Pulse radiolytic oxidation of chloral hydrate in oxygenated and deoxygenated aqueous solutions

Abstract

Dilute chloral hydrate solutions containing either N₂O or a N₂O + O₂ mixture were pulse irradiated and their optical absorption and electrical conductivity simultaneously recorded as functions of time. The first product of OH and H attack on chloral hydrate is the CCl₃Ċ(OH)₂ radical. The pK of its electrolytic dissociation was found to be 6.9 ± 0.2. In the absence of O₂, it disappears by disproportionation to yield trichloroacetic acid. The rate constant 2k is equal to (7.0 ± 1)× 10⁸ M^–1 s^–1 at pH = 5.5 and (4.4 ± 0.7)× 10⁸ M^–1 s^–1 at pH = 10.8. CCl₃Ċ(OH)₂ adds O₂ with k=(1.0 ± 0.2)× 10⁹ M^–1 s^–1. The resulting peroxy radical CCl₃O₂(OH)₂ is a bivalent acid with the pK-values of 3.3 ± 0.3, and 8.7 ± 0.3, respectively. Two peroxyradicals react with 2k=(1.7 ± 0.3)× 10⁸ M^–1 s^–1 to produce a product that finally disappears by first order kinetics. The product is assigned the structure of a hydrotetroxide, CCl₃C(OH)₂O₄H, which is strongly dissociated into CCl₃C(OH)₂·+ HO₂·. Its decay is explained by the loss of oxygen.