Pulse radiolysis of p-hydroxycinnamic acid in aqueous solution

Abstract

Using pulse radiolysis with optical detection it is shown that the hydroxyl radical OH reacts with p-hydroxycinnamic acid in acidic and near-neutral solutions predominantly by addition to the unsaturated substituent, forming benzyl-type radicals. Above pH 9 the spectrum obtained is identical to those obtained from the reaction of p-hydroxycinnamic acid with O^–, Cl^–₂, Br^–₂ and CH₂CHO radicals. It is suggested that OH radicals attack the ionized hydroxyl group under alkaline conditions to give phenoxyl derivatives.

In addition, the spectral data presented show a significant influence of the unsaturated substituent on the position of the absorption maxima in the case of phenoxyl-type radicals, i.e.λ= 545 and 595 nm with extinction coefficients 1500 and 1800 m² mol^–1, respectively.