Inhibition of humic substances mediated photooxygenation of furfuryl alcohol by 2,4,6-trimethylphenol: an evidence for reactivity of the phenol with humic triplet excited states .
Résumé
To probe the reactivity of 2,4,6-trimethylphenol with humic substances triplet excited states, we investigated its influence on the humic substances-mediated photo-oxygenation of furfuryl alcohol. Elliott soil humic and fulvic acids were employed for these experiments. Added in the concentration range 10-4-10-3 M, 2,4,6-trimethylphenol inhibited furfuryl alcohol photooxygenation to an extent depending on its concentration. The inhibiting effect decreased as oxygen concentration was increased. By postulating that 2,4,6-trimethylphenol competes with oxygen for reaction with humic substances triplet excited states and with furfuryl alcohol for reaction with singlet oxygen, we obtained kinetic laws describing the consumption profiles of furfuryl alcohol and 2,4,6-trimethylphenol. Experimental rates of 2,4,6-trimethylphenol and furfuryl alcohol loss could be satisfactorily fitted taking 1.09-1.16 for the ratio k2/k3, where k2 and k3 are the reaction rate constants of humic triplets excited states with oxygen and 2,4,6-trimethylphenol, respectively. These types of experiments could be extended to a variety of substrates in order to measure their reaction rate constant with humic triplet excited states.