Mechanism and Linear Free Energy Relationships in Michael-Type Addition of 4-Substituted Anilines to Activated Olefin in Acetonitrile



Kinetic studies for the Michael-type reactions of ethyl-3-(4′-N,N-dimethylaminophenyl)-2-(nonafluorobutane)sulfonylpro-penoate 1 with 4-X-substituted anilines 2a–e (X = OCH3, CH3, H, F, and Cl) have been investigated in acetonitrile at 20°C. A quadratic dependence of the pseudo–first-order rate constants (kobsd) versus [2a–e] has been observed and has been interpreted in terms of a dimer nucleophile mechanism. The finding of a relatively large negative ρ value (−3.09) for the Hammett plot suggests that the intermediate (I±) is highly zwitterionic in nature. A linear correlation (r2 = 0.9989) between the Hammett's substituent constants σ and nucleophilicity parameters N of 4-X-substituted anilines in acetonitrile has been observed. The electrophilicity parameters E of the olefin 1 is evaluated, using the correlations σ versus N and log k versus σ and compared with the electrophilicities of analogously Michael acceptors.