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Self-oscillation of polymer chains in an aqueous solution has been achieved. The ruthenium catalyst for the Belousov-Zhabotinsky reaction was polymerized by using N-isopropylacrylamide and dissolved into the solution containing the BZ substrates. Periodical soluble-insoluble changes of the polymer chain were spontaneously induced by the BZ reaction. The conformational oscillations of the polymer were measured as the optical transmittance changes of the solution. This is the first report that rhythmical and reversible soluble-insoluble changes of polymer chains are realized under constant and homogeneous conditions. The transducing system from chemical energy of the BZ reaction to optical information has been constructed.

Mecanisme de la reaction en solution acide. Le mecanisme consiste en 13 etapes elementaires et met en jeu IBr comme intermediaire

The responses of permanganate oscillating chemical reactions to factors that govern colloidal stability are examined. Various electrolytes are able to suppress oscillation in the MnO 4 - -Mn 2+ -H 2 PO 4 - and MnO 4 - -H 2 O 2 -H 2 PO 4 - systems, with the strength of the effect depending predominantly on the concentration, charge, and radius of the cation. The hydrophilic colloid gum arabic protects the oscillator against the influence of electrolytes, and the first permanganate oscillator without dihydrogen phospbate, arsenate, or vanadate ions has been designed (MnO 4 - +H 2 O 2 +gum arabic). These results identify the central role of colloidal Mn(IV) in these oscillators

The title reaction is the subject of current interest because the first experimental Turing patterns were observed recently in this system. Here, the authors report the first observation of oscillations that are long lived (over 1 h) in this system in a batch reactor; even after cessation the oscillations can be restarted several times by adding ClO{sub 2} to the exhausted system. These low-frequency low-amplitude (LL) oscillations were detected with both platinum and iodide-selective electrodes in the chlorite-iodide-malonic acid (original CIMA) reaction and in the closely related chlorine dioxide-iodide-malonic acid (minimal CIMA) system. The LL oscillations follow after the already known high frequency oscillations, sometimes separated by a second induction period. LL oscillations can appear without any induction period if appropriate concentrations of chlorine dioxide, iodomalonic acid, and chloride (CIMA-Cl system) are established in a dilute sulfuric acid medium. In this case neither iodine, iodide, nor malonic acid is needed. Some suggestions are made regarding the mechanism of these newly discovered oscillations. 33 refs., 6 figs., 1 tab.

The reaction between bromite and iodide ions in a flow reactor shows two steady states and sustained oscillations in pH, redox potential, and [I - ]. The oscillatory behavior is extremely sensitive to the inflow ratio [BrO 2 - ]/[I - ], the flow rate, the initial pH or the input solutions, and the stirring rate. Batch experiments suggest that the system behaves in several respects like the analogous chlorite-iodide oscillator

When subject to illumination, tetrathionate ion decomposes in an oscillatory fashion with a period of about 1 h to yield products identified as colloidal sulfur and trithionate ion. This system represents the first experimental example of a stirred, batch photochemical oscillator. A simple model consisting of four reaction steps and four adjustable rate parameters gives good agreement with the observed oscillatory behavior.

We report the structural color behavior of a periodic ordered mesoporous gel synchronized with the Belousov-Zhabotinsky (BZ) reaction. The structural colored concentric rings which were spatiotemporally spread out on the porous gel were observed during the BZ reaction. The color tone of the structural color, which is determined by the swelling ratio of the gel, was periodically changed. This is the first evidence that a self-sustaining peristaltic motion occurs on the surface of a gel.

La reaction entre H 2 O 2 et l'ion thiosulfate, en presence de Cu(II) presente un etat oscillatoire et 3 etats stationnaires. En l'absence de Cu, on ne trouve qu'un simple etat fondamental

La reaction du titre presente 3 types de bistabilite en couleur, en potentiel d'une electrode de Pt et dans la vitesse de degagement du gaz

In acidic aqueous solution at 25 OC, only slow or nonexistent reaction is observed for any two of the three species iodate ion, hydrogen peroxide, and manganous ion. However, if all three species are present, 0.002 M Mn2+ catalyzes the iodate oxidation of peroxide at a rate almost 1000 times that in the absence of a catalyst! This remarkable observation, which has already been reported by Cooke, can be explained by postulating that the radical oxidant .IO2 is very sluggish at abstracting hydrogen atoms from species like H202 but can oxidize Mn2+ by electron transfer. A detailed mechanism has been proposed that models semiquantitatively not only the manganous catalyzed iodate oxidation of peroxide but also the simultaneous induced disproportionation of the peroxide and the fact that the concentration of elementary iodine does not increase to a limiting value but rises to a maximum and then decreases toward a small value. Despite this single extremum, the subsystem does not exhibit oscillatory behavior.

Catalyse par l'acetate de cobalt(II) et le bromure de potassium. Un modele cinetique est presente

The reaction between arsenite and iodate at 25 "C and pH 2.25 in a stirred tank reactor exhibits bistability over a range of flow rates and input arsenite and iodate concentrations. Observed steady-state Iand I2 concentrations and points of transition between bistable and unistable behavior are in excellent agreement with values calculated from a simple model consisting of three overall component processes: (A) IO3+ 3HSAs0, = I+ 3H3As04; (B) 10; + 51+ 6H' = 312 + 3H20; (C) I2 + H3As03 + H 2 0 = 21+ H,As04 + 2H+. Implications for the recently discovered arsenite-iodate-chlorite-oscillating reaction are discussed. Studies of oscillating chemical reactions and related phenomena are of fundamental and rapidly increasing interest both because of the light they shed on the complexities of dynamic behavior possible for systems far from equilibrium and because they may provide experimentally tractable models for some of the endogenous rhythms observed in living systems. The ability of chemists to develop and test general theories of chemical oscillation has been hindered somewhat by the paucity of examples. In spite of intensive efforts in the last decade to design new oscillators, only two fundamentally different nonbiological, homogeneous oscillating reactions, the Bray-Liebhafsky3 (B-L) and the Belousov-Zhabotinsky4 (B-Z) systems, have been characterized. The array of known oscillators has been augmented by variations and hybrids of the above two reactions, as well as by systems of biological origin. Since oscillations in the B-L and B-Z systems were discovered serendipitously, it seems fair to summarize the techniques by which chemical oscillators have been found as (a) accident (the B-L and B-Z reactions), (b) variation on a theme (the uncatalyzed B-Z r e a c t i ~ n , ~ the Briggs-Rauscher reaction6), and (c) study of biological systems (glycolysis'). From the point of view of formulating general approaches to chemical oscillation, technique a is too unreliable, while b is unlikely to yield a sufficient variety of behavior, and the systems of type c tend to be both highly complex and difficult to monitor. Although no necessary and sufficient set of conditions for the existence of chemical oscillations has been established, several factors are known to be either essential or helpful in producing oscillatory behavior. For example, oscillating chemical systems must be far from equilibrium and must contain an appropriate nonlinear coupling mechanism, the most common example of which is autocatalysis.8 It would seem that even such a rudimentary understanding as this might make it possible to construct systematically new chemical oscillators by combining known reactions under appropriate conditions. In a recent communication (part 2l), we proposed a systematic approach to the design of chemical oscillators and applied it successfully to generate a new homogeneous oscillating reaction involving arsenite, iodate, and chlorite. This system has since been found to be the prototype of a family of chemical oscillators involving iodate, chlorite, and a reducing agent which produces iodide from iodate and/or from iodine at a suitable rate.9 The approach used to generate these new oscillators starts with an autocatalytic reaction in a continuous-flow stirred tank reactor (CSTR). The autocatalysis constitutes the destabilizing nonlinear coupling mechanism, while the CSTR guarantees that the system is maintained far from equilibrium. We then make use of a simple dynamical model developed by Boissonade and De Kepper," which suggests that oscillations can result from the application of an appropriate feedback step to an intrinsically bistable system. The next step in the search for oscillation is to seek a reaction which Centre de Recherche Paul Pascal, Domaine Universitaire, 33405 Talence Cedex. France. 0002-7863/8 1/1503-6121$01.25/0 perturbs the stability of the two stable branches on a suitable time scale so as to generate oscillation. The approach outlined above has a t least two virtues. The model is sufficiently simple and general that, unlike more detailed models of chemical ~ s c i l l a t i o n , ' ~ ~ ~ it can be applied directly to a wide range of reactions. Secondly, it splits the task of finding new oscillating systems into two more tractable subproblems, the discovery of bistable systems and the design of suitable feedback reactions. In this paper we report a series of experiments on the behavior of acidic mixtures of arsenite and iodate in a CSTR. The system exhibits bistability over a significant range of input concentrations and flow rates. Similar results have also been obtained by Papsin et al.14 We show here that calculations with a simple model consisting of three overall reaction steps yield results in excellent agreement with our experiments. In further papers we shall present studies of other bistable systems as well as of the detailed coupling of the arsenite-iodate reaction with the chlorite-iodide system to generate oscillation. Experimental Section The apparatus consists of a thermally regulated stirred tank glass (Pyrex) flow reactorI5 connected to a Sage Model 375A peristaltic pump which allows for one to four independent input flows. The constraints or variables controlled by the experimenter in this system are the temperature, which was maintained at 25.0 f 0.1 "C in this series of experiments, the residence time T , and the concentrations [Ailo that each input species A, would attain in the tank if no reaction took place. Measurements were made of the potential of an Orion iodide-specific electrode with respect to a mercury-mercurous sulfate reference electrode and of the absorbance at 460 nm, the wavelength of maximum absorbance of 12. Iodine concentrations are calculated by assuming that I2 is the only species which absorbs significantly at this wavelength. When nonnegligible concentrations of iodide ion are present, accurate [I21 values (1) Part 3 in the series Systematic Design of Chemical Oscillators. Part 2: De Kepper, P.; Epstein, I . R.; Kustin, K. J . Am. Chem. SOC. 1981, 103, 2133-2134. Part 1: Epstein, I. R.; Kustin, K.; Warshaw, L. Ibid. 1980 102, 3751-3798. (2) To whom correspondence should be addressed. (3) Bray, W. C. J . Am. Chem. SOC. 1921, 43, 1262-1267. (4) Belousov, B. P. Sb. ReJ Radiat. Med. 1959, 1958, 145. (5) Orbin, M.; Koros, E. J . Phys. Chem. 1978, 82, 1672-1674. (6) Briggs, T. S.; Rauscher, W. C. J . Chem. Educ. 1973, 50, 496. (7) Boiteux, A,; Hess, B. Symp. Faraday SOC. 1975, No. 9 , 202-214. (8) Franck, U. F. Symp. Faraday SOC. 1975, No. 9 , 137-149. (9) OrbPn, M.; De Kepper, P.; Epstein, I. R.; Kustin, K. Nature (London), (10) Boissonade, J.; De Kepper, P. J . Phys. Chem. 1980, 84, 501-506. (11) Prigogine, I.; Lefever, R. J . Chem. Phys. 1968, 48, 1695-1700. (12) Field, R. J.;Noyes, R. M. J . Am. Chem. SOC. 1974,60, 1877-1884. (1 3) Pacault, A,; Hanusse, P.; De Kepper, P.; Vidal, C.; Boissonade, J. Acc. (14) Papsin, G.; Hanna, A,; Showalter, K. J . Phys. Chem., in press. (15) Pacault, A.; De Kepper, P.; Hanusse, P.; Rossi, A. C. R . Hebd. in press. Chem. Res. 1976, 9, 438-445. Seances Acad. Sci., Ser. C 1975, 281, 215-220.

Sustained oscillations in redox potential, pH, and the concentration of dissolved O 2 are reported in the Cu(II)-catalyzed reaction between K 2 S 2 O 8 and Na 2 S 2 O 3 in a stirred tank reactor. A range of steady states is found, most of which can be unambiguously designated as either high or low pH, but there is no evidence of bistability. A free-radical mechanism in which Cu(I), Cu(III), and the radicals SO 4 .− and S 2 O 3 .− play key roles appears to be capable of accounting both for the observed kinetics of the batch reaction and for the oscillations in the flow system

A ten-step mechanism has been developed for the Briggs-Rauscher system which contains iodate, hydrogen peroxide, malonic acid, and manganese(I1) in acidic solution. The model is qualitatively identical with, though it differs quantitatively from, that proposed independently by Noyes and Furrow. It also bears strong similarities to the mechanistic suggestions of Cooke. Extensive numerical simulations of the reaction in a flow reactor show that the model predicts the observed topology of the "cross-shaped phase diagram" in which both bistability and oscillations appear as the input flows of the reactant species are varied. The observed hysteresis in the steady-state iodine concentration as a function of I2 flow and a variety of other dynamic behavior are also calculated in agreement with experiment. The remaining discrepancies between theory and experiment appear to result from an overestimation in the model of the stability of the nonradical steady state. A possible remedy for this problem is suggested. The Briggs-Rauscher (BR) reaction,' in which the acidic ox- idation of malonic acid by a mixture of hydrogen peroxide and iodate is catalyzed by manganous ion, is best known as the most visually impressive of the chemical oscillators. Under appropriate conditions and with the addition of a starch indicator, at room temperature a stirred batch solution goes through 15 or more cycles of colorless-gold-blue before expiring as a purplish solution with a strong odor of iodine. The BR reaction, however, exhibits a far richer collection of nonlinear dynamic phenomena than simple oscillation. In a flow reactor, complex oscillations* as well as multiple stable states3 accompanied by a variety of bifurcation and hysteresis phenomena have been obse~ed.~.~ The BR system was discovered some 8 years ago and is a hybrid of two other chemical oscillators, the Belousov-Zhabotinskii (BZ)5 and the Bray-Liebhafsky (BL) reactions,6 for which detailed mechanisms have been proposed and numerically evaluated.'~~ It is therefore surprising that until quite recently there had been no quantitative and very little qualitative discussion of the mechanism of the BR reaction. Cookeg has studied the BR and related systems experimentally and has made a number of mechanistic suggestions based on his results. No quantitative comparison between theory and exper- iment was carried out. More recently, Furrow and Noyes'O have conducted a systematic study of the reaction, investigating the kinetics of the reacting species taken two and three at a time. These authors have proposed a skeleton mechanism and have estimated rate constants for the elementary steps in that mech- anism. They have also reported a single numerical simulation1& with their model which shows that it can indeed give rise to oscillations. In this paper, we use a broad range of experimental data ob- tained mainly, but not exclusively, under flow conditions, to guide the construction of a mechanism for the BR reaction. Although we approach the problem from a rather different point of view, we have independently arrived at a mechanism similar to that of Cooke and nearly identical with that of Furrow and Noyes. We have carried out extensive calculations with our mechanism in an attempt to simulate not only the oscillatory behavior, but the multistability, hysteresis, and bifurcation phenomena as well. We find qualitative agreement with nearly all of the observed phe- nomena and quantitative agreement with some. Most of the discrepancies which remain between our calculations and the experimental results can be attributed to a single weakness of the model-its exaggeration of the stability of the nonradical steady state of the system. We suggest how the mechanism might be augmented to correct this failing. Modifications of the BR system in which malonic acid is re- placed by related organic specie^^^^*'^ are also known to oscillate. In particular, Furrow" has carried out a careful study of the BR reaction with methylmalonic acid and has found a significant lengthening of the oscillation period over that of the malonic acid system. By introducing Furrow's experimentally determined rate parameters for the methylmalonic acid-iodine reaction at the appropriate point in our model, we show that it indeed predicts the observed increase in the period of oscillation.

Etude de la reaction oscillante du permanganate de potassium avec les ions Mn 2+ sur une electrode de platine dans une solution aqueuse d'acide phosphorique