Acid-Induced Comproportionation of Halate and Halide

We discussed the disproportionation of molecular halogens to halate and halide in hot alkali (Section 7.2). The reverse process, called comproportiomtion, where two different oxidation states end up as one at the end of a reaction, happens in acidic solution. Thus, halate (X03 ), halide (X , X = Cl, Br, I), and protons react together to yield halogen molecules and water  

Given that the process is mediated by acid, a proton-coupled attack by X on XO3 seems 

We use the term proton-coupled attack as somewhat of a hedge to indicate that we do not have a good sense of the exact timing of the protonation, i.e., whether it occurs before, after, or synchronously with attack by X . A second proton-coupled attack by X on the above intermediate would then produce the first X2 molecule and halite (X02 ), the first reduction product of halate (XO3 ). 

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