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

摘要

Kinetic studies for the Michael-type reactions of ethyl-3-(4'-N,N-dimethylam-inophenyl)-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 (k_(obsd)) versus |2a-e| has been observed and has been interpreted in terms of a dimer nucleophile mechanism. The finding of a relatively large negative p value (—3.09) forthe Hammett plot suggests that the intermediate (I~±) is highly zwitterionic in nature. A linear correlation (r~2 = 0.9989) between the Hammett's substituent constants a 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 a versus N and log k versus a and compared with the electrophilicities of analogously Michael acceptors.