal at 12.5 δ upon the

addition of D2O to the solution indicates that, it is an acidic proton. The higher δ

value of the –OH group is attributed to the possible hydrogen bonding in the

Schiff’s bases. Absence of the signals around 12.5 δ were observed in all Copper

complexes indicating the involvement of the –OH group in chelation with Copper.

There was no other appreciable change in signals of the complexes when

compared with the Schiff’s bases [Orhan Buyukgungor et al., 2004].

3.5.4 Absorption Spectra of Synthesized Schiff’s Bases and their Copper Complexes

Under the experimental conditions, absorption spectra of Schiff’s bases

VMBT, VBT, VCBT and VBBT and their corresponding Copper complexes were

scanned at pH 5.89. Absorbance decreased from 370 nm to 500 nm for all the

four Schiff’s bases. Copper complexes of four Schiff’s bases show maximum

absorptions at 450 nm. Hence 450 nm was chosen as the wavelength for the

determination. Absorption spectra of VBT, VMBT, VCBT, VBBT and their Copper

complexes are shown in the Figures 3.1, 3.2, 3.3 and 3.4.

71

0

0.05

0.1

0.15

0.2

0.25

0.3

370 420 470 520 570

Wavelength

Abs

orba

nce

2

1

Figure 3.1: Absorption spectra of VBT and Cu-VBT 1. Absorption spectrum of VBT 2. Absorption spectrum of Cu-VBT

0

0.1

0.2

0.3

0.4

0.5

370 420 470 520 570Wave length (nm)

Abs

orba

nce

1

2

Figure 3.2: Absorption spectra of VMBT and Cu-VMBT

1. Absorption spectrum of VMBT 2. Absorption spectrum of Cu-VMBT

72

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

370 420 470 520 570

wave length

Abs

orba

nce

21

Figure 3.3: Absorption spectra of VCBT and Cu-VCBT

1. Absorption spectrum of VCBT 2. Absorption spectrum of Cu-VCBT

0

0.05

0.1

0.15

0.2

0.25

370 420 470 520 570

Wave length

Abs

orba

nce

2

1

Figure 3.4: Absorption spectra of VBBT and Cu-VBBT

1. Absorption spectrum of VBBT 2. Absorption spectrum of Cu-VBBT

73

3.5.5 Effect of pH The effects of pH on the absorbance of four Schiff’s base Copper

complexes at 450 nm were studied under different pH conditions. Maximum

absorbance for the complex was obtained at pH 5.89. Hence, pH 5.89 was

selected for the determination of Copper. It is also found that, the addition of

2 mL of buffer solution of pH 5.89 was sufficient for the pH adjustments.

3.5.6 Characteristics of the Copper Complexes

Light yellowish orange solutions of VMBT, VBT, VCBT and VBBT

solutions change to brownish yellow solutions immediately on the addition of

Copper ions at 5.89 pH in methanol solution with maximum absorption at 450 nm

and was stable for at least half an hour.

3.5.7 Calibration and spectral data of Copper Complexes Beer Lambert’s Range, optical Characteristics, such as, molar

absorptivity, Sandell's sensitivity, slope, intercept, correlation coefficient are

shown in Table 3.3. Sandell’s sensitivity (S) represents the number of

micrograms of the determinant per milliliter of a solution having an absorbance

(A) of 0.001 for a path length (l) of 1 cm. Thus S=10-3/a=µg cm-2 where ‘a’ is

specific absorptivity and its value in mL g-1 cm-1 corresponds to the determinant

in a cuvette with an optical length of 1 cm. Also,

a = 1000 x metaltheof wt.at.

ε

ε = (Molar absorptivity) = A/cl, where ‘c’ is the molar concentration of the

determinant and l =1 cm.

A typical plot showed unequivocally, that the stable 1:2 [M-L] complexes

are formed at pH 5.89 (λmax 450 nm). Calibration graph obtained by the

recommended procedure was linear over the range 0.4 to 3.8 µg mL-1 in the final

solution (Figure 3.6).

74

.

0

0.02

0.04

0.06

0.08

0.1

0 0.02 0.04 0.06 0.08

Metal concentration (µg / mL)

Abs

orba

nce

VBT Copper complexVCBT Copper complexVBBT Copper complexVMBT Copper complex

Figure 3.5: Calibration graph obtained for VBT, VMBT, VCBT and VBBT copper complexes

75

Table 3.3: Spectral data for the determination of Copper ions using VBT, VMBT, VCBT and VBBT Schiff’s bases as spectrophotometric reagents

Parameters Cu-VBT Cu-VMBT Cu-VCBT Cu-VBBT

Colour Brownish

yellow

Brownish

yellow

Brownish

yellow

Brownish

yellow

λmax (nm) 450 450 450 450

Stability (minutes) 30 30 30 30

Molar absorptivity,

(εmax) L mol-1 cm-1 2.87x103 2.94x103 2.2x103 1.53x103

Beer Lambert’s Range

(µg mL-1) 0.116-0.81 0.075-0.78 0.12-0.9 0.3-0.9

Sensitivity (µg cm-2) 2.2x10-3 2.14x10-3 2.9x10-3 4.12x10-3

Regression (r2) 0.9996 0.9855 0.9955 0.9995

Slope 1.0616 0.9373 1.0522 1.6713

Intercept 0.00047 0.00365 -0.0049 0.00035

Correlation Coefficient 0.9998 0.9927 0.9978 0.9998

3.5.8 Effect of foreign ions on the determination of metal ions An extensive study was made on the effect of foreign ions on the

determination of Copper in 5.8x10-5 M Copper solution buffered at pH 5.89. The

tolerance amounts of foreign ions are as shown in Table 3.4.

The tolerance limit of foreign ions was taken as that value, which caused

an error of not more than ±5% in the absorbance. Most of the cations do not

interfere with the determination of Copper.

76

Table 3.4: Effect of various cations and anions (0.59 µg mL-1 Copper added)

Ions / Substance

Amount added

(µg mL-1)

Copper found

(µg mL-1) with VBT

Error (µg mL-1)

Copper found

(µg mL-1) with VMBT

Error (µgmL-1)

Copper found

(µgmL-1) with

VCBT

Error (µg mL-1)

Copper Found

(µg mL-1) with

VBBT

Error (µg mL-1)

Cl - 70 0.059 0.0 0.059 0.0 0.059 0.0 0.059 0.0

SO4 2- 103 0.050 -0.009 0.052 -0.007 0.049 -0.01 0.048 0.059

NO3 - 90 0.059 0.0 0.059 0.0 0.059 0.0 0.059 0.0

F - 38 0.063 0.004 0.645 0.586 0.064 0.005 0.067 0.008

PO43-

122 0.068 0.009 0.07 0.011 0.073 0.014 0.072 0.013

DMG 1194 0.050 -0.009 0.049 -0.01 0.050 -0.009 0.052 -0.007

EDTA (0.1M) 0.05mL - - - - - - - -

Thiourea 170 0.0 -0.059 0.0 -0.059 0.0 -0.059 0.0 -0.059

Hg+2 1.25 0.052 -0.007 0.055 -0.004 0.054 -0.005 0.055 -0.004

Pb+2 1.08 0.044 -0.015 0.042 -0.017 0.042 -0.017 0.044 -0.015

Fe+2 2.02 0.052 -0.007 0.054 -0.005 0.054 -0.005 0.053 -0.006

Cd+2 2.12 0.054 -0.005 0.056 -0.003 0.053 -0.006 0.054 -0.005

Zn+2 2.02 0.049 -0.01 0.048 -0.011 0.048 -0.011 0.044 -0.015

Co+2 1.95 0.056 -0.003 0.057 0.002 0.057 -0.002 0.055 -0.004

Ni+2 1.09 0.045 -0.014 0.042 -0.017 0.044 -0.015 0.040 -0.019

77

3.6 CONCLUSIONS 1. Four new Schiff’s bases VBT, VMBT, VCBT and VBBT and their Copper

complexes were synthesized and characterized.

2. These Schiff’s bases react with Copper (II) ions in methanol solution to form

brownish yellow complexes at pH 5.89, with a stoichiometric ratio of

1:2 [Copper to ligand].

3. These Schiff’s bases are selective and specific spectrophotometric reagents

for the determination of Copper. The method is relatively free from

interference with most of the metal ions like Zinc, Cadmium, Cobalt, Lead,

Mercury and Iron.

4. Satisfactory results were obtained when the method was applied to the

determination of Copper in the industrial effluents.

These synthesized Schiff’s bases are very sensitive reagents for the

spectrophotometric determination of Copper ions. Hence, Copper alone can be

estimated from the industrial effluents. For the determination of the other metal

ions from the industrial effluents, we prepared a few organic dyes which contain

two auxochromic groups.

A dye molecule can usually bind a metal ion only if it contains in addition

to the atoms in the auxochromic groups, other electron donating atoms in

such position that together with the metal ion, they can form chelate rings of

five atoms. Such chelate rings are highly stable. The azodyes on formation of

metal complexes undergo greatest change in colour. Therefore literature survey

on heterocyclic azo dyes as spectrophotometric determination of metal ions has

been made and synthesized azo dyes, which are formed by the diazotization

reaction of 2-aminobenzothiazole and its 4-methyl, 6-chloro and 6-bromo

derivatives with 2-amino-3-hydroxy pyridine. These dyes formed purple

coloured complexes with Cu(II), Ni(II), Cd(II), Co(II) and Zn(II) metal ions.

Spectrophotometric determination of these metal ions with above synthesized

azo dyes as reagents have been standardized and procedure has been designed

for the determination of these metal ions from the industrial effluents and are

discussed in the subsequent Chapters.