p-Coumaric acid abatement by ozone in aqueous solution

The ozonation process of p-coumaric acid in aqueous solution is studied by identification and quantitative evaluation of intermediates and final oxidation products. In all the investigated pH range (2.0–8.0) the initial oxidation step is represented by the direct attack of ozone to the exocyclic double bond, following oxidation steps being regulated by the intervention of also the radical ozonation mechanism. The competition degree between the two mechanisms is significantly influenced by pH of the reacting mixture with a remarkable occurrence of the radical mechanism at basic pH. The high reactivities exhibited towards ozone by p-coumaric acid and p-hydroxybenzaldehyde intermediate make the rate of the ozonation process strictly controlled by diffusion. Product analysis allows to assess that direct ozonation mechanism of p-hydroxybenzaldehyde significantly proceeds through the anomalous reaction pathway.