A kinetic study of the mild oxidation of wheat starch by sodium hypochlorite in the alkaline pH range

Abstract (1) Some kinetic aspects of mild oxidation of wheat starch by sodium hypochlorite in the pH range 7.5–11.0 were studied. (2) No significant chlorate formation was observed at any time. From this and from other experimental evidence it is concluded that the reaction is most likely to be purely chemical in type and to proceed according to the overall scheme: (3) The reaction appears to be of the first order with respect to starch. (4) The reaction appears to be of the first order with respect to hypochlorite at pH = 8.0. At pH = 9.0 and 10.0, the reaction velocity is still approximately proportional to the concentration of the oxidant present, but the course of the reaction appears to be more complicated. (5) The reaction rate decreases with increasing pH of the oxidizing medium. An approximate empirical equation is proposed adequately representing the interdependence of the first‐order constant and pH in the pH range 7.5–10.0. (6) The activation energy of the reaction is within the range of 21–23 kcal./mole, i.e., that obtained for many homogeneous, truly chemical reactions. (7) The fact that the reaction rate of a starch solution is about 50% higher than the corresponding rate for a starch suspension would seem to indicate that the number of sites available for oxidation in a granule is about two‐thirds of that available when that granule is dissolved. (8) The addition of neutral salts had an accelerating effect on the reaction rate. Under the experimental conditions of the present paper, this effect was negligible, but at much higher salt concentrations it would have to be taken into account.