OXIDATION OF POLYSACCHARIDES BY LEAD TETRAACETATE IN DIMETHYL SULFOXIDE
Neutral polysaccharides can be oxidized by lead tetraacetate in dimethyl sulfoxide if 15–20% of glacial acetic acid is added to prevent oxidation of the solvent. The oxidation proceeds at a rate which is several times faster than that of periodate oxidation in aqueous solution, and the same amount of oxidant is consumed. Polysaccharides oxidized by lead tetraacetate in dimethyl sulfoxide can be recovered in excellent yield by precipitation with alcohol, and have been shown to contain free aldehyde groups. Identification of the products of reduction and hydrolysis of the oxidized polysaccharides showed that the oxidation followed the normal glycol-cleavage pattern given by lead tetraacetate in other solvents. Addition of potassium acetate to the oxidations in dimethyl sulfoxide decreased the consumption of lead tetraacetate by dextran (mainly α-(1 → 6) and α-(1 → 4)). Reduction and hydrolysis of dextrans oxidized in the presence and absence of potassium acetate yielded glycerol and erythritol in the respective ratios of 3.8:1 and 8.7:1. This result indicated that potassium acetate inhibited oxidation of the C-3, C-4 glycol groups in the dextran. Acidic polysaccharides behaved atypically in this oxidation system, and those containing a high proportion of uronic acid units were resistant to oxidation.