A New Bromite Oscillator. Large-Amplitude pH Oscillations in the Bromite-Thiosulfate-Phenol Flow System

The reaction between bromite and thiosulfate ions in aqueous solution with and without phenol has been studied under batch and flow conditions. The bromite oxidation of thiosulfate proceeds via two consecutive fast reactions, the first accompanied by a significant increase, the second by a large decrease in pH. The Hf production is autocatalytic and strongly influenced by phenol. The bromite-thiosulfate-phenol flow system exhibits bistability and large-amplitude pH oscillations. Several relevant reactions such as bromite-phenol, bromite-bromide, bromate-thiosulfate, and bromate-phenol were also investigated, and their participation in the batch and flow behavior of the bromite-thiosulfate-phenol system is discussed. A qualitative explanation of the pH oscillation is proposed. content of our sample was found to be 68.1%. The NaBrO3 in the sample was 14.0%. The solid NaBr@.3H20 contained about 15- 16% hygroscopic water. According to the literature,6 sodium bromite may be contaminated with NaOBr and NaBr as well. We found neither NaOBr nor NaBr in our sample. The presence of NaOBr was ruled out by using the method suggested by Lee and Lister.' The absorption spectrum of the aqueous bromite solution was taken, and the maxima at 296 and 330 nm, characteristic of bromite and hypobromite, respectively, were compared. The ratio found, 1.36, agrees with the literature value for a hypobromite-free sample. The stock solution of bromite was always freshly prepared and consumed within 5 h. Apparatus and Methods. The batch reaction between bromite and thiosulfate in the absence and presence of phenol was followed by measuring the change in pH (Orion pH meter, Aldrich combined glass pH electrode) and the potential of a Pt