Estimation of Carboxyl, Aldehyde, and Ketone Groups in Hypochlorous Acid Oxystarches

Purified wheat starch was oxidized at room temperature in approximately 0.05 to 0.09 M hypochlorous acid, preferably buffered to pH 4.0 or 4.2 with calcium acetate – acetic acid. The chemical efficiency of the oxidant was at least 56%. The fractions of oxystarch, insoluble and soluble in water, were isolated in a combined yield of 93% to 95%.So prepared, the water-soluble fraction (about 75% of the oxystarch) contained 45 to 58 mM. of carboxyl groups per anhydroglucose unit, probably all as uronic acid. Carbonyl groups amounted to 52 to 54 mM., 65% to 80% being aldehydes in the primary alcohol positions, and roughly 9% being ketone groups in the second positions. Between 80% and 90% of the total oxidation therefore concerned primary alcohol groups. Various estimations for carboxyl, total carbonyl, and aldehyde groups were compared.