Volume 4 @BULLET Issue 1 @BULLET 1000e115 J Thermodyn Catal ISSN: 2157-7544 JTC, an open access journal Editorial Open Access Why the Acidity of Bromic Acid Really Matters for Kinetic Models of Belousov-Zhabotinsky Oscillating Chemical Reactions (original) (raw)

Abstract

The cerium-catalyzed Belousov-Zhabotinsky oscillating reaction and its variants (Fe [5,6], Ru [7,, Mn ) are inherently connected to the chemistry of bromine oxoacids HBrO x . The growing interest in nonlinear chemical systems has provided strong incentives to study bromine chemistry, and especially the disproportionation of bromous acid has been studied in great detail . The bromine chemistry of the Belousov-Zhabotinsky reaction (BZR) involves hypobromous acid HOBr (1), bromous acid HOBrO (2) and bromic acid HBrO 3 (3), and the disproportionation reaction of bromous acid is a key step. H + + Br -+ HOBrO ⇄ 2 HOBr (R2) 2 H + + Br -+ BrO 3 -⇄ HOBr + HOBrO (R3) 2 HOBrO ⇄ HOBr + H + + BrO 3 -(R4) It is generally agreed that hypobromous acid (pK a (HOBr)=8.59 [30,31]) and bromous acid (pK a (HOBrO)=3.43 [29]) are not dissociated at pH values typical for the BZR. In contrast, it has been assumed that bromic acid is dissociated under BZR conditions even though the acidity of bromic acid has not been well established. Experimental pK a (3) values of 1.87 [30], 0.7 [31], and -0.29 [32] were reported and, most recently, Cortes and Faria concluded that pK a (3) < -0.5 . We wrote recently [34] that it will be important to firmly establish pK a (3) because this value decides whether reactions R3 and R4 should be replaced by reactions R3' and R4' , respectively, or whether reactions R3' and R4' need to be considered in addition to reactions R3 and R4. HOBrO 2 ⇄ H + + BrO 3 -(A(3)) H + + Br -+ HOBrO 2 ⇄ HOBr + HOBrO (R3') = (R3) + (A(3)) 2 HOBrO ⇄ HOBr + HOBrO 2 (R4') = (R4) -(A(3))

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