On the Reaction of Singlet Molecular Oxygen With N‐allylthiourea in Aqueous Solution

Abstract— Experiments on the photooxidation of N ‐allylthiourea, thiourea, and N‐allylurea sensitized by the dye phenosafranine show that in N ‐allylthiourea the thiourea group is the site of singlet oxygen attack, while the allyl moiety neither reacts with nor quenches this metastable form of O 2 (in neutral aqueous solutions). Low concentrations of N ‐ 3 (a known quencher of singlet oxygen) strongly reduce the photooxidation of allylthiourea by a mechanism which apparently obeys simple competition kinetics. From these results the rate constant of the reaction between allylthiourea and singlet oxygen is obtained ( k = 4 × 10 6 M ‐1 s ‐1 ; pH = 7.1).