Glycols cyclic 1,2-, periodate oxidation

Periodic acid and periodates have found wide application in organic chemistry as powerfiil oxidizing reagents [729-731]. The well-known periodate glycol oxidation involves the cyclic periodate esters as key intermediates however, none of the organic periodate esters have been isolated as stable compounds. 

There is no change in the oxidation state of either iodine or the glycol as a result of formation of the cyclic periodate. 

Oxidative Cleavage of a Glycol (Section 10.8E) HIO reacts with a glycol to form a five-membered cyclic periodate intermediate that undergoes carbon-carbon bond cleavage to form two carbonyl groups. 

Enzyme-catalyzed oxidation of the primary hydro)yl group at carbon 6 of a hexose yields a uronic acid, examples of which are common in both the plant and animal worlds. Periodic acid cleaves the carbon-carbon bond of a glycol in a reaction that proceeds through a cyclic periodic ester. This reaction was once useful in carbohydrate stmcture determination. 

The exact course of the periodate reaction has not yet been established. That an intermediate complex, compound, or ion is involved has been determined kinetically.28 269 261 262 283-286 The exact structure of this intermediate is still in doubt. The most universally accepted structure is a cyclic ester intermediate propounded by Criegee,27 285 analogous to his cyclic ester intermediate for another agent oxidizing 1,2-glycols, lead tetraacetate. 

Reagents that specifically oxidize vicinal glycols [e.g., NaI04, Pb-(02CCH3)4, and NaBi03 Section 16-9A] are quite helpful in determining the cyclic structures of sugars. With periodate, the numbers of moles of oxidant consumed and the moles of methanoic acid and methanal produced are... 

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. 

Lead tetraacetate is an alternative to periodate for glycol cleavage. It is particularly useful for glycols that have low solubility in the aqueous media used for periodate reactions. A cyclic mechanism is indicated by the same kind of stereochemistry-reactivity relationships discussed for periodate. Unlike periodate, however, glycols that cannot form cyclic intermediates are eventually oxidized. For... 

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