Starch derivatives of high degree of functionalization 9: carboxymethyl starches

This paper describes the synthesis of carboxymethyl starch (CMS) ID various alcohols (methanol, ethanol, isopropyl alcohol) as slurry media and with different starch types. The products were investigated regarding their degree of substitution (DS), their reaction efficiency (RE), and their pattern of functionalization. The highest DS obtained ID a one-step procedure was 1.40 with a RE of 82%, applying isopropyl alcohol as slurry medium. Moreover, by using the synthesis concept via a reactive microstructure, CMS samples with high DS values can be achieved ID a one-step synthesis as well. A multi-step carboxymethylation ID methanol, on the other hand, leads to maximal DS values of 2.3 after 10 conversions, dependent on the amylose content of the starch. ¹H NMR spectroscopic investigations show a reactivity ID the order O-2 > O-6 O-3 for the samples prepared ID alcoholic slurry media. ID contrast, the CMS synthesized via reactive microstructure reveals a preferred substitution ID position 6 and a non-statistic distribution of the carboxymethyl groups along the chain. A significant amount of 2,3,4,6-tetra--functionalization, caused by the branched structure of starch, was found.