Aminolyses of Y-substituted Phenyl 2-Furoates and Cinnamates: Effect of Nonleaving Group Substituent on Reactivity and Mechanism

Bulletin of the Korean chemical society

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 pK_a of the conjugate acid of the leaving aryloxides decreases. The pK_a at the center of the Br┆nsted curvature, defined as pK_a�?, 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 pK_a�? 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 pK_a�? 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