Radical Chain Reduction of CCl₄ Initiated by Illumination of SPEEK Solutions

Efficient reduction of CCl₄ took place upon exposure to 350-nm photons of aqueous solutions containing sulfonated poly(ether etherketone) (SPEEK) as a sensitizer and either poly(vinyl alcohol) (PVA) or HCO₂H/HCO₂^- buffer. The photoreaction formed chloride ions whose concentration increased linearly with time in solutions free of O₂, whereas slower reductions occurred in the presence of air. Utilization of formate buffer as the H-atom donor yielded photoreactions at least 10 times faster than those in the presence of PVA and generated CHCl₃ as another reaction product. The quantum yield of chloride ion formation, ø(Cl^-), was found to be a function of both the SPEEK concentration and concentration of formate buffer. Whereas the quantum efficiency increased steadily with decreasing solution acidity, a drastic surge in the reaction rate occurred in neutral solutions. ø(Cl^-) first increased rapidly to a maximum value exceeding 1 at pH 7.3 and then decreased thereafter. The dependence of r(Cl^-) on (I₀)^1/2, where I₀ is the light intensity, and the occurrence of postirradiation formation of Cl^- through the reduction of CCl₄ in the dark are further evidence that the photoreaction proceeded by a chain process. Several of the kinetic features were rationalized by means of a mechanism involving the α-hydroxy radicals of SPEEK and •CCl₃ as chain carriers.