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0037-96461811 $ 2.00 t 0.00
0 1987 Conit6 van Bebeer v m h o t B u l l e t i n
Bull. SOC. Chim. Belg. vo1.96/no 611987
THE
EFFECT
OF
SWE
ADDITIVES
ON
THE
AGGREGATION
OF
V.Z.Y.
DYES
M.G. Abd El Wahed, A.K. Abd El Kader and H.M. Killa
Chemistry Department, Faculty of Science, Zagazig r Al-Azhar Unlversities, Egypt
h c d v d : 03/03/1987
- kceptd
: 17/03/1987
ABSTRACT
The effect of additives such as ethanol, urea and KCl on the aggregation
behaviour of C.I. acid red 13 and H. acid azonitrobenzotriazol dyes has been
studied polarographically. The influence of surface active substances such as
albegal B, uniperol 0 am well as levapon AN was also investlgated. The thermodynamic parameters bG, AH and AS were calculated using van 't Hoff's equation.
The results indicate that the electroreduction process proceeds irreversibly
and is diffusion controlled.
INTRODUCTION
The forces of attraction responsible for the interactlone between dye specles and fibers are capable of causing physical interactions between dye species themselves. Consequently, many ionic dyer produce molecular entities ranging In size from dimor to aggregates containing many hundreds of molecules.
A number of techniques have been developed to m a n u r e such aggregation,
but only A few have proved to be satisfactory (1). The methods most c o m o n l y
used have been measuramentr of electrical conductivity and more especially of
diffuaion rates in presence of malts to overcome the potential barrier which
may be caused by the diffusion of some ions faster than the others (2). The
polarographic technique also can provide information on diffuslon coefficient
in presence of salts. It is, however, simpler and quicker, thus enabling the
degree of aggregation to be measured over a wide range of dye concentrations
(3).
The polarographic reduction of p-nitroaniline, m-nitrobenzoic acid as well
as p-nitrobenzaldehyde was studied in solutions of different pH values and varying concentrations of tylore, gelatine and agar (4). These surface active
substance8 not only suppress polarographic maxima, but alter the mechanism of
the process. It is demonstrated by formation of definite steps in the polarographic curves. Actually it possible that the binding by gelatine favours the
rplitting of the polarographic wave due to complex formation (5). Loshkarev
and Kryukova ( 6 ) explained that the effect of surface active substances was
attributed to the uniform penetration through a continuous layer of the absorbed nubstance of ions activated to a higher energy level. The view of such
retarded ion discharge war also considered by Martirosyan and Kryukova (7).
In a continuation of our recent polarographic studies ( 8 , 9 1 , the present
work was undertaken in order to shed light on the effects of some additives on
the aggregation behaviour of C.I. acid red (naphthyl-4-sulphonic acid azo-2hydroxynaphthalene-6-sulphonic acid) and H. acid azonitrobenzotriazol (2-nitrobenzotriazol-azo-2-hydroxy-3-~inon.phthalene-S,8-disodium sulphonate) dyes.
-
423
-
EXPERIHENTAL
The dyes employod woro d i s s o l v e d i n dimethylformamide t o r.move t h e i n o r ganic i m p u r i t i e s , then p r e c i p i t a t e d with acetone. The p r o c i p i t a t e was recryst a l l i s e d from alcohol/water mixture. The s u r f a c e a c t i v e substances, i.e.,
a l b e g r l B ( m p h o t e r i c p o l y g l y c o l ) (10) , u n i p e r o l 0 ( f a t t y alcohol-polyglycol
e t h e r ) (11) and levapon AN ( a l k y l - a r y l polyglycol e t h e r ) ( 1 2 ) were added t o
t h e s o l u t i o n i n s u c c e s s i v e p o r t i o n s by means of a microburette.
The c e l l used has been p r e v i o u s l y d e s c r i b e d ( 8 ) . Average current-potent i a l curves were recor!ed using a polarograph LP No. 1510 (Czechoslovakia).
The mercury h e i g h t wa. 35 cm, t h e rate of mercury flow 2 . 2 7 4 mg/s and d r o p time
2 . 7 3 2 ./drop.
Two methods were used ( 1 3 , 1 4 ) to c a l c u l a t e t h e aggregation number, A, of
dye molecules. They based on measurement of t h e d i f f u s i o n c u r r e n t of t h e dye
s o l u t i o n i n the presence of an excess of an i n e r t s a l t and comparison t o t h a t
o b t a i n e d from a s t a n d a r d i o n s o l u t i o n of t h e same molar c o n c e n t r a t i o n . The
d i f f u 8 i o n c o e f f i c i e n t , D, of t h e dye can then obtained. Knowledge of t h e mol e c u l a r weight of t h e molecule and aggregate allows f o r c a l c u l a t i o n of t h e
aggregation number.
RESULTS AND DISCUSSION
1. C . I . Acid Red 13
Figure 1 shows t h e e f f e c t of temperature on the e l e c t r o r e d u c t i o n of
1.6 x
M of t h e dye a t pH 6 . 2 . As expected, t h e d i f f u s i o n c u r r e n t i n c r e a ses w i t h i n c r e a s i n g temperature. From t h e dependence o f t h e l i m i t i n g c u r r e n t
on t h e e f f e c t i v e mercury head (i-KhX) , it is i n d i c a t e d t h a t the wave is d i f f u The c a l c u l a t e d a na term (n, is t h e number of eleca i o n c o n t r o l l e d (x
0.38).
t r o n s t r a n s f e r r e d per molecule and t h e t r a n s f e r c o e f f i c i e n t ) a t d i f f e r e n t t e m p e r a t u r e s i n d i c a t e s two-one e l e c t r o n r e d u c t i o n s t e p s . The f r e e energy, AG,
c a l c u l a t e d according to van ' t Hoff'e equation is sunmarlsod i n Table 1. I t
is c l e a r t h a t t h e d i f f u s i o n c u r r e n t , id, i n c r e a s e s with temperature and E 1/2
s h i f t s t o more n e g a t i v e v a l u e due t o p r o t o n a t i o n and dis-aggregation of t h e
dye molecule t o i t s monomeric form.
Table 2 s u m a r i s e d t h e e f f e c t of e t h a n o l on the polarographic behaviour
of a c i d red. The aggregation number, A, of t h e dye was c a l c u l a t e d according
-
U
Y
.-b
20
lo
0.3
0.6
0.9
1.2
E, V (SCE)
FIG.
1.
E f f e c t of temperature on a c i d red 1 3 .
-
424
-
1.5
1.8
t o t h e method of Singh ( 1 4 ) . The p l o t o f l o g ( i / ( i - i d )
v)
s E indicates that
t h e r e a c t i o n t a k e s p l a c e i n two s t e p 8 and proceeds i r r e v e r s i b l y a t l o w percent a g e of e t h a n o l . However, a t high a l c o h o l c o n c e n t r a t i o n , t h e r e d u c t i o n take.
p l a c e i n one s t e p . The a d d i t i o n of a p r o t o n donor s h i f t s t h e polarogram t o
more n e g a t i v e p o t e n t i a l s . The decrea8e o f id and D may be a t t r i b u t e d t o the
d i s a g g r e g a t i o n e f f e c t and the i n c r e a s e of t h e v i o c o s i t y of t h e medium on the
e l e c t r o d e s u r f a c e and t h e decrea8e i n i t s d i e l e c t r i c c o n s t a n t , E ( 1 5 ) .
TABLE 1
Temp.
AG
kJ/mol
O C
I
~
~
25
11.2
0.56
0.90
31
14.8
17.0
0.57
0.85
0.68
0.43
0.40
38
17.2
40
46
18.5
20.5
50
0.68
0.66
11.89
0.50
0.65
0.40
=H+
-
20
30
-
4.35
40
4.45
4.60
50
4.80
60
5.12
-
70
5.70
kJ/mol
-
PH
9
1 y:
~~
AS
kJ/mol/deg
8.87
TABLE 2
-
Ethanol
~
1.14
0.87
8.0
7.8
7.2
0.54
0.56
0.86
0.35
0.35
0.57
0.29
0.30
5.0
0.70
-
-
c
visoosit y
oentipolse
74.58
1.43
70.85
66.67
61.99
1.76
2.04
56.68
50.63
2.16
2.25
2.29
g
1.0
TABLE 3
~~~
Concen.
M
Urea
0.08
1.90
2.37
4.70
6.40
8.00
x
x
x
x
x
x
10'2
10-2
10-2
8.8
9.8
10.0
10.5
10.7
10-2
11.0
0.29
0.29
0.29
0.29
0.32
0.31
4.42
5.33
5.92
6.42
7.25
7.42
x
x
x
x
x
x
10-1
10-1
15.5
0.18
10-1
15.5
14.7
14.5
14.0
10-1
13.5
0.19
0.20
0.22
0.24
0.25
0.04
2.85
1
22.25 x
0.55
KC 1
10''
10-1
238.01
1.27
25.26 x
-
425
0.58
238.01
0.37
242.61
-
Table 3 i l l u m t r a t w t h a e f f e c t of urea on polarographic d a t a of a c i d rod
The polamgraaoconmimted of a mingle wave and the id increamem w i t h i n c r e a r i n g c o n c e n t r a t i o n of urea. The El12 was n e a r l y independent upon t h e urea conc e n t r a t i o n . Tho premence of urea caumem dimaggregation of t h e dye molecule#.
The rate c o n i t a n t K wam c a l c u l a t e d according to Esaa ( 1 6 ) and equal t o
3.07 x
The e f f e c t of KC1 i m mhown i n T a b l e 3. The l i m i t i n g c u r r e n t decreames
w i t h increaming K C l c o n c e n t r a t i o n and the half-wave p o t e n t i a l El12 is s l i g h t l y
s h i f t e d t o more negative valuem. Tho aggregation number A h a m been evaluated
uming Stokem-Einmtein aquation. T h e v a l u e s of A is given i n Table 4 i n d i c a t i n g
t h a t the premence of KC1 i n t h e dye molution causes an aggregation o f the dye
molecule8 and A increamem with i n c r e a s i n g both KC1 and the dye c o n c e n t r a t i o n .
The r e v o r m i b i l i t y o f t h e wavem are temted by p l o t t i n g log (i/(i-id)) v s E and
checked by the a p p l i c a t i o n of Tomem equation as rearranped by Meitem (17).
13.
TABLE 4
Concen. o f dye
M
8.0 x 10-4
8 . 0 x 10-4
8.0 x 10-4
1 . 2 x 10-4
3.7 x 10-5
7 . 4 x 10-5
Concen. of KC1
M
D
u.09
1 1 . 4 9 x 10-5
1 1 . 4 9 x 10-5
1 1 . 4 9 x 10-5
3.60 x 10-4
4 . 0 0 x 10-5
4 . 0 0 x 10-5
0.26
1.60
1.60
1.60
1.60
A
1.00
1.00
1.00
1.60
3.6Y
10.6
Tha polaroqraphic behaviour of 3 . 2 x lo-' M a c i d red i n pramence of d i f f e r e n t amounts o f a l b e g a l B is mhown i n FIG. 2 . The poiarograms mhow a mingle
wave with t h r e e maxima which d i s a p p e a r on a d d i t i o n of the s u r f a c e a c t i v e mubmtance, i . e . , a l b e g a l 8 . Am t h e percentage of a l b e g a l B increamem, id decreases and El,2
s h i f t s to more n e g a t i v e v a l u e r . The aggregation number ham been
c a l c u l a t e d , as shown i n Table 5, using H i l l s o n And Mckay method (13). I t is
increamed from 1 . 0 0 t o 3L.5U by i n c r e a s i n g t h e amount of a l b e g a i B. The obt a i n e d remults i n d i c a t e t h a t the number of e l e c t r o n consumed i n t h e r e d u c t i o n
procemr i8 equal t o two in an i r r e v e r m i b l e procems.
Uniperol 0 and lavapon AN s u r f a c e a c t i v e substances g i v e mimilar e f f e c t
on t h e polarographic bahaviour of a c i d r e d , as i l i u m t r a t e d i n Table V. The decreaming v a l u e of id i m a t t r i b u t e d t o t h e aggrogation e f f e c t of tne s u r f a c e
a c t i v e mubmtances and i t m ammociation t o t h a polymeric form. I n a l l r e d u c t i o n
procemmem the l o g a r i t h m i c analymim, i . e . , l o g (i/[i-id))
vs E l g i v e s s t r a i g h t
line..
2 . H. Acid Azonitrobenzotriazoi
Figure 3 mhowm t h e e f f e c t of temporature on the e l e c t r o r e d u c t i o n of
1.08 x
M dye a t pn 6 . 2 .
TI^ polarogrmmconsimt of two wavem. The remultm
i n d i c a t e that El12 f o r tha f i r r t wave remains unchanged over t h a temperature
range f r a n 23' t o 38OC and im m l i g h t l y s h i f t e d to more n e g a t i v e v a l u e s wer
38OC. However, t h e mecond wave behave. i n an o p p o s i t e d i r e c t i o n . The id f o r
both waves i n c r e a s e r w i t h t h e i n c r e a s e of temperature due t o dimaggregation of
-
426
-
t
30
-
.-TI
2
20
3
I
lo
00
0.6
0.3
0.9
1.5
1.2
1.8
E, V ( S C E )
FIG. 2.
Concen.
0
E f f e c t o f albegal B
2 ) 3.2 x
+ 9.9
4 ) 3.2 x
+ 2.9
6 ) 3.2 x
+ 4.9
-V
-id
E
1/2
0.59
0.62
0.62
0.60
0.58
0.61
17.80
17.80
17.20
17.00
0.68
x 10'2
x 10'2
x 10-2
8.2 x 10-2
11.5 x 10-2
16.0 x 10-2
13.20
13.00
12.50
0.77
0.80
0.84
1.9
2.9
4.7
7.4
x
x
x
x
x
x
x
TABLE 5
10-3
10-2
10-2
10'2
10-2
10-2
x 10'2
0.73
0.80
0.82
--
+ 0.00 M,
1) 3.2 x
M, 3 ) 3.2 x
M, 5 ) 3.2 x
M, 7) 3.2 x
+
+
+
1.9 x
3.9 x
5.9 x
-
an
Albegal B
-
1.00
1.30
2.38
8.24
9.50
32.50
-
0.35
1.09
-
1.60
Uniperol 0
kJ/rnol
8.86 x
lo"
331.77
325.29
319.64
-
25.20 x
0.83
1.00
0.97
Levapon AN
0.70
1.30
1.09
M,
M,
M.
AG
A
UA
20.00
18.90
16.95
14.05
12.05
11.00
9.9
1.9
2.9
3.9
4.9
5.9
on acid r e d 13.
x
49.14
50.09
49.01
50.09
58.44
-
14.00 x
40.76
tho dyo molecule t o i t r monomeric form. The a n a l y s i s o f tho wavor d e m o n r t r a t o r
t h a t tho reduction t a k e r p l a c o i r r o v e r s i b l y and it is d i f f u r i o n c o n t r o l l e d
(x .I 0.53).
The variour p o l a r o g r a p h i c and thermodynamic p a r a m e t o r s are g i v e n
i n T a b l e 6.
-
421
-
20
a
v
15
.-U
lo
5
0
0.0
0.3
0.6
1.5
1.2
0.9
E, V ( S C E )
FIG. 3.
acid azonitrobenzotriazol
E f f e c t of temperature on H.
TABLE 6
AS
kJ/mol
28.3
I
I
I
I
32.4
kJ/mol
18.4
I
I 17.9
I
I
kJ/mol/deg
i a t I 2nd
+
3.22
I
I 0.17
I
I
TABLE 7
Concen.
M
x 10-1
x 10-1
x 10-1
x 10-1
5 . 0 x 10-1
5.6 x 10-1
V
2.0
2.7
3.3
4.3
0.416
16.8 x
10
0.62
0.64
0.68
0.747
0.330
0.370
3.13
Tho e f f e c t of KC1 on t h e r e d u c t i o n of a z o n i t r o b e n z o t r i a z o l dye l a r e p o r t e d
The r e s u l t s i n d i c a t e t h a t the number of electrons consumed i n the
i n Table 7.
rate d e t e r m i n i n g s t e p is e q u a l t o one and t h a t t h o r e a c t i o n proceeds v i a an i r r e v e r s i b l e process. The reaction i s a d s o r p t i o n c o n t r o l l e d . The values of A
i n d i c a t e t h a t t h e preaence of K C l causes a a a o c i a t i o n of t h e dye moleculea.
Hence, the presence of t h a a a l t i n d y e b a t h s is recommended t o g i v e level sha-
-
428
-
de8 f o r t h e f i b e r s i n t h e dyeing process.
The e f f e c t of t h e 8urfaoe a c t i v e s u b s t a n c e s ( a l b e g a l B, u n i p e r o l 0 and
levapon FtW) on t h e a g g r e g a t i o n of a z o n i t r o b e n z o t r i a z o l dye is t a b u l a t e d i n
Table 8. I t is clear that t h e t h r e e s u r f a c e a c t i v e s u b s t a n c e s a f f e c t t h e agg r e g a t i o n mtate o f dye molecules (dimer o r trimer forms). The d e p r e s s i o n o f
id i 8 a t t r i b u t e d t o t h e i n c r e a r e of t h e ViSCO8ity of t h e medium, t h e aggregat i o n of the reduced s p e c i e s M t h e e l e c t r o d e s u r f a c e and to i t s presence i n
t h e polymeric s t a t e .
TABLE 8
I
SAS
1
1.
I
Percent of BAS
Albegal B
1.96
2.91
5.85
8.26
8.00
2 . Uniperol 0
x
x 10-2
x 10-2
x 10-2
x 10-3
4.00 x
8.00 x
1.04 x
2.91 x
5.66 x
9.09 x
1.67 x
3. Uvapon AN
10-2
10-2
10-1
10-2
10-2
10-2
10-1
I
1
A
I
1.00
1.15
1.34
1.57
1.00
1.19
2.02
3.21
1.00
1.18
1.40
2.61
Generally, a c i d r e d 13 and acid a z o n i t r o b e n z o t r i a z o l dyes may be regarded
posses8ing t w o d i s t i n c t f e a t u r e s . The hydrophobic aromatic p r o t i o n s t o which
a r e a t t a c h e d s t r u c t u r a l polar groups such a s hydroxyl and m i n o which i n t u r n
a t t r a c t water molecule8. I n a d d i t i o n t h e r e a r e charged group8 which a r e r e a p o n s i b l e , i n t h e main, f o r r e n d e r i n g t h e molecule water s o l u b l e , such as s u l phonic a c i d . The i n t e r f a c i a l a r e a c r e a t e d between t h e hydrophobic p o r t i o n of
each dye molecule and w a t e r , whenever dye molecules are d i s s o l v e d i n water, is
reduced by an overlapping of t h e hydrophobic a r e a s and hence t h e r e w i l l be a
tendency t o aggregate. T h i s is a n e n t r o p i c p r o c e s s brought about by t h e t e n dency of water molecules to r e g a i n t h e entropy l o s t through t h e i n i t i a l dissol u t i o n of the dye molecules. I t is c l e a r t h a t t h e a g g r e g a t e is dimer s i n c e t h e
aromatic r i n g system8 can be con8idered t o have t h e maximum o v e r l a p and t h e
i o n i c groups may be l o c a t e d on o p p o s i t e s i d e s of t h e dlmer making t h e electrical r e p u l s i o n minimal. However, a s t h e dye c o n c e n t r a t i o n i n c r e a s e a , t h e tendency f o r polymeric t o e x i s t w i l l i n c r e a s e .
The a d d i t i o n of e t h a n o l or u r e a to dimeric system cauaes d i 8 a g g r e g a t i o n
where they d e s t r o y t h e i c e b e r g s t r u c t u r e . The presence of u r e a i n c r e a s e s t h e
d i e l e c t r i c c o n s t a n t of water and cannot, t h e r e f o r e , favourably i n f l u e n c e t h e
r e p u l a i o n a l f o r c e s between i o n s t o produce d i s s o c i a t i o n .
The a g g r e g a t i o n i n f l u e n c e of t h e s u r f a c e a c t i v e s u b s t a n c e s as w e l l as
K C l w i l l be due to the i n c r e a s e i n t h e entropy of formation.
They w i l l e f f e c t i v e l y n e u t r a l i s e t h e charge on i n d i v i d u a l a g g r e g a t e s , which w i l l then e a s i l y
coalesce.
-
429
-
REFERENCES
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2. H o l m e m , F.H. and S t a n d i n g , H.A.,
Tranm. Faraday Soc., 4 1 , 542 ( 1 9 4 5 ) .
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4. Holleck, L. and Exner, H., Sbonik Mezinarod Polarog. Sjezdu., P r a z e 1 s t .
Cong. P t , I , 9 7 ( 1 9 5 1 ) .
5. h h h . y r P. and S t r a S O n W , J., J. Am. Chm. SOC., 73, 6232 ( 1 9 5 2 ) .
Zhur. Anal. K h h . , 6, 166 ( 1 9 5 1 ) .
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Abd E l m t t a l b , H., Abd E l Wahed, M.G. and Ayad, M.,
8. Abd E l Kader, A.K.,
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