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.