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1-butanol micelles on crystal violet basic hydrolysis
Influence of CTAB/1-Butanol Micelles on Crystal Violet Basic Hydrolysis M E R C E D E S V A L I E N T E AND ELVIRA R O D E N A S ~ Physical Chemistry Department, Alcald de Henares University, Alcal6 de Henares, Madrid, Spain
Received January I 1, 1988; accepted March 10, 1988 The influence of CTAB/1-BuOH micelles (hexadecyltrimethylammonium bromidel-butanol) on Crystal Violet basic hydrolysishas been studied. The kinetic results can be explained by means of the pseudophase kinetic model. The results strongly suggest that incorporation of 1-butanol to cationic CTAB micelles displaces the substrate from the micellar into the aqueous phase. Different theoretical approaches are discussed in order to explain the results. © 1989AcademicPress,Inc. INTRODUCTION Different nucleophilic substitution reactions (1-3) have been studied in microemulsion systems and it has already been reported that they act in the same way as typical aqueous surfactant solutions. So, microemulsions with cationic droplets catalyze bimolecular reactions with negative ions and inhibit reactions with positive ions, and vice versa ( 4 - 7 ) . The study of alcohol influence in micellar catalysis has considerable significance as alcohols are microemulsion components. In a previous paper the influence of 1-butanol on D D T dehydrohalogenation in cationic CTAB (8) micelles at low alcohol concentrations was reported. In this paper we study the influence of larger alcohol concentrations (nearly saturated solution) on the basic hydrolysis of Crystal Violet catalyzed by CTAB cationic micelles. MATERIALS AND METHODS The surfactant CTAB (Merck) was recrystallized from M e O H / E t 2 0 . Crystal Violet (Merck), l-Butanol (Merck), and N a O H (Carlo Erba) were used without further purification. All the reactions were run at 25.0 + 0.1 °C in the thermostated cuvettes of a Bausch & 1To whom correspondence should be addressed.
0021-9797/89 $3.00 Copyright @ 1989 by Academic Press, Inc. All rights of reproduction in any form reserved.
L o m b Spectronic 2000 spectrophotometer. The reaction was followed at 591 n m which corresponds to substrate absorbance in water. Crystal Violet (0.1 ml) stock solution (5 × I0-4 M in acetonitrile) was added to the suitable surfactant-alcohol-NaOH mixtures prepared in situ in the cuvettes so that the amount of CH3CN in the reaction mixture was 3.3% and the Crystal Violet concentration was 1.6 X 10-5 M in all the experiments. The reaction rate was affected by the a m o u n t ofacetonitrile in solution and other experiments using a substrate stock solution in water (5 X 10 -4 M ) were performed. The hydroxide ions were always greatly in excess with regard to the substrate, and the experimental results fit the pseudo-first-order rate equation. Values of the pseudo-first-order rate constant were obtained by least-squares and fitted correlation coefficients greater than 0.999. T h e values ofmicellar ionization degree, a, have been obtained from conductivity measurements with a C R I S O N 525 conductimeter. The solution flask containing the conductivity cell was immersed in a water bath at 25.0 + 0.1 °C. Previous to measurement, the mixtures ofsurfactant and alcohol were treated with N2, although this treatment did not affect the experimental conductivity values. The substrate distribution between the aqueous and the micellar phases has been
522 Journal of Colloid and Interface Science, Vol. 127, No. 2, February 1989
CTAB]I-BUTANOL MICELLES AND HYDROLYSIS
studied with ultrafiltration. These measurements have been made with the immersible Millipore CX-30 Ultrafilter (tool wt 30~000 out-off), vacuum-operated with a Millipore pump for 2 h. During the ultrafiltration experiments the mixtures were maintained at a constant temperature o f 25.0 +_0, l °C by thermostat, The amount o f acetonitrile in the solutions was 3.3%. The substrate and suffactant concentrations in both filtrate and filtrant were obtained by absorbance and conductivity measurements. The effective dielectric constant in the micellar surface has been estimated from the influence of the different micellar solutions on the intensity peak ratio I~/Im in the normal fluorescence pyrene spectra. The spectra were made in a Perkin-Elmer LS-5B spectrofluorometer, using temperature-controUed cells at 25.0 +_ 0. l°C. Pyrene (Merck) was recrystallized from Methanol; water was Milli-Q (Millipore). RESULTS AND DISCUSSION
The alcohol 1-butanol and acetonitrile increase the conductivity of simple CTAB micelles as can be seen in Fig. 1, where specific conductivities at different CTAB concentrations for different mixtures with and without
523
alcohol and acetonitrile are plotted. The conductivity results at surfactant concentrations below the critical micelle concentration are nearly the same as those for the aqueous CTAB solution. The ionization degrees of miceUes, a, can be obtained as a ratio (9) of slopes of the curves' conductivity vs surfactant concentration, above and below CMC. The values calculated for/5, /5 = 1 - a, for the mixed C T A B / 1 - B u O H micelles have been adapted to the following empirical expression as already reported (10), /3 = 0.80 - 0.5 [ROHM] [Dn] '
[1]
where 0.8 corresponds to the value of/3 for simple ( 1 I) CTAB micelles that according to the conductivity measurements can be considered constant with surfactant concentrations. ROHM and Dn indicate the micellized alcohol and surfactant concentrations. ROHM have been calculated taking into account the incorporation of n-butyl alcohol to CTAB micelles expressed with the equilibrium constant KROFf =
[ROHM ]
[ROHw]([Dn] + [ROHM]) "
[2]
The value of KROH for 1-butanol is 1.0 M -~
i 0.2 -
-1
o
C
E 0.1
-
0.O2
006
0.0~ [CTAB]
(M)
FIG. 1. Variation of the specific conductivity with CTAB concentration (O, [CH3CN] = 0.63 M; O, [1BuOH] = 0.51 M; O, [I-BuOH] = 0.5t M; and [CH3CN] = 0.63 M). Journal of Colloid and Interface Science, Vol. 127, No. 2, February 1989
524
VALIENTE AND RODENAS
as the one obtained by solubility measurements (12). The calculated values with Evans' treatment (13 ) for 13 in the presence of alcohol (using these conductivity measurements) are different from those obtained by the slope ratio, but the slope ratio results agree with other results obtained with a specific ion electrode (14). The 13values obtained for the mixed CTAB / 1-BuOH/acetonitrile micelles by conductivity measurements are well described by the empirical expression [R O H ~ ] [Dn] '
/3=0.74-0.5
[3]
where 0.74 corresponds to the value/3 for the CTAB/acetonitrile micelles at a fixed acetonitrile concentration (0.63 M). This value can be considered constant with surfactant concentrations (Fig. 1). The experimental pseudo-first-order rate constants for the reaction in simple CTAB
•
micelles with and without acetonitrile, at different N a O H concentrations, are represented by dots in Fig. 2. In Figs. 3 and 4 the results for the reaction in the mixtures C T A B / 1 B u O H (1/4 and 1/8) in the presence of acetonitrile are also represented by dots. The resuits at two fixed concentrations of alcohol, 0.096 and 0.51 M , in the presence of acetonitrile and different surfactant concentrations are shown by dots in Fig. 5. Values for the pseudo-first-order rate constant at different alcohol concentrations for fixed CTAB and N a O H amounts, in the absence and presence of acetonitrile, are represented in Fig. 6. In Fig. 7 the experimental pseudo-first-order rate constants for the reaction in the C T A B / 1 B u O H system (in presence of acetonitrile) at fixed CTAB and alcohol concentrations and different amounts of KBr are represented by dots. As you can see, alcohol and acetonitrile inhibit the reaction. The alcohol effect becomes
.~,. \ \ •
\
\
0.04
,.¢1
0.02
} 0.02
) 0.04
•
~
I 0.00
} 0.08 [CTAB] (N)
FIG. 2. Variation of the pseudo-first-orderrate constant,/~, with CTAB concentration in the absence of acetonitrile (0, [NaOH ] = 0.010 M; and O, [NaOH ] = 0.006 M) and in the presence of acetonitrile (O, [NaOH] = 0.010 M; ©, [NaOH] = 0.006 M; and O, [NaOH] = 0.002 M). Journal of Colloid and Interface Science, VoL 127, No. 2, February 1989
CTAB/1-BUTANOL MICELLES AND HYDROLYSIS I
I
525
I
I
Q
0.02
0
r
I
I
0.02
0.04
-
I
I
O.Ofi
0.08 [CTAB] (~
FIG. 3. Variation of the pseudo-first-orderrate constant, k4, in the CTAB/1-BuOH (l/4) system with CTAB concentration in the presence of acetonitrile (e, [NaOH] = 0.010 M; and (3, [NaOH] = 0.006 M). larger as alcohol incorporation in the micelles increases. All the kinetic results can be explained by means of the pseudophase kinetic model proposed by Menger (15) and developed by Bunton (16) and Romsted ( 17 ). This model considers the micelle phase different from the
aqueous phase and that the reaction occurs in both phases according to the scheme Sw + Dn ~ I k"
Ks
~ SM
.ProdJ
kM
where k~ and kM denote the pseudo-first-order
I
I
I
0,02
0.04
0.06
'tn
2 0.02
0
0.08 LCTAB] (M)
FIG. 4. Variation of the pseudo-first-order rate constant, k~, in the CTAB/l-BuOH (1/8) system with
CTAB concentration in the presence of acetonitrile (O, [NaOH] = 0.010 M; O, [NaOH] = 0.006 M; and O, [NaOH] = 0.002 M). Journal of Colloid and Interface Science, VoL 127, No. 2, February 1989
526
VALIENTE A N D RODENAS
r
r/
~
~
0
1
I
'
I 0.02
I 0.0~,
I
I
t 0.06
1| 0.08 [CTAS]
(1~
FIG. 5. Variation of the pseudo-first-order rate constant, k~, with CTAB concentration at fixed 1-BuOH (0.096 and 0.51 M ) concentrations in the presence ofacetonitrile ( e , [ N a O H ] = 0,010 M ; and ©, [ N a O H ]
= 0.0o6 M). rate constants for the reaction in aqueous and micellar pseudophases, respectively, k~, is given by k " = koH[OH,~] + kH2o, where koH is the second-order rate constant in the aqueous phase for the hydroxide ion attack on the substrate, with values 0.143 and 0.201 liter mole-1 s-1 (18 ) for the reaction with and without acetonitrile, and k m o is the rate constant for the reaction with H 2 0 with values 3.6 × 10 -4 and 1.94 × 10 -5 s -1 (18). The alcohol in the concentration range used did not affect the rate constant for the reaction in water. Values of the pseudo-first-order constants for the reaction in 1-butanol-H20 mixture at higher amounts of alcohol are given in Table I. These results can be adapted to a typical variation with the solution dielectric constant, Ink = Inko
ZAZBe 2 ¢aKT '
electric constant at 25°C for each of the components. kM, the rate constant for the reaction in micellar pseudophase, is written in terms of the mole ratio of micellized O H - bound to the micellized surfactant, with dimensions of a first-order rate constant. The substrate binding constant has been defined as
[SM] Ks = [Sw]([Dn] + [ROHM]) '
[5]
where [ROHM ] is the alcohol concentration in the micellar pseudophase given by Eq. [ 2 ]. A pseudo-first-order rate constant can be easily derived as koH[OH]
k~ =
+ kH20 + ( k M K s ( ( [ R O H M ]
+ [ D n ] ) / [ D n ] ) - kOH)[OHM] 1 + Ks([Dn] + [ROHM]) ' [63
[4]
with a value o f a = 3.9 A. The dielectric constant ~ has been calculated according to the expression (19) 6 ~ ~ROHXROH "~ 6CH3CNXCH3CN "~- ~H2OXH20~
where x is the volume fraction and ~ the diJournal of Colloidand InterfaceScience, Vol. 127,No. 2, February 1989
where [ O H ] = [ OHM ] + [ OHw ]. When two ions compete for the micellar head groups, Romsted (17) proposed a model for the reaction in simple surfactant micelles that considers/3 to be a constant and that ions were bound to miceUes according to the exchange model developed for resins. In the case
527
CTAB/I-BUTANOL M1CELLES AND HYDROLYSIS 1
I
I
t
I
0.0 Z
m v
0.02
...... 0
t
I
I
I
I
0.1
0.2
0.3
0.4
0.5 r 1-Bu0H] (M)
FIG. 6. Variation of the pseudo-first-order rate constant,/~, with 1-BuOH concentration at fixed CTAB (0.012 M) and NaOH (0.010 M) concentrations in the ( ~ ) absence and ( • ) presence of acetonitrile.
I
L
I
i
0,0 4
L .
.0:
0
I
I
I
0.02
0.04
0.06
0-08
[KBr~ (M)
FiG. 7. Variation o f the pseudo-first-order rate constant, k~, with K B r concentration at fixed N a O H (0.01 M ) and C T A B (0.012 M ) concentrations in the presence o f acetonitrile ( e , [1-BuOPI] = 0.0 M ; and II, [IBuOH] = 0.096 M). Journal of Colloid and Interface Science,
"Col.127,No. 2, February1989
528
VALIENTE A N D RODENAS TABLE I Variation of Pseudo-First-Order Rate Constant with the Dielectric Constant
In k 1/e × 100 XROH
-2.09 5.29 0.947
-2.77 4.92 0.923
-2.83 4.59 0.900
of competing O H - and Br- ions, the OHM value is given by [OHM] / 2
x \(([oH](_k~o~ 1-~6~+ - K °~ [X]) _ ~) fl[OH] (K °H - 1)[Dn]
= 0,
where K °r~ is the ion exchange equilibrium constant for OH- and Br- in the micellar surface and [Br] is the total concentration of bromide ions. In our treatment for the reaction in mixed micelles, we consider the same exchange equilibrium between OH- and Br- on the surface of mixed micelles but with a variation in the fraction of the neutralized micellar head group, t, given by the expressions [ 1, 3 ] that correspond to mixed CTAB/1-BuOH micelles and mixed CTAB / 1-BuOH / acetonitrile micelles. The experimental results can be adapted to this model by simulation techniques, with the values of known parameters, k ' , CMC, and ~, and using kM, Ks, and K °H as adjustable parameters. The values of CMC do not appreciably affect the values of the pseudo-first-order rate constant but the following variation (20, 21) with ions has been used for simple CTAB micelles and mixed micelles, lg CMC = -3.7671 - 0.2133 lg(CM + [OH]), where CM are the critical micelle concentrations in the absence of ions in solution: 9 × 10-4 M for simple CTAB micelles (22) and 1.3 × 10 -3 M for mixed CTAB/1-BuOH/ Journal of Colloid and Interface Science, Vol. 127, No. 2, February 1989
-3.32 4.31 0.877
-4.32 3.87 0.833
-8.56 1.29 0
acetonitrile micelles. No CM variation with alcohol incorporation has been considered because there is disagreement in the literature (14, 23-27 ) about these CM values and small changes in CMC do not affect our kinetic parameters. The values of parameters that explain the results for the reaction in simple CTAB micelles in the presence and absence of acetonitrile are shown in Table II. Values of t calculated with these parameters in the presence and absence of acetonitrile are solid and dashed lines in Fig. 2, respectively. In order to explain the results it is necessary to consider an increase in the value of the substrate binding constant to the micelle, Ks, explained by a salting-out effect (28-30) or by a decrease of Coulombic repulsion (31-33). This effect for additional Br- ion results has been taken into account for the following variation in Ks, Ks = / ~ + 700[KBr], where K ° is the substrate binding constant to simple CTAB micelles in the absence of additional Br- ions. The kinetic results in mixed CTAB/1BuOH/acetonitrile micelles can be explained TABLE II Parameters That Best Fit the Kinetic Results for Crystal Violet in CTAB [NaOH] (M)
k~ (s-t)
K~,(M -I)
h~ n
B
0.002 0.006 0.010 0.006 a 0.010 b
0.46 0.46 0.46 0.46 0.46
40 60 70 70 90
4 4 4 4 4
0.74 0.74 0.74 0.80 0.80
In absence of acetonitrile.
C T A B / I - B U T A N O L MICELLES A N D HYDROLYSIS
by using two different approaches. One considers the following empirical expressions for kM and Ks, = k° + c
[ROHM] [Dn]
[7]
K0
Ks = 1 + c ' ( [ R O H M ] / [ D n ] ) '
[8]
where k ° and K ° are the values of the parameters used in the reaction with simple micelles in the presence of acetonitrile, and a constant value for K °H. In Figs. 2-7 the calculated values for ~ with this treatment are shown by solid lines, with c ' = 1 0 a n d c = 0 . 9 7 s -~. The other approach considers the same variation in the micelle substrate binding constant, Ks, with alcohol incorporation, but it gives a constant value for kM and a decrease in the exchange equilibrium constant with the fraction of micellized alcohol given by the expression KOH =
K °H° 1 + c"([ROHM]/[Dn]) "
[91
The same values for parameters used in the former treatment and a value of c" = 4 explain the results. Calculated values of pseudo-firstorder rate constants are dashed lines in all the figures. Both approaches predict a decrease in Ks with the 1-butanol incorporation in the micelles. This variation in Ks with 1-butanol incorporation in the micelle is consistent with the ultrafiltration measurements. Table III shows the substrate absorbances and micellized surfactant concentrations in both filtrate TABLE III Substrate Absorbance and Micellized Surfactant Concentration Obtained from Ultrafiltration Measurements in Filtrate (F) and Filtrant (f) [I-BuOH] (M)
[Dn]f(34)
[Dn]F(M)
Absr
Absr
0 0 0,51
0.003 0.005 0,008
0 0 0,005
1.53 1.53 1.53
1.04 0.92 1.20
529
and filtrant. A value for substrate binding constant to simple CTAB micelles has been determined from the results in the absence of alcohol according to the theoretical treatment in the literature (34, 35), Ks -~ 122 M -1 . For micelles with 1-butanol, the results show that a large amount of miceUes passes through the ultrafilter pore agreeing with other results in the literature showing that alcohol incorporation produces a decrease in the micellar aggregation number (36-40) and the calculated value results to be Ks -~ 6 M -1 . The decrease in the substrate binding to micelles, for this positively charged substrate, can be related to the increase in micellar surface ionization. So increasing the positive charge on the micellar surface increases the repulsion to the substrate. This conclusion is consistent with others reported (32, 33) Ks values. The variation in the kM, rate constant for the reaction in the micellar phase, can be related with two different factors. It can be related to the influence of alcohol in the micellar surface dielectric constant because of the increase in the micelle ionization degree. And it is also associated to the presumable alcohol effect in the molar volume of the micellar surface where the reaction occurs. This micellar rate constant, kM, can be converted to a second-order rate constant, kin, considering the volume element (41) where the reactions occurs. For the reaction in simple CTAB micelles, the micellar pseudophase molar volume is 0.371 M -~, so that the second-order rate constant is k m = 0.173 M -1 s -1 . According to the fluorescence results, alcohol incorporation produces a decrease in the peak intensity ratio IJIm in the pyrene spectra (Table IV) agreeing with other results in the literature (36). This peak ratio can be correlated with the decrease in the micellar surface dielectric constant (42, 43). The peak ratio is practically unaffected either by the surfactant concentration or by the amount of acetonitrile used in the experiments (44). From all of the results (36 measurements at different surfactant and alcohol concentrations and [ ROHM ] / [ Dn ] ~ I) the following empirical expression Journal of Colloid and Interface Science, Vol. 127,No. 2, February 1989
530
VALIENTE AND RODENAS TABLE IV
Variation of Peak Intensity Ratio in the Pyrene Spectra at Fixed CTAB (0.010 M) Concentration with the Alcohol Concentration [ I-BuOH] (M) 1~/lm
0 1.31
0.11 1.27
0.22 1.24
0.32 1.21
0.43 1.18
can be obtained for the peak ratio with 1-butanol incorporated to the micelle, Ii]Iln = a + b
[ROHM] [Dn] '
with a = 1.29 __+0.01 and b = - 0 . 1 3 _+ 0.02. According to the results, there is a decrease in the micellar surface dielectric constant with the alcohol incorporation that ranges from a value of 33-36 for simple CTAB micelles down to a value of 12-17 when [ ROHM ] / [ Dn ] = 1. The decrease in ~ increases the second-order rate constant in the micellar phase, and can be estimated with expression [4] using as reference the second-order rate constant for the reaction in simple CTAB micelles. The error in the micellar surface dielectric constant determination does not allow the real rate constant value to be calculated and it is only possible to conclude that the increase explains the large variation in kM parameter. The second treatment is justified by considering that alcohol incorporation produces an increase in the miceUized hydroxide ions to micellized bromide ions ratio because of i o n dipole interactions between O H - and l-butanol. The constant value in the kM parameter and the big increase in the second-order rate constant, because of the variation in the micellar surface dielectric constant for alcohol incorporation, can be related to the increase in the volume of the micellar phase per mole of micellized surfactant. According to all these results we can conclude that the incorporation of alcohol in simple CTAB micelles inhibits basic hydrolysis of Crystal Violet. This inhibition effect is related to the decrease in the fraction of the micellar head group that is neutralized and in the disJournal of Colloid and Interface Science, Vol. 127, No. 2, February 1989
placement of this substrate from the micellar into the aqueous phase with alcohol incorporation (Eq. 8). Alcohol incorporation also produces a decrease in the micellar surface dielectric constant that increases the rate constant in the micellar phase, but it is not possible to determine if this variation is large enough to explain kinetic results with a variation in kM (Eq. 7), or if it is necessary to consider the increase in the micellar phase volume per mole of micellized surfactant and an additional amount of micelle-bound hydroxide ions (Eq. 9). REFERENCES 1. Athanassakis, V., Bunton, C. A., and de Buzzaccarini, F., J. Phys. Chem. 86, 5002 (1932); Bunton, C. A., and de Buzzaccarini, F., J. Phys. Chem. 86, 5010 (1982). 2. Bunton, C. A., Buzzacarini, F., and Hamed, F. H. J. Org. Chem. 48, 2461 (1983). 3. Martin, C. A., McGrann, P. H., Ward, M. D,, Angelus, G. H., and Jaeger, D. A., J. Org. Chem. 49, 4392 (1984). 4. Fendler, J, H., and Fendler, E. J., "Catalysis in Micellar and Macromolecular Systems." Academic Press, New York, 1975. 5. Martinek, K., Yatsimirski, A., Levashov, A. V,, and Berezin, I. V., "Micellization, Solubilization, and Microemulsions," (K. L. Mittal, Ed.), Vol. 2. Plenum, New York, 1977. 6. "Inorganic Reactions in Organized Media" (S. L. Holtz, Ed.). A.C.S. Symposium Series, Amer. Chem. Soc., Washington, DC, 1982. 7. Mittal, K. L., and Fendler, E. J., "Solution Behavior of Surfactants." Plenum, New York, 1982. 8. Otero, C., and Rodenas, E., J. Phys. Chem. 90, 5771 (1986). 9, Hoffmann, H., and Ulbricht, W., Z. Phys. Chem. N. F., 106, 167 (1977); Hoffmann, H., and Tagesson, B., Z. Phys. Chem. N. F., 110, 8 (1978). 10. Valiente, M., and Rodenas, E., An. Quim., in press. I 1. Sepfilveda, L., and Cortes, J., J. Phys, Chem. 89, 5322
(1985). 12. Gettins, J., Hall, D., Jobling, P. L., Rassing, J. E., and Wyn-Jones, E., J. Chem. Soc., Faraday Trans. 2 74, 1957 (1978). 13. Evans, H. C., £ Chem. Soc., 579 (1956). 14. Zana, R., Yiv, S., Strazielle, C., and Lianos, P. £ Colloid Interface Sci. 80, 208 (1981). 15. Menger, F. M., and Portnoy, C. E., J. Amer. Chem. Soc, 89, 4698 (1967). 16. Bunton, C. A., CataL Rev. Sci. Eng. 20, 1 (1979). 17. Romsted L. S., "Micellization, Solubilization, and
CTAB/1-BUTANOL MICELLES AND HYDROLYSIS Microemulsions (K. L., Mitlal, Ed.), Vol. 2, p. 509. Plenum, New York, 1977. 18. Ritchie, C. D., Wringht, D. J., Huang, D-S., and Kamego, A. A., J. Amer. Chem. Soc. 97, 1163 (1975). 19. Decroog, D., Bull. Soc. Chim. Fr., 127 (1964). 20. Shinoda, K., Nakagawa, T., Tamanuschi, B., and Isemura, T., "Colloidal Surfaetants." Academic Press, New York, 1963. 21. Bunton, C. A., and Robinson, L., J. Amer. Chem. Soc. 90, 5972 (1968). 22. Mukerjee, P., and Mysels, K. J., "Critical Micetle Concentration of Aqueous Surfactant Systems" Nation~ Bureau of Standards "Washington, DC, i971; NSRDS-NBS 20420. 23. Shirahama, K., and Kashiwabara, T., J. Colloid Interface Sci. 36, 65 (1971). 24. Miyagishi, S., Bull. Chem. Soc. Japan 48, 2349 (1975). 25. Singh, H. N., and Swarup, S., Bull. Chem, Soc: Japan 51, t534 (1978). 26. Abu-Hamdiyyah, M., J. Phys: Chem. 90, 1345 (I986). 27. Rao, V. 1., and Ruckestein, E., J. Colloid Interface Sci. 113, 375 (I986). 28. Bunton, C. A., Romsted, L. S., and Thamavit, C., J. Amer. Chem. Soc. 102, 390 (1980). 29. Rodenas, E., and Vera, S., J. Phys. Chem. 89; 513 (1985). 30. Otero, C., and Redenas, E., Canad. J. Chem. 63, 2892 (1985).
531
31. Bunton, C. A., Carraseo, N., Huang, S. K., Paik, C. H., and Romsted, L. S., J. Amer. Chem. Soe. 100, 5420 (1978). 32. Ortega, F., and Rodenas, E., J. Phys. Chem. 90, 2408 (I986). 33. Vera, S., and Rodenas, E., J. Phys. Chem. 90, 3414 (1986). 34. Langkruis, G. B., and Engberts, J. B. F. N., Tetra, hedron 41, 399i (1979). 35. Hirose, C., and Sepfflveda, L., J. Phys. Chem. 85, 3689 (1981). 36. Llanos, P., and Zana, R., Chem. Phys. Lett. 72, 171 (I980); 76, 62 (19:80). 37. Yiv; S., Zana, R., Ulbricht, W., and Hoffmann H., J. Colloid Interface Sci~ 80, 224 (1981). 38. Candau, S., and Zana, R., J. Colloid Interface Sci. 84, 206 (1981). 39. Almgren, M., and Swarup, S, J. Colloid Interface Sci. 91, 256 (198:3). 40. Lang, J., and Zana, R., or. Phys. Chem: 90, 5258 (t986). 41. Guveli, D. E., Hayes, J. B, and Davis, S~S., J. Colloid Interface Sei. 82, 307 (1981). 42. Dong, D., and Winnik, M. A., Photochem; Photobiol. 35; 17 (1982). 43. Kalyanasundaram, K., and Thomas, J. K., J. Amer. Chem. Soc. 99, 2039 (1977). 44. Results obtained in our laboratory for E. P6rez.
Journal of Colloid and Interface Science, Vol. 127~No. 2, February 1989
Received January I 1, 1988; accepted March 10, 1988 The influence of CTAB/1-BuOH micelles (hexadecyltrimethylammonium bromidel-butanol) on Crystal Violet basic hydrolysishas been studied. The kinetic results can be explained by means of the pseudophase kinetic model. The results strongly suggest that incorporation of 1-butanol to cationic CTAB micelles displaces the substrate from the micellar into the aqueous phase. Different theoretical approaches are discussed in order to explain the results. © 1989AcademicPress,Inc. INTRODUCTION Different nucleophilic substitution reactions (1-3) have been studied in microemulsion systems and it has already been reported that they act in the same way as typical aqueous surfactant solutions. So, microemulsions with cationic droplets catalyze bimolecular reactions with negative ions and inhibit reactions with positive ions, and vice versa ( 4 - 7 ) . The study of alcohol influence in micellar catalysis has considerable significance as alcohols are microemulsion components. In a previous paper the influence of 1-butanol on D D T dehydrohalogenation in cationic CTAB (8) micelles at low alcohol concentrations was reported. In this paper we study the influence of larger alcohol concentrations (nearly saturated solution) on the basic hydrolysis of Crystal Violet catalyzed by CTAB cationic micelles. MATERIALS AND METHODS The surfactant CTAB (Merck) was recrystallized from M e O H / E t 2 0 . Crystal Violet (Merck), l-Butanol (Merck), and N a O H (Carlo Erba) were used without further purification. All the reactions were run at 25.0 + 0.1 °C in the thermostated cuvettes of a Bausch & 1To whom correspondence should be addressed.
0021-9797/89 $3.00 Copyright @ 1989 by Academic Press, Inc. All rights of reproduction in any form reserved.
L o m b Spectronic 2000 spectrophotometer. The reaction was followed at 591 n m which corresponds to substrate absorbance in water. Crystal Violet (0.1 ml) stock solution (5 × I0-4 M in acetonitrile) was added to the suitable surfactant-alcohol-NaOH mixtures prepared in situ in the cuvettes so that the amount of CH3CN in the reaction mixture was 3.3% and the Crystal Violet concentration was 1.6 X 10-5 M in all the experiments. The reaction rate was affected by the a m o u n t ofacetonitrile in solution and other experiments using a substrate stock solution in water (5 X 10 -4 M ) were performed. The hydroxide ions were always greatly in excess with regard to the substrate, and the experimental results fit the pseudo-first-order rate equation. Values of the pseudo-first-order rate constant were obtained by least-squares and fitted correlation coefficients greater than 0.999. T h e values ofmicellar ionization degree, a, have been obtained from conductivity measurements with a C R I S O N 525 conductimeter. The solution flask containing the conductivity cell was immersed in a water bath at 25.0 + 0.1 °C. Previous to measurement, the mixtures ofsurfactant and alcohol were treated with N2, although this treatment did not affect the experimental conductivity values. The substrate distribution between the aqueous and the micellar phases has been
522 Journal of Colloid and Interface Science, Vol. 127, No. 2, February 1989
CTAB]I-BUTANOL MICELLES AND HYDROLYSIS
studied with ultrafiltration. These measurements have been made with the immersible Millipore CX-30 Ultrafilter (tool wt 30~000 out-off), vacuum-operated with a Millipore pump for 2 h. During the ultrafiltration experiments the mixtures were maintained at a constant temperature o f 25.0 +_0, l °C by thermostat, The amount o f acetonitrile in the solutions was 3.3%. The substrate and suffactant concentrations in both filtrate and filtrant were obtained by absorbance and conductivity measurements. The effective dielectric constant in the micellar surface has been estimated from the influence of the different micellar solutions on the intensity peak ratio I~/Im in the normal fluorescence pyrene spectra. The spectra were made in a Perkin-Elmer LS-5B spectrofluorometer, using temperature-controUed cells at 25.0 +_ 0. l°C. Pyrene (Merck) was recrystallized from Methanol; water was Milli-Q (Millipore). RESULTS AND DISCUSSION
The alcohol 1-butanol and acetonitrile increase the conductivity of simple CTAB micelles as can be seen in Fig. 1, where specific conductivities at different CTAB concentrations for different mixtures with and without
523
alcohol and acetonitrile are plotted. The conductivity results at surfactant concentrations below the critical micelle concentration are nearly the same as those for the aqueous CTAB solution. The ionization degrees of miceUes, a, can be obtained as a ratio (9) of slopes of the curves' conductivity vs surfactant concentration, above and below CMC. The values calculated for/5, /5 = 1 - a, for the mixed C T A B / 1 - B u O H micelles have been adapted to the following empirical expression as already reported (10), /3 = 0.80 - 0.5 [ROHM] [Dn] '
[1]
where 0.8 corresponds to the value of/3 for simple ( 1 I) CTAB micelles that according to the conductivity measurements can be considered constant with surfactant concentrations. ROHM and Dn indicate the micellized alcohol and surfactant concentrations. ROHM have been calculated taking into account the incorporation of n-butyl alcohol to CTAB micelles expressed with the equilibrium constant KROFf =
[ROHM ]
[ROHw]([Dn] + [ROHM]) "
[2]
The value of KROH for 1-butanol is 1.0 M -~
i 0.2 -
-1
o
C
E 0.1
-
0.O2
006
0.0~ [CTAB]
(M)
FIG. 1. Variation of the specific conductivity with CTAB concentration (O, [CH3CN] = 0.63 M; O, [1BuOH] = 0.51 M; O, [I-BuOH] = 0.5t M; and [CH3CN] = 0.63 M). Journal of Colloid and Interface Science, Vol. 127, No. 2, February 1989
524
VALIENTE AND RODENAS
as the one obtained by solubility measurements (12). The calculated values with Evans' treatment (13 ) for 13 in the presence of alcohol (using these conductivity measurements) are different from those obtained by the slope ratio, but the slope ratio results agree with other results obtained with a specific ion electrode (14). The 13values obtained for the mixed CTAB / 1-BuOH/acetonitrile micelles by conductivity measurements are well described by the empirical expression [R O H ~ ] [Dn] '
/3=0.74-0.5
[3]
where 0.74 corresponds to the value/3 for the CTAB/acetonitrile micelles at a fixed acetonitrile concentration (0.63 M). This value can be considered constant with surfactant concentrations (Fig. 1). The experimental pseudo-first-order rate constants for the reaction in simple CTAB
•
micelles with and without acetonitrile, at different N a O H concentrations, are represented by dots in Fig. 2. In Figs. 3 and 4 the results for the reaction in the mixtures C T A B / 1 B u O H (1/4 and 1/8) in the presence of acetonitrile are also represented by dots. The resuits at two fixed concentrations of alcohol, 0.096 and 0.51 M , in the presence of acetonitrile and different surfactant concentrations are shown by dots in Fig. 5. Values for the pseudo-first-order rate constant at different alcohol concentrations for fixed CTAB and N a O H amounts, in the absence and presence of acetonitrile, are represented in Fig. 6. In Fig. 7 the experimental pseudo-first-order rate constants for the reaction in the C T A B / 1 B u O H system (in presence of acetonitrile) at fixed CTAB and alcohol concentrations and different amounts of KBr are represented by dots. As you can see, alcohol and acetonitrile inhibit the reaction. The alcohol effect becomes
.~,. \ \ •
\
\
0.04
,.¢1
0.02
} 0.02
) 0.04
•
~
I 0.00
} 0.08 [CTAB] (N)
FIG. 2. Variation of the pseudo-first-orderrate constant,/~, with CTAB concentration in the absence of acetonitrile (0, [NaOH ] = 0.010 M; and O, [NaOH ] = 0.006 M) and in the presence of acetonitrile (O, [NaOH] = 0.010 M; ©, [NaOH] = 0.006 M; and O, [NaOH] = 0.002 M). Journal of Colloid and Interface Science, VoL 127, No. 2, February 1989
CTAB/1-BUTANOL MICELLES AND HYDROLYSIS I
I
525
I
I
Q
0.02
0
r
I
I
0.02
0.04
-
I
I
O.Ofi
0.08 [CTAB] (~
FIG. 3. Variation of the pseudo-first-orderrate constant, k4, in the CTAB/1-BuOH (l/4) system with CTAB concentration in the presence of acetonitrile (e, [NaOH] = 0.010 M; and (3, [NaOH] = 0.006 M). larger as alcohol incorporation in the micelles increases. All the kinetic results can be explained by means of the pseudophase kinetic model proposed by Menger (15) and developed by Bunton (16) and Romsted ( 17 ). This model considers the micelle phase different from the
aqueous phase and that the reaction occurs in both phases according to the scheme Sw + Dn ~ I k"
Ks
~ SM
.ProdJ
kM
where k~ and kM denote the pseudo-first-order
I
I
I
0,02
0.04
0.06
'tn
2 0.02
0
0.08 LCTAB] (M)
FIG. 4. Variation of the pseudo-first-order rate constant, k~, in the CTAB/l-BuOH (1/8) system with
CTAB concentration in the presence of acetonitrile (O, [NaOH] = 0.010 M; O, [NaOH] = 0.006 M; and O, [NaOH] = 0.002 M). Journal of Colloid and Interface Science, VoL 127, No. 2, February 1989
526
VALIENTE A N D RODENAS
r
r/
~
~
0
1
I
'
I 0.02
I 0.0~,
I
I
t 0.06
1| 0.08 [CTAS]
(1~
FIG. 5. Variation of the pseudo-first-order rate constant, k~, with CTAB concentration at fixed 1-BuOH (0.096 and 0.51 M ) concentrations in the presence ofacetonitrile ( e , [ N a O H ] = 0,010 M ; and ©, [ N a O H ]
= 0.0o6 M). rate constants for the reaction in aqueous and micellar pseudophases, respectively, k~, is given by k " = koH[OH,~] + kH2o, where koH is the second-order rate constant in the aqueous phase for the hydroxide ion attack on the substrate, with values 0.143 and 0.201 liter mole-1 s-1 (18 ) for the reaction with and without acetonitrile, and k m o is the rate constant for the reaction with H 2 0 with values 3.6 × 10 -4 and 1.94 × 10 -5 s -1 (18). The alcohol in the concentration range used did not affect the rate constant for the reaction in water. Values of the pseudo-first-order constants for the reaction in 1-butanol-H20 mixture at higher amounts of alcohol are given in Table I. These results can be adapted to a typical variation with the solution dielectric constant, Ink = Inko
ZAZBe 2 ¢aKT '
electric constant at 25°C for each of the components. kM, the rate constant for the reaction in micellar pseudophase, is written in terms of the mole ratio of micellized O H - bound to the micellized surfactant, with dimensions of a first-order rate constant. The substrate binding constant has been defined as
[SM] Ks = [Sw]([Dn] + [ROHM]) '
[5]
where [ROHM ] is the alcohol concentration in the micellar pseudophase given by Eq. [ 2 ]. A pseudo-first-order rate constant can be easily derived as koH[OH]
k~ =
+ kH20 + ( k M K s ( ( [ R O H M ]
+ [ D n ] ) / [ D n ] ) - kOH)[OHM] 1 + Ks([Dn] + [ROHM]) ' [63
[4]
with a value o f a = 3.9 A. The dielectric constant ~ has been calculated according to the expression (19) 6 ~ ~ROHXROH "~ 6CH3CNXCH3CN "~- ~H2OXH20~
where x is the volume fraction and ~ the diJournal of Colloidand InterfaceScience, Vol. 127,No. 2, February 1989
where [ O H ] = [ OHM ] + [ OHw ]. When two ions compete for the micellar head groups, Romsted (17) proposed a model for the reaction in simple surfactant micelles that considers/3 to be a constant and that ions were bound to miceUes according to the exchange model developed for resins. In the case
527
CTAB/I-BUTANOL M1CELLES AND HYDROLYSIS 1
I
I
t
I
0.0 Z
m v
0.02
...... 0
t
I
I
I
I
0.1
0.2
0.3
0.4
0.5 r 1-Bu0H] (M)
FIG. 6. Variation of the pseudo-first-order rate constant,/~, with 1-BuOH concentration at fixed CTAB (0.012 M) and NaOH (0.010 M) concentrations in the ( ~ ) absence and ( • ) presence of acetonitrile.
I
L
I
i
0,0 4
L .
.0:
0
I
I
I
0.02
0.04
0.06
0-08
[KBr~ (M)
FiG. 7. Variation o f the pseudo-first-order rate constant, k~, with K B r concentration at fixed N a O H (0.01 M ) and C T A B (0.012 M ) concentrations in the presence o f acetonitrile ( e , [1-BuOPI] = 0.0 M ; and II, [IBuOH] = 0.096 M). Journal of Colloid and Interface Science,
"Col.127,No. 2, February1989
528
VALIENTE A N D RODENAS TABLE I Variation of Pseudo-First-Order Rate Constant with the Dielectric Constant
In k 1/e × 100 XROH
-2.09 5.29 0.947
-2.77 4.92 0.923
-2.83 4.59 0.900
of competing O H - and Br- ions, the OHM value is given by [OHM] / 2
x \(([oH](_k~o~ 1-~6~+ - K °~ [X]) _ ~) fl[OH] (K °H - 1)[Dn]
= 0,
where K °r~ is the ion exchange equilibrium constant for OH- and Br- in the micellar surface and [Br] is the total concentration of bromide ions. In our treatment for the reaction in mixed micelles, we consider the same exchange equilibrium between OH- and Br- on the surface of mixed micelles but with a variation in the fraction of the neutralized micellar head group, t, given by the expressions [ 1, 3 ] that correspond to mixed CTAB/1-BuOH micelles and mixed CTAB / 1-BuOH / acetonitrile micelles. The experimental results can be adapted to this model by simulation techniques, with the values of known parameters, k ' , CMC, and ~, and using kM, Ks, and K °H as adjustable parameters. The values of CMC do not appreciably affect the values of the pseudo-first-order rate constant but the following variation (20, 21) with ions has been used for simple CTAB micelles and mixed micelles, lg CMC = -3.7671 - 0.2133 lg(CM + [OH]), where CM are the critical micelle concentrations in the absence of ions in solution: 9 × 10-4 M for simple CTAB micelles (22) and 1.3 × 10 -3 M for mixed CTAB/1-BuOH/ Journal of Colloid and Interface Science, Vol. 127, No. 2, February 1989
-3.32 4.31 0.877
-4.32 3.87 0.833
-8.56 1.29 0
acetonitrile micelles. No CM variation with alcohol incorporation has been considered because there is disagreement in the literature (14, 23-27 ) about these CM values and small changes in CMC do not affect our kinetic parameters. The values of parameters that explain the results for the reaction in simple CTAB micelles in the presence and absence of acetonitrile are shown in Table II. Values of t calculated with these parameters in the presence and absence of acetonitrile are solid and dashed lines in Fig. 2, respectively. In order to explain the results it is necessary to consider an increase in the value of the substrate binding constant to the micelle, Ks, explained by a salting-out effect (28-30) or by a decrease of Coulombic repulsion (31-33). This effect for additional Br- ion results has been taken into account for the following variation in Ks, Ks = / ~ + 700[KBr], where K ° is the substrate binding constant to simple CTAB micelles in the absence of additional Br- ions. The kinetic results in mixed CTAB/1BuOH/acetonitrile micelles can be explained TABLE II Parameters That Best Fit the Kinetic Results for Crystal Violet in CTAB [NaOH] (M)
k~ (s-t)
K~,(M -I)
h~ n
B
0.002 0.006 0.010 0.006 a 0.010 b
0.46 0.46 0.46 0.46 0.46
40 60 70 70 90
4 4 4 4 4
0.74 0.74 0.74 0.80 0.80
In absence of acetonitrile.
C T A B / I - B U T A N O L MICELLES A N D HYDROLYSIS
by using two different approaches. One considers the following empirical expressions for kM and Ks, = k° + c
[ROHM] [Dn]
[7]
K0
Ks = 1 + c ' ( [ R O H M ] / [ D n ] ) '
[8]
where k ° and K ° are the values of the parameters used in the reaction with simple micelles in the presence of acetonitrile, and a constant value for K °H. In Figs. 2-7 the calculated values for ~ with this treatment are shown by solid lines, with c ' = 1 0 a n d c = 0 . 9 7 s -~. The other approach considers the same variation in the micelle substrate binding constant, Ks, with alcohol incorporation, but it gives a constant value for kM and a decrease in the exchange equilibrium constant with the fraction of micellized alcohol given by the expression KOH =
K °H° 1 + c"([ROHM]/[Dn]) "
[91
The same values for parameters used in the former treatment and a value of c" = 4 explain the results. Calculated values of pseudo-firstorder rate constants are dashed lines in all the figures. Both approaches predict a decrease in Ks with the 1-butanol incorporation in the micelles. This variation in Ks with 1-butanol incorporation in the micelle is consistent with the ultrafiltration measurements. Table III shows the substrate absorbances and micellized surfactant concentrations in both filtrate TABLE III Substrate Absorbance and Micellized Surfactant Concentration Obtained from Ultrafiltration Measurements in Filtrate (F) and Filtrant (f) [I-BuOH] (M)
[Dn]f(34)
[Dn]F(M)
Absr
Absr
0 0 0,51
0.003 0.005 0,008
0 0 0,005
1.53 1.53 1.53
1.04 0.92 1.20
529
and filtrant. A value for substrate binding constant to simple CTAB micelles has been determined from the results in the absence of alcohol according to the theoretical treatment in the literature (34, 35), Ks -~ 122 M -1 . For micelles with 1-butanol, the results show that a large amount of miceUes passes through the ultrafilter pore agreeing with other results in the literature showing that alcohol incorporation produces a decrease in the micellar aggregation number (36-40) and the calculated value results to be Ks -~ 6 M -1 . The decrease in the substrate binding to micelles, for this positively charged substrate, can be related to the increase in micellar surface ionization. So increasing the positive charge on the micellar surface increases the repulsion to the substrate. This conclusion is consistent with others reported (32, 33) Ks values. The variation in the kM, rate constant for the reaction in the micellar phase, can be related with two different factors. It can be related to the influence of alcohol in the micellar surface dielectric constant because of the increase in the micelle ionization degree. And it is also associated to the presumable alcohol effect in the molar volume of the micellar surface where the reaction occurs. This micellar rate constant, kM, can be converted to a second-order rate constant, kin, considering the volume element (41) where the reactions occurs. For the reaction in simple CTAB micelles, the micellar pseudophase molar volume is 0.371 M -~, so that the second-order rate constant is k m = 0.173 M -1 s -1 . According to the fluorescence results, alcohol incorporation produces a decrease in the peak intensity ratio IJIm in the pyrene spectra (Table IV) agreeing with other results in the literature (36). This peak ratio can be correlated with the decrease in the micellar surface dielectric constant (42, 43). The peak ratio is practically unaffected either by the surfactant concentration or by the amount of acetonitrile used in the experiments (44). From all of the results (36 measurements at different surfactant and alcohol concentrations and [ ROHM ] / [ Dn ] ~ I) the following empirical expression Journal of Colloid and Interface Science, Vol. 127,No. 2, February 1989
530
VALIENTE AND RODENAS TABLE IV
Variation of Peak Intensity Ratio in the Pyrene Spectra at Fixed CTAB (0.010 M) Concentration with the Alcohol Concentration [ I-BuOH] (M) 1~/lm
0 1.31
0.11 1.27
0.22 1.24
0.32 1.21
0.43 1.18
can be obtained for the peak ratio with 1-butanol incorporated to the micelle, Ii]Iln = a + b
[ROHM] [Dn] '
with a = 1.29 __+0.01 and b = - 0 . 1 3 _+ 0.02. According to the results, there is a decrease in the micellar surface dielectric constant with the alcohol incorporation that ranges from a value of 33-36 for simple CTAB micelles down to a value of 12-17 when [ ROHM ] / [ Dn ] = 1. The decrease in ~ increases the second-order rate constant in the micellar phase, and can be estimated with expression [4] using as reference the second-order rate constant for the reaction in simple CTAB micelles. The error in the micellar surface dielectric constant determination does not allow the real rate constant value to be calculated and it is only possible to conclude that the increase explains the large variation in kM parameter. The second treatment is justified by considering that alcohol incorporation produces an increase in the miceUized hydroxide ions to micellized bromide ions ratio because of i o n dipole interactions between O H - and l-butanol. The constant value in the kM parameter and the big increase in the second-order rate constant, because of the variation in the micellar surface dielectric constant for alcohol incorporation, can be related to the increase in the volume of the micellar phase per mole of micellized surfactant. According to all these results we can conclude that the incorporation of alcohol in simple CTAB micelles inhibits basic hydrolysis of Crystal Violet. This inhibition effect is related to the decrease in the fraction of the micellar head group that is neutralized and in the disJournal of Colloid and Interface Science, Vol. 127, No. 2, February 1989
placement of this substrate from the micellar into the aqueous phase with alcohol incorporation (Eq. 8). Alcohol incorporation also produces a decrease in the micellar surface dielectric constant that increases the rate constant in the micellar phase, but it is not possible to determine if this variation is large enough to explain kinetic results with a variation in kM (Eq. 7), or if it is necessary to consider the increase in the micellar phase volume per mole of micellized surfactant and an additional amount of micelle-bound hydroxide ions (Eq. 9). REFERENCES 1. Athanassakis, V., Bunton, C. A., and de Buzzaccarini, F., J. Phys. Chem. 86, 5002 (1932); Bunton, C. A., and de Buzzaccarini, F., J. Phys. Chem. 86, 5010 (1982). 2. Bunton, C. A., Buzzacarini, F., and Hamed, F. H. J. Org. Chem. 48, 2461 (1983). 3. Martin, C. A., McGrann, P. H., Ward, M. D,, Angelus, G. H., and Jaeger, D. A., J. Org. Chem. 49, 4392 (1984). 4. Fendler, J, H., and Fendler, E. J., "Catalysis in Micellar and Macromolecular Systems." Academic Press, New York, 1975. 5. Martinek, K., Yatsimirski, A., Levashov, A. V,, and Berezin, I. V., "Micellization, Solubilization, and Microemulsions," (K. L. Mittal, Ed.), Vol. 2. Plenum, New York, 1977. 6. "Inorganic Reactions in Organized Media" (S. L. Holtz, Ed.). A.C.S. Symposium Series, Amer. Chem. Soc., Washington, DC, 1982. 7. Mittal, K. L., and Fendler, E. J., "Solution Behavior of Surfactants." Plenum, New York, 1982. 8. Otero, C., and Rodenas, E., J. Phys. Chem. 90, 5771 (1986). 9, Hoffmann, H., and Ulbricht, W., Z. Phys. Chem. N. F., 106, 167 (1977); Hoffmann, H., and Tagesson, B., Z. Phys. Chem. N. F., 110, 8 (1978). 10. Valiente, M., and Rodenas, E., An. Quim., in press. I 1. Sepfilveda, L., and Cortes, J., J. Phys, Chem. 89, 5322
(1985). 12. Gettins, J., Hall, D., Jobling, P. L., Rassing, J. E., and Wyn-Jones, E., J. Chem. Soc., Faraday Trans. 2 74, 1957 (1978). 13. Evans, H. C., £ Chem. Soc., 579 (1956). 14. Zana, R., Yiv, S., Strazielle, C., and Lianos, P. £ Colloid Interface Sci. 80, 208 (1981). 15. Menger, F. M., and Portnoy, C. E., J. Amer. Chem. Soc, 89, 4698 (1967). 16. Bunton, C. A., CataL Rev. Sci. Eng. 20, 1 (1979). 17. Romsted L. S., "Micellization, Solubilization, and
CTAB/1-BUTANOL MICELLES AND HYDROLYSIS Microemulsions (K. L., Mitlal, Ed.), Vol. 2, p. 509. Plenum, New York, 1977. 18. Ritchie, C. D., Wringht, D. J., Huang, D-S., and Kamego, A. A., J. Amer. Chem. Soc. 97, 1163 (1975). 19. Decroog, D., Bull. Soc. Chim. Fr., 127 (1964). 20. Shinoda, K., Nakagawa, T., Tamanuschi, B., and Isemura, T., "Colloidal Surfaetants." Academic Press, New York, 1963. 21. Bunton, C. A., and Robinson, L., J. Amer. Chem. Soc. 90, 5972 (1968). 22. Mukerjee, P., and Mysels, K. J., "Critical Micetle Concentration of Aqueous Surfactant Systems" Nation~ Bureau of Standards "Washington, DC, i971; NSRDS-NBS 20420. 23. Shirahama, K., and Kashiwabara, T., J. Colloid Interface Sci. 36, 65 (1971). 24. Miyagishi, S., Bull. Chem. Soc. Japan 48, 2349 (1975). 25. Singh, H. N., and Swarup, S., Bull. Chem, Soc: Japan 51, t534 (1978). 26. Abu-Hamdiyyah, M., J. Phys: Chem. 90, 1345 (I986). 27. Rao, V. 1., and Ruckestein, E., J. Colloid Interface Sci. 113, 375 (I986). 28. Bunton, C. A., Romsted, L. S., and Thamavit, C., J. Amer. Chem. Soc. 102, 390 (1980). 29. Rodenas, E., and Vera, S., J. Phys. Chem. 89; 513 (1985). 30. Otero, C., and Redenas, E., Canad. J. Chem. 63, 2892 (1985).
531
31. Bunton, C. A., Carraseo, N., Huang, S. K., Paik, C. H., and Romsted, L. S., J. Amer. Chem. Soe. 100, 5420 (1978). 32. Ortega, F., and Rodenas, E., J. Phys. Chem. 90, 2408 (I986). 33. Vera, S., and Rodenas, E., J. Phys. Chem. 90, 3414 (1986). 34. Langkruis, G. B., and Engberts, J. B. F. N., Tetra, hedron 41, 399i (1979). 35. Hirose, C., and Sepfflveda, L., J. Phys. Chem. 85, 3689 (1981). 36. Llanos, P., and Zana, R., Chem. Phys. Lett. 72, 171 (I980); 76, 62 (19:80). 37. Yiv; S., Zana, R., Ulbricht, W., and Hoffmann H., J. Colloid Interface Sci~ 80, 224 (1981). 38. Candau, S., and Zana, R., J. Colloid Interface Sci. 84, 206 (1981). 39. Almgren, M., and Swarup, S, J. Colloid Interface Sci. 91, 256 (198:3). 40. Lang, J., and Zana, R., or. Phys. Chem: 90, 5258 (t986). 41. Guveli, D. E., Hayes, J. B, and Davis, S~S., J. Colloid Interface Sei. 82, 307 (1981). 42. Dong, D., and Winnik, M. A., Photochem; Photobiol. 35; 17 (1982). 43. Kalyanasundaram, K., and Thomas, J. K., J. Amer. Chem. Soc. 99, 2039 (1977). 44. Results obtained in our laboratory for E. P6rez.
Journal of Colloid and Interface Science, Vol. 127~No. 2, February 1989