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, 12.2 X M, agrees with that in literature.1° From Figure 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 International Congress 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
560
The Journal of Physical Chemistry, Vol. 84, No. 5, 1980
evolution started immediately after the start of the reinitiated oscillation); (d) further addition of manganese(I1) or cerium(II1) may revive the exhausted catalyzed oscilM ten lation, e.g., at a manganese(I1) concentration of oscillations were recorded (at a composition given in Figure 1)while an additional amount of manganese (total conM) results in an additional 12 oscillacentration 2 X tions. It is most surprising that, inconsistent with earlier obs e r v a t i o n ~on~ ~bromate ~ oscillators, here bromine is not an inhibitor for the oscillation. The results can be explained as follows: During the uncatalyzed phase of the reaction acidic bromate reacts with the aromatics and at the termination of oscillation oxidation and bromination products of the starting aromatics are present in the system. When a BZ catalyst is added to this “exhausted” system which still contains unreacted bromate (since bromate is in large excess) the reduced form of the catalyst (M”+)is oxidized by bromate and bromine is formed simultaneously:
Mn+ + Br03-
H+
M(n+l)++ Br2
Bromine is not consumed since in the “exhausted” system only oxidizable and not brominateable species are present. Our separate experiments have shown that already during the preoscillatory period the starting aromatic was both partly brominated and oxidized, and the uncatalyzed oscillation stopped after total bromination. Fe(phen)t+ and Ru(bpy)?+ likely cannot give rise to further oxidation, however, cerium(1V) and especially manganese(II1) react with them as follows
Communications to the Editor
and by the formation of Mn+ the cycle can start again. Thus the accumulation of bromine follows a step function, as characteristic for final products in every oscillatory chemical system. The termination of the uncatalyzed oscillatory period does not mean the completion of the chemical reaction. The oxidative bromination processes progress further and result in organic compounds which cannot be, or can be only very slowly, oxidized by manganese(II1) or cerium(1V). This is likely the reason that chemical oscillation cannot be reinitiated if a certain period of time has elapsed from the termination of the uncatalyzed oscillation. We are of the opinion that the observations described in this communication will contribute to the discovery of novel types of bromate oscillators.
References and Notes M.Orbin and E. Koros, J. Phys. Chem., 82, 1672 (1978); A. Pacault and C. V i i l , Ed., ”Synergetics Far from Equilibrium”, Springer-Verlag, West Berlin, 1979, pp 43-46. (2) G. J. Kasparek and T. C. Bruice, J. Inorg. Chem., 10, 382 (1971). (3) Z. Noszticzius, J. Am. Chem. SOC.,101, 3177 (1979). (1)
Institute of Inorganic and Analytical Chemistry L. Eotvos University ti- 1443 Budapest, Hungary Received July 9, 1979
E. Koros
M. OrbBn” I. Habon
