ELECTROPHILIC DISPLACEMENT REACTIONS: XV. KINETICS AND MECHANISM OF THE BASE-CATALYZED PROTODEBORONATION OF ARENEBORONIC ACIDS
An investigation of the kinetics of the protodeboronation of benzeneboronic acid in water in the pH range 2.0 to 6.7 is described. In addition to the acid-catalyzed reaction studied earlier a reaction whose rate is independent of pH and one whose rate increases linearly with hydroxide ion concentration have been observed. The effect of malonate buffer concentration at low pH confirms the earlier observations of general acid catalysis. Changes in buffer concentration at pH 6.70 have no effect on rate indicating specific hydroxide ion catalysis. Effect of substituents in the ortho, meta, and para position of the benzene ring on the rate of protodeboronation have been examined. Ortho–para ratios for this reaction are high; possible reasons for this are discussed. The Hammett equation using σ correlates the rates for meta and para substituents.