558
J. Phys. Chem. 1980, 8 4 , 558-559
In summary, these findings indicate that nitrones like HOPBN can be covalently attached to silaceous surfaces through the CC linking agent. The immobilized nitrones are effective traps for short-lived free radicals in solution. Moreover, the resulting spin adducts can afford well-resolved ESR spectra while attached to the silaceous surface. That the spin adducts of these immobilized nitrones can give rise to relatively sharp-lined spectra indicates that these nitroxyl radicals are free to rotate about an axis which is perpendicular to the plane containing the nitroxyl z axis.12
Aclznowledgment. This work was supported in part by grants from the Natural and Engineering Science Council of Canada and NATO (Grant No. 1578). The experimental assistance of R. L. Dudley and stimulating discussions with C. A. Fyfe are gratefully acknowledged. References and Notes Janzen, E. G.;Wang, Y. Y. J. Phys. Chem. 1979, 83, 894-896. Dautartas, M. F.; Evans, J. F.; Kuwana, T. Anal. Chem. 1979, 57, 104-110. Yacynych, A. M.; Kuwana, T. Anal. Chem. 1978, 50, 640-645. Lin, A. W. C.; Yeh, P.; Yacynych, A. M.; Kuwana, T. J. Electroanal. Chem. 1977, 84, 411-419. Janzen, E. G.;Zawalski, R. C. J. Org. Chem. 1978, 43, 1900-1903. Janzen, E. G.;Dudley, R. L. Chemical Institute of Canada-American Chemical Society Joint Meeting, Montreal, Quebec, May 1977, Abstracts of Papers ORG-5 1. Nominal characteristics of these beads (CPG10, ElectroNucleonics, Inc., Fairfield, NJ) were as follows: mean bead diameter = 150 pm, mean pore diameter = 104 nm, pore volume = 1.16 mL g-I, total surface area = 29 m2 g-'. It is not known whether cross linking of CC occurs on the silica surface or whether some dimeric or telemeric CC forms as a result of hydrolysis by trace water in the benzene solvent. CC, HOPBN, and the phenyl adduct of HOPBN are all benzene soluble. Thus, the role of benzene here is both to provide a solvent for PAT and to solvate the attached spin trap and the resulting spin adduct. Under conditions of prolonged reaction in refluxing benzene, trace amounts of spin trap active HOPBN have been found to be retained on CPGlO which had not been previously exposed to CC. However, the quantity of retained nitrone is minuscule relative to that immobilized when the silaceous surface is first allowed to react with CC. The mode of retention of this trace amount of HOPBN (e.g., adsorption, entrapment in the porous structure, covalent attachment to the silaceous surface) is presently unknown. Although all observed resonances arise from nitroxyl radicals which are covalently attached to the silaceous surface, the terms "mobile" and "highly immobilized" refer to species which afford isotropic and anisotropic ESR spectra, respectively. See,for example, Griffith, 0. H.; Jost, P. C. in "Spin Labeling"; Berliner, L. G.,Ed.; Academic Press: New York, 1976; pp 466-467. Eric E. Bancroft Henry N. Blount'
Brown Chemical Laboratory The University o f Delaware Newark, Delaware 19711 Department o f Chemistry Guelph Waterloo Centre for Graduate Work in Chemistry University o f Guelph Guelph, Ontario, N I G 2 W 1 Canada
Edward G. Janzen"
Received October 15, 1979
Further Evidence for a Maximum in the Critical Micelle Concentration vs. Pressure Publication costs assisted by Fukuoka University
Sir: It has been reported by various authors'-6 that the critical micelle concentration (cmc) vs. pressure curve for ionic surfactants in aqueous solutions exhibits a maximum at a certain pressure, usually near 100 MPa. All methods used for determining the cmc under pressure have been based on electroconductivity measurements, in which a 0022-3654/80/2084-0558$0 1.OO/O
I
I
Y
11 01 0,l
,
102
,
,
200
PRESSLRE / \!Pa
Figure 1. The cmc of dodecylpyridinium bromide as a function of pressure at 303 K: (0)optical method; (0)electroconductivity method.
specific conductance vs. concentration plot shows a break at the cmc. Recently, Rodriguez and Offen7 insisted on the absence of the maximum in the cmc vs. pressure plot. They determined the differential absorbance of naphthalene AA(Amax-275 nm) as a function of pressure in two states: in saturated solution in a solubilizing system of sodium dodecyl sulfate (SDS), and in saturated solution in water. They adopted the concentration extrapolated to AA = 0 as the cmc at the particular pressure. Their cmc vs. pressure plot has no maximum but is monotonically increasing. They suggested that, since the behavior of an optical probe such as naphthalene is, in contrast to the conductivity, independent of hydrodynamic characteristics, it might be expected to offer a more reliable means of determining the cmc. We believe that it is impossible to attribute the origin of breaks in the plots of specific conductance vs. concentration to any source other than micellization, even in the presence of complicating factors arising at higher pressures. Furthermore, the volume change accompanying micelle formation, AT,,, of sodium decyl sulfate, which was determined by compressibility measurements, possessed a positive sign a t atmospheric pressure and decreased with pressure, becoming negative above approximately 100 MPa.8 This measured value of AT,,, agreed with that calculated by the following equation according to the pseudo-phase separation model for micelle formation: AVm = (1 + fi)RT(aIn cmc/aP),, where P refers to the effective degree of counterion binding by the m i ~ e l l e .In ~ other words, this agreement provides corroborating evidence that the cmc exhibits a maximum at the pressure where AVm = 0, near 100 MPa since fi -0.7 > 0. We suggest that the cmcs determined by Rodriguez and Offen is that for the formation of mixed SDS-naphthalene micelles, and thus related to the effect of pressure on the solubilization of naphthalene. In this report, we present further evidence for the cmc-pressure maximum by means of the optical method used by Rodriguez and Offen. When the cationic surfactant dodecylpyridinium bromide (DPB) associates to form micelles in water, a charge transfer (CT) band (Arna -290 nm) emerges and its absorbance increases linearly with concentration above the cmc as a result of the CT interaction of concentrated bromide anion and pyridinium cation on the micelle s u r f a ~ e . The ~ quartz cell with a rubber bellows containing an aqueous solution of DPB was placed in the pressure vessel and water was used as a pressure-transmitting fluid. With this arrangement, the absorbance of the CT band at 290 nm was measured under pressure. At high pressures, the absorbance of the CT band increased linearly with concentration above a critical
0 1980 American
Chemical Society
559
J . Phys. Chem. 1980, 84, 559-560
concentration, in the same manner as is the case a t atmospheric pressure. Thus, it is easy to determine a cmc under pressure. The cmc of DPB as a function of pressure a t 303 K by this optical method is shown in Figure 1, together with the cmc determined by an electroconductivity method. The cmc value at atmospheric pressure, M, agrees with that in literature.1° From Figure 12.2 X 1,we can claim the presence of a maximum in the cmc vs. pressure.
Acknowledgment. The authors express thanks to Dr. Tohru Inoue at Fukuoka University for a gift of DPB in this work.
References anid Notes (1) S. D. Hamann, J . Phys. Chem., 66, 1359 (1962). (2) P. F. Tuddenham and A. E. Alexander, J. Phys. Chem., 66, 1839 (1962). (3) J. Oosugi, M. Sato, arid N. Ifuku, Nippon Kagaku Zasshi, 87, 329 (1966). (4) S. Kaneshina, M. Tanaka, T. Tomida, and R. Matuura, J . Colloid Interface Sci., 48, 450 (1974). (5) M. Tanaka, S. Kaneshina, and G. Sugihara, Proceedings of the VIIth InternationalCongress on Surface Active Substances, Moscow, 1977. (6) T. S. Brun, H. HCiland, and E. Vikingstad, J . Colloid Interface Sci., 63,89 (1978). (7) S . Rodriguez and H. Offen, J. Phys. Chem., 81, 47 (1977). (8) M. Tanaka, S . Kaneshina, K. Shin-no, T. Okajima, and T. Tomida, J . Colloid Interface Sci., 46, 132 (1974). (9) W. D. Harkins, H. Krizek, and M. L. Corrin, J . Colloid Sci., 6, 576 (1951). (10) P. Mukerjee and K. J. Mysels, Natl. Stand. Ref. Data Ser., Natl. Bur. Stand., No. 36, 142-143 (1971). Editorial Note: Professor Offen has indicated that he is in agreement with the conclusions drawn by the authors of the above communication. Department of Chemistry Faculty of Science Fukuoka University Fukuoka 814, Japan
Nagamune Nlshikldo" Nobuyoshl Yoshlmura Mltsuru Tanaka
Received August 29, 1979
Chemical Oscillations during the Uncatalyzed Reaction of Araimatic Compounds with Bromate. 3. Effect of One-Electron Redox Couples on Uncatalyzed Brlomate Oscillators
Sir: In the course of our investigations on uncatalyzed oscillatory reactions1 we have been interested among others in the effect of one-electron redox couples (used in the Belousov-Zhabotinsky (BZ) systems as catalysts) on some phenol and aniline derivatives-bromate-sulfuric acid reactive systems. In this communication we report briefly on some unexpected results obtained during this study. 1,2,3Trihydroxybenzene (THB), 1,3-diaminobenzene, 3aminophenol, 2,,4-diaminodiphenylamine, phenol, and aniline, respectkely, were allowed to react with acidic bromate in the absence and in the presence of a catalyst. As an example, the behavior of the THB-bromatesulfuric acid system is described in detail.
s x
I1 1
Figure 1. Oscillation in the THB (0.02 M), bromate (0.1 M), and sulfuric acid (1.75 M) reacting system without and with a catalyst [ 10-3M Mn(II)] added.
,II 1
-'
k
"
' i o '
' i s '
'
'
ao
"
"
7ime mi"
Figure 2. Oscillation in the 2,4diamincdiphenylamine (0.01 M), bromate (0.1 M), and sulfuric acid (1.5 M) reacting system without and with a catalyst [ 10-3 M Ce(IV)] added.
To a solution composed of 0.02 M THB, 0.1 M NaBrO,, and 1.75 M H2S04four BZ catalysts [tris(phenanthroline)iron(II), tris(bipyridine)ruthenium(II), cerium(III), and manganese(II)] were added separately at different stages of the reaction: (a) before the start of the reaction, (b) during the oscillatory phase of the reaction, and (c) after the termination of oscillation. The observations are summarized in Table I. From Table I it is obvious that catalysts of relatively low redox potentials act as inhibitors, and those of higher redox potentials are able to reinitiate chemical oscillation in the "exhausted" oscillatory system. In most of the cases the reinitiated oscillation was more pronounced and more prolonged than the oscillation during the uncatalyzed phase. Typical potential traces, taken with Pt against a HgHg2S04-K2S04reference electrode, are shown in Figures 1 and 2. The results obtained so far are as follows: (a) manganese(I1) and cerium(II1) could reinitiate oscillation if the aromatic was THB, 1,3-diaminobenzene, 3-aminophenol, or 2,4-diaminodiphenylamine, but not phenol or aniline; (b) manganese (11)or cerium(II1) could reinitiate chemical oscillation only if it was added to the reacting system within few mintues after the termination of the uncatalyzed oscillatory reaction; (c) during the uncatalyzed reaction bromine did not form at all, however, during the reinitiated oscillation, bromine accumulated (bromine
TABLE I : Effect of BZ Catalysts on the THB-BrO,--H,SO, System at Different Stages of potenadding the catalyst t o the system tial,a catalyst V before the start of the reaction during oscillation Fe(phen)3z+ 1.06 no oscillation terminates oscillation terminates oscillation Ru(bpy),'+ 1 . 2 no oscillation Ce(II1) 1.44 oscillation occurs with higher amplitude, n o considerable change lower frequency and is rather irregular Mn(I1) 1.50 oscillation occurs and Br, evolves no considerable change a Standard redox potential of the one-electron couple. 0022-3654/80/2084-0599$01 .OO/O
"
Reaction
after termination of oscillation
no change no change oscillation is reinitiated (only few irregular oscillations) oscillation is reinitiated
0 1980 American Chemical Society
