2082
RIZWANUL HAQUE AND WAHIDU. MALIK
AFel grows with a power of n greater than unity) and the hydrophobic parameters reported here (- A F ~ , grows at less than the first POTVerOf Calculations using only these terms in the Partition functions give maxima between 50 and 100 monomers per micelle. DISCUSSION E. D. GODDARD (Lever Brothers Company).-It has yet to be established whether the main contribution to the positive A S values is due to the hydrocarbon chains or to the water molecules. Very likely it is a combined effect. These high values are in keeping with theories of micelle formation recently advanced; regarding the AH values, however, I would think it somewhat hazardous to extrapolate from a butane or propane chain to a dodecane chain. It would be very useful indeed if the experiments could be repeated to include higher chain length hydrocarbons. A. Wrs”Ia.-If it is agreed that the micellar interior is not very different from a hydrocarbon liquid, in which alkanes would form nearly ideal solutions, then the large positive A S of transfer represents some interaction between the alkane and the solvent. I t is the difficulty of conceiving either (a) exceptional van der Waals interactions between HzO and CH, or CH3 groups or ( b ) eignificant restriction of the translational, vibrational, and rotational motions of the short alkanes (beyond the effect of a condensed
Vol. 67
phase) which has led current theorists of water structure (e.g., ref. 20 and 23) to attribute the greatest part of the entropy of transfer of alkanes to some sort of redistribution in the number of structural bonded and unbonded water molecules. I nould expect that such considerations still hold, in large measure, for longer alkyl chains. A linear extrapolation of the Cs-Cr data for AH to Cl9 would indeed be rash, even if the data were firmly established; as I indicated in the text, this sets an upper limit, with the true A H ~ s a x s very likely less negative. Moreover, as I remarked, the pentane data, after a good many more experiments, are still tentative, and given to too many significant figuresin Table 11: it is not excluded that AHTRAKS for pentane is closer to zero. It is not yet clear whether the uncertainty arises from some variability in residual radioactive impurity or from a real effect of pentane on the micelles, even a t the low pressures used. I have just concluded a eeries of H3 butane experiments a t 25’ between 0.1 and 1.0 atm.; the observed increase in the ratio of Henry’s law coefficients Sx/Ss of about 5% cannot arise from the type of impurity encountered with pentane, and may represent an effect of high levels of butane binding on micellar size which should be easily accessible to light-scattering measurements. Such a system, which is more flexible than studies of detergents of increasing chain length, may illuminate some problems of niicellar structure and afford ~ micelle formation. another F a y of estimating Ape, and A F E of
A SPECTROPHOTOMETRIC STUDY OF THE INTERACTION OF SURFACE-ACTIVE AGEXTS WITH DYES1& BY RIZWANUL H A Q U EAND ’ ~ WAHIDU. MALIK Department o j Chemzstry, Alagarh Muslzm Vnlzverszty, Alagarh, Indza Receked ,March 8, 1963 The interaction of the anionic surface-active agents sulfonated phenyl-, tolyl-, and xylylstearic acids with rosaniline hydrochloride and the cationic agents like dodecyl pyridinium bromide and isothiourea dodecyl ether hydrobromide with congo red, methyl orange, and alizarin sulfonic acid was studied spectrophotometrically. A definite change in the absorption maxima of a dye in the presence of one of these surface-active agents was observed. ,This change in maximum was interpreted in terms of compound formation. The effect of pH and critical miaelle concentration also was Atiidied.
Introduction agents. Later, other ~ o r k e r s ~ 5used - ~ ~this method for the determination of the c.m.c. value. The other The interaction of surface-active agents with subof the interaction are the existence of “metaaspects stances such as proteins,2-5 polymers,6 nucleic acid,’ c h r ~ m a c y ” ~and ~ . ~ ~dye-detergent ~ o m p l e x i n g ~ ~ - * ~ hydrophobic S O ~ S , ~ Jmetal ions, lo and organic dyesll which have not been fully studied and need further has been studied by a number of workers to establish t o understand the phenomenon, especially the work their properties and extend their various uses. Among mechanism of dye-detergent interaction. I n conthese the interaction of dyes and surface-act’ive agents tinuation of our earlier work on the properties of surpresent some interesting features worth considering. face-active agentsZ4v29it was thought worthwhile to Hartleyl‘ noticed that the color of the dye changes investigate the abore aspects of the problem. The with the addition of surface-active agents, and he present conimunicatioii deals with the new interactions utilized this fact, in determining the c o i i c e n t r a t i ~ n l ~ ~ ~ ~ (i) anionic soaps like sulfonated phenyl-, tolyl-, and and critical micelle ~oncentratioiil~ of surface-active xylylstearic acid with rosaniline hydrochloride and (ii) (1) (a) Presented before the 37th National Colloid Symposium of the cationic soaps like dodecyl pyridinium bromide and isoAmerican Chemical Society held at, Ottawa, June 24-26, 1963; (b) Departthiourea dodecyl ether hydrobromide with congo red, ment of Chemistry, University of British Columbia, Vancouver 8, B. C.. Canada. (2) F. W. Putnam, “Advances in Protein Chemistry.” Vol. I V , Academic Press, Inc., New York, N. Y., 1948, p. 80. (3) E. G. Cockbain, Trans. Faraday Sac., 49, 104 (1953). (4) B. S. Harrap and J. H. Schulman, Discussions Faraday Sac., 13, 177 (1953).
(1959).
( 5 ) K. Aoki and J, Hori, J . A m . Chem. Soc., 81,1885 (6) (a) S . Saito, J. Colloid Sci., 16, 283 (1960); (b) Kolloid-Z.,
168, 128 (1960). (7) D. Guerritore and L. Bellelli, Nature, 184, 21, 1638(1950). (8) R. H. Ottewill and -4.Watanabe, Kolloid-Z., 170, 38, 132 (1960). (9) E . Rlatijevi6 and R. H. Ottewill, J . Colloid Sci., 13, 242 (1958). (10) J. H. Schulman, Australian J. Chem., 18, 236 (1960). (11) G. 9. Hartley, Trans. Faraday Soc., 30, 44 (1934). (12) G. 6 . Hartley and D. F. Runnicles, Proc. R o y . Sac. (London), A168, 420 (1938). (13) G. S.Hartley and C. S.Samis, Trans. Faraday Soc., 34, 1288 (1938). (14) G . S. Hartley, J . Chem. Soc., 1968 (1938).
(15) M. L. Corrin and W. D. Harkins, J . A m . Chem. Soc., 69,679 (1947). (16) I. hf. Kolthoff and W. Stricks, J. Phys. Colloid Chem., 62, 915
(1948).
(17) L. Arkin and C. R. Singletcrry, J . Am. Chem. Soc., 70, 3965 (1948). (18) P. Mukerjee and K. J. Mysele, ibid., 7 7 , 2937 (1955). (19) L. Lison, Arch. Biol., 46, 599 (1935). ( 2 0 ) W. C. Holmes, Stain. Technol., 1, 116 (1926). (21) C F. Hiskey and T. A. Downey, J. P h w . Chem., 6 8 , 835 (1954). (22) JI. Hayashi, Bull. Chem. 5oc. Japan, 84, 119 (1961). (23) T. Kondo and K. Meguro, ~ V i p p o nKagaki Zasshi, 77, 1240 (1956). (24) W. U. Malik and R. Haque, Anal. Chem., 82, 1628 (1960). (25) W. U. Malik and R. Haque, Z . anal. Chem., 180,425 (1960). (26) W. U. Malik and R. Haque, Naturwiss., 49,346 (1962). (27) TI‘. E. Malik and R. Haque, Z. anal. Chem., 189, 179 (1962). (28) TV. U. Malik and R. Haque, Nature, 194, 863 (1962). (29) R. Haque and W. U. Maiik, J. PoEarog. Soc., 8 , 36 (19d2).
OCt., 1963
SPEC'CROPHOTOMETRIC S T U D Y O F T H E I K T E R A C T I O N O F
TABLE I ABSORPTIONSPECTRAOF ROSANILINEHYDROCNLORIDE IN THE
SURFACE-ACTIVE AGENTSW I T H DYES 2083 TABLE I1
ABSORPTION SPECTRA OF DYESIN PRESENCE OF CATIONIC SOAPS
PRESENCE OF SULFONATED ARYLSTEARIC ACID Reactants
PH
+ SPSA + SPSA + KPSA + STSA STSA + STSA + SXSA + SXSA + SXSA
(1) Dye Dye Dye (2) Dye Dye+ Dye (3) Dye Dye Dye
Conon. of soap Change in maxima, to change i,he mp maxima in 10-6 M
560-525 560-525 560-525 560-530 560-530 561t530 560-530 560-530 561t530
2.3 4.5 7.0 2.3 4.5 7.0 2.3 4.5 7.0
361.90 180.95 72.38 20.57 18.00 18.00 9.14 9.14 8.00
methyl orange, and alizarin sulfonic acid as studied spectropliotometrica,Ily. Experimental 1. Reagents.-Sulfonated phenyl-, tolyl-, and xylylstearic acids (SPSA, $3TSA, and SXSA), dodecyl pyridinium bromide (DPB), and iciothiourea dodecyl ether hydrobromide (IDEH) were prepared as described earlier.29 The dyes were of B.D.H. products. 2. Apparatus and Tcschnique.-The absorption spectra of the solutions were measured with a Beckman DU spectrophotometer using a 1-em. corex cell with a tungsten lamp as a source of light. The absorbance A which was plotted as a function of wave length is defined by the familiar relation
A
=
1 0
log- = abc
I
(lois the intensity of the light emerging from the solvent, 1 the intensity of the light emerging from the solution, a the abslorptivity, b, the length of the light path through the absorption cell, and e the concentration of the absorbing species expressed in moles/l.) Meamxements were made a t 25 f 0.1'. The p H measurements were made with a Beckman p H meter Model H2. 3. Procedure.-Stock solutions (1.0 X 10-3 M ) of dye rvere prepared in doubly distilled water (all glass). Then 0.5 cc. of this solution was taken in different erlenmeyer flasks and 20 cc. of buffer solution of requisite p H was added. Aliquots of detergent solutions then mere added and the total volume in each case was made up to 25 cc., by the addition of buffer. A period of about 30 min. was allowed in each case to attain equilibrium. The following buffers were used: (i) Walpole buffer (sodium acetate and acetic acid) for acidic p H range; (ii) Clark and Lub's buffer (dipotassium hydrogen phosphate and sodium hydroride) for neutral pB; (iii) Kolthoff buffer (sodium carbonate and hydrochloric acid) for alkaline p H range.
Results and Discussion (a) Anionic Soap and Dye Interaction.-In preliminary experiments on the interaction of sulfonated aryl stearic acids (SPSA, STSA, and SXSA) with rosaniline hydrochloride in acidic and neutral media, it was observed that the color of the dye changes from red to reddish violet in the presence of these agents. By taking the absorption spectra of the dye in the presence of varying amounts of SPSA, STSA, and SXSA it was observed that the absorption peak of the dye was influenced considerably by these soaps. The results are summarized in Table I. The results enumerated therein lead to some interesting features of the reaction between the dye and the anionic soaps under discussion. The most remarka,ble single feature of the study is that the addition of small amounts of these soaps brings about a definite shift in the absorption peak of the dye (560-530 mp in the presence of STSA and SXSA and 560-525 m p in the presence of SPSA). Such a behavior naturally entails either some sort of molecular rearrangement, in
mp
Concn. of soap to ohange the maxima to 10-6 M
650-460 500-460 500-460 490-460 580-475 525-475 500-475 50e475 525-450 475-450 475-450 475-450 520-425 475-425 475-425
48.00 4.00 2.40 6.00 8.00 2.00 2.00 2.00 1200.00 200.00 160.00 120.00 200.00 6.40 4.00
430-450
1200.00
475-530
400.00
520-530
8.00
550-530
18.00
440-550
12.00
525-550
8.00
Change in maxima, Reactants
PH
+ + + + -+ + +
1.3 Congo red DPB 4.3 Congo red DPB 7.0 Congo red DPB 10.3 DPB Congo red 1.5 Congo red IDEH 3.0 Congo red IDEH 7.0 Congo red IDEH 10.2 Congo red IDEH 1.3 Methyl orange DPB 4.3 Methyl orange DPB 7.3 Methyl orange DPB 10.3 iMethyl orange DPB 1.6 Methyl orange IDEH Methyl orange IDEH 4.9 7.3 IDEH Methyl orange Alizarin sulfonic acid 1.6 DPB Alizarin sulfonic acid 4.9 DPB Alizarin sulfonic acid 7.0 DPB Alizarin sulfonic acid 10.3 DPB Alizarin sulfonic acid 3.0 IDEH Alizarin sulfonic acid 7.3 IDEH
+
+
+ + + + + +
+
+ + + + +
the dye molecule or interaction with the surface-active agent. As far as the possibility of the former is concerned it appears to be remote in view of the fact that change in pH from 2.3 to 7.0 does not bring about such a change in the presence of either of the anionic soaps used. However, there is another way by which the absorption value may be influenced, that is by pH. From Table I it may be seen that the amount of anionic soap required to shift the maxima is lesser at higher pH range and vice versa. This effect may be interpreted by assuming that in the acidic medium the ionization of the soap will be suppressed and, therefore a lesser amount of anion will be available for combination with the dye and hence more of the soap will be needed. Just the reverse will happen as the pH increases, i.e., a lesser amount of soap will be needed to give a definite shift. The experimental results support this. Another interesting point to be noted is that the minimum amount of soap required for bringing about a shift in the peak is of the order of c.m.c. with the order SPSA > STSA > SXSA. (b) Cationic Soap and Dye Interaction.-In preliminary experiments the following changes in the color of the dye were observed. (i) The color of congo red in the presence of DPB or I D E H changed from violet t o orange in acidic medium, red to yellowish orange in neutral, and reddish orange to orange in alkaline medium. (ii) The color of methyl orange in the presence of DPB or IDEH changed from orange to yellowish in an acidic medium and orange to yellowish orange in neutral medium. In an alkaline medium precipitation took place in the presence of IDEH, while the color changed from light yellow to yellowish orange in the case of DPB.
RIZWANUL HAQUEAND WAHIDU. MALIK
2084
(iii) The color of alizarin sulfonic acid in the presence of DPB or I D E H changed from yellow to pink in an acidic medium, red to pink in a neutral medium, and violet to pink in an alkaline medium. I n the case of DPB precipitation took place in highly acidic or alkaline medium. The results are summarized iii Table 11. The results described in the foregoing table can again be explained on the basis of definite compound formation between the dye and the cationic soap, although the dye structure here offers reasonable possibilities for the existence of zwitterions (accompanied by possible resonating structures) due to protonation of azo nitrogen. The influence of pH in this investigation cannot be totally ignored. It is especially so with the cationic soap where a high concentration of H+ ions does not in any way effect their ionization and the lesser availability of the cationic part for interaction with the dye cannot be explained in these terms. To account, therefore, for the higher amount of soap solution needed a t low pH, one seeks a probable interpretation in the structure of the dyes themselves. Congo red dye, with its amino and azo nitrogen behaves in a different way from methyl orange and in highly acidic medium would help in the attainment of quinoniod structure. 1. Congo red NHz
"2
I
S03Na
k3Nz(H+)
2.
Methyl orange
1"'
I
SOsNa
Vol. 67
I n Congo red, however, there is a n additional change, the protonation of the -KHz group, which is not present in sulfonic acid and methyl orange. Furthermore, the absence of the highly electron-donating nitrogen from alizarin sulfonic acid may also influence the observation to a certain extent. Both the contentions find support in the experimental results. As already stated a highly acidic medium is required for the protonation of the dye molecule, the fuiiction of the cationic soap appears to reverse the process (i) by attacking the hydrogen of the protonated molecule and (ii) by entering into complex formation with the dye. Since operation (ii) is feasible in the high p H ranges, the only apparent cause as to why more soap is required in the highly acidic solution may be that the hydrogen ion taken up by the dye is gradually removed from the molecule, this process being followed by chemical interaction. As to how much of the soap is used up in the deprotonation of the KH3+and EN+ it is rather difficult to say. It is equally difficult to know a t what stage the chemical interaction between the dye and the soap takes place. I n view of the colloid chemical nature of the substances as well as due to the difference in the structure, the simple interpretation put forward above would not hold good. The ansmer to the question as to why a lesser amount of soap is required in the case of congo red iii spite of the involved deprotonation of SHa+ and EN+ or why the alizarin DPB reaction does not take up the normal course can probably be found here. To sum up it can be said that the following generalizations can be made up regarding the dye-soap interaction: (i) compounds either in the form of double salts or complexes were formed; (ii) presence of soap checks the tendency of molecular rearrangement in the dye solutions with the result that the specific nature of the dye in changing its color within a particular pH range is not realized; (iii) some of the soap is used up in deprotoiiation of the dyes; and finally, (iv) the colloid chemical behavior of the interacting substances especially the c.m.c. of the soaps may markedly affect the course (i) to (iii) given above. Acknowledgments.-Thanks
are due to Professor
A. R. Kidwai for providing facilities, to Dr. RI. S. Ahmad for helpful discussion, and to the Council of Scientific and Industrial Research (India) and the University Grants Commission (India) for financial assistance. Thanks are also due to Dr. L. W. Reeves for his interest and to Professor C. A. McDowell for providing a travel grant to present the paper. We are grateful to Professor Eric Hutchinson of Stanford University for many suggestions.
