Elimination Reactions of (E)-O-Pivaloylbenzaldoximes

Elimination reactions of (E)-O-pivaloylbenzaldoximes promoted by Et₃N-MeCN, t-BuOK-t-BuOH, and t-BuOK-DMSO have been studied kinetically. The reactions produce benzonitrile quantitatively. The reactions are second-order and exhibit substantial values of ρ,β, and k_H/k_D and an E2 mechanism is evident. The rate of elimination from (E)-O-pivaloylbenzaldoxime increased with base-solvent system variation and gave relative rates of 1, 14.8, and 4.31 × 10⁴ for Et₃N-MeCN, t-BuOK-t-BuOH, t-BuOK-DMSO, respectively. The k_H/k_D value increased, but the Hammett ρ value increased and then decreased, with this change in the base-solvent system. These results are compared with the predictions of the More O'Ferrall-Jencks reaction coordinate diagram to assess its scope and limitations in the interpretation of the elimination reactions.