TEMPO-catalyzed oxidation of polysaccharides

2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-catalyzed oxidation enables efficient and position-selective conversion of primary hydroxy groups in water-soluble and water-insoluble polysaccharides to sodium carboxylate groups under mild conditions in water. TEMPO/NaBr/NaClO in water at pH 10 is an advantageous system in terms of the degrees of oxidation and reaction rates. TEMPO and NaBr behave as catalysts, and NaClO acts as the primary oxidant. However, oxidative depolymerization that is caused by the presence of NaBr and NaClO and the occurrence of side reactions on the polysaccharide molecules are unavoidable during oxidation. An alternative system is 4-acetamido-TEMPO/NaClO/NaClO2 in pH 5–7 buffer at 35–60 °C for 1–3 d, in which catalytic amounts of TEMPO and NaClO are used with NaClO2 as the primary oxidant. This oxidation system significantly inhibits depolymerization and yields oxidized products that contain no aldehydes. Various new water-soluble TEMPO-oxidized polysaccharides that contain significant amounts of sodium carboxylate groups have been prepared by TEMPO-catalyzed oxidation, and they have unique properties and functionalities. When crystalline native cellulose and chitin are oxidized by the TEMPO/NaBr/NaClO system under suitable conditions, the obtained water-insoluble oxidized products can be converted to various characteristic nanomaterials by mechanical disintegration in water, depending on the oxidation and disintegration conditions. TEMPO-catalyzed oxidation enables efficient and position-selective conversion of primary hydroxy groups in water-soluble and -insoluble polysaccharides to sodium carboxylate groups. TEMPO/NaBr/NaClO in water at pH 10 is an advantageous system in terms of the degrees of oxidation and reaction rates. Various new water-soluble TEMPO-oxidized polysaccharides have been prepared by TEMPO-catalyzed oxidation, and they have unique properties and functionalities. When crystalline native cellulose and chitin are oxidized by the TEMPO/NaBr/NaClO system under suitable conditions, the obtained water-insoluble oxidized products can be converted to characteristic nanomaterials by mechanical disintegration in water.