Bulletin of the Korean chemical society | |
Aminolyses of Y-substituted Phenyl 2-Furoates and Cinnamates: Effect of Nonleaving Group Substituent on Reactivity and Mechanism | |
Youn-Min Park1  Ik-Hwan Um1  Kalsoom Akhtar1  Sher Bahadar Khan1  | |
关键词: Aminolysis; Br©ªnsted-type plot; Rate-determining step; Concerted mechanism; Stepwise mechanism.; | |
DOI : | |
学科分类:化学(综合) | |
来源: Korean Chemical Society | |
【 摘 要 】
Second-order rate constants (kN) have been determined spectrophotometrically for reactions of Y-substituted phenyl 2-furoates (1a-h) with piperidine and morpholine in 80 mol % H2O/20 mol % DMSO at 25.0 �? 0.1 oC. The Br┆nsted-type plot exhibits a downward curvature for the reactions with strongly basic piperidine but is linear for the reactions with weakly basic morpholine. The slope of the curved Br┆nsted-type plot changes from -1.25 to ?0.28 as the pKa of the conjugate acid of the leaving aryloxides decreases. The pKa at the center of the Br┆nsted curvature, defined as pKa�?, was determined to be 6.4. The aminolysis of 1a-h has been concluded to proceed through a stepwise mechanism on the basis of the curved Br┆nsted-type plot. The reactions of Ysubstituted phenyl cinnamates (2a-g) with piperidine resulted in a curved Br┆nsted-type plot with a pKa�? values of 6.4. However, the curved Br┆nsted-type plot has been suggested to be not due to a change in the RDS but due to a normal Hammond effect of a concerted mechanism, since the Br┆nsted-type plot for the corresponding reactions with morpholine results in also a curved Br┆nsted-type plot with a pKa�? values of 6.1. The furoates with a basic leaving group (i.e., 1b-g) are less reactive than the corresponding cinnamates (i.e., 2b-g). The k2/ k-1 ratios for the reactions of 1b-h are much smaller than unity, which has been suggested to be responsible for their low reactivity.
【 授权许可】
Unknown
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