Hypoiodite ion

Iodine behaves as a powerful oxidizing agent in strong alkaline solution due to the formation of hypoiodite ion ... 

The hypoiodite ion, however, is unstable, decomposing to iodate and iodide ions ... 

The H202 first oxidizes the catalyst (I-) to hypoiodite ion (IO-) and then reduces the intermediate IO- back to I-. The catalyst does not appear in the overall reaction because it is consumed in step 1 and regenerated in step 2. The catalyst is, however, intimately involved in the reaction because I - appears in the observed rate law ... 

Consider the following concentration-time data for the reaction of iodide ion and hypochlorite ion (OC1-). The products are chloride ion and hypoiodite ion (OI-). 

The hypoiodite ion is much less stable than the other hypohalite ions, decomposing almost completely to iodate and iodide in a few hours, whereas the corresponding decomposition of hypochlorite at the same concentration and the same temperature requires several years. 

Practice Problem 6.12 Write the formula for (a) iodite ion and (b) hypoiodite ion. ... 

Iodine reacts with hydroxide ion in cold alkaline solution to form the hypoiodite ion, lO", and iodide ion ... 

Notice that the iodide ion, I , consumed in step 1 is regenerated in step 2, and the hypoiodite ion, lO , generated in step 1 is consumed in step 2. In principle, a single iodide ion could break down an unlimited amount of hydrogen peroxide. This is the characteristic of all catalytic pathways— the catalyst is never used up. It is regenerated and so becomes available for use again and again. 

Calculate the equilibrium constant for the reaction of hypoiodite ions (OI ) with water. 

The hypoiodite ion, 10 , absorbs at the blue end of the spectrum near 400 nm. The intensity of this absorption is proportional to [10 ], and you can use the absorption to determine the reaction rate. You can also follow the decomposition of N2O5 from the intensity of the red-brown color of the product NO2. 

In too alkaline a medium, hypoiodite ions are formed and the reaction exhibits a different course. Cyanate ions are formed ... 

The instability of hypoiodite ions is clearly apparent in the complete Pourbaix diagram when we consider the frontier straight lines I03 /I0 and lOs /HIO. If we limit ourselves to the zone for which pH > 11 by drawing a vertical line on the diagram, say at pH = 12, we obtain the diagram in Fig. 19.3. 

Preponderance areas of hypoiodite ions 10 are unconnected, which is not possible. Hence, hypoiodite ions disproportionate into iodate and iodide ions. 

Finally, it is interesting to note that hypoiodous acid and hypoiodite ions are more oxidizing than iodate, tri-iodide ions, and iodine in the range where they can (temporarily) coexist. 

Remark We shall see in iodatometry that iodine (+1) may be stabilized in other forms than as hypoiodous acid or hypoiodite ions. Indeed, the species ICl (iodine monochloride), ICl2 (iodine dichloride), IBr (iodine monobromide), IBr2 (iodine dibromide), and ICN (cyanogen iodide) exist. 

In the oxidation reaction by hypoiodite ions, we consider that the reacting species is hypoiodite ion. For example, during the oxidation of some aldehydes into carboxylate ions, the following two reactions occur ... 

However, acetaldehyde exhibits a different behavior from that of chloral. It gives the iodoform reaction (see below). Unfortunately, thehypoiodite ions/aldehydes reaction is not selective. Several organic compounds react with hypoiodite ions as a result, their determination may interfere with this reaction with aldehydes. 

Dimethyl ketone (acetone) may be titrated by hypoiodite ions, with the formation of... 

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