DECOMPOSITION OF OZONE IN AQUEOUS ACETIC-ACID SOLUTIONS (PH 0-4)

The decomposition of acidic O3 solutions containing acetic acid has been studied with the purpose of determining the rate of the initiation reaction for the radical-induced chain decomposition. The effects of acetic acid, ozone, oxygen, and hydrogen peroxide have been studied as a function of temperature over the pH range 0-4. Our interpretation of the mechanism in the O3-acetic acid system gives a rate constant at 31-degrees-C of k = (3.0 +/- 0.5) x 10(-6) s-1 for the precursor of radical formation. As expected this rate is constant in the acid pH range. The activation energy E(A) = 82.5 +/- 8.0 kJ mol-1 as determined over the temperature range 15-50-degrees-C is identical to that found in acidic solutions without acetic acid. It is found that O3 reacts with undissociated hydrogen peroxide, with a rate constant k = 0.065 dm3 mol-1 s-1 at 31-degrees-C and an activation energy of E(A) = 73.5 +/- 8.0 kJ mol-1 measured in the temperature range 15-45-degrees-C. We tentatively suggest an electronic excited state of ozone, formed in the dissociation/recombination reaction of O3, to be the precursor for the radical formation by its reaction with water.