Ketene-forming elimination reactions from aryl phenylacetates promoted by R₂NH in MeCN: Effects of base-solvent and β-phenyl group

Elimination reactions of C₆H₅C(R)HCO ₂C₆H₃-2-X-4-NO₂ [R = H (1), Ph (2), X = H (a), Cl (b), NO₂ (c)] promoted by R₂NH in MeCN have been studied kinetically. The reactions are second-order and exhibit Brönsted β = 0.46-0.89 and |β_1g| = 0.37-0.76 and an E2 mechanism is evident. When the base-solvent was changed from R ₂NH/R₂NH₂⁺-70 mol% MeCN(aq) to R₂NH-MeCN, β and |β_1g| values remained nearly the same within experimental error. For eliminations from 1 and 2, β and |β_1g| values were nearly identical, although the rate was retarded by the β-Ph group. Noteworthy is the relative insensitivity of the ketene-forming transition state to the base-solvent and β-R group variation.