Aminolysis of Y-Substituted Phenyl X-Substituted Cinnamates and Benzoates:  Effect of Modification of the Nonleaving Group from Benzoyl to Cinnamoyl

• Published in: Journal of organic chemistry 2007-06, Vol.72 (13), p.4816-4821
• Main Authors: Um, Ik-Hwan, Park, Youn-Min, Fujio, Mizue, Mishima, Masaaki, Tsuno, Yuho
• Format: Article
• Language: English
• Subjects: Amines - chemistry; Benzoates - chemical synthesis; Benzoates - chemistry; Chemistry; Cinnamates - chemical synthesis; Cinnamates - chemistry; Exact sciences and technology; Kinetics and mechanisms; Molecular Structure; Noncondensed benzenic compounds; Organic chemistry; Phenol - chemistry; Preparations and properties; Reactivity and mechanisms
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo0705061

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 °C. Reactions of 2,4-dinitrophenyl X-substituted cinnamates (1a−e) and benzoates (2a−e) with amines result in linear Yukawa−Tsuno plots. The ρX 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 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-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.