| Abstract
| - A kinetic study is reported for reactions of Y-substituted phenyl X-substituted cinnamates (1a−e and3a−g) and benzoates (2a−e and 4a−g) with a series of alicyclic secondary amines in 80 mol % H2O/20mol % DMSO at 25.0 ± 0.1 °C. Reactions of 2,4-dinitrophenyl X-substituted cinnamates (1a−e) andbenzoates (2a−e) with amines result in linear Yukawa−Tsuno plots. The ρX values are much smaller forthe reactions of 1a−e than for those of 2a−e. A distance effect and the nature of the reaction mechanism(i.e., a concerted mechanism for 1a−e) have been suggested to be responsible for the small ρX values.The Brønsted-type plots for the reactions of 2,4-dinitrophenyl X-substituted cinnamates (1a, 1c, and 1e)with amines are curved with a decreasing βnuc value from 0.65 to 0.3−0.4. The reactions of Y-substitutedphenyl cinnamates (3a−g) with morpholine also result in a curved Brønsted plot, while the correspondingreactions of Y-substituted phenyl benzoates (4a−e) exhibit a linear Brønsted plot. It has been concludedthat the curved Brønsted plots found for the reactions of the cinnamates (1a, 1c, 1e, and 3a−g) are notdue to a change in the rate-determining step (RDS) but due to a normal Hammond effect for a concertedmechanism, that is, an earlier transition state (TS) for a more reactive amine or substrate.
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