Periodic acid mechanism

The cleavage of 1,2-diols 1 by periodic acid is associated with the name of the French chemist Malaprade. The reaction mechanism is related to that outlined above, and is likely to involve a five-membered ring periodate ester intermediate 7 ... 

This mechanism is supported by these facts (1) the kinetics are second order (first order in each reactant) (2) added acetic acid retards the reaction (drives the equilibrium to the left) and (3) cis glycols react much more rapidly than trans glycols. For periodic acid the mechanism is similar, with the intermediate ... 

The mechanism of oxidation of vicinal glycols by HI04 has been studied by G.J. Buisst and C.A. Bunton (J. Chem. Soc., 1406, (1954). According to these workers, the reactive species is the para form of periodic acid (H5I06) which is formed by the action of water on HI04. 

Exercise 29-17 Polyvinyl alcohol prepared by hydrolysis of polyethenyl ethanoate (polyvinyl acetate Table 29-1) does not react with measurable amounts of periodic acid or lead tetraethanoate (Sections 16-9A and 20-4A). However, periodic acid or lead tetraethanoate treatment of the polymer does decrease the number-average molecular weight, for a typical sample from 25,000 to 5000. Explain what these results mean in terms of the polymerstructures and the mechanism of the polymerization. 

Fig. 17.23. Mechanism of the glycol cleavage with NaI04 or H5I06, respectively. A diester of iodo(VII) acid (periodic acid) is formed initially. The ester decomposes in a one-step reaction in which three valence electron pairs are shifted simultaneously.

Mechanism of staining Periodic acid opens the sugar rings at cis-diol bonds (i.e., the C-2—C-3 bond of glucose) to form two aldehyde groups and iodate (IOJ). Then the =+NH2 group of the dye reacts to form a so-called Schiff base bond with the aldehyde, thus linking the dye to the carbohydrate. The basic reaction is ... 

The use of iodate and periodic acid as oxidizers for noble metal CMP has also been attempted. Similar to W CMP, a surface oxidation or modification is required for the subsequent removal by mechanical force. For example, the potential use of ruthenium as bottom electrode capacitor for next-generation DRAM devices [40] has been explored. Owing to the fact that a dry-etch process can lead to the formation of toxic RUO4 [41], the possibility of using CMP to implement Ru has gained interest recently. The studies in this area have indicated that the formation of stable passive layers such as RUO2 [41,42] and RU2O5 [42] are important steps in the Ru CMP. 

The nature of a fatty add influences its fate. Short- and medium-tdiain fatty adds tend to be oxidised immediately to carbon dioxide, rather than deposited as TGs or phospholipids. The presence of double bonds ("unsaturations") in long-chain fatty adds influences the immediate fate of the add. Some evidence suggests that unsaturated fatty acids, such as 18 2, tend to be oxidized at a slightly faster rate in the hours following a meal than saturated fatty acids, such as 18 0 (Jones et al., 1985, Jones and Schoeller, 1988). More specifically, about 2% of a test meal of 18 0 may be oxidized in the 9 hours toUowing Ingestion, whereas about 10% of a test meal of 18 2 may be oxidized in the same period, The mechanisms that influence the fates of unsahirated and saturated fatty adds are only beginning to be understood. 

The mechanism of the cleavage of vicinal diols can be represented by the reaction of diols with periodic acid, HIO4 or H5IO6 (equation 296). 

E17.25 Periodic acid is by far the quicker oxidant. Recall that it exists in two forms in aqueous solution—HsIOs (the predominant form) and HIO4. Although the concentration of HIO4 is low, this four-coordinate species can form a complex with a potential reducing agent, providing for an efficient and rapid mechanism by which the redox reaction can occur (see Sections 17.13 and 17.14). 

The mechanism of 1,2-cleavage of glycols with sodium bismuthate is generally considered to be similar to that with lead tetraacetate and periodic acid [40CB563], although there is still some controversy [50JCS(C)1907]. A cyclic bismuthate diester is postulated as a plausible intermediate, though the rates of oxidation observed are not so different between cis- and trans-, 2-cyclohexanediols. 

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