Rate constants for the reaction of singlet oxygen with derivatives of p-aminobenzoic acid

Abstract

Summary p-Aminobenzoic acid and its derivatives are often topically applied to prevent damage to the skin by actinic radiation. It has recently been suggested that reaction of these compounds with photochemically generated singlet oxygen may contribute to the protective effect. The total rate constants for interaction (reaction plus quenching) of several p -aminobenzoic acid derivatives with singlet oxygen have been determined in chloroform. The low rate constants for interaction, ethyl p -aminobenzoate, 8 × 104M−1s−1 ethyl p-N, N-dimethylaminobenzoate, 5.5 × 106M−1s−1, and p-N,N-dimethylaminobenzaldehyde, 1.1 × 106M−1s−1, indicate that interaction with singlet oxygen is not an important mode of protection for these compounds.