Oxidation of potato starch with NO2:: characterization of the carboxylic acid salts

Oxidation of primary hydroxyl groups of potato starch to the corresponding carboxylic acids was performed in a fluidized bed using N-2-diluted NO2, as oxidant. FT-IR spectrum of the oxidized starch show the presence of two absorption bands at 1743 and 1379 cm(-1). The absorption at 1743 cm(-1) which normally attributed to carbonyl absorption vanishes after washing the oxidized starch by water. Then two new absorption bands appeared at 1650 and 1400 cm(-1) corresponding to the ionized carboxyl groups. The presence of nitrate favor the un-ionized form of carboxyl groups and then the band at 1743 cm(-1) can be observed. Furthermore, the ionized carboxyl absorption (1600, 1400 cm(-1)) are replaced by carbonyl absorption at 1743 cm(-1) by adding DCl. By means of C-13 NMR analysis, oxidized starch, show a band around 200 ppm attributed to carboxylic acid, no formic acid was detected indicating that no cleavage took place under the applied reactions conditions. (C) 2001 Elsevier Science B.V, All rights reserved.