Radical Chain Reduction of CCl 4 Initiated by Illumination of SPEEK Solutions

Efficient reduction of CCl 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 HCO H/HCO buffer. The photoreaction formed chloride ions whose concentration increased linearly with time in solutions free of O , 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 CHCl 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 (I ) , where I is the light intensity, and the occurrence of postirradiation formation of Cl through the reduction of CCl 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 •CCl as chain carriers.