Iodine‐poly(vinyl alcohol) interactions, 2. Anomalous slow quenching of the chromophore after extraction of free iodine with carbon tetrachloride

Abstract

AbstractAn equilibrium blue colored solution containing poly(vinyl alcohol) (PVA)‐iodine‐boric acid was prepared at 5°C. With increasing PVA concentration, at the same concentration of iodine, the absorption band of the chromophore I (λmax = 650 nm, band D) linearly increased and the intensities of the bands for both I− (λmax = 226 nm, band A) and I (λmax = 290 nm, band B) decreased. The band due to another iodide species (λmax = 355 nm, band C), tentatively assigned to I · I2, remained unchanged. Three solutions with different PVA concentration were then extracted with the same volume of carbon tetrachloride to remove I2 present in the system. It was found that the chomophore due to I gradually decays with repeated extractions. After one extraction the change of the absorbance of I with time was measured at 5°C. In the system with a high PVA concentration the chromophore recovers the equilibrium within three days without losing much intensity, while in the systems with lower PVA concentration recovering of equilibrium takes more than four days with a considerable loss of chromophore. In the latter case, free I2 extracted is supplied by the decomposition of polyiodide ions to I−. Analysis of the rate of re‐equilibration of iodine species revealed two reaction processes: one is a reaction involving free iodine species in an aqueous environment and the other is a slow reaction involving the polyiodide ions bound in a PVA cage.