The blue colored iodine-starch complex, formed in many iodine clock reactions, has been observed and studied for many years, but it is still unclear what the structure of the product is and by what mechanism it is formed. Using 3D-printed millifluidic devices as a reaction vessel to allow for spectral acquisition on a flowing, iodine clock reaction in real-time, UV-Vis absorption spectra were collected to probe the flow dynamics and study the effects of the solvation environment of the iodine clock reaction under various solvent conditions. When the solvent composition is changed from water to aqueous solutions of increasing amounts of methanol, ethanol, and 1-propanol bathochromic shifts of the complex absorbance features are observed. It is determined that the solvent environment surrounding the iodine-starch complex is integral to controlling the structure of the complex and the addition of alcohol to the solution easily perturbs the solvent network. An analysis of the laminar flow dynamics suggest that the iodine-starch complex my preferentially exist in solution where a stable solvation network is able to form and that the triiodide ion may form slightly before the complex in most aqueous solutions. The observed blue shifts of the visible absorptions of the product complex occur both as alcohol concentration and alcohol chain length increase. These shifts are not attributed to the decreasing polarity of the solvent but rather to the weakening of the solvation network around the complex as an alcohol is introduced. The observed solvatochromatic shifts are due to interactions of the solvent with the external starch portion of the complex and may provide benchmarks for the expected effects of different solvents on the electronic structure of the product complex.

Using millifluidic devices to investigate the role of the solvent environment for the iodine-starch complex

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.