Effects of Water and pH on the Oxidative Oligomerization of Chloro an Methoxyphenol by a Montmorillonite Clay

Abstract

This study focussed on the capacity of a montmorillonite clay to oxidize organic contaminants having activating (methoxyphenol) and deactivating (chlorophenol) substituent groups when pH and water conditions are changing. The amount and strength of Lewis and Br⊘nsted acidity of the clay was measured using organic indicator and titration methods. Water plays two distinct roles in the oxidation of such contaminants by clays: (1) it neutralizes the clay's Lewis acidity, thereby preventing chlorophenol from getting oxidized in significant yields; (2) it does not successfully compete with methoxyphenol for Lewis acid sites because high dimer yields are observed. The high capacity of Na+, Ca2+, and Fe3+ clays to oxidize phenolic compounds at high pH appears to be caused by phenolates being more reactive than the protonated form. The Lewis and Br⊘nsted acidity measurement of the various homoionic clays tested help explain the high capacity of the clays to oxidize phenolic compounds at low and high pH and their l...