Over 70 years ago, Bray discovered oscillations in iodine concentration during the iodate-catalyzed disproportionation of aqueous hydrogen peroxide. Although at least 50 papers have been published about this reaction, the mechanism has not been definitively established. We have now observed, apparently for the first time, that oscillations can be inhibited by very rapid stirring. The frequency can also be slowed greatly by sonication. We believe that transport of oxygen from supersaturated solution to surrounding atmosphere must be included in any detailed mechanistic explanation of the oscillations. We propose a skeleton mechanism which appears to explain at least most of the observed behaviors. Additional experiments are proposed which should either support or discredit the proposed new mechanism.

The influence of oxygen in Belousov−Zhabotinsky systems with substituted malonic acid derivatives RMA (R = H, Me, Et, Bu, phenyl, and benzyl) has been studied. A significant influence of oxygen and organic substrate has also been found for the autocatalytic oxidation of the catalyst by bromate. In both the presence and the absence of RMA, oxygen always increases inflection times of the autocatalysis when compared with anaerobic conditions (argon bubbling). In general, period lengths P of RMA−BZ systems increase with increasing Taft σ* constants of substitutent R and a linear log P − σ* relationship has been found. In aerobic conditions (oxygen bubbling) the MA−BZ system is an exception because malonic acid (MA) BZ period lengths are, at these conditions, significantly lower and deviate from the linear log P − σ* relationship. The deviation appears to be related to the increased release of bromide ion when MA−BZ systems come in contact with oxygen. Model computations indicate that the decrease in inflection time of the autocatalysis is related to the scavenging of BrO2 radicals, probably by RMA• and RMAOO• radicals. The increase of period lengths in RMA−BZ systems with increasing σ* values appears to be related to the bromination/enolization of the organic substrate as the determined enolization rates of RMA show.

The oxidation of iodine with hydrogen peroxide was studied spectrophotometrically and potentiometrically. At low concentrations of HClO4, after induction period (IP), the iodine concentration decreases sigmoidally and IP decreases with decreasing surface area of the solution interphase. We assume that •OH radicals are produced via the oxidation of iodide with H2O2 and, by their subsequent reaction with H2O2, the HO2• radicals are formed. By their disproportionation, 2 HO2•  ↔   H2O2 + 1O2, very reactive singlet oxygen is produced and the oxidation of iodine can start. The described experimental results are consistent with the Noyes-Treindl mechanism.

Rates of solvolysis of methanesulfonyl chloride and benzenesulfonyl chloride have been determined in H 2 0 and D,O. The free energy, enthalpy, entropy, and heat capacity of activation were calculated. The exceptional accuracy of the data permitted an estimation of dAC,*/dTfrom a four parameter temperature dependence of the kinetic rates.From these data we conclude that both sulfonyl chlorides hydrolyse by the same mechanism (SN2) The change in R from CH3 to CsH5 in RS02CI did not alter AC,* but AS* (20') was changed from -8.32 to -13.25 cal deg-' n~o l e -~, resoectivelv. The significance of this difference is attributed to the probability of bond formation rather than to differences-in solvent reorganization.Canadian Journal of Chemistry, 47. 4199 (1969) This paper is the first of a series reporting detailed studies of the hydrolysis of sulfonyl chlorides5. The experimental approach is the same'as that applied in preceding studies on the halides and sulfonates: a careful examination of the effect of temperature and of isotopic substitution in the solvent on the temperature dependence of the rate of hydrolysis.In the halide series we found a remarkable similarity in the values of the heat capacity of activation, AC,,' (lo), and in the differences in AG* for hydrolysis in H,O and D,O over a range of structures for which it was reasonable to expect different degrees of bond-making in the activation process (11). These observations led to the conclusion that the SN2 transition state was reached when the charge on the halide being displaced created interaction with the solvent equal to water-water interaction; i.e. the transition state corresponded to that degree of charge development where exothermic solvation of the quasi-halide was about to begin. Consequently, it followed that for a given temperature, the charge level (ti-) on the chlorine atom, for example, is the same whether the ion is being displaced from allyl, ethyl, or methyl chloride. This in turn implies that the charge level on the anion at the transition state of an SN2 displacement is independent of the degree of nucleophilic interaction. The evidence in favor of this con-'NRCC No. 10 915. ZPresent address: Chemistry Department, The University of Calgary, Calgary, Alberta. 3NRCC Postdoctoral Fellow, 1968-1969. 4NRCC Postdoctoral Fellow, 1965. 5For references to previous work, see refs. 1-9. clusion derived from the similarity in AC,* values and from the limited range of 6 4 H * = AHD2o* -AHHzo* for SN2 displacement for the hydrolysis of alkyl halides, is weakened by the possibility that the difference in the degree of bond-malung at the transition state for the hydrolysis of the available halides is small, a possibility suggested by the uniformity of our kinetic solvent isotope effect (k.s.i.e.) values (10).To fill this deficiency we were led to examine the hydrolysis of the sulfonyl chlorides, since in this series there are good indications that a greater degree of nucleophilic overlap is required at the transition state (10, 12). We assumed ...

Phase response analysis of light-perturbed closed and aging Ru-catalyzed Belousov-Zhabotinsky (BZ) reactions with malonic, methyl-, ethyl-, butyl-, and phenylmalonic acids as organic substrates suggests two major responses of the light-perturbed Ru-catalyzed BZ system. One is the photoproduction of bromous acid (HBrO 2 ) in the beginning of the reaction when little bromoorganic species are present, while another response is the photoproduction of bromide ions in the presence of bromomalonic acid or bromomalonic acid derivatives. From this analysis the light-induced production of bromide ions directly from bromate can be excluded. The experimentally observed phase response curves agree well with calculations performed with the Oregonator model. An oxidative quenching mechanism for the photoproduction of bromide is suggested. Interestingly, during illumination of theRu(II)/MA subsystem, i.e., in the absence of BrMA and bromate, the oxidative quenching does also occur.