Determination and studying the factors affecting on ...qu.edu.iq/scjou/wp-content/uploads/2015/11/Abbas-A.-A.-Kadhum.pdfDetermination and Studying the Factors Affecting the Stability

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Determination and Studying the Factors Affecting the Stability Constant Values of Some Azo Dyes .

Abbas A. A. Kadhum

Chem. Dept. College of Education

Univ. of AL – Qadisiya

Abstract .

The main object is the determination and studying the factors affecting on stability constants of

some of azo dyes production by the reaction m – fluoro phenol as acceptor with donor amines . The stability

constants for any dyes are evaluated at acidic , neutral ,and basic media , under PH values ( 5.4 , 7.6 , 9.3 )

respectively and five different temperature . Some experiments prove the formation of unstable complexes

and the failure of the evaluation of stability constant values for complexes is elected at PH=5.4 , other donors

imines form a stable dyes at pH 7.6 and 9.3 .

The thermodynamic of azo dyes formation led to the conclusion that such reactions are spontaneous

and exothermic as evident from negative sings of ΔG and ΔH thermodynamic parameters .The study shows a

mainly negative sing of ΔS parameter which is agreed with theoretical preduction .This study proved that

changing the structural formulas of imines and the position and the type of substitute have a clear effect on

stability constants values of azo dyes derived from them .

2

Introduction :

Since their original discovery by Perkin in 1856 (1)

, azo dyes have been extensively developed and

now have major commercial applications as coloring agents (2)

. Consequently there is considerable interest in

the factors that control their stability and colour fastness (3)

. The success of azo colorants is due to the

simplicity of their synthesis by diazotization and azo coupling , to the almost innumerable possibilities

presented by variation on the diazo compounds and coupling components , to the generally high molar

extinction coefficient , and to the medium to high light and wet fastness properties (4,5)

.

Stability constants are very important to study the nature of complex compounds it encourages almost all the

data that lead to better comprehension and understanding for the complex and the nature of its bonding ,

which identifies the shape and compound of the complex (6)

. The stability constants is regarded also an

evidence about the existence of the complex in solution (7)

. We can measure the concentration or the validity

of any ingredient in mixture at equilibrium from the number of stability constant , It is also used to measure

the standard Gibbs free energy ΔGº which limits the nature and direction of the reactions , for by it one can

count the other standard thermodynamic parameters like ΔSº and ΔHº (8)

.

There are two different types of stability constants : thermodynamic stability and kinetic stability ,

the first type deals with the energy of the metal-ligand band and stability constants , while the second type

includes the measurement of speed and mechanism of chemical reactions such as substitution reactions ,

Isomerization , Racemization , and Activated complex formation (9)

..It has been recognized that the stability

of mixed ligand complexes is strongly dependent on the type of the donor atoms available and the possibility

of π-band formation (10,11 )

. Taki (12)

and Gesso (13)

has been determinate the stability constant for some azo

dyes . In this study the effect of structural formulas of dyes on the stability constant has been calculated by

using Hammett Equation .

3

2. Experimental .

2.1. materials

All reagent were from commercial sources and were used without further purification . Hydrochloric acid , m-

fluoro phenol (mFP) , p-hydroxy aniline (pHA) , p- amino aniline (pAA ), p- methyl aniline and ethanol were

supplied by BDH.

2.2. Synthesis .

All of the investigated dyes were preparation by general coupling reaction method using equimolar

quantities (14)

, the synthesized dyes were filtrated and washed with cold distilled water for several times and

purified by chromatography on a silica column ( pentane/EtOAc 3:3:1 ) and then recrystallised from

EtOH/H2O to yield 2-(3-hydroxy aniline azo )-3- flouro phenol (HAAFP) as orange crystals ,m.p.196-199º

C ;UV-Vis λmax ( 330 ) nm , 2-(4-amino aniline azo)-3- flouro phenol (AAAFP) as brownish –orange

crystals 180-183 º C ; UV – Vis λmax ( 340 nm ) , 2-(4-methyl aniline azo)-3- flouro phenol (MAAFP) as

yellow crystals , m.p. 160-163º C ;UV-Vis λmax (370 nm ) . A precision research pH-meter , digital with

combined electrode was used . The changes in the pH can be measured with an accuracy of 0.005pH unit by a

Beckman pH meter . The electronic spectra and absarbances for aqueous solution of dyes were determined

by ShImadzu UV-Visible (1650 pc) spectrophotometer , FT-IR analysis was carried out by Shimadzu FT-IR

(84005) spectrophotometer using KBr disk in the range 400-4000 cm-1

.

The formation constant of dyes was determined spectrophotometrically by applying the molar ratio

method . The chemical structure and the purity of the azo dyes were confirmed by melting points, FTIR and

UV spectra .

4

3. Results and discussion .

3.1. FT-IR Spectral Studies .

The most characteristic bands of the dyes are summarized in table 1 .These spectra are

complicated owing to the extensive overlap of a number of bands arising due to ν(O – H), ν(N=N) .

The spectrum of dyes shows a very weak absorption band around 3350 cm-1

due to ν(O – H),this

suggests a strong intermolecular hydrogen bonding .

Tow absorption bands are observed at 1495 and 1470 cm-1

which are due to the azo group .

Table 1 : IR spectral frequencies for dyes .

Bond HAAFP AAAFP MAAFP

ν (OH) 3550 wbr 3450 wbr 3500wbr

ν ( N=N) 1480 s 1465 m 1475 m

ν (C=C) 1525 m 1520 m 1520 m

ν (C-F) 1200 m 1200 m 1200m

s = strong , w = weak , m = medium , br = broad

3.2.Estimation of stochiometry of dyes .

The empirical formula of azo dyes was formulated by the reaction of donor m- fluoro phenol with

diazotized salt as acceptor, and it was determined by the spectrophotometric method of mole ratio (15)

at the

pH = 5.4 , 7.6 and 9.3 respectively . The results Fig (1,2,3) proved the stoichiometry of the type (1:1) is

observed for all azo dyes compounds and the structure of the dyes may be written as follows :

N N

OH

F

OH

N N

F

OH

N N

F

OH

NH2CH3

HAAFP AAAFP MAAFP

5

0

0.2

0.4

0.6

0.8

1

1.2

0 0.25 0.5 0.75 1 1.25 1.5

mFP/Diazotized Reagent

A

PH=5.4PH=7.6PH=9.3

Fig. (1) Mole-ratio plot of the m-flouro phenol – 3-hydroxy aniline

Fig .(2) Mole-ratio plot of the m-flouro phenol – 4-amino aniline

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 0.5 1 1.5

mole mFP/ mole Diazotized Reagent

A

PH=5.4

PH=7.6

PH=9.3

Fig (3): Mole-ratio plot of the m-flouro phenol – 4-methyl aniline .

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.25 0.5 0.75 1 1.25 1.5

mFP/Diazotized Reagent

A

PH=5.4PH=7.6PH=9.3

6

3.2. Determination of stability constant of dyes .

Depending on the mole ratio method, which is mentioned in the previous part, azo dyes are

formulated out of reacting m- fluoro phenol with diazotized salt in (1:1) ratio as represented in the following

equation:

D + A ↔ DA …….1

The stability constant equation can be written as follows:

AD

DAK ……..2

The dissociation degree can be found by the following relationship:

Em

EsEm ………..3

Es = absorption of the azo solution which contains a stoicheometric amounts of reagent ( donor amines ) and

m- fluoro phenol .

Em = absorption of the azo solution containing excess amount of reagent (donor amines ) at optimum

conditions .

If (C) represents the concentration of the formulated azo dye, we can write the following equation:

CCC

CK

2

11

……….4

We can calculate (α ) from equation number (3) and the we can calculate( K) from equation (4) .

Sometimes compounds do not have the ability of formulating azo dyes in certain temperature

probably because the phenolic group is transformed from Enole to Keto form or other forms , which leads to

the destruction of the aromatic system and decreasing the density of electrons in bonding position .

Table (2) shows decrease in the stability constant vales of the dyes at different temperature which is

proved by increasing the dissociation degree (α ) .

7

Table 2 . Stability constant and dissociation degree for the formulated dyes at different temperature and pH .

Dyes pH T(K) Es Em α K ( l.mol-1

)

HAAFP

5.4

298 0.133 0.075 - -

308 0.141 0.091 - -

318 0.142 0.087 - -

328 0.119 0.094 - -

338 0.089 0.97 0.90824 1112.51

7.6

298 0.150 0.164 0.08536 117251.7

308 0.162 0.173 0.06358 2317871.2

318 0.042 0.056 0.25000 120000

328 0.052 0.066 0.21212 175123.3

338 0.037 0.042 0.11904 621707.8

9.3

298 0.145 0.159 0.08805 1176709.6

308 0.138 0.144 0.04166 240808.2

318 0.092 0.102 0.09803 939552.0

328 0.009 0.018 0.50000 20000

338 0.005 0.017 0.70588 5903.6

AAAFP

5.4

298 0.142 0.149 - -

308 0.182 0.199 - -

318 0.122 0.100 - -

328 0.095 0.141 0.32624 6332303

338 0.087 0.126 - -

7.6

298 0.136 0.165 0.17575 266920.3

308 0.114 0.184 0.38043 26289.9

318 0.092 0.123 0.25203 117772.0

328 0.141 0.177 0.20338 192606.3

338 0.114 0.128 0.10937 744673.9

9.3

298 0.098 0.099 0.01010 98990000

308 0.095 0.099 0.04040 3656441.7

318 0.086 0.091 0.05494 3139734.2

328 0.078 0.088 0.11363 686576.2

338 0.069 0.074 0.07246 176674.28

MAAFP

5.4

298 0.058 0.051 - -

308 0.050 0.044 - -

318 0.043 0.051 0.15686 342739.8

328 0.039 0.033 - -

338 0.042 0.038 - -

7.6

298 0.068 0.072 0.05882 2728057.9

308 0.062 0.069 0.11290 696310.8

318 0.051 0.059 0.15686 342739.8

328 0.045 0.051 0.13333 487713.5

338 0.053 0.058 0.09433 1018751.4

9.3

298 0.066 0.071 0.07575 1613001.7

308 0.060 0.066 0.09090 1100605.3

318 0.056 0.062 0.09677 937933.5

328 0.055 0.061 0.09836 932409.5

338 0.043 0.055 0.21818 164247.8

8

3.3. The effect of pH .

The stability constant for any azo are evaluated at acidic , neutral and basic media (pH values 5.4 ,

7.6 , 9.3 ) and five different temperature .

Some experiments prove the formation of unstable dyes and the failure in evaluation of stability

constant value is elected at PH=5.4 for some dyes . They are attributed to the partial or complete protonation

of donor imines and the formation of phenoxonnium or nitrilium ions or both .

At pH =7.6 a maximum stability constant value of any complex imine is observed due to the presence

of the latter in the enolic form . Conversely , a minimum stability constant value is obtained for the complex

at pH=9.3 , due to the tautomeric conversion of enol form to keto form in imine .

3.4.Effect of temperature and the thermodynamic parameters .

Different studies emphasized that temperature and the thermodynamic parameters have clear effects on

various reactions such as ionization of acids( 16 )

, tatutomerism ( 17)

. Agha (18)

had made a thermodynamic

study about the reaction of formulating diazotization coupling reaction .

we use the van t Hoff equation which is an expression for the slope of a plot of the stability constant (ln K)

as a function of reciprocal temperature .It may be expressed in the following equation :

ln K =constant – ΔH /RT ………..5

where ΔH is the enthalpy of the formulated azo dye at the temperature T . ΔG values are calculate from the

following equation :

ΔG = -RT lnK ………..6

While the entropy of the reaction azo dye is calculate from

ΔG = ΔH – TΔS …………7

The reactions of azo dyes formation are spontaneous and exothermic as evident from negative

signs of ΔG and ΔH thermodynamic parameters which can be noted in table (3) . The study shows mainly a

negative sign of ΔS parameter , which agreed with theoretical production and with some exclusions . The last

results are interpreted by the stronger hydrogen bonding ability in reactions as compared with azo dye

complexes . Table (3) shows decrease in stability constant with increase in temperature which is noted in the

increase of the dissociation degree .

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Dyes pH T (K) LnK ΔG (J.mol-1)

ΔGº (J.mol-1)

ΔH (J.mol-1)

ΔHº (J.mol-1)

ΔS (J.mol-1.K-

1)

ΔSº (J.mol1.K-1)

HA

AF

P

5.4

298 - -

-

-

-

-

-

308 - - - -

318 - - - -

328 - - - -

338 - - - -

7.6

298 7.014 -17377.6

-30366.6

-17445.2

-17418.3

-0.2264

+40.1335

308 11.672 -29888.6 -17991.3 +38.6275

318 14.656 -38748.2 -17542.6 +66.6842

328 11.695 -31892.1 -17213.1 +44.7530

338 12.073 -33926.7 -16899.6 +50.3760

9.3

298 13.340 -33050.8

-33223.8

-150632.3

-152521.1

-394.568

-375.343

308 13.978 -35793.6 -150821.2 -373.466

318 12.391 -32759.9 -150332.2 -369.724

328 13.453 -36686.2 -150298.5 -346.378

338 9.903 -27828.7 -160521.3 -392.581

AA

AF

P

5.4

298 8.683 -21512.7

-32761.0

-

-

-

-

308 - - - -

318 - - - -

328 - - - -

338 15.661 -44009.4 - -

7.6

298 - -

-30817.6

-

-153530.0

-

-380.751

308 12.494 -31993.5 -153240.4 -393.658

318 10.176 -26903.8 -153630.6 -398.511

328 11.067 -30179.6 -153744.5 -376.722

338 12.168 -34193.6 -153884.4 -354.114

9.3

298 13.520 -33496.7

-32644.2

-112390.5

-112739.7

-264.744

-229.762

308 18.410 -47142.7 -112656.1 -212.705

318 15.112 -39953.8 -112847.5 -229.225

328 14.959 -40793.0 -112862.3 -219.723

338 13.439 -37765.3 -112942.1 -222.416

MA

AF

P

5.4

298 - -

-34752.7

-

-

-

-

308 - - - -

318 12.744 -34752.7 - -

328 - - - -

338 - - - -

7.6

298 14.819 -36715.1

-35889.6

-45321.9

-45580.3

-28.881

-30.612

308 13.453 -34449.2 -45623.2 -36.279

318 12.744 -33693.2 -45351.8 -36.662

328 13.097 -35715.4 -45771.5 -30.658

338 13.834 -38875.3 -45832.9 -20.584

9.3

298 14.293 -35411.9

-29121.0

-85642.6

-86247.9

-168.559

-159.064

308 13.911 -35622.0 -85213.2 -161.010

318 13.751 -36355.6 -85421.3 -154.294

328 13.745 -37468.8 -87511.3 -152.568

338 12.009 -33746.8 -87451.3 -158.889

Table 3. Study of temperature and thermodynamic parameter for the formulated azo dyes .

10

(A)

0

2

4

6

8

10

12

14

16

18

20

0,0028 0,0029 0,003 0,0031 0,0032 0,0033 0,0034

1/T

lnK

pH=7.6pH=9.3

(B)

0

2

4

6

8

10

12

14

16

0,0028

5

0,0029 0,0029

5

0,003 0,0030

5

0,0031 0,0031

5

0,0032 0,0032

5

0,0033 0,0033

5

1/T

lnK

pH=7.6

pH=9.3

خطي

)pH=9.3(خطي

)pH=7.6(

(C)

0

2

4

6

8

10

12

14

16

18

0.0029 0.0029 0.003 0.003 0.0031 0.0031 0.0032 0.0032 0.0033 0.0033 0.0034

1/T

lnK

pH=7.6

pH=9.3

Fig.4 : Relation between lnK and 1/ T , (A) HAAFP , (B) AAAFP , (C) MAAFP at different pH .

11

3.5. Effect of structural formulas .

The change of structural formulas and substituents has a direct effect on the stability constants of the

diazotized complexes under the study. The effect of substituents has been studied ( OH, NH2, CH3) in 20Cº,

and different pH according to Hammett equation which is clarified as follows (19,20)

:

Log (K/Ko) =ρ . σ ………8

Where K= stability constant of the found complex from imines substituent from para position.

Ko= stability constant of the found complex from unsubstituented imines.

ρ= proportionality constant reflecting the sensitivity of absorption frequencies of the substituent effects .

σ = substituent constant , measures the electronic effect of the substituent(21)

(in a given position , meta or

para ) .

According to the above equation, we have drawn a relationship between log (K/Ko) and substituent

constant (σ) in 20Cº and different pH, and we reached to the following figures(5)from which straight lines in

negative slope are found. This represents that withdrawn groups increase the speed of complex formation

which is accompanied with the increase of stability constants. The figures show also that the value of negative

slope, which represents (ρ ) counted from the straight lines equation of every figure, is in a range between

(0.99-0.76 ) and the intercept of the straight lines equations as well as correlation coefficient (r) is in a range

between (0.79-0.91). We have expected better values of the intercept and correlation coefficient (r) . The

reason behind the resulted values is related to stability constant of azo dyes that contain NH2 which higher

than the stability constants of the azo dyes containing OH and CH3.The high value of stability constant is

related to NH2 group in para position which is a very strong withdrawing group and it is consolidated by ( ρ )

for substituent constants and resonance effect .

12

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-1 -0.5 0 0.5 1 1.5

log K

/Ko

PH=5.4T=318 KY=-0.45x -0.1435r=0.79)PH=5.4( خطي

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-1 -0.5 0 0.5 1

log K

/Ko

PH=7.6T=318 KY=-0.5058+0.336r=0.86

-1

-0.5

0

0.5

1

1.5

2

-1 -0.5 0 0.5 1 1.5

log K

/Ko

PH=9.3T=318 KY=-1.5721x +0.7668r=0.91

Fig 5 : relationship between (σ) with stability constant for dyes in water at 318K and different pH .

σ

σ

σ

13

References :

1- H. Zollinger , Colour Chemistry , Syntheses , Properties and Applications of Organic Dyes and Pigments ,

VCH , New York , 1987 .

2- J. Griffiths , Colour and Constitution of Organic Molecules , Academic Press , London , 1976 .

3- J. T. Spadaro , L. Isabelle and V.Rengnathan , Environ. Sci. Technol. , 1994 , 28 , 1398 .

4- D. Z. Mijin G. S. Uscumlic and N. U. Perisic , Chemical physics letters , 418 , 223-229 , 2006 .

5- H.Zollinger , Color Chemistry .VCH , Weinheim , 1987 .

6- F. S. Chmid , Phys. Rev. ,1969 , 55 ,5774 .

7- J. Barret , P. Gijsman , J. Swagten and R.F.M. Lange , 2002 , 76 , 3 , 441-448 .

8- J. J. Choi , Y. I. K. Choi , S. N. J. Kor , Chem. Soc. , 1995 , 39 , 466 .

9- F. Basolo , R.Johnson “ Coordination Chemistry “ , Menlopark , California , 1964 , pp. 1-2 , 41-45 .

10-H. Sigel , R. Griesser , and B. Prijis , Z.Naturforsch. , 1972 , 27b , 2229 .

11- F. S. M. Hassan , T. A. J. For Science and Engineering , 2005 , 30 , 1A , 29-37 .

12- A. G. Taki , M.S.C. Thesis , Mosul university , 1996 .

13- S. Gh . Gesso , M.S.C. Thesis , Mosul university ,1990 .

14- I. Vogel , “ A Text book of practical organic chemistry’’ , 3rd

ed. , Longmans , Green and Co.Ltd.London , pp.622-

623 , 1964 .

15- W. J.Geary , Coord. Chem. Rev. , 7, 81 , 1971 .

16- J. G. Dauber and M. M. Crane , J. Chem . Edie. , 44 , p. 150 , 1967 .

17- A. S. Azzoz and Kh. I. Al.Niemi , J. Edu. Sci. , 16 , 1 , p-59 , 2004 .

18- A. N. O. Agha ,M. SC. Thesis , Mosul University , 2002 .

19- C. D. Jonhson , (1980) , “ The Hammett Equation “ , Combridge University Press , London , pp. 1-30 .

20- G. B. Kauffman , (1981) , “ Inorganic Coordination Compounds “ , Hyden and Son . Ltd. , p. 18 .

21- M. Charton , Proj. Phys. Org. Chem. ,13 , 178 , 1981 .

14

عىايم انًؤثرة عهي قيى ثىابج اسخقرار بعض إصباغ االزو حعيٍ ودراست ان

عباس عبد األيير كاظى

كهيت انخربيت –جايعت انقادسيت

قسى انكيًياء

: الصةالخ ال

يع فيُىل فهىرو -بارا األزو انًخكىَت يٍ يفاعهت أصباغيىضىع اندراست انرئيسي هى حعيٍ ثىابج اسخقرار بعض ٌأ

( عهعي انخرحيع 3.9, 6.7, 4.5الورياحي . درسج ثىابج االسخقرار نكم صبغت ازو عُد انعداالث انااييعيت انع )د ا األييٍيهح

أيعا عُعد اندانعت ( 4.5 نااييعيت ازو يسعخقرة عُعد اندانعت ا أصعباغاندراسعت ععدو حكعىٌ وأثبخعج حراريعت يتخهفعت عُد خًس درجعاث و

حفعاع)ث حهقائيعت أَهعاثىابعج اسعخقرار . حبعيٍ يعٍ ثريىدايُيًيكيعت حكعىيٍ األصعباغ عهعي فقد حى اناصعىل( 3.9 ( و 6.7 اناايييت

انسعانبت رةاإلشعا أٌانسعانبخيٍ يععا , كًعا بيُعج اندراسعت َفسعها اناعرة انًاخىي اناعراري وانااقعت إشارحيوباع ت نهارارة يٍ خ)ل

ع انًععى فعي األيعيٍ نعث حعوثير واضعح عهعي قعيى حغيعر َعى أٌاندراسعت أثبخعج. كًعا األصعباغنهدانت االَخروبي كاَج يخفقت يع حكعىيٍ

ثىابج اسخقرار أصباغ االزو انًخكىَت يُها .