Abstract
The mechanism of the periodate oxidation of glycerol, mesoerythritol, glycollic aldehyde, and glyceraldehyde, was investigated over a wide range of pH and reactant concentration at 0 C. Chemical kinetic and polarographic techniques were used, supplemented by measurements of pH, during reaction. The work with glycerol established the formation of a glycerol-periodate complex, of greater acid strength than periodic acid and in equilibrium with the reactants. The kinetics of the oxidation of glycollic aldehyde, which is formed by sigma-glycol cleavage of glycerol, was studied and the results showed that in the oxidation of glycerol, oxidation of the aldehyde must be allowed for at all pH values, except with a very large excess of polyalcohol. The variation of equilibrium constants, for the formation of the complex, and also the rate constants for its decomposition, with pH, is similar to that for 1:2-diols, showing that the monovalent complex is the only decomposing species over the pH range studied. From the results, the dissociation constants for the complex were calculated. Similar studies were made of meso-erythritol and glyceraldehyde, which is formed by initial sigma-glycol cleavage of erythritol. The results showed that the sigma-glycol cleavage of erythritol by periodate is similar to that of glycerol and 1:2-diols. The periodate oxidation of glyceraldehyde occurs via a complex in the pH region 6 - 9. At lower pH values, the kinetics showed that glycollic aldehyde is formed by the initial oxidation of glyceraldehyde. It was possible to follow the formation of polyalcohol-periodate complexes by polarography. Results at high pH suggest that two types of complex may be formed. The equilibrium constants for the formation of the divalent glycerol and meso-erythritol-periodate complexes are mush greater than those of 1:2-diols. To account for this, a triester structure has been proposed, although it does not altogether explain the variation of the formation and dissociation constants with structural changes.