Regioselectively oxidized 3-O-alkyl ethers of cellulose: Synthesis and characterization

Water insoluble 3-mono-O-methyl- and 3-O-butyl celluloses as well as water soluble 3-mono-O-ethyl cellulose were oxidized with 2,2,6,6-tetramethylpiperidine-1-oxyl radical/NaBr/NaClO in water. The insoluble starting materials dissolved during the course of oxidation forming water soluble 3-O-alkyl-6-carboxy celluloses. The reaction rate decreases with increasing crystallinity of the starting materials. Structure analysis by means of 13C NMR spectroscopy revealed the selective oxidation of the primary OH group to the carboxylate moiety without affecting position 2. Size exclusion chromatography measurements showed polymer degradation as a side reaction of oxidation but no indication of aggregation in aqueous solution. The oxidized cellulose ethers reduce the surface tension of water depending on the alkyl chain length. The lowest value of σ = 40.5 mN/m was determined for a 0.5% aqueous solution of 3-O-butyl-6-carboxy cellulose.