Decomposition of hydrolysates of chemical warfare agents using photoactivated periodate

The kinetics and mechanism of periodate and photoactivated periodate oxidation of the hydrolysates of chemical warfare agents (HCWAs), thiodiglycol (TDG), 3,3-dithiopropanol (TDP), and 1,4-thioxane (TX), were investigated at pH 3, pH 7, and pH 10 under dark (in the absence of light) and monochromatic UV light irradiation. Dark reactions occurred by oxygen addition to sulfur atoms in HCWAs at pH 3 and pH 7 following the trend: TDP > TX > TDG. At pH 10 in the absence of light, both Malaprade and oxygen addition reaction mechanisms occurred in the reaction of H3IO62− with HCWAs but at slower reaction rates compared to low pH dark reactions following the order: TDG > TDP > TX. The presence of monochromatic UV light at 220 nm, 240 nm, or 254 nm had insignificant improvements on HCWA degradation at low pH. At pH 10, the presence of 220 nm light resulted in an increase in degradation of HCWAs compared to dark reactions following the trend of electron density on the sulfur atom of the compound (TDP > TDG > TX). However, TDG, the compound with the largest dark reaction rate constant at pH 10 had the smallest percent increase in degradation due to the addition of light. Conversely, TX had the smallest dark reaction rate constant and the largest percent increase in degradation due to the addition of light. In the presence of light, the addition of t-butanol decreased degradation rates at pH 10 suggesting that OH plays an important role in the reactions. Degradation trends and kinetic modeling also suggest that iodyl radicals are involved in TX reactions.