Mechanistic studies in strongly basic media. Part VI. The kinetics of base-induced hydrogen-isotope exchange and autoxidation of fluorene in t-butyl alcohol

Abstract

Deuteron removal from 9,9-dideuteriofluorene by potassium t-butoxide or benzyltrimethylammonium hydroxide in t-butyl alcohol takes place at a rate which is proportional to the ionisation ratio of the indicator p-nitroaniline in the reaction medium. The rate of base-induced autoxidation of fluorene in t-butyl alcohol is given by the equation v=k[Fluorene][O₂]ϕ, where ϕ is a function of the basicity of the reaction medium, and is much faster using benzyltrimethylammonium hydroxide than using potassium t-butoxide as the base. Autoxidation of 9,9-dideuterio-fluorene in the presence of potassium t-butoxide occurs at the same rate as the autoxidation of fluorene itself. When the quaternary ammonium hydroxide is used, however, the instantaneous rate coefficient increases with time, eventually reaching a steady value equal to that for autoxidation of fluorene. A kinetic expression for this behaviour is derived, and from it a value for the kinetic isotope effect on the autoxidation is obtained. The implications of the results are briefly discussed.