Kinetic Study of the Formation and Decomposition of Amylose-iodine-iodide Complex

Abstract

Abstract The complex formation reaction among amylose, iodine and iodide ion in aqueous solution was investigated with a stopped-flow apparatus. The forward reaction rate was found to be expressed as v=k[Amylose]([I3−]–θ) for [I3−]>θ, where θ is a critical value determining the mechanism. For [I3−]>θ, the rate was considered to be determined by the process between a free amylose unit and free I3−. For [I3−]<θ, the rate-determining step is considered to be intramolecular conversion from an intermediate to a final product. The rate of the reaction between amylose units and I3− is close to that of a diffusion-controlled process (7×108 m−1 sec−1). These conclusions are supported by the study of the decomposition reaction of complex, using Na2S2O3 or Ce(SO4)2.