Aminolysis of Y-substituted phenyl X-substituted cinnamates and benzoates: effect of modification of the nonleaving group from benzoyl to cinnamoyl.
A kinetic study is reported for reactions of Y-substituted phenyl X-substituted cinnamates (1a-e and 3a-g) and benzoates (2a-e and 4a-g) with a series of alicyclic secondary amines in 80 mol % H2O/20 mol % DMSO at 25.0 +/- 0.1 degrees C. Reactions of 2,4-dinitrophenyl X-substituted cinnamates (1a-e) and benzoates (2a-e) with amines result in linear Yukawa-Tsuno plots. The rho(X) values are much smaller for the 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 rho(X) 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 betanuc value from 0.65 to 0.3-0.4. The reactions of Y-substituted phenyl cinnamates (3a-g) with morpholine also result in a curved Brønsted plot, while the corresponding reactions of Y-substituted phenyl benzoates (4a-e) exhibit a linear Brønsted plot. It has been concluded that the curved Brønsted plots found for the reactions of the cinnamates (1a, 1c, 1e, and 3a-g) are not due to a change in the rate-determining step (RDS) but due to a normal Hammond effect for a concerted mechanism, that is, an earlier transition state (TS) for a more reactive amine or substrate.
Um
Ik-Hwan
IH
Division of Nano Sciences, Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea. ihum@ewha.ac.kr
Park
Youn-Min
YM
Fujio
Mizue
M
Mishima
Masaaki
M
Tsuno
Yuho
Y
D000588:Amines / Q000737:chemistry*; D001565:Benzoates / Q000138:chemical synthesis / Q000737:chemistry*; D002934:Cinnamates / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D019800:Phenol / Q000737:chemistry*
D000588:Amines; D001565:Benzoates; D002934:Cinnamates; D019800:Phenol