Oxidative Cleavage of 1,2-Diols
Oxidative Cleavage of Vicinal Diols with Periodic Acid: Application
The oxidative cleavage with periodic acid has been succesfully applied in the constitutional analysis of sugars. The presence of several pairs of vicinal diols during oxidation with periodic acid can lead to the formation of complex product mixtures. Treatment of a sugar with sufficient amounts of oxidizing agent yields C1 -fragments. For example, reaction of glucose with 5 equivalents of HIO4 gives five equivalents of formic acid and one equivalent of methanal (formaldehyde). An analogous degradation of fructose yields three equivalents of formic acid, two equivalents of formaldehyde and one equivalent of carbon dioxide.
A sugar containing a terminal hydroxyl group (here C6 ) adjacent to another hydroxylated carbon can be oxidized to formaldehyde and an aldose containing one less carbon atom than the educt.
Products of the oxidation of terminal aldehydes are derived from the corresponding hydrated forms, geminal diols, which are in equilibrium with the aldehydes. The oxidation now yields formic acid and a one-carbon atom less aldose.
In the case of a terminal hydroxymethyl group adjacent to a carbonyl function (fructose), oxidative cleavage proceeds also through a geminal diol and produces formaldehyde and carboxylic acid.
If the generated acid contains an α-hydroxyl group, oxydation produces carbon dioxide and an aldehyde that can be degraded further.
In summary, the basic skeleton of sugars is degraded during oxidative cleavage with periodic acid into formic acid, formaldehyde and carbon dioxide. The ratio of the individual fragments depends on the constitution of the sugar.